Erucic acid-induced alteration of cardiac triglyceride hydrolysis

Mustard oil and cardiovascular health: Why the controversy?

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in the United States (US) and worldwide. Among South Asians living in the US, ASCVD risk is four-fold higher than the local population. Cardioprotective dietary patterns necessitate replacement of dietary saturated fats with healthier oils such as canola, corn, olive, soybean, safflower, and sunflower oil. Mustard oil is a liquid oil that is low in saturated fat and is popular in South Asia.It contains a large proportion of erucic acid, a fatty acid associated with myocardial lipidosis in rodents. This evidence prompted the US Food and Drug Administration (FDA) to ban the use of mustard oil for cooking. However, Australia, New Zealand and the European Union (27 countries) have established upper limits for tolerable intake of mustard oil. In contrast mustard oil is one of the most popular cooking oils in Asia, particularly in India where it is recommended as a heart-healthy oil by the Lipid Association of India (LAI). The conflict between various guidelines warrants clarification, particularly because use of mustard oil in cooking is increasing among both Americans and Indian immigrants in the US, despite the FDA ban on human consumption of mustard oil. Hence, we endeavored to: (1) Review current evidence regarding potentially harmful versus beneficial effects of cooking with mustard oil, (2) Clarify the basis for disparities between the FDA ban on human consumption of mustard oil and dietary recommendations from the LAI and other groups, and (3) Provide practical suggestions for Indians and other South Asians who are accustomed to consuming mustard oil on ways to incorporate alternate heart-healthy oils (E.g. Canola, Olive, Sunflower, Soybean oil) in the diet while enhancing flavor and texture of food. A new FDA review is recommended on the safety limits of erucic acid because 29 countries have allow limited amounts of mustard oil (erucic acid) for human consumption and also because there are some health benefits that have been reported for mustard oil in humans.

Comparison of Erythrocyte Membrane Lipid Profiles between NAFLD Patients with or without Hyperlipidemia

Nonalcoholic fatty liver disease (NAFLD) and hyperlipidemia (HL) are common metabolic disorders due to overnutrition and obesity. NAFLD is often associated with hyperlipidemia. The aim of this study was to identify and compare the erythrocyte membrane lipids profile in NAFLD patients with or without HL. Methods. A total of 112 subjects (with similar age and body mass index) were divided into four groups: (1) normal controls, (2) NAFLD alone, (3) HL alone, and (4) NAFLD combined with HL (NAFLD + HL). Lipid was extracted from the erythrocyte membrane, and lipid profiles of subjects were analyzed by liquid chromatography mass spectrometry (LC-MS). Results. Data sets from 103 subjects were adopted for lipidomic analysis. Significant changes of lipid species were observed in patient groups, especially in the HL group and NAFLD + HL group. The HL group showed increased level of most lipid species, and decreased level of most lipid species was observed in the NAFLD + HL group. The weight percent of myristic acid, stearic acid, erucic acid, and docosahexaenoic acid also showed distinct variation between different groups. Conclusions. NAFLD, HL, and NAFLD + HL all had an impact on lipid profiling of the erythrocyte membrane. The influence of NAFLD alone is less important compared with HL. Some lipids should be highlighted because of their specific role in cell function and systemic metabolism.

On the mechanism of stimulation of peroxisomal beta-oxidation in rat heart by partially hydrogenated fish oil

