STEPWISE ACTIVATION OF THE GONADOTROPIC SIGNAL-TRANSDUCTION PATHWAY, AND THE ABILITY OF PROSTAGLANDIN-F2-ALPHA TO INHIBIT THIS ACTIVATED PATHWAY

Through selective activation of the gonadotropic signal transduction p athway, we have determined the probable site of the antigonadotropic e ffects of prostaglandin F-2 alpha (PGF(2 alpha)) in the human granulos a-luteal cell (hGLC), The gonadotropic signal transduction pathway was activated at the level of the receptor (luteinizing hormone and beta- adrenergic), stimulatory G protein (GS), adenylate cyclase (AC), and p rotein kinase A (PKA) by human chorionic gonadotropin (hCG) and isopro terenol (Iso), cholera toxin (CTX), forskolin, and dibutryl cAMP (Db c AMP), respectively. Concomitantly, the ability of PGF(2 alpha) to inhi bit progesterone production in response to the activation of this casc ade at these different levels was examined. hGLCs were obtained from i n vitro fertilization patients and were precultured for 8 d in Medium 199 supplemented with fetal bovine serum (M199; 10% FBS), Following th e preculture period, cells were treated with either vehicle or one of the above activators of the gonadotropic pathway, either in the absenc e or presence of PGF(2 alpha) (in M199; No FBS), Following the treatme nt period, media were collected and assayed for progesterone by RIA, P rostaglandin F-2 alpha (10(-6) M) significantly inhibited hCG (1 IU/mL ), Iso (10(-5) M), CTX (1 mu g/mL), and forskolin- (10-5 M) stimulated progesterone production. Conversely, PGF(2 alpha) did not inhibit pro gesterone production stimulated by a saturating concentration of Db cA MP (10-6 M). The ability of PGF(2 alpha) to inhibit hCG- or CTX-stimul ated progesterone production was attenuated by pertussis toxin (PTX; 5 0 ng/mL), In conclusion, through a pertussis toxin-sensitive G protein , PGF(2 alpha) inhibits progesterone production at a level below AC, a nd above the activation of PKA by cAMP.