ACTH hypertension modifies the haemodynamic effects of prostacyclin infusions in sheep.

1. The haemodynamic effects of short-term prostacyclin infusions (0.05-0.50 microgram/kg per min) were investigated in conscious adult sheep. 2. Haemodynamic dose-response curves to prostacyclin were performed before, during and after production of ACTH-induced hypertension. 3. Prior to ACTH administration prostacyclin produced dose-dependent reductions in mean arterial pressure, total peripheral resistance and stroke volume and these were accompanied by increased in heart rate and cardiac output. 4. After 5 days of ACTH-induced hypertension prostacyclin produced similar effects on mean arterial pressure to those seen prior to ACTH but the effects on heart rate, cardiac output, stroke volume and total peripheral resistance were markedly increased. 5. These studies demonstrate that the responsiveness of the circulation to prostacyclin is altered in ACTH-induced hypertension.