By feeding rats a diet containing 20% (w/w) partially hydrogenated fish oil (PHFO), an apparent 6.3-fold increase in the cyanide insensitive palmitoyl-CoA-dependent NAD+ reduction was observed for the heart peroxisomal fractions. This finding was confirmed by a 7.6-fold and 7.9-fold increase in the specific activity of fatty acyl-CoA oxidase, with palmitoyl-CoA and erucoyl-CoA as the substrates, respectively. Immunoblots after SDS-PAGE of rat heart peroxisomal fractions revealed a 12-fold increase in the 52 kDa fatty acyl-CoA oxidase (FAO) subunit for PHFO-fed rats, whereas the 72 kDa subunit of FAO and several other peroxisomal proteins (including the trifunctional enzyme delta 3,delta 2-enoyl-CoA isomerase, 2-enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase) increased only 2- to 3-fold. The increase in the 52 kDa subunit was markedly higher than the increase in the steady-state mRNA level of FAO (2.0-fold), and is most likely caused by a rather selective stabilization of the 52 kDa FAO subunit. Interestingly, PHFO feeding caused a larger increase in fatty acyl-CoA oxidase and catalase activities than did clofibrate in the heart. The opposite was the case in the liver, especially for fatty acyl-CoA oxidase. Rats fed a semisynthetic diet containing 6% (w/w) erucic acid (C22:1(n - 9), cis) or brassidic acid (C22:1(n - 9), trans) revealed a 5-fold and 3-fold increase vs. the control (pellet fed) rats in heart FAO activity, respectively, as well as a proportional and selective increase in the specific content of 52 kDa FAO subunit. Thus, the relatively high content of C22 monoene fatty acids appears to be one of the main factors responsible for the increase in rat heart peroxisomal FAO activity during PHFO feeding. However, the PHFO diet increased the heart peroxisomal FAO activity more than diets containing a similar amount of C22:1 in the form of erucic or brassidic acid, and additional compounds of lipid or a more xenobiotic nature may also play a role. SDS-PAGE electrophoresis of highly purified rat liver peroxisomes revealed that the specific content of polypeptides with mobilities corresponding to that of the beta-oxidation enzyme system, increased by a factor of < 2 as a result of feeding the PHFO diet. The 3.1-fold increase in cyanide insensitive palmitoyl-CoA-dependent NAD+ reduction was comparable to the increase (4.1-fold) in the acyl-CoA oxidase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

1H-NMR spectroscopy can accurately quantitate the lipolysis and oxidation of cardiac triacylglycerols

Triacylglycerol metabolism in isolated, perfused hearts from rats fed a diet containing 20% rapeseed oil (RSO) was studied using 1H-NMR spectroscopy. RSO-induced elevation in cardiac triacylglycerols is associated with an increase in the peak area of fatty acid 1H-NMR resonances. The ratio of methyl, gamma-methylene or methylene protons adjacent to a carbon-carbon double bond to the number of methylene protons in these hearts measured by 1H-NMR spectroscopy gives values similar to those derived from previously reported chemical analyses. In addition, the triacylglycerol content of these hearts determined by chemical analysis directly correlates with their content of 1H-NMR visible fatty acid resonances. This quantitative relationship allows the real-time measurement of the rates of cardiac triacylglycerol lipolysis using 1H-NMR spectroscopy. Rates of triacylglycerol lipolysis measured using 1H-NMR spectroscopy are similar to those previously measured by chemical methods. Triacylglycerol lipolysis measured using 1H-NMR spectroscopy occurs at a significantly faster rate in hearts perfused in the presence or absence of glucose when compared to hearts perfused with glucose and acetate or medium-chain fatty acids. Finally, the rate of triacylglycerol lipolysis in glucose perfused hearts is linearly related to work output. These results demonstrate that 1H-NMR spectroscopy can accurately quantitate triacylglycerol content and metabolism in the rapeseed oil-fed rat model. 1H-NMR spectroscopic or imaging techniques may be useful in the real-time evaluation of cardiac triacylglycerol content and metabolism.

