Carnitine In Rats Research Articles

Excess Dietary Lysine Increases Skeletal Muscle and Plasma Trimethyllysine in Rats

Trimethyllysine, a carnitine precursor, is a cation. This study was designed to determine whether dietary potassium and lysine concentration or oral lysine supplementation affects tissue carnitine and trimethyllysine concentration in rats. In Experiment 1, rats were fed a control diet, a low or high potassium diet, or a high lysine diet. In Experiment 2, rats were given by gavage a solution containing either L-proline (control) or L-lysine. In Experiment 1, rats fed the high lysine diet had significantly lower plasma total carnitine concentration than controls. Rats fed the high lysine diets had significantly higher concentrations of free trimethyllysine in skeletal muscle and plasma relative to control rats and rats fed the high potassium diet. Rats fed the low potassium diet had a similar increase in skeletal muscle free trimethyllysine. In Experiment 2, rats given lysine had significantly lower plasma total carnitine concentration, and significantly greater skeletal muscle and plasma trimethyllysine concentration relative to controls. We conclude that dietary potassium and lysine, and oral lysine, have a significant effect upon the distribution of carnitine and trimethyllysine in rats. The distributional changes caused by lysine, however, seem to be due to effects other than exchange of lysine for carnitine or trimethyllysine in tissues.

Effect of electroacupuncture preconditioning on bupivacaine-induced cardiotoxicity in rats

Objective To evaluate the effect of electroacupuncture(EA)preconditioning on bupivacaine-induced cardiotoxicity in rats. Methods Sixteen SPF adult male Sprague-Dawley rats, weighing 180-240 g, aged 2 months, were randomly assigned into either bupivacaine group(group B, n=8)or EA preconditioning group(group EP, n=8). Bilateral Neiguan(PC6), Zusanli(ST36)and Fenglong(ST40)acupoints were stimulated with an electric stimulator(dense-sparse waves, frequency 2 Hz, voltage 1 mA, wave length 0.2-0.6 ms)for 30 min, followed by another 30 min stimulation after a 1 h interval.At 3 h after the end of electric stimulation, 0.5% bupivacaine 10 mg/kg was injected intravenously, and the rats suffering heart arrest received cardiopulmonary resuscitation.The duration of QRS and QT interval increased by 20% of baseline value, the time for apnea and cardiac arrest and resuscitation time were recorded.The left ventricular myocardial tissues were harvested at 25 min after bupivacaine administration in successfully resuscitated rats and immediately after death in unsuccessfully resuscitated rats for measurement of carnitine content in the myocardial cytoplasm and mitochondria by enzyme linked immunosorbent assay. Results In B and EP groups, the incidence of cardiac arrest was 8/8 and 4/8, respectively, and the rate of successful resuscitation was 3/8 and 4/4, respectively.Compared with group B, the incidence of cardiac arrest was significantly decreased, the rate of successful resuscitation was increased, the duration of QRS and QT interval increased by 20% of baseline value and time for apnea were prolonged, the resuscitation time was shortened, carnitine content in the myocardial cytoplasm was decreased, and carnitine content in the myocardial mitochondria was increased in group EP(P<0.05). Conclusion EA preconditioning can increase the tolerance to bupivacaine-induced cardiotoxicity, and the mechanism is related to elevated level of mitochondrial carnitine in rats. Key words: Electric stimulation therapy; Ischemic preconditioning; Bupivacaine; Drug toxicity; Myocardium

