Muscle Carnitine Research Articles

Assessment of dietary lysine requirement for silver perch ( Bidyanus bidyanus) juveniles

A 10-week rearing trial was conducted to assess the lysine requirement of juvenile silver perch, and to evaluate the effects of dietary lysine levels on the morphological measurements, body composition, hematological traits and muscle carnitine status of the fish. Seven isonitrogenous and isolipidic diets were formulated to contain multiple intact proteins and pre-coated crystalline amino acids. l-lysine HCl was supplemented to the experimental diets at the expense of a dispensable amino acid mixture to achieve lysine levels from 0.90 and 2.70% of dry diet. Each diet was randomly assigned to triplicate groups of 10 fish and was fed to apparent satiation five times daily. At the end of the trial, percent weight gain increased with increasing dietary lysine from 0.90% to 2.10%, then the value decreased slightly. A similar trend was observed in the feed efficiency, protein efficiency ratio, productive protein value and daily protein deposition. The condition factor, hepatosomatic index, intraperitoneal fat and viscerosomatic index were markedly affected by the dietary lysine level. Crude protein contents of the whole body, muscle and liver were significantly depressed in the fish fed lysine-deficient diets, while the whole body lipid content was higher in these fish. The hematocrit value, hemoglobin concentration and free lysine levels in plasma were lower in the silver perch given lower lysine diets. Although muscle carnitine status was not clearly affected by the dietary lysine level, the values of free carnitine and acid soluble carnitine tended to be lower in the fish fed lower lysine diets. Based on the quadratic broken-line model, the dietary lysine requirement for maximum growth of the silver perch juveniles was satisfied at 2.32% lysine in the dry diet, corresponding to 5.96% of the dietary protein. Furthermore, 2.06% of chemically available lysine in the diet (equivalent to 5.30% dietary protein) was required for the optimal growth of the fish.

Activity of hepatic but not skeletal muscle carnitine palmitoyltransferase enzyme is depressed by intravenous glucose infusions in lactating dairy cows*

A positive energy balance in dairy cows pre-partum may decrease hepatic carnitine palmitoyltransferase (CPT) enzyme activity, which might contribute to disturbances of lipid metabolism post-partum. The purpose of this study was to investigate whether skeletal muscle CPT activity can also be downregulated during positive energy balance. Mid-lactating dairy cows were maintained on intravenous infusion of either saline (control) or glucose solutions that increased linearly over 24 days, remained at the 24-day level until day 28 and were suspended thereafter. Liver and skeletal muscle biopsies, as well as four diurnal blood samples, were taken on days 0, 8, 16, 24, and 32, representing infusion levels equivalent to 0%, 10%, 20%, 30% and 0% of the net energy for lactation (NE(L)) requirement respectively. Glucose infusion increased serum insulin concentrations on day 16 and 24 while plasma glucose levels were increased at only a single time point on day 24. Serum beta-hydroxybutyric acid concentrations decreased between day 8 and 24; whereas changes in non-esterified fatty acids were mostly insignificant. Total lipid contents of liver and skeletal muscle were not affected by treatment. Hepatic CPT activity decreased with glucose infusion (by 35% on day 24) and remained decreased on day 32. Hepatic expression levels of CPT-1A and CPT-2 mRNA were not significantly altered but tended to reflect the changes in enzyme activity. In contrast to the liver, no effect of glucose infusion was observed on skeletal muscle CPT activity. We conclude that suppression of CPT activity by positive energy balance appears to be specific for the liver in mid-lactating dairy cows.

