Liver Carnitine Concentrations Research Articles

Carnitine dynamics and their effects on hyperammonemia in cirrhotic Japanese patients

Supplementation with levocarnitine preparations has been reported to improve hepatic encephalopathy, but no detailed investigations have addressed the dynamics of carnitine or its supplementation indication in cirrhosis patients. We studied carnitine dynamics in cirrhotic patients by measuring serum and liver tissue carnitine levels and tested the effects of levocarnitine supplementation on concurrent hyperammonemia. In a pilot cohort of seven patients with liver cirrhosis and five patients without cirrhosis, the serum and liver carnitine concentrations were measured. Then the serum carnitine fractions were analyzed in 70 liver cirrhosis patients. Among them, a levocarnitine preparation (1800mg/day) was supplemented orally for 3months in 27 patients with refractory hyperammonemia, and the effects were evaluated. A significant correlation was observed between serum and liver tissue carnitine concentrations (r = 0.69, P <0.05). The serum total carnitine concentration was 68.4 ± 4.7μmol/L, the free carnitine concentration was 53.2 ± 2.6μmol/L, and the acylcarnitine concentration was 13.2 ± 1.1μmol/L in 70 cirrhotic patients (reference values are 45-91, 36-74, 6-23μmol/L, respectively). There was no correlation between blood ammonia and serum carnitine concentrations. The serum carnitine concentration rose with levocarnitine supplementation, reaching steady state after 1month and, in parallel, refractory hyperammonemia was significantly improved. The cut-off level for a 20% decrease in blood ammonia was identified as 62.0μmol/L total carnitine concentration by receiver-operating characteristic curve analysis, with an area under the curve of 0.69. Serum carnitine concentrations were within standard levels in the majority of liver cirrhosis patients. In patients with concurrent hyperammonemia, the levocarnitine supplementation reduced blood ammonia levels.

Genes involved in carnitine synthesis and carnitine uptake are up-regulated in the liver of sows during lactation

BackgroundConvincing evidence exist that carnitine synthesis and uptake of carnitine into cells is regulated by peroxisome proliferator-activated receptor α (PPARA), a transcription factor which is physiologically activated during fasting or energy deprivation. Sows are typically in a negative energy balance during peak lactation. We investigated the hypothesis that genes involved in carnitine synthesis and uptake in the liver of sows are up-regulated during peak lactation.FindingsTranscript levels of several PPARα target genes involved in fatty acid uptake (FABP4, SLC25A20), fatty acid oxidation (ACOX1, CYP4A24) and ketogenesis (HMGCS2, FGF21) were elevated in the liver of lactating compared to non-lactating sows (P < 0.05). In addition, transcript levels of genes involved in carnitine synthesis (ALDH9A1, TMLHE, BBOX1) and carnitine uptake (SLC22A5) in the liver were greater in lactating than in non-lactating sows (P < 0.05). Carnitine concentrations in liver and plasma were about 20% and 50%, respectively, lower in lactating than in non-lactating sows (P < 0.05), which is likely due to an increased loss of carnitine via the milk.ConclusionsThe results of the present study show that PPARα is activated in the liver of sows during lactation which leads to an up-regulation of genes involved in carnitine synthesis and carnitine uptake. The PPARα mediated up-regulation of genes involved in carnitine synthesis and uptake in the liver of lactating sows may be regarded as an adaptive mechanism to maintain hepatic carnitine levels at a level sufficient to transport excessive amounts of fatty acids into the mitochondrion.

Effects of activation of peroxisome proliferator-activated receptor-a by clofibrate on carnitine homeostasis in laying hens

