Low-dose T(3) improves the bed rest model of simulated weightlessness in men and women.
This study tested the hypothesis that low-dose 3,5, 3'-triiodothyronine (T(3)) 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 degrees head-down tilt for 28 days followed by 5-day recovery. Fifty micrograms per day of T(3) (n = 8) or placebo (n = 6) were given during bed rest. Serum T(3) concentrations increased twofold, whereas thyroid-stimulating hormone was suppressed in treated subjects. T(3)-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 [(13)C]leucine kinetics) increased 31% in the T(3) group but only 8% in the placebo group. T(3)-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 T(3) to the bed rest model of muscle unloading improves the ground-based simulation of spaceflight and unmasks several important gender differences.
Lovejoy
J C
JC
Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana 70808, USA. lovejoj@mhs.pbrc.edu
Smith
S R
SR
Zachwieja
J J
JJ
Bray
G A
GA
Windhauser
M M
MM
Wickersham
P J
PJ
Veldhuis
J D
JD
Tulley
R
R
de la Bretonne
J A
JA
D000328:Adult; D001510:Bed Rest / Q000009:adverse effects; D001786:Blood Glucose / Q000032:analysis; D001823:Body Composition / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005215:Fasting / Q000502:physiology; D005260:Female; D019382:Human Growth Hormone / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism / Q000502:physiology; D000078790:Insulin Secretion; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D011673:Pulsatile Flow; D012727:Sex Characteristics; D014284:Triiodothyronine / Q000008:administration & dosage* / Q000097:blood / Q000494:pharmacology; D018474:Weightlessness Simulation
D001786:Blood Glucose; D007328:Insulin; D014284:Triiodothyronine; D019382:Human Growth Hormone; D007930:Leucine