Lysine limitation alters the storage pattern of protein, lipid and glycogen in on-growing Atlantic salmon

This experiment aimed to test the interaction of lysine limitation with nutrient accretion and muscle carnitine depot in Atlantic salmon. Fish were fed adequate or low-lysine diets for 3 months. Lysine intake was signi¢cantly less (48%) in ¢sh fed the low-lysine diet as compared with that fed the adequate one. There was no diierence in dietary amino acids between treatments, with the exception of lysine. The lower lysine intake was re£ected in plasma free lysine being 52% less while the free lysine concentration in the liver and muscle were unaiected. Although there was no signi¢cant diierence between voluntary feed intakes among treatments, ¢sh fed the low-lysine diet had reduced growth, protein and energy deposition as compared with ¢sh fed the adequate lysine diet. White trunk muscle contained more glycogen and less protein in ¢sh fed the low-lysine diet while no diierence in lipid was observed. The livers from ¢sh fed the low-lysine diet contained less glycogen and slightly more fat and protein than the livers from ¢sh fed the adequate lysine diet. Lysine limitation reduced carnitine in the liver without affecting muscle carnitine depot. Thus, low-lysine diets did not likely aiect the fatty acid oxidation capacity. This fact was supported by unaiected fatty acid pro¢les and lipid classes between treatments during the 3-month study. In conclusion, lysine limitation does not deplete the muscle carnitine depot during the on-growing seawater phase of Atlantic salmon, but aiects the deposition pattern of nutrients.

P4.55 Molecular genetic analysis in 45 patients with muscle carnitine palmitoyltransferase (CPT) II deficiency

Carnitine palmitoyltransferase (CPT) II deficiency is the most common inherited disorder of long-chain fatty acid oxidation affecting muscle. There is a lethal neonatal form, a severe infantile hepato-cardio-muscular form and a myopathic form characterized by exercise-induced myalgia, weakness, and myoglobinuria. Genetic studies have identified a common S113L mutation in the myopathic form. We report on molecular genetic and clinical data in a large cohort of 45 patients (36 index patients) with muscle CPT II deficiency.

Effect of dietary ascorbate on lipogenesis and lipolysis activities in black sea bream, Acanthopagrus schlegelii

To assess the effect of dietary ascorbate on lipid metabolism, 1-year black sea bream (Acanthopagrus schlegelii) were reared on a casein-based purified diet and an ascorbate fortified diet (1,100 mg of L: -ascorbyl-2- monophosphate-Mg/kg diet). The fortified ascorbate was effectively incorporated into the fish body and elevated muscle carnitine content. Fortifications of dietary ascorbate depressed activities of glucose-6-phosphate dehydrogenase and NADP-isocitrate dehydrogenase as lipogenic enzymes in the hepatopancreas and intraperitoneal fat body. Starvation after feeding experiment activated carnitine palmitoyltransferase as a lipolysis enzyme in the hepatopancreas in both control and vitamin C(VC) groups, while the lipolysis activity was significantly higher in VC group. These results confirmed that dietary ascorbate depressed lipogenesis and activated lipolysis, i.e., influenced the lipid metabolism of black sea bream.

Uterine contractility is strongly influenced by steroids and glucose metabolism: an in vitro study on bovine myometrium

Background. Energetic substrates and hormonal phase are important for uterine contractions. Etomoxir a muscle carnitine palmitoyltransferase-1 inhibitor, able to diverge uterine metabolic pathways towards glycolysis, facilitates glucose utilisation. The aim of this study was to evaluate its effect on uterine contractility in different hormonal situations.Methods. Uterine samples were collected from 60 cows during follicular phase, luteal phase and pregnancy. The cows were slaughtered at a local abattoir. Longitudinal strips were mounted vertically in a 30-ml organ bath connected to an isometric force transducer. Contractions were recorded with an ink-writing polygraph. After the equilibration period, etomoxir was added to the organ bath at different concentrations. The amplitude and frequency of contractions were registered before and after addition of etomoxir.Results. In 17 strips from pregnant cows, etomoxir increased the amplitude (p < 0.05) of contractions but not the frequency in comparison with basal conditions. In 15 strips from cows in the luteal phase, etomoxir increased the amplitude (p < 0.05) and frequency of contractions (p < 0.05 at 5 μM and p < 0.01 at 8 and 10 μM). In 18 strips from cows in the follicular phase, etomoxir increased the frequency of contractions but not the amplitude (p < 0.01 at 5 μM and p < 0.05 at 8 and 10 μM).Conclusions. This study confirms the importance of glucose for uterine contractility and, moreover, it underlines different patterns of contraction with regard to the hormonal status.

