Effects of Angiotensin II and Noradrenaline on Intrarenal Haemodynamies in the Rat*

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Abstract
The hemodynamic effects of angiotensin II [A-II] and noradrenaline [norepinephrine] were studied in the rat kidney. These pressors were given by i.v. infusion in stepwise increasing doses. Intrarenal hemodynamics were analyzed by the 133Xe washout technique, 85Kr autoradiography and silastic casting of the renal vascular tree. A-II induced significant changes in intrarenal hemodynamics before any changes in systemic blood pressure were detected. The decrease in mean renal blood flow (2.91 ml/min per g in controls, 1.76 ml/min per g in rats given 50 .mu.g of A-II/kg per h) reflected a reduction in component I blood flow rate (from 3.9-2.9 ml/min-1 per g-1) and a decrease in the fraction of total renal blood flow supplied to component I of the washout curve (from 84-62%). 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 per g in controls to 1.55 ml/min per g in rats given 1000 .mu.g of noradrenaline kg/h) reflected a decrease in component I blood flow rate with lower infusion rates and a drop in component I flow fraction (from 82-52%) with 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.