[Role of the adrenal medulla in the effect of antihypertensive drugs].

Recent studies have suggested a role for adrenaline in the pathogenesis of essential hypertension. In the present study, the effects of several anti-hypertensive agents were compared in normal (plasma adrenaline concentration: 0.267 + 0.040 ng/ml) and adrenomedullectomised (plasma adrenaline concentration: 0.063 + 0.011 ng/ml; p less than 0.01) dogs. The hypotensive and tachycardic effects of phentolamine (1.5 mg/kg i.v.) or dihydralazine (1 mg/kg i.v.) were the same in the two groups of dogs. Verapamil (0.2 mg/kg i.v.)-induced hypotension was less pronounced in dogs without adrenal medulla. In these adrenomedullectomised dogs, clonidine (10 micrograms/kg i.v. or 1 microgram/kg i.c.) elicited tachycardia and its hypotensive properties were delayed. In dogs with neurogenic hypertension, the antihypertensive properties of propranolol (1 mg/kg i.v.) remained unchanged. These results show the importance of adrenal medulla in the antihypertensive action of clonidine, or verapamil. These agents (but not dihydralazine, propranolol or phentolamine) could reduce adrenaline secretion from the adrenal medulla.