Effects of angiotensin II and noradrenaline on intrarenal haemodynamics in the rat.

The haemodynamic effects of angiotensin II and noradrenaline were studied in the rat kidney. These pressors were given by intravenous infusion in stepwise increasing doses. Intrarenal haemodynamics were analyzed by the 133xenon washout technique, 85krypton autoradiography and silastic casting of the renal vascular tree. Angiotensin II induced significant changes in intrarenal haemodynamics before any changes in systemic blood pressure were detected. The decrease in mean renal blood flow (2.91 ml.min-1.g-1 in controls, 1.76 ml.min-1.g-1 in rats given 50 mug of angiotensin II.kg-1.h-1) reflects a reduction in component I blood flow rate (from 3.9 to 2.9 ml.min-1.g-1) as well as a decrease in the fraction of total renal blood flow supplied to component I of the washout curve (from 84% to 62%). With noradrenaline an increase in total renal resistance occurred simultaneously with the elevation of mean arterial blood pressure. The resulting reduction in mean renal blood flow (from 2.76 ml.min-1.g-1 in controls to 1.55 ml.min-1.g-1 in rats given 1000 mug of noradrenaline kg-1.h-1) reflects a decrease in component I blood flow rate with lower infusion rates and a drop in component I flow fraction (from 82% to 52%) whith higher doses. In contrast to canine kidneys, no evidence for a patchy cortical vasoconstriction was found in the rat. Using autoradiography it was possible to attribute component I to the renal cortex and subcortical area of the kidney.