Sources of triacylglycerol accumulation in livers of rats fed a cholesterol-supplemented diet

The source of free fatty acids (FFA) and the pathways contributing to the accumulation of neutral fats in livers of rats fed a cholesterol-enriched diet were investigated in this report. Supplementation with 1% cholesterol in the diet for four weeks resulted in hepatomegaly in the rats. The contents of cholesterol and triacylglycerols (TG) per gram liver measured in rats fasted overnight increased by 48 mg (∼tenfold) and 66 mg (∼fourfold), respectively. The activities of glycerophosphate acyltransferase and diacylglycerol acyltransferase, the two key enzymes for TG synthesis in liver microsomes, were found to increase by 23 and 19%, respectively, in the cholesterol-fed rats. The secretion of plasma TG present predominantly in very low density lipoprotein was found to decrease by ∼30%. The incorporation of tritium from tritiated water in liver FFA increased by twofold in rats fed the cholesterol-supplemented diet, whereas the activity of CPT I in liver mitochondria decreased by 23%. The uptake of plasma FFAin vivo in livers of fasted rats maintained on the cholesterol-supplemented diet decreased by 60%. Our data thus indicate that the excess TG accumulated in livers of rats fed the cholesterol-enriched diet resulted from increased synthesis and decreased secretion of TG. To meet the demand of fatty acids for this purpose,de novo lipogenesis increased, whereas β-oxidation decreased. Although difference in the uptake of extrahepatic FFA may be discounted, a difference in the uptake of chylomicron remnants between the control and cholesterol-fed rats may not be ruled out.     

The prevention of alcoholic fatty liver using dietary supplements: Dihydroxyacetone,pyruvate and riboflavin compared to arachidonic acid in pair-fed rats

Male Sprague-Dawley rats were fed for 30 days a high-fat liquid ethanol diet with dihydroxyacetone, pyruvate and riboflavin added as supplements (AMA-). Plasma triglyceride (TG) levels were 6-fold greater in these rats than in those fed and alcohol with without the supplements (AA-). The liver TG content in rats fed the AMA-diet was similar to that of rats fed a control diet (CA-) in which alcohol was replaced with isocaloric amounts of dextrose. Livers of rats fed the AA- diet had 3 times more TG than controls. Alcohol ingestion also enhanced the hepatic content of cholesteryl esters (CE) and phospholipids (PL). These lipids were reduced to levels found in livers of rats fed the control diet (CA-) when dihydroxyacetone, pyruvate and riboflavin were included in the alcohol diet. The fatty acid compositions of TG, CE and PL from livers of rats fed the AMA-diet were similar to those of corresponding lipids from rats fed the control diet (CA-) but differed from compositions when fed the alcohol diet (AA-). Regardless of the diet fed, TG had the same fatty acid composition in plasma and liver. The same was true of PL fatty acid composition. However, the fatty acid composition of CE differed between liver and plasma. The major fatty acid in liver CE was 18∶1 whereas in plasma it was arachidonic acid (20∶4). Reduced fatty liver was observed in an earlier study when rats were fed ad libitum an ethanol diet containing 20∶4. In the present study, we pair-fed the same diet and fatty liver was not reduced. Dihydroxyacetone, pyruvate and riboflavin did not prevent alcohol-induced fatty liver when 20∶4 was included in the AMA-diet. Our results confirm that dietary dihydroxyacetone, pyruvate and riboflavin prevent alcohol-induced fatty liver, and show that this effect may result from increased mobilization of fat from liver.     