Oral Acetyl- l -Carnitine Therapy and Insulin Resistance

To the Editor: We reported recently that oral acetyl-l-carnitine supplementation improved hypertension in patients at increased cardiovascular risk, as well as whole body glucose use in those with advanced insulin resistance, but not yet diabetes mellitus.1 These findings led us to suggest that acetyl-l-carnitine treatment corrects a relative carnitine deficiency in this population. However, in a recent letter to the editor, Muniyappa2 states that oral l-carnitine supplementation cannot achieve the plasma carnitine levels required to increase skeletal muscle carnitine concentration and improve insulin sensitivity. He refers to previous studies suggesting an insulin-sensitizing effect of intravenous l-carnitine that he reports …

The plasma carnitine concentration regulates renal OCTN2 expression and carnitine transport in rats

Previous findings in rats and in human vegetarians suggest that the plasma carnitine concentration and/or carnitine ingestion may influence the renal reabsorption of carnitine. We tested this hypothesis in rats with secondary carnitine deficiency following treatment with N-trimethyl-hydrazine-3-propionate (THP) for 2 weeks and rats treated with excess l-carnitine for 2 weeks. Compared to untreated control rats, treatment with THP was associated with an approximately 70% decrease in plasma carnitine and with a 74% decrease in the skeletal muscle carnitine content. In contrast, treatment with l-carnitine increased plasma carnitine levels by 80% and the skeletal muscle carnitine content by 50%. Treatment with l-carnitine affected neither the activity of carnitine transport into isolated renal brush border membrane vesicles, nor renal mRNA expression of the carnitine transporter OCTN2. In contrast, in carnitine deficient rats, carnitine transport into isolated brush border membrane vesicles was increased 1.9-fold compared to untreated control rats. Similarly, renal mRNA expression of OCTN2 increased by a factor of 1.7 in carnitine deficient rats, whereas OCTN2 mRNA expression remained unchanged in gut, liver or skeletal muscle. Our study supports the hypothesis that a decrease in the carnitine plasma and/or glomerular filtrate concentration increases renal expression and activity of OCTN2.

Time-course Effects of Increased Fatty Acid Supply on the Expression of Genes Involved in Lipid/Glucose Metabolism in Muscle Cells

Fatty acid (FA) oversupply in skeletal muscle is related with metabolic disorders associated to obesity, and also with normal physiological responses. We studied, in vivo and in vitro, the chronological response to physiological increases of FA, analyzing the expression of selected genes important for glucose/lipid metabolism. An in vivo sequential model of fasting (known to increase circulating FA) and refeeding was used in male Wistar rats to study soleus (more oxidative) and gastrocnemius (more glycolytic) muscles, and a chronological study was made in C2C12 muscle cells under treatment of oleic/linoleic FA mixture, at physiological concentration. Body weight, muscle glycogen and blood parameters (glucose, insulin, free fatty acids -FFA-, triglycerides) were monitored. mRNA levels of muscle carnitine palmitoyl transferase 1 (mCPT1), GLUT 4, insulin receptor (InsR), MyoD1, peroxisome proliferator activated receptor (PPAR) γ coactivator 1α (PGC1α) and β (PGC1β), PPARα, PPARδ, pyruvate dehydrogenase kinase 4 (PDK4) and uncoupling proteins (UCPs) 2 and 3 were analyzed by quantitative RT-PCR. The main results were the quick induction of PGC1α, UCP3 and PDK4 in vivo (more marked in gastrocnemius) and of PGC1α, PGC1β, InsR, PDK4, UCP2 and UCP3 in vitro. It is concluded that FA are able to rapidly induce the expression in muscle cells of key genes involved in their catabolism and that the oleic/linoleic acid mixture has a positive role increasing the expression of master metabolic regulators and their downstream target genes, facilitating the transition from a more glycolytic to a more lipid-oxidative metabolism.

