Plasma [met]enkephalin concentrations after endocrine and pharmacological modifications

Plasma [met]enkephalin was evaluated in rats either after the ablation of endocrine organs or after pharmacological modulation of the catecholaminergic and/or indoleaminergic systems. Plasma concentrations of [met]enkephalin were greatly increased after adrenalectomy both in normal and hypophysectomized rats, while there were not significant differences between female and male rats or after gonadectomy or hypophysectomy alone. Moreover, [met]enkephalin plasma concentrations were significantly decreased in rats treated with drug affecting the serotoninergic system such as reserpine, 5,7-dihydroxytryptamine or parachlorophenylalanine, while depletion of the catecholaminergic system by alfa-methyl-thyrosine did not affect the concentrations of the peptide.