Cardio-protective effects of carnitine in streptozotocin-induced diabetic rats

BackgroundStreptozotocin-induced diabetes (STZ-D) in rats has been associated with carnitine deficiency, bradycardia and left ventricular enlargement.AimThe purpose of this study was to determine whether oral carnitine supplementation would normalize carnitine levels and cardiac function in STZ-D rats.MethodsWistar rats (48) were made hyperglycemic by STZ at 26 weeks of age. Same age normal Wistar rats (24) were used for comparison. Echocardiograms were performed at baseline 2, 6, 10, and 18 weeks after STZ administration in all animals. HbA1c, serum carnitine and free fatty acids (FFA) were measured at the same times. Since STZ-D rats become carnitine deficient, 15 STZ-D rats received supplemental oral carnitine for 16 weeks.ResultsThe heart rates for the STZ-D rats (290 ± 19 bpm) were less than control rats (324 ± 20 bpm) (p < 0.05). After 4 weeks of oral carnitine supplementation, the serum carnitine and heart rates of the STZ-D rats returned to normal. Dobutamine stress increased the heart rates of all study animals, but the increase in STZ-D rats (141 ± 8 bpm) was greater than controls (79 ± 8 bpm) (p < 0.05). The heart rates of STZ-D rats given oral carnitine, however, were no different than controls (94 ± 9 bpm). The left ventricular mass/body weight ratio (LVM/BW) in the diabetic animals (2.7 ± 0.5) was greater than control animals (2.2 ± 0.3) (p < 0.05) after 18 weeks of diabetes. In contrast, the LVM/BW (2.3 ± .2) of the STZ-D animals receiving supplemental carnitine was the same as the control animals at 18 weeks.ConclusionThus, supplemental oral carnitine in STZ-D rats normalized serum carnitine, heart rate regulation and left ventricular size. These findings suggest a metabolic mechanism for the cardiac dysfunction noted in this diabetic animal model.

Enhancement of learning capacity and cholinergic synaptic function by carnitine in aging rats.

The effects of a carnitine derivative, acetyl-L-carnitine (ALCAR), on the cognitive and cholinergic activities of aging rats were examined. Rats were given ALCAR (100 mg/kg) per os for 3 months and were subjected to the Hebb-Williams tasks and a new maze task, AKON-1, to assess their learning capacity. The learning capacity of the ALCAR-treated group was superior to that of the control. Cholinergic activities were determined with synaptosomes isolated from the cortices. The high-affinity choline uptake by synaptosomes, acetylcholine synthesis in synaptosomes, and acetylcholine release from synaptosomes on membrane depolarization were all enhanced in the ALCAR group. This study indicates that chronic administration of ALCAR increases cholinergic synaptic transmission and consequently enhances learning capacity as a cognitive function in aging rats.

Increases in VO 2max and metabolic markers of fat oxidation by caffeine, carnitine, and choline supplementation in rats

We have previously shown that the combination of caffeine, carnitine, and choline supplementation decreased body fat and serum leptin concentration in rats and was attributed to increased fat utilization for energy. As a result, it was hypothesized that the supplements may augment exercise performance including physiological and biochemical indexes. Twenty 7-week-old male Sprague-Dawley rats were given free access to a nonpurified diet with or without supplementation of caffeine, carnitine, and choline at concentrations of 0.1, 5, and 11.5 g/kg diet, respectively. One half of each dietary group was exercised on a motor-driven treadmill for 3 weeks and maximal aerobic power (VO 2max) was determined on the 18th day of exercise. Rats were killed 24-hr postexercise, and blood, regional fat pads, and skeletal muscle were collected. The VO 2max was increased ( P < 0.05) in the supplemented/exercised group; however, the respiratory quotient (RQ) was not affected. Postexercised concentrations of serum triglycerides were decreased but β-hydroxybutyrate, acylcarnitine, and acetylcarnitine were increased in the supplemented animals. The changes in serum metabolites were complemented by the changes in the muscle and urinary metabolites. The magnitude of increase in urinary acylcarnitines (34–45-fold) is a unique effect of this combination of supplements. Cumulative evidence indicates enhanced β-oxidation of fatty acids without a change in the RQ because acetyl units were excreted in urine as acetylcarnitine and not oxidized to carbon dioxide. For this phenomenon, we propose the term “fatty acid dumping.” We conclude that supplementation with caffeine, carnitine, and choline augments exercise performance and promotes fatty acid oxidation as well as disposal in urine.

Effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor, on tissue carnitine and lipid levels in rats.