Propionyl l-carnitine: intermittent claudication and peripheral arterial disease

Peripheral arterial disease (PAD) is a clinical manifestation of underlying aorto-iliac and leg atherosclerosis that is characterized by different stages of stenosis and obstruction. It affects approximately 12% of the adult population and about 20% of people over the age of 70 years, and is associated with increased cardiovascular (CV) and cerebrovascular morbidity. Intermittent claudication (IC) is the major symptom of PAD; it is defined as cramping leg pain (in the buttock, thigh, or calf) while/after clim bing one or two flights of stairs, or during walking. The goals of IC management are to: slow the progression of local and systemic atherosclerosis, prevent major fatal and nonfatal CV events (myocardial infarction and stroke), improve walking capacity, prevent and reduce resting pain and cutaneous lesions. Propionyl L-carnitine is an acyl derivative of levocarnitine (L-carnitine) and is indicated for patients with peripheral arterial occlusive disease. It corrects secondary muscle carnitine deficiency in patients with PAD, significantly improving the walking capacity; it is a free radical that produces positive effects on endothelial function; it protects from oxidative stress; and it enhances most measures of quality of life. The recent Trans-Atlantic Inter-Society Consensus II update recommends the use of propionyl L-carnitine in combination with physical training to improve the symptoms associated with PAD.

Muscle carnitine deficiency: adult onset lipid storage myopathy with sensory neuropathy

Muscle carnitine deficiency usually results in a lipid storage myopathy, but more rarely, neuropathy occurs in this condition. We report herein a 29-year-old man with muscle carnitine deficiency who developed not only a lipid storage myopathy, but also a severe sensory neuropathy. Oral therapy with levo-carnitine (3 g per day) for 3 months produced a remarkable improvement of the myopathy and sensory neuropathy. Six months later, he remained in good condition under strict dietary control. This report emphasizes that severe neuropathy may occur in some patients with muscle carnitine deficiency, and highlights the need for the neurologist's familiarity with those afflicted to achieve optimal clinical management.

A Comparative Study of the Effects of Erabu Sea Snake (Laticauda semifasciata) Lipids, Green Tea Extract and Conjugated Linoleic Acid on the Swimming Endurance of Mice

The aim of this study was to assess the interaction between physical and biochemical parameters in mice fed 1 % sea snake lipids (SSL) and compare these with animals fed diets containing 0.2 % green tea extract (GTE) or 0.5 % conjugated linoleic acid (CLA). The swimming times of the SSL group were significantly increased at Weeks 12 and 16 (p<0.001), and those of the GTE group, at Week 12 (p<0.005), but not those of the control or CLA group, compared with those at Week 0. The increase tended to be significant in the SSL group compared with the control group at Week 12 (p=0.09). Both the SSL and GTE groups had significantly longer swimming times than the CLA group at Weeks 12 and 16 (p<0.001). After 5 minutes of swimming exercise, the SSL group exhibited significantly lower levels of plasma and muscle lactates (p<0.01), and plasma non-esterified fatty acid (NEFA) (p<0.001) than the control group. There were no significant differences in any of plasma glucose, muscle and liver glycogens, muscle lactate dehydrogenase (LDH), carnitine palmitoyltransferase (CPT), or monocarboxylate transporter 1 (MCT1) between SSL and control groups. The results suggest that the intake of 1 % SSL improved endurance more than the intake of 0.2 % GTE or 0.5 % CLA in mice. This action may involve the promotion of lactate oxidation for utilization.

