Testosterone-binding Globulins in Human Plasma: Studies on Sex Distribution and Specificity

When human plasma is mixed with testosterone-(3)H and subjected to electrophoresis on paper in glycine acetate buffer at pH 8.6, at least two proteins other than albumin bind the testosterone. In normal women 80.5 +/- 1.9% (SEM) of the recovered radioactivity migrates with the beta-globulins, 7.3 +/- 0.80% with the inter-alpha-globulins, and 4.3 +/- 0.40% with albumin. In normal men the percentages are 69.3 +/- 3.0%, 14.3 +/- 1.6%, and 6.2 +/- 1.1%, respectively. These differences between men and women in binding among the beta-globulins and inter-alpha-globulins are statistically significant (P < 0.001). The highest percentages of radioactivity associated with the beta-globulins are seen in infants of both sexes, men receiving diethylstillbestrol, and pregnant women. These same subjects have the lowest percentages of radioactivity associated with the inter-alpha-globulins. Experiments with carrier testosterone indicate that at least some of the differences between the normal men and women and infants can be explained by differences in the concentration of endogenous testosterone. This factor alone, however, cannot explain the increased binding among the beta-globulins in the men receiving diethylstilbestrol or in the pregnant females. In this system estrone, estradiol, dehydroisoandrosterone, androsterone, 17alpha-hydroxyprogesterone, and 19-nortestosterone compete with testosterone for binding sites on the proteins. None is as potent as testosterone itself.