No evidence of insulin-like growth factor-binding protein 3 proteolysis during a maximal exercise test in elite athletes

The aim of the present study was to examine the GH/insulin-like growth fact or (IGF) axis, post exercise, with emphasis on TGF-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 s amples were drawn at baseline, t = 0 tend 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 e xercise coincidently with the IGFBP-6 peak. IGFBP-3, measured by immunoradi ometric assay, increased after exercise (P < 0.0005) but not after albumin adjustment. IGFBP-3 proteolysis (%) (measured by a specific in vitro proteo lytic activity assay) and IGFBP-3 (measured by Western ligand blotting) wer e 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 exerci se induces major acute changes in the GH/IGF axis. To what degree the prote in anabolic effects of regular exercise are associated with acute alteratio ns in the GH/IGF axis remains unclear.