Developmental pattern of androgen-binding protein secretion during the critical period of sexual differentiation

Androgen-binding protein (ABP) distribution in the fluids and tissues of fetal and neonatal rats was determined by radioimmunoassay during the critical period of sexual differentiation from 12 days postconception (PC) to 6 days postpartum. No significant differences in plasma ABP concentrations were detected between litters of the same age. Fetal plasma ABP in both sexes was high at 18 days PC and decreased to birth. At birth, this level increased, then continued its decline during the neonatal period. After 4 days, the level in females was significantly lower than that of males; this was the only time a significant difference in ABP levels between the sexes was observed. Amniotic fluid ABP was low at 12 days and increased to a peak at 18 days PC. Thereafter, it decreased as in plasma. ABP concentrations in fetal livers and placentas were almost negligible and changed in parallel with fluid concentrations. No ABP was detected in maternal plasma. Fetal production of ABP begins at the approximate time of gonadal differentiation and reaches a peak at 18 days, the time of peak androgen production. ABP may function as a protection against excessive concentrations of free androgen in the developing fetus and neonate.