Angiotensin as a Possible Intrarenal Hormone in Isolated Dog Kidneys

The distribution of renal blood flow was measured in isolated blood-perfused dog kidneys using radioactive labeled microspheres. The kidneys were perfused at a constant systolic pressure of 140 mm Hg. For the first 50 minutes of perfusion, flow to the outer zones of the renal cortex was 79±2% (SE) of the total renal blood flow, and inner cortical blood flow accounted for 21±2%. With continued perfusion, inner cortical blood flow increased progressively, reaching 34±3% by 150 minutes—a time when renin substrate was depleted in the perfusates. Infusions of the tetradecapeptide renin substrate (5–50 μg/min) reestablished the fractional distribution of renal blood flow observed in the initial 50 minutes of perfusion, i.e., inner cortical blood flow was reduced significantly from 36±2% to 23±4% (P < 0.05). In contrast, infusions of angiotensin II (1–10 μg/min) did not reduce the fractional distribution of renal blood flow to the inner cortex. These data provide evidence to support the hypothesis that angiotensin might be formed as an intrarenal hormone which participates in the regulation of deep cortical and medullary vascular resistances. Circulating angiotensin II does not appear to serve a similar function.