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(Hypertension. 2009;53:1048.)
© 2009 American Heart Association, Inc.

Original Articles

Effects of Renal Perfusion Pressure on Renal Medullary Hydrogen Peroxide and Nitric Oxide Production

Chunhua Jin; Chunyan Hu; Aaron Polichnowski; Takefumi Mori; Meredith Skelton; Sadayoshi Ito; Allen W. Cowley, Jr

From the Department of Physiology (C.J., A.P., T.M., M.S., A.W.C.), Medical College of Wisconsin, Milwaukee; and the Division of Nephrology, Endocrinology, and Vascular Medicine (C.H., T.M., S.I.), Tohoku University Graduate School of Medicine, Sendai, Japan.

Correspondence to Allen W. Cowley, Jr, Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd, Milwaukee, WI 53226. E-mail cowley{at}mcw.edu

Studies were designed to determine the effects of increases of renal perfusion pressure on the production of hydrogen peroxide (H₂O₂) and NO₂^–+NO₃^– within the renal outer medulla. Sprague-Dawley rats were studied with either the renal capsule intact or removed to ascertain the contribution of changes of medullary blood flow and renal interstitial hydrostatic pressure on H₂O₂ and NO₂^–+NO₃^– production. Responses to three 30-minute step changes of renal perfusion pressure (from 85 to 115 to 145 mm Hg) were studied using adjustable aortic occluders proximal and distal to the left renal artery. Medullary interstitial H₂O₂ determined by microdialysis increased at each level of renal perfusion pressure from 640 to 874 to 1593 nmol/L, as did H₂O₂ urinary excretion rates, and these responses were significantly attenuated by decapsulation. Medullary interstitial NO₂^–+NO₃^– increased from 9.2 to 13.8 to 16.1 µmol/L, with parallel changes in urine NO₂^–+NO₃^–, but decapsulation did not significantly blunt these responses. Over the range of renal perfusion pressure, medullary blood flow (laser-Doppler flowmetry) rose 30% and renal interstitial hydrostatic pressure rose from 7.8 to 19.7 cm H₂O. Renal interstitial hydrostatic pressure and the natriuretic and diuretic responses were significantly attenuated with decapsulation, but medullary blood flow was not affected. The data indicate that pressure-induced increases of H₂O₂ emanated largely from increased tubular flow rates to the medullary thick-ascending limbs of Henle and NO largely from increased medullary blood flow to the vasa recta. The parallel pressure-induced increases of H₂O₂ and NO indicate a participation in shaping the "normal" pressure-natriuresis relationship and explain why an imbalance in either would affect the blood pressure salt sensitivity.

Key Words: renal medullary oxidative stress • hydrogen peroxide • nitrate and nitrite • nitric oxide • pressure natriuresis • renal medullary blood flow

This article has been cited by other articles:

				A. J. Polichnowski and A. W. Cowley Jr Pressure-Induced Renal Injury in Angiotensin II Versus Norepinephrine-Induced Hypertensive Rats Hypertension, December 1, 2009; 54(6): 1269 - 1277. [Abstract] [Full Text] [PDF]