MET-88, 3-(2,2,2-trimethylhydrazinium) propionate, suppresses carnitine synthesis by inhibiting (gamma-butyrobetaine hydroxylase. The purpose of this study was to clarify the effects of suppression of carnitine synthesis on carnitine and lipid contents in tissues. MET-88 (50, 100, 200 or 400 mg/kg/d) was administered orally to male SD rats for 10, 30 or 60 d. Total carnitine and lipid (triglycerides, non-esterified fatty acids) contents were measured in heart and liver. In both tissues, treatment with MET-88 dose-dependently decreased total carnitine levels, and the reduction reached the plateau state after 30 d at each dose. MET-88 had no effect on lipid content in the heart, but increased the lipid content in the liver at the highest doses. Treatment with MET-88 at 400 mg/kg for 60 d resulted in no pathologic findings in the histological study, and also had no effect on parameters of liver function such as glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase as judged from the results of blood biochemical analysis. We concluded that long-term treatment with MET-88 decreased the carnitine content to a constant level in both heart and liver, but had no effect on lipid contents in the heart, although it affected lipid metabolism in the liver.

Acetyl- [formula omitted] -Carnitine Decreases Glycation of Lens Proteins: in vitro Studies

Although the role of carnitine system in the ocular tissues is not clearly understood, earlier studies showed that lenticular levels of l -carnitine were the highest among ocular tissues and there was a dramatic depletion of lenticular l -carnitine and acetyl- l -carnitine in streptozotocin-diabetic rats. As protein glycation has been implicated in the development of several diabetic complications including cataracts, this study was initiated to show the possible effects of l -carnitine and acetyl- l -carnitine on the glycation and advanced glycation (AGEs) of lens proteins. Calf lens soluble fraction (crystallins) was incubated with 50 m m glucose (containing14C glucose) with or without 5–50 m ml -carnitine, 5–50 m m acetyl- l -carnitine and 5–50 mm acetyl salicylic acid, for 15 days. The results show that while l -carnitine did not have any effect on in vitro glycation of lens crystallins, acetyl- l -carnitine and acetyl salicylic acid decreased crystallin glycation by 42% and 63%, respectively—this decrease was concentration dependent. Glycated crystallins were separated on HPLC which showed that the rate of glycation is in the following order: α>β>γ. Interestingly, acetyl- l -carnitine inhibited glycation of α crystallin more than other crystallins. In vitro incubations with [3H-acetyl] acetyl- l -carnitine showed that acetyl- l -carnitine acetylates lens crystallins (non-enzymatically) and α crystallin is the major acetylated protein. Furthermore, there was a 70% reduction in anti-AGE antibody reactivity when 50 m m acetyl- l -carnitine was included in the incubation of lens crystallins and 10 m m erythrose, suggesting that inhibition of glycation by acetyl- l -carnitine also affected the generation of AGEs. This in vitro study shows, for the first time, that acetyl- l -carnitine could acetylate potential glycation sites of lens crystallins, and protect them from glycation-mediated protein damage.

Successful lowering of epididymal carnitine by administration of pivalate to rats.

This study was designed to lower the epididymal content of carnitine in male rats and to examine subsequent effects on fertility and sperm motility. As carnitine is transported from serum into the epididymal lumen a method to lower serum carnitine was sought. Administration of 20 mmol/L sodium pivalate in the drinking water for up to 5 weeks substantially lowered serum carnitine (to 20% of control levels within 1 week) and reduced epididymal carnitine content (to 25% of control levels in the proximal and 52% of control in distal regions) within 2 weeks. Carnitine in distal cauda epididymal fluid was also reduced (to 30% of control levels) but no changes were observed in the sperm carnitine content. The percentage motility and kinematic parameters of spermatozoa released from four epididymal regions and diluted into artificial medium were unaltered by the treatment, and all males retained their fertility in mating tests performed at weekly intervals. Increasing the dose of sodium pivalate administered to 60 mmol/L for 2 weeks lowered serum carnitine concentration more but did not further decrease epididymal carnitine content and altered neither sperm motility nor male fertility. The rat epididymis secretes an excessive amount of carnitine into its lumen so that substantially lowering the tissue content does not reduce sperm carnitine or affect their motility or fertilizing ability.

