[Effect of opioid peptides on progesterone production by rat luteal cells in vitro]

The effect of exogenous opioid peptides on progesterone production by incubated rat luteal cells was studied. beta-endorphin (beta-EP) stimulated progesterone production in a dose-dependant manner (10(-8)-10(-6) mol/L); dynorphin exhibited a stimulatory effect only at 10(-6) mol/L, while Met-enkephalin had no substantial effect at dose from 10(-10)-10(-6) mol/L. mu-opioid receptor agonists DAGO and morphine also stimulated progesterone production. The stimulatory actions of beta-EP, DAGO and morphine were reversed completely by naloxone. On account of the fact that the beta-EP level in rat plasma is lower than that in the ovary, it seemed that beta-EP may be an intra-ovarian luteotrophic factor and be involved in the regulation of progesterone production. This action of beta-EP may be mediated by mu-opioid subtype receptors.