Intrarenal role of angiotensin II. Homeostatic regulation of renal blood flow in the dog.

The analogue, l-sarcosine-8-alanine-angiotensin II, a specific competitive antagonist of the vascular action of angiotensin II in the rat, blocked the decrease in renal blood flow after a single intrarenal injection of angiotensin II but not after an injection of norepinephrine in normal dogs, in a sodium-depleted dog, and in a dog with thoracic vena caval constriction. Infusion of the analogue at 0.2 /ig/kg mininto the renal artery consistently increased renal blood flow and decreased renal resistance in both sodiumdepleted dogs and dogs with vena caval constriction but did not alter these functions in normal dogs. In five sodium-depleted dogs, renal blood flow increased from an average control value of 196 ± 5 ml/min to 222 ±11 and 246 ± 12 ml/min after 20 and 40 minutes of antagonist infusion (P<0.01 and P < 0.005, respectively); renal resistance fell from 0.71 ± 0.03 mm Hg/ml minto 0.62 ± 0.06 and 0.54 ± 0.03 mm Hg/ml min" (P < 0.005 for the 40-minute value). In five dogs with vena caval constriction, renal blood flow increased from 143 ± 16 ml/min to 178 ± 23 and 190 ± 19 ml/min after 20 and 40 minutes of analogue infusion (P<0.02 and P < 0.005, respectively); renal resistance fell from 0.90 ± 0.14 mm Hg/ml minto 0.73 ± 0.14 and 0.64 ± 0.10 mm Hg/ml min(P<0.01 and P < 0.02, respectively). Mean arterial blood pressure was not altered significantly by the analogue when-1 it was infused at 0.2 fig/'kg min"". Infusion of the analogue at 2.0 /xg/kg min decreased arterial blood pressure and renal resistance and increased renal blood flow in five sodium-depleted dogs and in three dogs with vena caval constriction. These observations suggest an important intrarenal role for angiotensin II in the homeostatic regulation of renal blood flow in sodiumdepleted dogs and in dogs with vena caval constriction.