Chris Wilcox | Georgetown University (original) (raw)
Papers by Chris Wilcox
Hypertension, 1991
Radioisotopic renal scanning after angiotensin converting enzyme inhibition (ACEI) has proven to ... more Radioisotopic renal scanning after angiotensin converting enzyme inhibition (ACEI) has proven to be an exciting area for research. The biologic activity of markers such as DTPA and hippuran, when combined with the physiological effects of ACEI, may provide noninvasive methods of diagnosing both renal artery stenosis and renovascular hypertension. Recent investigators have demonstrated that the sensitivities and specificities of these tests may vary widely; these differences are probably due to variations in study design, patient population, diagnostic criteria, and outcome measurements. We have reviewed these studies and discuss these possible sources of variation and their impact on the clinical usefulness of these diagnostic tests, especially in relation to the prevalence of disease in the population. Current results suggest that the post-ACEI DTPA scan is relatively accurate in the diagnosis of renal artery stenosis, with sensitivity generally greater than 90% and specificity around 95%. However, the best results in predicting the response to angioplasty or surgery in patients with renal artery stenosis have been with the use of post-ACEI hippuran in combination with furosemide (sensitivity, 96%; specificity, 95%). With confirmation of these findings and continued investigation, it is expected that accurate noninvasive tests will be available for widespread clinical use in the near future. (Hypertension 1991;18:299-303) A mong the hypertensive population, some / \ 0.2-2% have radiological evidence of a nar-J. \-rowing of one or both renal arteries or a branch within the kidney (renal artery stenosis). Around half of these patients may be controlled or cured by relieving this obstruction (renovascular hypertension). Angiography has been the "gold standard" for the diagnosis of renal artery stenosis; however, alternative methods have been sought that are less invasive, expensive, and dangerous, and that might predict which patients will have a favorable response to angioplasty or surgery. Renography using I-orthohippurate (hippuran) was widely evaluated during the 1960s since it is noninvasive and safe even in patients with renal insufficiency in whom radiological contrast studies are hazardous. Unfortunately, results of large trials revealed sensitivity and specificity of only approximately 75% each.
Iso prostaglandin F 2a (8-ISO) is formed nonenzymatically from the attack of superoxide radical o... more Iso prostaglandin F 2a (8-ISO) is formed nonenzymatically from the attack of superoxide radical on arachidonic acid. Therefore, 8-ISO is a marker of oxidative stress in vivo. We have recently shown that short-term administration of the membrane-permeable, metal-independent superoxide dismutase mimetic tempol (4-hydroxy- 2, 2, 6, 6-tetramethyl piperidinoxyl) normalizes blood pressure in spontaneously hypertensive rats (SHR). The present study was
Renal Autoregulation in Health and Disease
Physiological reviews, 2015
Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration ra... more Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltag...
Determination of reduced and oxidized homocysteine and related thiols in plasma by thiol-specific pre-column derivatization and capillary electrophoresis with laser-induced fluorescence detection
Journal of chromatography. B, Biomedical sciences and applications, Jan 10, 1999
A new sensitive and rapid capillary electrophoresis (CE) assay for measuring reduced and oxidized... more A new sensitive and rapid capillary electrophoresis (CE) assay for measuring reduced and oxidized thiols in human plasma has been developed. To prevent oxidation of the thiols, whole blood was immediately centrifuged after collection and the plasma proteins were precipitated with perchloric acid. The reduced thiols in the supernatant were derivatized quantitatively at 25 degrees C, pH 7.5 with a fluorescent reagent, fluorescein-5-maleimide (FM). The total plasma concentration of thiols, including the fraction coupled to proteins, was assayed after an initial reduction of the disulfide linkage in plasma with dithiothreitol. The separation of FM-thiols was performed in an acetonitrile/10 mM sodium phosphate-50 mM SDS buffer [25:75 (v/v); pH 7.0] using a fused-silica capillary (57 cm x 75 microm I.D.) at 45 degrees C. A 3-mW argon-ion laser (lambda(ex) 488 nm/lambda(em) 520 nm) was employed for FM-thiol detection. With the electric field of 530 V/cm, the time needed for the separation ...
Journal of the American Society of Nephrology : JASN, 1993
Patients with an aldosterone-producing adenoma (APA) characteristically fail to show an increase ... more Patients with an aldosterone-producing adenoma (APA) characteristically fail to show an increase in plasma aldosterone (PA) concentration with maneuvers that increase angiotensin II (Ang II), yet they retain a brisk response of PA to adrenocorticotrophic hormone. Therefore, adrenal Ang II receptor binding was characterized in a patient with APA who had a blocked PA response to Ang II infusion before adrenalectomy. The binding of [125I]Sar1,IIe5-Ang II in adrenal gland and tumor was fully displaced by excess Ang II. In the tumor, 98% of [125I]Sar1,IIe5-Ang II binding was displaced by the AT, receptor antagonist losartan, yet only 5% was displaced by the AT2 receptor antagonist PD-123,319. Autoradiography of the adrenal gland itself showed a predominance of AT1 receptors in the cortex and AT2 receptors in the medulla. The tumor showed a predominance of AT1 receptors, but there was some evidence of a limited population of AT2 receptors. The tumor and adjacent adrenal contained high con...
Microvascular Endothelial Dysfunction and Enhanced Thromboxane and Endothelial Contractility in Patients with HIV
Journal of AIDS & clinical research, 2013
The prevalence of cardiovascular disease is increased with human immunodeficiency virus (HIV) inf... more The prevalence of cardiovascular disease is increased with human immunodeficiency virus (HIV) infection, but the mechanism is unclear. We hypothesized that HIV increases microvascular reactive oxygen species, thereby impairing endothelial function and enhancing contractility. Subcutaneous microarterioles were isolated from gluteal skin biopsies in premenopausal, African American, HIV positive women receiving effective anti-retroviral therapy, but without cardiovascular risk factors except for increased body mass index (n=10) and healthy matched controls (n=10). The arterioles were mounted on myographs, preconstricted and relaxed with acetylcholine for: endothelium-dependent relaxation, endothelium-dependent relaxation factor (nitric oxide synthase-dependent relaxation), endothelium-dependent hyperpolarizing factor (potassium-channel dependent relaxation) and endothelium-independent relaxation (nitroprusside). Contractions were tested to endothelium-dependent contracting factor (acet...
Effects of Ang II Type I and Type II Receptors on Oxidative Stress and Renal Nadph Oxidase and Sod Expression
American Journal of Physiology: Regulatory, Integrative and Comparative Physiology
Thromboxane Synthase Expression in Renal Transplant Patients with REJECTION1
Transplantation, 1995
Thromboxane synthase (TS) catalyzes the formation of thromboxane (TxA2) in monocytes/macrophages,... more Thromboxane synthase (TS) catalyzes the formation of thromboxane (TxA2) in monocytes/macrophages, platelets, and various tissues. TxA2 is likely to play a role in graft dysfunction due to its vasoconstrictive and platelet aggregatory properties. We studied the expression of TS in 7 normal native kidneys, 29 consecutive renal allograft biopsies (performed for rising serum creatinine, n = 23, and delayed graft function, n = 6), and one transplant nephrectomy specimen with severe acute rejection. TS expression was determined by immunocytochemistry using a monoclonal antibody against human TS, Kon-7. Histologic grading of the transplant biopsy specimens was based on the Banff classification. The degree of TS staining was graded in the glomeruli, interstitium, tubules and vessels from 0 to 3+. Of 29 biopsies, 13 had chronic nephropathy (CN), 6 had acute rejection (AR) with chronic nephropathy (AR/CN), 4 had acute rejection (AR), and 6 had acute tubular necrosis (ATN). TS staining of native kidneys showed sporadic interstitial cells. The biopsy and transplant nephrectomy specimens showed significant staining, predominantly in the glomeruli and interstitium. Positively staining cells appeared to be of macrophage/monocyte lineage by morphology. The mean glomerular staining grade was significantly increased in specimens with AR (2.3 +/- 0.9) and the mean interstitial staining was increased in specimens with AR/CN (2.2 +/- 0.9). Follow-up renal function 6 months post-biopsy showed that patients with higher TS staining grades had a faster decline in graft function. In conclusion, TS expression is increased in patients with acute rejection with or without chronic nephropathy and is associated with more rapid deterioration in function.
