1. When the angiotensin II-(4-8)-pentapeptide was infused intravenously at rates of 0.31-5.55 nmol min−1 kg−1 for 10–120 min into five normal men or two patients with Bartter's syndrome, no significant change was observed in blood pressure, plasma renin activity and plasma aldosterone, and the lowest dose did not inhibit the captopril-induced increase in plasma renin activity in the normal men.
2. An intravenous infusion of the pentapeptide at 9–0 nmol min−1 kg−1 for 15 min significantly raised blood pressure in the five normal men but not in patients with Bartter's syndrome. Blood pressure returned to the pre-treatment level 60 min after the cessation of the infusion in the normal men.
3. At the same dose level none of the seven subjects examined showed any significant change in plasma renin activity and plasma aldosterone.
4. Angiotensin II-(5-8)-tetrapeptide was infused intravenously into one of the normal men at a rate of 41.5 nmol min−1 kg−1 for 15 min, but it caused no significant change in blood pressure, plasma renin activity and plasma aldosterone.
5. These results suggest that the pentapeptide and probably the tetrapeptide do not possess renin-suppressing and steroidogenic actions in man but that the former peptide does elicit a modest pressor action with a prolonged duration.