Variation of plasma and kidney renin activities among substrains of spontaneously hypertensive rats.

Plasma and kidney renin activity (PRA, KRA) were determined in the spontaneously hypertensive (SHR) rats, the stroke-resistant and -prone substrains (SHRSR, SHRSP) from 5 to 30 weeks of age. Results were compared with those of two normotensive strains, Wistar-Kyoto (WKY) and Donryu (DON) rats. PRA in the SHRSP at 20 and 30 weeks of age were significantly increased when compared to other strains of rats (P < 0.01). In SHRSP rats at these ages, blood pressure exceeded the critical level of 220 mmHg and cerebral lesions were observed in 41% at autopsy. There were no significant differences in PRA among other hypertensive and normotensive strains. KRA in three substrains of the SHR were normal or subnormal as compared to WKY and DON rats. These results indicate that a direct role of the renin-angiotensin system in the SHR and its substrains can be excluded in the initiation and the maintenance of hypertension. However, the activated renin-angiotensin system in SHRSP rats in the course of malignant hypertension at 20 weeks of age and later, could participate in raising blood pressure above the levels of the SHR and SHRSR. Considering out data and others, there are many similarities in renin profile between the SHR and its two substrains, and human essential hypertension in which PRA can be classified as low, normal or high.