title: High-affinity binding of testosterone in serum from normal developing chick embryos and during the graft-versus-host reaction.
abstract: The sera of developing chicken embryos contain high-affinity, low-capacity protein binding sites for testosterone. The affinities remain constant throughout development, with mean values for the association constants of approx. 3.6 X 10(8) M-1 at 25 degrees C, whereas the concentration of sites varies markedly as a function of age: from approx. 2 nmol/g serum proteins in 11-day embryos, it rises to a peak of approx. 5-8 nmol at 14-16 days, then drops to approx. 2.6 nmol at 18 days and only 0.8-1 nmol in adults. Testosterone binding is inhibited by corticosterone, progesterone and dihydrotestosterone, and is little affected by estradiol. The testosterone and corticosterone binding properties of chicken sera show close similarities: parallel ontogenic patterns; constant ratios, throughout development, of the equilibrium binding parameters of the two steroids; mutual binding inhibition. The evidence strongly suggests that the two activities are associated, at least in part, with a common protein carrier(s). In growing embryos which undergo a graft-versus-host reaction, elicited by the graft of adult spleen tissue at 9 days of age, the testosterone and corticosterone binding activities are significantly decreased. This decrease is due to a fall in the number of sites, whereas association constants are not affected. This is the first high-affinity, saturable, testosterone-binding property to be described in an embryonic serum.
mesh_terms: D000367:Age Factors; D000818:Animals; D001667:Binding, Competitive; D002642:Chick Embryo; D002645:Chickens; D003345:Corticosterone / Q000097:blood / Q000378:metabolism; D013196:Dihydrotestosterone / Q000097:blood / Q000378:metabolism; D004958:Estradiol / Q000097:blood / Q000378:metabolism; D005260:Female; D006087:Graft vs Host Reaction; D008297:Male; D011485:Protein Binding; D012737:Sex Factors; D013739:Testosterone / Q000097:blood / Q000378:metabolism*
chemical_list: D013196:Dihydrotestosterone; D013739:Testosterone; D004958:Estradiol; D003345:Corticosterone