Total Inhibition of Hepatic β-Lipoprotein Production in the Rat by Orotic Acid

Reduction of fatty liver in rats by nicotinamide via the regeneration of the methionine cycle and the inhibition of aldehyde oxidase

Nonalcoholic fatty liver disease, which has been rapidly increasing in the world in recent years, is roughly classified into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis. This study was based on our previous reports that stated that the combination treatment of N1-methylnicotinamide (MNA) and hydralazine (HYD) improves fatty liver in NAFL model rats. This finding was attributed to the MNA metabolism inhibition by HYD, which is a strong inhibitor of aldehyde oxidase (AO); this results in an increase in hepatic MNA and improved fatty liver. We hypothesized that orally administered nicotinamide (NAM), which is the precursor of MNA and is a form of niacin, would be efficiently metabolized by nicotinamide N-methyltransferase in the presence of exogenous S-adenosylmethionine (SAM) in NAFL rats. To address this issue, NAFL model rats were orally administered with NAM, SAM, and/or HYD. As a result, liver triglyceride (TG) and lipid droplet levels were barely altered by the administration of NAM, SAM, NAM+SAM, or NAM+HYD. By contrast, the triple combination of NAM+SAM+HYD significantly reduced hepatic TG and lipid droplet levels and significantly increased hepatic MNA levels. These findings indicated that the combination of exogenous SAM with AO inhibitors, such as HYD, has beneficial effects for improving fatty liver with NAM.

Effects of Fatty Liver Induced by Excess Orotic Acid on B-Group Vitamin Concentrations of Liver, Blood, and Urine in Rats

Fatty liver is caused when rats are given orotic acid of the pyrimidine base in large quantities. The lack of B-group vitamins suppresses the biosynthesis of fatty acids. We investigated how orotic acid-induced fatty liver affects the concentrations of liver, blood, and urine B-group vitamins in rats. The vitamin B6 and B12 concentrations of liver, blood, and urine were not affected by orotic acid-induced fatty liver. Vitamin B2 was measured only in the urine, but was unchanged. The liver, blood, and urine concentrations of niacin and its metabolites fell dramatically. Niacin and its metabolites in the liver, blood, and urine were affected as expected. Although the concentrations of vitamin B1, pantothenic acid, folate, and biotin in liver and blood were decreased by orotic acid-induced fatty liver, these urinary excretion amounts showed a specific pattern toward increase. Generally, as for the typical urinary excretion of B-group vitamins, these are excreted when the body is saturated. However, the ability to sustain vitamin B1, pantothenic acid, folate, and biotin decreased in fatty liver, which is hypothesized as a specific phenomenon. This metabolic response might occur to prevent an abnormally increased biosynthesis of fatty acids by orotic acid.

The role of dietary nucleotides in single-stomached animals

The transition from liquid to solid feed during weaning results in morphological, histological and microbial changes in the young animal's intestinal tract and often is associated with diarrhoea. The ban of in-feed antibiotics in pig production in the European Union has led to increasing interest in alternatives to overcome weaning-associated problems. Among others, nucleotides may have the potential to alleviate health impairments due to weaning. Nucleotides are natural components of the non-protein fraction of milk and have important effects on the maintenance of health in young animals. Nucleotides and their related metabolic products play key roles in many biological processes and become essential dietary components when endogenous supply is insufficient for normal function. The present review summarises nucleotide composition of milk from different species, the biology of nucleotides and possible effects of dietary nucleotides on intestinal morphology and function, intestinal microbiota, immune function, nutrient metabolism, hepatic morphology and function as well as growth performance. Special attention is given to data available for pigs, and suggestions are made for inclusion of nucleotides in the diet to benefit piglets' health and reduce the consequences accompanying early weaning.