Effect of EFA deficiency on lipid transport from liver

Studies are reported of the effect of an essential fatty acid (EFA) deficiency on synthesis of triglycerides (TG) and phospholipids (PL) and secretion of these compounds by livers of male Sprague-Dawley rats. Animals were fed a semipurified diet containing corn oil or hydrogenated coconut oil (HCO) as the sole source of fat or no fat from weaning to 20 weeks of age. Liver function of the animals in each group was compared by an isolated liver perfusion technique with perfusates containing erythrocytes and linoleate, and in vivo experiments via tail vein injection of palmitate-³H. Perfusion experiments showed that an EFA deficiency reduced the ability of the liver to secrete TG and PL. Accumulation of TG in the liver and its diminished secretion into the blood of EFA deficient animals were demonstrated by in vivo experiments with palmitate-³H. The rate of conversion of linoleate to arachidonate and synthesis of PL was greater in livers of EFA deficient rats than in the control, corn oil fed animals. The results suggest a relationship of EFA metabolism to lipid transport. One of five papers to be published from the Symposium “Lipid Transport” presented at the AOCS Meeting, New Orleans, April 1970.     

Influence of medium-chain triglycerides on lipid metabolism in the rat

Lipid metabolism was studied in rats fed diets containing corn oil, coconut oil, or medium-chain triglyceride (MCT), a glyceride mixture containing fatty acids of 8 and 10 carbons in length. The ingestion of MCT-supplemented, cholesterolfree diets depressed plasma and liver total lipids and cholesterol as compared with corn oil-supplemented diets. In rats fed cholesterol-containing diets, plasma cholesterol levels were not influenced by dietary MCT, but liver cholesterol levels were significantly lower than in animals fed corn oil. In vitro cholesterol synthesis from acetate-1-¹⁴C was lower in liver slices of rats that consumed MCT than in similar preparations from corn oil-fed rats. Studies of fatty acid carboxyl labeling from acetate-1-¹⁴C and the conversion of palmitate-1-¹⁴C to C₁₈ acids by liver slices showed that chain-lengthening activity is greater in the liver tissue of rats fed MCT than in the liver of animals fed corn oil. The hepatic fatty acid desaturation mechanisms, evaluated by measuring the conversion of stearate-2-¹⁴C to oleate, was also enhanced by feeding MCT. Adipose tissue of rats fed MCT converts acetate-1-¹⁴C to fatty acids at a much faster rate than does tissue from animals fed corn oil. Evidence is presented to show that the enhanced incorporation of acetate into fatty acids by the adipose tissue of rats fed MCT represents de novo synthesis of fatty acids and not chain-lengthening activity. Data are also presented on the fatty acid composition of plasma, liver, and adipose tissue lipids of rats fed the different fats under study.     

Liver and serum lipids and lipoproteins of rats fed 5% L-lysine

Soybean protein and casein supplemented with 1% Arg were compared for their ability to prevent fatty livers caused by excess dietary Lys. The concentrations of serum lipids and lipoproteins of rats fed 5% Lys and having vatty livers were also compared with those of rats fed the identical diet but lacking fatty livers when killed. The total liver lipids, triglycerides and cholesterol of rats fed 15% casein +5% Lys were 3.9, 12.4 and 2 times control values, respectively. Rats fed 5% Lys +1% Arg or 5% Lys with 15% soybean protein had liver lipid concentrations similar to controls fed no supplemental Lys. Serum total lipids, triglycerides, cholesterol, phospholipids and free fatty acids also did not change, and serum ketone bodies were slightly elevated with Lys feeding whether the rats had fatty livers or not. The concentrations of circulating HDL were slightly depressed in all rats fed 5% Lys while LDL were significantly elevated, particularly in rats without fatty livers. Serum VLDL did not change with 5% dietary Lys. Overall, excessive dietary Lys caused fatty livers which were prevented by varying the diet or length of feeding. Excess Lys feeding altered lipoprotein metabolism shown by decreased serum HDL and a substantial elevation in LDL. The latter was more apparent when the fat accumulation in liver was less severe or absent. The data suggest that the fatty liver from Lys excess is probably unrelated to increased fat mobilization from storage, decreased fat oxidation or to a major block in the transport of triglycerides from the liver to the circulation.     

