Analytical subcellular fractionation studies on different cell types isolated from normal rat liver

Investigation of tissue organelles by a combination of analytical subcellular fractionation and enzymic microanalysis: a new approach to pathology

Classical approaches to the study of pathological tissue have relied mainly on morphological techniques. In an attempt to quantitate the abnormalities and to investigate the pathogenesis of tissue disorders at a subcellular level we have combined analytical subcellular fractionation by sucrose density gradient centrifugation with microanalysis of tissue enzymic activities. The methodological problems of performing these studies on milligram quantities of tissue are discussed. Details of the appropriate equipment are provided, and its application to the study of human liver specimens is described. As an example of this approach, biochemical and subcellular fractionation experiments on tissue from patients with both primary and secondary hepatic lysosomal storage diseases are discussed. Examination of the lysosomal changes reveals that increased enzyme activity is a common finding in these disorders but tissue damage occurs only when there is evidence of enhances lysosomal fragility with intracellular release of degradative enzymes. Other tissues which have proved amenable to study in this manner and in which profitable results in the investigation of their disorders have been obtained are listed.

Effects of phenobarbital upon triacylglycerol metabolism in the rabbit

1. The association between hepatic microsomal enzyme induction and triacylglycerol metabolism was examined in fasting male rabbits (2kg body wt.) injected intra-peritoneally with 50 mg of phenobarbital per kg for 10 days. 2. Occurrence of enzyme induction was established by a significant increase in hepatic aminopyrine N-demethylase activity and cytochrome P-450 content, as well as a doubling of microsomal protein per g of liver and a 54% increase in liver weight. Parallel increments in hepatic gamma-glutamyltransferase (EC 2.3.2.2) activity occurred; these were more pronounced in the whole homogenate than in the microsomes, which only accounted for 12.5% of the total enzyme activity in the controls and 17.0% in the animals given phenobarbital. Increased activity of gamma-glutamyltransferase activity was also observed in the blood serum of the test animals. 3. The rabbits given phenobarbital manifested increased hepatic triacylglycerol content and the triacylglycerol concentration of blood serum was also elevated. These changes were accompanied by a significantly enhanced ability of cell-free fractions of liver from the test animals (postmitochondrial supernatant and microsomal fractions) to synthesize glycerolipids in vitro from sn-[14C] glycerol 3-phosphate and fatty acids, when expressed per whole liver. Relative to the protein content of the fraction, glycerolipid synthesis in vitro was significantly decreased in the microsomes, presumably consequent upon the dramatic increase in their total protein content, whereas no change occurred in the postmitochondrial supernatant, possibly due to the protective effect of cytosolic factors present in this fraction and known to enhance glycerolipid synthesis. 4. Microsomal phosphatidate phosphohydrolase accounted for 85% of the total liver activity of this enzyme and its specific activity was 20-fold higher than that of the cytosolic phosphatidate phosphohydrolase (EC 3.1.3.4), when each was measured under optimal conditions. A significant increase in the activity of both enzymes per whole liver occurred in the rabbits given phenobarbital. A closer correlation between hepatic triacylglycerol content and and microsomal phosphatidate phosphohydrolase, as well as the above observation, suggest that this, rather than the cytosolic enzyme, may be rate-limiting for triacylglycerol synthesis in rabbit liver. 5. Significant correlations were observed between the various factors of hepatic microsomal-enzyme induction (aminopyrine N-demethylase and gamma-glutamyltransferase activity as well as cytochrome P-450 content) and hepatic triacylglycerol content, suggesting that that microsomal enzyme induction may promote hepatic triacylglycerol synthesis and consequently hypertriglyceridaemia in the rabbit.