In this study, the hypothesis was investigated that activation of peroxisome proliferator-activated receptor (PPAR)-α regulates homeostasis of carnitine in laying hens. Therefore, laying hens received either a control diet or a diet supplemented with 0.15% clofibrate as a synthetic PPAR α agonist for 4 weeks. Feed intake was not different between both groups of hens while egg production rate was slightly reduced in the group of hens treated with clofibrate (P < 0.05). Hens treated with clofibrate had an increased expression of the classical PPAR α target genes carnitine palmitoyltransferase-1 and acyl CoA oxidase in the liver compared to control hens (P < 0.05), indicative of an activation of PPAR α. In hens treated with clofibrate, mRNA concentration of novel organic cation transporter (OCTN)-2, the most important carnitine transporter, in the liver as well as carnitine concentrations in plasma, liver, egg yolk and albumen were increased compared to control hens (P < 0.05). mRNA concentrations of enzymes of hepatic carnitine synthesis as well as concentrations of the carnitine precursors trimethyllysine and γ-butyrobetaine in plasma, liver and muscle were unchanged in hens treated with clofibrate, suggesting that activation of PPAR α did not influence carnitine biosynthesis. In conclusion, this study shows that activation of PPAR α up-regulates expression of OCTN2 in the liver of laying hens, such as in mammalian species and causes an increase of carnitine concentrations in liver, plasma and egg.

PPARα Mediates Transcriptional Upregulation of Novel Organic Cation Transporters-2 and -3 and Enzymes Involved in Hepatic Carnitine Synthesis

We tested the hypothesis that transcription of novel organic cation transporters (OCTNs) is directly regulated by peroxisome proliferator-activated receptor (PPAR)-alpha. Therefore, wild-type mice and mice deficient in PPAR alpha (PPAR alpha-/-) were treated with the PPAR alpha agonist WY 14,643. Wild-type mice treated with WY 14,643 had a greater abundance of OCTN2 mRNA in their liver, muscle, kidney, and small intestine and a greater abundance of OCTN3 mRNA in kidney and small intestine than did untreated wild-type mice (P < 0.05). Moreover, wild-type mice treated with WY 14,643 had greater mRNA abundances of enzymes involved in hepatic carnitine synthesis (4-N-trimethylaminobutyraldehyde dehydrogenase, gamma-butyrobetaine dioxygenase) and increased carnitine concentrations in liver and muscle than did untreated wild-type mice (P < 0.05). Untreated PPAR alpha-/- mice had a lower abundance of OCTN2 mRNA in liver, kidney, and small intestine and lower carnitine concentrations in plasma, liver, and kidney than did untreated wild-type mice (P < 0.05). In PPAR alpha-/- mice, treatment with WY 14,643 did not influence mRNA abundance of OCTN2 and OCTN3 and carnitine concentrations in all tissues analyzed. The abundance of OCTN1 mRNA in all the tissues analyzed was not changed by treatment with WY 14,643 in wild-type or PPAR alpha-/- mice. In conclusion, this study shows that transcriptional upregulation of OCTN2 and OCTN3 in tissues and of enzymes involved in hepatic carnitine biosynthesis are mediated by PPAR alpha. It also shows that PPAR alpha mediates changes of whole-body carnitine homeostasis in mice by upregulation of carnitine transporters and enzymes involved in carnitine synthesis.

Clofibrate treatment up-regulates novel organic cation transporter (OCTN)-2 in tissues of pigs as a model of non-proliferating species

Recent studies have shown that treatment of rodents with agonists of peroxisome proliferator-activated receptor (PPAR)-α causes an up-regulation of novel organic cation transporter (OCTN)-2, a carnitine transporter, and increases carnitine concentration in the liver. This study was performed to investigate whether such effects occur also in pigs which like humans have a lower expression of PPARα and are less responsive to treatment with PPARα agonists than rodents. An experiment with 18 pigs was performed which were fed a control diet or the same diet supplemented with 5 g clofibrate/kg for 28 days. Pigs treated with clofibrate had higher relative mRNA concentrations of OCTN2 in liver (3.1-fold), skeletal muscle (1.5-fold) and epithelial cells from small intestine (1.8-fold) than control pigs ( P < 0.05). Pigs treated with clofibrate had also higher concentrations of free and total carnitine in the liver and a higher concentration of free carnitine in skeletal muscle than control pigs ( P < 0.05). Concentrations of γ-butyrobetaine, the precursor of endogenous formation of carnitine, in liver, muscle and plasma did not differ between both groups; the activity of γ-butyrobetaine dioxygenase, the rate limiting enzyme of carnitine synthesis, in the liver was lower in pigs treated with clofibrate than in control pigs ( P < 0.05). This study shows for the first time that treatment with a PPARα agonist causes an up-regulation of OCTN2 in liver, muscle and enterocytes from small intestine of pigs. This in turn increases carnitine concentrations in liver and muscle probably by enhancing carnitine uptake into cells.

