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Papers by Julian Lombard

American journal of hypertension, 2011

Nitric oxide (NO)-dependent vasodilation is impaired in middle cerebral arteries (MCAs) from Dahl... more Nitric oxide (NO)-dependent vasodilation is impaired in middle cerebral arteries (MCAs) from Dahl salt-sensitive (SS) rats that are fed normal salt (NS) diet, due to low plasma renin activity and chronic exposure to low plasma angiotensin II (ANG II) levels. NO-dependent vasodilator responses are rescued in MCAs from Ren1-BN congenic rats, which have a 2.0 Mbp portion of Brown Norway (BN) chromosome 13 containing the renin gene introgressed onto the Dahl SS genetic background. Vascular superoxide levels were measured with dihydroethidium (DHE) fluorescence in basilar arteries from 10- to 14-week-old, male Dahl SS and Ren1-BN congenic rats that fed NS diet. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and xanthine oxidase (XO) activity were also measured in cerebral artery tissue homogenates. Expression of the superoxide dismutase (SOD) enzymes was evaluated via western blotting in cerebral arteries from the two rat strains. Superoxide levels were significantly higher ...

American journal of physiology. Heart and circulatory physiology, Jan 4, 2015

Nuclear factor (erythroid-derived 2)-like-2 (NRF2) is a master antioxidant and cell protective tr... more Nuclear factor (erythroid-derived 2)-like-2 (NRF2) is a master antioxidant and cell protective transcription factor that upregulates antioxidant defenses. In this study we developed a strain of Nrf2 null mutant rats to evaluate the role of reduced NRF2-regulated antioxidant defenses in contributing to endothelial dysfunction and impaired angiogenic responses during salt-induced ANG II suppression. Nrf2((-/-)) mutant rats were developed using TALEN technology in the Sprague-Dawley genetic background, and exhibited a 41 base pair deletion that included the start codon for Nrf2 and an absence of immunohistochemically-detectable NRF2 protein. Expression of mRNA for the NRF2-regulated indicator enzymes hemeoxygenase-1, catalase, superoxide dismutase 1, superoxide dismutase 2, and glutathione reductase was significantly lower in livers of Nrf2((-/-)) mutant rats fed high salt (HS; 4% NaCl) for two weeks compared to wild type controls. Endothelium-dependent dilation to acetylcholine (ACh) ...

American journal of physiology. Heart and circulatory physiology, Jan 23, 2015

To determine the impact of progressive elevations in peripheral vascular disease (PVD) risk on mi... more To determine the impact of progressive elevations in peripheral vascular disease (PVD) risk on microvascular function, we utilized eight rat models spanning "healthy" to "high PVD risk" and used a multi-scale approach to interrogate microvascular function and outcomes. Healthy: Sprague-Dawley rats (SDR), lean Zucker rats (LZR); Mild Risk: SDR on high salt diet (HSD), SDR on high fructose diet (HFD); Moderate Risk: reduced renal mass hypertension (RRM), spontaneously hypertensive rats (SHR); High Risk: obese Zucker rats (OZR) and Dahl salt sensitive rats (DSS). Vascular reactivity and biochemical analyses demonstrated that even mild elevations in PVD risk severely attenuated nitric oxide bioavailability and caused progressive shifts in arachidonic acid metabolism increasing thromboxane A2 levels. With the introduction of hypertension, arteriolar myogenic activation and adrenergic constriction were increased. However, while functional hyperemia and fatigue resistan...

