Differential effects of prostaglandin F2alpha on in vitro luteinized bovine granulosa cells

Prostaglandins have been implicated in various aspects of ovarian function including ovulation and luteolysis. In this study, the expression and regulation of inducible prostagland in G/H synthase (PGHS-2) and PGF(2alpha) receptors were investigated in bovine granulosa cells at various stages of differentiation. Firstly, the induction of PGF(2alpha) receptor mRNA and PGHS-2 mRNA in preovulatory granulosa cells was evaluated. Granulosa cells were collected from preovulatory follicles and cultured for 1, 4, 7 or 10 days. Cells were treated with hCG (10 iu) or with increasing doses of forskolin (0-10 micromol l(-1)) for 24 h. Forskolin increased steady-state concentrations of mRNA for PGHS-2 (> 20-fold) and PGF(2alpha) receptor (> 1000-fold) in a dose-dependent fashion. Use of selective protein kinase A inhibitor (H89) reduced both hCG- and forskolin-induced expression of PGF(2alpha) receptor mRNA and PGHS-2 mRNA. The hypothesis that luteinized granulosa cells would acquire PGF(2alpha) responsiveness similar to responses to PGF(2alpha) observed in vivo was also evaluated. Treatment with PGF(2alpha) (100 nmol l(-1)) reduced forskolin-induced expression of PGF(2alpha) receptor mRNA on days 4, 7 and 10, but not on day 1 of culture (n = 3). Treatment with PGF(2alpha) did not change forskolin-induced expression of PGHS-2 mRNA on or before day 4 of culture. In contrast, PGF(2alpha) significantly increased PGHS-2 mRNA expression in granulosa cells primed with forskolin for 7 or 10 days. In conclusion, expression of PGHS-2 and PGF(2alpha) receptor mRNA is protein kinase A-dependent in preovulatory bovine granulosa cells. Granulosa cells become PGF(2alpha)-responsive soon after expression of PGF(2alpha) receptor, whereas further differentiation is required before PGF(2alpha) induces PGHS-2 mRNA upregulation. These results demonstrate that at least two key transitions are required in PGF(2alpha)-induced luteal regression in the mid-cycle corpus luteum.