O7-5 Muscle carnitine deficiency in pathogenesis of myopathy and cardiomyopathy of Duchenne muscular dystrophy (DMD)

Objective: To determine tissue Carnitine (Cn) levels in the C57BL/10ScSn-Dmdmdx male mouse, murine model of DMD. Background:Muscle and cardiacmetabolism and function are dependent on the oxidation of fatty acids and glucose for ATP production, for which Cn serves as an essential cofactor. Skeletal muscle contains >90% of total body Cn stores and uptake across the muscle plasma membrane occurs against a 50 to 70 fold concentration gradient, mediated by the plasmalemmal Cn transporter, OCTN2. Muscle Cn deficiency and reduced long-chain fatty acid oxidation (FAO) have been reported in DMD muscle. We speculate that dystrophin deficiency in DMD, which causes disruption of the plasma membrane, likely disrupts OCTN2, leading to significant secondary tissue Cn depletion. Methods:We determined tissue Cn concentrations according to Cederblad and Lindstedt (1972) in the skeletal muscle (gluteus/quadriceps), diaphragm and ventricles of mdx mice (n = 10) compared to normal male controls: C57BL/6 (n=6), C3H (n=12) and C57BL/10 (n=10) mice. Results: Comparison of the mean Cn concentrations (± standard error mean) in mmol/g dry weight of muscle of the controls vs mdx mice is shown in the table.

Longitudinal study of the effects of chronic hypothyroidism on skeletal muscle in dogs

To study the effects of experimentally induced hypothyroidism on skeletal muscle and characterize any observed myopathic abnormalities in dogs. 9 female, adult mixed-breed dogs; 6 with hypothyroidism induced with irradiation with 131 iodine and 3 untreated control dogs. Clinical examinations were performed monthly. Electromyographic examinations; measurement of plasma creatine kinase, alanine aminotransferase, aspartate aminotransferase, lactate, and lactate dehydrogenase isoenzyme activities; and skeletal muscle morphologic-morphometric examinations were performed prior to and every 6 months for 18 months after induction of hypothyroidism. Baseline, 6-month, and 18-month assessments of plasma, urine, and skeletal muscle carnitine concentrations were also performed. Hypothyroid dogs developed electromyographic and morphologic evidence of myopathy by 6 months after treatment, which persisted throughout the study, although these changes were subclinical at all times. Hypothyroid myopathy was associated with significant increases in plasma creatine kinase, aspartate aminotransferase, and lactate dehydrogenase 5 isoenzyme activities and was characterized by nemaline rod inclusions, substantial and progressive predominance of type I myofibers, decrease in mean type II fiber area, subsarcolemmal accumulations of abnormal mitochondria, and myofiber degeneration. Chronic hypothyroidism was associated with substantial depletion in skeletal muscle free carnitine. Chronic, experimentally induced hypothyroidism resulted in substantial but subclinical phenotypic myopathic changes indicative of altered muscle energy metabolism and depletion of skeletal muscle carnitine. These abnormalities may contribute to nonspecific clinical signs, such as lethargy and exercise intolerance, often reported in hypothyroid dogs.

Association of the CPT1B Gene with Skeletal Muscle Fat Infiltration in Afro‐Caribbean Men

Skeletal muscle fat is greater in African ancestry individuals compared with whites, is associated with diabetes, and is a heritable polygenic trait. However, specific genetic factors contributing to skeletal muscle fat in humans remain to be defined. Muscle carnitine palmitoyltransferase-1B (CPT1B) is a key enzyme in the regulation of skeletal muscle mitochondrial beta-oxidation of long-chain fatty acids, and as such is a reasonable biological candidate gene for skeletal muscle fat accumulation. Therefore, we examined the association of three nonsynonymous coding variants in CPT1B (G531L, I66V, and S427C; a fourth, A320G, could not be genotyped) and quantitative computed tomography measured tibia skeletal muscle composition and BMI among 1,774 Afro-Caribbean men aged > or =40, participants of the population-based Tobago Health Study. For all variants, no significant differences were observed for BMI or total adipose tissue. Among individuals who were homozygous for the minor allele at G531L or I66V, intermuscular adipose tissue (IMAT) was 87% (P = 0.03) and 54% lower (P = 0.03), respectively. In contrast, subcutaneous adipose tissue (SAT) was 11% (P = 0.017) and 7% (P = 0.049) higher, respectively, than among individuals without these genotypes. These associations were independent of age, body size, and muscle area. Finally, no individuals with type 2 diabetes were found among those who were homozygous for the minor allele of either at G531L and I66V whereas 14-18% of men with the major alleles had type 2 diabetes (P = 0.03 and 0.007, respectively). Our results suggest a novel association between common nonsynonymous coding variants in CPT1B and ectopic skeletal muscle fat among middle-aged and older African ancestry men.

