Human luteolysis--interaction between HCG and oestradiol-17beta in an in-vitro model.

Corpora lutea (CL) were excised from each of 24 women undergoing laparotomy at different and well-classified stages of the luteal phase of the menstrual cycle. Pieces were incubated for intervals between 30 min and 4 h, the incubations being carried out in the presence or absence of human chorionic gonadotrophin (HCG) and oestradiol-17beta (E2) along and in combination. Following incubation, the tissue levels of cAMP and the media concentrations of progesterone and, in certain cases, pregnenolone, were determined. HCG stimulated the production of cAMP and progesterone in CL of all ages. This effect on the formation of progesterone was significantly counteracted by E2 in CL of the early and mid-luteal phases. The addition of indomethacin to the incubation media did not alter this anti-gonadotrophic effect of E2 in-vitro. The formation of cAMP was not influenced by E2 in-vitro. These results suggest that the well-known luteolytic effect of E2 in-vivo is caused by inhibition of the gonadotrophin-stimulated synthesis of progesterone by corpora lutea, an effect mediated neither by prostaglandins nor cAMP.