Influence of dietary fat on metabolism of (14-14C)erucic acid in the perfused rat liver. Distribution of metabolites in lipid classes

Two groups of rats were fed diets containing 20% by weight of either partially hydrogenated marine oil supplemented with sunflower seed oil (PHMO) or palm oil (PO) for 8 wk. Using a liver perfusion system, the effect of dietary long chain monoenoic fatty acids on the uptake and metabolism of [14-¹⁴C]erucic acid was studied. The perfusion times were 15 and 60 min, respectively. The two groups showed equal ability for erucic acid uptake in the liver but differed in the channeling of the fatty acids into various metabolic pathways. A higher metabolic turnover of 22∶1 in the PHMO livers relative to the PO livers was demonstrated by an increased recovery of total [¹⁴C]labeling in the triglyceride (TG) and phospholipid (PL) fractions, already evident after 15 min of perfusion. The chainshortening capacity was highest in the PHMO group, reflected by a higher [¹⁴C]18∶1 incorporation in both TG and PL, and increasing from 15 to 60 min of perfusion. The amount of [¹⁴C]18∶1 found in PL and TG after 60 min of perfusion of livers from rats fed PO corresponded to that shown for the PHMO group after 15 min. The PL demonstrated a discrimination against 22∶1 compared to TG, and, when available, 18∶1 was highly preferred for PL-synthesis. The total fatty acid distribution in the TG, as determined by gas liquid chromatography (GLC), reflected the composition of the dietary fats. In the total liver PL, 22∶1 and 20∶1 were present in negligible amounts, although the PHMO diet contained 12–13% of both 22∶1 and 20∶1. In the free fatty acid fraction (FFA), the major part of the radioactivity (≈80%) was [14-¹⁴C]erucic acid, and only small amounts of [¹⁴C]18∶1(<2%) were presents, even after 60 min of perfusion. The shortened-chain 18∶1 was readily removed from the FFA pool and preferentially used for lipid esterification.     

Metabolism of erucic acid in perfused rat liver: Increased chain shortening after feeding partially hydrogenated marine oil and rapeseed oil

The metabolism of [14-¹⁴C] erucic acid was studied in perfused livers from rats fed on diets containing partially hydrogenated marine oil or rapeseed oil for three days or three weeks. Control rats were given groundnut oil. Chain-shortening of erucic acid, mainly to 18∶1, was found in all dietary groups. In the marine oil and rapeseed oil groups, the percentage of chain-shortened fatty acids in very low density lipoproteins-triacylglycerols (VLDL-TG) exported from the liver increased after prolonged feeding. A similar increase was found in liver TG only with partially hydrogenated marine oil. This oil, rich intrans fatty acids, thus seemed to be more effective in promoting chain-shortening. The fatty acid composition of the secreted and stored TG differed both with respect to total fatty acids and radioactively labeled fatty acids, indicating that at least 2 different pools of TG exist in the liver. The lack of lipidosis in livers from rats fed dietary oils rich in 22∶1 fatty acids is discussed in relation to these findings. In conclusion, a discussion is presented expressing the view that the reversal of the acute lipidosis in the hearts of rats fed rapeseed oil or partially hydrogenated marine oils is, to a large extent, derived from the increased chain-shortening capacity of erucic acid in liver.     

Dietary arachidonic acid reduces fatty liver,increases diet consumption and weight gain in ethanol-fed rats

