Effect of training on esterified fatty acids and carnitine in muscle and on lipolysis in adipose tissue in vitro

Effect of exercise training on the fatty acid composition of lipid classes in rat liver, skeletal muscle, and adipose tissue

The aim of the present study was to examine the effects of 8 weeks of exercise training on the fatty acid composition of phospholipids (PL) and triacylglycerols (TG) in rat liver, skeletal muscle (gastrocnemius medialis), and adipose tissue (epididymal and subcutaneous fat). For this purpose, the relevant tissues of 11 trained rats were compared to those of 14 untrained ones. Training caused several significant differences of large effect size in the concentrations and percentages of individual fatty acids in the aforementioned lipid classes. The fatty acid composition of liver PL, in terms of both concentrations and percentages, changed with training. The TG content of muscle and subcutaneous adipose tissue decreased significantly with training. In contrast to the liver, where no significant differences in the fatty acid profile of TG were found, muscle underwent more significant differences in TG than PL, and adipose tissue only in TG. Most differences were in the same direction in muscle and adipose tissue TG, suggesting a common underlying mechanism. Estimated fatty acid elongase activity was significantly higher, whereas Delta(9)-desaturase activity was significantly lower in muscle and adipose tissue of the trained rats. In conclusion, exercise training modified the fatty acid composition of liver PL, muscle PL and TG, as well as adipose tissue TG. These findings may aid in delineating the effects of exercise on biological functions such as membrane properties, cell signaling, and gene expression.

Sudden infant death syndrome (SIDS): disordered brown fat metabolism and thermogenesis

Foster found areas with the highest incidence of SIDS in USA in 1983-1984 coincided with the highest areas recorded with the highest incidence of goitre in First World War troops (1). Reid compared the two populations described as having the highest incidence of SIDS worldwide. Both were selenium deficient areas (King County WA, USA and Canterbury, New Zealand). Besides being a selenium livestock responsive area, Canterbury school children, prior to 1925, had a 56% incidence of goitre (2-6). Brown adipose tissue (BAT) synthesises fatty acids from glucose. BAT is a major tissue in fatty acid metabolism for the generation of heat (7). BAT has the specific property of converting thyroxine (T4) to triodothyronine (T3) via Type II deiodinase enzyme. There is a many fold increase in the activity of this deiodinase in BAT after exposure of rats to sudden cold, which is greatly impaired in selenium deficient animals (7). The accepted picture of SIDS worldwide is that there is an increased incidence in infants of young smoking mothers. The incidence peaks in the second and third month of life, in winter and as latitude increases.

Total carnitine content of the middle gluteal muscle of thoroughbred horses: normal values, variability and effect of acute exercise

There was no detectable loss of total carnitine associated with intense exercise from the middle gluteal muscle of Thoroughbred horses. Measurements made on a single biopsy obtained during the course of a normal training and exercise programme may, therefore, be considered representative of the normal content at rest. The variability in total carnitine content within the normal muscle biopsy area amounted to 13.2 per cent of the normal mean content. Approximately 50 per cent of this variability could be attributed to covariation with citrate synthase, to which it was highly significantly correlated. The muscle carnitine content of yearling Thoroughbred horses ranged from 10.5 to 18.8 mmol/kg dry muscle (dm); the ranges in untrained, lightly trained and fully trained two-year-olds were 18.5 to 34.7, 14.1 to 24.2 and 22.9 to 26.9 mmol/kg dm, respectively. In horses aged over three years total carnitine ranged from 21.3 to 35.5 mmol/kg dm. A trend toward higher contents of total carnitine with age and training appeared to be largely a consequence of underlying changes in mitochondria density as indicated by differences in levels of citrate synthase activity. There was a marked difference in ratios of total carnitine to citrate synthase activity between training yards, reflecting possible differences in management regimens and/or bloodstock selection.

Nutrition and fuel utilization in the athletic horse

Substrate depletion and end product accumulation are two important factors in exercise fatigue. Fatigue during long-term exercise results from a depletion of muscle and liver glycogen and coincides with an inability to maintain blood glucose levels. During high intensity exercise, the rapid catabolism of carbohydrate and the resultant production of lactate and hydrogen ions cause a reduction in muscle pH that inhibits maximum force generation. Dietary manipulations that can influence carbohydrate status or lactate accumulation may be beneficial to performance. In human athletes, carbohydrate loading and carbohydrate supplementation can enhance endurance time during long-term exercise. These practices have not been explored extensively in the equine athlete, although glycogen loading does not enhance the performance of horses during short-term intense work. Short-term work can be detrimentally affected if glycogen levels are inadequate. The most marked effect of exercise on nutrient requirements is in the energy requirement. Horses in heavy training may require more energy than they can consume on a conventional diet. Fat has been added to horse diets to increase energy density, usually at levels between 6% and 12% of the total diet. Although protein requirements may be slightly increased in the working horse, supplementing protein as a means of adding calories is not an efficient practice. In addition, although studies with horses are not available, human studies indicate that there are no benefits to vitamin supplementation above required levels. At this point, more is unknown than is known about feeding performance horses. Most information on fuel utilization is extrapolated from studies with rats and humans. Areas that have received little attention but are critical to optimizing feeding practices are the timing of pre-event feeding and the determination of ideal body composition in equine athletes of different types.

