Lowered plasma erythropoietin in hypoxic rats with kidney tubule lesions (original) (raw)
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Demonstration of high levels of erythropoietin in rat kidneys following hypoxic hypoxia
Pfl�gers Archiv European Journal of Physiology, 1981
Controversial hypotheses exist as to whether hypoxic kidneys produce biologically active erythropoietin (Ep) or an inactive erythropoietic factor that generates Ep from plasma protein in the blood. To clarify the role of the kidney in Ep production we attempted to extract Ep from kidneys of normal and of hypoxia exposed (6 h at 0.42 atm) Sprague-Dawley rats. Ep was measured in the microsomal fraction of kidney homogenates, using the exhypoxic polycythemic mouse assay for Ep. The Ep content was also determined in kidneys that were flushed free of blood with isotonic phosphate-buffer prior to extirpation. We found 0.04 U Ep/g in blood-depleted kidneys of normal rats. Upon exposure of the animals to hypoxia the Ep level increased to 0.92 U/g kidney. Ep levels were significantly higher in the kidney cortex than in the medulla. The erythropoietic activity in renal extracts was not enhanced after incubation of samples with homologous serum. Ep extracted from hypoxic kidneys behaved identically with plasma-Ep in the following biochemical tests: heat stability, affinity chromatography, with wheat germ lectin, ion exchange chromatography, molecular sieve chromatography, and neuraminidase inactivation. These studies support the hypothesis that kidney cortex cells are capable of producing biologically active Ep.
Temporal pattern of erythropoietin titers in kidney tissue during hypoxic hypoxia
Pfl�gers Archiv European Journal of Physiology, 1982
Plasma titers of erythropoietin (Ep) are known to increase initially during hypoxia and to return then towards prehypoxia values. To find out if this pattern of plasma Ep might be related to changes in the production of the hormone, I have compared plasma with kidney Ep titers in hypoxic rats. Rats were exposed to hypoxia in a hypobaric chamber at 0.42 atm for various time intervals for up to 4 days. Kidney Ep titers were assayed in extracts from kidneys that had been flushed free of blood in situ. It was found that kidneys of normal rats do not store significant amounts of Ep. Kidney Ep titers increased transiently during hypoxia. They reached maximum values after 6h and then declined to almost undetectable levels at continued hypoxia. In the plasma, maximum values were found after 12-18h of hypoxia. Additional studies were done on the effects of discontinuous hypoxia. It was found that, even after 3 days of previous hypoxia exposure, plasma and kidney Ep titers increased again in rats when these were maintained intermittently in normoxia for 18 h. It is concluded that the rise and fall in plasma Ep titers during hypoxia reflect similar changes in kidney Ep production.
O2-supply to the kidneys and the production of erythropoietin
Respiration Physiology, 1989
The concentration oferythropoietin (Ep) in blood increases little following a reduction ofthe renal blood flow (rbf). In the present study we examined whether a reduction of rbf in rats induces a lowering of the renal venous Po,. In addition, the combined effects of reduced rbf and hypobaric hypoxia on the production of Ep were studied. To lower rbf, silver clips with stepwisely reduced inner diameters were applied on both renal arteries. The Po2 of renal venous blood decreased gradually to values below 10 mm Hg, when rbf was reduced from 80 to 10~ of normal. Under these conditions plasma Ep increased only moderately from 20 + 6 to 69 + 24 mU/ml within 18-20 h. However, plasma Ep of rats exposed to hypobaric hypoxia (simulated altitude of 6000 m for 18-20 h) was 431 + 68 mU/ml, when rbfwas 100-80% of normal, compared to 931 + 91 mU/ml, when rbf was reduced to 40-10 %. Thus, a reduction of the blood flow to the kidney appears to be no major stimulus for the production of Ep, even when the Po2 in the kidney becomes very low. However, plasma levels of Ep increase markedly, when the whole body 02 offer is lowered. These results support the view that Ep production is not only dependent on the Po2 in the kidney but also under the control of extrarenal 02 sensitive mechanisms. For example, the hypothalamichypophyseal system is thought to influence the production of Ep.
