Effect of beta-endorphin on cAMP and progesterone accumulation in rat luteal cells.

The aim of this study is to investigate the effect of beta-endorphin on cAMP and progesterone accumulation in rat luteal cells. Luteal cells of 4-day-old corpora lutea were cultured for 3 h in the absence or presence of 0.001 or 0.01 IU/ml hCG, and cAMP, progesterone and beta-endorphin levels in the medium were measured by RIA. hCG stimulated the production of cAMP, progesterone and beta-endorphin. In the presence of hCG, treatment with islet-activating protein (IAP) led to overall augmentation of cAMP and progesterone accumulation in comparison with untreated controls. In the absence or presence of low doses of hCG (0.001 IU/ml), beta-endorphin did not affect progesterone production, but inhibited cAMP accumulation. This inhibitory effect was abolished by pre-treatment with IAP. In the presence of high doses of hCG (0.01 IU/ml), however, beta-endorphin stimulated progesterone production without a corresponding increase in cAMP. This stimulatory effect was also abolished by IAP-treatment. These results suggest that luteal cells produce and release beta-endorphin that affects cAMP and progesterone production via IAP-sensitive mechanisms.