Accumulation and excretion of long-chain acylcarnitine by rat hearts; studies with aminocarnitine

During Langendorff perfusion of rat heart with aminocarnitine, long-chain acylcarnitine (LCAC) accumulates in heart cells, from which it is excreted by the heart. The heart function remains intact during this process. The accumulation of LCAC can be inhibited by the simultaneous addition of an inhibitor of the outer membrane carnitine palmitoyl-coenzyme A transferase (CPT-1), indicating that aminocarnitine is a specific inhibitor of the inner membrane isoenzyme (CPT-2). LCAC accumulation is associated with glycogen depletion. After 60 min perfusion with aminocarnitine, electron microscopy shows large multilamellar lipid vesicles, especially in cardiomyocytes, which are depleted in glycogen granula. Multilamellar lipid vesicles are also found in the blood vessels. Extraction of the perfusate shows the presence of LCAC, fatty acid and phosphatidylethanolamine. Morphological analysis with freeze fracturing and thin sectioning furthermore reveals that the sarcolemma is not deteriorated during the export of LCAC to the coronary vessels. Since cardiac structures and functions are intact, LCAC alone is not the clue for ischemic damage. Therefore the present work supports the hypothesis that acidosis rather than LCAC is of primary importance to ischemic damage.

Involvement of lysosome-like particles in the metabolism of endogenous myocardial triglycerides during ischemia/reperfusion. Uptake and degradation of triglycerides by lysosomes isolated from rat heart

The hormonal regulation and enzymatic basis of endogenous lipolysis in heart are not yet completely elucidated. The lysosomal fraction from rat heart appeared to be markedly enriched in triglycerides and a significant reduction in triglycerides in this fraction was found after prolonged perfusion or stimulation of lipolysis with glucagon. The enhanced rate of lipolysis, measured as glycerol release from the isolated perfused rat heart, was abolished 10-15 min after continuous glucagon administration. Omission of glucagon for another 60 min restored the ability of glucagon to stimulate lipolysis, indicating the limited availability of endogenous triglycerides and the presence of a transfer-system for triglycerides from a non-metabolically active pool to a metabolically active pool. The enhanced lipolysis induced by low-flow ischemia was found to be inhibited by the lysosomotropic agent methylamine (5 mM). Methylamine-perfusion during low-flow ischemia was accompanied by an increased recovery of myocardial triglycerides in the lysosomal fraction. The possible role of lysosome-like particles in myocardial triglyceride homeostasis was further investigated by studying the kinetics of uptake and degradation of labeled triglycerides by membrane-particles recovered in the subcellular fraction enriched with lysosomal marker enzymes. It appeared that isolated lysosomal membranes take up added triglycerides at an average rate of 30 nmoles/min/g protein. The bulk of these triglycerides taken up is stored whereas 20% is degraded to diglycerides and free fatty acids. More than 90% of the free fatty acids formed were released from the lysosomes into the supernatant. The uptake and degradation of triglyceride-filled liposomes by isolated myocardial lysosomes was inhibited during incubation with methylamine (5 mM). On the other hand, a lowering of pH during in vitro incubation increased the rate of uptake and degradation of added triglycerides by isolated lysosomes. These results indicate that lysosomes or lysosome-like particles are involved in the enhanced lipolysis during myocardial ischemia.

Increased liver lipase activity in rats with essential fatty acid deficiency

Liver lipase activity was measured in EFA-deficient rats (long-term) and in control rats and rats fed an EFA-deficient diet for two weeks (short-term). Liver lipase activity was significantly enhanced by EFA deficiency, both in long-term and short-term experiments. The enhanced liver lipase activity could be normalized by feeding these rats normal laboratory chow for 14 days. Since during EFA deficiency prostaglandin synthesis is impaired, the possible involvement of prostaglandins in the observed changes in liver lipase activity during EFA deficiency was studied. Administration of the prostaglandin synthesis inhibitor indomethacin (5 mg/kg body weight, i.p.) to normally fed rats for two days led to an increase of liver lipase activity. Prostaglandin E2 was found to inhibit the secretion of liver lipase activity by freshly isolated parenchymal liver cells in vitro. These results indicate that the increase in liver lipase activity during EFA deficiency may be due to an impairment of the prostaglandin synthesis.

