Antihypertensive effect of 0.1-Hz blood pressure oscillations to the kidney

Background-Physiological blood pressure (BP) fluctuations with frequencies >0.1 Hz can override renal blood flow autoregulation. The influence of such immediate changes in renal perfusion pressure (RPP) on daily BP regulation , eg, via shear stress-stimulated liberation of renal endothelial NO, howev er, is unknown. Thus, we studied the effects of such RPP oscillations on re nal function and on systemic BP during the onset of renal hypertension. Methods and Results-Seven beagles (randomly assigned to each of the followi ng protocols) were chronically instrumented for the measurement of systemic BP, RPP, and renal excretory function. An inflatable cuff was used to redu ce and to oscillate RPP over 24 hours in the freely moving dog. Reducing RP P to 87+/-2 mm Hg diminished excretion of sodium and water and doubled plas ma renin activity (PRA, n=7, P<0.01) but had no significant effect on urina ry nitrate excretion (n=6), a marker of NO generation. Superimposing 0.1-Hz oscillations (+/-10 mm Hg) onto the reduced RPP blunted hypertension, retu rned fluid excretion almost to control levels, and doubled renal sodium eli mination. Nitrate excretion peaked at 8 hours, only to return to control va lues shortly thereafter. PRA, conversely, was significantly reduced during the last third of the experimental protocols. Conclusions-BP fluctuations transiently stimulate NO liberation and induce a reduction in PRA, which enhances 24-hour sodium and water excretion and m arkedly attenuates the acute development of renovascular hypertension.