Dietary oxidised fat up regulates the expression of organic cation transporters in liver and small intestine and alters carnitine concentrations in liver, muscle and plasma of rats

It has been shown that treatment of rats with clofibrate, a synthetic agonist of PPARalpha, increases mRNA concentration of organic cation transporters (OCTN)-1 and -2 and concentration of carnitine in the liver. Since oxidised fats have been demonstrated in rats to activate hepatic PPARalpha, we tested the hypothesis that they also up regulate OCTN. Eighteen rats were orally administered either sunflower-seed oil (control group) or an oxidised fat prepared by heating sunflower-seed oil, for 6 d. Rats administered the oxidised fat had higher mRNA concentrations of typical PPARalpha target genes such as acyl-CoA oxidase, cytochrome P450 4A1 and carnitine palmitoyltransferases-1A and -2 in liver and small intestine than control rats (P < 0.05). Furthermore, rats treated with oxidised fat had higher hepatic mRNA concentrations of OCTN1 (1.5-fold) and OCTN2 (3.1-fold), a higher carnitine concentration in the liver and lower carnitine concentrations in plasma, gastrocnemius and heart muscle than control rats (P < 0.05). Moreover, rats administered oxidised fat had a higher mRNA concentration of OCTN2 in small intestine (2.4-fold; P < 0.05) than control rats. In conclusion, the present study shows that an oxidised fat causes an up regulation of OCTN in the liver and small intestine. An increased hepatic carnitine concentration in rats treated with the oxidised fat is probably at least in part due to an increased uptake of carnitine into the liver which in turn leads to reduced plasma and muscle carnitine concentrations. The present study supports the hypothesis that nutrients acting as PPARalpha agonists influence whole-body carnitine homeostasis.

Effect of l-Carnitine Infusion and Feed Restriction on Carnitine Status in Lactating Holstein Cows

Previously we determined that abomasal infusion of l-carnitine increased in vitro hepatic fatty acid oxidation, decreased liver lipid accumulation, and supported higher fat-corrected milk yield in feed-restricted lactating cows. The objectives of this study were to examine the effects of supplemental l-carni-tine and amount of feed intake on free carnitine and carnitine ester concentrations in liver, muscle, milk, and plasma of lactating dairy cows. Eight lactating Holstein cows (132±36 d in milk) were used in a replicated 4×4 Latin square design with 14-d periods to test factorial combinations of water or l-carnitine infusion (20g/d; d 5 to 14) and ad libitum or restricted (50% of previous 5-d intake; d 10 to 14) dry matter intake. Plasma was obtained 3 times daily on d 4, 8, and 12; milk samples were collected on d 8, 9, 13, and 14. Liver and muscle were biopsied on d 14 of each period. Free carnitine, short-chain acylcarnitine, and long-chain acylcarnitine concentrations were determined using a radioenzymatic assay coupled with ion exchange chromatography. Abomasal l-carnitine infusion increased total carnitine in plasma on d 8 and d 12. All liver carnitine fractions were increased by carnitine infusion. Feed restriction elevated concentrations of free carnitine, long-chain acylcarnitine, and total carnitine in liver tissue from carnitine-infused cows but not in those infused with water. In muscle, acid-soluble carnitine, long-chain acylcarnitine, and total carnitine concentrations were increased by carnitine infusion and feed restriction without significant interaction. Feed restriction increased free carnitine concentrations in muscle from water-infused cows but not in carnitine-infused cows. Carnitine infusion increased the concentration of each milk carnitine fraction as well as milk carnitine output on d 8 to 9. On d 13 to 14, all carnitine fractions except short-chain acylcarnitine were increased in milk from water-infused, feed-restricted cows, whereas all fractions were increased in carnitine-infused, feed-restricted cows. Carnitine infusion increased total carnitine in plasma, liver, muscle, and milk during feed restriction, whereas feed restriction alone increased carnitine concentrations in muscle and milk but not in liver. Liver carnitine concentrations might limit hepatic fatty acid oxidation capacity in dairy cows during the periparturient period; therefore, supplemental l-carnitine might decrease liver lipid accumulation in periparturient cows.