Enhanced lipolysis of myocardial triglycerides during low-flow ischemia and anoxia in the isolated rat heart

We studied lipolysis in the isolated rat heart, measured as glycerol release during anoxia, low-flow ischemia and subsequent reperfusion. It was found that the rate of lipolysis was enhanced during ischemia/anoxia while the lipase activities in tissue extracts involved in the myocardial lipolysis and the amount of triglycerides were not affected. This indicates the dominant occurrence of a lipolysis-reesterification principle in ischemic and anoxic tissue. A common observation of ischemia/anoxia is an increase in the tissue NADH/NAD+ ratio. Therefore we investigated the effect of lactate and malate, both of which enhance the tissue redox state on myocardial lipolysis. Perfusion in the presence of lactate (10 mM) and malate (10 mM) both stimulated myocardial lipolysis by about five times. This suggests that the rate of reesterification of product fatty acids to triglycerides, which is determined by the NADH/NAD+ ratio, because of the increased formation of glycerol 3-phosphate from dihydroxy acetone phosphate, plays an important role in the regulation of lipolysis. The existence of triglyceride-fatty acid-triglyceride cycle is discussed.

Testing a short-term feeding trial to assess compositional and histopathological changes in hearts of rats fed vegetable oils

Male, female and castrated rats, three wk of age, were fed a low-fat diet for 14 wk followed by high-fat diets (20% by weight) for one wk containing graded levels of erucic acid from 1 to 50%, to evaluate the effect of short-term feeding and interaction of male sex hormones on formation of heart lesions. Some rats within each group were returned to the low-fat diet for one wk after the test period. For comparison, one group of three-wk-old male rats was fed the high fat 50% erucic acid diet for 15 wk. Erucic acid depressed growth rate and food consumption and increased cardiac lipidosis and triglycerides proportional to the erucic acid content of the diet. There were no sex differences, and the effects disappeared once rats were returned to the low-fat diet for one week. There was a significance (P less than 0.05) in the incidence of myocardial necrosis among male rats fed increased levels of erucic acid for one week, but the response was not linear to the increase in dietary erucic acid. Furthermore, the response was much less than in males fed the 50% erucic acid diet continually for 15 weeks. These results suggest that the short-term model is not a suitable substitute for the long-term feeding trial to test the cardiopathogenicity of a vegetable oil. The significantly lower incidence in myocardial lesions in female and castrated male rats compared with male rats suggests involvement of sex hormones.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tumor necrosis factor (TNF) on lipolytic activities of rat heart

Tumor Necrosis Factor (TNF) inhibits lipoprotein lipase activity in cultured myocytes and in the Langendorff rat heart after 3 h perfusion with TNF of glucocorticoid-pretreated rats. TNF acutely stimulates glyc(ogen)olysis and concomitantly endogenous lipolysis. The latter was significantly increased only when rats had been pretreated with glucocorticoid or fed a trierucate-rich diet. Under these conditions, contractile activity of the Langendorff hearts was acutely increased by TNF. The mechanism of the acute increase of contractile function and the accompanying increased glycolytic and lipolytic activities, by TNF, may be explained by increased cytosolic Ca2+ and cAMP levels.

Cardiac lipase: effect of ethanol and stress

The effect of ethanol (0, 0.5, 3.0 g/kg) and restraint stress on cardiac neutral (NL) and lipoprotein (LPL) lipase was studied. Although ethanol (3.0 g/kg) or stress decreased NL and increased LPL, ethanol pretreatment significantly attenuated stress induced changes in both enzymes. These results support previous research on the protective effects of ethanol and may be one mechanism through which ethanol may alter susceptibility to certain forms of heart disease.