Fenofibrate prevents orotic acid--induced hepatic steatosis in rats

The experiments performed in this report were designed to investigate the mechanisms involved in the metabolic alterations associated with orotic acid-induced hepatic steatosis and the effect of fenofibrate, a stimulant of peroxisome proliferators-activated receptor alpha (PPARalpha), on these alterations. Male Wistar rats were divided into three experimental groups: 1) fed a balanced diet (C); 2) fed a balanced diet supplemented with 1% orotic acid (OA); 3) fed OA diet containing 100 mg.kg(-1) bw.day(-1) fenofibrate (OA+F), for 9 days. Administration of OA to rats induced significant increase in the hepatic total lipids content, marked microvesicular steatosis and decrease in plasma lipids concentrations compared to control group. Fenofibrate treatment prevented fatty liver induction, caused an additional reduction on plasma lipids concentrations and caused a 40% decrease in the lipogenic rate in adipose tissue. The results also showed a 40% increase in lipoprotein lipase (LPL) activity in adipose tissue from OA treated group and fenofibrate administration induced a 50% decrease in LPL activity. The liver mRNA expression of PPARalpha and ACO (acyl CoA oxidase) were 85% and 68% decreased in OA group when compared to control, respectively. Fenofibrate treatment increased the PPARalpha and ACO expressions whereas the CPT-1 (carnitine palmitoyl transferase-1) expression was not altered. Our results have shown that fenofibrate treatment decreases the hepatic lipid content induced by OA which is mediated by an important increase in fatty acid oxidation consequent to an increase in hepatic mRNA expression of PPARalpha and ACO.

Effects of fatty liver induced by niacin-free diet with orotic acid on the metabolism of tryptophan to niacin in rats

The effects of dietary orotic acid on the metabolism of tryptophan to niacin in weaning rats was investigated. The rats were fed with a niacin-free, 20% casein diet containing 0% (control diet) or 1% orotic acid diet (test diet) for 29 d. Retardation of growth, development of fatty liver, and enlargement of liver were observed in the test group in comparison with the control group. The concentrations of NAD and NADP in liver significantly decreased, while these in blood did not decrease compared to the control group. The formation of the upper metabolites of tryptophan to niacin such as anthranilic acid, kynurenic acid, and 3-hydroxyanthranilic acid were not affected, but the quinolinic acid and beyond, such as nicotinamide, N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide, were significantly reduced by the administration of orotic acid. Therefore, the conversion ratio of tryptophan to niacin significantly decreased in the test group in comparison with the control group.

Preventive effects of dehydroepiandrosterone acetate on the fatty liver induced by orotic acid in male rats

Preventive effects of dehydroepiandrosteone acetate (DHEA-A) and clofibrate (positive control substance) on the fatty liver induced by orotic acid (OA) were examined on the male Sprague-Dawley rats fed a high sucrose based diet containing 1% OA and this diet further mixed with 0.5% DHEA-A or 0.5% clofibrate for 2 weeks. Numerous lipid droplets were observed in the hepatocytes of the rats treated with OA alone, but not in those treated with DHEA-A or clofibrate. In comparison to the group with OA alone, the DHEA-A or clofibrate treated rats showed a larger relative liver weight (to body weight) which was accompanied by increased peroxisomes in the hepatocytes. These results indicate that DHEA-A, as well as clofibrate, may prevent OA-induced fatty liver.

