Growth Hormone and Insulin-like Growth Factor-I Molecular Weight Isoform Responses to Resistance Exercise Are Sex-Dependent
Joseph R. Pierce, Brian J. Martin, Kevin R. Rarick, Joseph A. Alemany, Jeffery S. Staab, William J. Kraemer, Wesley C. Hymer, Bradley C. Nindl
Abstract
Purpose To determine if acute resistance exercise-induced increases in growth hormone (GH) and insulin-like growth factor-I (IGF-I) were differentially responsive for one or more molecular weight (MW) isoforms and if these responses were sex-dependent. Methods College-aged men (n=10) and women (n=10) performed an acute resistance exercise test (ARET; 6 sets, 10 repetition maximum (10-RM) squat, 2-min inter-set rest). Serum aliquots from blood drawn Pre-, Mid-, and Post-ARET (0, +15, and +30-min post) were processed using High Performance Liquid Chromatography (HPLC) fractionation and pooled into 3 MW fractions (Fr.A: >60; Fr.B: 30-60; Fr.C: Fr.A > Fr.B, p≤0.03). Sex×time interactions indicated that women experienced earlier and augmented increases in all serum GH MW isoform fraction pools (p Fr.B > Fr.C, p≤0.01). Furthermore, we observed increases in IGF-I Fr. A (ternary complexes) in men only (p≤0.05), and increases in Fr.C (free/unbound IGF-I) in women only (p≤0.05) vs. baseline, respectively. Conclusions These data indicate that the processing of GH and IGF-I isoforms from the somatotrophs and hepatocytes are differential in their response to strenuous resistance exercise and reflect both temporal and sex-related differences.