Effects of cholinergic stimulation on levels and fatty acid composition of diacylglycerols in mouse pancreas

Abstract

1. During 15 min after intraperitoneal injection of 1 mg pilocarpine in vivo in the mouse, the level of diacylglycerol in the pancreas rose from 0.47 to 0.80 mumol per g wet weight. There were increase in the levels of all of the individual fatty acids which were measured in the diacylglycerol pool. The major increases were in palmitic and linoleic acids. These accounted for 65% o the total increase. 2. After in vitro incubation of mouse pancreas for 80 min, the levels of diacylglycerol (expressed in mumol/g wet weight) in unstimulated tissue and in tissue incubated with 10 micrometer or 100 micrometers acetylcholine (plus 100 micrometers eserine) were, respectively, 0.51 1.30 and 3.73. Increases in palmitic, oleic and linoleic acids in the diacylglycerol pool accounted for 75% of the total increase. With 100 micrometers acetylcholine, the proportions of individual fatty acids in diacylglycerol showed a significant enrichment of stearic and arachidonic acid at 40 min and of linoleic and arachidonic acids at 80 min. With the exception of an enrichment of stearic and arachidonic acids, the fatty acid composition of the new diacylglycerol resembled that of the triacylglycerol pool more closely than that of other classes of lipid in the pancreas. 3. After addition of atropine to acetylcholine-stimulated tissue, the level of diacylglycerol fell so that, after 40 min, the levels and proportions of all individual fatty acids in the diacylglycerol were not significantly different from those in unstimulated tissue. 4. In both the in vivo and in vitro experiments, the changes in levels of stearic and arachidonic acids in diacylglycerol indicated that only a small proportion of the total increase in diacylglycerol level could have been derived from the breakdown of stearoyl, arachidonoyl phosphatidylinositol which occurs in response to cholinergic stimulation in the pancreas. The major effect of acetylcholine in diacylglycerol metabolism in mouse pancreas in separate, therefore, from the effect on phosphatidylinositol metabolism.