Acute regulation of IGF-1 by differential growth-factor-binding-protein expression, inhibition, and proteolysis

Abstract

The purposes of this investigation were to examine the acute regulation of IGF-1 via insulin-like growth factor binding-protein (IGFBP) expression, inhibition, and proteolysis. Eight recreationally-active college-aged males completed three identical high-intensity interval training protocols followed by each of three randomly ordered post-exercise 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, respectively). Blood samples were obtained pre-exercise, immediately post-exercise, at ten minute intervals for 80 minutes post-exercise, and at 20 minute intervals until 160 minutes post-exercise. Blood samples were analyzed for GH, 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 ANOVAs with repeated measures. Additionally, total area under the curve scores were calculated for insulin and analyzed using one-way ANOVAs with repeated measures on condition. The a priori significance level for all analyses was p < 0.05. Significant post-exercise increases in free IGF-1 concentrations were observed in the essential amino acid/ carbohydrate group only. Additionally, significant increases in post-exercise MMP activity were observed in all groups. These results indicate that post-exercise macronutrient ratio is a determinant of free concentrations of IGF-1 and that high-intensity exercise results in increased MMP activity.