Effect of insulin on human chorionic gonadotrophin secretion by placental explants

The effect of physiological concentrations of insulin (5–50µU/ml) was tested on human chorionic gonadotrophin (HCG)secretion by first trimester (7–9 weeks) and term placentalexplants using both static and dynamic culture models. In staticcultures, insulin exerted a significant biphasic inhibitoryeffect (80% at 5 µU/ml and 40% at 50 µU/ml) on HCGsecretion by placental explants. At approximate fasting plasmalevels, 25 µU/ml insulin added to superfused explantsfor 8 min also had a rapid inhibitory effect. A delayed inhibitoryeffect on HCG pulsatility was also observed using 25 µU/mlinsulin, with a 2-fold decrease in HCG pulse amplitude and a4-fold decrease in the area under the curve following overnightpre-incubation (P < 0.01). Insulin had no effect in staticcultures at term. The effect of insulin-like growth factor (IGF-I)and fibroblast growth factor (bFGF) on HCG secretion in staticcultures was not statistically significant. In conclusion, physiologicalconcentrations of insulin inhibit HCG secretion in first trimesterplacenta in vitro. This effect is gestational age dependentand specific since it is not mimicked by IGF-I or bFGF. Thus,insulin may be an important modulator of trophoblastic HCG secretionduring early pregnancy.