Ghrelin-cell physiology and role in the gastrointestinal tract

Ghrelin was discovered in 1999; extensive research and clinical studies on ghrelin have been published in the last 20 years. Physiological research on ghrelin ranges from its appetite-stimulating effects to its association with energy homeostasis. The physiological effects of ghrelin in the gastrointestinal tract and its relevance in the pathological conditions of the gastrointestinal tract have gradually become clearer. The purpose of the review is to provide current information on ghrelin cell biology and physiology, particularly in the gastrointestinal tract.Ghrelin-producing cells in the stomach are characterized as X/A-like cells, but immunohistochemical analyses have revealed co-expression of several secreted proteins and hormones in ghrelin-producing cells such as nesfatin-1, somatostatin, and pancreastatin. Furthermore, the local physiological roles and/or mechanisms of ghrelin in gastrointestinal functions such as gastric motility and inflammation are discussed.Ghrelin is a brain-gut hormone with a wide range of physiological actions; hence, it is important to understand its effects on the physiological functions of the gastrointestinal tract to elucidate the biological significance of ghrelin.