Heart Carnitine Research Articles

Differential effects of the chronic and acute zinc exposure on carnitine composition, kinetics of carnitine palmitoyltransferases I (CPT I) and mRNA levels of CPT I isoforms in yellow catfish Pelteobagrus fulvidraco

The present study is conducted to determine the effect of acute and chronic zinc (Zn) exposure on carnitine concentration, carnitine palmitoyltransferases I (CPT I) kinetics, and expression levels of CPT I isoforms in liver, muscle and heart of yellow catfish Pelteobagrus fulvidraco. To this end, yellow catfish are subjected to chronic waterborne Zn exposure (0.05mgZnL−1, 0.35mgZnL−1 and 0.86mgZnL−1, respectively) for 8weeks and acute Zn exposure (0.05mgZnL−1 and 4.71mgL−1Zn, respectively) for 96h, respectively. Reduced Michaelis–Menten constants (Km) and maximal reaction rates (Vmax) values in liver and muscle are observed in fish exposed to chronic Zn concentration. In contrast, Vmax and Km values in heart increase with increasing Zn concentration. Chronic Zn exposure also significantly influences the contents of free carnitine (FC), total carnitine (TC) and acylcarnitine (AC) in liver and heart, but not in muscle. The acute Zn exposure significantly increases FC, AC, TC contents in liver and muscle, but reduces their contents in heart. The chronic and acute Zn exposure influences the mRNA levels of four CPT I isoforms (CPT Iα1b, CPT Iβ, CPT Iα2a and CPT Iα1a) in liver, muscle and heart. Furthermore, correlations are observed in the mRNA levels between CPT I isoforms and Km, and between isoforms expression and activity of CPT I. Thus, chronic and acute Zn exposure shows differential effects on carnitine content, CPT I kinetics and mRNA levels of four CPT I isoforms in yellow catfish, which provides new mechanism for Zn exposure on lipid metabolism and also novel insights into Zn toxicity in fish.

Comparative study on the kinetic behaviour of carnitine palmitoyltransferase I between Javelin gobySynechogobius hasta(carnivorous) and grass carpCtenopharyngodon idella(herbirovous)

Up to date, the carnitine palmitoyltransferase (CPT) system in fish nutrition receives little attention. The present study compared CPT I kinetic behaviour of Synechogobius hasta (carnivorous) and Ctenopharyngodon idella (herbivorous). The optimal conditions (temperature, incubation time, mitochondrial protein concentration and pH) for maximum CPT I activity showed no significant difference between S. hasta and C. idella. CPT I activities in S. hasta were significantly higher than those in C. idella. Affinity constants (Km) for carnitine in liver, heart, white muscle and spleen of S. hasta were significantly higher than those in C. idella. Km for palmitoyl-CoA in liver and heart of S. hasta were significantly higher than those in C. idella. Vmax for carnitine and palmitoyl-CoA in S. hasta tended to be higher than those in C. idella. Catalytic efficiencies (Vmax/Km) for carnitine in liver, white muscle and spleen of C. idella were significantly higher than those in S. hasta. Vmax/Km values for palmitoyl-CoA in liver and heart of C. idella were higher than those in S. hasta. Our study demonstrated that the lower catalytic efficiency for carnitine in liver of S. hasta indicated that the fish showed a low capacity for energy generation through β-oxidation of long-chain fatty acids, which easily caused fatty liver syndrome. This is the first study in which, by using carnitine and palmitoyl-CoA as the substrates, the complete kinetic characterization of CPT I in fish has been described, which increases our knowledge about lipid metabolism and its critical role in lipid utilization in fish.

Dietary L-arginine supplementation reduces abdominal fat content by modulating lipid metabolism in broiler chickens

