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Differential responses of IGF-I molecular complexes to military operational field training

¹Military Performance Division, ²Thermal and Mountain Medicine Division, ³Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachussetts 01760; ⁴Diagnostic Systems Laboratories Canada, and ⁵Department of Laboratory Medicine and Pathobiology, University of Toronto and Mount Sinai Hospital, Toronto, Canada M5G 1X5

Submitted 12 December 2002 ; accepted in final form 19 May 2003

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, -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 4,500 kcal/day) with caloric (1,600 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 (1.2%), ternary (87.4%), or nonternary (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.

somatotropic hormones; nutritional status; binary concentrations; magnetic exclusion separation; fasting

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