Placental Transfer and Metabolism of 4-¹⁴C-Cortisol in the Pregnant Monkey

Abstract

THE concentration of cortisol in human maternal plasma exceeds that of foetal plasma by as much as two to five-fold^1–3. This difference has been attributed primarily to the large quantity of non-diffusible cortisol in the maternal circulation—that is, cortisol bound to transcortin (cortisol binding globulin), an α-globulin with selective affinity for cortisol⁴. This concept was challenged by the studies of Gold et al.⁵, who demonstrated that the concentration of unbound Porter–Silber chromogens in foetal plasma was lower than that found in maternal plasma, suggesting that simple differences in binding globulin concentrations alone cannot account for the distribution of cortisol between maternal and foetal compartments. The more rapid disposition of cortisol by the foetal–placental unit could account, in part, for the differences in cortisol concentration in the mother and foetus.