Dexamethasone suppresses sex-hormone binding globulin.

Dexamethasone suppression (DEX-S) for 14 days has been used to determine the probable source of androgen excess. The exact mechanism(s) of DEX-S is still unclear. The authors postulated that dexamethasone (DEX) inhibits either the synthesis or secretion of sex-hormone binding globulin (SHBG). To examine this hypothesis, 14 women with polycystic ovarian disease (PCOD) and 3 volunteers were given DEX for 14 days. The PCOD group included obese and nonobese women (+/- 15% ideal body weight). Plasma determinations by radioimmunoassay of total testosterone, free testosterone, androstenedione, dehydroepiandrosterone sulfate, luteinizing hormone; follicle-stimulating hormone; cortisol, and SHBG were made. DEX suppressed SHBG levels (P less than 0.01). SHBG levels were significantly lower in the obese than in the nonobese (P less than 0.01). All androgens were suppressed by DEX, with the exception of androstenedione post-DEX levels, which were significantly greater than pre-DEX levels in 6 of 14 subjects (P greater than 0.05). This observation is consistent with DEX suppression of SHBG.