Modification of the Haemodynamic Effects of ACTH by Angiotensin II in Sheep

The study was performed to examine the hypothesis that adrenocorticotrophic hormone (ACTH) induced hypertension in sheep would be enhanced if the blood level of angiotensin II (ANG II), normally suppressed during ACTH administration, was kept at control levels by intravenous infusion of ANG II. Administration of ACTH at 1.0 μg/kg/day for 6 days produced a half maximum rise in mean arterial pressure, Δ 14 mmHg, associated with hypokalaemia and initial urinary sodium retention. A rate of ANG II infusion, (0.9 μg/kg/day) for 6 days, was contrived to produce a small increase in peripheral resistance and mean arterial pressure, Δ 10 mmHg. Pressor responses to concomitant infusion of ACTH and ANG II were additive, Δ 25 mmHg. There was no potentiation of ACTH hypertension by ANG II in the sheep.