Biliary phospholipases in the prairie dog model for cholesterol cholelithiasis

Lysolecithin has been implicated as a contributing factor in the pathogenesis of cholecystitis and cholesterol cholelithiasis. The phospholipases are key enzymes in the generation of a number of metabolites including lysolecithin, but conflicting reports exist concerning the presence of these enzymes in the biliary tract. In this study, measurement of phosphatidylcholine-specific phospholipase activity by means of the hydrolysis of radiolabeled phosphatidylcholine (100 nmol) by 90 μg of homogenate protein during a 60-min incubation demonstrated substantial enzyme activities in gastric fundus and distal ileum (90% and 70% hydrolysis, respectively), whereas activity was virtually undetectable in gallbladder mucosa (0.7% hydrolysis). Additional studies were conducted in prairie dogs fed diets high in cholesterol or with trace amounts of cholesterol using homogenates of gallbladder mucosa, seromuscularis and full-thickness tissue, as well as samples of hepatic and gallbladder bile. The only hydrolytic activity in excess of blank values that was detected was a highly variable phospholipase A2 activity in several gallbladder biles from animals given diets with both low levels and high levels of cholesterol, with the enzyme activities of the two dietary groups being similar. These results demonstrate that prairie dog gallbladder contains extremely low levels of phospholipase activity, in marked contrast to other gastrointestinal tissues. However, there was evidence of a phospholipase A2 activity in gallbladder bile. In light of the low activity in gallbladder tissue, the source of this enzyme appears to be the liver and not the gallbladder. The fact that hydrolytic activity after cholesterol feeding was similar to that in control animals suggests that the increases in lysolecithin concentration in gallbladder bile that occur during early cholelithiasis may result from stasis rather than from an increased hepatic secretion of phospholipase. (Hepatology 1994;19:743-749).