American Journal of Physiology Heart and Circulatory Physiology, May 1, 1992

A mathematical model of oxygen transport in tissue was used to analyze the effects of microvessel... more A mathematical model of oxygen transport in tissue was used to analyze the effects of microvessel rarefaction and nonhomogeneous oxygen consumption on tissue oxygen distribution. The model was based on the diffusion equation with a nonhomogeneous consumption term. Solutions were computed for several configurations of vessel and oxygen sink distributions on a finite domain using the finite element method. A microcirculatory unit consisting of a tissue slice of 100-microns depth and 40-microns width was chosen. Symmetry boundary conditions were applied so that the entire tissue consisted of a series of such microvascular units placed side by side. The boundary condition at the surface of the unit was chosen to simulate a tissue suffusion experiment in which the suffusion oxygen was varied from 0 to 37 mmHg. Results of the model, which were compared with direct measurements with oxygen microelectrodes, indicate that vascular oxygen delivery strongly dominates the tissue oxygen field for suffusion PO2 values of less than 20 mmHg, whereas above this level tissue oxygen is dominated by the suffusion PO2. Reduction of vessel density within the tissue was found to have the largest effect on tissue oxygen levels at low suffusion oxygen. Finally, under some configurations of oxygen sources (vessels) and sinks (mitochondria), extremely low PO2 levels may exist within the area of high consumption, which could limit the metabolic activity of the tissue.

American Journal of Physiology Heart and Circulatory Physiology, Oct 1, 2001

This study determined the effects of hypoxia on diameter, vascular smooth muscle (VSM) transmembr... more This study determined the effects of hypoxia on diameter, vascular smooth muscle (VSM) transmembrane potential (E(m)), and vascular cAMP levels for in vitro cannulated skeletal muscle resistance arteries (gracilis arteries) from Sprague-Dawley rats fed a low-salt (LS) or a high-salt (HS) diet. Arterial diameter and VSM E(m) were measured in response to hypoxia, iloprost, cholera toxin, forskolin, and aprikalim. In HS rats, arterial dilation and VSM hyperpolarization after hypoxia, iloprost, and cholera toxin were impaired versus responses in LS rats, whereas responses to forskolin and aprikalim were unaltered. Blockade of prostaglandin H(2) and thromboxane A(2) receptors had no effect on responses to hypoxia or iloprost in vessels from both rat groups, suggesting that inappropriate activation of these receptors does not contribute to the impaired hypoxic dilation with HS. Hypoxia, cholera toxin, and iloprost increased vascular cAMP levels in vessels of LS rats only, whereas forskolin increased cAMP levels in all vessels. These data suggest that reduced hypoxic dilation of skeletal muscle microvessels in rats on a HS diet may reflect an impaired ability of VSM to produce cAMP after exposure to prostacyclin.

The Faseb Journal, Apr 1, 2009

American Journal of Physiology Heart and Circulatory Physiology, Apr 1, 2001

Cytochrome P-450 -hydroxylase: a potential O 2 sensor in rat arterioles and skeletal muscle cells... more Cytochrome P-450 -hydroxylase: a potential O 2 sensor in rat arterioles and skeletal muscle cells. Am J Physiol Heart Circ Physiol 280: H1840-H1845, 2001.-The purposes of this study were to 1) further evaluate the possible role that vasoconstrictor metabolites of cytochrome P-450 (CYP) -hydroxylase plays in O 2 -induced constriction of arterioles in the rat skeletal muscle microcirculation, 2) determine whether -hydroxylases are expressed in rat cremaster muscle, and 3) determine whether the enzyme is located in the parenchyma or the arterioles. O 2 -induced constriction of third-order arterioles in the in situ cremaster muscle of Sprague-Dawley rats was significantly inhibited by the CYP inhibitors N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS; 50 M) and 17-octadecynoic acid (ODYA; 10 M). Immunoblot analysis with antibody raised against CYP4A protein indicated the presence of immunoreactive proteins in the cremaster muscle and in isolated arterioles and muscle fibers from this tissue. However, the molecular mass of the immunoreactive proteins was 85 kDa instead of the expected 50-52 kDa for CYP4A -hydroxylase isolated from rat liver or kidney. Treatment of the cremaster muscle with deglycosidases shifted the bands to the expected range which indicates that these proteins are likely glycosylated in skeletal muscle. Immunohistochemistry revealed intense staining of both muscle fibers and microvessels in the cremaster muscle. The results of this study indicate that O 2 sensing in the skeletal muscle microcirculation may be mediated by CYP4A -hydroxylases in both arterioles and parenchymal cells.

