CORTICOSTERONE BINDING BY MOUSE SERA DURING FOETAL AND POST-NATAL DEVELOPMENT

Abstract

The binding properties of corticosterone binding globulin (CBG) of mouse sera were studied by equilibrium dialysis and electrophoretic techniques, at different stages of fetal and post-natal development. Scatchard analysis demonstrated in all cases a single class of high affinity saturable binding sites for corticosterone. Remarkable increases of the binding capacities were observed in the fetal and pregnant sera, compared to normal adult and immature levels. The mean values of n1M1 [number of binding sites .times. moles of binding protein] .times. g-1 of serum proteins (concentration of binding sites, n1 .times. moles of binding proteins (M1) were 21 .times. 10-8 in 14-19 day pregnant females, 17 .times. 10-8 in the amniotic fluid, 4.2 .times. 10-8 in 14-19 day embryos, and only 0.8 .times. 10-8 in the normal adult female. Neonatal mice, aged 0-6 days exhibited no CBG activities. The association constants showed values of 2.5-4.1 .times. 108 M-1 when measured with fetal sera, and of 1.2-2.1 .times. 108 M-1 with pregnant or control adult sera and with the amniotic fluid, at 25.degree. C. Comparative electrophoretic, thermal denaturation and competition studies with fetal and pregnant plasma CBG are also reported. The results are discussed in relation to the origin of CBG in the fetal serum, and also with respect to similar studies in the rat, guinea pig and man. The possible biological implications of serum steroid binding proteins in mammalian development are briefly outlined.