TEST and GH

Am J Physiol Endocrinol Metab. 2007 Jun 5

Long-Term Testosterone Supplementation Augments Overnight Growth Hormone Secretion in Healthy Older Men.

Muniyappa R, Sorkin JD, Veldhuis JD, Harman SM, Munzer T, Bhasin S, Blackman MR.

NCCAM, NIH, Bethesda, Maryland, United States.

Context: Circulating testosterone (T) and GH/IGF-I are diminished in healthy aging men. Short-term administration of high doses of T augments GH secretion in older men. However, effects of long-term, low-dose T supplementation on GH secretion are unknown. Objective: Evaluate effects of long-term, low-dose T administration on nocturnal GH secretory dynamics and AM concentrations of IGF-I and IGFBP-3 in healthy older men (65-88 yr, n=34) with low-normal testosterone and IGF-I. Design: In a double-masked, placebo-controlled, randomized study, we assessed effects of low-dose T supplementation (100 mg IM every 2 weeks) for 26 weeks on nocturnal GH secretory dynamics (8 PM-8 AM, q20 min sampling, analyzed by multiparameter deconvolution and Approximate Entropy (ApEn) algorithms). Results: T administration increased serum total T by 33 % (P = 0.004) and E2 by 31% (p=0.009), and decreased SHBG by 17% (p = 0.002), versus placebo. T supplementation increased nocturnal integrated GH concentrations by 60 % (P = 0.02), and pulsatile GH secretion by 79%, (P = 0.05), primarily due to a two-fold increase in GH secretory burst mass (P = 0.02), and a 1.9 fold increase in basal GH secretion rate (P = 0.05), versus placebo. There were no significant changes in GH burst frequency or orderliness of GH release (ApEn). IGF-I levels increased by 22 % (P = 0.02) with no significant change in IGFBP-3 levels, after T versus placebo. Conclusions: Low-dose T supplementation for 26 weeks increases spontaneous nocturnal GH secretion and morning serum IGF-I concentrations in healthy older men. Key words: GH , Pulsatility, T ReplaKalpaent, Aging.