Nitric oxide, oxidative stress, and progression of chronic renal failure
Seminars in Nephrology, 2004
Cellular injury or organ dysfunction from oxidative stress occurs when reactive oxygen species (R... more Cellular injury or organ dysfunction from oxidative stress occurs when reactive oxygen species (ROS) accumulate in excess of the host defense mechanisms. The deleterious effect of ROS occurs from 2 principal actions. First, ROS can inactivate mitochondrial enzymes, damage DNA, or lead to apoptosis or cellular hypertrophy. Second, nitric oxide (NO), which is a principal endothelial-derived relaxing factor, reacts with superoxide anion (O2-) to yield peroxynitrite (ONOO-), which is a powerful oxidant and nitrosating agent. The inactivation of NO by O2- creates NO deficiency. Oxidative stress can promote the production of vasoconstrictor molecules and primary salt retention by the kidney. Several hypertensive animal models showed increased activity of nicotine adenine dinucleotide phosphate (NADPH) oxidase, which is the chief source of O2- in the vessel wall and kidneys. NO regulates renal blood flow, tubuloglomerular feedback (TGF), and pressure natriuresis. Animal models of NO deficiency develop hypertension, proteinuria, and glomerulosclerosis. Evidence is presented that chronic renal failure (CRF) is a state of NO deficiency secondary to decreased kidney NO production and/or increased bioinactivation of NO by O2-. Patients with CRF show decreased endothelium-dependent vasodilatation to acetylcholine, have increased markers of oxidative stress, and diminished antioxidant activity. Therapy for oxidative stress has focused on antioxidants and agents that modify the renin-angiotensin system. The effects of such treatments are more compelling in animal models than in human studies.
Pharmacological Research, 2009
Asymmetric (N G ,N G) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitr... more Asymmetric (N G ,N G) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitric oxide synthase (NOS) that generates nitric oxide (NO) and cationic amino acid transporters (CAT) that supply intracellular NOS with its substrate, L-arginine from the plasma. Therefore, ADMA and its transport mechanisms are strategically placed to regulate endothelial function. This could have considerable clinical impact since endothelial dysfunction has been detected at the origin of hypertension and chronic kidney disease (CKD) in human subjects and may be a harbinger of large vessel disease and cardiovascular disease (CVD). Indeed, plasma levels of ADMA are increased in many studies of patients at risk for, or with overt CKD or CVD. However, the levels of ADMA measured in plasma of about 0.5 μmol • l −1 maybe below those required to inhibit NOS whose substrate, L-arginine, is present in concentrations manifold above the Km for NOS. However, NOS activity may be partially inhibited by cellular ADMA. Therefore, the cellular production of ADMA by protein arginine methyltransferase (PRMT) and protein hydrolysis, its degradation by N G , N G-dimethylarginine dimethylaminohydrolase (DDAH) and its transmembrane transport by CAT that determines intracellular levels of ADMA may also determine the state of activation of NOS. This is the focus of the review. It is concluded that cellular levels of ADMA can be 5-to 20-fold those in plasma and in a range that could tonically inhibit NOS. The relative importance of PRMT, DDAH and CAT for determining the intracellular NOS substrate: inhibitor ratio (L-arginine:ADMA) may vary according to the pathophysiologic circumstance. An understanding of this important balance requires knowledge of at least these three processes that regulate the intracellular levels of ADMA and arginine. Keywords Nitric oxide synthase (NOS); protein arginine methyl transferase (PRMT); cationic amino acid (CAA); cationic amino acid transporter (CAT); cardiovascular disease; chronic kidney disease (CKD); hypertension; reactive oxygen species and oxidative stress
Kidney International, 2005
Effects of NADPH oxidase inhibitor in diabetic nephropathy. Background. We used apocynin to test ... more Effects of NADPH oxidase inhibitor in diabetic nephropathy. Background. We used apocynin to test the hypothesis that superoxide anion (O − 2) from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase underlies the development of diabetic nephropathy in the rat. Methods. Rats received apocynin (16 mg/kg/day) from 2 to 8 weeks after inducing diabetes mellitus (DM) with streptozotocin. Results. DM increased excretion of hydrogen peroxide (H 2 O 2), lipid peroxidation products (LPO), nitric oxide products (NOx), and protein. The kidneys of rats with DM had increased expression of p47phox and gp91phox and endothelial nitric oxide synthase (eNOS), and increased mesangial matrix with expression of fibronectin and collagen I. Apocynin prevented the increase in excretion of H 2 O 2 , LPO, and protein in diabetic rats, increased renal NOx generation, and prevented the increased renal expression of gp91phox and the membrane fraction of p47phox, and reverted the mesangial matrix expansion. Conclusion. Activation of NADPH oxidase with translocation of p47phox to the membrane underlies the oxidative stress and limited NO generation, despite enhanced eNOS expression in a model of diabetic nephropathy. Apocynin prevents these changes and the associated proteinuria. The balance between the production of reactive oxygen species (ROS), notably superoxide anion (O − 2) and hydrogen peroxide (H 2 O 2), and the antioxidant defense system that includes superoxide dismutase (SOD) and peroxidases, determines the degree of oxidative stress. An increased production and/or decreased metabolism of ROS have been implicated in the pathogenesis of renal injury in diabetes mellitus (DM) [1, 2]. An important source of ROS production is nicotinamide adenine dinucleotide phosphate (NADPH)
Endothelial dysfunction and reduced nitric oxide in resistance arteries in autosomal-dominant polycystic kidney disease
Kidney International, 2003
Patients with autosomal-dominant polycystic kidney disease (ADPKD) have defective endothelium-dep... more Patients with autosomal-dominant polycystic kidney disease (ADPKD) have defective endothelium-dependent relaxation (EDR). We investigated the relationship between endothelial dysfunction and nitric oxide generation in hypertension and chronic renal insufficiency (CRI) in ADPKD. We contrasted acetylcholine (ACh)-induced EDR, 3-morphollinosydnonimine (SIN-1)-induced endothelium-independent relaxation (EIDR) and constitutive nitric oxide synthase (cNOS) activity in subcutaneous resistance vessels and plasma levels and excretion of NO2-/NO3- (NOX) in normal, control (N = 10) patients with ADPKD or essential hypertension. EDR was decreased significantly in normotensive ADPKD (N = 9), but more severely in hypertensive ADPKD (N = 6), or those with CRI (N = 5) and in essential hypertension (N = 9). The increases in EDR with l-arginine and decreases with LG-nitro-l-arginine methyl ester (L-NAME) were lost in all groups of patients with ADPKD and in essential hypertension except for a modest effect of L-NAME in normotensive ADPKD. EIDR was unimpaired throughout. Vascular cNOS activity and renal NOX excretion were reduced profoundly in patients with all categories of ADPKD and especially in those with hypertension. EDR in resistance vessels from patients with ADPKD is impaired even in the absence of hypertension or CRI, but becomes more marked as hypertension develops. Patients with ADPKD have defective nitric oxide generation from diminished cNOS activity. Endothelial dysfunction and impaired cNOS activity in ADPKD may predispose to hypertension whose occurrence is accompanied by a further sharp deterioration in EDR.