This study investigated the effects of different levels of dietary L-arginine (L-Arg) supplementation on the abdominal fat pad, circulating lipids, hepatic fatty acid synthase (FAS) gene expression, gene expression related to fatty acid β-oxidation, and the performance of broiler chickens. We tested whether the dietary L-Arg levels affected the expression of genes related to lipid metabolism in order to reduce body fat deposition. A total of 192 broiler chickens (Cobb 500) aged 21 days with an average BW of 920 ± 15 g were randomly assigned to four groups (six broilers per replicate and eight replicates per treatment). The control group was fed a basal diet, whereas the treatment groups were fed basal diets supplemented with 0.25%, 0.50%, or 1.00% L-Arg for 3 weeks. The average daily feed intake, average daily gain and feed : gain ratio were not affected by the dietary L-Arg levels. However, chickens supplemented with L-Arg had lower abdominal fat content, plasma triglyceride (TG), total cholesterol (TC) concentrations, hepatic FAS mRNA expression and increased heart carnitine palmitoyl transferase1 (CPT1) and 3-hydroxyacyl-CoA dehydrogenase (3HADH) mRNA expression. These findings suggest that the addition of 0.25% L-Arg may reduce the plasma TC concentration by decreasing hepatic 3-hydroxyl-3-methylglutaryl-CoA reductase mRNA expression. This may lower the plasma TG and abdominal fat content by suppressing hepatic FAS mRNA expression and enhancing CPT1 and 3HADH (genes related to fatty acid β-oxidation) mRNA expression in the hearts of broiler chickens.

Systematic Evaluation of Key L-Carnitine Homeostasis Mechanisms during Postnatal Development in Rat

BackgroundThe conditionally essential nutrient, L-carnitine, plays a critical role in a number of physiological processes vital to normal neonatal growth and development. We conducted a systematic evaluation of the developmental changes in key L-carnitine homeostasis mechanisms in the postnatal rat to better understand the interrelationship between these pathways and their correlation to ontogenic changes in L-carnitine levels during postnatal development.MethodsmRNA expression of heart, kidney and intestinal L-carnitine transporters, liver γ-butyrobetaine hydroxylase (Bbh) and trimethyllysine hydroxylase (Tmlh), and heart carnitine palmitoyltransferase (Cpt) were measured using quantitative RT-PCR. L-Carnitine levels were determined by HPLC-UV. Cpt and Bbh activity were measured by a spectrophotometric method and HPLC, respectively.ResultsSerum and heart L-carnitine levels increased with postnatal development. Increases in serum L-carnitine correlated significantly with postnatal increases in renal organic cation/carnitine transporter 2 (Octn2) expression, and was further matched by postnatal increases in intestinal Octn1 expression and hepatic γ-Bbh activity. Postnatal increases in heart L-carnitine levels were significantly correlated to postnatal increases in heart Octn2 expression. Although cardiac high energy phosphate substrate levels remained constant through postnatal development, creatine showed developmental increases with advancing neonatal age. mRNA levels of Cpt1b and Cpt2 significantly increased at postnatal day 20, which was not accompanied by a similar increase in activity.ConclusionsSeveral L-carnitine homeostasis pathways underwent significant ontogenesis during postnatal development in the rat. This information will facilitate future studies on factors affecting the developmental maturation of L-carnitine homeostasis mechanisms and how such factors might affect growth and development.

Sex steroid hormones affect carnitine concentrations of blood and organs in rats

Males and females exhibit different rates of central obesity, cardiovascular disease and diabetes. Furthermore, altered concentrations of sex steroid hormones can lead to altered rates of these diseases in the afflicted populations, suggesting these hormones can affect metabolism and, in the long term, have clinical repercussions. Carnitine, an amino acid derivative involved in fat oxidation, was used to examine differences in metabolism between the sexes based on changes in the hormonal milieu. Rats (178 males and 176 females) were administered one of the following treatments: estradiol injection, testosterone injection, castration, and hypophysectomy. Total carnitine was measured in plasma, liver, heart, muscle, and epididymis. In both sexes, estradiol appears to increase liver carnitine while decreasing plasma, muscle and heart carnitine; testosterone, on the other hand, increases plasma, muscle and heart carnitine. In males, estradiol decreases and testosterone increases epididymis carnitine. Hypophysectomy decreased carnitine in all compartments for males and all compartments except for heart and muscle in females. This study demonstrates that estradiol, testosterone and the pituitary gland greatly influence carnitine concentrations of the body and are key to the observed sex differences in carnitine.