We fed young male Sprague-Dawley rats for 4 wk ad libitum liquid diets containing 34% of the calories as ethanol and 35% as fat with (AA+) and without (AA−) arachidonic acid (20∶4). Additional rats in the control groups were fed similar diets made isocaloric with dextrose with (CA+) and without (CA−) 20∶4. The liver triglyceride (TG) content of rats in the AA+ group was reduced ca. 3-fold over that of rats in the AA-group. The diet consumption and body wts of rats in the AA+ group were significantly greater than those of rats fed alcohol without the 20∶4 supplement (AA−). Also livers from rats in the AA+ group were as large as those from rats in control groups (CA+, CA−) and ca. twice as large as those from rats in the AA-group. The fatty acid composition of liver TG in rats fed the alcohol diet was similar to that of dietary fat. Levels of 20∶4 and docosatetraenoic acid (22∶4) in liver TG fatty acids from rats fed diets without arachidonate (AA−, CA−) were low (trace to 1.6%). After ingestion of arachidonic acid, 20∶4 increased to ca. 10% and 22∶4 to ca. 5%. The content of liver phospholipids was higher in livers of rats fed ethanol (AA−) than in those of controls (CA−). Presented at the ISF/AOCS World Congress, April 27-May 1, 1980, New York City.     

Hepatic lipid metabolism in experimental diabetes: III. Synthesis and utilization of triglycerides

Livers removed from normal rats, from alloxan diabetic rats maintained on insulin for two weeks (ADI+), and from insulin-treated diabetic rats from which insulin had been withdrawn two days before use (AD) were perfused in vitro with 120 mg (468 μmoles) palmitic acid-1-C¹⁴. Under these conditions, output of TG (triglyceride) was depressed in livers from ADI+ rats and was negligible with livers from AD animals. The total incorporation of C¹⁴ into perfusate TG paralleled the chemical measurments of TG output. The concentration of hepatic TG increased during perfusion of livers from normal or ADI+ rats but decreased during perfusion of livers from AD animals. A load of 120 mg of palmitic acid/3 hr was inadequate to maintain net accumulation of TG in livers from AD rats; furthermore it is implicit in this observation that the total load of NEFA (nonesterified fatty acid) perfusing livers from AD rats must be increased considerably to obtain a fatty liver. The total incorporation of C¹⁴ into hepatic TG and the specific activity of hepatic TG were depressed during perfusion of livers from AD rats. The production of ketone bodies by livers from AD animals was about five times the normal rates; the output of ketone bodies did not differ from results of other experiments (1) in which the load of palmitic acid added to the medium was varied from 0–80 mg. These observations were discussed with reference to mechanisms for ketogenesis and fatty liver in alloxan diabetes.     

Nutritional properties of medium-chain triglycerides

The biological effects of MCT (medium-chain triglycerides) differed from those of conventional fats, and certain of these suggested examination of the fatty acid composition and triglyceride structure of the adipose tissues and other organs of rats which were fed medium- or long-chain triglyceride mixtures with two levels of linoleic acid. Fatty acid compositions and TG patterns varied with the tissue, with the dietary fat, and with the level of linoleate in the diet. Increasing the latter resulted in the deposition of more linoleate at the expense of oleate and in the deposition of more of the dietary fatty acids. The percentage of completely saturated triglyc-erides (S₃), in adipose tissue with the higher linoleate supplement in the rats fed MCT, decreased in those fed LCT and was unchanged in the controls fed a fat-free diet. The increased deposition of the dietary fatty acids was more pronounced in the S₃ band. Supported by Grants U-1347 and U-1510 from the Health Research Council of the City of New York.     

