Metformin treatment reduces ovarian cytochrome P-450c17alpha response to human chorionic gonadotrophin in women with insulin resistance-related polycystic ovary syndrome

It has recently been proposed that hyperinsulinaemic insulin resistance and increased ovarian cytochrome P-450c17alpha activity, two features of the polycystic ovary syndrome (PCOS), are pathogenetically linked. The aim of the present study was to test the hypothesis of the linkage between hyperinsulinaemia and supranormal activity of cytochrome P-450c17alpha using the human chorionic gonadotrophin (HCG) challenge, which is a more direct ovarian stimulus than gonadotrophin-releasing hormone (GnRH) in detecting modifications in ovarian steroidogenesis. Eleven women with insulin resistance-related PCOS were studied. HCG (10 000 IU) was given i.m., and blood samples were obtained 0, 8, 12, 16 and 24 h thereafter. Next day, metformin was given at a dose of 500 mg three times a day for 30-32 days, at which time the pretreatment study was repeated. Two women ovulated after metformin treatment. The administration of metformin was associated with a decrease in area under the curve for insulin during a 2h, 75g oral glucose tolerance test, in plasma free testosterone concentrations and an increase in plasma sex hormone binding globulin concentration. The plasma 17-hydroxyprogesterone response to HCG was significantly lower after metformin treatment. The present study gives a direct demonstration that metformin leads to a reduction in stimulated ovarian cytochrome P-450c17alpha activity in women with polycystic ovary syndrome.