Opioid peptides in the regulation of TSH and prolactin secretion in the rat.

Abstract

Listen

Translate article

The effect of beta-endorphin, met-enkephalin and leu-enkephalin on cold-stimulated TSH and prolactin secretion after infusion of the drugs into the 3rd ventricle or into the posterior hypothalamus (PH) was investigated in male rats. beta-endorphin (0.25 microgram/rat, but not 0.05, 0.5 and 1 microgram/rat) increased and met-enkephalin (20 and 100 micrograms/rat) decreased TSH secretion when infused into the 3rd ventricle. After bilateral infusion into the PH, beta-endorphin (0.25 microgram/side, but not 0.05 and 1 microgram/side) increased TSH secretion, but met-enkephalin (1 and 10 micrograms/side) induced no changes. beta-endorphin (0.05-1 microgram/rat) and met-enkephalin (100 micrograms/rat) both increased prolactin secretion when infused into the 3rd ventricle, but only a high dose of beta-endorphin (1 microgram/side) was effective after infusion into the PH. Leu-enkephalin had no effect on TSH or prolactin secretion at the hypothalamic level. These results favour the hypothesis that mu-receptors mediate the inhibitory effect and other types (possible epsilon-receptors) of opiate receptors mediate the stimulatory effect of opioid peptides on TSH secretion at periventricular sites. However, only stimulatory mu-receptors affect prolactin secretion at these sites. After infusion into the PH, the effect of a high dose of beta-endorphin on prolactin secretion may also be mediated through periventricular sites, but its effect on TSH secretion is evidently mediated through opiate receptors in the PH.