Synthesis, storage and degradation of myocardial triglycerides

In the mammalian myocardium, an active triglyceride synthesis pathway is operating, (re)esterifying activated fatty acids from endogenous or exogenous sources, with the glycolytically derived three-carbon intermediates dihydroxyacetone-phosphate and glycerol-3-phosphate by the so-called Kennedy pathway. The seven enzymes of triglyceride synthesis are membrane bound and located at the sarcoplasmic reticulum. The first enzyme in the glycerol-3-phosphate pathway, glycerol-3-phosphate acyltransferase, is proposed to be rate limiting for triglyceride formation. This microsomal enzyme is regulated by phosphorylation (inactiycation)-dephosphorylation (activation) coupled to the beta-receptor--adenyl cyclase--protein kinase system. Additional regulatory steps in triglyceride formation are the reactions catalyzed by the microsomal phosphatidic acid phosphatase and diglyceride acyltransferase. Intracellular triglycerides occur as free floating cytosolic droplets, membrane-bound particles and lipid-filled lysosomes. No consensus exists about the metabolically active portion of myocardial triglycerides. Various lipases have been proposed to be involved in endogenous lipolysis: the lysosomal acid, microsomal and soluble neutral triglyceride, intracellular lipoprotein lipases and the microsomal di- and monoglyceridase. It has been acknowledged that the bulk of the intracellular neutral lipase represents the precursor of vascular lipoprotein lipase. The presence of a neutral lipase, as distinct from lipoprotein lipase, in the rat heart was recently advocated. Endogenous lipolysis is a hormone-sensitive process. Hormone-sensitivity may involve direct alteration of enzyme activity by protein phosphorylation-dephosphorylation but is also dependent on the removal rate of product fatty acids, since feedback inhibition is a common property of all lipases in the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein lipases and stress hormones: studies with glucocorticoids and cholera toxin

The intravenous injection of cholera toxin in rats 17 h prior to experimentation results in increased levels of insulin and corticosterone in the blood. This is accompanied by a rise in lipoprotein lipase activity in muscle and a decrease in adipose tissue. Pre- and postheparin blood levels of the enzyme are increased, representing the higher overall muscle activity. Hepatic lipase is decreased by cholera toxin treatment. These enzyme changes are accompanied by increased levels of non-esterified fatty acids, ketone bodies and unesterified cholesterol in the blood, whereas triacylglycerol levels are lowered. The lipoprotein triacylglycerol secretion is not affected by cholera toxin, suggesting increased triacylglycerol removal from the blood. On the other hand the unesterified cholesterol removal may be decreased due to the decreased hepatic lipase activity. Administration of excess glucocorticoid 2 days prior to blood and tissue sampling also resulted in a rise in lipoprotein lipase, a decrease in hepatic lipase activity and an increase of non-esterified fatty acids. In contrast to the effect of cholera toxin, the triacylglycerol levels were increased. Adrenalectomy, whether by inhibition of 11-beta-steroid hydroxylase or by surgical intervention, did not abolish the choleratoxin effects. It is concluded that corticosterone increase is not essential to the cholera toxin effects. Corticosterone itself probably causes an increase of cyclic AMP and/or Ca2+ levels, as is discussed.

Studies on the involvement of lipolytic enzymes in endogenous lipolysis of the isolated rat heart

Rat hearts were depleted in vivo from both the heparin-releasable lipoprotein lipase and heparin-resistant tissue neutral triacylglycerol lipase activity by treatment of the animals with cycloheximide (2 mg/kg body weight), intraperitoneally injected 2.5 and 5 h prior to perfusion. The tissue acid lipase, mono- and diacylglycerol lipase activities were not affected by cycloheximide-induced inhibition of protein synthesis. Myocardial basal and glucagon-stimulated lipolysis, determined by the rate of glycerol production and release from the isolated hearts, was not significantly different in control and cycloheximide-treated rats. Tissue triacylglycerols were recovered with the highest relative specific distribution in the lysosomal fraction isolated from heart homogenates. Upon prolongation of the perfusion-duration the relative specific distribution of triacylglycerols in the lysosomal fraction decreased. In addition, the specific lysosomal triacylglycerol content (micrograms/mg protein) dropped significantly, indicating an important role of lysosomes in myocardial triacylglycerol turnover. Our data strongly suggest that the heparin-resistant neutral triacylglycerol lipase activity may not be the only determinant of endogenous lipolysis in the isolated rat heart and indicate that lipolysis may additionally be mediated by the lysosomal, acid lipase in concert with the microsomal mono-and diacylglycerol lipase.

