REGULATION OF HEPATIC LDL TRANSPORT IN VIVO

最初提案的目标是开发方法 为了研究肝脏低密度脂蛋白在体内转运的调节和 然后将这种方法论应用到饮食和药物的研究中 已知可以改变低密度脂蛋白水平的操作。在.期间 在过去的两年里，我们已经证明了肝脏是主要的 低密度脂蛋白分解代谢的部位，主要通过受体依赖的 可饱和和可调节的路径。我们还定义了 受体依赖性和非依赖性低密度脂蛋白的动力学 在大鼠和仓鼠体内各器官的转运。 最后，我们已经证明，饮食中的胆固醇可以下调 肝脏受体依赖的低密度脂蛋白转运和 甘油三酯的类型对下调的影响很大 出现在饮食中。在拟议的两年延期期间，我 将试图更准确地定义饮食中的胆固醇和 甘油三酯调节细胞内受体依赖性低密度脂蛋白的转运 肝脏。此外，还将进行研究，以确定这些 饮食中的脂质会影响极低密度脂蛋白和低密度脂蛋白的产生，如果 那么，怎么做呢？动物将被喂以含有不同数量的 胆固醇加或减多不饱和、单不饱和或 饱和甘油三酯。肝脏受体依赖性低密度脂蛋白的比率 转运将在体内进行量化，并与 低密度脂蛋白受体信使核糖核酸和低密度脂蛋白受体蛋白(用配基评估 印迹)在相同的动物身上测量。这些饮食的效果 肝细胞膜脂成分的研究及临床应用 由受体吸收的其他配体的运输也将是 下定决心。这些研究将表明，如果对 肝脏低密度脂蛋白受体通过膳食脂质在 转录水平或通过影响脂类成分 质膜反过来可以影响受体的结合， 内部化或再循环。因为饮食的影响 甘油三酯似乎至少需要一些 饮食中的胆固醇、胆固醇吸收和胆汁酸 将在喂食各种甘油三酯的动物身上测量合成 来看看甘油三酯的作用是否仅仅是改变了毛发 整个肝脏的胆固醇平衡。膳食脂类的作用 还将确定极低密度脂蛋白和低密度脂蛋白的产生，并 将尝试确定低密度脂蛋白的产生 受监管的。最后，各种药物对饮食诱导的影响。 高脂血症将被研究。这些研究将提供 将对制定养生法有价值的信息 旨在降低人的血浆低密度脂蛋白水平。

The objectives of the original proposal were to develop methods for studying the regulation of hepatic LDL transport in vivo and then to apply this methodology to the study of dietary and drug manipulations that are known to alter LDL levels. During the past two years we have demonstrated that the liver is the main site of LDL catabolism, largely via a receptor-dependent pathways that is saturable and regulatable. We have also defined the kinetics of receptor-dependent and -independent LDL transport in the various organs of rats and hamsters in vivo. Finally, we have shown that dietary cholesterol can down-regulate hepatic receptor-dependent LDL transport and that the degree of down-regulation is greatly influenced by the type of triglyceride present in the diet. During the proposed two-year extension, I will attempt to define more precisely how dietary cholesterol and triglycerides regulate receptor-dependent LDL transport in the liver. In addition, studies will be undertaken to determine if these dietary lipids affect the rate of VLDL and LDL production, and if so, how? Animals will be fed diets containing various amounts of cholesterol plus or minus polyunsaturated, monounsaturated or saturated triglyceride. Rates of hepatic receptor-dependent LDL transport will be quantitated in vivo and compared with levels of LDL receptor mRNA and LDL receptor protein (assessed by ligand blotting) measured in the same animals. The effect of these diets on the lipid composition of hepatic membranes and on the transport of other ligands taken up by receptors will also be determined. These studies will indicate if the regulation of hepatic LDL receptors by dietary lipid is mediated at the transcriptional level or through effects on the lipid composition of plasma membranes which, in turn, could effect receptor binding, internalization or recycling. Since the effect of dietary triglycerides seems to require the presence of at least some cholesterol in the diet, cholesterol absorption and bile acid synthesis will be measured in animals fed the various triglycerides to see if the effect of triglycerides is simply to alter gross cholesterol balance across the liver. The effect of dietary lipids on VLDL and LDL production will also be determined and an attempt will be made to determine how LDL production is regulated. Finally, the effects of various drugs on diet induced hyperlipidemia will be studied. These studies will provide information that will be valuable in the development of regimens aimed at lowering plasms LDL levels in man.