Antioxidant activity of propionyl- l-carnitine in liver and heart of spontaneously hypertensive rats

Oxidative stress plays an important role in arterial hypertension and propionyl- l-carnitine (PLC) has been found to protect cells from toxic reactive oxygen species. In this work, we have evaluated the antioxidant capacity of chronic PLC treatment in spontaneously hypertensive rats (SHR) by measuring the activity of antioxidant enzymes and the lipid peroxidation in liver and cardiac tissues. The activity of glutathione peroxidase was decreased in liver and cardiac tissues of SHR when compared with their normotensive controls, Wistar– Kyoto (WKY) rats, this alteration being prevented by PLC treatment. Glutathione reductase activity was increased in hypertensive rats and no effect was observed after the treatment. No significant changes in superoxide dismutase activity were observed among all experimental groups. Liver of hypertensive rats showed higher catalase activity than that of normotensive rats, and PLC enhanced this activity in both rat strains. Thiobarbituric acid reactive substances, determined as a measure of lipid peroxidation, were increased in SHR compared with WKY rats, and PLC treatment decreased these values not only in hypertensive rats but also in normotensive ones. The content of carnitine in serum, liver and heart was higher in PLC-treated rats, but PLC did not prevent the hypertension development in young SHR. In addition, triglyceride levels, which were lower in SHR than WKY rats, were reduced by chronic PLC treatment in both rat strains. These results demonstrate: i) the hypotriglyceridemic effect of PLC and ii) the antioxidant capacity of PLC in SHR and its beneficial use protecting tissues from hypertension-accompanying oxidative damage.

Carnitine depletion in rat pups from mothers given mildronate: A model of carnitine deficiency in late fetal and neonatal life

Mildronate (3-(2,2,2,-trimethylhydrazinium)propionate), is a butyrobetaine analogue that is known to inhibit γ-butyrobetaine hydroxylase, the enzyme catalyzing the last step of carnitine biosynthesis. When administered to adult rats it determines a systemic carnitine deficiency and may therefore serve as an animal model for human carnitine depletion. The aim of this study was to evaluate the effect of mildronate administration to pregnant and lactating rats on tissue carnitine concentrations in 4- and 13-day-old rat pups. At 14 days of gestation female rats began to receive mildronate in the diet (200 mg/kg/d) and this continued for entire lactation period. Mildronate treatment determined a large reduction of carnitine levels in the milk of lactating dams. Because organ carnitine concentrations in neonatal rats are directly related to dietary supply, pups from mildronate group had significantly depleted levels of total carnitine in serum, heart, liver, muscle, brain and pancreas relative to controls, at 4 and 13 days of age. Correspondingly, an increase in triglyceride levels was observed in liver, heart and muscle of mildronate pups. This is in agreement with a reduction of basal rate of oxidation of [U- 14C]-palmitate to 14CO 2 and 14C-acid-soluble products observed in liver homogenates from carnitine-deficient pups. All functional and biochemical modifications were compatible with a carnitine deficiency status. In conclusion our results describe a model of carnitine depletion in pups, suitable for the investigation of carnitine deficiency in fetal-neonatal nutrition, without any concomitant mildronate-mediated metabolic alterations.

Tyrosine nitration of carnitine palmitoyl transferase I during endotoxaemia in suckling rats

Heart carnitine palmitoyl transferase I (CPTI) is inhibited in vivo during endotoxaemia and in vitro by peroxynitrite but the biochemical basis of this inhibition is not known. The aim of this study was to determine which isoform of CPT I is inhibited during endotoxaemia and whether the inhibition is due to increased tyrosine nitration. Cardiac mitochondria were isolated from endotoxaemic suckling rats. To determine whether M- or L-CPTI was inhibited, we carried out titrations with DNP-etomoxir-CoA. Slopes of the titration curves with DNP-etomoxir-CoA were no different between control and endotoxaemia, suggesting that M-CPTI was specifically inhibited. Immunoprecipitation was carried out using an anti-nitrotyrosine antibody. Immunoprecipitated proteins were identified by Western blotting with L- and M-CPTI specific antibodies. L-CPTI was nitrated both in control and in 2- and 6-h endotoxaemia mitochondria but there was no significant difference in the level of nitration. M-CPTI was also nitrated in control mitochondria but nitration was significantly increased at both 2- and 6-h endotoxaemia. Either 10 mM 3-nitrotyrosine plus 40 μg nitrated-albumin or 0.5 M dithionite, during immunoprecipitation, greatly decreased immunopositivity for M- and L-CPTI on WB. M-CPTI appears to be a novel target for peroxynitrite during endotoxaemia, which would alter myocardial substrate selection.

