Low-dose T3 improves the bed rest model of simulated weightlessness in men and women

Jennifer C. Lovejoy, Steven R. Smith, Jeffrey J. Zachwieja, George A. Bray, Marlene M. Windhauser, Peter J. Wickersham, Johannes D. Veldhuis, Richard Tulley, Jacques A. De La Bretonne

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


This study tested the hypothesis that low-dose 3,5,3'-triiodothyronine (T3) administration during prolonged bed rest improves the ground-based model of spaceflight. Nine men (36.4 ± 1.3 yr) and five women (34.2 ± 2.1 yr) were studied. After a 5-day inpatient baseline period, subjects were placed at total bed rest with 6°head-down tilt for 28 days followed by 5- day recovery. Fifty micrograms per day of T3 (n = 8) or placebo (n = 6) were given during bed rest. Serum T3 concentrations increased twofold, whereas thyroid-stimulating hormone was suppressed in treated subjects. T3-treated subjects showed significantly greater negative nitrogen balance and lost more weight (P = 0.02) and lean mass (P < 0.0001) than placebo subjects. Protein breakdown (whole body [13C]leucine kinetics) increased 31% in the T3 group but only 8% in the placebo group. T3-treated women experienced greater changes in leucine turnover than men, despite equivalent weight loss. Insulin sensitivity fell by 50% during bed rest in all subjects (P = 0.005), but growth hormone release and insulin release were largely unaffected. In conclusion, addition of low-dose T3 to the bed rest model of muscle unloading improves the ground-based simulation of spaceflight and unmasks several important gender differences.

Original languageEnglish (US)
Pages (from-to)E370-E379
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number2 40-2
StatePublished - Aug 1 1999


  • Gender differences
  • Growth hormone
  • Insulin resistance
  • Spaceflight
  • Thyroid hormones

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)


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