The effects of acute exercise on plasma apelin and its relation to glucose homeostasis and insulin sensitivity

The blood glucose and insulin responses to acute maximal and submaximal aerobic exercise are well characterized (Marliss & Vranic, 2002), though our understanding of the molecular mechanisms effecting improved insulin sensitivity following acute exercise remains incomplete. Apelin has been reported to enhance glucose uptake and insulin sensitivity in vitro and in vivo (Dray et al., 2010). Apelin, therefore, merits examination as a potential regulator of the acute enhancement of insulin sensitivity in vivo. PURPOSE: To investigate apelin's response to acute bouts of maximal and submaximal aerobic exercise, so as to elucidate apelin's influence on glucose homeostasis and insulin sensitivity. METHODS: Twelve (22.8 ± 2.9 yrs) apparently healthy male (n=7) and female (n=5) subjects completed maximal (VO2max) and submaximal (70-75% VO2max) aerobic treadmill tests, as well as a 54g glucose challenge (GC), each separated by at least 3 days but not more than 14 days. Blood was sampled four times (Pre-, Post-, 1 hr post- and 24 hrs post-treatment) and assessed immediately for hematocrit and blood glucose and assayed for plasma apelin and plasma insulin. Insulin sensitivity was determined via HOMA-IR index. RESULTS: No main effect existed for apelin by condition (p=0.324) or by time (p=0.633). Blood glucose and plasma insulin were significantly elevated following VO2max and GC, but not following submaximal exercise. Insulin sensitivity, as measured via HOMA-IR score, was significantly improved at one-hour post-submaximal exercise. Resting plasma apelin was significantly correlated with plasma insulin (R=0.702, p=0.011), as well as with resting HOMA-IR score (R=0.738, p=0.006). Following submaximal exercise, plasma apelin was significantly correlated with HOMA-IR score (R=0.672, p=0.017). CONCLUSION: Though plasma apelin was not significantly altered by either exercise intensities or GC, our results suggest that elevated plasma apelin is associated with increased incidence of insulin resistance and that lower levels may be related to enhancements in insulin sensitivity