Ghrelin is present in pancreatic α-cells of humans and rats and stimulates insulin secretion

Ghrelin, a novel growth hormone-releasing peptide isolated from human and rat stomach, is a 28-amino acid peptide with a posttranslational acylation modification that is indispensable for stimulating growth hormone secretion by increasing intracellular Ca2+ concentration. It also functions in the regulation of feeding behavior, energy metabolism, and gastric acid secretion and motility. Using two different antibodies against the NH2- and COOH-terminal regions of ghrelin, we studied its localization in human and rat pancreas by immunohistochemistry. Ghrelin-immunoreactive cells were identified at the periphery of pancreatic islets in both species. Ghrelin co-localized exclusively with glucagon in rat islets, indicating that it is produced in alpha-cells. We identified ghrelin and des-acyl ghrelin in the rat pancreas using reverse-phase high-performance liquid chromatography combined with two radioimmunoassays. We also detected mRNA encoding ghrelin and its receptor in the rat pancreatic islets. Ghrelin increased the cytosolic free Ca2+ concentration in beta-cells and stimulated insulin secretion when it was added to isolated rat pancreatic islets. These findings indicate that ghrelin may regulate islet function in an endocrine and/or paracrine manner.