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Acute Regulation Of Igf-1 By Differential Binding Protein Expression, Inhibition, And Proteolysis: 2411Board #56 May 29 9:00 AM - 10:30 AM

Fisher, Gordon; Foster, Byron; Pascoe, David D. FACSM

Medicine & Science in Sports & Exercise: May 2009 - Volume 41 - Issue 5 - p 337
doi: 10.1249/01.MSS.0000355576.43750.f9
E-29 Free Communication/Poster - Endocrinology: MAY 29, 2009 7:30 AM - 12:30 PM ROOM: Hall 4F

Auburn University, Auburn, AL.


(No relationships reported)

Introduction: Strong evidence supports the roles of Insulin Growth Factor Binding Proteins (IGFBPs) in regulating Insulin Growth Factor 1 (IGF-1) bioavailability and individual regulation dynamics. A large percentage of circulating IGF-1 is bound in a ternary complex consisting of IGF-1, IGFBP-3, and hepatically-produced acid labile subunit. IGF-1 bound in binary complexes with IGFBP-1, -2, -4, -5, and -6 constitute an additional 4% of circulating IGF-1, the remainder is 'free‘ IGF-1. This free fraction of IGF-1 is able to bind to type 1 IGF receptor and elicit biological effects. Exercise (EX) combined with proper post-EX nutrition elicits metabolic signals that would serve to maximize bioavailability of free, dissociable IGF-1.

PURPOSE: This study investigated differential contributions of IGFBPs on bioavailability of IGF-1 and the individual regulation of each of these binding proteins in exercising humans.

METHODS: Eight recreationally-active college-aged males completed three identical high-intensity interval training protocols followed by each of three randomly ordered post-EX nutritional protocols: 1) non-caloric placebo; 2) carbohydrate-only (0.85 g/kg lbw); and 3) essential amino acid/carbohydrate (0.35 g/kg and 0.5 g/kg lbw). Blood samples were obtained pre-EX, immediately post-EX, 10 min intervals for 80 min post-EX, and 20 min intervals until 160 min post-EX. Blood samples were analyzed for growth hormone, free IGF-1, insulin, hematocrit, hemoglobin, plasma amino acid concentrations, and matrix metalloproteinase (MMP) activity. Analytes were compared relative to baseline and across conditions using repeated measures ANOVA. Total area under the curve was calculated for insulin and analyzed using one-way ANOVAs with repeated measures on condition. A priori significance level was p < 0.05.

RESULTS: Significant post-EX increases in free IGF-1 concentrations were observed only for essential amino acid/ carbohydrate group. Additionally, significant increases in post-EX MMP activity were observed in all groups.

CONCLUSION: Results indicate that post-EX macronutrient ratio is a determinant of free concentrations of IGF-1 and high-intensity EX results in increased MMP activity.

© 2009 American College of Sports Medicine