The effect of exercise on lipid metabolism in men and women

Lipoprotein abnormalities constitute a major risk for development of cardiovascular disease. These substances, which are comprised of various lipids and proteins (apoproteins), are influenced by specific enzymes which effect their concentrations. It has been demonstrated that elevated total cholesterol and LDL cholesterol are directly associated with the development of coronary artery disease, whereas HDL cholesterol has an inverse relationship with coronary heart disease (CHD). Although more controversial, triglycerides may also be directly associated with coronary atherosclerosis. Favourable changes in lipid levels have been shown to reduce coronary mortality. Exercise may constitute a non-pharmacological approach to lipoprotein therapy. Many exogenous factors also influence lipoprotein concentrations. Changes in diet, body composition, age, as well as medication and alcohol usage may directly alter lipid levels. In addition, they can be artificially affected by the analytical method. The immediate effects of one to several bouts of physical activity appear to influence lipoprotein level. A reduction in triglycerides has been shown after physical exertion, especially among trained individuals and those with hypertriglyceridaemia. These acute changes may reflect the utilisation of both muscle and plasma triglycerides as fuels during exertion. After more prolonged training, changes in lipoproteins may also occur. However, since exercise is accompanied by many co-variables which also favourably alter these levels (e.g. lower percentage of body fat, dietary alterations), it is difficult to determine the direct effect of regular physical activity. Initial studies of exercise training's effects on total cholesterol did not differentiate changes in HDL and LDL cholesterol. Subsequent research has observed these specific cholesterol fractions. Consistent reduction in LDL cholesterol levels have not been convincingly demonstrated. Although HDL cholesterol has been shown to increase in certain studies, the response has been variable in other investigations. These latter responses may have been due to the fact that HDL cholesterol changes may be dependent on levels prior to conditioning. Assessment of HDL cholesterol subfractions (HDL2 and HDL3), which could additionally impact on cardiovascular risk reduction, have shown favourable increases in HDL2, but as yet these HDL moieties have not been adequately investigated. Reductions in triglyceride levels after training among those with elevated values and beneficial apoprotein changes post-training have been reported, although few studies exist.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of oral supplementation with L-carnitine on maximum and submaximum exercise capacity

Two trials were conducted to investigate the effects of L-carnitine supplementation upon maximum and submaximum exercise capacity. Two groups of healthy, untrained subjects were studied in double-blind cross-over trails. Oral supplementation of 2 g per day L-carnitine was used for 2 weeks in the first trial and the same dose but for 4 weeks in the second trial. Maximum and submaximum exercise capacity were assessed during a continuous progressive cycle ergometer exercise test performed at 70 rpm. In trial 1, plasma concentrations of lactate and beta-hydroxybutyrate were measured pre- and post-exercise. In trial 2, pre- and post-exercise plasma lactate were measured. The results of treatment with L-carnitine demonstrated no significant changes in maximum oxygen uptake (VO2max) or in maximum heart rate. In trial 1, there was a small improvement in submaximal performance as evidenced by a decrease in the heart-rate response to a work-load requiring 50% of VO2max. The more extensive trial 2 did not reproduce the significant result obtained in trial 1, that is, there was no significant decrease in heart rate at any given submaximal exercise intensity, under carnitine-supplemented conditions. Plasma metabolic concentrations were unchanged following L-carnitine, in both trials. It is concluded, that in contrast to other reports, carnitine supplementation may be of little benefit to exercise performance since the observed effects were small and inconsistent.

Carnitine status, plasma lipid profiles, and exercise capacity of dialysis patients: effects of a submaximal exercise program