Kidney International, 1994
Differential expression and induction of mRNAs encoding two inducible nitric oxide synthases in r... more Differential expression and induction of mRNAs encoding two inducible nitric oxide synthases in rat kidney. We used quantitative PCR methods and renal microdissection to characterize the expression of inducible nitric oxide synthase (iNOS) mRNAs in rat kidney and cultured glomerular mesangial cells. A partial cDNA homologous to murine macrophage iNOS (macNOS), but distinct from rat vascular smooth muscle iNOS (vsmNOS), was cloned from normal rat kidney. macNOS was the principal iNOS isoform tonically expressed in microdissected glomeruli, proximal tubules, medullary thick ascending limbs (mTAL), cortical and inner medullary collecting ducts (IMCD), and cultured mesangial cells, whereas vsmNOS was the major isoform expressed in arcuate and interlobular arteries. Basal macNOS expression was greatest in mTALs and IMCDs. Restriction mapping of RT-PCR products indicated that basal expression of macNOS mRNA was comparable to that of vsmNOS in cortex, but greater than vsmNOS in outer and inner medulla. However, compared to controls, lipopolysaccharide (LPS)-treated rats exhibited a much greater proportion of vsmNOS mRNA and higher levels of total iNOS mRNA in each zone. Similarly, TNFa and IF-y preferentially induced expression of vsmNOS mRNA in cultured mesangial cells. We conclude that two 1NOS isoforms are constitutively and heterogeneously expressed in the normal rat kidney, and that endotoxemia and cytokines differentially induce their expression. Nitric oxide (NO), a labile radical gas, is an important intercellular messenger that plays a prominent role in a host of physiological and pathophysiological processes [reviewed in 1 and 2]. Recent evidence indicates that NO has potent effects on renal function, including modulation of renal and glomerular hemodynamics, renin secretion, the tubuloglomerular feedback response, and sodium excretion [reviewed in 3]. NO production is mediated by the activity of NO synthase (NOS), a family of at least three isoenzymes that synthesizes NO from a terminal guanidino nitrogen of L-arginine. NOS Types I (neuronal, [4]) and III (endothehal, [5]) are constitutively expressed, but quiescent until activated by increased Ca2 levels that sustain calmodulin binding [1]. In contrast, Type II, or "inducible" NOS (iNOS) is strongly expressed after transcriptional activation by cytokines or lipopolysaccharide (LPS) [6], the major component of bacterial endotoxin. This form of the enzyme remains active for sustained periods and
Kidney International, 2003
after correction of baseline data to exclude the influence of Renal function and outcome of PTRA ... more after correction of baseline data to exclude the influence of Renal function and outcome of PTRA and stenting for atherothe expected regression to the mean. sclerotic renal artery stenosis. Conclusions. Patients with atherosclerotic RAS fulfilling strict Background. Prior studies of percutaneous transluminal recriteria of severity may have significant improvements in BP nal artery angioplasty and stenting (PTRAS) for atherosclerotic one year after PTRAS but only modest in GFR. The initial renal artery stenosis (RAS) have shown that renal function is GFR may anticipate whether the benefits in the outcome will improved in about 25%, stabilizes in about 40%, but worsens be in renal function enhancement (those with an initially dein about 25% of patients. The factors predicting benefit remain pressed GFR) or in hypertension control (those with an initially controversial. We tested the hypothesis that the baseline glonormal or mildly impaired GFR). merular filtration rate (GFR) predicts the changes in GFR and blood pressure (BP) after PTRAS. Methods. Treated hypertensive patients with positive renal color-coded duplex Doppler velocimetry and clinical criteria Renal artery stenosis (RAS) causing renovascular diswere screened by arteriography. Patients (N ϭ 105) were included ease was considered a rare cause of secondary hypertenif they had an RAS Ն70%, a transluminal pressure gradient sion. However, with improvements in techniques for Ն30 mm Hg and, they had more than 100 days of follow-up. GFR was calculated from the serum creatinine concentration screening and with the widespread use of vascular im-(S Cr). Patients were divided by baseline GFR into subgroups aging, it is now recognized that 40 to 50% of patients with normal to mildly impaired (N ϭ 52) or moderately to with occlusive disease of the lower limb [1] and 15 to 30% severely impaired (N ϭ 53) initial GFR, according to a GFR of patients with coronary artery disease have identifiable Ն50 or Ͻ50 mL • min Ϫ1 respectively. All received PTRAS. RAS [2]. Reports of patients with established, or newly Results. For the entire group, after a mean follow-up period diagnosed, end-stage renal disease (ESRD) indicate a of 371 days, there were significant reductions in systolic and diastolic BP (before, 160 Ϯ 26/91 Ϯ 12 vs. after, 145 Ϯ 20/83
Kidney International, 1993
Nitric oxide mediates renal vasodilation during erythropoietin-lnduced polycythemia. The renal bl... more Nitric oxide mediates renal vasodilation during erythropoietin-lnduced polycythemia. The renal blood flow (RBF) of patients with polycythemia rubra vera is increased despite the high hematocrit (Hct) which elevates the whole blood viscosity. Since blood viscosity determines the shear force on the endothelium which is a major stimulus to nitric oxide (NO) release, we investigated the hypothesis that renal vasodilation during erythropoietin-induced erythrocytosis is mediated by the L-arginine-NO pathway. Groups of Sprague-Dawley rats received thrice weekly injections of crythropoietia (E) for two to five weeks; responses were contrasted with normal rats (N) which received sham injections. The first group was studied after five weeks of erythropoietin injections which led to sharp increases in Hct (B: 72 3 vs. N: 44 1%) and mean arterial pressure (MAP: 126 3 vs. 107 3 mm Hg). These rats had an elevated basal RBF whether measured by the clearance and renal extraction of PAH or by a transit-time renal blood flow meter. Subsequent groups were studied after two to three weeks of erythropoietin which raised the Hct more modestly to 59 2%. In this group, the basal MAP was similar in B and N rats. Graded doses of the NO synthase inhibitor, N'-moaomethyl-L-argithne (L-NMA) led to a steeper rise in MAP in E than N; at the highest doses, the MAP had increased by 36 2 in B and 23 3 mm Hg in N (P < 0.01). Therefore, to assess the effects of L-NMA on renal vascular resistance without the confounding effects of differences in MAP, the renal perfusion pressure (RPP) was controlled with a suprarenal aortic clamp. In the basal state, the RBF was higher in F than N (F: 5.33 0.54 vs. N: 3.85 0.28 ml' min' 100 g'; Pc 0.025). L-NMA caused a greater reduction in RBF, and a greater rise in filtration fraction (FE) and renal vascular resistance (RVR) in erythropoietin-treated rats. During L-NMA, the RBF became similar in the two groups (F: 2.19 0.50 vs. N: 2.42 0.32 ml min' 100 g'; NS). We conclude that an enhanced generation of NO from L-arginine maintains normotension and mediates renal vasodilation in rats with erythropoietin-induced erythrocytosis. In vitro studies have shown that the hematocrit (Hct) is the major determinant of whole blood viscosity which increases exponentially with Hct values above the physiologic range [1, 21. Indeed, increases in the Hct of blood perfusing a dog's hind limb preparation [3] or an isolated perfused dog's kidney [4] in which active vasomotor changes are prevented, reduce blood flow. In contrast, an abrupt increase in the Hct of blood perfusing a dog's kidney in which vasomotor changes are intact
Kidney International, 1994
Renal vasoconstriction during inhibition of NO synthase: Effects of dietary salt. Since dietary s... more Renal vasoconstriction during inhibition of NO synthase: Effects of dietary salt. Since dietary salt loading enhances nitric oxide (NO) generation in the kidney, we investigated the hypothesis that changes in salt intake have specific effects on vascular resistance in the kidney mediated by the L-arginine-NO pathway. We contrasted changes in renal and hindquarter vascular resistances (RVR and HQVR) in anesthetized rats during intravenous infusions of graded doses of the NO synthase inhibitor N°-nitro-L-arginine methyl ester (L-NAME). Groups (N = 8 to 10) of rats were maintained on a high salt (HS) or low salt (LS) diet for two weeks. Compared to those on LS, rats on HS had a greater increase in mean arterial pressure (AMAP; +32 4 vs. +22 3%; P 0.05) and RVR (+ 160 17 vs. +83 10%; P < 0.005) and a greater fall in renal blood flow (zRBF;-47 3 vs.-32 4%; P < 0.01); changes in HQVR were similar in the two groups. The enhanced RVR response to L-NAME in HS rats could not be ascribed to the higher renal perfusion pressure (RPP) since it persisted in rats whose RPP was controlled by adjustment of a suprarenal aortic clamp. Changes in RVR with an NO donor (SIN-i) were similar in HS and LS rats. L-NAME reduced plasma renin activity in both HS and LS rats. After inhibition of ACE with captopril, or of angiotensin II type I (AT1) receptor with losartan, the increase in RVR with L-NAME remained greater in HS than LS rats. In conclusion, an increase in dietary salt potentiates the renal vascular response to L-NAME. This effect is specific for the kidney and cannot be ascribed to changes in NO responsiveness or RPP or to effects of Ang II generation or action on AT1 receptors. Generation of nitric oxide (NO) from L-arginine by nitric oxide synthase (NOS) leads to vasorelaxation of renal and systemic blood vessels [1-4]. Micropuncture and microperfusion studies in vivo have disclosed a functional role for NO as a signalling molecule between the macula densa (MD) and the afferent arteriole [5]. This MD-derived NO vasodilates the afferent arteriole and counteracts vasoconstrictor stimuli generated by the tubuloglomerular feedback (TGF) response [5]. Dietary salt loading enhances the renal production of NO, as indexed by the excretion of NO2 and NO3 and cyclic guanosine monophosphate (cGMP) [6]. Since TGF is a specific renal response, the first aim of these studies was to examine the hypothesis that there is a specific renal vasodilator pathway mediated by L-arginine-derived NO that is activated by dietary salt loading. Some investigators have shown that increases in renal vascular
