Current knowledge of the roles of ghrelin in regulating food intake and energy balance in birds

A decade has passed since the peptide hormone ghrelin was first discovered in rat stomach. During this period, ghrelin has been identified not only in other mammals but also in fish, amphibians, reptiles and birds, and its physiological functions have been widely investigated. Avian ghrelin was first identified in chickens in 2002 and to date, the amino acid sequences of six different avian ghrelin peptides have been reported. In mammals, ghrelin is the only known gut-derived hormone to stimulate food intake when administered centrally or peripherally. In studies on chickens and quail, however, ghrelin inhibits food intake when injected centrally, while the effects on feeding behavior elicited by ghrelin injected peripherally are equivocal. This review summarizes what is currently known about the regulation of food intake and energy balance by ghrelin in birds.