Carnitine status, blood lipid profiles, and exercise capacity were evaluated in a combined group of hemodialysis (N = 4) and continuous ambulatory peritoneal dialysis (N = 6) patients before and after an 8-week submaximal exercise program. Maximal aerobic capacity (VO2max) was only 18.5 +/- 5.9 (mean +/- SD) mL O2/kg/min, well below the expected 30 to 35 mL O2/kg/min for age-matched sedentary controls. Plasma short-chain acylated carnitine levels, which were two to three times normal values, were reduced after the exercise program, but the long-chain acylcarnitines were significantly reduced during acute exercise. Muscle biopsies of the vastus lateralis were performed at rest in five patients prior to and after the 8-week exercise program. Total carnitine in skeletal muscle was 3.09 (.076 SD) mumol/g ww, with only 11.3% acylated prior to the exercise program, which was much lower than the 4.25 +/- 1.27 mumol/g ww, with 28.5% acylated in a group of healthy athletic subjects (N = 28). Muscle free carnitine concentrations decreased significantly following the 8-week training period, with only a slight reduction in total carnitine. The percent of acylated carnitine was therefore significantly increased (P less than 0.05) from 11.3% to 25.2% after the experimental period. Pretraining carnitine palmitoyl transferase activity at rest was 0.57 +/- 0.28 nmol palmitoyl carnitine formed/5 min/mg mitochondrial protein, which was not changed by exercise training v 1.80 +/- 0.51 nmol/5 min/mg protein in 28 healthy normals (P less than 0.001). Free fatty acid concentrations were reduced significantly during acute exercise as a result of the exercise training program whereas other plasma lipids were not altered. (ABSTRACT TRUNCATED AT 250 WORDS)

The effect of a 20-week endurance training program on adipose-tissue morphology and lipolysis in men and women

In order to assess the effect of endurance training on adipose-tissue morphology and lipolysis, 22 adult subjects (11 men and 11 women) took part in a 20-week ergocycle training program, four to five days a week, 40 minutes a day, at 80% of their maximal heart rate. Before and after training, they were submitted to an adipose-tissue biopsy in the suprailiac region. Fat cell weight (FCW), and lipolytic activity were determined on isolated fat cells. For the whole sample, training significantly reduced FCW (pre: 0.40 +/- 0.13 (mean +/- SD) versus post: 0.36 +/- 0.13 micrograms; P less than 0.05), percentage of fat (pre: 22.0 +/- 8.3 versus post: 19.7 +/- 8.1%; P less than 0.05), and increased adipocyte epinephrine maximal stimulated lipolysis (ESL) (pre: 1.08 +/- 0.49 versus post: 1.69 +/- 0.67 mumol glycerol/30 min/10(6) cells; P less than 0.001). No changes were observed in fat cell number. In women, however, training induced no changes in the fatness indicators (% fat, sum of skinfolds, FCW). The exercise program significantly lowered the adiposity of men (% fat: P less than 0.001; sum of skinfolds: P less than 0.01; FCW: P less than 0.05). In both sexes, a significant increase in ESL was observed after training. ESL of men, however, responded better than that of women to training (ESL of women: 1.36 +/- 0.67 versus ESL of men: 2.02 +/- 0.50 mumol glycerol/30 min/10(6) cells; P less than 0.05), with increases over pre-training values of 46% and 66% in women and men, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Commentary on the reduced urinary noradrenaline excretion following cold stress and exercise in physically trained rats

Urinary catecholamine excretions of rats trained by swimming or running were compared with those of cold-acclimated rats and controls i.e. sedentary warm-acclimated rats. During cold stress the trained rats excreted less noradrenaline (NA) than did controls. In fact rats trained by swimming excreted less NA than did cold-acclimated rats, while rats trained by running excreted about the same amount as did cold-acclimated rats. 2 h of swimming increased the urinary catecholamine (CA) excretion of all groups but trained rats excreted less NA than did controls and cold-acclimated rats, which had excretions of similar magnitude. The NA excretions of the two trained groups never deviated statistically from each other. It is concluded that concerning NA requirement in order to maintain homeostasis, training produces "cross tolerance" to cold stress but cold-acclimation does not produce "cross tolerance" to acute exercise. Furthermore the positive effect of training on NA excretion during the stress of cold or that of acute exercise seems essentially to be an effect of increased locomotor activity as such regardless of the type of training. It is also suggested that increased levels of locomotor activity of the rat may be of importance for seasonal acclimation of the species by increasing its tolerance to cold.

Lipoprotein lipase activity in adipose tissue and skeletal muscle of runners: relation to serum lipoproteins

