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.