Corticosteroid-binding globulin status at the fetomaternal interface during human term pregnancy

The status of the corticosteroid-binding globulin (CBG) at the fetomaterial interface, especially in the maternal intervillous blood space (I), was in vestigated and compared to that of CBC in the maternal (M) and fetal (umbil ical arteries [A] and vein M) peripheral circulations at term. Immunoquanti tation of plasma CBG showed that the CBG concentration in I was 30% less th an that in M (P < 0.001) and threefold higher than that in umbilical cord b lood (P < 0.001). The microheterogeneity of CBG studied by immunoaffinoelec trophoresis in the presence of concanavalin A and Western blotting indicate d that the CBC in I was mainly of maternal origin and different from fetal CBG. A CBG mRNA, but no classic 50- to 59-kDa CBG, was found in isolated te rm trophoblastic fens.-The steroid environment of the CBG in I differed gre atly from that in the peripheral maternal and fetal circulations, because t he progesterone:cortisol molar ratio in I was 75-fold higher than that in M and 7- to 10-fold higher than that in the fetal circulation. Binding studi es revealed that the affinity constants of CBG for cortisol in I, A, and V were significantly lower than that in M plasma (P < 0.02) in their respecti ve hormonal contexts. The binding parameters for I-CBC stripped of endogeno us steroids and lipids were dose to those for M-CBG but different from thos e of fetal CBC (P < 0.001). These data reflect the physiological relevance of the CBG-steroid interaction, especially with very CBG-loaded progesteron e at the fetomaternal interface during late pregnancy.