1. The effect of continuous infusion of captopril (80 μg/h) for up to 5 days on blood pressure, adrenal angiotensin II receptors and vascular reactivity to exogenous angiotensin II, arginine vasopressin and noradrenaline was studied in the rat.
2. In treated rats, blood pressure decreased transiently to a minimum after 2 days (−18 mmHg). Vascular reactivity to angiotensin II, but not to arginine vasopressin, was also increased significantly after 2 days, but vascular reactivity to noradrenaline decreased. After 5 days, vascular reactivity to angiotensin II had returned to normal and was similar to that of sham-treated controls. Adrenal angiotensin II receptor concentrations decreased significantly after 1 and 2 days, but at 5 days were again similar to controls. There was no change in receptor affinity.
3. Converting enzyme inhibition with captopril causes transient specific changes in adrenal angiotensin II receptors and vascular reactivity. The receptor and vascular effects may facilitate and oppose, respectively, the early changes in blood pressure with captopril, but a long-term contribution from either is unlikely.