Effects on renal hemodynamics of intra-arterial infusions of angiotensins I and II.

Experiments were conducted in anesthetized dogs to evaluate the differences between the effects of intrarenal conversion of angiotensin I (ANG I) to angiotensin II (ANG II) and those of circulating ANG II on renal blood flow (RBF), glomerular filtration rate (GFR), peritubular capillary pressure (PCP), proximal tubular free-flow pressure (PTP), and stop-flow pressure (SFP). Equiconstrictor doses of ANG I and ANG II were infused into the renal arteries of dogs kept on normal and high sodium diets. In clearance experiments, RBF decreased by 23% (low dose) and 33% (high dose) during the infusion of either ANG I or ANG II; GFR was significantly reduced only during the ANG I infusion. In micropuncture experiments, in which the GFR responses were similar, there were significant reductions in PTP (23 +/- 3%) and PCP (33 +/- 3%) during the intrarenal ANG I infusion; SFP was not altered significantly. Afferent and efferent arteriolar resistances increased significantly during ANG I infusion as well as during infusion of ANG II. These results indicate that during intra-arterial infusion of ANG I, the conversion to ANG II within the kidney occurs early enough to decrease glomerular filtration rate through an apparent increase in preglomerular resistance.