Effects of Triton WR 1339 and orotic acid on biliary and serum dolichols in rats

Two lysosomal storage diseases, aspartylglucosaminuria and mannosidosis, are associated with highly elevated serum dolichol concentrations. To elucidate possible mechanisms leading to elevated serum dolichols, we studied the effects of Triton WR 1339 (known to increase serum cholesterol) and orotic acid (known to decrease serum cholesterol) on blood and biliary dolichol and beta-hexosaminidase levels in rats. In Triton WR 1339-treated rats, serum dolichol was markedly increased compared with saline-treated controls 1 (400 +/- 70 ng/mL, n = 7 v 85 +/- 11 ng/mL, n = 8, P < .001), 4 (789 +/- 70 ng/mL, n = 10 v 110 +/- 10 ng/mL, n = 7, P < .0001), and 8 (549 +/- 43 ng/mL, n = 8 v 87 +/- 8 ng/mL, n = 7, P < .001) days after administration of the drug. By contrast, serum dolichol was decreased (64 +/- 5 ng/mL, n = 8 v 119 +/- 7 ng/mL, n = 8, P < .0001) after a 7-day orotic acid feeding compared with controls. Serum beta-hexosaminidase was unaffected by both treatments. Orotic acid also increased biliary dolichol (280 +/- 47 ng/100 g body weight [BW]/h, n = 7 v 83 +/- 15 ng/100 g BW/h, n = 7, P < .01) and beta-hexosaminidase (21 +/- 3 mU/100 g BW/h, n = 7 v 8.3 +/- 2 mU/100 g BW/h, n = 9, P < .01) excretion compared with controls. Thus, both Triton WR 1339 and orotic acid have an effect on dolichol metabolism, and it is conceivable--based on our results--that serum dolichol concentrations are regulated, at least in part, by a mechanism similar to that for serum cholesterol levels.

Prevention of orotic-acid-induced fatty liver in male rats by dehydroepiandrosterone and/or phenobarbital

Dehydroepiandrosterone (DHEA) is a steroid hormone which induces the peroxisome proliferation in rodents. The fatty liver induced by orotic acid and a high sucrose diet in male rats was prevented by the administration of DHEA and/or phenobarbital (PB). A significant increase in the liver weight was induced in the DHEA group (relative weight) and the DHEA + PB group (absolute and relative weight). The liver weight increased more conspicuously in the DHEA + PB group than in the DHEA group. The increase in the liver weight was caused by an increase in the cell size and peroxisome number. In addition, the administration of DHEA alone and the combination of DHEA and PB prevented the lipid droplet accumulation in hepatocytes. The administration of PB alone also prevented the accumulation of lipid droplets without any increase in the liver weight.

Morphological changes in hepatocytes of rats deprived of dietary nucleotides

The aim of the present study was to investigate the influence of dietary nucleotides on liver morphology. Adult rats were fed for 21 d on a nucleotide-containing diet or the same diet free of nucleotides. Liver sections were examined by light and transmission electron microscopy, as well as for nucleic acid and protein contents. Morphometric analysis was performed for different variables. Deprivation of dietary nucleotides resulted in a reduction in hepatocyte nuclear and nucleolar areas as well as in nuclear chromatin condensation. In addition, the rough endoplasmic reticulum was reduced, as were ribosome association and abundance, whereas fat accumulated. These findings portray dietary nucleotides as required nutrients for the liver under normal physiological conditions and suggest that an inadequate supply of nucleotides for a certain period of time has transient negative effects on liver ultrastructure and function.

Influence of orotic acid and estrogen on hepatic lipid storage and secretion in the goose susceptible to liver steatosis

Fatty liver in the goose results from an increased hepatic lipogenesis in response to overfeeding, together with a deficient secretion of triacylglycerol as very-low-density lipoproteins (VLDL). Orotic acid and estrogen, which both modify lipid metabolism in the liver, were used in male geese as tools to understand the alterations of liver lipids and plasma lipoproteins during the induction of liver steatosis. Liver lipids were analyzed after solvent extraction and plasma lipoproteins after separation by density gradient ultracentrifugation. Contrary to what is known in the rat, orotic acid (1% in food for 2 weeks) failed to induce liver steatosis. In force-fed geese, liver weight increased from approximately 100 g to approximately 800 g in 2 weeks, as a consequence of a specific accumulation of triacylglycerol. In both groups, VLDL contained less triacylglycerol (35%) than normal. Such an uncoupling of triacylglycerol synthesis and secretion, of which the precise reason is still unknown, may facilitate their accumulation when force-feeding increases hepatic lipogenesis. As with force-feeding, triacylglycerol synthesis was enhanced by estrogen, but their secretion as VLDL was very efficient and prevented liver steatosis almost completely. Since HDL concentrations were considerably decreased by estrogen, VLDL were the main lipoprotein species, with 48 g/l and 62% triacylglycerol. Where estrogen-treated geese were force-fed concomitantly, VLDL concentration was even higher (62 g/l), but triacylglycerol secretion could not prevent liver steatosis (liver weight 640 g). The data are discussed in relation to in vitro studies showing that channelling of triacylglycerol towards secretion as VLDL or hepatic storage depends on their residence time in the different intracellular compartments.

