DOES HUMAN CHORIONIC-GONADOTROPIN HAVE HUMAN THYROTROPIC ACTIVITY IN-VIVO

Current evidence indicates that thyroid cells are sensitive to human c horionic gonadotropin (hCG) stimulation. In turn, thyroid hormones app ear to influence ovarian and endometrial physiology and reproductive f unction. Our studies addressed the possible effect of endogenous and e xogenous hCG on in vivo thyroid function in normal pregnancy and contr olled ovarian hyperstimulation, respectively. Circulating concentratio ns of hCG in pregnant women during gestation were positively correlate d with serum free thyroxine (r = 0.43, p = 0.02) and negatively correl ated with thyrotropin levels in the same patients (r = 0.42, p = 0.02) . By contrast, exogenous administration of hCG to effect follicular ma turation in non-pregnant patients undergoing ovarian hyperstimulation resulted in lower circulating hCG concentrations than seen in pregnanc y and failed to alter free thyroxine or thyrotropin levels (p > 0.22). Endogenous isoforms of hCG in early pregnancy appear to have thyrotro pic activity in vivo. However, the results indicate that, under clinic al conditions of controlled ovarian hyperstimulation for assisted repr oduction, exogenous hCG does not affect the hypothalamic-pituitary-thy roid axis.