TRANSPLACENTAL GRADIENTS OF SEX‐HORMONE‐BINDING GLOBULIN IN HUMAN AND SIMIAN PREGNANCY

Abstract

An attempt has been made to clarify the degree and control of production of the concentration gradient of sex-hormone-binding globulin (SHBG) between human mother and fetus. SHBG was measured by an improved ammonium sulphate precipitation method using 5α-dihydrotestosterone as ligand. Maternal and fetal (cord blood) plasma SHBG was measured at delivery in twenty-three normal, four twin and one anencephalic pregnancies and in non-pregnant subjects. Comparison was also made with two macaque species, the rhesus monkey (M. mulatto) and the bonnet monkey (M. radiata), sampled shortly after delivery. In the human, a highly consistent gradient (mean 21-fold) was found between mother and fetus, which was independent of fetal sex and weight. Fetal but not maternal SHBG was significantly higher in the twin pregnancies. Maternal SHBG was 5-fold higher than in forty non-pregnant women, and fell with a half-life of 7.1 days immediately post-partum. In the two monkey species, SHBG with similar binding-characteristics exists but levels were 2.5-fold higher in the non-pregnant adult females than in women. In pregnancy, maternal SHBG levels were unchanged in the bonnet (nine observations) and fell markedly in the rhesus monkey (twenty-three observations); levels in the infants were comparably low in all three species, though more variable in the monkeys. In seven bonnet monkey mother-infant pairs sampled again 2 or 8 weeks later, SHBG had risen markedly (mean 6.1-fold) in the infants as has been shown previously in the human. The species differences in the non-pregnant females and the mothers may in part be related to species differences in oestrogen production. The macaque monkey appears suitable for studying further the mechanism of the neonatal SHBG rise, in which oestrogens cannot be implicated but thyroid hormones may be involved.