A retrospective study of 77 cats with severe hepatic lipidosis: 1975-1990

The physical, clinicopathologic, and survival rates of 77 cats with severe spontaneous hepatic lipidosis are detailed in this report. Cats were subdivided into groups designated as idiopathic lipidosis if no other disease process was recognized, or secondary lipidosis if another disease process was diagnosed. Cats were also subdivided into groups designated as survivors or nonsurvivors on the basis of successful recuperation at 4 months after initial diagnosis. Differences between disease and survival groups were evaluated for significance. Overall, more female cats and middle-aged cats were affected. Presenting complaints of vomiting, anorexia, weakness, and weight loss were common. Physical assessment of most cats showed obvious hepatomegaly, jaundice, dehydration, and a weight loss > or = 25% of usual body weight. Neurobehavioral signs indicative of hepatic encephalopathy, other than ptyalism and depression, were rare. Clinicopathologic features are characterized by hyperbilirubinemia and increased activities of serum ALT, AST, and ALP, with only small if any increase in gamma GT activity. Clinical features distinguishing cats with hepatic lipidosis from those with other serious cholestatic disorders include absence of hyperglobulinemia and low gamma GT activity relative to ALP activity. Although coagulation tests were abnormal in 45% of cats tested (n = 44), few cats showed clinical bleeding tendencies. Most cats received prophylactic vitamin K1 therapy. Forty two cats received aggressive nutritional and supportive care and of these 55% survived. Cats with idiopathic disease were significantly younger, had significantly higher ALP activity and bilirubin concentration, and had a slightly better survival rate than cats with secondary lipidosis. Low PCV, hypokalemia, and an older age were significantly related to nonsurvival. Because of the variety of diets and food supplements used in case management, the influence of nutritional factors on survival could not be evaluated.

Effect of dietary nucleotides on the fatty acid composition of rat liver microsomes

The present study was designed to evaluate the influence of dietary nucleotides on the lipid composition of liver microsomes in weanling rats. Rats at weaning were fed, one group with a semipurified nucleotide-free diet and three groups with the same diet supplemented with three different levels of each of the nucleotides AMP, GMP, IMP, UMP and CMP, during 4 weeks. Long chain polyunsaturated fatty acids of the n-6 and n-3 series were increased in phospholipids of liver microsomes for rats fed the nucleotide supplemented diets; however, the cholesterol/phospholipid phosphorus ratio was maintained fairly constant. The results obtained suggest that dietary nucleotides modify the polyunsaturated fatty acid metabolism through a lower rat liver delta-9 desaturase activity and through increased activities of delta-5 and delta-4 desaturases.

Changes in liver microsome lipids and plasma fatty acids induced by dietary orotate in the weanling rat

1. Dietary orotate produced a decrease in total plasma fatty acids which was reflected in low values of saturated, monounsaturated and polyunsaturated fatty acids longer than 18 carbon atoms of the n-6 series. The relative content of saturated fatty acids in microsomes of animals fed orotate was also decreased. 2. Rat liver delta-9 desaturase activity was lower in the group fed orotate. However, delta-6 desaturase activity did not show significant differences between the groups. 3. Microsomal cholesterol content was lower in rats fed orotate than in controls but phospholipid phosphorus contents were similar. These results suggest a direct effect of dietary orotate on the key enzymes which regulates cholesterol liver metabolism.