Kidney International, 2003
Contributions of nitric oxide, EDHF, and EETs to endothe-Endothelium-derived nitric oxide is the ... more Contributions of nitric oxide, EDHF, and EETs to endothe-Endothelium-derived nitric oxide is the principal melium-dependent relaxation in renal afferent arterioles. diator of acetylcholine-induced endothelium-dependent Background. Acetylcholine-induced endothelium-dependent relaxation in large conduit arteries, while the contriburelaxation in the renal afferent arteriole has been ascribed to tions of hyperpolarizing vasodilators [endothelium-derived nitric oxide, but the role of endothelium-derived hyperpolarizhyperpolarizing factors (EDHFs)] often predominate in ing factors (EDHFs) and 14,15-epoxyeicosatrienoic acid (14,15small resistance vessels [1]. Technical limitations in the EET) are unclear. Methods. Single afferent arterioles were dissected from kid-study of isolated afferent arterioles have limited the ney of normal rabbits and microperfused in vitro at 60 mm Hg. ability to assess contributions of mediators to endothe-Vessels were preconstricted submaximally with norepinephrine lium-dependent relaxation in this key preglomerular re-(10 Ϫ8 mol/L). Relaxation was assessed following cumulative sistance vessel, absent influences which might contribaddition of ACh (10 Ϫ9 to 10 Ϫ4 mol/L) alone, or in the presence ute in more complex, intact preparations. Nitric oxideof indomethacin (to inhibit cyclooxygenase), N w-nitro-l-argimediated vasodilation usually depends on activation of nine (L-NNA) (to inhibit nitric oxide synthase), methylene soluble guanylyl cyclase in smooth muscle cells, leading to blue (to inhibit soluble guanylate cyclase), or a combination of L-NNA ϩ methylene blue. To assess contributions by EDHF, increments of cyclic guanosine monophosphate (cGMP) studies were repeated with either apamin ϩ charybdotoxin [to and activation of cGMP-dependent kinases, which can diblock Ca 2ϩ-activated K ϩ channels (K Ca)] or with 40 mmol/L minish the Ca 2ϩ-sensitivity of the contractile apparatus [2]. KCl. To asses the role of 14,15-EET, relaxations were evaluated Mediators of endothelium-dependent hyperpolarization in the presence of its competitive inhibitor 14,15-epoxyeicosavary with species and vascular bed and include epoxyei-5(Z)-enoic acid (14,15-EEZE). cosatrienoic acids (EETs) [3], endocannabinoids [4], K ϩ Results. Relaxation by acetylcholine was abolished following endothelial denudation. It was unaffected by indomethacin [5], hydrogen peroxide (H 2 O 2) [6, 7], or nitric oxide itself but was inhibited 54% Ϯ 5% (P Ͻ 0.001) by L-NNA, 57% Ϯ [8-10]. Hyperpolarization of the vascular myocyte cell 5% by methylene blue, and 60% Ϯ 4% by the combination of membrane closes voltage-dependent Ca 2ϩ channels, lim-L-NNA plus methylene blue. Relaxation was inhibited further iting intracellular free [Ca 2ϩ ] and effecting relaxation [11]. by KCl (80% Ϯ 6%) or by apamin ϩ charybdotoxin (96% Ϯ EETs are endothelium-derived, cytochrome P-450-2%). 14,15-EEZE, alone, inhibited acetylcholine-induced redependent oxidative (epoxide) metabolites of arachilaxation by 29% Ϯ 3%, and by 80% Ϯ 5% in the presence of donic acid which act as EDHFs in the coronary circula-L-NNA. Conclusion. Acetylcholine-induced afferent arteriolar retion [12]. Nonspecific inhibitors of cytochrome P-450 laxation depends strongly on both nitric oxice, acting via soluhave been used as probes of EDHF effect, but they may ble guanylate cyclase, and on an EDHF, likely 14,15-EET, inhibit the synthesis of a variety of vasoactive factors with acting via K Ca. opposing effects and can, themselves, act as K ϩ channel blockers in some preparations, confounding their use [13]. Recently, highly selective, competitive inhibitors of
Kidney International, 1995
Biopsies were obtained under ultrasonographic guidance using a modified Vim-Silverman needle or a... more Biopsies were obtained under ultrasonographic guidance using a modified Vim-Silverman needle or an automated biopsy gun. The tissues were fixed in a proprietary buffered formaldehyde ionized zinc solution (Z-fix, Anatech Ltd., Battle Creek, MI), embedded in paraffin wax, and processed for routine histological studies including hematoxylin-eosin and periodic acid-Schiff stains. The
Kidney International, 2000
The l-arginine-nitric oxide (NO) pathway has been aseffects of salt intake and angiotensin. signe... more The l-arginine-nitric oxide (NO) pathway has been aseffects of salt intake and angiotensin. signed many important functions in the kidney, including Background. Nitric oxide (NO) is generated from NO synthe regulation of vascular resistance and glomerular filthase (NOS) isoforms. These enzymes can be inhibited by asymtration rate (GFR), tubular NaCl reabsorption in the metric dimethylarginine, which is inactivated by N G-N G-dimethproximal tubule, loop and collecting duct segments, renin ylarginine dimethylaminohydrolase (DDAH). The neuroneal (nNOS) type I and endothelial (eNOS) type III constitutive NOS release, and tubuloglomerular feedback (TGF) [1, 2]. This isoforms are expressed predominantly in the macula densa and pathway is implicated in the renal responses to changes microvascular endothelium of the renal cortex, respectively. in salt intake [3-7] and blood pressure (BP) [8, 9]. DDAH is expressed at sites of NOS expression. Since NO may Two constitutive isoforms of NO synthase (NOS) are coordinate the renal responses to angiotensin II (Ang II) and changes in salt intake, we tested the hypothesis that salt intake expressed in the kidney. The protein or mRNA for type I regulates the expression of nNOS, eNOS and DDAH by Ang II or neuronal NOS (nNOS) is expressed heavily in the acting on type 1 (AT 1) receptors. macula densa, with additional expression in the efferent Methods. Groups (N ϭ 6) of rats were adapted to low-salt arterioles, Bowman's capsule, some cells of the cortical (LS) or high-salt (HS) intakes for 10 days. Other groups of LS thick ascending limb (TAL) of the loop of Henle, and and HS rats received the AT 1 receptor antagonist losartan for six days (to test the effects of salt independent of AT 1 recepthe collecting ducts [1, 2, 10-15]. The protein [14, 16, 17] tors). A further group of HS rats received an infusion of Ang II or mRNA [18] for type III, or endothelial NOS (eNOS), for six days (to test the effect of Ang II independent of salt is expressed in the endothelium of the afferent and efferintake). ent arterioles and the glomerular capillaries. Results. Compared with HS rats, there was a significant (P Ͻ 0.05) increase in LS rats of nNOS protein in kidney and immu-Several mechanisms have been identified that could nohistochemical expression in the macula densa, and of eNOS regulate constitutive NOS activity in the kidney. NOS protein expression and immunohistochemical expression in the is inhibited competitively by endogenous asymmetrical microvascular endothelium, and of DDAH protein expression. dimethylarginine (ADMA) [17]. NOS activity in macula Losartan prevented these effects of salt on the expression of densa cells of salt-restricted rats is limited by cellular up-eNOS or DDAH, both of which were also increased by Ang II infusions in HS rats. In contrast, losartan did not prevent the take of l-arginine via a specific cationic amino acid transeffects of salt on nNOS expression, which was unresponsive porter, termed y ϩ [6]. l-arginine uptake via system y ϩ into to Ang II infusion. The generation of NO Ϫ 2 released by slices of renal tubular epithelial cells is inhibited by both ADMA renal cortex, in the presence of saturating concentrations of and symmetric dimethylarginine (SDMA) [17]. ADMA is l-arginine, was increased by LS, compared to HS, independent of losartan and by Ang II during HS. metabolized by N G-N G-dimethylarginine dimethylamino-Conclusion. The expressions of eNOS in cortical microvashydrolase (DDAH) to l-citrulline and is thereby inacticular endothelium and DDAH in kidney are enhanced by Ang II vated. DDAH is heavily expressed in specific sites in the acting on AT 1 receptors. The expression of nNOS in the macula kidney that correspond to those of NOS expression [17].
