The Effect of Ligation of the Common Bile Duct on Cholesterol Synthesis in the Rat

Abstract

Obstruction of the biliary tract has long been known to be accompanied by hypercholesterolemia (1). This phenomenon has been studied in the rat by Chanutin and Ludewig (2) and, more extensively, by Byers, Friedman, and their colleagues (3-7). In a recent review the latter authors have mentioned possible mechanisms involved, including altered absorption, synthesis, excretion, and destruction of cholesterol (8).The purpose of the present study was to investigate by isotopic methods the effect of bile duct ligation on cholesterol synthesis in the rat. As indices of the rate of cholesterol synthesis we used the incorporation of carboyxl carbon from 1-C14-acetate, and hydrogen from tritium-labelled water, into cholesterol in the intact animal, in liver slices, or in cell-free homogenates.In all the systems which we employed, the rate of incorporation of these isotopes into cholesterol was increased following ligation of the common bile duct. EXPERIMENTALRats utilized in these studies were of the Sprague-Dawley and Wistar strains, both males and females, weighing between 140 and 320 gin., and unless otherwise specified, were maintained on a steroid-free, fat-free diet of the following composition: casein (vitamin-free) 125 gin., sucrose 355 gln., salt mixture "W" (9) 20 tim., choline chloride 500 rag., thiamine hydrochloride i0 rag., riboflavine 10 rag., pyridoxine hydrochloride 10 rag., nicotinic acid 10 nag., calcium-d-pantothenate 20 rag., and llnoleic acid 0.47 gin. All surgical procedures were performed under ether anesthesia. Ligations of the common bile duct were made with double silk ligatures. Maintenance of obstruction was determined at autopsy by the presence of a dilated, bile-filled duct proximal to the ligatures with no evidence of leakage. The peritoneal cavities of all control animals were opened and the intestines manipulated.Isolation and Assay of Cholesterol.---Cholesterol was isolated from fiver in the following manner: 0.5 gin. of liver was hydrolyzed in 2.5 ml. of a 15 per cent solution of KOtt in 95 per cent ethanol for 16 hours at 100°C. An equal volume of water was then added, followed by extraction with four 10 ml. portions of petroleum ether (b.p. 30-60°). The extracts were combined and taken to dryness on the steam bath, the residue was dissolved in 4 ml. of 1 : 1 acetone-

Failure of bile acids to control hepatic cholesterogenesis: evidence for endogenous cholesterol feedback

“…For example, such diverse conditions as biliary diversion (14-16), biliary obstruction (14,20), ileal resection or bypass, (42) and the feeding of cholestyramine (17) are all known to enhance the rate of hepatic cholesterol synthesis. Each of these conditions is associated with a decreased amount of bile acid in the intestinal lumen and, hence, interruption of the enterolymphatic circulation of cholesterol.…”

“…In the case of homogenates, the liver was first flushed in situ by injecting 20 for the incorporation of mevalonate into cholesterol in control and bile-fistula animals are the same, the comparison of rates measured under these conditions is valid.…”

“…Thus, to date there are available no valid experimental data based upon the effects of bile acids added to liver preparations in vitro that support the concept that bile acids exert direct control on the rate of hepatic cholesterogenesis. Second, not only does external biliary diversion and cholestyramine feeding, as outlined above, enhance hepatic sterol synthesis, but ligation of the common bile duct also leads to an elevated rate of cholesterogenesis in the liver (20). Fi-nally, since bile acid functions in a number of other physiological processes, e.g.…”

The Lipid Composition of Serum in Patients With Liver Disease*

“…Although the liver apparently synthesizes lecithin and free cholesterol, the hyperlipemia could result from an inability of the liver to excrete these lipids into the bile as a result of parenchymal damage or from a regurgitation of the bile lipids into the blood as a result of biliary obstruction. Evidence offered against this hypothesis has been the demonstration of an increased rate of synthesis of plasma cholesterol following bile duct ligation in the rat (53) and of an increased rate of plasma phospholipid synthesis in patients with jaundice and hyperlipemia (54). It is conceivable, however, that the increased rate of synthesis of these lipids may represent an increment in synthesis that ordinarily is excreted into the bile but in jaundiced patients finds its way into the plasma.…”

Ultracentrifugal Characterization of the Lipoprotein Spectrum in Obstructive Jaundice: Studies of Serum Lipid Relationships in Intra- And Extrahepatic Biliary Obstruction 1

“…Simple retention of bile, increased plasma cholate (20), alteration in serum cholesterol esterifying enzyme activity (21,22) and increased hepatic cholesterol synthesis (23) have been suggested in explanation. While as much as 50 per cent of the cholesterol absorbed from the intestinal tract is present as cholesterol ester in the thoracic duct lymph (24), animal studies by Friedman and Byers (25) The metabolic significance of these correlations is not evident from this study.…”