Exercise serum increases GLUT4 in human adipocytes.

NEW FINDINGS: What is the central question of this study? Do circulating factors mediate exercise-induced effects on adipose tissue GLUT4 expression? What is the main finding and its importance? Serum (10%) obtained from human volunteers immediately after a single exercise bout increased GLUT4 protein levels in human adipocytes in culture. This result suggests that circulating factors might mediate the effects of exercise on adipose tissue GLUT4 and prompts further effort to identify the specific factor(s) and tissue(s) of origin. ABSTRACT: In this study, we tested the hypothesis that circulating factors generated during exercise increase adipose tissue GLUT4 expression. Serum was obtained from eight healthy subjects before and after 60 min of cycling exercise, and primary adipocytes were cultured from stromal vascular fractions that were isolated from subcutaneous abdominal adipose tissue samples from one healthy, male volunteer. A 48 h exposure of human primary adipocytes to 10% serum obtained after exercise increased GLUT4 protein expression, on average, by 12% compared with exposure to 10% serum obtained at rest, before exercise. GLUT4 mRNA levels were increased after 12 h of exposure to exercise serum but were unchanged after 6 and 24 h of exposure. Our results suggest that circulating factors might mediate the effects of exercise on adipose tissue GLUT4 expression and encourage further efforts to identify the potential factor(s), tissue(s) of origin and physiological relevance.