Faces of ghrelin--research for the 21st century

In this issue of Neurogastroenterology and Motility we find three new articles on different aspects of ghrelin, dealing with physiological and pathophysiological actions of the peptide. For the reader this is food for thoughts: Does this peptide do everything? Ghrelin is a gut peptide hormone well established to stimulate motility throughout most parts of the gastrointestinal (GI) tract and appetite. Ghrelin has been linked to various GI regulatory mechanisms, the most evident being hunger, over-eating and obesity. In this setting ghrelin has been studied under physiological conditions converging on obesity as a pathophysiological process where the peptide has been employed as an interesting tool for studying the development of obesity. With a widespread distribution of ghrelin receptors on various immune cells, it has been assumed that ghrelin also possesses immunoregulatory properties, thus also being of interest in intestinal inflammation research. Anti-inflammatory effects of exogenous ghrelin have been claimed in experimental colitis in mice. Further studies on this concept using ghrelin gene knock-out mice, however, show an increased inflammatory activity in experimental colitis in wild-type mice pointing to ghrelin as an enhancer of the inflammatory course of the disease. Taken together, recent studies on ghrelin indicate that the peptide is not only a regulatory agent in pathophysiological processes, but also participates in pathological disease conditions with actions that seem to even involve genetic mechanisms.