Levy E, Garofalo C, Rouleau T, Gavino V, Bendayan M
Department of Nutrition, Centre de Recherche, Hôpital Ste-Justine, Université de Montréal, Quebec, Canada.
Hepatology. 1996 Apr;23(4):848-57. doi: 10.1053/jhep.1996.v23.pm0008666341.
The major aim of the current investigation was to define whether essential fatty acid (EFA) deficiency modifies the intrahepatic metabolism and biliary output of sterols in rats. EFA-deficient diet caused an impoverishment in linoleic, arachidonic, and docosahexaenoic acids, and a marked enrichment in the eicosatrienoic acid of the plasma, liver, and hepatic microsomes. During a short term of biliary drainage, a significant decline of the pool size of biliary sterols was noted in EFA-deficient rats compared with control rats. To assess the biosynthesis of biliary components, the common bile duct was cannulated and the pool size depleted (24 hours). Subsequently, a 6-hour bile collection disclosed a significant decrease (nmoles/min/g liver) in bile acids (4.8 +/- 0.3 vs. 8.4 +/- 0.7, P < .005), cholesterol (0.26 +/- 0.01 vs. 0.34 +/- 0.02, P < .05), and phospholipids (1.49 +/- 0.11 vs. 2.82 +/- 0.32, P < .005) in EFA-deficient rats compared with controls (n = 6/group). When cholesterogenesis was measured by the incorporation of [14C]acetate and 3H20 into cholesterol, using liver slices, it was also found to be significantly (P < .001) reduced in EFA-deficient rats. The activity of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol biosynthesis, was consistently lower (80 percent, P < .001) in EFA-deficient rats. In parallel experiments, the direct measurement of microsomal acyl-CoA:cholesterol acyl-transferase (ACAT) showed a decrease averaging 52 percent (P < .001). This is in striking contrast to the elevated activity (157 percent, P < .005) of cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in bile acid biosynthesis. Current experiments also suggest that the enzyme regulation involving phosphorylation and dephosphorylation is modified by EFA deficiency. Among the structural alterations observed in the morphology of hepatocytes in EFA-deficient rats, the lumen of bile canaliculi was reduced in size. These results underline the importance of EFA in the major mechanisms involved in the maintenance of hepatocyte sterol balance.
当前研究的主要目的是确定必需脂肪酸（EFA）缺乏是否会改变大鼠肝脏内的甾醇代谢及胆汁中甾醇的排出量。缺乏EFA的饮食导致亚油酸、花生四烯酸和二十二碳六烯酸减少，同时血浆、肝脏及肝微粒体中的二十碳三烯酸显著增加。在短期胆汁引流过程中，与对照大鼠相比，EFA缺乏的大鼠胆汁中甾醇池大小显著下降。为评估胆汁成分的生物合成，将胆总管插管并使池大小减少（24小时）。随后，6小时的胆汁收集显示，与对照组相比（每组n = 6），EFA缺乏的大鼠胆汁酸（4.8±0.3对8.4±0.7，P <.005）、胆固醇（0.26±0.01对0.34±0.02，P <.05）和磷脂（1.49±0.11对2.82±0.32，P <.005）显著减少（纳摩尔/分钟/克肝脏）。当用肝切片通过[14C]乙酸盐和3H2O掺入胆固醇来测定胆固醇生成时，还发现EFA缺乏的大鼠胆固醇生成也显著减少（P <.001）。肝脏3-羟基-3-甲基戊二酰辅酶A还原酶是胆固醇生物合成中的限速酶，其活性在EFA缺乏的大鼠中始终较低（降低80%，P <.001）。在平行实验中，微粒体酰基辅酶A：胆固醇酰基转移酶（ACAT）的直接测量显示平均降低52%（P <.001）。这与胆汁酸生物合成中的限速酶胆固醇7α-羟化酶活性升高（升高157%，P <.005）形成鲜明对比。当前实验还表明，涉及磷酸化和去磷酸化的酶调节因EFA缺乏而改变。在EFA缺乏的大鼠肝细胞形态观察到的结构改变中，胆小管腔大小减小。这些结果强调了EFA在维持肝细胞甾醇平衡的主要机制中的重要性。