Influence of medium-chain triglycerides on lipid metabolism in the chick

The effect of corn oil, coconut oil, and medium-chain triglyceride (MCT, a glyceride mixture consisting almost exclusively of fatty acids of 8 and 10 carbons in length) ingestion on lipid metabolism was studied in chicks. In chicks fed cholesterol-free diets, MCT ingestion elevated plasma total lipids and cholesterol and depressed liver total lipids and cholesterol when compared to chicks receiving the corn oil diet. As a consequence of the opposite effects of MCT ingestion on plasma and liver cholesterol and total lipids, the plasma-liver cholesterol pool was not altered. When cholesterol was included in the diets, dietary MCT depressed liver and plasma total lipids and cholesterol as compared with corn oil, consequently also lowered the plasmaliver cholesterol pool. The in vitro cholesterol and fatty acid synthesis from acetate-1-¹⁴C was higher in liver slices from chicks fed MCT than in those from chicks fed corn oil. The percentage of radioactivity from acetate-1-¹⁴C incorporated into the carboxyl carbon of fatty acids by liver slices was not altered by MCT feeding, indicating that the increased acetate incorporation represented de novo fatty acid synthesis. The conversion of palmitate-1-¹⁴C to C₁₈ acids was increased in liver of chicks fed MCT, implying that fatty acid chain elongating activity was also increased. Studies on the conversion of stearate-2-¹⁴C to mono- and di-unsaturated C₁₈ acids showed that hepatic fatty acid desaturation activity was enhanced by MCT feeding. Data are presented on the plasma and liver fatty acid composition of chicks fed MCT-, corn oil-, or coconut oil-supplemented diets. The principles of laboratory animal care, as promulgated by the National Society for Medical Research, were observed.     

Serum apolipoproteins B and A-I and naturally occurring fatty liver in dairy cows

Serum lipids and apolipoprotein (apo) B and A-I concentrations were determined in 164 dairy cows which had undergone liver biopsy in early lactation. The animals were divided into groups according to fatty liver severity on the basis of hepatic triglyceride content. The serum free fatty acid (FFA) concentration was higher in cows that developed fatty livers than in normal cows, and it correlated highly with liver triglycerides. Serum total cholesterol and triglyceride levels did not correlate with hepatic triglycerides. Both apo B and apo A-I levels were significantly decreased in fatty liver cows. In particular, apo B levels showed a strongly negative correlation with liver triglycerides. The present results suggest that hepatic apolipoprotein synthesis is impeded in fatty liver cows.     

Interrelations of linoleic acid with medium-chain and long-chain saturated triglycerides

1. Effects of medium-chain (C₆–C₁₂) saturated triglycerides (MCT) and long-chain (C₁₄–C₁₈) saturated triglycerides (LCT) with and without linoleic acid (LA) supplementation were studied on rats fed purified diets
2. With 2% linoleic acid rats fed MCT and LCT grew somewhat better than those on a low-fat diet with the same supplement. Without linoleic acid those fed MCT grew better, and those fed LCT grew worse than those on the corresponding low-fat diet. MCT seemed to decrease, and LCT to increase linoleic acid requirements.
3. In survival studies 14 out of 18 rats fed 20% MCT were alive after 2 years; of their controls fed 20% lard, 10 out of 19 survived.
4. Reproduction studies in females gave equally poor results on unsupplemented low-fat, MCT, and LCT diets regarding implantation, birth weight, and survival rate. The weaning weights of the young on MCT were however the highest. With 2% LA weaning weights were equally high with LCT and MCT but lower with low-fat diet.
5. In animals fed low-fat diets not supplemented with LA, low serum cholesterol was associated with high liver cholesterol. With MCT, serum values were higher and liver values were significantly lower. With unsupplemented LCT, serum and liver values were high. When the three diets were supplemented with 2% LA, there were no longer any differences in the serum levels and in the liver levels. Whether ar not the presence of some oleate in the MCT and LCT influenced the cholesterol results is not certain.
6. The differences in the effects of MCT and LCT are discussed.

     

Effect of ethanol on liver triglyceride concentration in fed and fasted rats

The effect of ethanol, given by gastric tube or by intraperitoneal injection, on the liver triglyceride concentration in fasted and ad libitum fed rats was investigated. Ethanol, independent of the route of administration, increased the liver triglyceride concentration in fasted rats during an 8 hr period but caused a much smaller increase in the ad libitum fed rats. The incorporation of intravenous injected³H-oleic acid into the liver triglycerides increased significantly after ethanol feeding in fasted but not in fed rats. Based upon this and the plasma free fatty acid concentrations, it is concluded that ethanol causes a marked increase in the utilization of plasma free fatty acids for synthesis of liver triglycerides in fasted but not in fed rats. It is suggested that this is part of the explanation for the different responses to ethanol of the liver triglyceride concentrations in fasted and fed rats.     