Metabolic Effects of Abomasal l-Carnitine Infusion and Feed Restriction in Lactating Holstein Cows

l-Carnitine is required for mitochondrial fatty acid oxidation, but the effects of carnitine supplementation on nutrient metabolism during dry matter intake depression have not been determined in dairy cows. Studies in other species have revealed responses to l-carnitine that may be of specific benefit to dairy cows during the periparturient period. Eight lactating Holstein cows (132±36 d in milk) were used in a replicated 4×4 Latin square experiment with 14-d periods. Treatments were factorial combinations of abomasal infusion of either water or l-carnitine (20g/d; d 5 to 14) and either ad libitum or restricted intake (50% of previous 5-d dry matter intake; d 10 to 14) of a balanced lactation diet. Liver and muscle biopsies were obtained on d 14 of each period. Feed restriction induced negative balances of energy and metabolizable protein. In feed-restricted cows, carnitine infusion increased 3.5% fat-corrected milk yield compared with those infused with water. Total carnitine concentration in liver was increased in feed-restricted cows infused with carnitine but not in feed-restricted cows infused with water. Carnitine infusion stimulated in vitro oxidation of [1-14C] palmitate to acid-soluble products and decreased the proportion of [1-14C] palmitate that was converted to esterified products by liver slices. Feed-restricted cows infused with carnitine had lower liver total lipid concentration and tended to have decreased triglyceride accumulation compared with feed-restricted cows infused with water. Plasma nonesterified fatty acid concentration was not altered by carnitine infusion but was increased by feed restriction; serum β-hydroxybutyric acid was increased by carnitine infusion in feed-restricted cows. In cows fed for ad libitum intake, carnitine infusion affected β-hydroxybutyric acid, insulin, and urea N in serum, liver glycogen concentration, and in vitro alanine oxidation by liver slices, suggesting that hepatic and peripheral nutrient metabolism was influenced. l-Carnitine infusion effectively decreased liver lipid accumulation during feed restriction as a result of greater capacity for hepatic fatty acid oxidation. Further research examining dietary supplementation of l-carnitine during the periparturient period is warranted.

Changes in Kinetics of Carnitine Palmitoyltransferase in Liver and Skeletal Muscle of Dogs (Canis familiaris) throughout Growth and Development

This study was conducted to investigate developmental changes in the kinetics of carnitine palmitoyltransferase (CPT) within hepatic and skeletal muscle tissues of the canine species. Carnitine concentrations, CPT activity and the apparent K(m) for carnitine were measured in tissue homogenates from dogs in six age categories: newborn; 24-h-old; 3-, 6- and 9-wk-old; and adult. Hepatic CPT activity was low at birth, increased by 100% during the suckling period (P < 0.05) and then declined after weaning to adult levels. In contrast, CPT activity in muscle continued to increase with age, reaching adult levels after 9 wk. Congruent with CPT activity, nearly identical concentration profiles of liver and muscle acylcarnitines were observed. The apparent K(m) of hepatic CPT for carnitine also paralleled the increase in CPT activity during the suckling period; however, free and total liver carnitine concentrations declined by 50% during this time (P < 0.05). Beginning at 3 wk of age, the hepatic concentration of free carnitine was at or below the apparent K(m) of CPT for carnitine. A similar relationship existed in muscle of young dogs, but in adults, the free carnitine concentration was markedly increased and exceeded the apparent K(m) by 5-fold. Collectively, we infer that fatty acid oxidation capacity increases rapidly after birth in the canine, after ontogenic increases in CPT activity. Furthermore, based on the relatively low tissue carnitine concentrations when compared with the apparent carnitine K(m) of CPT, we suggest that carnitine may have an important role in the regulation of fatty acid oxidation and that increased dietary carnitine may improve fatty acid oxidative capacity in developing dogs.

