Evidence for decreased secretion of gonadotropin-releasing hormone in pubertal boys during short-term testosterone treatment.

Information about the site(s) of action as well as the age-dependent effects of sex steroids on gonadotropin-releasing hormone and gonadotropin secretion during human puberty is limited. To begin to address these questions, we evaluated the effects of a depot preparation of testosterone (testosterone enanthate) on gonadotropin secretion and pituitary responses to synthetic GnRH in 10, early to mid-pubertal boys who had either isolated GH deficiency (n-2) or delayed adolescent maturation (n-8). Chronological and bone age ranges were 13 1/12-16 1/12 and 11-14 yr, respectively. Frequent blood withdrawal studies (every 20 min for 20 consecutive h) were performed in the Clinical Research Center over two consecutive weekends. Following each study, gonadotropin responses to GnRH (0.25 microgram/kg iv bolus) were determined. During the initial study, all boys showed a sleep-entrained increase in luteinizing hormone (LH) and testosterone (T) secretion; mean nocturnal concentrations of LH and T were 2.3-fold greater than daytime values. At the end of the first study, testosterone enanthate was given im (0, 25, 50, or 75 mg/m2). Six days later, mean plasma T concentrations were in the pubertal to mid adult male range and were constant throughout the day: 25 mg/m2, 3.7 +/- 0.4 (SE) ng/ml; 50 mg/m2, 4.6 +/- 0.2 ng/ml; and 75 mg/m2, 6.7 +/- 0.4 ng/ml. T treatment had no effect on pituitary responses to GnRH: mean LH increment was 8.5 mIU/ml before and 10.0 mIU/ml after T treatment.(ABSTRACT TRUNCATED AT 250 WORDS)