Hypertension, 1991
Radioisotopic renal scanning after angiotensin converting enzyme inhibition (ACEI) has proven to ... more Radioisotopic renal scanning after angiotensin converting enzyme inhibition (ACEI) has proven to be an exciting area for research. The biologic activity of markers such as DTPA and hippuran, when combined with the physiological effects of ACEI, may provide noninvasive methods of diagnosing both renal artery stenosis and renovascular hypertension. Recent investigators have demonstrated that the sensitivities and specificities of these tests may vary widely; these differences are probably due to variations in study design, patient population, diagnostic criteria, and outcome measurements. We have reviewed these studies and discuss these possible sources of variation and their impact on the clinical usefulness of these diagnostic tests, especially in relation to the prevalence of disease in the population. Current results suggest that the post-ACEI DTPA scan is relatively accurate in the diagnosis of renal artery stenosis, with sensitivity generally greater than 90% and specificity around 95%. However, the best results in predicting the response to angioplasty or surgery in patients with renal artery stenosis have been with the use of post-ACEI hippuran in combination with furosemide (sensitivity, 96%; specificity, 95%). With confirmation of these findings and continued investigation, it is expected that accurate noninvasive tests will be available for widespread clinical use in the near future. (Hypertension 1991;18:299-303) A mong the hypertensive population, some / \ 0.2-2% have radiological evidence of a nar-J. \-rowing of one or both renal arteries or a branch within the kidney (renal artery stenosis). Around half of these patients may be controlled or cured by relieving this obstruction (renovascular hypertension). Angiography has been the "gold standard" for the diagnosis of renal artery stenosis; however, alternative methods have been sought that are less invasive, expensive, and dangerous, and that might predict which patients will have a favorable response to angioplasty or surgery. Renography using I-orthohippurate (hippuran) was widely evaluated during the 1960s since it is noninvasive and safe even in patients with renal insufficiency in whom radiological contrast studies are hazardous. Unfortunately, results of large trials revealed sensitivity and specificity of only approximately 75% each.
Iso prostaglandin F 2a (8-ISO) is formed nonenzymatically from the attack of superoxide radical o... more Iso prostaglandin F 2a (8-ISO) is formed nonenzymatically from the attack of superoxide radical on arachidonic acid. Therefore, 8-ISO is a marker of oxidative stress in vivo. We have recently shown that short-term administration of the membrane-permeable, metal-independent superoxide dismutase mimetic tempol (4-hydroxy- 2, 2, 6, 6-tetramethyl piperidinoxyl) normalizes blood pressure in spontaneously hypertensive rats (SHR). The present study was
Renal Autoregulation in Health and Disease
Physiological reviews, 2015
Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration ra... more Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltag...
Determination of reduced and oxidized homocysteine and related thiols in plasma by thiol-specific pre-column derivatization and capillary electrophoresis with laser-induced fluorescence detection
Journal of chromatography. B, Biomedical sciences and applications, Jan 10, 1999
A new sensitive and rapid capillary electrophoresis (CE) assay for measuring reduced and oxidized... more A new sensitive and rapid capillary electrophoresis (CE) assay for measuring reduced and oxidized thiols in human plasma has been developed. To prevent oxidation of the thiols, whole blood was immediately centrifuged after collection and the plasma proteins were precipitated with perchloric acid. The reduced thiols in the supernatant were derivatized quantitatively at 25 degrees C, pH 7.5 with a fluorescent reagent, fluorescein-5-maleimide (FM). The total plasma concentration of thiols, including the fraction coupled to proteins, was assayed after an initial reduction of the disulfide linkage in plasma with dithiothreitol. The separation of FM-thiols was performed in an acetonitrile/10 mM sodium phosphate-50 mM SDS buffer [25:75 (v/v); pH 7.0] using a fused-silica capillary (57 cm x 75 microm I.D.) at 45 degrees C. A 3-mW argon-ion laser (lambda(ex) 488 nm/lambda(em) 520 nm) was employed for FM-thiol detection. With the electric field of 530 V/cm, the time needed for the separation ...
Journal of the American Society of Nephrology : JASN, 1993
Patients with an aldosterone-producing adenoma (APA) characteristically fail to show an increase ... more Patients with an aldosterone-producing adenoma (APA) characteristically fail to show an increase in plasma aldosterone (PA) concentration with maneuvers that increase angiotensin II (Ang II), yet they retain a brisk response of PA to adrenocorticotrophic hormone. Therefore, adrenal Ang II receptor binding was characterized in a patient with APA who had a blocked PA response to Ang II infusion before adrenalectomy. The binding of [125I]Sar1,IIe5-Ang II in adrenal gland and tumor was fully displaced by excess Ang II. In the tumor, 98% of [125I]Sar1,IIe5-Ang II binding was displaced by the AT, receptor antagonist losartan, yet only 5% was displaced by the AT2 receptor antagonist PD-123,319. Autoradiography of the adrenal gland itself showed a predominance of AT1 receptors in the cortex and AT2 receptors in the medulla. The tumor showed a predominance of AT1 receptors, but there was some evidence of a limited population of AT2 receptors. The tumor and adjacent adrenal contained high con...
Microvascular Endothelial Dysfunction and Enhanced Thromboxane and Endothelial Contractility in Patients with HIV
Journal of AIDS & clinical research, 2013
The prevalence of cardiovascular disease is increased with human immunodeficiency virus (HIV) inf... more The prevalence of cardiovascular disease is increased with human immunodeficiency virus (HIV) infection, but the mechanism is unclear. We hypothesized that HIV increases microvascular reactive oxygen species, thereby impairing endothelial function and enhancing contractility. Subcutaneous microarterioles were isolated from gluteal skin biopsies in premenopausal, African American, HIV positive women receiving effective anti-retroviral therapy, but without cardiovascular risk factors except for increased body mass index (n=10) and healthy matched controls (n=10). The arterioles were mounted on myographs, preconstricted and relaxed with acetylcholine for: endothelium-dependent relaxation, endothelium-dependent relaxation factor (nitric oxide synthase-dependent relaxation), endothelium-dependent hyperpolarizing factor (potassium-channel dependent relaxation) and endothelium-independent relaxation (nitroprusside). Contractions were tested to endothelium-dependent contracting factor (acet...
Effects of Ang II Type I and Type II Receptors on Oxidative Stress and Renal Nadph Oxidase and Sod Expression
American Journal of Physiology: Regulatory, Integrative and Comparative Physiology
Thromboxane Synthase Expression in Renal Transplant Patients with REJECTION1
Transplantation, 1995
Thromboxane synthase (TS) catalyzes the formation of thromboxane (TxA2) in monocytes/macrophages,... more Thromboxane synthase (TS) catalyzes the formation of thromboxane (TxA2) in monocytes/macrophages, platelets, and various tissues. TxA2 is likely to play a role in graft dysfunction due to its vasoconstrictive and platelet aggregatory properties. We studied the expression of TS in 7 normal native kidneys, 29 consecutive renal allograft biopsies (performed for rising serum creatinine, n = 23, and delayed graft function, n = 6), and one transplant nephrectomy specimen with severe acute rejection. TS expression was determined by immunocytochemistry using a monoclonal antibody against human TS, Kon-7. Histologic grading of the transplant biopsy specimens was based on the Banff classification. The degree of TS staining was graded in the glomeruli, interstitium, tubules and vessels from 0 to 3+. Of 29 biopsies, 13 had chronic nephropathy (CN), 6 had acute rejection (AR) with chronic nephropathy (AR/CN), 4 had acute rejection (AR), and 6 had acute tubular necrosis (ATN). TS staining of native kidneys showed sporadic interstitial cells. The biopsy and transplant nephrectomy specimens showed significant staining, predominantly in the glomeruli and interstitium. Positively staining cells appeared to be of macrophage/monocyte lineage by morphology. The mean glomerular staining grade was significantly increased in specimens with AR (2.3 +/- 0.9) and the mean interstitial staining was increased in specimens with AR/CN (2.2 +/- 0.9). Follow-up renal function 6 months post-biopsy showed that patients with higher TS staining grades had a faster decline in graft function. In conclusion, TS expression is increased in patients with acute rejection with or without chronic nephropathy and is associated with more rapid deterioration in function.
