Brain and kidney renin-angiotensin activity in spontaneously hypertensive rats

Renin activity in peripheral plasma (PRA), renal cortex and brain tissue (cortex, stem, medulla oblongata) homogenates was studied in a bioassay after Serebrovskaya's modification of the method of Pickens. Fourty-nine spontaneously hypertensive rats (SHR) and 26 normotensive Wistar rats (NWR) were used. The results show that: 1) In spite of very high systolic blood pressure, PRA in SHR is in normal ranges; 2) Renin activity exists not only in the brain of NWR, but in the brain of SHR as well. 3) Renin activity in the different parts of the brain is not equal both in NWR and in SHR. 4) Renin activity in the cortex, the stem and the medulla oblongata of SHR is in normal ranges. 5) Renin activity in the medulla is higher than in other areas of the brain, both in NWR and in SHR, the difference being statistically significant in the latter. 6) No perceptible interrelation between arterial blood pressure, PRA, renal renin activity and renin activity in the cortex, and in the stem of the brain was established. It is suggested that higher renin activity in the medulla oblongata might be considered as an indication of the importance of the brain renin-angiotensin system, and its function in the cerebral (neural) regulation of the cardiovascular system. A causal connection between the renal and the brain renin-angiotensin systems, and the onset and maintenance of hypertension is assumed.