1. The in vitro basal lipid metabolism of rat pancreatic fragments was compared with that in adipose tissue fragments and liver slices. 2. [1-14C]Acetate added to the media was mostly incorporated into palmitic acid and to a lesser extent into oleic acid. In addition, pancreatic tissue exhibited a marked capacity for elongation of polyunsaturated fatty acids by [1-14C]acetate and resulting desaturation when compared to adipose tissue and liver. 3. Data obtained in the presence of [U-14C]glucose, [1-14C]palmitate and 3H20 indicate that acetyl-CoA derived from glucose and from beta-oxidation of fatty acids contributed to de novo lipogenesis. 4. Oxidation of [1-14C]palmitic acid was 9-13 times higher in the pancreas than in adipose tissue or liver when expressed on a wet weight basis. 5. The fatty acid moiety of pancreatic glycerolipids could be derived from de novo synthesis, fatty acids added to the medium, or from fatty acids formed from the hydrolysis of endogenous lipids. The glycerol moiety could be derived either from glucose, or directly from glycerol through participation of glycerol kinase.

1. The concentration of carbamylcholine, bombesin, pancreozymin, pentagastrin and secretin evoking a similar 4--5-fold maximal increase in amylase secretion from rat pancreatic fragments were 3.10(-6), 10(-7), 10(-8), 3.10(-6), and 3.10(-6) M, respectively. The maximal concentration of vasoactive intestinal peptide tested (3.10(-6) M) increased amylase secretion by 250%. The six secretagogues could be separated into two groups according to their effects on lipid metabolism and ATP levels. 2. When used at their optimal concentrations, carbamylcholine, bombesin, pancreozymin, and pentagastrin lowered pancreatic ATP levels by 18-26% and increased net release of free fatty acids by 68-105%. 3. The effects of 3.10(-6) M carbamylcholine and 10(-8) M pancreozymin on the metabolism of 3H2O, D-[U-14C]glucose and [1-14C]acetate were similar; the incorporation of radioactivity in the fatty acid moiety of glycerolipids decreased by 20--50% whereas the incorporation of 3H from 3H2O and of 14C from [U-14C]glucose increased by 20--35% in the glycerol moiety. In addition, the oxidation of [U-14C]glucose, [1-14C]acetate and [1-14C]palmitate to 14CO2 increased by 15--32% while the esterification of [1-14C]palmitate, [1-14C]-linoleate, and [1-14C]arachidonate was inhibited by 14--23%. The spectrum of fatty acids labeled with [1-14C]acetate indicated an inhibition of the malonic acid pathway whereas the elongation of polyenoic fatty acids was unaltered.

Carbamylcholine, bombesin, pancreozymin, and pentagastrin elicited a similar increase in amylase secretion and phosphatidylinositol turnover in rat pancreatic fragments. The concentration of each secretagogue that provoked half-maximal stimulation of amylase secretion was three to six times lower than that which induced half-maximal stimulation of phosphatidylinositol turnover. The increased turnover of phosphatidylinositols due to carbamylcholine or pancreozymin, but not the secretory response, persisted in a calcium-free medium or in 90% heavy water. The replacement of the media Na+ with Li+ increased an atropine-resistant turnover of phosphatidylinositols, but did not stimulate secretion. The ionophore A-23187 (in a medium containing 2.5 mM Ca2+) and 10 mM NaF induced a high secretory response, but exerted no effect on phosphatidylinositol turnover. K+ at a 70 mM concentration provoked a phosphatidylinositol effect and hypersecretion. Secretin, vasoactive intestinal peptide, dibutyryl cAMP, dibutyryl cGMP, 8-bromo cGMP, and N2-monobutyryl cGMP stimulated amylase secretion without an increased turnover of phosphatidylinositols. It is concluded that, in the rat pancreas, the increased turnover of phosphatidylinositols was directly associated with secretagogues inducing calcium movements.

1. The turnover of phosphatidylinositols and other glycerolipids was examined in rat pancreatic fragments incubated in the presence of carbamylcholine and pancreozymin used at a concentration inducing maximal alpha-amylase hypersecretion. 2. In stimulated tissue, [1-14C]acetate-labeled fatty acids were incorporated into phosphatidylinositols, 1,2-diacylglycerols, and phosphatidic acids in preference to phosphatidylcholines, phosphatidylethanolamines, triacylglycerols, monoacylglycerols, and free fatty acids. Variations in the percent distribution of 14C among fatty acids and in specific activity of individual fatty acids in each lipid class suggested that the secretagogues reduced selection of newly synthesized 1,2-diacylglycerols which occurred in the resting state before their incorporation into phosphatidylinositols. Secretagogues also promoted recycling of endogenous 1,2-diacylglycerols (produced from hydrolysis of unlabeled glycerolipids) for the biosynthesis of phosphatidylinositols. 3. Increased rate of incorporation of [1-14C]palmitate, [1-14C]linoleate, [1-14C]arachidonate and [1(3)(n)-3H]glycerol into phosphatidylinositols was detrimental to phosphatidylcholines. 4. The lipolytic effects of carbamylcholine and pancreozymin as illustrated by the release of 1,2-diacylglycerols and free fatty acids, were markedly inhibited in calcium-free medium enriched with 1 mM EGTA but increased turnover of phosphatidylinositols as determined from incorporation of radioactive precursors was only moderately affected.

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