The role of angiotensin in the pressor response to propranolol and the hypotensive response to phentolamine

Experiments were conducted to determine the cause of the pressor response to propranolol in phentolamine-treated rats. Adrenal-demedullation prevented both the hypotensive response to phentolamine and the pressor response to propranolol. Both effects could be restored if the drugs were administered during the concomitant infusion of threshold pressor concentrations of epinephrine. The hypotensive effect of phentolamine in adrenal-demedullated rats also could be restored by prior bilateral nephrectomy or administration of either captopril (SQ14,225) or saralasin. In adrenal-intact rats the hypertensive response to propranolol could be inhibited by either nephrectomy or prior administration of captopril.