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Sex Hormone-binding Globulin

المؤلف:  Norman, A. W., & Henry, H. L.

المصدر:  Hormones

الجزء والصفحة:  3rd edition , p262

2026-04-16

393

Following secretion from the tissue of origin, all steroid hormones are bound to one or more plasma proteins. Of the total testosterone in the circulation, 0.5 to 3% is free (not bound to protein), 54–68% is bound to albumin with relatively low affinity and the remainder is bound to sex hormone binding globulin, SHBG, with high affinity. SHBG, synthesized in the liver, is a dimeric glycosylated protein with a molecular mass of 84 kDa. SHBG has a preference for steroids with a 17β-hydroxyl [Kd ≅ (1–5)×10⁻¹⁰ M] so it binds T, DHT, and estradiol, but not, for example, progesterone or cortisol. Thus, it serves as the specific transport protein for both testos terone and estradiol. Plasma levels of SHBG are two fold greater in nonpregnant women than in men. The synthesis, and therefore the plasma concentration, of SHBG is increased in pregnancy and hyperthyroidism and is decreased by androgens, glucocorticoids, insulin, and growth hormone.