Alteration of serum lipoprotein metabolism by polychlorinated biphenyls and methionine in rats fed a soybean protein diet

The effects of dietary supplementation of methionine to a 20% soybean protein isolate diet on serum lipoprotein profiles and secretion rate of VLDL in rats receiving polychlorinated biphenyls (PCB) were investigated. Serum cholesterol levels were higher in rats fed PCB or a methionine supplement than in controls. The effects of PCB and methionine were synergistic. The feeding of PCB resulted in more cholesterol in all fractions of serum lipoproteins tested, especially HDL (HDL1 and HDL2). Dietary supplementation of methionine primarily increased HDL cholesterol. The elevation of serum lipoprotein cholesterol due to PCB and/or methionine was significant in HDL1, which showed alpha-mobility. These results showed that methionine and PCB significantly influenced HDL metabolism. The secretion rate of VLDL was higher in rats fed PCB than in controls, but the addition of methionine to diets did not affect the secretion rate of VLDL cholesterol. This implies that PCB increased serum cholesterol partly through the stimulation of VLDL cholesterol secretion.

Effect of dietary nucleotides and orotate on the blood levels of prostacyclin (PGI2) and thromboxane (TXA2) in the weanling rat

Dietary nucleotides affect the maintenance of immune responses, tissue repair and polyunsaturated fatty acid metabolism. Orotate, a pyrimidine nucleotide precursor, induces fatty livers by impairing VLDL hepatic secretion. The aim of this study was to evaluate the changes in the blood levels of fatty acids and prostacyclin (PGI2) and thromboxane (TXA2) in the weanling rat caused by the dietary intake of nucleotides and orotate. Three groups of rats at weaning were fed a control diet, an orotate supplemented diet (O-50) and a nucleotide supplemented diet (N-50) during 4 weeks, respectively. Absolute values of plasma polyunsaturated fatty acids greater than 18 carbon atoms of the n-6 and n-3 series were increased in the N-50 group and decreased in O-50 with regard to the control. However, the relative fatty acid composition of plasma lipid fractions was mostly unaffected. Plasma 6-keto-PGF1 alpha showed a trend to be increased in N-50 and serum TXB2 was significantly increased in that group. Both eicosanoids were unchanged by dietary orotate intake. These results may be explained because of the increased plasma 20:4n-6 found in rats fed a supplemented nucleotide diet. Thus, nucleotides present in foods appear to modulate PUFA conversion and eicosanoids synthesis in early life.

Effect of orotic acid on the generation of reactive oxygen and on lipid peroxidation in rat liver

The pyrimidine precursor orotic acid (OA) is a constituent of dairy products and therapeutic drugs. Several recent publications point towards a tumor promoting activity of OA in rat liver. An increased production of reactive oxygen has been discussed as a possible mechanism, leading to lipid peroxidation and DNA single strand breaks. In view of contradictory results, this postulated prooxidative action of OA was reexamined with new experimental techniques. Weanling Sprague-Dawley rats were fed 1% OA in different diets for 4-35 days. The NADPH-mediated lipid peroxidation in liver homogenate and microsomes was determined in vitro by analysis of low-level chemiluminescence (CL) and the strongly correlated formation of malondialdehyde (MDA). In no case did treatment with OA result in an increase of lipid peroxidation in vitro nor did such treatment enhance the generation of reactive oxygen as measured by lucigenin CL. In accordance, the total cytochrome P-450 content as well as the activity of individual P-450 isoenzymes were unchanged. Treatment with OA did not elevate the MDA content of fresh liver homogenate when butylated hydroxytoluene (BHT) was present in the test system. However, when the antioxidant was omitted, increased levels of thiobarbituric acid reactive material were found which correlated with the triglyceride content. This could explain some published data that have been taken as indication for a prooxidative action of OA. Evidence against an increased lipid peroxidation in vivo is given by the analysis of ethane exhalation. Furthermore, no increase in DNA single strand breaks by OA treatment could be observed by the alkaline elution technique. These results do not support the hypothesis of a prooxidative activity of OA. The observed reversible decrease of the GSH/GSSG ratio is assumed to result from the reduced size of the phosphopyridine nucleotide pool due to purine deficiency and an increased consumption of NADPH by the enhanced reductive degradation of pyrimidines.

