Role of Renal Nerves and Salt Intake on Erythropoietin Secretion in Rats following Carbon Monoxide Exposure

Abstract

Because the data from the literature contain conflicting results regarding the role of renal nerves and angiotensin II in hypoxiainduced erythropoietin (EPO) secretion, we evaluated the effect of renal nerves and salt intake in rats on EPO secretion stimulated by carbon monoxide (CO). Serum levels and renal mRNA content of EPO were similarly elevated by exposure to different CO concentrations in a dose-dependent manner in rats with bilateral renal denervation (DNX) and in sham-denervated controls (INN). However, at 600 ppm CO, serum concentrations and mRNA of EPO were significantly higher in DNX compared with INN rats (p Ͻ 0.05). This increase of EPO secretion in DNX rats could be blocked by administration of neuropeptide Y (NPY) (p Ͻ 0.05), whereas the NPY receptor antagonist did not enhance EPO secretion in INN rats after CO exposure. Agonists and antagonists of ␤-adrenergic receptors had no effect on EPO secretion. High-salt (HS) diet reduced EPO secretory response at 600 ppm CO by 55% compared with INN rats on normal salt diet (p Ͻ 0.01). In addition, DNX increased EPO secretion in rats on low-salt and HS diet, whereas plasma renin activity did not correlate with EPO levels under these experimental conditions. In summary, our data suggest that renal nerves contribute to the half-maximal EPO secretory response to CO exposure, possibly via NPY receptors.Erythropoietin (EPO), a glycoprotein hormone, is an essential growth factor that regulates erythropoiesis, and in adult laboratory animals and in humans, it is predominantly synthesized in the kidneys (Jelkmann, 1992;Jelkmann and Metzen, 1996). EPO secretion and renal mRNA content are inversely correlated to renal oxygen supply (Scholz et al., 1991). Because renal ischemia in isolated perfused kidneys elicited a much weaker EPO secretory response compared with systemic hypoxia in vivo, it was postulated that additional factors such as nerves and humoral factors may contribute to EPO secretory response to hypoxia (Pagel et al., 1989).Despite that multiple studies have investigated the role of renal nerves on EPO secretion, the published data are contradictory. Beynon (1977). reported increased EPO levels in rats exposed to 6 h of hypoxia (10% O 2 ) following denervation (DNX) of the left kidney and after contralateral nephrectomy compared with control rats with intact renal nerves. In contrast Fink and Fisher (1976) found reduced EPO levels in rabbits exposed to 5 h of hypoxia (0.42 atmospheres) following bilateral renal denervation in control animals. Eckardt et al. (1992) showed in rats that denervation of one kidney does not effect EPO mRNA following systemic exposure to hypoxia, hemorrhage, and carbon monoxide (CO) compared with the contralateral innervated control kidney.Moreover, combination of renal denervation and ␤-adrenergic receptor blockade showed to inhibit the hypoxia-stimulated EPO secretion compared with controls (Fink and Fisher, 1976). However, Jelkmann et al. (1979) could not confirm these findings, since his group reported unchanged ...

Expression and Localization of S-Adenosylhomocysteine-Hydrolase in the Rat Kidney Following Carbon Monoxide Induced Hypoxia

“…It is well known that under hypoxic or anaemic conditions, when arterial pO 2 is lowered, the EPO production increases in the renal tissue [18,[32][33][34][35][36]. Our data are in accordance with these previous studies and show that under CO exposure rat kidney cells can serve as experimental model for transcriptionally active nuclei.…”

“…The actual CO concentration was monitored by a CO sensor (Testo, Reutlingen). The deleterious effects of high CO concentrations in the inspired air on humans and animals have been reviewed and described by many authors [16][17][18]. After 4h of CO exposure rats were anesthetized with thiopental 90mg/kg i.p.…”

Lack of effect of extracellular adenosine generation and signaling on renal erythropoietin secretion during hypoxia

“…Adenosine is known to accumulate in the kidney in response to ischemia or increased tubular workload (27,35,36) and can change intrarenal hemodynamics by induction of vasoconstriction in the kidney and thus change local O 2 concentrations (52). The enzyme ecto-5Ј-nucleotidase, converting extracellular AMP into adenosine, is present on the cell surface of interstitial cells, which also positively stained for EPO mRNA (2,9,22). Furthermore, ARs and CD73 itself are transcriptionally induced by HIF-1 (34,48).…”

“…For carbon monoxide (CO) exposure [200 to 1,400 parts per million (ppm) CO], conscious male and female mice (paired in all groups, n ϭ 5-7 per group) were placed into a ventilated cage as previously described (9). In the normobaric hypoxic group, mice were exposed to 8% O 2.…”