PPAR‐alpha agonist increases skeletal muscle carnitine palmitoyltransferase‐1 activity and fatty acid oxidation in obese insulin‐resistant monkeys

The selective PPAR‐alpha agonist K‐111 (Kowa Co. Ltd., Tokyo, Japan) decreases plasma triglycerides and improves insulin sensitivity in obese, insulin‐resistant rhesus monkeys. The purpose of this study was to determine whether K‐111 improves skeletal muscle fatty acid oxidation and enzymes involved in fatty acid metabolism. Five obese, insulin‐resistant adult monkeys were studied at baseline and again after treatment with K‐111 at 3 mg/kg μday for 7 weeks. Acyl‐CoA synthase (ACS), carnitine palmitoyltransferase‐1 (CPT‐1), β‐hydroxy‐acyl CoA dehydrogenase ( β‐HAD), citrate synthase (CS) and total fatty acid oxidation were measured in skeletal muscle homogenates at baseline and following K‐111. CPT‐1 activity significantly increased (0.012 ± 0.004 vs. 0.019 ± 0.004 pmol/min μ;mg protein, p&lt;0.05) and total fatty acid oxidation tended to increase (2.1 ± 0.6 vs. 4.0 ± 1.1 pmol/min μmg protein, p&lt;0.07) following treatment. ACS activity (128 ± 25 vs. 180 ± 11 pmol/min μmg protein), β‐HAD activity (0.182 ± 0.05 vs. 0.190 ± 0.03) and CS activity (0.108 ± 0.02 vs. 0.116 ± 0.01 µmol/min μmg protein) were not significantly affected by treatment. The change in total fatty acid oxidation was associated with the change in ß‐HAD and CS activity (p&lt;0.01) but not to CPT‐1 activity. These results suggest that the mechanism by which PPAR‐alpha agonist treatment improves fatty acid oxidation is through changes in ß‐HAD and CS activity.

Peroxisome proliferator–activated receptor α and enzymes of carnitine biosynthesis in the liver are down-regulated during lactation in rats

This study investigated the hypothesis that lactation lowers gene expression of peroxisome proliferator–activated receptor (PPAR) α in the liver and that this leads to a down-regulation of hepatic enzymes involved in carnitine synthesis and novel organic cation transporters (OCTNs). Thirty-two pregnant female rats were divided into 4 groups. In the first group, all pups were removed, whereas in the other groups, litters were adjusted to sizes of 4, 10, or 18 pups per dam. Dams suckling their litters, irrespective of litter size, had lower relative messenger RNA concentrations of PPARα, various classic PPARα target genes involved in fatty acid catabolism, as well as enzymes involved in carnitine synthesis (trimethyllysine dioxygenase, 4-N-trimethylaminobutyraldehyde dehydrogenase, γ-butyrobetaine dioxygenase) and OCTN1 in the liver than dams whose litters were removed (P < .05). Moreover, dams suckling their litters had a reduced activity of γ-butyrobetaine dioxygenase in the liver and reduced concentrations of carnitine in plasma, liver, and muscle compared with dams without litters (P < .05). In conclusion, the present study demonstrates for the first time that lactation leads to a down-regulation of PPARα and genes involved in hepatic carnitine synthesis and uptake of carnitine (OCTN1) in the liver, irrespective of litter size. It is moreover suggested that down-regulation of PPARα in the liver may be a means to conserve energy and metabolic substrates for milk production in the mammary gland.

