1. The effects of infusions of equimolar doses of angiotensin II (AII) and of Des1-angiotensin II (heptapeptide) on plasma renin activity, blood pressure and plasma aldosterone were compared in normal anaesthetized dexamethasone-suppressed dogs.
2. Plasma renin activity was equally suppressed by both compounds. The increase in blood pressure induced by the heptapeptide averaged 43–62% of the increase during AII infusions. No significant differences in aldosterone increase were observed between AII and the heptapeptide. Plasma aldosterone, however, dropped significantly faster in heptapeptide-treated dogs after the end of the infusions.
3. Sar1-Ala8-angiotensin II (saralasin, 400 pmol min—1 kg—1) suppressed plasma aldosterone that was stimulated by heptapeptide (20 pmol min—1 kg—1) completely. The same angiotensin antagonist had only a moderate effect on plasma aldosterone stimulated by AII. After stopping the antagonist infusion, plasma aldosterone rose significantly higher in dogs infused with AII than in those receiving the heptapeptide.
4. The results demonstrate differences between the effects of AII and the heptapeptide both on blood pressure and on plasma aldosterone. They do not support the hypothesis that the heptapeptide may be the main mediator of aldosterone secretion.