Effect of various levels of supplementation with sodium pivalate on tissue carnitine concentrations and urinary excretion of carnitine in the rat

In previous studies, sodium pivalate has been administered to rats in their drinking water (20 mmoles/L; equivalent to 0.3% of the diet) as a way to lower the concentration of carnitine in tissues and to produce a model of secondary carnitine deficiency. Although this level of supplementation results in a marked decrease in carnitine concentration in a variety of tissues, it does not produce the classical signs of carnitine deficiency (i.e., decreased fatty acid oxidation and ketogenesis). The present study was designed (1) to determine if increasing the level of pivalate supplementation (0.6, 1.0% of the diet) would further reduce the concentrations of total and free carnitine in rat tissues without altering growth or food intake, and (2) to examine the effect of length of feeding (4 vs. 8 weeks) on these variables. Male, Sprague-Dawley rats were randomly assigned to either a control (0.2% sodium bicarbonate) or experimental diet (0.3, 0.6, 1.0% sodium pivalate) for either four or eight weeks. Animals ( n = 6/group) were housed in metabolic cages; food and water were provided ad libitum throughout the study. Supplementation with sodium pivalate did not alter water intake or urine output. Ingestion of a diet containing 1.0% pivalic acid decreased food intake (g/day; P < 0.05), final body weight ( P < 0.007), and growth rate ( P < 0.001) after four weeks. The concentration of total carnitine in plasma, heart, liver, muscle, and kidney was reduced in all experimental groups ( P < 0.001), regardless of level of supplementation or length of feeding. The concentration of free carnitine in heart, muscle, and kidney was also reduced ( P < 0.001) in rats treated with pivalate for either four or eight weeks. The concentration of free carnitine in liver was reduced in animals supplemented with pivalate for eight weeks ( P < 0.05), but no effect was observed in livers from rats treated for four weeks. Excretion of total carnitine and short chain acylcarnitine in urine was increased in pivalate supplemented rats throughout the entire feeding period ( P < 0.001). Free carnitine excretion was increased during Weeks 1 and 2 ( P < 0.01), but began to decline during Week 3 in experimental groups. During Weeks 6 and 8, free carnitine excretion in pivalate supplemented rats was less than that of control animals ( P < 0.01). In summary, no further reduction in tissue carnitine concentration was observed when rats were supplemented with sodium pivalate at levels greater than 0.3% of the diet. Food intake (g/day) and growth were decreased in rats fed a diet containing 1.0% sodium pivalate. These data indicate that maximal lowering of tissue carnitine concentrations is achieved by feeding diets containing 0.3% sodium pivalate or less.

Abdominal Fat Deposition and Fatty Acid Synthesis Are Lower and β-Oxidation Is Higher in Broiler Chickens Fed Diets Containing Unsaturated Rather than Saturated Fat

We evaluated the effects of dietary fat type on fat metabolism and deposition in broiler chickens. Birds were fed diets containing either 8 g dietary saturated (beef tallow) or polyunsaturated fat (sunflower oil)/100 g for 32 d. The abdominal fat deposition of chickens fed the sunflower oil-enriched diet was significantly lower than that of chickens fed the tallow-enriched diet (2.63 +/- 0.47 versus 3.03 +/- 0.44 g/100 g live wt.; P = 0.033). The specific activities of heart carnitine palmitoyltransferase I and L-3-hydroxyacyl-CoA dehydrogenase were higher (P < or = 0.03) in chickens fed the sunflower oil-enriched diets, indicating a greater rate of beta-oxidation. Liver fatty acid synthetase activity was lower (P = 0.01) in chickens fed the sunflower oil-enriched diet, suggesting reduced hepatic lipogenesis in this group. Postprandial plasma triglyceride levels were significantly lower (P < 0.05) in birds fed the sunflower oil-enriched diet, indicating a higher rate of dietary lipid clearance from the bloodstream to tissues. In conclusion, the lower fat deposition observed in broilers fed sunflower oil-enriched diets appears to be the net result of an increased rate of lipid catabolism and lower rate of fatty acid synthesis despite higher dietary fat absorption.

Carnitine deprivation adversely affects cardiac performance in the lipopolysaccharide- and hypoxia/reoxygenation-stressed piglet heart.