Male Sprague-Dawley rats were maintained on a low-salt (LS) diet (0.4% NaCl) or changed to a high... more Male Sprague-Dawley rats were maintained on a low-salt (LS) diet (0.4% NaCl) or changed to a high-salt (HS) diet (4% NaCl) for 3 days. Increases in intracellular Ca2+ ([Ca2+]i) in response to methacholine (10 microM) and histamine (10 microM) were significantly attenuated in aortic endothelial cells from rats fed a HS diet, whereas thapsigargin (10 microM)-induced increases in [Ca2+]i were unaffected. Methacholine-induced nitric oxide (NO) production was eliminated in endothelial cells of aortas from rats fed a HS diet. Low-dose ANG II infusion (5 ng x kg(-1) x min(-1) iv) for 3 days prevented impaired [Ca2+]i signaling response to methacholine and histamine and restored methacholine-induced NO production in aortas from rats on a HS diet. Adding Tempol (500 microM) to the tissue bath to scavenge superoxide anions increased NO release and caused N(omega)-nitro-L-arginine methyl ester-sensitive vascular relaxation in aortas from rats fed a HS diet but had no effect on methacholine-induced Ca2+ responses. Chronic treatment with Tempol (1 mM) in the drinking water restored NO release, augmented vessel relaxation, and increased methacholine-induced Ca2+ responses significantly in aortas from rats on a HS diet but not in aortas from rats on a LS diet. These findings suggest that 1) agonist-induced Ca2+ responses and NO levels are reduced in aortas of rats on a HS diet; 2) increased vascular superoxide levels contribute to NO destruction, and, eventually, to impaired Ca2+ signaling in the vascular endothelial cells; and 3) reduced circulating ANG II levels during elevated dietary salt lead to elevated superoxide levels, impaired endothelial Ca2+ signaling, and reduced NO production in the endothelium.

Journal of Hypertension Supplement Official Journal of the International Society of Hypertension, Oct 1, 1989

Control of blood flow is mediated by a variety of metabolic, neurogenic, myogenic and other mecha... more Control of blood flow is mediated by a variety of metabolic, neurogenic, myogenic and other mechanisms. The basic response of the myogenic mechanisms is a mechanical stimulus that activates vascular muscle via a sensor within the vessel wall. We studied the way in which increases in transmural pressure within the physiological range can activate cerebral and renal vascular muscle by depolarizing the muscle cell membrane. These membrane electrical effects depend on the external calcium concentration [( Ca2+]o) and on the presence of an intact vascular endothelium. Bioassay experiments have shown that an elevation in pressure releases a vasoactive product(s) from endothelial cells, which mediates the pressure-dependent membrane depolarization in these vessels. These responses may affect the autoregulation of blood flow in that vessels become smaller as pressures increase between 60 and 160 mmHg.

Ajp Heart and Circulatory Physiology, May 1, 2001

The purposes of this study were to 1) further evaluate the possible role that vasoconstrictor met... more The purposes of this study were to 1) further evaluate the possible role that vasoconstrictor metabolites of cytochrome P-450 (CYP) omega-hydroxylase plays in O(2)-induced constriction of arterioles in the rat skeletal muscle microcirculation, 2) determine whether omega-hydroxylases are expressed in rat cremaster muscle, and 3) determine whether the enzyme is located in the parenchyma or the arterioles. O(2)-induced constriction of third-order arterioles in the in situ cremaster muscle of Sprague-Dawley rats was significantly inhibited by the CYP inhibitors N-methyl-sulfonyl-12,12-dibromododec-11-enamide (DDMS; 50 microM) and 17-octadecynoic acid (ODYA; 10 microM). Immunoblot analysis with antibody raised against CYP4A protein indicated the presence of immunoreactive proteins in the cremaster muscle and in isolated arterioles and muscle fibers from this tissue. However, the molecular mass of the immunoreactive proteins was 85 kDa instead of the expected 50--52 kDa for CYP4A omega-hydroxylase isolated from rat liver or kidney. Treatment of the cremaster muscle with deglycosidases shifted the bands to the expected range which indicates that these proteins are likely glycosylated in skeletal muscle. Immunohistochemistry revealed intense staining of both muscle fibers and microvessels in the cremaster muscle. The results of this study indicate that O(2) sensing in the skeletal muscle microcirculation may be mediated by CYP4A omega-hydroxylases in both arterioles and parenchymal cells.

