Adrenergic and dopaminergic regulation of circulating beta-endorphin-like immunoreactivity in hypertension.

The central alpha-2-adrenergic receptor agonist, clonidine (300 micrograms daily) significantly increased the plasma beta-endorphin-like immunoreactivity (beta ELI) in 12 patients with mild to moderate essential hypertension in a randomized, crossover study. A significant linear correlation between the increase in plasma beta ELI and the decrease in blood pressure (both systolic and diastolic) was found after clonidine administration. The role of the reduced central sympathetic tone, induced by alpha-2-adrenoceptor stimulation, in the elevation of circulating beta ELI can be suggested. The plasma beta ELI increased also significantly after the dopaminergic D-2 receptor agonist, bromocryptine treatment, (5 mg, daily) in 13 patients with borderline and mild essential hypertension in a randomized, crossover study. A significant drop in circulating noradrenaline and in arterial blood pressure and a significant linear correlation between the changes of plasma noradrenaline level and blood pressure was found after bromocryptine administration. There was no correlation between the rise in plasma beta ELI and the decrease in blood pressure after bromocryptine. The importance of the central sympathetic activity and not only a direct pituitary dopaminergic agonist effect on the beta-endorphin secretion can be stressed in the effect of bromocryptine on the immunoreactive beta-endorphin level.