Ghrelin regulates insulin release and glycemia: physiological role and therapeutic potential.
Insulin release from pancreatic islet beta-cells is stimulated by glucose. Glucose-induced insulin release is potentiated or suppressed by hormones and neural substances. Ghrelin, a novel acylated 28-amino acid peptide isolated from stomach, is the endogenous ligand for the growth hormone (GH) secretagogue-receptor (GHS-R). Circulating ghrelin is produced predominantly in stomach. Ghrelin is a potent stimulator of GH release and feeding as well as exhibiting positive cardiovascular effects. In relation to the glucose metabolism, initial studies indicated that low plasma ghrelin levels are associated with elevated fasting insulin levels, insulin resistance, and obesity. It has recently been demonstrated that ghrelin suppresses glucose-induced insulin release via G alpha(i2) subtype of GTP-binding proteins and delayed outward K(+) (Kv) channels, representing a novel signaling mechanism, and that the ghrelin originating from islets regulates insulin release and thereby glycemia. Furthermore, elimination of ghrelin enhances insulin release to prevent or ameliorate glucose intolerance in high-fat diet fed mice and ob/ob mice. This review focuses on the physiological roles of ghrelin in regulating insulin release and glycemia, the insulinostatic mechanisms of ghrelin in islet beta-cells, and the potential of ghrelin-GHS-R system as the therapeutic target to treat type 2 diabetes.
Yada
Toshihiko
T
Division of Integrative Physiology, Department of Physiology, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan. tyada@jichi.ac.jp
Dezaki
Katsuya
K
Sone
Hideyuki
H
Koizumi
Masaru
M
Damdindorj
Boldbaatar
B
Nakata
Masanori
M
Kakei
Masafumi
M
D000818:Animals; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy*; D054439:Ghrelin / Q000172:deficiency / Q000494:pharmacology / Q000502:physiology* / Q000627:therapeutic use*; D005951:Glucose Tolerance Test / Q000379:methods; D006706:Homeostasis; D006801:Humans; D006943:Hyperglycemia / Q000139:chemically induced; D007328:Insulin / Q000097:blood / Q000378:metabolism / Q000502:physiology*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000502:physiology; D007515:Islets of Langerhans / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D054440:Receptors, Ghrelin / Q000037:antagonists & inhibitors
D001786:Blood Glucose; D054439:Ghrelin; D007328:Insulin; D054440:Receptors, Ghrelin