Growth Hormone Signaling in Response to Acute Exercise

Abstract

Growth hormone (GH) is a powerful stimulator of the Janus Kinase-2/Signal Transducer and Activator of Transcription 5 (JAK2/STAT5) pathway in animal and cellular research. Acute exercise is a known stimulus for GH secretion. The purpose of this study was to determine the phosphorylation of the JAK2/STAT5 pathway in human skeletal muscle in response to acute aerobic exercise. Twelve young (22.1 ± 0.7, Mean ± SE), healthy, aerobically trained males performed 30 min of cycling at 70% VO2max. Blood samples were collected at 10 to 15 min intervals during rest, exercise (E) and recovery and analyzed for human GH and immunofunctional (IF) GH. Muscle biopsies from the vastus lateralis were taken pre-E, post-E, 30 min and 60 min into recovery. Muscle samples were analyzed for tyrosine phosphorylation changes in JAK2 and STAT5, as well as, changes in JAK2 and STAT5 protein content. Multivariate ANOVA with post hoc comparisons demonstrated that GH and IF GH were significantly elevated immediately after E compared to pre-E (P<0.003). Exercise significantly increased the phosphorylation of JAK2 immediately after E (P=0.001) and an increasing trend in the phosphorylation of STAT5 after E was observed (P=0.057). Muscle JAK2, and STAT5 protein content did not change. Peak IF GH was positively related to the fold-change in STAT5 phosphorylation (r=0.66, P=0.037). Results demonstrate that the JAK2/STAT5 pathway is activated in response to acute aerobic exercise in human skeletal muscle and suggests that the exercise-induced release of GH may play a pivotal role in the activation of this pathway. Funding: Kate R Barrett and Susan Stout awards.