Part of “CHAPTER 72 – SYNTHESIS AND METABOLISM OF CORTICOSTEROIDS“

Substantial variability exists in the production rate of the various steroids by males and females (see Table 72-3). Steroid products are secreted into the circulation as free hormones, where they bind to plasma proteins36,37 (Table 72-4). Only the free hormone is biologically active. However, the amount of hormone that is potentially available to tissues is determined by the equilibrium of the free and bound fractions. Bound hormone may be freed from the binding protein as the free hormone is metabolized or taken up into tissues. Thus, binding to plasma proteins increases the amount of hormone that can circulate in the blood and serves as a mechanism for transport of steroids in an inactive form. Binding makes the hormones more resistant to metabolism, thereby increasing the plasma half-life (t_1/2).