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1 Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, USA
2 Department of Physiology, Monash University, Melbourne, Victoria, Australia
* To whom correspondence should be addressed. E-mail: roger.evans{at}med.moansh.edu.au.
We investigated the roles of the renin-angiotensin system, and the significance of interactions between angiotensin II and nitric oxide, in responses of regional kidney perfusion to electrical renal nerve stimulation (RNS) in pentobarbital anesthetized rabbits. Under control conditions, RNS (0.5 - 8 Hz) reduced total renal blood flow (RBF; -89 ± 3% at 8 Hz) and cortical perfusion (CBF; -90 ± 2% at 8 Hz) more than medullary perfusion (MBF; -55 ± 5% at 8 Hz). Angiotensin II type 1 (AT1-) receptor antagonism (candesartan) blunted RNS-induced reductions in RBF (P=0.03), CBF (P=0.007) and MBF (P=0.04), particularly at 4 and 8 Hz. Nitric oxide synthase inhibition with NG-nitro-L-arginine (L-NNA) enhanced RBF (P=0.003), CBF (P=0.001) and MBF (P=0.03) responses to RNS, particularly at frequencies of 2 Hz and less. After candesartan pre-treatment, L-NNA significantly enhanced RNS-induced reductions in RBF (P=0.04) and CBF (P=0.007) but not MBF (P=0.66). Renal arterial infusion of angiotensin II (5 ng kg-1min-1) selectively enhanced responses of MBF to RNS in L-NNA pre-treated-, but not vehicle pre-treated-rabbits. In contrast, greater doses of angiotensin II (5-15 ng kg-1min-1) blunted responses of MBF to RNS in rabbits with intact nitric oxide synthase. These results suggest that endogenous angiotensin II enhances, while nitric oxide blunts, neurally mediated vasoconstriction in the renal cortical and medullary circulations. In the renal medulla, but not the cortex, angiotensin II also appears to be able to blunt neurally-mediated vasoconstriction in the medullary circulation.
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