Androgen Transport and Plasma Levels in the Normal Female

Abstract

In normal women, 99% of circulating T is bound and biologically inactive. Testosterone is bound in the plasma to testosterone-binding globulin (TeBG), also called steroid-hormone- binding globulin (SHBG), a specific beta-globulin produced by the liver with a high affinity for T, and it is also bound to albumin. In normal women, the TeBG level is approximately double that of men. TeBG binds 78% of T, while albumin binds approximately 20% of T. Albumin has a lower affinity for T but has a larger binding capacity. In a study by Nisula and Dunn (689) total testosterone bound to albumin was 57.4% while the TeBG bound total T was 41.2%. These differences reflect different methods for characterization of testosterone binding to both albumin and TeBG. DHT and 5α-androstane-3α, 17β-diol (3α-diol), 5α-androstane-3β,l7β-diol (3β-diol) and E₂ are also bound to TeBG. It appears that steroids with a l7β-hydroxyl group are tightly bound to TeBG (Table 3-1) (733).