Regional renin release by the cat kidney in vitro and in vivo

Differences in the rate of renin release by superficial and deep areas of the cat kidney cortex were studied in vitro and in vivo. Renin release in vitro by outer cortical slices was significantly higher than by their inner counterparts: 19.6 +/- 2.3 vs. 12.8 +/- 1.95 ng angiotensin I-h-1-mg fresh tissue-1-h of incubation-1. In vivo blood was sampled from subcapsular (outer cortical) and deep (inner cortical and medullary) renal venous circulation from anesthetized cats. Renal venous minus arterial plasma renin concentration was respectively, 4.3 +/- 1.12 and 1.9 +/- 1.04 ng angiotensin I-ml-1-h-1 (P less than 0.01). By assuming that in these experiments renal blood flow distribution was approximately equal to each of the two areas of venous drainage, as reported in the isolated perfused cat kidney, we infer from the regional differences in arteriovenous concentration that the rate of renin release of the outer cortex is higher than that of the innder cortex in the cat kidney in vivo. Tissue content of renin was found to decrease toward the deep cortex. The results support the concept that the rate of regional renin release correlates with tissue renin content, at least under the conditions of the present experiments.