The effect of progesterone upon first trimester trophoblastic cell differentiation and human chorionic gonadotrophin secretion.

The effect of progesterone (P) upon first trimester placental secretion of human chorionic gonadotrophin (HCG) and cellular differentiation was studied using both static and kinetic methods. At 1 microM, P inhibited spontaneous episodic secretion of HCG when given in short pulses (1-4 min) to placental explants in superfusion. Both HCG pulse frequency and amplitude were reduced. At 0.1-0.01 microM P concentrations, the effect of HCG secretion was milder. P also blocked the maximally effective concentration 100 pM of gonadotrophin releasing hormone (GnRH) analogue, a known HCG stimulant, when given together with it for 1 min. This inhibitory effect lasted for 1 h after P administration. Progesterone at 1 microM, added daily for 1 week blocked HCG secretion by isolated trophoblastic cells in static culture. This inhibitory effect lasted until the fifth day. No effect on differentiation and long-term viability was noticed in P-treated cells. Incubation with 0.1-1.0 microM P did not affect HCG secretion by explants after 24 h. In contrast, the effect of 1 microM cortisol or 1 nM oestradiol was stimulatory. In conclusion, P exerts both a rapid and delayed inhibitory effect upon HCG secretion and production. It may do so by counteracting the stimulatory effect of endogenous GnRH on gonadotrophin secretion by the placenta.