Sepsis and hypoxia are important stressors for the neonate. Newborn infants receiving total parenteral nutrition are routinely deprived of carnitine and develop low carnitine plasma and tissue levels. Because of its high metabolic rate and dependence on fatty acids for energy, the newborn heart may be particularly vulnerable to stress in the face of an inadequate carnitine supply. To investigate whether carnitine deprivation affects cardiac performance under stress, 23 neonatal piglets received parenteral nutrition for 2-3 weeks that was either carnitine free (CARN -) or supplemented (CARN +) with L-carnitine (400 mg/L). Bacterial endotoxin (lipopolysaccharide (LPS), 250 microg/kg intravenous bolus) or saline vehicle was administered to anesthetized piglets 3 h prior to study of isolated perfused hearts. Left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure, and left ventricular developed pressure (LVDP) were measured in vitro under aerobic, hypoxic, and reoxygenation conditions in all animals. Plasma and tissue carnitine values were lower in CARN - than in CARN + piglets. In hearts from LPS-treated animals prior to hypoxia, there was no difference in ventricular compliance between CARN - and CARN + groups. LVSP and LVDP were lower in CARN - than CARN + hearts. During hypoxia, LVSP and LVDP fell, but left ventricular end diastolic pressure increased in hearts from both LPS- and saline- treated piglets. Reoxygenation led to poorer recovery in CARN - than CARN + hearts from LPS-treated animals, but not from saline controls. During hypoxia/reoxygenation, lactate efflux initially rose and then fell, while carnitine efflux increased continually. Acetyl- and medium-chain acylcarnitines were detected in the coronary effluent. Our findings suggest that carnitine deprivation diminishes heart carnitine concentrations and impairs cardiac recovery from combined endotoxic and hypoxic stress. Possible mechanisms include reduced acyl buffering and/or impaired transport of fatty acyl groups into mitochondria.

Cardiomegaly in the juvenile visceral steatosis (JVS) mouse is reduced with acute elevation of heart short-chain acyl-carnitine level after l-carnitine injection

The long-term administration of l-carnitine was very effective in preventing cardiomegaly in juvenile visceral steatosis (JVS) mice, which was confirmed by heart weight as well as the lipid contents in heart tissue. After i.p. injection of l-carnitine, the concentration of free carnitine in heart remained constant, although serum free carnitine level increased up to 80-fold. On the other hand, a significant increase in short-chain acyl-carnitine level in heart was observed. These results suggest that increased levels of short-chain acyl-carnitine, not free carnitine, might be a key compound in the protective effect of l-carnitine administration in JVS mice.

Dietary choline supplementation in rats increases carnitine concentration in liver, but decreases plasma and kidney carnitine concentrations

Choline and choline-containing compounds are used in the treatment of certain neurological disorders. Limited information is available regarding the metabolic consequences of choline supplementation. The effect of both acute and chronic dietary choline supplementation on carnitine concentration in plasma, urine and tissues was studied in adult, male Sprague-Dawley rats. Eight groups of rats (n = 6/group) were assigned to four timepoints and two diets. Carnitine concentrations in choline supplemented (CS) (10 g choline chloride/kg diet) rats were measured after 1, 3, 21, and 42 days and results compared to control (C) animals (1 g choline chloride/kg). The carnitine concentration of plasma, urine, liver, heart, kidney, and gastrocnemius muscle was determined by radioenzymatic assay. Urinary choline and betaine levels were analyzed by single proton NMR spectroscopy. Both choline and betaine excretion were higher in CS animals throughout the study period. A single choline supplemented feeding (one 3 h meal) produced no significant changes in carnitine concentrations 3 h post prandial. Plasma and kidney carnitine concentrations increased over time in both dietary groups ( P = 0.0001, P = 0.0004, respectively) and choline supplementation depressed concentrations in both of these pools when compared to controls ( P = 0.0001, P = 0.006, respectively). No effect on urinary carnitine excretion was observed. Heart carnitine concentration increased over the course of the study in both dietary groups ( P = 0.006). Carnitine concentration in liver was increased due to supplementation ( P= 0.016). We conclude that the administration of a single, large dose of choline in rats does not alter carnitine concentrations during the first 3 h post prandial. Chronic choline administration decreased plasma and kidney carnitine concentrations and increased liver concentration. Choline supplementation influences the distribution of carnitine in specific body compartments, perhaps, by influencing the the transport of carnitine into or out of the liver.

