Mario Monti

Clinical Physiology: Microcalorimetric Measurements of Heat Production in Whole Blood and Blood Cells of Normal Persons

Microcalorimetric measurements have been made of the heat production in whole blood and its major cell fractions. All measurements were made with samples from normal subjects. The average heat effect value found (plus or minus S.D.) for whole blood was 62 plus or minus 7 mW/l. The value obtained for erythrocytes was 82 plus or minus 6 mW per liter of packed cells suspended in phosphate buffer at pH 7.4. For lymphocytes and for polymorphonuclear leukocytes heat effect values were 4.6 plus or minus 1.8 and 1.2 plus or minus 0.4 pW/cell, respectively, for cells suspended in buffer. For plasma suspensions corresponding values were 2.2 plus or minus 1.4 and 3.5 plus or minus 1.0 pW/cell, respectively. For thrombocytes suspended in plasma the heat effect value was 59 plus or minus 8 fW/cell. Heat production in cell-free plasma was close to zero. Using heat effect values determined for the different cell fractions, values could be calculated for whole blood samples which were in full agreement with the values obtained by direct measurements of whole blood.

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.

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.

Microcalorimetric Measurements of Heat Production in Human Erythrocytes I. Normal Subjects and Anemic Patients

Heat production in human erythrocytes has been measured by a new microcalorimetric technique. The calorimeter consisted of a twin thermopile heat conduction unit. A 1 ml sample was enclosed in a steel ampoule which was introduced into the measuring zone of the calorimeter through a heat exchange system. Measurements were made on erythrocytes suspended in plasma and in phosphate buffer (pH 7.4) containing glucose. Heat effects produced per liter erythrocytes were 79 ± 11 mW and 79 ± 8 mW, respectively (mean ± S.D.). In various types of anemia significantly higher values were found, mean value 126 ± 29 mW/l erythrocytes.

Heat production by adipocytes from obese subjects before and after weight reduction

Microcalorimetry has been employed to measure the heat production by adipocytes obtained by percutaneous biopsy from lean subjects and from obese subjects before and after weight reduction. Cellular heat production was significantly lower in obese than in lean subjects. After weight reduction cellular heat production increased in fat cells from the obese subjects but was still significantly lower than in cells from control subjects. A number of variables reflecting uptake and mobilization of depot fat have measured and correlated to the heat production values in the obese subjects. The findings are consistent with the view that a decreased total metabolic activity might contribute to the development or perpetuation of obesity.

Heat production in human blood lymphocytes. A methodological study

Heat production rates (thermal power) in peripheral blood lymphocytes from healthy subjects were determined under some defined experimental conditions in an attempt to establish by microcalorimetry a basal metabolic reference range for lymphocytes in the non-activated state. The effects of cell isolation method, the presence of other types of blood cells, cell concentration, temperature, pH and type of suspension medium on the rate of heat production by lymphocytes were evaluated. The results indicate that microcalorimetry is suitable for monitoring the metabolism of these cells with good precision in the physiological range of cell concentration.

Microcalorimetric Measurements of Heat Production in Human Erythrocytes: III. Influence of pH, Temperature, Glucose Concentration, and Storage Conditions

Heat production in human erythrocytes has been measured under different conditions of pH, glucose concentration, and temperature. Storage conditions have also been varied. The erythrocytes, which were from healthy subjects, were suspended either in autologous plasma or in phosphate buffer. The heat effect, P, was shown to increase linearly in the physiological pH range: 1.2% per 0.01 pH unit. Variation of the glucose concentration within a wide range, 3-32 mmol/1, did not affect the P value. The temperature coefficient for P was determined to be Q10 = 2.8 for the temperature range 32-42 degrees C. A constant energy of activation was found, 82.6 kJ/mol, for the temperature range 25-42 degrees C. When the erythrocytes were stored at 4 degrees C, P values (measured at 37 degrees C) increased initially by 6%/h. After 24 h of storage P was about 50% higher than the initial value. Determinations of glucose consumption were made in parallel with most of the calorimetric experiments.

Erythrocyte thermogenesis in hyperthyroid patients: Microcalorimetric investigation of sodium/potassium pump and cell metabolism

Erythrocyte thermogenesis was studied by microcalorimetry in 11 patients before and after treatment for hyperthyroidism. Cell heat production rate and intracellular Na+ and K+ levels were measured in plasma suspensions of erythrocytes with and without specific inhibition of Na/K ATPase by ouabain. The ouabain induced change in the heat production rate (the Na/K pump thermal power); the erythrocyte intracellular Na+ content and the ouabain sensitive Na+ transport were used to estimate the Na/K pump function. The mean value for heat production rate was 131 +/- 4 mW/L erythrocytes before treatment, which is significantly higher than in euthyroid subjects. A significant decrease (P less than 0.01) to normal levels was recorded following therapy. This decrease, as determined in samples with ouabain, correlated to changes in serum levels of triiodothyronine, T3, (r = .74, P less than 0.01). The Na/K pump thermal power was 11 +/- 2 mW/L erythrocytes (8 +/- 2% of total heat production rate) before and 9 +/- 2 mW/L erythrocytes (8 +/- 2%) after treatment. These two values were not different from those obtained in euthyroid subjects. The erythrocyte Na+ content decreased from 9.9 +/- 2.1 to 4.9 +/- 0.5 mmol/L erythrocytes (P less than 0.001) following normalization of thyroid function. The decrease in intracellular Na+ concentration correlated to the decrease in serum T3 levels, but only when calculated from the data obtained in samples with ouabain (r = .60, P less than 0.05). The relative increase in intracellular Na+ concentrations following addition of ouabain was significantly lower (P less than 0.05) before than after treatment for hyperthyroidism, 37 +/- 10% and 61 +/- 5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Microcalorimetric Measurements of Heat Production in Human Erythrocytes: IV. Comparison between Different Calorimetric Techniques, Suspension Media, and Preparation Methods

Heat production in human erythrocytes from healthy subjects has been measured under different experimental conditions. Simultaneous measurements were made on the same samples using different types of microcalorimeters: a static ampoule calorimeter, an air perfusion calorimeter, and a flow calorimeter. Obtained heat effect values for specified standard conditions, P degrees, were within uncertainty limits the same for the different calorimeters. Cells were suspended either in autologous plasma or in a phosphate buffer. P degrees values for buffer suspensions were significantly higher than those for plasma suspensions. Erythrocyte samples prepared by the column adsorption technique gave higher P degrees values than those obtained by a conventional centrifugation procedure.