Plasma corticosterone binding capacity in the partially decapitated chick embryo

The C₂₁-steroid binding capacity (i.e., CBG or transcortin) was measured in the normal and partially decapitated (i.e., hypophysectomized) chicken embryo. In normal embryos the transcortin levels increased up to Day 15 of incubation and then sharply decreased until Day 20. The total plasma protein concentration increased until Day 17 and then stabilized. The early partial decapitation of embryos prevented (a) the increase of transcortin level from Days 13 to 15, (b) the decrease in transcortin level from Days 15 to 20, and (c) the increase in total plasma protein after Day 13. The hypophysis-dependent changes in transcortin concentrations are discussed in relation to the effects of partial decapitation on the C₂₁-steroid concentration and the late differentiation of target organs.