Marsh J B, Sparks C E
J Clin Invest. 1979 Nov;64(5):1229-37. doi: 10.1172/JCI109577.
Livers from normal and nephrotic rats were perfused by the nonrecirculating technique. Nephrosis was studied on the 7th d after the injection of puromycin animonucleoside. Amino acid-labeled lipoproteins (d < 1.21) were isolated from the perfusion medium by agarose column chromatography or by sequential density ultracentrifugation. In both groups of animals, in addition to very low density lipoproteins and nascent high density lipoproteins, column chromatography revealed the presence of a peak of 2-3 x 10(6) daltons. This peak contained lipoproteins of densities corresponding to <1.006, 1.006 < d < 1.02, and 1.02 < d < 1.06, which indicated that rat liver secretes a heterogeneous mixture of triglyceride-rich lipoproteins. The amount of these lipoprotein density classes was measured and their lipid and apoprotein composition and their apoprotein specific activity were determined. In both groups of rats there was a progressive rise in phospholipid and decrease in triglyceride content as the isolation density increased from 1.006 and 1.06. The lipoproteins from the nephrotics had higher amounts of cholesterol. The livers from the nephrotic rats secreted two to three times as much lipoprotein as controls in all density classes in the first 20 min, but during the next 40 min only the 1.02 < d < 1.06 and nascent high density lipoproteins remained at this high level compared to controls. A larger total liver pool of apolipoproteins in nephrotic livers was inferred from their lower specific activities during the first 20 min. The apoprotein composition of liver perfusate lipoproteins from nephrotics differed from controls. There was a 40% decrease in the amount of low molecular weight apoproteins in all density classes, with corresponding increases in apo B and apo E in the triglyceride-rich fractions. The apo A-1 content of nascent HDL was increased from 16% in controls to 52% in nephrotics, with corresponding decreases in apo C and apo E. When these results were combined with specific activity measurements of the individual apoproteins and the net secretion rate of total protein in each lipoprotein class, it was possible to estimate the total amount of each apoprotein secreted and the total incorporation of labeled amino acids into each. The incorporation of label gave results similar to those obtained by direct measurement of the amounts of apoproteins. Apo E secretion was increased by a factor of 1.8, apo B by 2.8, and apo A-1 by 8.4, whereas the secretion of apo C was not significantly altered. We explain these results by postulating that the primary stimulus to hepatic plasma protein synthesis in response to proteinuria is general and that subsequent negative feedback regulation affects individual apolipoprotein synthesis rates. A corollary of this hypothesis is that the biosynthesis and secretion of an apoprotein may be regulated independently of the lipoprotein density class in which it is found.
采用非循环灌注技术对正常大鼠和肾病大鼠的肝脏进行灌注。在注射嘌呤霉素氨基核苷后第7天研究肾病情况。通过琼脂糖柱色谱法或连续密度超速离心法从灌注培养基中分离氨基酸标记的脂蛋白（d < 1.21）。在两组动物中，除了极低密度脂蛋白和新生高密度脂蛋白外，柱色谱法显示存在一个2 - 3×10⁶道尔顿的峰。该峰包含密度对应于<1.006、1.006 < d < 1.02和1.02 < d < 1.06的脂蛋白，这表明大鼠肝脏分泌富含甘油三酯的脂蛋白的异质混合物。测定了这些脂蛋白密度类别的量，并确定了它们的脂质和载脂蛋白组成以及载脂蛋白比活性。在两组大鼠中，随着分离密度从1.006增加到1.06，磷脂含量逐渐增加，甘油三酯含量逐渐减少。肾病大鼠的脂蛋白胆固醇含量更高。在最初20分钟内，肾病大鼠肝脏分泌的所有密度类别的脂蛋白量是对照组的两到三倍，但在接下来的40分钟内，与对照组相比，只有1.02 < d < 1.06的脂蛋白和新生高密度脂蛋白保持在这个高水平。从最初20分钟内较低的比活性推断，肾病肝脏中载脂蛋白的肝脏总池更大。肾病大鼠肝脏灌注液脂蛋白的载脂蛋白组成与对照组不同。所有密度类别的低分子量载脂蛋白量减少40%，富含甘油三酯部分的载脂蛋白B和载脂蛋白E相应增加。新生高密度脂蛋白的载脂蛋白A - 1含量从对照组的16%增加到肾病大鼠的52%，载脂蛋白C和载脂蛋白E相应减少。当将这些结果与各个载脂蛋白的比活性测量值以及每个脂蛋白类别的总蛋白净分泌率相结合时，就可以估计每种载脂蛋白分泌的总量以及标记氨基酸在每种载脂蛋白中的总掺入量。标记掺入得到的结果与直接测量载脂蛋白量得到的结果相似。载脂蛋白E的分泌增加了1.8倍，载脂蛋白B增加了2.8倍，载脂蛋白A - 1增加了8.4倍，而载脂蛋白C的分泌没有显著改变。我们通过假设对蛋白尿的肝脏血浆蛋白合成的主要刺激是普遍的，随后的负反馈调节影响个体载脂蛋白合成速率来解释这些结果。这个假设的一个推论是，载脂蛋白的生物合成和分泌可能独立于其所在的脂蛋白密度类别进行调节。