Characterization of mono-, di- and triacylglycerol lipase activities in the isolated rat heart

The lipolytic activities of heart tissue towards full and partial acylglycerols were characterized. Tissue lysosomal, acid lipase activity (pH 4.8) was inhibited by high salt, protamine sulfate, NaF, MgATP, Triton X-100, serum and the esterase-inhibitor diethylparanitrophenyl phosphate. The tissue neutral triacylglycerol lipase activity (pH 7.4) was recovered predominantly in the microsomal and soluble fractions and exhibited essentially identical properties towards activators (serum, apolipoprotein C-II) and reagents (NaCl, Triton X-100, NaF, MgATP and diethylparanitrophenyl phosphate) relative to vascular lipoprotein lipase, except for protamine sulfate which increased the serum-stimulated neutral triacylglycerol lipase activity. Triacylglycerol hydrolysis at acid pH was incomplete, whereas at neutral pH full hydrolysis occurred. Myocardial mono- and diacylglycerol lipase activities, with pH optima of 8.0 and 7.4, respectively, were recovered in the microsomal fraction. They differed immunologically from neutral lipase and lipoprotein lipase and did not bind to heparin-Sepharose 4B. They were kinetically different, partially inhibited by NaCl and differentially affected by protamine sulfate. NaF, Triton X-100 and diethylparanitrophenyl phosphate. Our data suggest that endogenous hydrolytic activity against full and partial acylglycerols is mediated by separate enzymes.

Protection by acyl-carnitines and phenylmethylsulfonyl fluoride of rat heart subjected to ischemia and reperfusion

Perfusion of rat hearts according to the Langendorff technique with micromolar concentrations of palmitoylcarnitine or millimolar concentrations of phenylmethylsulfonyl fluoride protect the heart from deterioration by reperfusion after total-ischemia. This is based on the retention of the cytosolic enzymes determined (lactate dehydrogenase, glycogen phosphorylase and glycogen synthase) and of myoglobin, as well as on the resumption of contractile activity. Palmitoylcarnitine, like phenylmethylsulfonyl fluoride, could protect through plasma membrane stabilization, since more hydrophilic compounds had no effect.

Localization and function of myocardial lipolysis

Mobilization of triacylglycerol stored in heart cells is accomplished by the combined action of lysosomal (acid) lipase and microsomal monoacylglycerol lipase or carboxylesterase. Non(heparin)-releasable neutral or alkaline lipase is similar to non(readily)-releasable lipoprotein lipase (LPL). The enzyme is mainly localized extracellularly. Non(readily)-releasable LPL probably represents LPL in caveola or vacuolae of vascular endothelium and/or LPL on myocardial interstitium. It contributes to the uptake of lipoprotein constituents in heart cells. Glycerol, an endproduct of lipolysis, is not a reliable marker for the net mobilization of lipid stored in heart cells. It is formed both intra- and extracellularly, and does not reflect the rate of oxidation of part of free fatty acids formed.

Regulation of liver lipase. I. Evidence for several regulatory sites, studied in corticotrophin-treated rats

