Gitten Cederblad

A method for the determination of carnitine in the picomole range

Abstract A method is described for the determination of L -carnitine in the range 20–2000 pmoles. Incubation of L -carnitine with [1-14C]acetyl-coenzyme A and acetyl-CoA: carnitine O-acetyltransferase (EC 2.3.1.7) yields labeled acetylcarnitine. The formed acetylcarnitine is separated from labeled acetyl-coenzyme A by passing the reaction mixture through a column of the anion exchange resin Dowex 2-X8 and its isotope content determined in a liquid scintillation counter. Short-chain acyl derivatives of L -carnitine are substrates for the enzyme and will also be determined through exchange in the enzymic reaction. In 33 samples of human blood plasma the concentration of carnitine (+short-chain acyl carnitine) was 51 ± 10.5 μmoles/l (mean ± S.D.). In biopsies of human skeletal muscle obtained at surgery the concentration was 12.8 ± 2.9 μmoles/g dry weight, in mouse skeletal muscle 1.73 ± 0.27 μmoles/g dry weight, and in mouse heart 4.66 ± 0.73 μmoles/g dry weight. The precision of the method expressed as relative standard deviation of duplicate analyses was 2–5%. The recovery of carnitine added to plasma or to perchloric acid extracts of muscle was 97 ± 12.5% and 103 ± 5.9%, respectively.

Concentration of carnitine in human muscle tissue

Abstract The concentration of acid-soluble carnitine has been determined in human muscle tissue and in plasma. One group of subjects consisted of patients mainly suffering from cholecystolithiasis or varicose veins. Biopsies were surgically obtained under general anesthesia. The other group consisted of normal subjects in which the biopsies were obtained by a percutaneous technique. We could not demonstrate a significant change in concentration of carnitine along a muscle fiber bundle or a difference in the concentration between specimens from superficial and deep levels. The rectus abdominis muscle had a lower carnitine concentration than the muscles of the leg. The median values were 13.7 μmoles/g dry weight (range 7.7–32.5) and 17.9 μmoles/g dry weight (range 6.5–24.1), respectively. Men had slightly higher concentrations in the rectus adbominis muscle than women. Median values were 15.4 μmoles/g dry weight (range 7.7–32.5) and 12.9 μmoles/g dry weight (range 9.8–17.7), respectively. Two subjects from whom biopsies were obtained with an interval of 91 and 42 days showed nearly the same values on both occasions. No correlation was found between age and carnitine concentration in muscle tissue. The carnitine concentration in two biopsies of human heart muscle was 4.2 μmoles/g dry weight and 4.8 μmoles/g dry weight, respectively. The median value of plasma carnitine concentration was 46.2 μmoles/1 (range 17.9–74.7). The concentration of carnitine in plasma was not correlated with the concentration of carnitine in muscle tissue.

Extrusion cooking of a high-fibre cereal product 2. Effects on apparent absorption of zinc, iron, calcium, magnesium and phosphorus in humans

1. The effect of extrusion cooking, using mild conditions, of a high-fibre cereal product on apparent small bowel absorption of zinc, iron, calcium, magnesium and phosphorus was studied. 2. Seven ileostomy subjects were studied during two periods (each of 4 d), on a constant low-fibre diet supplemented with either 54 g/d of a bran-gluten-starch mixture or the corresponding extruded product. 3. The apparent absorption of Zn, Mg and P was significantly decreased (P less than 0.05) during the period with extruded product compared with the period with bran-gluten-starch. No difference was found for Fe and Ca. 4. The negative effect of extrusion cooking of a product containing phytic acid on availability of Zn, Mg and P was small but could be of nutritional relevance in foodstuffs that are consumed frequently and in infant formulas.

Plasma carnitine and body composition.

Plasma carnitine has been determined in 16 men and 45 women without known muscular disorders. Mean values were 57.3 mumoles/l +/- 12.8 (S.D.) for men and 46.5 mumoles/l +/- 12.4 (S.D.) for women. The difference was statistically significant. Of the variables tested, a positive significant relationship was found between plasma carnitine and age, but not for different variables of body composition, e.g. body cell mass or plasma cholesterol and triglycerides. The daily urinary excretion of carnitine has been compared in a healthy individual during two periods, one on an ordinary diet and one on a gruel diet, giving a constant carnitine intake. The mean value of carnitine excretion (241 mumoles per 24 h) of the two periods did not differ and although the variance was less on the gruel diet, no statistical difference was found.

Metabolism of labeled carnitine in the rat

In two series of rats, the concentration of carnitine in plasma was 39.9 and 37.8 μmol/ liter, in skeletal muscle tissue 2.97 and 3.26 μmol/g dry wt and the urinary excretion 3.2 and 2.4 μmol/24 h. The renal clearance of carnitine was calculated to 88 and 76 ml/24 h. L-[Me-14C]Carnitine and DL-[Me-14C]carnitine have been administered to rats. Only labeled l-carnitine has been found on chromatographic analysis of plasma, urine, and muscle tissue. The specific radioactivity of carnitine in plasma, urine, and muscle tissue has been followed for up to 16 days. A two-compartment metabolic model has been used to interpret the result of the experiment with labeled l-carnitine and the rate constants and compartment sizes have been calculated. The total body content of carnitine was 57 μmol (about 35 μmol/100 g body wt) and the daily turnover was about 7% of the body pool. The daily synthesis of carnitine in the rat is estimated to about 2 μmol/100 g body wt.

