Somatostatin-28: selective action on the pancreatic beta-cell and brain.

Somatostatin-28 (SS-28) is 380 times as potent as somatostatin-14 (SS-14) to inhibit acutely insulin secretion induced by arginine in vivo; SS-28 is only 3 times as potent as SS-14 to inhibit glucagon secretion induced by arginine. D-Trp substitution in position 28 of SS-28 increase potency to 2600 times that of SS-14 for inhibition of arginine induced insulin secretion. SS-28 in 10 and [D-Trp22]-SS-28 is 100 times as potent as SS-14 to act within the central nervous system to inhibit bombesin induced hyperglycemia. SS-28 compared to SS-14 shows pancreatic beta-cell and brain selectivity of action.