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This Article Full Text Full Text (PDF) All Versions of this Article: 293/3/E769    most recent 00709.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Muniyappa, R. Articles by Blackman, M. R. Search for Related Content PubMed PubMed Citation Articles by Muniyappa, R. Articles by Blackman, M. R.

Long-term testosterone supplementation augments overnight growth hormone secretion in healthy older men

¹Endocrine Section, Laboratory of Clinical Investigation, National Center for Complementary and Alternative Medicine, National Institutes of Health, Bethesda, Maryland; ²Endocrine and ³Metabolism Sections, National Institute on Aging, National Institutes of Health; ⁴Division of Geriatrics and Gerontology, Department of Medicine, Department of Veterans Affairs and Veterans Affairs Medical Center, Baltimore Geriatric Research, Education, and Clinical Center, and the University of Maryland School of Medicine, Division of Gerontology, Baltimore, Maryland; ⁵Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinical Research Center, Rochester, Minnesota; ⁶Kronos Longevity Research Institute, Phoenix, Arizona; ⁷Geriatric Medicine and Rehabilitation, Bürgerspital, St. Gallen, Switzerland; and ⁸Endocrine, Diabetes, and Nutrition Section, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts

Submitted 22 December 2006 ; accepted in final form 30 May 2007

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, Q₂₀ 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 E₂ 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.

pulsatility; testosterone replacement; aging