Zou A P, Li N, Cowley A W
Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, USA.
Hypertension. 2001 Feb;37(2 Pt 2):547-53. doi: 10.1161/01.hyp.37.2.547.
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.
本研究对大鼠肾脏不同区域中超氧化物（O₂⁻）产生的生化途径进行了表征，并确定了O₂⁻在肾髓质血流量（MBF）控制和肾功能中的作用。通过使用微量滴定板的二氢乙锭/DNA荧光光谱法，当将来自不同肾脏区域的组织匀浆与主要的O₂⁻产生酶（如NADH/NADPH氧化酶、黄嘌呤氧化酶和线粒体呼吸链酶）的底物一起孵育时，监测O₂⁻的产生。通过NADH氧化酶产生的O₂⁻在肾皮质和外髓质（OM）中比在乳头中更多（P<0.05）。OM中线粒体产生O₂⁻的酶活性比皮质和乳头中更高（P<0.05）。与NADH氧化酶和线粒体酶相比，在这种情况下，黄嘌呤氧化酶和NADPH氧化酶在肾脏中产生的O₂⁻要少得多。总体而言，肾OM表现出最大的O₂⁻产生酶活性。在麻醉大鼠中，肾髓质间质输注超氧化物歧化酶抑制剂二乙基二硫代氨基甲酸盐可显著降低肾MBF和钠排泄。二乙基二硫代氨基甲酸盐（通过肾髓质间质输注[RI]，每分钟5mg/kg）使肾髓质激光多普勒血流信号从0.6±0.04降至0.4±0.03V，降低了33%，尿流和钠排泄均减少了49%。相反，一种可透过膜的超氧化物歧化酶模拟物4-羟基四甲基哌啶-1-氧基（TEMPOL，每分钟30μmol/kg RI）使MBF和钠排泄分别增加了34%和69%。用N⁰-硝基-L-精氨酸甲酯（每分钟10μg/kg RI）预处理并没有改变TEMPOL对肾MBF和钠排泄的这些作用。我们得出结论：（1）肾髓质O₂⁻主要在肾OM中产生；（2）NADH氧化酶和线粒体酶均负责该肾脏区域中的O₂⁻产生；（3）O₂⁻对肾MBF发挥紧张性调节作用。
