title: Corticosteroid-binding proteins in human colostrum and milk and rat milk.
abstract: A corticosteroid-binding protein was detected in the whey of human colostrum and milk which resembles serum corticosteroid-binding globulin in certain respects: the equilibrium association constants for cortisol and progesterone binding and the apparent molecular size, as determined by Sephadex G-200 chromatography, were similar, and cortisol andd progesterone competed strongly for binding to the same site in each instance. Dexamethasone-binding activity could not be detected. The concentration of corticosteroid-binding protein in the colostrum obtained before parturition is about 0.1 muM; the concentration declines rapidly after parturition to about 0.01 muM. A corticosteroid-binding protein was found, also, in the whey of mature rat milk at levels of about 0.3 muM. This protein resembles rat serum corticosteroid-binding globulin: the equilibrium association constants for cortisol, corticosterone, and progesterone binding, and the apparent molecular size, as determined by Sephadex G-200 chromatography, were similar; the elution behavior of the respective proteins on anion exchange chromatography with DEAE-Sephadex A-50 was similar, also. Identity of the corticosteroid-binding proteins in whey with corticosteroid-binding globulin in serum is not presumed, however. Rat and human whey exhibited very little testosterone- or 17 beta-estradiol-binding activity. It is suggested the corticosteroid-binding proteins may play a significant physiological role in regulating the concentration of the bound and unbound forms of progesterone and cortisol in the fluids bathing the epithelial cells lining the mammary ducts and acini.
mesh_terms: D000305:Adrenal Cortex Hormones / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D003126:Colostrum / Q000378:metabolism*; D003345:Corticosterone / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D008892:Milk / Q000378:metabolism*; D008894:Milk Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008895:Milk, Human / Q000378:metabolism*; D008970:Molecular Weight; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D011956:Receptors, Cell Surface; D013739:Testosterone / Q000378:metabolism
chemical_list: D000305:Adrenal Cortex Hormones; D008894:Milk Proteins; D011956:Receptors, Cell Surface; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D003907:Dexamethasone; D003345:Corticosterone; D006854:Hydrocortisone