Influence of Captopril on Red Cell Velocity in the Vasa Recta of the Renal Medulla

Abstract

Previous studies from our laboratory have indicated an important role for angiotensin II (All) in the regulation of renal medullary haemodynamics during normal physiological conditions. In order to investigate further the influence of endogenous All on the juxtamedullary vascular resistance in anaesthetized rats the velocity of fluorescentlylabeled red cells (vRBCw) as measured with a cross-correlation technique in the vasa recta before and after infusion of the angiotensin I- converting enzyme inhibitor captopril or ve hicle. Irrespectiveo f treatment, vRBCw as higher in the descending vasa recta (DVR) than in the ascending vasa recta (AVR). In time control animals vRBCin DVR and AVR and mean arterial blood pressure (MAP) remained stable over the 45 min study period. In animals receiving captopril (3 mg -h-’ kg” bw) vRBCin creased almost proportionally in DVR and AVR; by 26 Yo in DVR (from 1.02 k 0.12 to 1.28 f 0.10 mms-’, pc0.05) and by 19 Yo in AVR (from 0.46 f 0.05 to 0.55 k 0.07 mms”, pc0.05). MAP decreased by 9 Yo (from 107 f 3 to 97 k 2 mm Hg, pc0.05). These results give further support to the suggestion of an involvement of All in the regulation of juxtamedullary vascular resistance during normal physiological conditions.