Plasma Apelin Unchanged With Acute Exercise Insulin Sensitization

Blood glucose and insulin responses to aerobic exercise are well defined yet the mechanisms effecting post-exercise insulin sensitization remain incomplete. Apelin has been reported to enhance glucose uptake and insulin sensitivity in vivo, but its role as a regulator of insulin sensitivity following acute aerobic exercise has not been investigated. Therefore, the purpose of this study was to investigate apelin's response to acute bouts of maximal and submaximal aerobic exercise and to elucidate apelin's influence on insulin sensitivity. Twelve (22.8 ± 2.9 yrs) healthy male (n = 7) and female (n = 5) subjects completed a graded to maximal (VO₂max) and submaximal (70-75% VO₂max) treadmill running bouts, as well as a 50g glucose challenge (GC). Blood was obtained at four time points (pre, post, 1hr post and 24hrs post) and assessed for glucose, insulin and apelin. Hepatic insulin sensitivity was assessed at rest and at 1hr and 24hrs via HOMA-IR and QUICKI indices. Results demonstrated that plasma apelin did not significantly change by condition (p = 0.324) or time (p = 0.633). Blood glucose and plasma insulin were significantly elevated immediately after VO₂max and GC, but remained stable after submaximal exercise. Insulin sensitivity was significantly improved 1hr post-submaximal exercise, per HOMA-IR (p = 0.034) and QUICKI (p = 0.018) indices. Plasma apelin was significantly correlated with plasma insulin (r = 0.699, p = 0.011), HOMA-IR (r = 0.626, p = 0.029) and QUICKI (r = 0.660, p = 0.019) at rest. We conclude that, although hepatic insulin sensitivity was improved 1hr post-submaximal exercise, this exercise-induced insulin sensitization occurred independent of plasma apelin changes.