| Abstract: | We investigated homologous and heterologous downregulation of FSH receptor mRNA in porcine granulosa cells from ovaries of immature pigs. Cultures were treated with 0, 40, or 200 ng/ml porcine FSH or medium and terminated at 24 hr intervals for Northern analysis of FSH receptor and cytochrome P450 side chain cleavage (P450scc) mRNA, and for radioimmunoassay of progesterone. Cells luteinized over 96 hr, and control cultures displayed increases in P450scc (8–10 fold) and FSH receptor (2 fold) mRNA and progesterone (100 fold). FSH reduced FSH receptor mRNA by 50–90%, increased P450scc mRNA 8 fold within 48 hr, and elevated progesterone logarithmically over 96 hr. Luteinized cells, (after 96 hr) received FSH or LH (1–200 ng/ml) or prostaglandin E2 (0.01–1.0 mg/ml) for 6 hr resulting in increased P450scc mRNA (2–8 fold), and progesterone (2–5 fold), and reduced FSH receptor mRNA. FSH (200 ng/ml) or the cAMP analog, dbcAMP (1 mM) for 0–24 hr reduced FSH receptor mRNA to 15% of control from 4–24 hr and elevated P450scc mRNA at 4 and 6 hr, respectively, to maxima at 12–24 hr. Forskolin (1–10 mM) increased P450scc mRNA (2–3 fold) and downregulated FSH receptor mRNA, effects reversed by the inhibitor of cAMP, rpcAMPs. Both epidermal growth factor, and the activator of the protein kinase C pathway, phorbol 12‐myristate, 13‐acetate (PMA) at 10 nM reduced FSH receptor mRNA. We conclude that downregulation of FSH receptor mRNA in luteinized granulosa cells is mediated by both homologous and heterologous ligands which employ cAMP, and that growth factors that activate the PKC pathway reduce FSH receptor and P450scc mRNA abundance. Mol. Reprod. Dev. 53:198–207, 1999. © 1999 Wiley‐Liss, Inc. |