The Faseb Journal, Apr 1, 2010

Pflugers Arch Eur J Physiol, 1994

The cellular mechanisms mediating hypoxiainduced dilation of cerebral arteries have remained unkn... more The cellular mechanisms mediating hypoxiainduced dilation of cerebral arteries have remained unknown, but may involve modulation of membrane ionic channels. The present study was designed to determine the effect of reduced partial pressure of 02, PO2, on the predominant K + channel type recorded in cat cerebral arterial muscle cells, and on the diameter of pressurized cat cerebral arteries. A K+-selective single-channel current with a unitary slope conductance of 215 pS was recorded from excised inside-out patches of cat cerebral arterial muscle cells using symmetrical KC1 solution. The open state probability (NPo) of this channel displayed a strong voltage dependence, was not affected by varying intracellular ATP concentration [(ATP]~) between 0 and 100 pM, but was significantly increased upon elevation of iutracellular free Ca 2+ concentration ([Ca2+]~). Low concentrations of external tetraethylammonium (0.1-3 raM) produced a concentration-dependent reduction of the unitary current amplitude of this channel. In cell-attached patches, where the resting membrane potential was set to zero with a high KC1 solution, reduction of 02 from 21% to < 2% reversibly increased the NPo, mean open time, and event frequency of the Ca2+-sensitive, high-conductance single-channel K + current recorded at a patch potential of + 20 mV. A similar reduction in PO2 also produced a transient increase in the activity of the 215-pS K + channel measured in excised inside-out patches bathed in symmetrical 145 mM KC1, an effect which was diminished, or not seen, during a second application of hypoxic superfusion. Hypoxia had no effect on [Ca2+]~ or intracellular pH (pHi) of cat cerebral arterial muscle cells, as measured using Ca 2+-or pH-sensitive fluorescent probes. Reduced PO2 caused a significant dilation of pressurized cerebral arterial segments, which was attenuated by pretreatment with i mM tetraethylammonium. These results suggest that reduced POz increases the activity of a high-conductance, Ca>-sensitive K + channel in cat cerebral arterial muscle cells, and that these effects are mediated by cytosolic events independent of changes in [Ca2+]i and pHi.

