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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 fluorescently-labeled red cells (vRBC) was measured with a cross-correlation technique in the vasa recta before and after infusion of the angiotensin I- converting enzyme inhibitor captopril or vehicle.
Irrespective of treatment, vRBC was higher in the descending vasa recta (DVR) than in the ascending vasa recta (AVR). In time control animals vRBC in DVR and AVR and mean arterial blood pressure (MAP) remained stable over the 45 min study period. In animals receiving captopril (3 mg·h−1·kg−1 bw) vRBC increased almost proportionally in DVR and AVR; by 26% in DVR (from 1.02 ± 0.12 to 1.28 ± 0.10 mm·s−1, p < 0.05) and by 19% in AVR (from 0.46 ± 0.05 to 0.55 ± 0.07 mm·s−1, p<0.05). MAP decreased by 9% (from 107 ± 3 to 97 ± 2 mm Hg, p<0.05).
These results give further support to the suggestion of an involvement of All in the regulation of juxtamedullary vascular resistance during normal physiological conditions.