Gonadotropin and testosterone measurements after estrogen administration to adult men, prepubertal and pubertal boys, and men with hypogonadotropism: evidence for maturation of positive feedback in the male.

Nineteen male subjects were fiven five daily injections of 17beta-estradiol and circulating levels of estradiol (E2), testerone (T), and gonadotropins were determined by radioimmunoassay before, during, and after the steroid course. Peak levels of E2 attained during the 5 days of treatment ranged from 173-577 pg/ml. Four of seven normal adult men and one castrate man demonstrated suppression of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) with a subsequent rise in LH (positive feedback) while E2 levels remained elevated. A rise in T was associated with the LH increment in the four normal men. Nine pre-, early, or midpubertal boys and two men with hypogonadotropic hypogonadism displayed only gonadotropin suppression after E2 administration. The difference in LH response to estrogen (i.e., positive feedback) between the adult men with normal or elevated gonadotropin levels as compared with the endocrinologically normal boys is significant (P less than 0.01).