Dietary l-Carnitine Supplementation in Obese Cats Alters Carnitine Metabolism and Decreases Ketosis during Fasting and Induced Hepatic Lipidosis

This study was designed to determine whether dietary carnitine supplement could protect cats from ketosis and improve carnitine and lipid metabolism in experimental feline hepatic lipidosis (FHL). Lean spayed queens received a diet containing 40 (CL group, n = 7) or 1000 (CH group, n = 4) mg/kg of L-carnitine during obesity development. Plasma fatty acid, beta-hydroxybutyrate and carnitine, and liver and muscle carnitine concentrations were measured during experimental induction of FHL and after treatment. In control cats (CL group), fasting and FHL increased the plasma concentrations of fatty acids two- to threefold (P < 0.0001) and beta-hydroxybutyrate > 10-fold (from a basal 0.22 +/- 0.03 to 1.70 +/- 0.73 after 3 wk fasting and 3.13 +/- 0.49 mmol/L during FHL). In carnitine-supplemented cats, these variables increased significantly (P < 0.0001) only during FHL (beta-hydroxybutyrate, 1.42 +/- 0.17 mmol/L). L-Carnitine supplementation significantly increased plasma, muscle and liver carnitine concentrations. Liver carnitine concentration increased dramatically from the obese state to FHL in nonsupplemented cats, but not in supplemented cats, which suggests de novo synthesis of carnitine from endogenous amino acids in control cats and reversible storage in supplemented cats. These results demonstrate the protective effect of a dietary L-carnitine supplement against fasting ketosis during obesity induction. Increasing the L-carnitine level of diets in cats with low energy requirements, such as after neutering, and a high risk of obesity could therefore be recommended.

Changes in fatty acid concentrations in tissues of African catfish, Clarias gariepinus Burchell, as a consequence of dietary carnitine, fat and lysine supplementation.

A study was undertaken to examine the effect of different dietary carnitine (200 and 1000 mg/kg diet) and fat (90 and 190 g/kg diet) supplementation on growth and fatty acid concentrations of fish fed either with a low- (13 g/kg) or a high-lysine (21 g/kg) diet. African catfish (22.7 g/fish), Clarias gariepinus Burchell, juveniles were stocked (sixteen aquaria, twenty-five fish per aquarium) and fed for a maximum of 74 d. Dietary lysine had a clear effect on growth performance and feed conversion ratios, but dietary carnitine supplements had no effect. High-carnitine supplements increased total carnitine content (P<0.0004) and reduced tissue free carnitine: acyl-carnitine ratio (P<0.05) compared with low-carnitine supplements. High-fat supplements decreased liver carnitine concentrations. Clear effects on liver fatty acid concentrations were observed in high-carnitine-fed fish compared with low-carnitine-fed fish. The primary liver fatty acids affected were n-6 (linoleic acid), n-3 (eicosapentanoic acid) and n-3 (docosahexanoic acid). The whole-body fatty acid balance suggested that n-3 disappeared (apparently by beta-oxidation) more readily than n-6 and/or n-3. From 774 mg n-3 eaten by high-lysine-high-fat-low-carnitine fish, 58 % was not assimilated into body tissues. High-carnitine-fed fish showed an increase in n-3 oxidation by 7 % compared with low-carnitine fish. Although dietary carnitine did not improve body growth, these results support the hypothesis that carnitine can enhance the mobilisation of long-chain fatty acids towards oxidation.

Plasma and liver carnitine status of children with chronic liver disease and cirrhosis.

Carnitine is an essential cofactor in the transfer of long-chain fatty acids across the inner mitochondrial membrane for oxidation. As its synthesis is performed in the liver, alterations in carnitine metabolism is expected in liver diseases, especially in cirrhosis. In this study, we investigated plasma and liver carnitine concentrations of 68 children with chronic liver disease, 36 of whom had cirrhosis as well. Carnitine level was determined by enzymatic method. Plasma and liver carnitine concentrations were not correlated. Mean plasma carnitine level of cirrhotic children was significantly lower than that of the control group (P<0. 0001). While there was no difference between liver carnitine concentrations of children with chronic liver disease and cirrhosis (P>0.05), mean plasma level of cirrhotics were lower (P<0.05). Plasma carnitine was correlated with albumin, triglyceride and gamma glutamyl transpeptidase (GGT) in patients with chronic liver disease (P<0.05). Liver carnitine was correlated with GGT in cirrhotic patients (P<0.005). Children with malnutrition had higher plasma and liver carnitine levels (P<0.05). The highest plasma and liver carnitine levels were detected in children with biliary atresia and criptogenic cirrhosis, respectively. Both the lowest plasma and liver carnitine levels were detected in Wilson's disease. Children with cirrhosis have low plasma carnitine concentrations. This finding is prominent in children with Wilson's disease. As carnitine is an essential factor in lipid metabolism, the carnitine supplementation for patients with cirrhosis in childhood, especially with Wilson's disease, seems to be mandatory.

