Interlobular arterial resistance: Influence of renal arterial pressure and angiotensin II

Abstract

Pressure in the distal third of the interlobular arteries (P(ila)) was measured in anesthetized rats by micropuncture through corticotomy. Control P(ila) was 83.9 (SD 11.9) mm Hg at a renal arterial pressure (RAP) of 113.1 (SD 12.8) mm Hg. Reduction of RAP by 20 mm Hg caused no consistent change of total renal blood flow (RBF) or P(ila). Relative interlobular arterial resistance, R(ila) = (RAP - P(ila)/RBF, fell by 40 to 50%, and then remained practically unchanged at further reduction of RAP. Blood flow measured by radiolabeled microspheres (10.7 μm) showed similar values in intact cortex and in the tissue beneath the corticotomy, both varying in proportion to RBF. Intravenous infusion of angiotensin II (AII) 40 to 90 ng/min reduced RBF by 29% and increased RAP by 19 mm Hg. P(ila) rose by only 8 mm Hg and R(ila) increased to 209% of control. Reduction of RAP to control level during continued AII infusion did not change RBF, while R(ila) fell to 131% of control. We conclude that: 1) dilatation and constriction of the interlobular arteries contribute importantly to autoregulation of outer cortical blood flow, probably through a myogenic mechanism (Bayliss); 2) the constriction of interlobular arteries elicited by i.v. AII reflects mainly an autoregulatory response to increased arterial pressure, and to a smaller extent, a direct constrictor effect of AII.