EFFECTS OF INDIVIDUAL AND COMBINED TREATMENT WITH PROSTAGLANDINS-E2 AND F2-ALPHA ON PROGESTERONE SECRETION BY OVINE LUTEAL CELLS SUPPLEMENTED WITH HOMOLOGOUS SERUM-LIPOPROTEINS INVITRO

Prostaglandin F2alpha (PGF2alpha) is a potent luteolysin, whereas prostaglandin E2 (PGE2) is generally luteotropic in vivo. To establish a model system for investigations of the mechanisms involved in these actions, we examined the effects of individual and combined treatment with PGE2 and PGF2alpha on basal and ovine LH-stimulated progesterone secretion during long-term incubations conducted with and without supplemental homologous low-density lipoprotein (IDL) as substrate. Effects of both PGE2 and PGF2alpha were concentration- and time-dependent and were further influenced by the presence of LDL and/or LH in medium. Neither of the prostaglandins exerted any significant effect before 48 h in culture, but distinctly different patterns of response to PGE2 and PGF2alpha emerged thereafter. Low, but not high, concentrations of PGE2 increased progesterone secretion in the absence of LH, whereas PGF2alpha (alone and in combination with PGE2) inhibited progesterone production in all medium formulations. The transcriptional inhibitor actinomycin effectively blocked the actions of PGF2alpha but had no effect on response to LH or PGE2. These data demonstrate that both the putative luteotropic actions of PGE2 and the potent, luteolytic effects of PGF2alpha in vivo can be reproduced in long-term cultures of ovine luteal cells in vitro, and they suggest that the mechanism of PGF2alpha-induced luteolysis may involve new protein synthesis.