Effect of dopaminergic drugs on hypothalamic and pituitary immunoreactive beta-endorphin concentrations in the rat.

Beta-endorphin concentrations have been evaluated in the hypothalamus, pituitary lobes and plasma after 1-and 3-week treatment with 2-Br-alpha-ergocriptine or lisuride, two potent dopaminergic drugs. Hypothalamic beta-endorphin concentrations were significantly decreased after the administration of the dopaminergic agents for 1 or 3 weeks. Similarly, beta-endorphin concentrations decreased in the neurointermediate lobe and plasma. After gel chromatography, it appeared that in the anterior pituitary, beta-lipotropin concentrations were unchanged or lightly increased concomitantly with a decrease of beta-endorphin. Our data indicate that, both in the hypothalamus and the neurointermediate pituitary lobe, beta-endorphin is under an inhibitory dopaminergic tone. The latter may also play a role in inhibiting beta-endorphin cleavage from beta-lipotropin in the anterior pituitary.