NADPH Oxidase in the Renal Medulla Causes Oxidative Stress and Contributes to Salt-Sensitive Hypertension in Dahl S Rats

Abstract

Abstract-Dahl salt-sensitive (SS) rats exhibit increased renal medullary oxidative stress and blood pressure salt-sensitivity compared with consomic, salt-resistant SS-13 BN rats, despite highly similar genetic backgrounds. The present study examined potential sources of renal medullary superoxide in prehypertensive SS rats fed a 0.4% NaCl diet by assessing activity and protein levels of superoxide producing and scavenging enzymes. Superoxide production was nearly doubled in SS rats compared with SS-13 BN rats as determined by urinary 8-isoprostane excretion and renal medullary oxy-ethidium microdialysate levels. Medullary superoxide production in tissue homogenates was greater in SS rats, and the NADPH oxidase inhibitor diphenylene iodonium preferentially reduced SS levels to those found in SS-13 BN rats. Dinitrophenol, a mitochondrial uncoupler, eliminated the remaining superoxide production in both strains, whereas inhibition of xanthine oxidase, NO synthase, and cycloxygenase had no effect. L-arginine, NO synthase, superoxide dismutase, catalase, and glutathione peroxidase activities between SS and SS-13 BN rats did not differ. Chronic blood pressure responses to a 4% NaCl diet were then determined in the presence or absence of the NADPH oxidase inhibitor apocynin (3.5 g/kg per minute), chronically delivered directly into the renal medulla. Apocynin infusion reduced renal medullary interstitial superoxide from 1059Ϯ130 to 422Ϯ80 (oxyethidium fluorescence units) and mean arterial pressure from 175Ϯ4 to 157Ϯ6 mm Hg in SS rats, whereas no effects on either were observed in the SS-13 BN . We conclude that excess renal medullary superoxide production in SS rats contributes to salt-induced hypertension, and NADPH oxidase is the major source of the excess superoxide.

Renal medullary 11β-hydroxysteroid dehydrogenase type 1 in Dahl salt-sensitive hypertension

“…It is also possible that excess glucocorticoids may exacerbate oxidative stress (20). Nitric oxide deficiencies as well as oxidative stress in the renal medulla have been shown in physiological studies to contribute to Dahl SS hypertension (8,30,42). Yet another possibility is that excess glucocorticoids might upregulate local expression of angiotensinogen in the renal medulla, reminiscent of the observations in mice overexpressing 11␤-HSD1 (28,31).…”

“…1 Animals. Male SS and consomic SS-13 BN rats were generated as described previously (10,25,42). Rats were maintained on a purified AIN-76A rodent diet (Dyets, Bethlehem, PA) containing 0.4% NaCl and had free access to water.…”

“…The rats were uninephrectomized, and a catheter was implanted in the renal medulla as described previously (29,42,47) ϳ2 wk prior to the injection. shRNA plasmids (100 g) were combined with in vivo-jetPEI (PolyPlus, New York, NY) at a ratio of 8 following the manufacturer's instructions and injected into the catheter over 1 min.…”

“…Chronic monitoring of arterial blood pressure in freely moving rats using indwelling femoral arterial catheters was performed as described previously (29,42,47).…”

“…Yet the blood pressure salt sensitivity is substantially reduced in SS-13 BN (10). SS-13 BN has become a valuable control strain for the study of the SS model (5,6,10,13,42).…”