Abstract

PIP: Differential precipitation of plasma proteins after equilibration of the plasma with tracer amounts of testosterone (T) was used to measure free and not-T-estradiol binding globulin (TeBG)-bound T in 20 women and 10 men. Tritiated T was the tracer used. Comparison of this method with the equilibration dialysis method produced a good agreement in accuracy. The method is described as simple and reproducible, allowing routine assay of 20 plasma samples in duplicate by 1 technician. Normal values for men were 497 ng/100 ml (total T), 42 ng/100 ml(free T), 137 ng/100 ml (non-TeBG bound), and .5 mcg/100 ml (TeBG). Women's values were 52 ng/100 ml (Total T), 2.6 ng/100 ml (free T), 5 ng/100 ml (nonTeBG) and .9 mcg/100 ml (TeBG). Significant increases in total (p less than .05), free (p less than .01), non-TeBG-bound (p less than .05), and TeBG-T (p less than .01) were found for women taking norethindrone and mestranol. Women taking norgestrel-ethinyl estradiol had significant increase (p less than .01) in non-TeBG-bound T. It is concluded that estrogens increase the binding capacity of TeBG, and this is inhibited by norgestrel.