Production and actions of superoxide in the renal medulla.
The present study characterized the biochemical pathways responsible for superoxide (O(2)(-.)) production in different regions of the rat kidney and determined the role of O(2)(-.)in the control of renal medullary blood flow (MBF) and renal function. By use of dihydroethidium/DNA fluorescence spectrometry with microtiter plates, the production of O(2)(-. )was monitored when tissue homogenate from different kidney regions was incubated with substrates for the major O(2)(-.)-producing enzymes, such as NADH/NADPH oxidase, xanthine oxidase, and mitochondrial respiratory chain enzymes. The production of O(2)(-. )via NADH oxidase was greater (P<0.05) in the renal cortex and outer medulla (OM) than in the papilla. The mitochondrial enzyme activity for O(2)(-.)production was higher (P<0.05) in the OM than in the cortex and papilla. Compared with NADH oxidase and mitochondrial enzymes, xanthine oxidase and NADPH oxidase produced much less O(2)(-. )in the kidney under this condition. Overall, the renal OM exhibited the greatest enzyme activities for O(2)(-.)production. In anesthetized rats, renal medullary interstitial infusion of a superoxide dismutase inhibitor, diethyldithiocarbamate, markedly decreased renal MBF and sodium excretion. Diethyldithiocarbamate (5 mg/kg per minute by renal medullary interstitial infusion [RI]) reduced the renal medullary laser-Doppler flow signal from 0.6+/-0.04 to 0.4+/-0.03 V, a reduction of 33%, and both urine flow and sodium excretion decreased by 49%. In contrast, a membrane-permeable superoxide dismutase mimetic, 4-hydroxytetramethyl-piperidine-1-oxyl (TEMPOL, 30 micromol/kg per minute RI) increased MBF and sodium excretion by 34% and 69%, respectively. These effects of TEMPOL on renal MBF and sodium excretion were not altered by pretreatment with N(G)-nitro-L-arginine methyl ester (10 microgram/kg per minute RI). We conclude that (1) renal medullary O(2)(-. )is primarily produced in the renal OM; (2) both NADH oxidase and mitochondrial enzymes are responsible for the O(2)(-.)production in this kidney region; and (3) O(2)(-. )exerts a tonic regulatory action on renal MBF.
Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, USA.
A P
AP
Zou
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N
Li
A W
AW
Cowley
D000818:Animals; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004050:Ditiocarb / Q000494:pharmacology; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007672:Kidney Cortex / Q000098:blood supply / Q000378:metabolism; D007679:Kidney Medulla / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009318:Natriuresis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects; D012079:Renal Circulation / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013113:Spin Labels; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013481:Superoxides / Q000032:analysis / Q000378:metabolism*
D003497:Cyclic N-Oxides; D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D013113:Spin Labels; D013481:Superoxides; D004050:Ditiocarb; D013482:Superoxide Dismutase; C023107:NADH oxidase; D009247:NADH, NADPH Oxidoreductases; C001803:tempol