[The effect of steroids on binding of transcortin with human syncytiotrophoblasts]

The effects of steroids on specific binding of transcortin (corticosteroid-binding globulin, CBG) variants (nCBG and vCBG) from pregnant women sera to the microvesicular membrane fraction derived from placental syncytiotrophoblast brush border have been studied. It was shown that native CBG variants stripped of steroids lose their ability to interact with specific membrane sites. Specific binding of CBG variants was found to increase in parallel with an increasing per cent content of glycoproteins associated with cortisol, reaching a maximum at cortisol concentrations of 5.10(-8)-5.10(-7) M which is saturating for the complex formation. Specific binding sites in the syncytiotrophoblast membrane do not differentiate between the nCBG complexed to cortisol, corticosterone, progesterone or testosterone but show a selectivity towards the vCBG-cortisol complex.