The Journal of Physiology, 2015

Recent studies have shown that some of the deleterious effects of a high-salt (HS) diet are indep... more Recent studies have shown that some of the deleterious effects of a high-salt (HS) diet are independent of elevated blood pressure and are associated with impaired endothelial function. Increased generation of cyclo-oxygenase (COX-1 and COX-2)-derived vasoconstrictor factors and endothelial activation may contribute to impaired vascular relaxation during HS loading. The present study aimed to assess the regulation of microvascular reactivity and to clarify the role of COX-1 and COX-2 in normotensive subjects on a short-term HS diet. The present study demonstrates the important role of COX-1 derived vasoconstrictor metabolites in regulation of microvascular blood flow during a HS diet. These results help to explain how even short-term HS diets may impact upon microvascular reactivity without changes in blood pressure and suggest that a vasoconstrictor metabolite of COX-1 could play a role in this impaired tissue blood flow. The present study aimed to assess the effect of a 1-week high-salt (HS) diet on the role of cyclo-oxygenases (COX-1 and COX-2) and the vasoconstrictor prostaglandins, thromboxane A2 (TXA2 ) and prostaglandin F2α (PGF2α ), on skin microcirculatory blood flow, as well as to detect its effect on markers of endothelial activation such as soluble cell adhesion molecules. Young women (n = 54) were assigned to either the HS diet group (N = 30) (∼14 g day(-1) NaCl ) or low-salt (LS) diet group (N = 24) (&amp;amp;amp;lt;2.3 g day(-1) NaCl ) for 7 days. Post-occlusive reactive hyperaemia (PORH) in the skin microcirculation was assessed by laser Doppler flowmetry. Plasma renin activity, plasma aldosterone, plasma and 24 h urine sodium and potassium, plasma concentrations of TXB2 (stable TXA2 metabolite) and PGF2α , soluble cell adhesion molecules and blood pressure were measured before and after the diet protocols. One HS diet group subset received 100 mg of indomethacin (non-selective COX-1 and COX-2 inhibitor), and another HS group subset received 200 mg of celecoxib (selective COX-2 inhibitor) before repeating laser Doppler flowmetry measurements. Blood pressure was unchanged after the HS diet, although it significantly reduced after the LS diet. Twenty-four hour urinary sodium was increased, and plasma renin activity and plasma aldosterone levels were decreased after the HS diet. The HS diet significantly impaired PORH and increased TXA2 but did not change PGF2α levels. Indomethacin restored microcirculatory blood flow and reduced TXA2 . By contrast, celecoxib decreased TXA2 levels but had no significant effects on blood flow. Restoration of of PORH by indomethacin during a HS diet suggests an important role of COX-1 derived vasoconstrictor metabolites in the regulation of microvascular blood flow during HS intake.

The American journal of physiology

P-450 -hydroxylase senses O 2 in hamster muscle, but not cheek pouch epithelium, microcirculation... more P-450 -hydroxylase senses O 2 in hamster muscle, but not cheek pouch epithelium, microcirculation. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H503-H508, 1999.-The goal of this study was to investigate the role of cytochrome P-450 -hydroxylase in mediating O 2induced constriction of arterioles in the microcirculation of the hamster. Male Golden hamsters were anesthetized with pentobarbital sodium, and the cremaster muscle or cheek pouch was prepared for observation by intravital microscopy. Arteriolar diameters were measured during elevations of superfusate PO 2 from ϳ5 to 150 mmHg. Arteriolar responses to elevated PO 2 were determined in the cremaster muscle, in the retractor muscle where it inserts on the cheek pouch, and in the epithelial portion of the cheek pouch. Elevation of superfusion solution PO 2 caused a vigorous constriction of arterioles in the cremaster and retractor muscles and in the epithelial portion of the cheek pouch. Superfusion with 10 µM 17-octadecynoic acid, a suicide substrate inhibitor of cytochrome P-450 -hydroxylase, and intravenous infusion of N-methylsulfonyl-12,12-dibromododec-11-enamide, a mechanistically different and highly selective inhibitor of cytochrome P-450 -hydroxylase, caused a significant reduction in the magnitude of O 2 -induced constriction of arterioles in the cremaster and retractor muscles. However, arteriolar constriction in response to elevated PO 2 was unaffected by 17-octadecynoic acid or N-methylsulfonyl-12,12-dibromododec-11-enamide in the epithelial portion of the cheek pouch. These data confirm that there are regional differences in the mechanism of action of O 2 on the microcirculation and indicate that cytochrome P-450 -hydroxylase senses O 2 in the microcirculation of hamster skeletal muscle, but not in the cheek pouch epithelium.

SUMMARY. The goal of this study was to determine whether electrophysiological mechanisms contribu... more SUMMARY. The goal of this study was to determine whether electrophysiological mechanisms contribute to the relaxation of cat middle cerebral artery in response to decreased ambient Pch and whether decreased P02 alters the myogenic depolarization and contraction of this vessel in response to elevations in transmural pressure. In one series of experiments, arterial segments (200-500 ^m outer diameter) were isolated

