Effects of growth hormone and/or sex steroid administration on whole-body protein turnover in healthy aged women and men

Xin Huang, Marc R. Blackman, Karen Herreman, Katharine M. Pabst, S. Mitchell Harman, Benjamin Caballero

Research output: Contribution to journalArticlepeer-review

Abstract

Aging is associated with reduced activities of the growth hormone (GH), insulin-like growth factor I (IGF-I), and sex steroid axes, and with decreased lean body mass and protein synthesis. Using a randomized, double-blinded, placebo-controlled design, we studied the effects of 6 months of administration of GH alone, sex hormone alone (hormone replacement therapy in women, testosterone enanthate [T] in men), or GH plus sex hormone on protein turnover in healthy men (n = 60) and women (n = 43), aged 65 to 88 years (mean, 71 ± 4.4 years). Growth hormone administration significantly increased IGF-I levels in both sexes, more markedly in men. Sex steroid administration increased the levels of estrogen and testosterone in women and men, respectively (P = .05). Protein turnover was measured before and after the 26-week treatment period by means of a primed, constant l-[1-13C]leucine infusion. In men, GH plus T administration increased leucine flux from 80.2 ± 2.8 to 93.6 ± 4.2 μmol·h-1·kg-1 (P = .02). Leucine oxidation did not change significantly after hormone treatment in either sex. Growth hormone treatment led to nonsignificant upward trends in nonoxidative leucine disposal in men (9.1 ± 5.2 mol·h -1·kg-1) and women (7.6 ± 7.1 mol·h-1·kg-1). Among all groups combined, changes in nonoxidative leucine disposal were directly related to those of serum IGF-I level (r = 0.248, P < .02). Whole-body protein turnover increased in GH plus T-treated men (0.6 ± 0.2 g protein·kg -1·d-1; P < .01). These data suggest that low-dose GH administration increases protein synthesis in healthy aged women and men, and that the coadministration of testosterone plus GH enhances this effect in elderly men.

Original languageEnglish (US)
Pages (from-to)1162-1167
Number of pages6
JournalMetabolism: clinical and experimental
Volume54
Issue number9
DOIs
StatePublished - Sep 2005

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology

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