LUTEOTROPIC EFFECTS OF FOLLICLE-STIMULATING-HORMONE (FSH) .2. FSH, LUTEINIZING-HORMONE, AND PROLACTIN EFFECTS ON SECOND MESSENGER SYSTEMS IN THE CORPUS-LUTEUM OF THE PREGNANT HAMSTER

We have recently shown that FSH, LH, and prolactin (PRL)-alone or comb ined-act as luteotropins when incubated with luteal cells from pregnan t hamsters (Yuan and Greenwald, Biol Reprod 1994; 51:43-49). The purpo se of the present study was to determine which second messenger system s are affected by these hormones with progesterone (P-4) synthesis as the principal endpoint after 4 h of incubation with 100 000 luteal cel ls. Luteal cells on Days 4, 10, or 12 of pregnancy were incubated with the following reagents: 10 ng of recombinant human FSH (r-hFSH), ovin e to) FSH, oLH, oPRL, forskolin, db-cAMP, protein kinase A inhibitor ( PKI), protein kinase C activator (phorbol 12-myristate 13-acetate; PMA ), or various combinations of the reagents. Forskolin and db-cAMP each stimulated P-4 in a dose-dependent manner, while PKI significantly in hibited forskolin-, r-hFSH-, oFSH-, and oLH-stimulated P-4 on Day 4 of pregnancy. PMA (0.001-1.0 mu M) did not affect basal P-4 On Day 4, 10 , or 12 of pregnancy; however, 100 nM PMA inhibited db-cAMP-, forskoli n-, oFSH-, and oLH-stimulated P-4 synthesis on Days 4 and 12. The anta gonistic effects of PMA were reversed in all cases by concurrent incub ation with a PKC inhibitor, H-7. On Day 4 of pregnancy, Pq was stimula ted by oFSH and oLH with the highest levels observed in medium stimula ted by the luteotropic complex of oFSH, oLH, and oPRL. Recombinant hFS H enhanced P-4 production in a dose-dependent manner; doses of 10 ng a nd above resulted in statistically significant differences from the co ntrol values (P < 0.05). Given alone, r-hFSH, oFSH, oLH, and forskolin stimulated media cAMP production by luteal cells, whereas oPRL only b arely increased cAMP. The most effective combination of hormones to fu rther Stimulate cAMP production was the luteotropic complex. The resul ts show that FSH and LH stimulate P-4 synthesis by hamster luteal cell s during pregnancy via the PKA-cAMP pathway, which is antagonized by a ctivation of the PKC pathway.