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No Evidence of Insulin-Like Growth Factor-Binding Protein 3 Proteolysis during a Maximal Exercise Test in Elite Athletes¹

Medical Department M (R.D., J.O.L.J., J.S.C., A.F.), Aarhus Kommunehospital, DK-8000 Aarhus C, Denmark; Sports Medicine Research Unit (K.H.W.L., M.K.), Bispebjerg Hospital, DK-2400 Copenhagen, Denmark; and Medical Research Laboratories (H.Ø., A.F.), Aarhus University, DK-8000 Aarhus C, Denmark

Address all correspondence and requests for reprints to: Rolf Dall, M.D., Medical Department M, Aarhus Kommunehospital, Norrebrogade 42–44, DK-8000 Aarhus C, Denmark. E-mail: rd{at}dadlnet.dk

The aim of the present study was to examine the GH/insulin-like growth factor (IGF) axis, post exercise, with emphasis on IGF-binding protein (IGFBP)-3 proteolysis. Sixteen elite rowers (8 female/8 male) performed a stepwise submaximal rowing test followed by a 6- to 7-min-long maximal test. Blood samples were drawn at baseline, t = 0 (end of exercise) and t = 15, 30, 60, 90, and 120 min. GH and IGFBP-1 levels increased post exercise (P < 0.0005). Total IGF-I and IGF-II increased significantly post exercise (P < 0.0005) but not after albumin correction. Free IGF-I decreased after exercise with nadir coincidently with the IGFBP-1 peak, and free IGF-II decreased post exercise coincidently with the IGFBP-6 peak. IGFBP-3, measured by immunoradiometric assay, increased after exercise (P < 0.0005) but not after albumin adjustment. IGFBP-3 proteolysis (%) (measured by a specific in vitro proteolytic activity assay) and IGFBP-3 (measured by Western ligand blotting) were unchanged post exercise. Albumin-adjusted levels of IGFBP-6 increased by 18% (P < 0.0005), whereas IGFBP-2 and IGFBP-4 did not change significantly post exercise.

Our findings do not support the hypothesis that short-term strenuous exercise induces major acute changes in the GH/IGF axis. To what degree the protein anabolic effects of regular exercise are associated with acute alterations in the GH/IGF axis remains unclear.

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