Autoregulation of blood flow in renal medulla of the rat: no role for angiotensin II.

Autoregulation of blood flow was assessed by a dual-slit technique in descending and ascending vasa recta of the exposed renal papillae of antidiuretic rats. There was complete autoregulation of blood flow in descending vasa recta. The lower limit of autoregulation was approximately 85 mmHg (1 mmHg = 133.3 Pa) and the upper limit was greater then 160 mmHg. Autoregulation in ascending vasa recta was also good. To test the role of angiotensin II in this autoregulation, the converting enzyme inhibitor captopril was infused. Captopril had no effect on autoregulation of blood flow in either descending or ascending vasa recta. We conclude that blood flow in vasa recta of renal medulla is efficiently autoregulated and that this autoregulation is independent of angiotensin II.