Differential responses of IGF-I molecular complexes to military operational field training.
Insulin-like growth factor (IGF) I and IGF binding proteins (IGFBPs) modulate metabolic activity and tissue repair and are influenced by nutritional status. IGF-I circulates in free, ternary [IGF-I + IGFBP-3 + acid labile subunit (ALS)], and binary (IGF-I + IGFBP) molecular complexes, and the relative proportions regulate IGF-I extravascular shifting and bioavailability. This study examined the hypothesis that sustained physical activity and sleep deprivation superimposed on a short-term energy deficit would alter the IGFBP concentrations and alter the proportions of IGF-I circulating in ternary vs. binary molecular complexes. Components of the IGF-I system (total and free IGF-I; IGFBP-1, -3, and ALS; nonternary IGF-I and IGFBP-3), biomarkers of metabolic and nutritional status (transferrin, ferritin, prealbumin, glucose, free fatty acids, glycerol, beta-hydroxybutyrate), and body composition were measured in 12 men (22 +/- 3 yr, 87 +/- 8 kg, 183 +/- 7 cm, 20 +/- 5% body fat) on days 1, 3, and 4 during a control and experimental (Exp) period. During Exp, subjects performed prolonged work (energy expenditure of approximately 4500 kcal/day) with caloric (1600 kcal/day) and sleep (6.2 h total) restriction. IGF-I and IGFBP-3 were measured by immunoassay before and after immunoaffinity depletion of ALS-based complexes (i.e., ternary complex removal). Exp produced losses in body mass (-3.0%), lowered total IGF-I (-24%), free IGF-I (-42%), IGFBP-3 (-6%), nonternary IGF-I (-27%), and IGFBP-3 (-16%), and increased IGFBP-1 (256%). No Exp effects were observed for ALS. No changes were observed in the proportion of IGF-I circulating in free ( approximately 1.2%), ternary ( approximately 87.4%), or nonternary ( approximately 11.4%) molecular complexes. During Exp, glucose concentrations were lower on day 3, but days 1 and 4 were statistically similar. In conclusion, during a short-term energy deficit in young, healthy men, 1). IGF-I system components differentially respond (both in direction and magnitude) to a given metabolic perturbation and 2). the relative proportion of IGF-I sequestered in ternary vs. nonternary molecular complexes appears to be well maintained.
Nindl
Bradley C
BC
Military Performance Division, United States Army Research Institute of Environmental Medicine, Natick, MA 01760, USA. Bradley.Nindl@NA.AMEDD.Army.Mil
Castellani
John W
JW
Young
Andrew J
AJ
Patton
John F
JF
Khosravi
M Javad
MJ
Diamandi
Anastasia
A
Montain
Scott J
SJ
D015502:Absorptiometry, Photon; D000328:Adult; D015415:Biomarkers; D001823:Body Composition / Q000502:physiology; D002149:Energy Intake / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D005508:Food Deprivation / Q000502:physiology; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008889:Military Personnel; D009752:Nutritional Status; D010809:Physical Fitness / Q000502:physiology*; D012892:Sleep Deprivation / Q000503:physiopathology*
D015415:Biomarkers; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I