Insulin-lowering treatment reduces aromatase activity in response to follicle-stimulating hormone in women with polycystic ovary syndrome

OBJECTIVE: To investigate the effects of reduction of insulin resistance and hyperinsulinemia associated with the polycystic ovary syndrome (PCOS) on FSH-stimulated ovarian aromatase activity. DESIGN: Prospective study. SETTING: Academic health center, Siena, Italy. PATIENT(S): Twenty women 18 to 26 years of age in whom PCOS was diagnosed on the basis of oligomenorrhea or amenorrhea and hyperandrogenemia. INTERVENTION(S): Recombinant FSH was administered. The next day, therapy with metformin (500 mg t.i.d.) was begun. After 35 to 40 days of treatment, the pretreatment protocol was repeated. MAIN OUTCOME MEASURE(S): Plasma levels of estradiol (E(2)), androstenedione (A), and testosterone (T). The ratios of basal levels and areas under the curve (AUCs) of products and substrates were compared before and after metformin administration to detect differences in aromatase activity. RESULT(S): Metformin treatment was associated with significant reduction in basal free testosterone plasma levels, insulin plasma levels, and insulin response to oral glucose tolerance testing. Administration of FSH was followed by a significantly lesser E(2) response after metformin therapy than before this therapy. The ratios of AUC(E2) to AUC(A) and to AUC(T), indicative of aromatase activity in response to FSH, were significantly lower after metformin therapy than before. CONCLUSION(S): Metformin therapy in women with PCOS is associated with a reduction in aromatase activity in response to FSH. Insulin affects production of both androgen and estrogen. Insulin therefore plays a central role in regulating the activity of thecal and granulosa cells.