The blunted insulin release after exercise and the relationship with gastric inhibitory polypeptide and glucagon-like peptide-1

Abstract

Introduction: During exercise training, an increase in insulin sensitivity is accompanied by a decrease in plasma insulin concentrations during an oral glucose tolerance test (OGTT). The purpose of this study was to investigate the role incretin hormones play in the blunted insulin release after exercise. Gastric inhibitory polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1) are incretin hormones that cause insulin release after glucose ingestion. We hypothesized that insulin, GLP-1, and GIP concentrations during an OGTT would be lower after exercise compared to after 7 days of inactivity. Methods: Nine healthy men (n = 5) and women (n = 4) currently engaged in endurance exercise (23 ± 2 y) underwent 5 d of exercise at ~75% VO2peak for 60 min. An OGTT was performed immediately post-exercise (IPE), one day after exercise (Day 1), and one week later (Day 7). Subjects were inactive between Day 1 and Day 7 (no exercise exceeding the intensity of activities of daily living). Results: No change in body mass or body composition occurred during the study period. Glucose area under the curve (mmol/L x min) was significantly lower (P < 0.05) on Day 1 (160 ± 65) compared with IPE (233 ± 65) and was similar on Day 7 (186 ± 94). Although insulin sensitivity, as calculated by insulin-glucose index (pmol/L · min x mmol/L · min x 10), did not reach significance between Day 1 (569 ± 328) and Day 7 (1,023 ± 810), the plasma insulin response curve was significantly higher during the Day 7 OGTT compared with IPE (P < 0.05). Similarly, plasma GIP concentrations during the Day 7 OGTT were significantly higher than Day 1 (P < 0.05). No differences occurred within GLP-1 areas or