Liaison du sulfate d'oestrone par les proteines seriques du rat au cours de son developpement

Abstract

The binding of estrone sulfate by rat serum has been studied comparatively, with an equilibrium dialysis technique, in the embryo and the pregnant rat at the 19th day of pregnancy, as well as during post-natal development. The sera of the embryo and the new-born rat almost bind no estrone sulfate; in contrast, this binding is high in the 21-days-old and in the adult animal. A significant reduction of the affinity index is shown in the pregnant rat serum. The binding of testosterone sulfate is 3–4 times lower than that of estrone sulfate. There is no fixation of estradiol glucuronide in any of the tested sera. A positive correlation has been found between the albumin level of the different sera and their affinity index for the estrone sulfate. The albumin purified from embryo sera and the adult serum albumin have similar high affinity indexes for estrone sulfate. The binding curves for the estrogen conjugate with these two purified proteins and the whole sera of normal and pregnant adult rats are not appreciably different. In all cases, two kinds of binding sites are demonstrated: relatively strong binding sites, with an association constant of about 1.5·10 5 M −1 at 25°C and numerous low affinity binding sites, with an association constant of about 3·10 3 M −1 at 25 °C. There are probably two strong binding sites per serum albumin molecule ( n 1 ∼ 2). From these results, it is concluded that albumin is the main protein that binds estrone sulfate in the rat serum. The absence of binding in the embryo is due to the low levels of this protein and not to a qualitatively different behavior of the foetal serum albumin. The lack of binding of estrone sulfate in the embryo is in contrast with the high affinity of the embryo sera for estrone and estradiol-17β.