Intestinal very-low-density lipoprotein secretion in the genetically obese Zucker rat

The objectives of this study were to measure intestinal very-low-density lipoprotein (VLDL) production in obese Zucker rats and to assess an eventual effect of a high-fat diet. VLDL secretion was specifically inhibited by orotic acid, and intestinal VLDL output was measured following the Triton WR-1339 method. After a control diet, total VLDL secretion (without orotic acid) was 4.8 +/- 0.3 and 1.4 +/- 0.1 mg triacylglycerol/ml in obese and lean rats, respectively, decreasing by 30% in obese rats after fat-feeding. Intestinal VLDL production was similar in obese and lean rats fed the control diet (0.32 +/- 0.05 and 0.27 +/- 0.05 mg triacylglycerol/ml, respectively), increasing 2.5-fold after fat-feeding in both genotypes. Thus, intestine contributed 21 and 60% of total VLDL in lean but only 7 and 24% in obese rats with the control and high-fat diets, respectively. These results show that the intestine of obese Zucker rats does not contribute to their hypertriglyceridemia, suggesting that it originates solely from liver. Moreover, their intestinal VLDL production was stimulated by fat-feeding to the same extent as in lean animals.

Effects of Triton WR 1339 and orotic acid on lipid metabolism in rats

In order to investigate the effect of hepatic cholesterol flux on biliary bile acids, Triton WR 1339 and orotic acid were administered to rats, and the biliary cholesterol, phospholipids and bile acids were analyzed together with serum lipoproteins and hepatic lipids. Triton, which raised serum very low density lipoprotein and lipid levels and decreased serum high density lipoprotein liver lipid levels, increase the biliary cholic acid group/chenodeoxycholic acid group ratio (CA/CDCA) in the bile without affecting the total amount of bile acids and the other biliary lipids. Orotic acid, which decreased serum lipid and lipoprotein concentrations and increased liver lipid levels, increased the biliary excretion of cholesterol and phospholipids, but produced no significant change in the total amount of bile acids and in the CA/CDCA ratio in bile.

Hepatic lipoprotein biosynthesis

Methods for the study of hepatic lipoprotein synthesis and secretion have been described, and the advantages of each system discussed. Attention has been focused on intact cell systems. The isolated perfused liver constitutes a standard of comparison for all others, even though it, too, has limitations. Table IV below gives our assessment of some of the advantages and disadvantages of the techniques for studying hepatic lipoprotein biosynthesis.

Hypolipidemic activity of 6-amino-2-mercapto-5-methyl-pyrimidine-4-carboxylic acid and related derivatives in rodents

6-Amino-2-mercapto-5-methylpyrimidine-4-carboxylic acid proved to be a potent hypolipidemic agent in rodents at the low dose of 20 mg/kg/d. The agent effectively reduced the liver enzyme activities required for the synthesis of triglycerides and cholesterol. Lower lipid levels in tissue were observed in mice but not in rats. Preliminary studies indicate that the agent accelerated the excretion of cholesterol and its metabolites from the body. The agents lowered the low-density lipoprotein (LDL) cholesterol content and raised the high-density lipoprotein (HDL) cholesterol content. These changes in lipoprotein cholesterol content suggest that the agent may be helpful in protecting against coronary disease. The agent is more effective than the commercially available agent, i.e., clofibrate at 150 mg/kg/d.

Hypolipidemic activity of 4-pyrimidinecarboxylic acids in CF1 mice

A series of 4-pyrimidinecarboxylic acids were evaluated for hypolipidemic activity in mice at 20-30 mg/kg/d ip. A number of these derivatives were observed to be active at this dose. Substitution of the hydroxyl group in position 2 and 6 of the 4-pyrimidinecarboxylic acid with a sulfhydryl and an amino group, respectively, led to a compound which produced a greater than 40% reduction of serum cholesterol and triglyceride levels in mice. Similarly, a compound which was substituted with an amino group in position 2 and an isobutyl group in position 5 led to equally potent activity as a hypolipidemic agent.