To evaluate the potential role of impaired renin-angiotensin system (RAS) function in contributin... more To evaluate the potential role of impaired renin-angiotensin system (RAS) function in contributing to reduced vascular relaxation in Dahl salt sensitive (S) rats, responses to acetylcholine (10 -6 mol/L) and hypoxia (PO 2 reduction to 40-45 mm Hg), were determined in isolated middle cerebral arteries of Dahl S rats, Brown Norway (BN) rats, and consomic rats having chromosome 13 (containing the renin gene) or chromosome 16 of the BN rat substituted into the Dahl S genetic background (SS-13 BN and SS-16 BN , respectively). Arteries of BN rats on LS diet (0.4% NaCl) dilated in response to acetylcholine and hypoxia, while dilation in response to these stimuli was absent in Dahl S rats on LS diet. Vasodilation to acetylcholine and hypoxia was restored in SS-13 BN rats on LS diet, but not in SS-16 BN rats. High salt diet (4% NaCl), to suppress ANG II, eliminated vasodilation to hypoxia and acetylcholine in BN and in SS-13 BN rats.

Abstract—This study investigated the role of impaired angiotensin II (Ang II) modulation,in contr... more Abstract—This study investigated the role of impaired angiotensin II (Ang II) modulation,in contributing to reduced vascular relaxation in isolated middle cerebral arteries (MCA) (100 to 200 m in diameter) of normotensive,Dahl salt-sensitive (SS) rats maintained on low salt (LS) diet (0.4% NaCl) for 9 to 10 weeks. MCA from SS rats on LS diet (n6 to 9) constricted in response

Commonly used methods for assessing reductions in microvascular density (rarefaction) in hyperten... more Commonly used methods for assessing reductions in microvascular density (rarefaction) in hypertension detect only perfused microvessels. In the present study, samples of cremaster and spinotrapezius muscles were taken from rats with chronic (4-week) reduced renal mass hypertension and normotensive sham-operated control rats, as well as from 12-week-old spontaneously hypertensive rats and their normotensive Wistar-Kyoto control strain. Mean arterial pressure was

American journal of hypertension, 2013

Elevated blood pressure, elevated angiotensin II (ANG II), and ANG II suppression with high salt ... more Elevated blood pressure, elevated angiotensin II (ANG II), and ANG II suppression with high salt (HS) diet all contribute to vascular dysfunction. This study investigated the interplay of HS diet and vascular function in a high renin model of hypertension. Male Sprague-Dawley rats were subjected to 2 kidney-1 clip (2K1C) Goldblatt hypertension for 4 weeks and compared with sham-operated controls. Middle cerebral arteries (MCA) of 2K1C rats and sham-operated controls fed normal salt (NS; 0.4% NaCl) diet dilated in response to acetylcholine (ACh) and reduced partial pressure of oxygen (PO2). Switching to HS (4% NaCl) diet for 3 days to reduce plasma renin activity (PRA) eliminated vasodilation to ACh and reduced PO2 in sham-operated controls, with no effect on vasodilation in 2K1C rats. AT1 receptor blockade (losartan, 20 mg/kg/day; 1 week) eliminated vasodilator responses to ACh and reduced PO2 in 2K1C rats fed NS or HS diet. ANG II infusion (5 ng/kg/min, intravenous) for 3 days to p...

American journal of physiology. Heart and circulatory physiology, 2002

The goal of this study was to determine how myogenic responses and vascular responses to reduced ... more The goal of this study was to determine how myogenic responses and vascular responses to reduced Po(2) interact to determine vascular smooth muscle (VSM) transmembrane potential and active tone in isolated middle cerebral arteries from Sprague-Dawley rats. Stepwise elevation of transmural pressure led to depolarization of the VSM cells and myogenic constriction, and reduction of the O(2) concentration of the perfusion and superfusion reservoirs from 21% O(2) to 0% O(2) caused vasodilation and VSM hyperpolarization. Myogenic constriction and VSM depolarization in response to transmural pressure elevation still occurred at reduced Po(2). Arterial dilation in response to reduced Po(2) was not impaired by pressure elevation but was significantly reduced at the lowest transmural pressure (60 mmHg). However, the magnitude of VSM hyperpolarization was unaffected by transmural pressure elevation. This study demonstrates that myogenic activation in response to transmural pressure elevation d...