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Am J Physiol Regul Integr Comp Physiol 279: R891-R898, 2000;
0363-6119/00 $5.00
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Vol. 279, Issue 3, R891-R898, September 2000

Leptin responses to physical inactivity induced by simulated weightlessness

Stéphane Blanc1, Sylvie Normand2, Christiane Pachiaudi2, Monique Duvareille1, and Claude Gharib1

1 Laboratoire de Physiologie de l'Environnement, Faculté de Médecine Lyon Grange-Blanche, 69373 Lyon Cedex 08; and 2 Centre de Recherche en Nutrition Humaine de Lyon, Faculté de Médecine Laënnec, 69372 Lyon Cedex 08, France

Physical inactivity induced by head-down bed rest (HDBR) affects body composition (BC). Leptin is involved in BC regulation by acting on fuel homeostasis. We investigated whether leptin and counterregulatory hormone levels are affected by a 7-day HDBR. Fasting blood was sampled daily (0700) in males (n = 8) and on alternating days in females (n = 8) for measurements of leptin, insulin, norepinephrine (NE), epinephrine (Epi), growth hormone (GH), cortisol, nonesterified fatty acid (NEFA), and glucose. BC was measured by H218O dilution. Energy intake (men 10.5 ± 0.2 MJ/day, women 7.9 ± 0.3 MJ/day) and BC were unchanged by HDBR. Increased levels of leptin (men 40%, P = 0.003; women 20%, P = 0.050), insulin (men 34%, P = 0.018; women 25%, P = 0.022), and the insulin-to-glucose ratio (men 30%, P = 0.049; women 25%, P = 0.031) were noted. GH, NE, Epi, and cortisol levels were unaltered. NEFA dropped in both sexes, but glucose decreased only in women. In conclusion, HDBR increased leptin levels independently of stress response, changes in fat mass, energy intake, or gender. These changes were correlated to the insulin-resistance development in men. Further analyses are required, but the results have to be considered for longer HDBR periods with 1) the well-described drop in energy intake and 2) the BC changes.

gender; microgravity; spaceflight; body composition


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