Nitric oxide, oxidative stress, and progression of chronic renal failure
Seminars in Nephrology, 2004
Cellular injury or organ dysfunction from oxidative stress occurs when reactive oxygen species (R... more Cellular injury or organ dysfunction from oxidative stress occurs when reactive oxygen species (ROS) accumulate in excess of the host defense mechanisms. The deleterious effect of ROS occurs from 2 principal actions. First, ROS can inactivate mitochondrial enzymes, damage DNA, or lead to apoptosis or cellular hypertrophy. Second, nitric oxide (NO), which is a principal endothelial-derived relaxing factor, reacts with superoxide anion (O2-) to yield peroxynitrite (ONOO-), which is a powerful oxidant and nitrosating agent. The inactivation of NO by O2- creates NO deficiency. Oxidative stress can promote the production of vasoconstrictor molecules and primary salt retention by the kidney. Several hypertensive animal models showed increased activity of nicotine adenine dinucleotide phosphate (NADPH) oxidase, which is the chief source of O2- in the vessel wall and kidneys. NO regulates renal blood flow, tubuloglomerular feedback (TGF), and pressure natriuresis. Animal models of NO deficiency develop hypertension, proteinuria, and glomerulosclerosis. Evidence is presented that chronic renal failure (CRF) is a state of NO deficiency secondary to decreased kidney NO production and/or increased bioinactivation of NO by O2-. Patients with CRF show decreased endothelium-dependent vasodilatation to acetylcholine, have increased markers of oxidative stress, and diminished antioxidant activity. Therapy for oxidative stress has focused on antioxidants and agents that modify the renin-angiotensin system. The effects of such treatments are more compelling in animal models than in human studies.
Pharmacological Research, 2009
Asymmetric (N G ,N G) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitr... more Asymmetric (N G ,N G) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitric oxide synthase (NOS) that generates nitric oxide (NO) and cationic amino acid transporters (CAT) that supply intracellular NOS with its substrate, L-arginine from the plasma. Therefore, ADMA and its transport mechanisms are strategically placed to regulate endothelial function. This could have considerable clinical impact since endothelial dysfunction has been detected at the origin of hypertension and chronic kidney disease (CKD) in human subjects and may be a harbinger of large vessel disease and cardiovascular disease (CVD). Indeed, plasma levels of ADMA are increased in many studies of patients at risk for, or with overt CKD or CVD. However, the levels of ADMA measured in plasma of about 0.5 μmol • l −1 maybe below those required to inhibit NOS whose substrate, L-arginine, is present in concentrations manifold above the Km for NOS. However, NOS activity may be partially inhibited by cellular ADMA. Therefore, the cellular production of ADMA by protein arginine methyltransferase (PRMT) and protein hydrolysis, its degradation by N G , N G-dimethylarginine dimethylaminohydrolase (DDAH) and its transmembrane transport by CAT that determines intracellular levels of ADMA may also determine the state of activation of NOS. This is the focus of the review. It is concluded that cellular levels of ADMA can be 5-to 20-fold those in plasma and in a range that could tonically inhibit NOS. The relative importance of PRMT, DDAH and CAT for determining the intracellular NOS substrate: inhibitor ratio (L-arginine:ADMA) may vary according to the pathophysiologic circumstance. An understanding of this important balance requires knowledge of at least these three processes that regulate the intracellular levels of ADMA and arginine. Keywords Nitric oxide synthase (NOS); protein arginine methyl transferase (PRMT); cationic amino acid (CAA); cationic amino acid transporter (CAT); cardiovascular disease; chronic kidney disease (CKD); hypertension; reactive oxygen species and oxidative stress
Kidney International, 2005
Effects of NADPH oxidase inhibitor in diabetic nephropathy. Background. We used apocynin to test ... more Effects of NADPH oxidase inhibitor in diabetic nephropathy. Background. We used apocynin to test the hypothesis that superoxide anion (O − 2) from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase underlies the development of diabetic nephropathy in the rat. Methods. Rats received apocynin (16 mg/kg/day) from 2 to 8 weeks after inducing diabetes mellitus (DM) with streptozotocin. Results. DM increased excretion of hydrogen peroxide (H 2 O 2), lipid peroxidation products (LPO), nitric oxide products (NOx), and protein. The kidneys of rats with DM had increased expression of p47phox and gp91phox and endothelial nitric oxide synthase (eNOS), and increased mesangial matrix with expression of fibronectin and collagen I. Apocynin prevented the increase in excretion of H 2 O 2 , LPO, and protein in diabetic rats, increased renal NOx generation, and prevented the increased renal expression of gp91phox and the membrane fraction of p47phox, and reverted the mesangial matrix expansion. Conclusion. Activation of NADPH oxidase with translocation of p47phox to the membrane underlies the oxidative stress and limited NO generation, despite enhanced eNOS expression in a model of diabetic nephropathy. Apocynin prevents these changes and the associated proteinuria. The balance between the production of reactive oxygen species (ROS), notably superoxide anion (O − 2) and hydrogen peroxide (H 2 O 2), and the antioxidant defense system that includes superoxide dismutase (SOD) and peroxidases, determines the degree of oxidative stress. An increased production and/or decreased metabolism of ROS have been implicated in the pathogenesis of renal injury in diabetes mellitus (DM) [1, 2]. An important source of ROS production is nicotinamide adenine dinucleotide phosphate (NADPH)
Endothelial dysfunction and reduced nitric oxide in resistance arteries in autosomal-dominant polycystic kidney disease
Kidney International, 2003
Patients with autosomal-dominant polycystic kidney disease (ADPKD) have defective endothelium-dep... more Patients with autosomal-dominant polycystic kidney disease (ADPKD) have defective endothelium-dependent relaxation (EDR). We investigated the relationship between endothelial dysfunction and nitric oxide generation in hypertension and chronic renal insufficiency (CRI) in ADPKD. We contrasted acetylcholine (ACh)-induced EDR, 3-morphollinosydnonimine (SIN-1)-induced endothelium-independent relaxation (EIDR) and constitutive nitric oxide synthase (cNOS) activity in subcutaneous resistance vessels and plasma levels and excretion of NO2-/NO3- (NOX) in normal, control (N = 10) patients with ADPKD or essential hypertension. EDR was decreased significantly in normotensive ADPKD (N = 9), but more severely in hypertensive ADPKD (N = 6), or those with CRI (N = 5) and in essential hypertension (N = 9). The increases in EDR with l-arginine and decreases with LG-nitro-l-arginine methyl ester (L-NAME) were lost in all groups of patients with ADPKD and in essential hypertension except for a modest effect of L-NAME in normotensive ADPKD. EIDR was unimpaired throughout. Vascular cNOS activity and renal NOX excretion were reduced profoundly in patients with all categories of ADPKD and especially in those with hypertension. EDR in resistance vessels from patients with ADPKD is impaired even in the absence of hypertension or CRI, but becomes more marked as hypertension develops. Patients with ADPKD have defective nitric oxide generation from diminished cNOS activity. Endothelial dysfunction and impaired cNOS activity in ADPKD may predispose to hypertension whose occurrence is accompanied by a further sharp deterioration in EDR.
