Effects of ghrelin on insulin and glucagon secretion: a study of isolated pancreatic islets and intact mice

• Published in: Regulatory peptides Vol. 118; no. 3; pp. 143 - 150
• Main Authors: Salehi, Albert, Dornonville de la Cour, Charlotta, Håkanson, Rolf, Lundquist, Ingmar
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier B.V 15.05.2004; Amsterdam Elsevier
• Subjects: 1-Methyl-3-isobutylxanthine - pharmacology; Animals; Arginine - pharmacology; Basic Medicine; Biological and medical sciences; Blood Glucose - analysis; Carbachol - pharmacology; Cell and Molecular Biology; Cell- och molekylärbiologi; Dose-Response Relationship, Drug; Female; Fundamental and applied biological sciences. Psychology; Ghrelin; Glucagon - blood; Glucagon - metabolism; Glucose - metabolism; Glucose - pharmacology; Glucose Tolerance Test; Insulin - blood; Insulin - metabolism; Insulin Secretion; Islet hormone secretion; Islets of Langerhans - drug effects; Islets of Langerhans - metabolism; Medical and Health Sciences; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; Mice; Pancreas - drug effects; Pancreas - metabolism; Peptide Hormones - pharmacology; Peptide Hormones - physiology; Signal Transduction - drug effects; Signal Transduction - physiology; Time Factors; Vertebrates: endocrinology; Ghrelin; Islet hormone secretion; Pancreatic hormone; Glucagon; Peptide hormone; Rodentia; Langerhans islet; Insulin; Endocrine secretion; Vertebrata; Mammalia; Mouse; Animal; Endocrine pancreas
• ISSN: 0167-0115; 1873-1686; 1873-1686
• DOI: 10.1016/j.regpep.2003.12.001

We combined in vitro and in vivo methods to investigate the effects of ghrelin, a novel gastric hormone, on insulin and glucagon release. Studies of isolated mouse islets showed that ghrelin concentrations in the physiological range (0.5–3 nmol l −1) had no effect on glucose-stimulated insulin release, while low ghrelin concentrations (1–100 pmol l −1) inhibited and high (0.1 and 1 μmol l −1) stimulated. The insulin response to glucose was enhanced in the presence of a high ghrelin concentration (100 nmol l −1). Glucagon release was stimulated by ghrelin (0.1 pmol l −1 to 1 μmol l −1); this effect was maintained in the presence of glucose (0–20 mmol l −1). In intact mice, basal plasma insulin was suppressed by 1 and 10 nmol kg −1 of ghrelin, 2 and 6 min after i.v. injection. Ghrelin (0.2–10 nmol kg −1 i.v.) suppressed also the glucose-stimulated insulin response and impaired the glucose tolerance (at a ghrelin dose of 3.3 nmol kg −1). Ghrelin (1 or 10 nmol kg −1 i.v.) inhibited the insulin response to the phospholipase C stimulating agent carbachol and enhanced the insulin response to the phosphodiesterase inhibitor isobutyl-methylxanthine (IBMX) but did not affect the response to the membrane-depolarizing amino acid l-arginine. These observations suggest that the inhibitory effect of ghrelin on glucose-induced insulin release is in part exerted on phospholipase C pathways (and not on Ca 2+entry), while the stimulatory effect of high doses of ghrelin depends on cyclic AMP. In contrast to the spectacular glucagon-releasing effect of ghrelin in vitro, ghrelin did not raise plasma glucagon. Carbachol, IBMX and l-arginine stimulated glucagon release. These responses were impaired by ghrelin, suggesting that it suppresses the various intracellular pathways (phospholipase C, cyclic AMP and Ca 2+), that are activated by the glucagon secretagogues. Together these observations highlight (but do not explain) the different effects of ghrelin on glucagon release in vitro and in vivo. The results show that ghrelin has powerful effects on islet cells, suggesting that endogenous ghrelin may contribute to the physiological control of insulin and glucagon release. However, the narrow “window” of circulating ghrelin concentrations makes this doubtful.