Distribution of erythropoietin producing cells in rat kidneys during hypoxic hypoxia
Kidney …, 1993
Distribution of erythropoietin producing cells in rat kidneys during hypoxic hypoxia. We have used in situ hybridization to determine the localization and distribution of cells expressing the erythropoietin (EPO) gene in kidneys of rats exposed to reduced oxygen tensions to characterize the control of renal EPO formation during hypoxic hypoxia. Animals were subjected to severe hypoxia (7.5% 02) for4, 8 and
Erythropoietin production by interstitial cells of hypoxic monkey kidneys
British Journal of Haematology, 1996
Previous studies which demonstrated that interstitial cells of the peritubular capillary bed of the kidneys are the site of erythropoietin (Epo) production have been performed in non-primate species. In this study, kidneys from adult rhesus monkeys exposed to 18 h hypoxia (0. 42 atm) with high serum (5685 mU/ml) and kidney (814 mU/g, includes serum EPO in the kidney) levels of Epo were compared with a kidney from a nonhypoxic normal rhesus monkey. Localization of Epo mRNA by in situ hybridization was carried out with either anti-sense or sense RNA probes generated from a 645 base pair KpnI-BglII fragment of a monkey Epo cDNA. Epo mRNA was demonstrated only in interstitial cells in the peritubular capillary bed of the hypoxic and normal monkey kidneys utilizing the antisense probe. The finding that the same type of cell that produces EPO in mice, rats and sheep also produces EPO in a higher primate species strongly supports the contention that renal interstitial cells also produce EPO in the human.
Erythropoietin: A potential remedy for renal tubular injury?
Kidney International, 2004
Depending upon its extent, renal hypoxic or toxic insults lead either to frank tubular necrosis, programmed cell death (apoptosis), or sublethal reversible cell injury. Both programmed cell death and sublethal injury repair are energy-dependent processes, associated with the activation of numerous cellular reactions. This response ultimately ends with apoptotic death for some cells, and in adaptive preconditioning of the remaining viable tissue to withstand recurrent injury. Some of the energy consuming reparative responses, such as the activation of poly-(ADP-ribose) polymerase for the restoration of DNA breaks, may intensify cellular ATP depletion and oxygen debt and might paradoxically accentuate tissue damage [1]. This underscores the importance of coactivation of other factors required for a balanced cellular response. Many of those reactions to hypoxic stress are initiated by the so-called hypoxia-inducible factors (HIF). HIF are heterodimers consisting of constitutively expressed b-subunit and an oxygen-dependent and transcriptionally active a-subunit. HIF-a subunits are regulated by oxygen-dependent proteolysis. Recently, special prolyl-hydroxylases were discovered to act as cell oxygen sensors and as key enzymes of HIF-a degradation. Under low cellular oxygen tension prolyl hydroxylase activity is reduced, HIF-a accumulates within the cytoplasm, and binds to HIF-b, which allows HIF-a to translocate into the nucleus. The ab heterodimer binds to nuclear "hypoxia-responsive elements," leading to transcriptional activation of a wide set of genes, including erythropoietin (EPO). HIF-target genes are responsible for changes in cell cycle, glucose uptake, metabolism, and scavenging of free radicals. Genes controlling the expression of various heat-shock proteins, of angiogenesis, and vascular tone are also dominated by HIF [2, 3]. Up-regulation of these genes is in large part responsible for the well-known phenomenon of delayed hypoxic preconditioning (i.e., improved tolerance to repeated hypoxic stress). Indeed, HIF isoforms appear in tubular, interstitial, and vascular endothelial cells at the margin of infracted regions within the kidney [4], and in the outer and inner medulla in response to the well-characterized
The detection of erythropoietin (Epo) protein by Western blotting has required pre-purification of the sample. We developed a new Western blot method to detect plasma and urinary Epo using deglycosylation. Epo in urine and tissue and erythropoiesis-stimulating agents (ESAs) in urine were directly detected by our Western blotting. Plasma Epo and ESAs were detected by our Western blotting after deglycosylation. The broad bands of Epo and ESAs were shifted to 22 kDa by deglycosylation except PEG-bound epoetin β pegol. The 22 kDa band from anemic patient urine was confirmed by Liquid Chromatography/Mass Spectrometry (LC/MS) to contain human Epo.Sever hypoxia (7% O2, 4 hr) caused a 400-fold increase in deglycosylated Epo expression in rat kidneys, which is consistent with the increases in both Epo gene expression and plasma Epo concentration. Immunohistochemistry showed Epo expression in nephrons but not in interstitial cells under control conditions, and hypoxia increased Epo expression...
Role of the hypophysis in erythropoietin production during hypoxia
Blood
Hypophysectomized or sham-operated male rats were exposed to hypoxia (0.42--0.40 or 0.37--0.35 atm for 6, 12, or 24 hr) applied 2 wk to 7 mo after surgery. Erythropoietin (Ep) levels in rat serum were evaluated on the basis of the exhypoxic polycythemic mouse assay. Ep activity evoked by hypoxia was significantly lower in hypophysectomized rats than in sham-operated controls. Progressive increase of the EP response to hypoxia correlated with extension of the time interval between hypophysectomy and hypoxia from 2 wk to 2--4 mo apparently mediated by the simultaneous inverse decline of red cell mass (RCM) values, i.e., of the "relative plethora" induced by a low O2 demand associated with relatively high RCM values. However, after 3--7 mo hypoxic Ep activity was still lower than in sham-operated controls. In these ablated animals the relative plethora became negligible or absent; accordingly, the Ep response apparently had reached plateau levels. These studies indicate that ...