Ghrelin Is Present in Pancreatic α-Cells of Humans and Rats and Stimulates Insulin Secretion

Ghrelin Is Present in Pancreatic α-Cells of Humans and Rats and Stimulates Insulin Secretion Yukari Date 1 2 , Masamitsu Nakazato 1 , Suzuko Hashiguchi 3 4 , Katsuya Dezaki 3 , Muhtashan S. Mondal 1 , Hiroshi Hosoda 2 , Masayasu Kojima 2 , Kenji Kangawa 2 , Terukatsu Arima 4 , Hisayuki Matsuo 2 , Toshihiko Yada 3 and Shigeru Matsukura 1 1 Department of Internal Medicine, Miyazaki Medical College, Miyazaki, Japan 2 National Cardiovascular Center Research Institute, Osaka, Japan 3 Department of Physiology, Jichi Medical School, Tochigi, Japan 4 Second Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Kagoshima, Japan Abstract 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 Ca 2+ concentration. It also functions in the regulation of feeding behavior, energy metabolism, and gastric acid secretion and motility. Using two different antibodies against the NH 2 - 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 α-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 Ca 2+ concentration in β-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. Footnotes Address correspondence and reprint requests to Masamitsu Nakazato, PhD, Third Department of Internal Medicine, Miyazaki Medical College, Kiyotake, Miyazaki 889-1692, Japan. E-mail: nakazato{at}post.miyazaki-med.ac.jp . Received for publication 8 August 2001 and accepted in revised form 3 October 2001. [Ca 2+ ] i , cytosolic free Ca 2+ concentration; GH, growth hormone; GHS, growth-hormone secretagogue; GHS-R, GHS receptor; ICV, intracerebroventricularly; IV, intravenously; KRB, Krebs-Ringer bicarbonate buffer; PBS, phosphate-buffered saline; RIA, radioimmuno