Testosterone supplementation in older men restrains insulin-like growth factor's dose-dependent feedback inhibition of pulsatile growth hormone secretion.

Background: Pulsatile GH secretion declines in older men. The causal mechanisms are unknown. Candidates include deficient feedforward (stimulation) by endogenous secretagogues and excessive feedback (inhibition) by GH or IGF-I due to age and/or relative hypoandrogenemia.

Estradiol supplementation in postmenopausal women attenuates suppression of pulsatile growth hormone secretion by recombinant human insulin-like growth factor type I.

Background: Why pulsatile GH secretion declines in estrogen-deficient postmenopausal individuals remains unknown. One possibility is that estrogen not only enhances stimulation by secretagogues but also attenuates negative feedback by systemic IGF-I. SITE: The study took place at an academic medical center.