Serum and Muscle Carnitine Levels in Epileptic Children Receiving Sodium Valproate

The purpose of this study was to determine whether children with epilepsy undergoing valproate therapy and who are otherwise healthy have lower levels of serum and muscle carnitine. A total of 50 patients with epilepsy, 3 to 14 years of age, who were treated solely with valproate and free of abnormal neurologic findings or nutritional problems were selected. The control group consisted of 30 healthy children. The total carnitine levels in serum were 28.1 +/- 10.3 and 55.6 +/-7.3 microg/mL, and the free carnitine levels in serum were 16.5 +/-10.2 and 44.6 +/-7.3 microg/mL, the total carnitine levels in muscle were 12.1 +/- 1.8 and 45.3 +/- 5.9 micromol/g noncollagen protein and the free carnitine levels in muscle were 5.6 +/- 1.6 and 39.3 +/- 6.0 micromol/g noncollagen protein in the valproic acid-treated and control groups, respectively (P < .05). In conclusion, valproate monotherapy depletes both muscle and serum carnitine levels in otherwise healthy epileptic children.

Plasma acylcarnitine and fatty acid profiles during exercise and training in Standardbreds

To evaluate alterations in skeletal muscle carnitine metabolism during exercise and training by measuring changes in plasma acylcarnitine concentrations in Standardbreds. 10 Standardbred geldings with a mean +/- SD age of 20 +/- 2 months and weight of 384 +/- 42 kg. In a 32-week longitudinal study, training on a treadmill was divided into 4 phases as follows: phase 1, acclimatization for 4 weeks; phase 2, 18 weeks with alternating endurance and high-intensity exercise training; phase 3, increased training volume and intensity for another 6 weeks; and phase 4, deconditioning for 4 weeks. In phase 3, horses were randomly assigned to 2 groups as follows: control horses (which continued training at the same level as in phase 2) and high-intensity exercise trained horses. At the end of each phase, a standardized exercise test (SET) was performed. Plasma acylcarnitine, fatty acids, and lactic acid and serum beta-hydroxybutyric acid (BHBA) concentrations were assessed before and at different time points after each SET. Plasma lactic acid, total nonesterified fatty acids, 3-hydroxyisobutyric acid, and acetylcarnitine (C2-carnitine) concentrations significantly increased during SETs, whereas serum BHBA, plasma propionylcarnitine (C3-carnitine), and plasma butyryl- and isobutyrylcarnitine (C4-carnitine) concentrations decreased significantly, compared with those before SETs. Our findings indicated that the plasma acylcarnitine profile in horses likely reflects skeletal muscle carnitine metabolism following exercise, thereby providing a possible practical method to investigate potential disorders in carnitine metabolism in horses with myopathy.

L-Carnitine Supplementation

Carnitine (L-3-hydroxytrimethylamminobutanoate) is a naturally occurring compound that can be synthesized in mammals from the essential amino acids lysine and methionine or ingested through diet. Primary sources of dietary carnitine are red meat and dairy products; however, commercially produced supplements also are available and have been shown to be safe in humans. Carnitine is stored primarily in skeletal muscle, with lower concentrations in plasma. Biologically, carnitine is essential for the transport of long-chain (carbon chain length = 10) fatty acids across the outer- and inner-mitochondrial membranes (carnitine palmitoyltransferanse I and II, respectively). Conflicting results characterized the early research focused on L-carnitine supplementation's ability to enhance endurance performance, and studies showed no changes occurred in muscle carnitine levels. Nevertheless, promising findings for its use have been observed for various pathologies, including cardiovascular diseases, which show it might mitigate some negative effects and enhance physical function. Recent studies have focused upon a different paradigm for L-carnitine in regulating hypoxic stress and enhancing recovery from exercise.