Biological Actions Somatostatin
Stimuli that promote insulin secretion also stimulate SS. These stimuli include glucose, tolbutamide, arginine, gastrin, secretin, cholecystokinin, and GH. SS is found in the general circulation but because of its short half-life of 3 minutes, its function as a hormone is unclear. Some suggest that SS in the gut may act as a hormone in addition to its known paracrine effects. Its function on the islets is paracrine. When insulin levels are high and blood glucose low, SS inhibits insulin and, when insulin is low and blood glucose high, it inhibits the release of glucagon. SS acts in the gut to inhibit GI hormone secretion, pepsin secretion, motility, and blood flow. For more information on its action on the anterior pituitary, see section V, chapter 2.