Change in Expression of Heart Carnitine Palmitoyltransferase I Isoforms with Electrical Stimulation of Cultured Rat Neonatal Cardiac Myocytes

Electrical stimulation of neonatal rat cardiac myocytes in culture produces increases in myocyte size (hypertrophy) and organization of actin into myofibrillar arrays. The maturation of the cells is associated with enhanced contractile parameters and cellular calcium content. The numbers and intensity of cellular mitochondrial profiles increase, as measured by scanning laser confocal microscopy. Consistent with the hypertrophic response is increased cellular content of beta-myosin heavy chain and cytochrome oxidase subunit Va messages, as well as increases in cytochrome oxidase activity in the stimulated cardiac myocytes. Myocyte contractile capacity is associated with increased expression of the muscle carnitine palmitoyltransferase (CPT-I) isoform as measured by Northern analysis, immunoblotting, and altered sensitivity of CPT-I activity to malonyl-CoA in the stimulated cells. The data suggest that a switch from the liver isoform of CPT-I, prominent in the neonatal rat heart, to the muscle CPT-I which predominates in adult rat heart, takes place in the neonatal cardiac myocytes over the same time period as the hypertrophic-mediated changes in myofibrillar assembly and increased contractile activity.

Accumulation of unsaturated acylcarnitine molecular species during acute myocardial ischemia: metabolic compartmentalization of products of fatty acyl chain elongation in the acylcarnitine pool.

Long-chain acylcarnitines accumulate during myocardial ischemia and contribute to membrane dysfunction in ischemic zones. On the basis of the 3-fold selectivity for saturated fatty acid accumulation during myocardial ischemia, it was implicitly assumed that saturated long chain acylcarnitine molecular species predominantly accumulated in ischemic myocardium. By exploiting the analytical power of electrospray ionization mass spectroscopy, we now report that unsaturated acylcarnitines are the predominant molecular species of acylcarnitine which accumulate during myocardial ischemia (rank order: octadecadienoyl carnitine > octadecanoyl carnitine > hexadecanoyl carnitine > octadecanoyl carnitine). The aliphatic chain distribution of myocardial acylcarnitine molecular species identified by electrospray ionization mass spectroscopy was independently substantiated by sequential HPLC purification and capillary gas chromatography. Detailed analysis of the individual molecular species of long-chain acylcarnitine demonstrated that fatty acyl chain elongation was prominent in ischemic myocardium (e.g., following 20 min of ischemia, greater than 15% of the accumulated acylcarnitines consisted of 20-carbon unsaturated molecular species). Chain-elongated lipids were essentially confined to the long chain acylcarnitine pool since [9,10-3H]octadec-9'-enoic acid was converted to [3H]eicosenoyl carnitine (12% of the radiolabeled acylcarnitine pool) in ischemic hearts without substantive amounts of [3H]eicosenoyl residues in the fatty acid, triglyceride, and phospholipid pools. Collectively, these results demonstrate the preponderance of unsaturated acylcarnitines in ischemic myocardium and document the metabolic compartmentation of downstream products of fatty acyl chain elongation in the acylcarnitine pool during ischemia.

L-Carnitine improvement of cardiac function is associated with a stimulation in glucose but not fatty acid metabolism in carnitine-deficient hearts

Increasing myocardial carnitine content can improve heart function in patients with carnitine deficiency. We were interested in determining the effects of L-carnitine on cardiac function and substrate metabolism in a rat model of carnitine deficiency. Carnitine deficiency was induced in male Sprague-Dawley rats by supplementing the drinking water with 20 mM sodium pivalate. Control animals received an equimolar concentration of sodium bicarbonate. Following treatment, cardiac function and myocardial substrate utilization were determined in isolated working hearts perfused with glucose and relevant levels of fatty acids. To increase tissue levels of carnitine, hearts were perfused with 5 mM L-carnitine for a period of 60 min. Hearts from sodium pivalate-treated animals demonstrated a 60% reduction in total heart carnitine content, depressions in cardiac function and rates of palmitate oxidation, and elevated rates of glycolysis compared to control hearts. Treatment with L-carnitine increased total carnitine content and reversed the depression in cardiac function seen in carnitine-deficient hearts. However, this was not associated with any improvement in palmitate oxidation. Rates of glycolysis and glucose oxidation, on the other hand, were increased with L-carnitine. Our findings indicate that acute L-carnitine treatment is of benefit to cardiac function in this model of secondary carnitine deficiency by increasing overall glucose utilization rather than normalizing fatty acid metabolism.

