1. The renin inhibitor N-acetyl-pepstatin was infused for 14 days or 5 days into the cerebral ventricular system of young and adult spontaneously hypertensive rats respectively.
2. The blood pressure and heart rate of the young animals was significantly lower as a result of this treatment, whereas the pressure of the adult animals tended to decrease.
3. The mechanism involved in the hypotensive effect of N-acetyl-pepstatin appeared to be independent of the peripheral renin-angiotensin system. The possible involvement of a decreased sympathetic outflow is suggested.
4. The present data indicate that the brain renin-angiotensin system contributes to the development of hypertension in the spontaneously hypertensive rat.