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.

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.

Effect of carnitine loading on long-chain fatty acid oxidation, maximal exercise capacity, and nitrogen balance.

Carnitine has a potential effect on exercise capacity due to its role in the transport of long-chain fatty acids into the mitochondria for beta-oxidation, the export of acyl-coenzyme A compounds from mitochondria and the activation of branched-chain amino acid oxidation in the muscle. We studied the effect of carnitine supplementation on palmitate oxidation, maximal exercise capacity and nitrogen balance in rats. Daily carnitine supplementation (500 mg.kg-1 body mass for 6 weeks) was given to 30 rats, 15 of which were on an otherwise carnitine-free diet (group I) and 15 pair-fed with a conventional pellet diet (group II). A control group (group III, n = 6) was fed ad libitum the pellet diet. Palmitate oxidation was measured by collecting 14CO2 after an intraperitoneal injection of [1-14C]palmitate and exercise capacity by swimming to exhaustion. After carnitine supplementation carnitine concentrations in serum were supranormal [group I, total 150.8 (SD 48.5), free 78.9 (SD 18.4); group II, total 170.9 (SD 27.9), free 115.8 (SD 24.6) mumol.l-1] and liver carnitine concentrations were normal in both groups [group I, total 1.6 (SD 0.3), free 1.2 (SD 0.2); group II, total 1.3 (SD 0.3), free 0.9 (SD 0.2) mumol.g-1 dry mass]. In muscle carnitine concentrations were normal in group I [total 3.8 (SD 1.2), free 3.2 (SD 1.0) mumol.g-1 dry mass] and increased in group II [total 6.6 (SD 0.5), free 4.9 (SD 0.9) mumol.g-1 dry mass].(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium Pivalate Treatment Reduces Tissue Carnitines and Enhances Ketosis in Rats

Sodium pivalate, a compound conjugated to carnitine and excreted in the urine was used to induce a secondary carnitine deficiency. In the first series of experiments, rats received in their drinking water either 20 mmol/L sodium pivalate (experimental) or 20 mmol/L sodium bicarbonate (control) for 4 d, 2 wk, or 8 wk. Tissues and urine were collected, and carnitine concentrations in liver, skeletal muscle, heart, plasma and urine were determined. The total carnitine concentrations in tissues and plasma of pivalate-treated rats were significantly depressed (P less than 0.05) at all time points, except at 4 d for skeletal muscle and at 4 d and 2 wk for liver. The acylcarnitine:free carnitine ratios in urine and plasma of the pivalate-treated animals were significantly higher at all time points relative to the controls. In the second experiment, rats received either the pivalate or the bicarbonate treatments for 15 d followed by a 2-d fast. After fasting, the plasma beta-hydroxybutyrate of pivalate-treated rats was significantly higher relative to controls, but there was no significant difference in plasma glucose concentrations. The reduced plasma and tissue carnitine concentrations, increased acylcarnitine:free carnitine ratio in plasma and urine, and fasting ketosis found in pivalate-treated rats are findings also reported for human secondary carnitine deficiency due to organic acidurias.