Reduction in triacylglycerol levels by fish oil correlates with free fatty acid levels inad libitum fed rats

Rats were fed (for 2 or 6 wk) purified diets containing lard (LD) or menhaden oil (MO) at two levels of dietary fat,i.e., at 11.5 and 20.8% of energy in the low fat (LF) and the medium fat (MF) diets, respectively. Following the diet period, rats were sacrificed after either an overnight fast or after uninterruptedad libitum feeding. The studies were designed to investigate the dependence of our previously reported effects of MO,i.e. the reduction of plasma free fatty acid (FFA) levels and accumulation of hepatic triacylglycerols, on the dietary fat concentration and the nutritional state of the animal at the time of sacrifice. Reductions in plasma triacylglycerol and cholesterol levels in MO-fed relative to LD-fed rats were observed under all conditions. FFA levels were consistently reduced by MO-feeding at both dietary fat concentrations, but only when blood was sampled fromad libitum fed rats. Under these conditions there was a significant positive relationship between plasma FFA and triacylglycerol concentrations. Reduction in plasma FFA levels may be an additional mechanism associated with the triacylglycerol-lowering effect of fish oil (FO). The LF and MF MO diets caused a rise in plasma glucose levels with no significant change in insulin concentration, indicating that the reduction of FFA by MO was not related to changes in insulin concentration or insulin sensitivity. The MO diets had no effect on skeletal muscle or epididymal adipose tissue lipoprotein lipase activity, demonstrating that catabolism of triacylglycerol-rich lipoproteins contributes little, if any, to the MO-dependent reductions of plasma triacylglycerol and FFA. The previously reported accumulation of hepatic triacylglycerols after high fat (HF; 30% of energy) MO-feeding was not observed with the LF or MF MO diets, suggesting that the apparent direct inhibition of triacylglycerol secretion by FO imposes a rate-limitation only when feeding HF diets.     

High-Fat Diet Alters Serum Fatty Acid Profiles in Obesity Prone Rats: Implications for In Vitro Studies

High‐fat diets (HFD) are commonly used in rodents to induce obesity, increase serum fatty acids and induce lipotoxicity in various organs. Invitro studies commonly utilize individual free fatty acids (FFA) to study lipid exposure in an effort to model what is occurring in vivo; however, these approaches are not physiological as tissues are exposed to multiple fatty acids in vivo. Here we characterize circulating lipids in obesity‐prone rats fed an HFD in both fasted and fed states with the goal of developing physiologically relevant fatty acid mixtures for subsequent in vitro studies. Rats were fed an HFD (60 % kcal fat) or a control diet (10 % kcal fat) for 3 weeks; liver tissue and both portal and systemic blood were collected. Fatty acid profiles and absolute concentrations of triglycerides (TAG) and FFA in the serum and TAG, diacylglycerol (DAG) and phospholipids in the liver were measured. Surprisingly, both systemic and portal serum TAG were ~40 % lower in HFD‐fed compared to controls. Overall, compared to the control diet, HFD feeding consistently induced an increase in the proportion of circulating polyunsaturated fatty acids (PUFA) with a concomitant decline in monounsaturated fatty acids (MUFA) and saturated fatty acids (SFA) in both serum TAG and FFA. The elevations of PUFA were mostly attributed to increases in n‐6 PUFA, linoleic acid and arachidonic acid. In conclusion, fatty acid mixtures enriched with linoleic and arachidonic acid in addition to SFA and MUFA should be utilized for in vitro studies attempting to model lipid exposures that occur during in vivo HFD conditions.     

