Indices d'affinité comparés de certains stéroïdes pour les protéines sériques et placentaires humaines

Summary In previous experiments [1], evidence has been provided for binding affinity of several steroids to cytosoluble fraction of human placental tissue. In order to compare these binding properties with those of human pregnancy serum, we have determined a «displacement index according to the formerly described method [2], using the same steroids for the proteins obtained from the cytosoluble fractions of two different placentas and from one homologous pregnancy serum. All determinations have been made on the protein fractions precipitated by ammonium sulphate, between 30 and 45 per cent of saturation. The displacement of labelled testosterone bound to proteins by increasing amounts of non-radioactive steroids has been studied with the following compounds: testosterone, dihydro-testosterone, 5-androstenediol, 4-androstenediol, 5α-androstanediol, 19-nortestosterone, 19-nor-5-androstenediol, 16α-hydroxytestosterone, 16α-hydroxy-5-androstenediol and estradiol. Bound and unbound steroids were measured at equilibrium by a modification of the technique of Pearlman and Crepy [8] and graphs established according to the method of Rodbard and al. [10] and Rees Midgley and al. [11], which allows a linear relationship between the decrease of bound labelled testosterone and the increasing amount of free non-radioactive steroid. The displacement index is expressed as the ratio of unlabelled testosterone (ng) to the quantity of the tested substance (ng) required to decrease the bound [ 3 H]-testosterone to 50 per cent of its initial value. If 5α-androstanediol and dihydrotestosterone present the highest displacement index with both proteins, differences occur with 4-androstenediol and 5-androstenediol. These two compounds have a greater affinity than testosterone for placental proteins and a lower one for pregnancy serum proteins. In human placental tissue, high binding affinity for androgenic steroids possessing an hydroxyl group in the 17β-position has been shown. Affinity decreases with the presence of a 16α-hydroxyl group or loss of the 19 angular methyl group, with the exception of 19-nor-5-androstenediol which shows a high affinity.