Physiological roles of ghrelin in the regulation of gastrointestinal motility in vertebrates

Ghrelin is known to be a multifunctional peptide hormone that stimulates not only growth hormone secretion and feeding but also gastrointestinal (GI) functions, including motility, secretion and mucosa proliferation. The aim of this review is to provide a comprehensive overview on the physiological roles of ghrelin in the regulation of GI motility from a comparative perspective. The effects of ghrelin on GI motility differ depending on the species, and ghrelin is a possible regulator of gastric migrating motor complexes (MMCs) in rodents, dogs and house musk shrew (suncus). However, the role of ghrelin has not been clarified in detail in other mammals, including humans and rabbits. Ghrelin is also effective to cause contraction in the GI tract of some non-mammals, but its physiological role is also not clarified at present. Distribution of the growth hormone secretagogue receptor (GHSR, ghrelin receptor) in the GI tract might be connected with the regulatory role of ghrelin in vertebrates. Comparative studies of ghrelin among animals and identification of knowledge gaps must lead us to the functional transition and importance of ghrelin in the GI tract.