Effects of low casein and fish oil on hyperlipidemia and proteinuria in nephritic rats

The effects of amino acid-fortified low casein and fish oil (FO) diets on hyperlipidemia and proteinuria were studied in rats with nephrotoxic serum nephritis. After an antiserum injection, rats were maintained for 14 d on four different experimental diets: a 20% casein diet containing corn oil (CO) or FO, or an 8% casein diet supplemented with cystine plus threonine containing CO or FO. The 8% casein diets reduced urinary protein excretion in nephritic rats without inducing severe growth retardation or fatty liver compared with the basal 20% casein diets. Both the 8% casein diet and the FO diet decreased serum cholesterol, triglyceride and phospholipid levels in nephritic rats, and nonesterified fatty acid levels were decreased by FO feeding. In nephritic animals, hepatic cholesterol synthesis was decreased by the 8% casein diets compared with the 20% casein diets, and tended to be reduced by FO feeding between groups at the same casein levels. No effect of diet was observed on fatty acid synthesis among the nephritic rats. FO administration to the nephritic animals suppressed fecal steroid excretion. While lipoprotein lipase activity was unchanged among the nephritic rats, hepatic triglyceride lipase activity was reduced by either the 8% casein or FO diet. The results suggest that the hypolipidemic action of low casein diets may, at least in part, be due to reduced hepatic cholesterol synthesis and suppressed triglyceride secretion from the liver. They also suggest that the hypolipidemic action of FO may, at least in part, be due to reduced hepatic cholesterol synthesis and decreased fatty acid mobilization from peripheral adipose tissue.     

脂肪酶促乌桕脂组分甘油解及其反应机理研究

Glycerolysis of Chinese vegetable tallow （CVT） fraction was investigated using a 1,3-specific lipase from Rhizopus arrhizus as catalyst. Based upon a binary gradient HPLC with an evaporative light-scattering detector （ELSD）, the contents of free fatty acids （FFA）, monoglycerides （MG）, diglycerides（DG） and triglycerides （TG） with their positional isomers during the glycerolysis were determined. The effects of water content and the ratio of glycerol to oil on the product distribution of glycerolysis were studied. Under the optimum reactant conditions： 250 units lipase per gram oil at 37℃ with 1：2 molar ratio of oil to glycerol in a solvent-free system, after 24 h reaction, the product consisted of 7.2% TG, 25.6% MG, 56.1% DG and 4.9% FFA （all by mass）. Furthermore, the mechanism of glycerolysis was discussed in detail.     

Erucic acid-induced alteration of cardiac triglyceride hydrolysis

Male Wistar rats were fed for 3 or 10 days with high erucic acid rapeseed oil (HEAR) or trierucate (TE). These diets produced increased myocardial triglyceride (TG) levels. Cardiac lipid accumulation was related to basal-and hormone- (glucagon, norepinephrine) stimulated lipolysis, determined as glycerol release, which proved to be enhanced in isolated, perfused hearts from HEAR- and TE-fed rats. Endogenous TG levels in isolated hearts from rats fed the stock and the sunflowerseed oil (SSO) diet were low and probably rate-limiting for tissue lipolytic activities. HEAR feeding of rats did not modify the rate of erucic acid (22∶1) oxidation in heart. Prolonged HEAR and TE feeding led to a decrease in the endogenous TG level, a process in which the increased rate of TG hydrolysis might play an important role. The enhanced breakdown of tissue TG in hearts from TE-and HEAR-fed rats was accompanied by an increased release of fatty acids into the coronary effluent. Erucic acid was a major constituent of the perfusate fatty acids. Evidence is presented that the site of the intracellular TG breakdown is associated with lysosomes, since a subcellular fraction enriched in acid lipase, N-acetyl-β-glucosaminidase and TG could be isolated from heart homogenates of TE-fed rats. Fatty acids seemed to be an important regulator of tissue lipase activity: palmitate inhibited glucagon-stimulated lipolysis, which suggests the tissue lipase is subject to product inhibition by fatty acids.