Kidney International, 1994
Differential expression and induction of mRNAs encoding two inducible nitric oxide synthases in r... more Differential expression and induction of mRNAs encoding two inducible nitric oxide synthases in rat kidney. We used quantitative PCR methods and renal microdissection to characterize the expression of inducible nitric oxide synthase (iNOS) mRNAs in rat kidney and cultured glomerular mesangial cells. A partial cDNA homologous to murine macrophage iNOS (macNOS), but distinct from rat vascular smooth muscle iNOS (vsmNOS), was cloned from normal rat kidney. macNOS was the principal iNOS isoform tonically expressed in microdissected glomeruli, proximal tubules, medullary thick ascending limbs (mTAL), cortical and inner medullary collecting ducts (IMCD), and cultured mesangial cells, whereas vsmNOS was the major isoform expressed in arcuate and interlobular arteries. Basal macNOS expression was greatest in mTALs and IMCDs. Restriction mapping of RT-PCR products indicated that basal expression of macNOS mRNA was comparable to that of vsmNOS in cortex, but greater than vsmNOS in outer and inner medulla. However, compared to controls, lipopolysaccharide (LPS)-treated rats exhibited a much greater proportion of vsmNOS mRNA and higher levels of total iNOS mRNA in each zone. Similarly, TNFa and IF-y preferentially induced expression of vsmNOS mRNA in cultured mesangial cells. We conclude that two 1NOS isoforms are constitutively and heterogeneously expressed in the normal rat kidney, and that endotoxemia and cytokines differentially induce their expression. Nitric oxide (NO), a labile radical gas, is an important intercellular messenger that plays a prominent role in a host of physiological and pathophysiological processes [reviewed in 1 and 2]. Recent evidence indicates that NO has potent effects on renal function, including modulation of renal and glomerular hemodynamics, renin secretion, the tubuloglomerular feedback response, and sodium excretion [reviewed in 3]. NO production is mediated by the activity of NO synthase (NOS), a family of at least three isoenzymes that synthesizes NO from a terminal guanidino nitrogen of L-arginine. NOS Types I (neuronal, [4]) and III (endothehal, [5]) are constitutively expressed, but quiescent until activated by increased Ca2 levels that sustain calmodulin binding [1]. In contrast, Type II, or "inducible" NOS (iNOS) is strongly expressed after transcriptional activation by cytokines or lipopolysaccharide (LPS) [6], the major component of bacterial endotoxin. This form of the enzyme remains active for sustained periods and
Kidney International, 2003
after correction of baseline data to exclude the influence of Renal function and outcome of PTRA ... more after correction of baseline data to exclude the influence of Renal function and outcome of PTRA and stenting for atherothe expected regression to the mean. sclerotic renal artery stenosis. Conclusions. Patients with atherosclerotic RAS fulfilling strict Background. Prior studies of percutaneous transluminal recriteria of severity may have significant improvements in BP nal artery angioplasty and stenting (PTRAS) for atherosclerotic one year after PTRAS but only modest in GFR. The initial renal artery stenosis (RAS) have shown that renal function is GFR may anticipate whether the benefits in the outcome will improved in about 25%, stabilizes in about 40%, but worsens be in renal function enhancement (those with an initially dein about 25% of patients. The factors predicting benefit remain pressed GFR) or in hypertension control (those with an initially controversial. We tested the hypothesis that the baseline glonormal or mildly impaired GFR). merular filtration rate (GFR) predicts the changes in GFR and blood pressure (BP) after PTRAS. Methods. Treated hypertensive patients with positive renal color-coded duplex Doppler velocimetry and clinical criteria Renal artery stenosis (RAS) causing renovascular diswere screened by arteriography. Patients (N ϭ 105) were included ease was considered a rare cause of secondary hypertenif they had an RAS Ն70%, a transluminal pressure gradient sion. However, with improvements in techniques for Ն30 mm Hg and, they had more than 100 days of follow-up. GFR was calculated from the serum creatinine concentration screening and with the widespread use of vascular im-(S Cr). Patients were divided by baseline GFR into subgroups aging, it is now recognized that 40 to 50% of patients with normal to mildly impaired (N ϭ 52) or moderately to with occlusive disease of the lower limb [1] and 15 to 30% severely impaired (N ϭ 53) initial GFR, according to a GFR of patients with coronary artery disease have identifiable Ն50 or Ͻ50 mL • min Ϫ1 respectively. All received PTRAS. RAS [2]. Reports of patients with established, or newly Results. For the entire group, after a mean follow-up period diagnosed, end-stage renal disease (ESRD) indicate a of 371 days, there were significant reductions in systolic and diastolic BP (before, 160 Ϯ 26/91 Ϯ 12 vs. after, 145 Ϯ 20/83
Kidney International, 1993
Nitric oxide mediates renal vasodilation during erythropoietin-lnduced polycythemia. The renal bl... more Nitric oxide mediates renal vasodilation during erythropoietin-lnduced polycythemia. The renal blood flow (RBF) of patients with polycythemia rubra vera is increased despite the high hematocrit (Hct) which elevates the whole blood viscosity. Since blood viscosity determines the shear force on the endothelium which is a major stimulus to nitric oxide (NO) release, we investigated the hypothesis that renal vasodilation during erythropoietin-induced erythrocytosis is mediated by the L-arginine-NO pathway. Groups of Sprague-Dawley rats received thrice weekly injections of crythropoietia (E) for two to five weeks; responses were contrasted with normal rats (N) which received sham injections. The first group was studied after five weeks of erythropoietin injections which led to sharp increases in Hct (B: 72 3 vs. N: 44 1%) and mean arterial pressure (MAP: 126 3 vs. 107 3 mm Hg). These rats had an elevated basal RBF whether measured by the clearance and renal extraction of PAH or by a transit-time renal blood flow meter. Subsequent groups were studied after two to three weeks of erythropoietin which raised the Hct more modestly to 59 2%. In this group, the basal MAP was similar in B and N rats. Graded doses of the NO synthase inhibitor, N'-moaomethyl-L-argithne (L-NMA) led to a steeper rise in MAP in E than N; at the highest doses, the MAP had increased by 36 2 in B and 23 3 mm Hg in N (P < 0.01). Therefore, to assess the effects of L-NMA on renal vascular resistance without the confounding effects of differences in MAP, the renal perfusion pressure (RPP) was controlled with a suprarenal aortic clamp. In the basal state, the RBF was higher in F than N (F: 5.33 0.54 vs. N: 3.85 0.28 ml' min' 100 g'; Pc 0.025). L-NMA caused a greater reduction in RBF, and a greater rise in filtration fraction (FE) and renal vascular resistance (RVR) in erythropoietin-treated rats. During L-NMA, the RBF became similar in the two groups (F: 2.19 0.50 vs. N: 2.42 0.32 ml min' 100 g'; NS). We conclude that an enhanced generation of NO from L-arginine maintains normotension and mediates renal vasodilation in rats with erythropoietin-induced erythrocytosis. In vitro studies have shown that the hematocrit (Hct) is the major determinant of whole blood viscosity which increases exponentially with Hct values above the physiologic range [1, 21. Indeed, increases in the Hct of blood perfusing a dog's hind limb preparation [3] or an isolated perfused dog's kidney [4] in which active vasomotor changes are prevented, reduce blood flow. In contrast, an abrupt increase in the Hct of blood perfusing a dog's kidney in which vasomotor changes are intact
Kidney International, 1994
Renal vasoconstriction during inhibition of NO synthase: Effects of dietary salt. Since dietary s... more Renal vasoconstriction during inhibition of NO synthase: Effects of dietary salt. Since dietary salt loading enhances nitric oxide (NO) generation in the kidney, we investigated the hypothesis that changes in salt intake have specific effects on vascular resistance in the kidney mediated by the L-arginine-NO pathway. We contrasted changes in renal and hindquarter vascular resistances (RVR and HQVR) in anesthetized rats during intravenous infusions of graded doses of the NO synthase inhibitor N°-nitro-L-arginine methyl ester (L-NAME). Groups (N = 8 to 10) of rats were maintained on a high salt (HS) or low salt (LS) diet for two weeks. Compared to those on LS, rats on HS had a greater increase in mean arterial pressure (AMAP; +32 4 vs. +22 3%; P 0.05) and RVR (+ 160 17 vs. +83 10%; P < 0.005) and a greater fall in renal blood flow (zRBF;-47 3 vs.-32 4%; P < 0.01); changes in HQVR were similar in the two groups. The enhanced RVR response to L-NAME in HS rats could not be ascribed to the higher renal perfusion pressure (RPP) since it persisted in rats whose RPP was controlled by adjustment of a suprarenal aortic clamp. Changes in RVR with an NO donor (SIN-i) were similar in HS and LS rats. L-NAME reduced plasma renin activity in both HS and LS rats. After inhibition of ACE with captopril, or of angiotensin II type I (AT1) receptor with losartan, the increase in RVR with L-NAME remained greater in HS than LS rats. In conclusion, an increase in dietary salt potentiates the renal vascular response to L-NAME. This effect is specific for the kidney and cannot be ascribed to changes in NO responsiveness or RPP or to effects of Ang II generation or action on AT1 receptors. Generation of nitric oxide (NO) from L-arginine by nitric oxide synthase (NOS) leads to vasorelaxation of renal and systemic blood vessels [1-4]. Micropuncture and microperfusion studies in vivo have disclosed a functional role for NO as a signalling molecule between the macula densa (MD) and the afferent arteriole [5]. This MD-derived NO vasodilates the afferent arteriole and counteracts vasoconstrictor stimuli generated by the tubuloglomerular feedback (TGF) response [5]. Dietary salt loading enhances the renal production of NO, as indexed by the excretion of NO2 and NO3 and cyclic guanosine monophosphate (cGMP) [6]. Since TGF is a specific renal response, the first aim of these studies was to examine the hypothesis that there is a specific renal vasodilator pathway mediated by L-arginine-derived NO that is activated by dietary salt loading. Some investigators have shown that increases in renal vascular