Pivalate Affects Carnitine Status but Causes No Severe Metabolic Changes in Rat Liver

To investigate the carnitine deficiency induced by pivalate, rats had free access to drinking water with or without pivalate. Consumption of 20 mmol/L pivalate for 1 wk decreased the levels of both free and total carnitine in plasma to ∼20% of levels before treatment. After 4 wk, the concentrations of free carnitine in the liver, heart and muscle of pivalate-treated rats were ∼60–80% of the control, and in the kidney, 26% of the control. Fractional excretion of free carnitine (FEFC) in pivalate-treated rats was measured; however, the treatment for 3 or 8 d did not affect the values relative to those obtained before treatment. Treatment with pivalate for 4 wk did not affect plasma concentrations of glucose, ammonia and free fatty acids (FFA) in the rats; however, the concentration of 3-hydroxybutyrate (3-OHB) was higher, and the FFA/3-OHB ratio was lower than those of controls. In a liver perfusion study, ketogenesis from oleate and gluconeogenesis from lactate and pyruvate in rats treated with pivalate for 4 wk were not different from controls. These results suggest that administration of pivalate did not induce the excessive excretion of free carnitine in urine, and secondary carnitine deficiency induced by intake of 20 mmol/L pivalate for 4 wk did not cause severe metabolic changes in rat liver.

Distribution of endogenous and exogenous carnitine inrats with sepsis and acute liver failure

The distribution of carnitine was investigated in male Wistar rats with sepsis or acute liver failure. Sepsis was produced by cecal ligation and puncture, while acute liver failure was induced by intraperitoneal injection of carbon tetrachloride. Then 14C-carnitine or L-carnitine was injected intravenously. In healthy control rats and rats with sepsis, both 14C-radioactivity and carnitine were increased in the liver and kidneys. When the carnitine fractions were investigated, it was found that free carnitine and short-chain acylcarnitine were increased. In the rats with acute liver failure, 14C-radioactivity decreased in the liver, but carnitine increased, with free carnitine and short-chain acylcarnitine levels rising. These findings suggested that exogenous free carnitine accumulated directly in the organs with carnitine deficiency in rats with sepsis and acute liver failure. In addition, there was differential regulation of the fractions of both exogenous and endogenous carnitine (free carnitine, short-chain acylcarnitine, and long-chain acylcarnitine). Furthermore, the distribution of exogenous carnitine differed between sepsis and acute liver failure.

Relationship of carnitine transport across the epididymis to blood carnitine and androgens in rats.

The aim of this study was to establish whether a rise in plasma carnitine and testosterone stimulates carnitine uptake in the epididymis. Three groups of rats were injected SC with testosterone enanthate (2.35, 2.40, and 3 mg/kg body weight, respectively, three times a week for 4 weeks) and compared to controls. All three doses proved effective and induced a rise in the weight of the seminal vesicles and prostate, thus reflecting a rise in plasma androgen levels. Testosterone enanthate reduced both testicular weight and the number of spermatozoa in the testes. It raised the level of blood carnitine by 40% in group 1 and by 150% in groups 2 and 3, but the carnitine concentration in the epididymal fluid did not change. These results suggest that the system of carnitine transport across the epididymis is saturated, and that it is not activated by a rise in plasma testosterone.

Effects of short- and long-term feeding of L-carnitine and congeners on the production of eicosanoids from rat peritoneal leucocytes.

