Leptin responses to physical inactivity induced by simulated weightlessness.
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 H(2)(18)O 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.
Blanc
S
S
Laboratoire de Physiologie de l'Environnement, Faculté de Médecine Lyon Grange-Blanche, 69373 Lyon Cedex 08, France.
Normand
S
S
Pachiaudi
C
C
Duvareille
M
M
Gharib
C
C
D000328:Adult; D001510:Bed Rest; D001786:Blood Glucose; D001823:Body Composition; D004734:Energy Metabolism; D004837:Epinephrine / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007328:Insulin / Q000097:blood; D020738:Leptin / Q000097:blood*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D015596:Nutrition Assessment; D010809:Physical Fitness; D012737:Sex Factors; D013312:Stress, Physiological / Q000378:metabolism; D014893:Weightlessness; D018474:Weightlessness Simulation
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D020738:Leptin; D019382:Human Growth Hormone; D006854:Hydrocortisone; D009638:Norepinephrine; D004837:Epinephrine