Tamoxifen suppresses gonadotropin-induced 17 alpha-hydroxyprogesterone accumulation in normal men.

Intramuscular administration of 1500 IU hCG daily for 3 days induced a transient accumulation of 17 alpha-hydroxyprogesterone (17 OHP) relative to testosterone (T) in normal men, reaching its maximum 24 h after the first injection (17 OHP to T ratio, 1.7 +/- 0.3 times baseline; P < 0.01). Simultaneous administration of hCG and the estrogen antagonist tamoxifen (20 mg twice daily) almost completely abolished the hCG-induced steroidogenic block localized between 17 OHP and T (17 OHP to T ratio at 24 h, 1.1 +/- 0.1 times baseline; P < 0.01 vs. hCG alone). These data indirectly suggest that, in man, the hCG-induced steroidogenic lesion might be mediated through its estrogen-stimulating effect.