Carnitine and left ventricular function in haemodialysis patients

Left ventricular function was non-invasively studied in 28 randomly selected haemodialysis patients before and after administration of L-carnitine, 2 g i.v. three times per week or saline in a double blind designed study over a six-week period. Cardiac function variables showed no relationship to muscle (vastus lateralis) and plasma carnitine concentrations. No apparent deficiency in muscle carnitine was found, whereas total plasma carnitine was lower in female patients than in female controls, p less than 0.002. The echocardiographic left ventricular end-diastolic diameter was initially increased in about one third and the ejection fraction was depressed in about one fifth of the patients. An increased A:H ratio was found in 15%. Systolic time intervals were deranged in 30% of the patients. After carnitine administration, marked increases of muscle and plasma carnitine levels were found, p less than 0.01, but no effects were recorded in any of the cardiac tests. Muscle carnitine increased from 14.6 mmol/kg dry weight to a median of 23.7 mmol/kg. We found no support for the hypothesis that carnitine depletion is responsible for cardiac dysfunction in haemodialysis patients.

Excretion of l-carnitine in man

Abstract 1. 1. The method for carnitine determination described by Marquis and Fritz has been adapted for determination of carnitine in human urine. 2. 2. The excretion of carnitine in normal men was 175 ± 80.7 μmoles per day (mean ± S.D.) and in women 86 ± 72.6 μmoles per day. The difference in carnitine excretion between men and women was statistically significant. 3. 3. Considerable inter- and intraindividual variations in carnitine excretion were noted. The carnitine excretion during the night was lower than during the day. 4. 4. After administration of carnitine (1520 μmoles of l -carnitine) to 3 subjects the additional excretion in urine over a 3-day period was 18, 43, and 66%.

L-carnitine and haemodialysis: double blind study on muscle function and metabolism and peripheral nerve function

Twenty-eight haemodialysis patients were randomized to L-carnitine, 2 g i.v. three times a week, and saline over a 6-week period. No obvious deficiency of carnitine was found in vastus lateralis with a median value of 12.9 mmol/kg dry weight; range 6.2-21.4. Female patients had lower total plasma carnitine compared to female controls, p less than 0.002, whereas no decrease was found in males. No relationship was found between muscle and total plasma carnitine. After carnitine administration the muscle carnitine level increased about 60%, p less than 0.01, and the total plasma carnitine level more than tenfold, whereas the initially high degree of acylation decreased, p less than 0.02. Maximum dynamic muscular strength was reduced with a mean value of 44% compared with healthy controls. Total metabolic activity of isolated skeletal muscle fibres, measured as heat production with a new technique using a perfusion microcalorimeter, showed a median value of 0.40 mW/g, 25% lower than normal, p less than 0.02. Carnitine administration had no effect on several different tests of muscular function. Neurophysiologically, discrete improvements in the temperature responses were recorded, but no changes in sensory and motor nerve conduction velocities or in vibration thresholds were noted. No symptomatic improvement was observed even in patients with the lowest carnitine levels prior to treatment. Our data do not support the hypothesis that carnitine deficiency contributes to muscle and nerve dysfunction in patients on chronic haemodialysis.

Plasma lipoproteins, liver function and glucose metabolism in haemodialysis patients: lack of effect of L-carnitine supplementation

The effects of L-carnitine administration (2 g i.v. three times weekly for 6 weeks) were studied in a double blind trial comprising 2 X 14 patients on regular haemodialysis treatment. The initial plasma carnitine concentrations were normal in the male, but slightly lowered in the female participants and rose more than ten-fold in the patients receiving active treatment. The majority (15/28) of patients had moderate hypertriglyceridaemia, whereas plasma HDL cholesterol levels were normal. Activities of hepatic and lipoprotein lipase were decreased and fat tolerance impaired. The S-triiodothyronine and/or thyroxine levels were subnormal in 11 patients. Four patients had fasting hyperinsulinemia, and 6 demonstrated abnormal B-glucose patterns after a peroral glucose load. The galactose elimination rate demonstrated moderately impaired hepatocyte function in four patients. No effects of carnitine treatment on any of the variables could be detected.

Carnitine Concentration in Relation to Enzyme Activities and Substrate Utilization in Human Skeletal Muscles

The relationships between the carnitine concentration and enzyme activities representative of different metabolic pathways, glycogenolysis, glycolysis, beta-oxidation of fatty acids, citric acid cycle, and respiratory chain were studied in skeletal muscle tissue from 18 volunteering subjects. In addition, the in vitro incorporation rates of glucose-carbon and palmitate-carbon into different metabolites, and the concentration of glycogen, triglycerides, and phospholipids were determined in the same tissue specimen. The carnitine concentration correlated positively and statistically significantly with the activities of 3-OH-acyl-CoA dehydrogenase and citrate synthase, with the incorporation rate of palmitate-carbon into CO2, and the incorporation rate of glucose-carbon into lactate in the muscle tissue. The results indicate a coupling between the concentration of carnitine and the capacity for long-chained fatty acid oxidation in human skeletal muscles.