Effects of somatostatin-28 on circulating concentrations of insulin and gut hormones in sheep.

The effects of intravenous somatostatin-28 (S28) infusion on glucose-stimulated and glucagon-like peptide-1(7-36)amide (GLP-1)-augmented insulin secretion were studied in sheep. S28 was infused via a jugular catheter for 15 min at a rate of 1.1 pmol/kg/min either alone or together with GLP-1 and/or glucose. S28 infusion did not significantly lower circulating basal insulin concentrations in fed sheep. Glucose-stimulated insulin secretion was significantly inhibited by S28 infusion, serum concentrations decreasing from about 200 to 150 pmol/l. GLP-1 significantly augmented glucose-stimulated insulin secretion, serum concentrations increasing from about 230 to 280 pmol/l. S28 completely counteracted this effect of GLP-1. S28 infusion also significantly decreased the circulating concentrations of glucose-dependent insulinotrophic polypeptide (GIP) and GLP-1 in fed sheep (from about 110 to 45 pmol/l for GIP and from about 25 to 15 pmol/l for GLP-1). The physiological implications of these observations are discussed with particular reference to the ruminant. It is concluded that S28 may have an important endocrine role in the control of insulin secretion and regulation of nutrient partitioning.