Carnitine et performance physique

The effect of methionine supplementation of the AIN-93G semi-synthetic diet on the levels of homocysteine and lipids in experimental rats

OBJECTIVES

The studies were carried out on 36 growing albino Wistar rats. PARTICIPANTS/MEASUREMENTS: The animals were randomly divided into six equinumerous groups (six rats per group), and were fed six different diets for 42 days. The control group (I) was fed with AIN-93G semi-synthetic diet, whereas groups II-VI were fed with AIN-93G semi-synthetic diet supplemented with: 2, 4, 8, 16 and 32 g of methionine/kg diet, respectively. There were assessed enzymatically, in rats' blood serum, the contents of homocysteine, total cholesterol, HDL fraction and triacyloglicerols. In addition, the LDL+VLDL cholesterol content was calculated.

RESULTS

The methionine content of the diet was found to be highly positively correlated with the homocysteine content (r = 0.981) and negatively correlated with the triacylglycerols content (r = -0.916) of the experimental animals' blood serum.

CONCLUSION

In the blood serum of rats fed the highest-methionine diet (32 g methionine/kg diet), the homocysteine content was significantly higher, as were the levels of total cholesterol and its HDL fraction, while the triacylglycerols content was lower as compared to the values obtained for rats fed other diet types.

Carnitine and Sports Medicine: Use or Abuse?

Carnitine has important roles in skeletal muscle bioenergetics. Skeletal muscle carnitine deficiency is associated with profound impairment of muscle function. It has thus been natural to ask if carnitine supplementation can improve skeletal muscle function and athletic performance in healthy individuals. Oral carnitine doses of several grams cause no significant clinical toxicity, further encouraging the use of carnitine as a supplement. Despite this strong foundation and 20 years of research, no compelling evidence exists that carnitine supplementation can improve physical performance in healthy subjects. The available data have been reviewed in recent publications. Several key issues are relevant to a potential therapeutic benefit of carnitine supplementation, and addressing these may provide insight into trials of carnitine therapy in healthy subjects: (1) Can carnitine supplementation increase skeletal muscle carnitine content in healthy subjects? Muscle carnitine content is not easily increased with carnitine supplementation. This reflects both the systemic pharmacokinetics of carnitine and the systems controlling transmembrane transport of carnitine in skeletal muscle. (2) How much carnitine is required to support optimal metabolism in skeletal muscle? Data are not available to definitively define the relationship between muscle carnitine content and muscle metabolic function. Extrapolation of data from several models suggests that very low amounts of carnitine are required to support muscle function. (3) Does carnitine supplementation alter energy homeostasis in healthy subjects? Several, but not all, studies suggest that subjects on carnitine supplementation have altered regulation of fuel homeostasis. However, the mechanisms of these changes, the tissues affected, and the relevance of these phenomena to exercise performance are all ill defined. (4) How can changes in performance be assessed in healthy subjects? Most studies have failed to demonstrate an objective performance improvement in healthy subjects taking carnitine. However, these negative studies must be interpreted with caution. Performance studies in athletes are conducted against a background of aggressive training regimens and nutritional interventions. Small changes, which may be very important to the athlete, may be very hard to objectify in the laboratory. Assessments must differentiate between changes in maximal aerobic capacity, ability to sustain effort at varied workloads, and the subject's perception of exertion. The interaction of carnitine supplementation with exercise training may be particularly important on theoretical and experimental bases. Systematic research in each of these areas is required to better understand the physiology, biochemistry, and pharmacology of carnitine supplementation. While data do not allow a conclusion to be drawn that carnitine is beneficial, the negative has not been proven either.