Effect of food restriction on tissue carnitine concentration in rats

The effect of feeding different amounts of a standard laboratory pellet diet on tissue carnitine concentration was studied in four groups of rats. Group I was fed ad libitum, whereas food intake was restricted to 25, 20, and 15g protein/kg body weight/day in group II, III, and IV, respectively. The intake of food, protein, energy and carnitine was constant and adjusted to actual body weight in groups 2–4. Six weeks food restriction had no effect on muscle carnitine. Restricted diet caused lowered concentrations of carnitine in serum (group I, fed ad libitum, total 95.0 ± 13.8, free 80.2 ± 2.7; group II total 78.4 ± 8.4, free 56.9 ± 4.7; group III total 81.7 ± 8.8, free 66.0 ± 8.8; and group IV total 73.8 ± 8.7, free 59.5 ± 7.6 μmol/l) and urinary carnitine excretion (group I, total 7.1 ± 3.3, free 6.3 ± 3.1; group II, total 2.5 ± 0.7, free 2.2 ± 0.7; group III, total 1.9 ± 0.8, free 1.6 ± 0.8; and group IV, total 1.3 ± 0.4 free 1.1 ± 0.3 μmol/day). In contrast, the liver carnitine tended to increase when dietary intake was reduced (group I total 1.1 ± 0.1, free 1.0 ± 0.1; group II total 1.5 ± 0.2, free 1.4 ± 0.2; group III total 1.3 ± 0.1, free 1.1 ± 0.1; and group IV total 1.5 ± 0.2, free 1.4 ± 0.2 μmol/g dry wt). The highest liver carnitine concentrations were observed during the lowest dietary intake when also the serum and urine carnitine were lowest. We conclude that the amount of food intake has a direct impact on carnitine concentrations in the liver, serum, and urine while muscle carnitine concentration remains relatively stable despite wide variations in food intake.

The Carnitine-Deprived Newborn Rabbit: A Potential Model To Study Carnitine Deficiency

This report describes the novel development of an animal model for neonatal carnitine deficiency using the artificially fed newborn rabbit. Each litter was separated from the mother following the first colostrum feeding and divided into 2 groups, one of which was fed a purified rabbit formula that was essentially free of carnitine; the other received the same formula supplemented with L-carnitine (100 mg/l). At 9-13 d of age, rabbit pups receiving the carnitine-free formula had lower concentrations of total, free and acylcarnitine in plasma and urine, as well as lower total acid soluble carnitine concentrations in liver, muscle, heart and brown adipose tissue than those receiving the same formula supplemented with L-carnitine. Their plasma and tissue levels were also lower, but their urinary carnitine concentrations were higher than those in naturally-raised pups. The findings suggest that the described animal model may prove to be a useful tool for the investigation of certain aspects of neonatal carnitine deficiency.

Carnitine and creatine content of tissues of normal and alloxan-diabetic sheep and rats

1. 1. The concentration of carnitine in liver increased 28-fold and urinary carnitine excretion 5-fold in alloxan-diabetic sheep. In contrast there were no similar increases in alloxan-diabetic rats. 2. 2. The creatine content of liver decreased 3-fold and creatine excretion decreased 2-fold in diabetic sheep. In contrast the creatine content of liver increased nearly 4-fold in diabetic rats with no change in creatine excretion. 3. 3. The marked increased in production of carnitine by the liver of the diabetic sheep appears possible because of decreased production and excretion of creatine.

Sex steroid regulation of urinary excretion of carnitine in rats

The concentration of acid soluble carnitine was determined in several body tissues and fluids in rats under various conditions of sex steroid regulation. Intact female rats had significantly greater liver carnitine concentrations and urinary excretion rates, and lower blood plasma and heart carnitine concentrations than intact male rats. Ovariectomy increased blood plasma carnitine concentrations ( P < 0.01) and the excretion of carnitine in the urine ( P < 0.05). The administration of either estradiol or testosterone to ovariectomized rats did not alter blood plasma concentrations or urinary excretion of carnitine. Orchidectomized rats had similar blood plasma carnitine concentrations when compared to intact males but excreted significantly ( P < 0.01) greater quantities of carnitine in their urine. Administration of testosterone to orchidectomized rats reduced ( P < 0.01), whereas estradiol stimulated ( P < 0.05) the excretion rate of carnitine in the urine; however, blood plasma carnitine concentrations were not affected by these hormones. These data suggest that a major site for modulation of body carnitine concentration in the male resides in the control of kidney excretion by androgens. Liver, heart and skeletal muscle carnitine concentrations were not altered by the administration of either estradiol or testosterone to orchidectomized or ovariectomized rats.