1. Three-week-old spontaneously hypertensive rats (SHR) showed markedly elevated specific renin activity in the adrenal and the mesenteric vessels compared with control Wistar-Kyoto (WKY)rats.
2. In 17-week-old SHR with established hypertension, adrenal renin remained markedly elevated over that of WKY rats, whereas no significant difference was observed in renin of the mesenteric vessels.
3. The specific renin activity of the aorta showed no significant difference compared with that of WKY rats at 3 or 17 weeks of age.
4. These results suggest possible involvement of adrenal and vascular renin in the pathogenesis of hypertension in SHR.