What is the Origin of Sex Hormone Binding Capacity?

This concept is a fundamental aspect of endocrinology, arising from the discovery and characterization of SHBG, a glycoprotein synthesized primarily in the liver. The term highlights the protein's role as a transport and regulatory reservoir for sex steroids. Assessing binding capacity is clinically important because it helps explain discrepancies between total hormone levels and a patient's clinical presentation.

What is the Mechanism of Sex Hormone Binding Capacity?

SHBG binds to sex hormones with high affinity, effectively sequestering them and preventing their immediate diffusion into cells. The binding capacity is influenced by numerous factors, including liver function, thyroid hormone status, and insulin levels, which can up- or down-regulate SHBG synthesis. A high binding capacity leads to lower free hormone levels, while a low capacity increases the fraction of free, active hormones.

Sex Hormone Binding Capacity ∞ Area

Sex Hormone Binding Capacity

Meaning

Sex Hormone Binding Capacity refers to the maximal quantity of sex hormones, primarily testosterone and estradiol, that can be bound by the circulating protein Sex Hormone Binding Globulin (SHBG) in the blood plasma. This capacity is a critical determinant of the concentration of free, biologically active hormones available to target tissues. Changes in binding capacity directly impact hormonal signaling and systemic effects.