The activity of liver lipase, an enzyme that can be released from the liver by heparin, varies under several hormonal conditions. The site(s) at which regulation of the enzyme activity may occur was investigated in vitro. As a model, rats were used which had been treated with a corticotrophin analogue, to induce hypercortisolism, a condition in which liver lipase activity is lowered. Lipases isolated from heparin-containing perfusates of livers from ACTH or control rats were identical with respect to heat stability and specific activity as determined by immunotitration and binding to isolated non-parenchymal liver cells, indicating that the enzyme structure was not affected by the treatment. The secretion of liver lipase by isolated parenchymal liver cells was studied. During incubation of parenchymal cells derived from ACTH rats, less enzyme activity was found to be secreted when compared with hepatocytes isolated from control rats (ACTH rats, 2.30 +/- 0.2 mU/10(6) cells; control rats, 3.3 +/- 0.3 mU/10(6) cells). Liver lipase partially purified from control rats could be bound specifically to saturation by non-parenchymal cells, isolated from ACTH or control rats. Non-parenchymal cells from ACTH rats bound less lipase activity (29 mU/mg cell protein) than cells from control rats (50 mU/mg cell protein). This reduction in binding capacity seems to be due to a diminished number of binding sites, since the affinity based on Scatchard analysis and half-maximal binding was not different. These results suggest that the lowered liver lipase activity found during hypercortisolism may be due to an impaired synthesis and/or secretion of the enzyme by the parenchymal cells and to a reduced binding capacity of the non-parenchymal cells for liver lipase.

The effect of excess (acyl) carnitine on lipid metabolism in rat heart

During Langendorff perfusion of rat hearts with Intralipid, the resulting fat accumulation in the hearts can be inhibited by the addition of 5 mM L-carnitine to the perfusion medium. The mechanism of this phenomenon is probably the inhibition of lipid accumulation in the heart by acylcarnitine rather than stimulation of fatty acid oxidation by excess carnitine addition. Palmitoylcarnitine was found to stimulate trioleoylglycerol hydrolysis at neutral pH in heart homogenates, when it was tested in the presence of relatively much protein. At higher palmitoylcarnitine: protein ratios, however, lipolysis was inhibited. Inhibition of lipolysis was also observed in lipid-enriched hearts during retrograde perfusion by the addition of 5 mM carnitine suggesting that also in intact heart long-chain acylcarnitine excess may inhibit lipolytic activity.

Intracellular origin and regulation of endogenous lipolysis in rat heart

The rate of glycerol release from isolated, perfused rat hearts was used as an index for endogenous lipolysis. Pharmacological and metabolic interventions were performed in order to obtain information about the intracellular site of action and regulation of tissue triglyceride (TG) hydrolysis in heart. It proved that endogenous lipolysis probably is of lysosomal origin. The activity of tissue lipolysis is dependent on the amount of stored TG and on the contractile status of the heart and is subject to feedback inhibition by production of fatty acids. Evidence is presented that Ca2+ plays an important role in the regulation and hormonal modification of lipolysis since all mechanisms inducing alterations in Ca2+ homeostasis influence myocardial lipolysis. Our experimental data and current knowledge are discussed in the light of a new hypothesis which relates intracellular Ca2+ and the rate of fatty acid utilization to the activity (activities) of tissue lipase(s). It is proposed that inhibition of endogenous lipolysis may be the main mechanism of action of antiarrhythmic agents (lidocaine, quinidine, phenothiazines).

Dual localization of lipoprotein lipase in rat heart. Its relationship to chylomicron degradation

Rat hearts were perfused retrogradely using a modified technique that allows the separate collection of coronary (Qrv) and interstitial (Qi) effluents. Evidence is presented that Qrv contains products from the coronary vasculature and that Qi contains products arising from cardiac myocytes. Heparin perfusion of rat hearts led to a release of lipolytic activity in Qrv and Qi which was characterized as lipoprotein lipase (LPL). The relative amounts of LPL released in Qrv and Qi were dependent on the feeding condition of the rat. A high LPL activity was recovered from Qrv of fasted rats, and Qi was high in LPL during feeding. On perfusion of hearts with [3H]cholesterol-labeled chylomicrons, the tissue uptake of cholesterol was highest in the fasted state, whereas release of radioactivity in Qi was predominant in the fed state. This radioactivity in Qi appeared to be associated with chylomicron degradation products (remnants and surface fragments). Our experiments indicate that cholesterol uptake during chylomicron breakdown is inhibited in the fed state, and the relationship between myocyte LPL activity and interstitial formation of chylomicron degradation products suggests a role for the myocyte LPL in lipoprotein metabolism.