Suppression of testosterone-estradiol binding globulin by medroxyprogesterone acetate in polycystic ovary syndrome

Serum androgen binding capacity is decreased in hirsute women and normal women receiving medroxyprogesterone acetate. A sensitive radioimmunoassay was used to measure the main androgen binding protein, testosterone-estradiol-binding globulin, in 13 patients with hirsutism and the polycystic ovary syndrome. Testosterone-estradiol-binding globulin concentrations were determined before, during, and after treatment with medroxyprogesterone acetate. Testosterone-estradiol-binding globulin was lower in untreated polycystic ovary syndrome patients than in normal controls (21.9 +/- 3.7 versus 64 +/- 4 nmol/L, P less than .01). Administration of medroxyprogesterone acetate (400 mg intramuscularly every 15 days for nine months) to polycystic ovary syndrome patients caused a decrease of serum testosterone and further lowering of testosterone-estradiol-binding globulin (7.6 +/- 1.9 nmol/L, P less than .01). In two patients the concentration of testosterone-estradiol-binding globulin reached values as low as 0.9 and 0.8 nmol/L, approximately 1/60 and 1/70 of the normal level. Testosterone-estradiol-binding globulin returned to basal levels (15.1 +/- 1.3 nmol/L) between one and two years after discontinuation of medroxyprogesterone acetate. Corticosteroid binding globulin levels were normal in polycystic ovary syndrome and did not change with medroxyprogesterone acetate. It was concluded that: medroxyprogesterone acetate causes marked lowering of plasma testosterone-estradiol-binding globulin; the effect is not mediated by sex hormone levels; and the decrease in testosterone-estradiol-binding globulin offsets, at least partially, the beneficial action of medroxyprogesterone acetate.