Effects of Somatostatin-14 and Somatostatin-28 on Plasma Hormonal and Gastric Secretory Responses to Cephalic and Gastrointestinal Stimulation in Man

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Abstract
This study was designed to determine the influence of cephalic and gastrointestinal meal stimulation on plasma levels of somatostatin-like immunoreactivity (SLI) and to compare plasma hormonal and gastric secretory effects of somatostatin-14 (SS-14) and its putative prohormone, somatostatin-28 (SS-28), in humans. Cephalic stimulation induced by modified sham feeding did not affect plasma SLI; a gastric liver extract meal caused a significant increase in SLI. Infusion of SS-28 dose-dependently suppressed gastric acid, serum gastrin and plasma pancreatic polypeptide (PP) responses to cephalic and gastrointestinal stimulation. SS-28 was equipotent with SS-14 as gastric inhibitor when compared on the basis of molar doses infused but was 4-10 times less potent on the basis of plasma SLI concentrations obtained. A lower and more physiological dose of SS-14 (75 pmol/kg-h) reduced gastric acid and PP responses but failed to affect the serum gastrin response to a meal; a larger, pharmacological dose (500 pmol/kg-h) also suppressed serum gastrin responses. Meal releases SLI into the circulation and that SS-28 mimics the gastric secretory and plasma hormonal effects of SS-14 but is several times less potent than SS-14 in terms of circulating hormone levels.