Kidney International, 2003
Contributions of nitric oxide, EDHF, and EETs to endothe-Endothelium-derived nitric oxide is the ... more Contributions of nitric oxide, EDHF, and EETs to endothe-Endothelium-derived nitric oxide is the principal melium-dependent relaxation in renal afferent arterioles. diator of acetylcholine-induced endothelium-dependent Background. Acetylcholine-induced endothelium-dependent relaxation in large conduit arteries, while the contriburelaxation in the renal afferent arteriole has been ascribed to tions of hyperpolarizing vasodilators [endothelium-derived nitric oxide, but the role of endothelium-derived hyperpolarizhyperpolarizing factors (EDHFs)] often predominate in ing factors (EDHFs) and 14,15-epoxyeicosatrienoic acid (14,15small resistance vessels [1]. Technical limitations in the EET) are unclear. Methods. Single afferent arterioles were dissected from kid-study of isolated afferent arterioles have limited the ney of normal rabbits and microperfused in vitro at 60 mm Hg. ability to assess contributions of mediators to endothe-Vessels were preconstricted submaximally with norepinephrine lium-dependent relaxation in this key preglomerular re-(10 Ϫ8 mol/L). Relaxation was assessed following cumulative sistance vessel, absent influences which might contribaddition of ACh (10 Ϫ9 to 10 Ϫ4 mol/L) alone, or in the presence ute in more complex, intact preparations. Nitric oxideof indomethacin (to inhibit cyclooxygenase), N w-nitro-l-argimediated vasodilation usually depends on activation of nine (L-NNA) (to inhibit nitric oxide synthase), methylene soluble guanylyl cyclase in smooth muscle cells, leading to blue (to inhibit soluble guanylate cyclase), or a combination of L-NNA ϩ methylene blue. To assess contributions by EDHF, increments of cyclic guanosine monophosphate (cGMP) studies were repeated with either apamin ϩ charybdotoxin [to and activation of cGMP-dependent kinases, which can diblock Ca 2ϩ-activated K ϩ channels (K Ca)] or with 40 mmol/L minish the Ca 2ϩ-sensitivity of the contractile apparatus [2]. KCl. To asses the role of 14,15-EET, relaxations were evaluated Mediators of endothelium-dependent hyperpolarization in the presence of its competitive inhibitor 14,15-epoxyeicosavary with species and vascular bed and include epoxyei-5(Z)-enoic acid (14,15-EEZE). cosatrienoic acids (EETs) [3], endocannabinoids [4], K ϩ Results. Relaxation by acetylcholine was abolished following endothelial denudation. It was unaffected by indomethacin [5], hydrogen peroxide (H 2 O 2) [6, 7], or nitric oxide itself but was inhibited 54% Ϯ 5% (P Ͻ 0.001) by L-NNA, 57% Ϯ [8-10]. Hyperpolarization of the vascular myocyte cell 5% by methylene blue, and 60% Ϯ 4% by the combination of membrane closes voltage-dependent Ca 2ϩ channels, lim-L-NNA plus methylene blue. Relaxation was inhibited further iting intracellular free [Ca 2ϩ ] and effecting relaxation [11]. by KCl (80% Ϯ 6%) or by apamin ϩ charybdotoxin (96% Ϯ EETs are endothelium-derived, cytochrome P-450-2%). 14,15-EEZE, alone, inhibited acetylcholine-induced redependent oxidative (epoxide) metabolites of arachilaxation by 29% Ϯ 3%, and by 80% Ϯ 5% in the presence of donic acid which act as EDHFs in the coronary circula-L-NNA. Conclusion. Acetylcholine-induced afferent arteriolar retion [12]. Nonspecific inhibitors of cytochrome P-450 laxation depends strongly on both nitric oxice, acting via soluhave been used as probes of EDHF effect, but they may ble guanylate cyclase, and on an EDHF, likely 14,15-EET, inhibit the synthesis of a variety of vasoactive factors with acting via K Ca. opposing effects and can, themselves, act as K ϩ channel blockers in some preparations, confounding their use [13]. Recently, highly selective, competitive inhibitors of
Kidney International, 1995
Biopsies were obtained under ultrasonographic guidance using a modified Vim-Silverman needle or a... more Biopsies were obtained under ultrasonographic guidance using a modified Vim-Silverman needle or an automated biopsy gun. The tissues were fixed in a proprietary buffered formaldehyde ionized zinc solution (Z-fix, Anatech Ltd., Battle Creek, MI), embedded in paraffin wax, and processed for routine histological studies including hematoxylin-eosin and periodic acid-Schiff stains. The
Kidney International, 2000
The l-arginine-nitric oxide (NO) pathway has been aseffects of salt intake and angiotensin. signe... more The l-arginine-nitric oxide (NO) pathway has been aseffects of salt intake and angiotensin. signed many important functions in the kidney, including Background. Nitric oxide (NO) is generated from NO synthe regulation of vascular resistance and glomerular filthase (NOS) isoforms. These enzymes can be inhibited by asymtration rate (GFR), tubular NaCl reabsorption in the metric dimethylarginine, which is inactivated by N G-N G-dimethproximal tubule, loop and collecting duct segments, renin ylarginine dimethylaminohydrolase (DDAH). The neuroneal (nNOS) type I and endothelial (eNOS) type III constitutive NOS release, and tubuloglomerular feedback (TGF) [1, 2]. This isoforms are expressed predominantly in the macula densa and pathway is implicated in the renal responses to changes microvascular endothelium of the renal cortex, respectively. in salt intake [3-7] and blood pressure (BP) [8, 9]. DDAH is expressed at sites of NOS expression. Since NO may Two constitutive isoforms of NO synthase (NOS) are coordinate the renal responses to angiotensin II (Ang II) and changes in salt intake, we tested the hypothesis that salt intake expressed in the kidney. The protein or mRNA for type I regulates the expression of nNOS, eNOS and DDAH by Ang II or neuronal NOS (nNOS) is expressed heavily in the acting on type 1 (AT 1) receptors. macula densa, with additional expression in the efferent Methods. Groups (N ϭ 6) of rats were adapted to low-salt arterioles, Bowman's capsule, some cells of the cortical (LS) or high-salt (HS) intakes for 10 days. Other groups of LS thick ascending limb (TAL) of the loop of Henle, and and HS rats received the AT 1 receptor antagonist losartan for six days (to test the effects of salt independent of AT 1 recepthe collecting ducts [1, 2, 10-15]. The protein [14, 16, 17] tors). A further group of HS rats received an infusion of Ang II or mRNA [18] for type III, or endothelial NOS (eNOS), for six days (to test the effect of Ang II independent of salt is expressed in the endothelium of the afferent and efferintake). ent arterioles and the glomerular capillaries. Results. Compared with HS rats, there was a significant (P Ͻ 0.05) increase in LS rats of nNOS protein in kidney and immu-Several mechanisms have been identified that could nohistochemical expression in the macula densa, and of eNOS regulate constitutive NOS activity in the kidney. NOS protein expression and immunohistochemical expression in the is inhibited competitively by endogenous asymmetrical microvascular endothelium, and of DDAH protein expression. dimethylarginine (ADMA) [17]. NOS activity in macula Losartan prevented these effects of salt on the expression of densa cells of salt-restricted rats is limited by cellular up-eNOS or DDAH, both of which were also increased by Ang II infusions in HS rats. In contrast, losartan did not prevent the take of l-arginine via a specific cationic amino acid transeffects of salt on nNOS expression, which was unresponsive porter, termed y ϩ [6]. l-arginine uptake via system y ϩ into to Ang II infusion. The generation of NO Ϫ 2 released by slices of renal tubular epithelial cells is inhibited by both ADMA renal cortex, in the presence of saturating concentrations of and symmetric dimethylarginine (SDMA) [17]. ADMA is l-arginine, was increased by LS, compared to HS, independent of losartan and by Ang II during HS. metabolized by N G-N G-dimethylarginine dimethylamino-Conclusion. The expressions of eNOS in cortical microvashydrolase (DDAH) to l-citrulline and is thereby inacticular endothelium and DDAH in kidney are enhanced by Ang II vated. DDAH is heavily expressed in specific sites in the acting on AT 1 receptors. The expression of nNOS in the macula kidney that correspond to those of NOS expression [17].