COMPETITIVE BINDING OF FREE AND CONJUGATED OESTROGENS TO PLASMA PROTEINS

Abstract

SUMMARY Human plasma was dialysed against increasing concentrations of [4-14C]oestradiol-17β, [4-14C]oestrone, Na[6,7-3H]oestradiol-17β-glucuronide and Na[6,7-3H]oestrone sulphate. When the oestrogens were dialysed separately, binding to a protein with a limited number of binding sites (probably a globulin) could be shown. At comparable concentrations oestrone sulphate was bound to a greater extent than the free compounds and the glucuronide. When free and conjugated oestrogens were dialysed together a displacement of the conjugates from globulin to albumin was demonstrated. This observation was confirmed by the results of the equilibrium dialysis of plasma of ovarian vein blood obtained from a mare and a donkey after injection of [4-14C]oestradiol-17β and Na[6,7-3H]oestradiol-177β-glucuronide into a Graafian follicle of the homolateral ovary. The possible physiological significance of this competition between free and conjugated oestrogens is discussed.