Exercise-induced Ghrelin Secretion is Associated with Increased Lipolysis

Abstract

0996 PURPOSE: Ghrelin is a gastrointestinal hormone that has been implicated in signaling increased energy need as a rise in its plasma concentration precedes food intake and occurs after weight loss (Cummings, et al., 2001, 2002). Ghrelin is inhibited by postprandial insulin release (Saad, et al., 2002) and is a growth hormone secretagogue (Kojima, et al., 1999). It is not known whether ghrelin secretion is responsive to increases in energy expenditure due to exercise as exercise intensity sufficient to elicit growth hormone secretion was reported to have no effect on plasma ghrelin (Dall, 2002). Therefore, we hypothesized that (1) exercise-induced increases in energy expenditure will increase ghrelin secretion and (2) exercise during postprandial increases in insulin secretion will suppress ghrelin secretion. METHODS: In this experiment, eight postmenopausal women engaged in moderate intensity exercise in the form of an AM and PM two-hour bout of walking, each producing an expenditure of approximately 400 Kcal and timed before (ExBM) or after (ExAM) two daily weight maintenance meals. We evaluated the effects of fasting and postprandial exercise on plasma ghrelin, insulin, and free fatty acid (FFA) concentrations. Energy expenditure was measured by indirect calorimetry. The increase in plasma FFA concentration was used as a physiological marker of postabsorptive energy need. RESULTS: Plasma ghrelin increased only when exercise was performed in the fasted state (ExBM F = 11.6, p = 0.0019) and not when exercise was performed after the meal. Lipolysis increased by approximately 50% in the ExBM condition compared to the ExAM (F = 11.02, p = 0.0006). There was a significant correlation between ghrelin and FFA concentrations during the diurnal period (0600–2200 hr) in both exercise conditions (ExBM F = 24.12, p = < 0.0001; ExAM F = 10.45, p = 0.0032). CONCLUSIONS: Our results show that ghrelin secretion increases in response to exercise performed in a fasted state. A significant correlation between plasma ghrelin and FFA concentrations suggests that the functional role of ghrelin may be to stimulate lipolysis by way of increased growth hormone secretion.