1. Specific angiotensin II (ANGII) receptor binding was measured in regions of the brains of the New Zealand genetically hypertensive and normal rats.
2. ANGII receptor binding was consistently lower in the septum, midbrain, thalamus and posterior medulla of the genetically hypertensive rats than in normal rats.
3. Blood pressure responses to intraventricular injections of ANGII and an ANGII antagonist [Sar1,Ala8]angiotensin were studied in conscious and pentobarbitone-anaesthetized genetically hypertensive and normal rats. In conscious rats no significant difference between the two strains of rat was detected.
4. In pentobarbitone-anaesthetized rats intraventricular injection of 40 μg of [Sar1,Ala8]angiotensin had a hypotensive effect which was three times greater in the genetically hypertensive rats than that observed in normal rats. The latency of this hypotensive effect was longer than the latency of the hypertensive effect of ANGII.
5. The drinking responses to intraventricular injections of ANGII were similar in genetically hypertensive and normal rats.
6. The physiological role of the ANGII system is discussed and it is concluded that an abnormality of this system in the brain may well be responsible for the hypertension found in the genetically hypertensive rat.