TY - JOUR
T1 - Low-dose T3 improves the bed rest model of simulated weightlessness in men and women
AU - Lovejoy, Jennifer C.
AU - Smith, Steven R.
AU - Zachwieja, Jeffrey J.
AU - Bray, George A.
AU - Windhauser, Marlene M.
AU - Wickersham, Peter J.
AU - Veldhuis, Johannes D.
AU - Tulley, Richard
AU - De La Bretonne, Jacques A.
PY - 1999/8
Y1 - 1999/8
N2 - 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.
AB - 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.
KW - Gender differences
KW - Growth hormone
KW - Insulin resistance
KW - Spaceflight
KW - Thyroid hormones
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U2 - 10.1152/ajpendo.1999.277.2.e370
DO - 10.1152/ajpendo.1999.277.2.e370
M3 - Article
C2 - 10444434
AN - SCOPUS:0032827098
SN - 0193-1849
VL - 277
SP - E370-E379
JO - American Journal of Physiology - Endocrinology and Metabolism
JF - American Journal of Physiology - Endocrinology and Metabolism
IS - 2 40-2
ER -