Ultrastructural changes of hepatocyte organelles induced by chemicals and their relation to fat accumulation in the liver

Fatty liver was induced in the rats shortly after administration of cycloheximide, ethionine, orotic acid, monensin or colchicine. It was strongly suggested that derangements in one or more of the hepatic lipoprotein metabolic steps, which occur at the levels of endoplasmic reticulum, Golgi apparatus and secretory vacuoles lead to an accumulation of triglyceride within hepatocytes.

Metabolism of orotic acid: lack of orotate phosphoribosyltransferase in rat intestinal mucosa

The main enzymes involved in orotic acid metabolism, orotate phosphoribosyltransferase and orotidine 5'-phosphate decarboxylase, are associated as a multienzyme complex (complex U) which is present in the liver of most vertebrate species. Orotic-acid-enriched diets produce increased pyrimidine synthesis which competes with purine synthesis for 5-phosphoribosyl diphosphate, resulting in decreased adenylate levels in liver cells. Inhibition of secretion of very low density lipoproteins and hepatic steatosis is then observed. In contrast, lipoproteins secretion by the intestine is not impaired and fat does not accumulate in enterocytes. The aim of this work was to investigate whether orotate is differently metabolized in gut and in liver thus explaining the lack of effect on the intestinal lipoproteins secretion. Complex U was found in appreciable amounts in rat, mouse and rabbit livers; the intestinal mucosa of the two last species contains a much lower level of multienzyme complex whereas in rat intestine its activity cannot be detected. Indeed, radioactive aspartate and orotate were not incorporated into intestinal cells RNA. The absence of orotate metabolisation by lack of orotate phosphoribosyltransferase and orotidine 5'-phosphate decarboxylase activity in rat intestine would explain why this organ, in contrast to the liver, is protected against disturbances of nucleotide metabolism and lipoproteins secretion induced by orotic-acid-supplemented diets.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on lipid profiles in tissue of the Fischer rat

Female Fischer 344 rats were given single oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 10, 50 or 100 microgram/kg, and sacrificed 1, 3, 10, 14 or 21 days later. The fatty livers caused by a sub-lethal dose of TCDD involved a temporary increase in triglyceride and free fatty acid levels, with a persistent decrease in levels of sterol esters. In contrast, the fatty livers resulting from a lethal dose of TCDD involved a large increase in cholesterol esters and free fatty acids, with little change in triglyceride levels. These changes appeared to result in part from damage sustained by lysosomes. TCDD also altered the lipoprotein composition of the serum, the fatty acid composition of various lipid classes in liver and serum, and the ultrastructure of the liver (formation of myeloid bodies). A rapid, dose-dependent effect of TCDD, was the elevation of levels of organic-soluble fluorescent pigment in the heart. This pigment was found to match a previously characterized fraction of lipofuscins in fluorescence spectrum and chromatographic properties. The relatioship of these observations to a possible mechanism of toxicity for TCDD involving radical-induced lipid peroxidation is discussed.

Liver lipid alterations in rats fed arginine deficient diets

Arginine deficiency is associated with a marked increase in liver lipids in the rat. Triglyceride accumulation accounts for most of the fatty infiltration. Cholesterol concentration per gram of liver increased approximately 280% above control rats receiving dietary arginine. The percentage of phospholipids was significantly decreased in the arginine-deficient rat liver compared to controls. The fatty acid composition revealed a significant reduction in the reduction in the percentage of palmitic, palmitoleic, oleic, and linoleic acids. However, both stearic and arachidonic acids were increased approximately 250 and 160%, respectively, in arginine-deficient livers compared to controls. Arginine deficiency in the rat causes a marked alteration in lipid metabolism similar to that observed with orotic acid feeding. The similarities or arginine deficiency and orotic acid feeding are discussed.