1. Rabbits were actively immunized against angiotensin II (AII).
2. Basal plasma aldosterone concentration was 0.058 ±0.027 pmol/ml (20.7±9.6 pg/ml) (mean±SD) in immunized and 0.056±0.021 pmol/ml (20.2±7.5 pg/ml) in control animals during suppression of adrenocorticotrophic hormone by dexamethasone. When the endogenous formation of AII was stimulated by frusemide, by haemorrhage or by feeding with low sodium diet, a significant increase of plasma aldosterone was observed with no difference between immunized and non-immunized animals.
3. In non-immune rabbits, the average mean arterial blood pressure rose 13 mmHg during the infusion of AII (5 pmol min−1 kg−1) and 27 mmHg during the infusion of 50 pmol min−1 kg−1. In contrast, there was no clear increase in blood pressure in the immunized animals. The blood pressure rose in immune animals (15 mmHg) and in non-immune animals (36 mmHg) during the infusion of 200 pmol min−1 kg−1 AII. Plasma aldosterone rose in all animals in response to each of the three infusions with no significant difference between the two groups.
4. It is concluded that the immunization against AII blocked only the pressor effect of the peptide but had no clear influence on the response of plasma aldosterone to increased AII. Differences between the affinities of the adrenal and vascular AII receptors may explain these findings.