The effect of short- and long-term feeding with L-carnitine, L-acetyl carnitine and L-propionyl carnitine on the production of eicosanoids from in vitro stimulated carrageenan-induced rat peritoneal macrophages was investigated. Both young (4 weeks) and old (18 months) rats were used. A lower number of cells was isolated from the peritonea of treated than control young rats after 4 d feeding, but after 60 d no differences were observed. A similar reduction in cell number was found when old animals were given L-acetyl carnitine or L-propionyl carnitine (acutely) or L-acetyl carnitine or L-carnitine (chronically). Plasma carnitine levels were higher in young rats given carnitine both chronically and acutely. Carnitine derivatives were without effect. In contrast, levels of total carnitine in the plasma of old rats given L-carnitine and L-acetyl carnitine for 4 d and 60 d were higher than in controls. There was no correlation between total plasma carnitine level and effects on prostaglandin, thromboxane and leukotriene B4 (LTB4) production. In young rats the most important changes were observed in relation to the production of prostacyclin (PGI2), measured as 6 keto-prostaglandin F1 alpha. Prostacyclin production was higher in the groups given carnitine or its derivatives. The net result of the changes in PGI2 was that the 6 keto-prostaglandin F1 alpha: thromboxane B2 and the 6-keto-prostaglandin F1 alpha: LTB4 ratios tended to be higher in cells from young animals following short-term feeding with L-carnitine.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cyclosporine treatment on carnitine and myo-inositol in diabetic rats

1. The effect of long-term (20 wk) treatment of cyclosporine A (CyA) was studied in urine, blood, liver, kidney and pancreatic concentrations of acid-soluble carnitine and free myo-inositol in streptozotocin diabetic rats. 2. Diabetic rats excreted significantly higher concentrations of carnitine and myo-inositol; CyA prevented the urinary loss of carnitine but not myo-inositol. 3. Blood carnitine levels were not different between normal and diabetic rats, however, CyA significantly decreased these levels. Conversely, blood myo-inositol concentrations were higher in diabetic than in normal rats; CyA prevented this increase. 4. Hepatic concentrations of both carnitine and myo-inositol were increased in diabetic rats; CyA treatment caused even further increase. 5. Pancreas from diabetic rats contained less carnitine and myo-inositol compared to normal pancreas. CyA treatment did not affect pancreatic carnitine, but it normalized myo-inositol in diabetic rats. 6. The kidney carnitine or myo-inositol levels were not influenced either by diabetes or by CyA treatment. 7. These results suggest that CyA treatment causes changes in carnitine and myo-inositol concentrations in biologic fluids and certain tissues.

Effect of short- and long-term diabetes on carnitine and myo-inositol in rats

1. 1. The effect of short- (2 wk) and long-term (20 wk) streptozotocin diabetes was studied on urine, blood, liver, heart, brain, skeletal muscle, pancreas and kidney concentrations of acid-soluble carnitine and free myo-inositol. 2. 2. Short-term diabetic rats excreted significantly higher concentrations of carnitine as well as myo-inositol than normal rats. Blood carnitine and myo-inositol were not different between normal and diabetic rats. Diabetes caused a decrease in liver, brain and pancreatic carnitine, but not in heart, skeletal muscle and kidney. Myo-inositol concentration was decreased in liver, heart and kidney but not in brain, pancreas and skeletal muscle. 3. 3. Long-term diabetic rats had higher urinary excretions of both carnitine and myo-inositol. Blood carnitine did not change; however, myo-inositol was higher in diabetic than in normal rats. Diabetes caused a significant increase in liver and a decrease in heart, brain, skeletal muscle and pancreatic content of carnitine; no difference in kidney carnitine was noted. Myo-inositol content was elevated only in liver of diabetic rats. 4. 4. We suggest that carnitine and myo-inositol concentrations are influenced both by short- and long-term diabetes through changes in tissue metabolism.

Development of intestinal carnitine transport in rats.

The intestinal transport of carnitine in suckling rats (12 and 16 days old) and weaned rats (28 and 75 days old) was studied in vitro using everted small intestinal sacs. The sacs were incubated in a mucosal medium without carnitine or with added carnitine at a 200-microM concentration. The release of endogenous carnitine and its esters into the serosal medium was greatest in the 12-day-old pups and lowest in the postweaning period. In contrast, the transport of carnitine from the mucosal to the serosal compartment was lowest in the 12-day-old pups and higher in the older groups. The present study suggests that the transfer of carnitine from the mucosal to the serosal compartment is influenced by the presence of endogenous carnitine in the intestinal mucosa, which in turn is determined by the age of the animals.

