Whole kidney response to reduced arterial pressure during converting enzyme inhibition in the rat

Autoregulatory efficiency of renal blood flow (RBF) and glomerular filtration rate (GFR) was evaluated in male Sprague-Dawley rats during interference with the renin-angiotensin system by a converting enzyme inhibitor (CEI), captopril (3 mg X h-1 X kg-1 BW). RBF and GFR were approximately 25 (p less than 0.01) and 20% (p less than 0.02) higher, respectively, in rats infused with CEI than in control rats at spontaneous renal arterial pressure (RAP). A reduction of RAP to 100 mm Hg (within the autoregulatory range) resulted in effective autoregulation of GFR and RBF in control rats. In rats given CEI, however, the autoregulation of GFR was markedly impaired. GFR decreased by 35% (p less than 0.001), while RBF remained relatively unchanged. This caused the filtration fraction to decrease from 0.33 +/- 0.01 to 0.29 +/- 0.01 (p less than 0.001). RAP had a consistent effect on the urine flow rate, even though both GFR and RBF were well autoregulated in control rats. No significant decrease in electrolyte excretion was detected within the autoregulatory range in control rats, but during converting enzyme blockade this excretion decreased progressively as RAP was reduced, and the decrease correlated well to the reduction in GFR. In summary, these results suggest that the renin-angiotensin system plays an important intrarenal role in the autoregulation of GFR, probably through an efferent arteriolar mechanism. Furthermore, it is demonstrated that the contralateral kidney efficiently compensates in urinary electrolyte excretion for an acute unilateral reduction of RAP.(ABSTRACT TRUNCATED AT 250 WORDS)