Normalization of blood pressure and plasma concentrations of beta-endorphin and leucine-enkephalin in patients with primary hypertension after treatment with clonidine.

Opioid peptides are thought to be involved in blood pressure regulation, possibly via an interaction with the sympathetic nervous system (CNS). To further elucidate this hypothesis the plasma concentrations of beta-endorphin, leucine-enkephalin and noradrenaline were determined overnight (9 p.m. to 8 a.m.) in young patients with mild essential hypertension and then compared to normotensive controls. The mean concentrations of beta-endorphin during the early night (9 p.m. to 2 a.m.) and leucine-enkephalin were lower (p less than 0.05, p less than 0.01, respectively) than in the normotensive subjects, but the noradrenaline concentration was higher. After 14 days of treatment with clonidine, which decreases sympathetic activity via a central action, beta-endorphin, leucine-enkephalin, and noradrenaline concentrations did not differ between both groups. It is concluded that the lower plasma concentrations of beta-endorphin and leucine-enkephalin in the hypertensive group could reflect reduced opioidergic activity in the CNS and in the peripheral sympathetic neurons and also could be involved in the increased sympathetic activity of these patients. Besides via sympathetic inhibition, clonidine also may reduce the increased blood pressure further by normalizing central beta-endorphin release.