Luteotropic effects of follicle-stimulating hormone (FSH): II. FSH, luteinizing hormone, and prolactin effects on second messenger systems in the corpus luteum of the pregnant hamster

Abstract

We have recently shown that FSH, LH, and prolactin (PRL)-alone or combined-act as luteotropins when incubated with luteal cells from pregnant hamsters (Yuan and Greenwald, Biol Reprod 1994; 51:43-49). The purpose of the present study was to determine which second messenger systems are affected by these hormones with progesterone (P4) synthesis as the principal endpoint after 4 h of incubation with 100 000 luteal cells. Luteal cells on Days 4, 10, or 12 of pregnancy were incubated with the following reagents: 10 ng of recombinant human FSH (r-hFSH), ovine (o) 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 P4 in a dose-dependent manner, while PKI significantly inhibited forskolin-, r-hFSH-, oFSH-, and oLH-stimulated P4 on Day 4 of pregnancy. PMA (0.001-1.0 μM) did not affect basal P4 on Day 4, 10, or 12 of pregnancy; however, 100 nM PMA inhibited db-cAMP-, forskolin-, oFSH-, and oLH-stimulated P4 synthesis on Days 4 and 12. The antagonistic effects of PMA were reversed in all cases by concurrent incubation with a PKC inhibitor, H-7. On Day 4 of pregnancy, P4 was stimulated by oFSH and oLH with the highest levels observed in medium stimulated by the luteotropic complex of oFSH, oLH, and oPRL. Recombinant bFSH enhanced P4 production in a dose-dependent manner; doses of 10 ng and above resulted in statistically significant differences from the control values (p < 0.05). Given alone, r-hFSH, oFSH, oLH, and forskolin stimulated media cAMP-production by luteal cells, whereas oPRL only barely increased cAMP. The most effective combination of hormones to further stimulate cAMP production was the luteotropic complex. The results show that FSH and LH stimulate P4 synthesis by hamster luteal cells during pregnancy via the PKA- cAMP pathway, which is antagonized by activation of the PKC pathway.