Physically well-trained people generally have lower VLDL-triglyceride and higher HDL-cholesterol levels than sedentary subjects. To examine the underlying mechanisms of this lipoprotein pattern, we measured the lipoprotein lipase (LPL) activity in needle biopsy specimens of adipose tissue and skeletal muscle of competitive runners and of body weight-matched, physically less-active controls. The active sportsmen were either sprinters, whose training program consisted mainly of athletics of short duration or long distance runners undergoing a strenuous endurance exercise program. In sprinters (all males) the serum lipid and lipoprotein concentrations did not differ significantly from those of controls and the mean LPL activities in muscle and adipose tissue were also similar in these two groups. The long distance runners (both sexes), on the other hand, had higher means levels of HDL-cholesterol than the respective controls. The LPL-activity of both adipose tissue (p less than 0.05) and skeletal muscle (p less than 0.01) was significantly higher in male long distance runners than in control males. Female runners had higher muscle LPL activity than controls (p less than 0.01) but in adipose tissue the difference in LPL activity was not significant. Rough estimates calculated for LPL activity present in whole body adipose tissue and skeletal muscle indicated that total LPL activity was 2.3 times higher in male long distance runners and 1.5 times higher in female long distance runners than in the respective controls. In combined groups of male runners and controls, there was a highly significant positive correlation between the serum HDL-cholesterol level and the LPL activity of adipose tissue expressed per tissue weight (r = +0.72, p less than 0.001) or per whole body fat (r = +0.62, p less than 0.001). The group means of HDL-cholesterol and adipose tissue LPL activity in the five cohorts studied (male sprinters, distance runners and controls and female distance runners and controls) were also positively correlated (r = +0.94). It is concluded that endurance training is associated with an adaptive increase of LPL activity not only in skeletal muscle but also in adipose tissue. These changes are not observed in sprinters who are trained by exercises of shorter duration. The high HDL-cholesterol levels of physically well-trained people are probably accounted for, at least partly, by the increased LPL activity and the concomitant rapid turnover or triglyceride-rich lipoproteins.

Carnitine-induced uptake of L-cartinine into cells from an established cell line from human heart (CCL 27)

L-Carnitine is actively transported into Girardi human heart cells, an established cell line from human heart. The present study was undertaken to investigate the effect of different concentrations of L-Carnitine in the growth medium on the rate of uptake of L-[3H] carnitine. Increasing the concentration of L-Carnitine from 2 to 100 mumol/l in the growth medium of cells, increased the rate of uptake of L-[3H] carnitine by about 50%. The maximal effect was reached after approx. 72 h incubation. The increase in rate seemed to be caused by synthesis of increased number of carriers, as judged by the increase of V with unchanged apparent Km for the transport process. This effect of L-carnitine could be inhibited by cycloheximide, indicating the dependence on intact protein synthesis. The morphology of the cells was studied by electron microscopy. No myofilaments were found, thus the cells are dedifferentiated and no longer typical muscular cells.

Comparison of the effects of physical exercise, cold acclimation and repeated injections of isoprenaline on rat muscle enzymes

The metabolic effects on rat cardiac and skeletal muscle of a strenous program of swimming, of cold acclimation and of isoprenaline treatment (0.3 mg/kg daily for 5 five-day weeks) were compared. Exercised and cold-exposed rats gained less body weight than did controls or isoprenaline-treated rats. In all treated groups the heart and the intercapular brown adipose tissue hypertrophied. The size of the adrenals increased only in isoprenaline-treated animals. Cold-acclimation and physical training increased and isoprenaline treatment reduced or did not affect the activities of succinate dehydrogenase, malate dehydrogenase and citrate synthase of cardiac muscle. In the skeletal muscle all treatments resulted in increased activities of these enzymes. Of the anaerobic enzymes analysed, only the activity of hexokinase increased in response to the treatements used. This increase was the same in cardiac as in skeletal muscle, but it was significantly greater with isoprenaline-treatment than with training or with cold-acclimation. The activities of lactate dehydrogenase and phosphofructokinase did not differ significantly. All treatments improved cold resistance, but only swimming exercise and cold acclimation significantly increased tolerance to exercise. It is concluded that prolonged stimulation of adrenergic beta-receptors by catecholamines is responsible for the metabolic changes observed.

Adipose tissue cellularity and lipolysis. Response to exercise and cortisol treatment

Male rats a 5 wk of age were subjected to 13 wk of intensive treadmill running to study the effect of exercise on adipose tissue cellularity and lipolysis. Untrained controls of the same age remained sedentary in their cages for the duration of the experiment. Adipocyte numbers were similar in eqidiymal fat pads from trained and untrained rats (12.7 plus or minus 1.3 X 10(6) vs. 15.3 plus or minus 1.3 X 10(6) cells/pad), however trained rats had smaller fat pads containing smaller cells (0.09 plus of minus 0.01 vs. 0.20 plus or minus 0.04 mug triglyceride/cell). Adipocytes from trained rats possessed greater epinephrine-sensitive lipase activity than sedentary rats on a per cell, per milligram protein, per gram adipose tissue, or per fat pad basis. Although the smaller cells of the trained rats had greater epinephrine-sensitive lipase activity than the larger cells of the untrained rats, lipolysis was positively correlated with cell size within both treatment groups. Cortisol treatment of intact animals did not significantly affect in vitro adipose tissue lipolysis. The results of this study indicate that exercise training increased the potential of adipose tissue cells to release free fatty acids in response to epinephrine stimulation. Exercise training initiated at 5 wk of age had only a small effect on adipose tissue cell numbers but significantly decreased cell size.