Renal hemodynamics in response to a kinin analogue antagonist

The influence of endogenous kinins on renal hemodynamics was studied using a kinin analogue antagonist ([DArg0-Hyp3-Thi5-DPhe7-Thi8]bradykinin) in eight sodium-restricted anesthetized dogs. Clearance periods were run during intrarenal infusion of vehicle or 50 micrograms/min of analogue during normal and reduced renal perfusion pressure within (95 mmHg) and below (65 mmHg) the range of renal autoregulation. During normal renal perfusion, the analogue did not affect arterial pressure, glomerular filtration rate (GFR), or sodium excretion but decreased renal blood flow (RBF) by 20% (6.41 +/- 0.35 vs. 5.61 +/- 0.38 ml.min-1.g kidney wt-1, P less than 0.05) due to increased renal vascular resistance (RVR, 0.44 +/- 0.03 vs. 0.54 +/- 0.04 U, P less than 0.01). The analogue increased renin secretion rate (RSR, 311 +/- 190 vs. 654 +/- 202 ng angiotensin I/min, P less than 0.001). With reduced renal perfusion (95 mmHg), RBF was unchanged, and sodium excretion and RVR decreased. Vehicle did not change GFR, but the analogue abolished autoregulation of GFR (-37%, P less than 0.02) and decreased filtration fraction (24 +/- 4 vs. 34 +/- 4%, P less than 0.05). Renal perfusion pressure of 65 mmHg decreased RBF, GFR, and sodium excretion similarly with vehicle or analogue. Converting-enzyme inhibition eliminated the changes in RVR. Thus kinin antagonism increased RSR and consequently RVR at normal renal perfusion. As renal perfusion pressure decreased, kinin antagonism diminished autoregulation of GFR but not of RBF. These results suggest that kinin antagonism may either modify the arteriolar resistance or alter the coefficient of filtration, resulting in decreased GFR at reduced renal perfusion pressure.