Attenuation of ethanol metabolism by supplementary carnitine in rats

The purpose of this study was to examine the effect of supplementary D,L-carnitine on blood-ethanol levels and ascertain if the effect was a result of altered absorption or metabolism of ethanol. Mature male Sprague-Dawley rats were fed Purina Rat Chow as such or supplemented with various levels of D,L-carnitine. First it was established that supplementing carnitine at 1% (w/w) level produced steady state concentrations of carnitine in blood after 3 days of feeding. When a single dose of ethanol was given orally after 5 days of carnitine supplementation, the blood levels of ethanol remained significantly elevated for 2–8 hours in the carnitine supplemented animals. Time course of blood-ethanol concentrations revealed that carnitine did not affect the rates of ethanol absorption and therefore, the effect must be due to the attenuation of ethanol clearance from the blood.

Catabolic pathways for high-dosed L(-)- or D(+)-carnitine in germ-free rats?

Gnotobiotic rats received up to 3 mmol L-carnitine/day with the drinking water during 9 days. They excreted about a quarter of the administered dose with the urine, partially in form of acetyl-L-carnitine, but trimethylamine, trimethylamine N-oxide or gamma-butyrobetaine were not detectable in urine or faeces in contrast to conventional animals. After oral loading with D-carnitine the unphysiological isomer was absorbed and either excreted unchanged in urine or metabolized to acetonyltrimethylammonium. With regard to the development of carnitine deficiency syndromes and the degradation of nutritional carnitine the conclusion has to be drawn, that the bacteria of the gastro-intestinal tract, but not the tissues of the mammals, are responsible for the metabolization of L-carnitine to gamma-butyrobetaine or trimethylamine.

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.

Antiketonemic and Antiketogenic Actions of Carnitine in Vivo and in Vitro in Rats

The effect of carnitine on ketone and lipid metabolism in intact rats and in isolated tissues was investigated. DL-Carnitine (200 mg/100 g body weight) administered orally lowered by approximately 40–65% plasma concentrations of ketone bodies in suckling rats and fasted adult rats. It also suppressed hyperketonemia induced by corn oil feeding in suckling and adult rats by approximately 30–60%. Carnitine did not change β-hydroxybutyrate oxidation in heart and kidney mitochondria. Incubation of carnitine with tissue slices of cerebral cortex, kidney and diaphragm did not affect 14CO2 production or lipid synthesis from DL-[3-14C]-β-hydroxybutyrate. The compound reduced the urinary concentration and excretion of ketone bodies in rats fed corn oil but had no effect in rats not treated with corn oil. Although DL-carnitine at concentrations ranging from 0.2 to 20 mm stimulated ketone production in hepatocytes, at a higher concentration (i.e., 40 mm) it produced a sharp depression in ketogenesis. These results indicate that carnitine does not stimulate ketone utilization by extrahepatic tissues. The antiketonemic effect of carnitine in rats treated with a high dose of the compound most likely results from inhibition of hepatic ketone production. An excessive increase in free carnitine by exogenous administration could upset the equilibrium for conversion of acylcarnitine to acylCoA in mitochondria and hence suppress β-oxidation and ketogenesis.carnitine hyperketonemia ketone utilization ketogenesis

Brown adipose tissue and carnitine in cold-adapted rats.

Cold-adapted (CA) and warm-adapted (WA) rats (5 and 28 degrees C) were infused with noradrenaline (4 microgram.kg-1.min-1) for 15 min. Blood was collected from Sulzer's vein coming from brown adipose tissue and analyzed for total carnitine, free carnitine, and beta-hydroxybutyrate content, before and up to 45 min after the infusion. Acylcarnitine (total minus free carnitine) levels increased more and total carnitine levels decreased more in the CA group than in the WA group. beta-Hydroxybutyrate content increased to the same extent (from about 0.16 to 0.8 mM) in both groups. Brown fat was found not to release carnitine into the circulation after NA infusion. Twenty minutes after the end of the infusion brown fat retained both ketones and acylcarnitine in the CA rats only.