Ghrelin Responses to Acute Exercise and Training
Energy homeostasis is regulated by a complex neuroendocrine system including central and peripheral tissues (1 , 2 ). Therefore, the hypothalamus in the brain appears to centrally integrate the various metabolic and hormonal signals, and has an important
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Ghrelin Responses to Acute Exercise and Training Jaak Jürimäe, PHD and Toivo Jürimäe, PHD CONTENTS Introduction Ghrelin During Growth and Maturation in Children Ghrelin Relationships with Adiposity and Energy Availability Ghrelin Responses to Acute Exercise Chronic Exercise Training and Ghrelin Responses Conclusions and Future Directions References
INTRODUCTION Energy homeostasis is regulated by a complex neuroendocrine system including central and peripheral tissues (1, 2). Therefore, the hypothalamus in the brain appears to centrally integrate the various metabolic and hormonal signals, and has an important role in the central responses to changes in energy balance (3). Important in this regulatory system is also the existence of several gut, pancreatic and adipose tissue hormones that communicate the status of body energy stores to the hypothalamus (1). Among the gut hormones secreted in response to nutrient ingestion, ghrelin, peptide YY, cholecystokinin and glucagon-like peptide-1 are involved in regulating both acute and chronic energy homeostasis (4, 5). Therefore, peptide YY, cholecystokinin and glucagon-like peptide-1 function as negative feedback signals, suppressing appetite and food intake once nutrients are ingested (5, 6), and peptide YY has received more attention among appetite and food consumption suppressing peptides (4, 6–9). In contrast, to date, ghrelin remains unique as the only known circulating hormone that stimulates appetite and
From: Endocrinology of Physical Activity and Sport: Second Edition Edited by: N. Constantini and A.C. Hackney, DOI 10.1007/978-1-62703-314-5_12 © Springer Science+Business Media New York 2013 207
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food consumption (6, 10). This chapter focuses on the available information about the effects of acute exercise and chronic training on the secretion of ghrelin. Ghrelin, a 28-amino-acid-residue peptide produced by distinct endocrine cells of the stomach, was first described as an endogenous ligand for the growth-hormonesecretagogue receptor (11). Ghrelin has been found to promote positive energy balance by increasing appetite and food intake (12, 13). The rise in circulating ghrelin before a meal is a physiological signal for hunger and the body’s cue for meal initiaion (14, 15). Therefore, it is interesting to note that the rise in ghrelin levels and hunger occurs independent of food and time of day cues (14, 15). Meal responses of ghrelin are related to acute caloric intake over a typical day of eating in normal-weight subjects (16). In addition, fasting total ghrelin concentrations are shown to be negatively correlated to 24-h caloric intake (17). Accordingly, ghrelin concentrations increase while fasting and decrease after caloric intake (14). The decrease in ghrelin release is related to the amount of calories ingested (15, 18). Ghrelin is responsive to diet- and exercise-induced changes in body mass (16, 19). In addition to total ghrelin, acylated and unacylated forms of ghrelin have been found (20, 21). The acylated form of ghrelin is
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