Augmentation of growth hormone secretion after testosterone treatment in boys with constitutional delay of growth and adolescence: Evidence against an increase in hypothalamic secretion of growth hormone-releasing hormone

The increase in pituitary GH secretion that occurs during mid-late puberty in boys follows an increase in circulating testosterone (T) concentration; the direct mechanism by which this occurs is unknown. We hypothesized that T increases GH secretion during puberty by augmenting hypothalamic output of GHRH. Using constant infusions of a GHRH antagonist, we tested this hypothesis in six early pubertal boys with constitutional delay of growth and adolescence who had a mean chronological age of 14.0 ± 0.3 yr and mean bone age of 11.4 ± 0.2 yr. Blood samples were obtained from subjects every 15 min for 24 h during the overnight infusion of normal saline (2000–0600 h) and again during the overnight infusion of GHRH antagonist (0.33 μg/kg/h) the following night. Subjects then received transdermal T (5-mg patch) for 12 h nightly and were studied again after 4 wk of treatment. Serum samples were assayed for GH and total ghrelin; the percent suppression of GH during GHRH antagonist infusion was calculated. Morning ...