Long-term testosterone supplementation augments overnight growth hormone secretion in healthy older men.
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. Our objective was to 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 T and IGF-I. In a double-masked, placebo-controlled, randomized study we assessed effects of low-dose T supplementation (100 mg im every 2 wk) for 26 wk on nocturnal GH secretory dynamics [8 PM to 8 AM, Q(20) min sampling, analyzed by multiparameter deconvolution and approximate entropy (ApEn) algorithms]. The results were that T administration increased serum total T by 33% (P = 0.004) and E(2) by 31% (P = 0.009) and decreased SHBG by 17% (P = 0.002) vs. 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 twofold increase in GH secretory burst mass (P = 0.02) and a 1.9-fold increase in basal GH secretion rate (P = 0.05) vs. 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 vs. placebo. We conclude that low-dose T supplementation for 26 wk increases spontaneous nocturnal GH secretion and morning serum IGF-I concentrations in healthy older men.
Muniyappa
Ranganath
R
Endocrine Section, Laboratory of Clinical Investigation, National Center for Complementary and Alternative Medicine, National Institutes of Health, Bethesda, Maryland, USA.
Sorkin
John D
JD
Veldhuis
Johannes D
JD
Harman
S Mitchell
SM
Münzer
Thomas
T
Bhasin
Shalender
S
Blackman
Marc R
MR
D000368:Aged; D002940:Circadian Rhythm / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood*; D020249:Hormone Replacement Therapy / Q000379:methods*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D013739:Testosterone / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*
D018972:Insulin-Like Growth Factor Binding Protein 3; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone