IN-VITRO EFFECTS OF INTERACTIONS OF FOLLICLE-STIMULATING-HORMONE, LUTEINIZING-HORMONE, AND PROLACTIN ON PROGESTERONE SYNTHESIS BY RAT LUTEAL CELLS DURING PREGNANCY

The in vitro ability of ovine to) follicle-stimulating hormone (FSH), (o)luteinizing hormone (LH), (o)prolactin (PRL), and recombinant human FSH (rhFSH) to stimulate progesterone (P-4) synthesis by rat corpora lutea on Day 4 of pregnancy was investigated. Dispersed luteal cells ( large + small cells) were incubated in the presence of the gonadotropi ns (1-100 ng) alone or in various combinations (10 ng each) for 4 or 2 4 hr. Given alone, all the ovine preparations stimulated P-4 in a dose -dependent manner with even 1 ng of each hormone significantly enhanci ng P-4 production. significantly, rhFSH-which is devoid of LH contamin ation-at 10 and 100 ng also stimulated P-4 production, thus clearly es tablishing for the first time that FSH is a luteotropic hormone in the rat. The combination of oFSH + LH + PRL (10 ng each) significantly st imulated P-4 synthesis to a greater extent than the combination of any two hormones or individual hormones at both 4 hr or an additional 24 hr of incubation (P < 0.05). This verified in vitro a previously estab lished in vivo luteotropic complex, One hundred nanamolars of phorbol 12-myristate 13-acetate (PMA) did not affect basal P-4 secretion but i nhibited cAMP, oFSH, and oLH stimulation of P-4. Thus, the luteotropic effects of FSH, LH, and activators of protein kinase A are antagonize d by the protein kinase C pathway.