Effect of bovine pancreatic polypeptide on the opossum lower esophageal sphincter

Abstract

The purpose of the present investigation was to study the effect and mechanism of action of bovine pancreatic polypeptide on the lower esophageal sphincter of the opossum. The pressures from the lower esophageal sphincter were measured by a continuously perfused catheter assembly which was anchored in the sphincter. The pancreatic polypeptide was administered through the arterial supply of the sphincter. The pancreatic polypeptide produced an almost linear dose-related rise in the sphincter pressure in doses ranging from 0.15 to 5 μg/kg. The smaller doses of 0.037 μg/kg and 0.075 μg/kg also caused a rise in sphincter pressure, but this was not statistically significant (P > 0.05). A dose of 10 μg/kg produced a smaller increase in pressure than a dose of 5 μg/kg. The effect of very high doses of 40 and 80 μg/kg was studied in one animal. These doses produced inhibition of the sphincter. The contractile effect of pancreatic polypeptide was partly antagonized by tetrodotoxin and atropine. The sphincter contraction was not antagonized by adrenergic, serotoninergic, and histaminergic antagonists or prostaglandin synthesis inhibitor. These studies suggest that: (a) bovine pancreatic polypeptide causes contraction of the opossum lower esophageal sphincter, and (b) its action is partly due to stimulation of cholinergic neurons and partly due to the direct activation of the sphincter smooth muscle.