L-Propionylcarnitine effects on cardiac carnitine content and function in secondary carnitine deficiency

Long-term treatment with sodium pivalate, a compound conjugated to carnitine and excreted in the urine, results in carnitine deficiency and cardiac dysfunction. Since L-propionylcarnitine (LPC) is generally of benefit to cardiac function, it was of interest to determine whether it is effective in preventing the reductions in both heart carnitine content and function from occurring in carnitine deficiency. Secondary carnitine deficiency was induced in male Sprague-Dawley rats by supplementing the drinking water with 20 mM sodium pivalate for 26 weeks. Control animals received an equimolar concentration of sodium bicarbonate. At 13 weeks into treatment, a subgroup of control and sodium pivalate animals were given 80 mg/kg of LPC in their drinking water. Following treatment, isolated working hearts were perfused with buffer containing 11 mM glucose and 0.4 mM palmitate. Hearts from sodium pivalate treated animals demonstrated a severe reduction in tissue carnitine. When mechanical function was measured in these hearts, heart rate, rate-pressure product, and aortic flow were significantly depressed. Treatment with LPC, however, prevented the depletion in cardiac carnitine content and improved these cardiac parameters. Our results demonstrate that LPC treatment is beneficial in preventing the depression in cardiac function from occurring in this model of secondary carnitine deficiency.

Carnitine Depletion in Rat Pups of Lactating Mothers Given Sodium Pivalate

The purpose of this study was to determine the effect of pivalate administration in the pregnant and lactating rat upon tissue carnitine concentrations in 1- and 5-day-old rat pups, as well as in the lactating rats. At 17 days of gestation, 5 rats began receiving 20 mmol/l sodium pivalate in their drinking water, while an additional 5 rats (control) received equimolar NaHCO3. There were no significant differences in litter size, or in pup weights at day 1 (p > 0.05). However, the pups from the pivalate group did weigh significantly less at 5 days of age relative to the control group. Neonatal rats in the pivalate group had significantly depressed levels of total carnitine in plasma, heart and liver, relative to the control group, at both 1 and 5 days of age. Similar depressions were noted for the lactating rats from the pivalate group. This study demonstrates the utility of pivalate administration in depressing carnitine concentrations in newborn rats.

Carnitine requirement of vascular endothelial and smooth muscle cells in imminent ischemia.

Vascular endothelial and -smooth muscle cells have been shown to use fatty acids as substrates for oxidative phosphorylation. Endothelial cells are more vulnerable to oxidative stress than muscle cells and are prone to loose carnitine early during hypoperfusion. This has been suggested by two observations. The first is that incubation of isolated endothelial cells in a low carnitine medium leads to oleate oxidation, dependent upon carnitine addition, whereas smooth muscle cells do not depend on carnitine addition during in vitro incubation, although aminocarnitine, a specific inner-membrane carnitine palmitoyltransferase inhibitor, inhibits fatty acid oxidation. The second observation is that rat hearts labeled in vivo with 14C-carnitine loose, as paced Langendorff heart, only 4% of their carnitine in 20 min perfusion, following 60 min global ischemia. The carnitine released had a much higher specific radioactivity than the carnitine that was not released. It indicates compartmentation of carnitine in heart. As earlier and presently discussed work shows endothelial vulnerability, it is to be expected that this cell type may become carnitine deficient during pacing and ischemia. Endothelial incompetence in flow regulation could be delayed by the presence of carnitine and fatty acids in pre-ischemia. It is speculated how activated fatty acids could protect endothelium.

Mechanisms regulating cardiac fuel selection in hyperthyroidism.

Starvation (48 h) decreases fructose 2,6-bisphosphate (Fru-2,6-P2) concentrations and the ratio of free to acylated carnitine in hearts of euthyroid rats. These decreases, which are indicative of increased lipid fuel oxidation, are accompanied by decreased rates of glucose uptake and phosphorylation, assessed by using radioactive 2-deoxyglucose. Cardiac concentrations of acylated carnitines were increased at the expense of free carnitine even in the fed state in response to experimental hyperthyroidism, but neither Fru-2,6-P2 concentrations nor rates of glucose utilization were suppressed. Starvation (48 h) did not further increase the proportion of acylated carnitine in the heart in hyperthyroidism, and suppression of Fru-2,6-P2 concentrations and glucose utilization rates by starvation was attenuated. Although glucose utilization rates were decreased, starvation did not decrease immunoreactive GLUT 4 protein concentrations. Furthermore, although hyperthyroidism was associated with a statistically significant (30-40%) increase in relative abundance of GLUT 4 mRNA, the amount of GLUT 4 protein was not increased by hyperthyroidism in either the fed or the starved state. The results demonstrate a significant effect of hyperthyroidism to enhance cardiac glucose utilization in starvation by a mechanism which does not involve changes in GLUT 4 expression but may be secondary to changes in glucose-lipid interactions at the tissue level.