The nature and extent of growth hormone release inhibiting hormone (GH RIH, somatostatin) induced inhibition of pancreatic secretion of bicarbonate and protein, an index of enzyme secretion, were studied by administration of exogenous secretin or for endogenous release of these hormones in fasted pancreatic fistula dogs with and without an infusion of GH RIH. The results of this study show that GH RIH inhibits the pancreatic fluid and bicarbonate secretion induced by both duodenal acidification and exogenous secretin. The kinetic analysis shows that the interaction between GH RIH and secretin affecting pancreatic bicarbonate secretion possesses the characteristics of competitive inhibition. GH RIH does not change the pancreatic protein response to exogenous CCK, but profoundly inhibits pancreatic response to a variety of the endogenous stimulants of CCK release, including duodenal perfusion of sodium oleate, amino acid mixture, or feeding of a peptone meal. The authors conclude that GH RIH is a very potent inhibitor of the endogenous release of CCK from the intestinal mucosa and inhibits competitively the action of secretin but not CCK on the exocrine pancreatic secretion.
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