Serum gastric inhibitory polypeptide was measured in dogs prepared with Heidenhain pouches and Mann-Bollman fistulae following the intraduodenal (ID) infusion of isotonic saline, 20% glucose, or 20% mannitol. Following ID 20% glucose, serum GIP concentrations rose significantly (P<0.05) between 30 and 120 min and there was a significant inhibition (P<0.05) of acid secretion in the Heidenhain pouches between 15 and 75 min. A good correlation (r=0.925) was found between the rise in serum GIP and the inhibition of acid secretion. Although neither ID isotonic saline nor 20% mannitol stimulated GIP release, the latter produced a significant (P<0.05) inhibition of acid secretion between 60 and 105 min. We conclude: (1) the inhibitory effect of acid secretion following ID glucose is mediated in part by the release of endogenous GIP; (2) glucose and mannitol probably inhibit gastric acid secretion by different mechanisms.
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