Effect of chronic wheel running on the fatty acid composition of phospholipids and triacylglycerols in rat skeletal muscle and heart

Introduction

Studies addressing the effect of exercise, both acute and chronic, on the fatty acid composition of animal tissues have been appearing in the literature at a rising rate in recent years. However, there is no consensus as to the effect of exercise, probably because of the near uniqueness of each of these studies in terms of type of exercise, species, subcellular fraction, lipid class and diet of the animals or humans examined. Therefore, the purpose of this study was to shed some new light on this controversial topic by examining the effects of long-term wheel running of rats on the fatty acid composition of phospholipids (PL) and triacylglycerols (TG) in two skeletal muscles of different type and in heart.

Methods

Male Wistar rats were divided randomly into a trained (n = 20) and an untrained group (n = 14). The members of the trained group exercised ad libitum for 8 weeks in cages equipped with a wheel. Upon completion of the training period, the eleven most active trained animals (having run, on average, over 2 km/d) and the untrained animals were decapitated and their soleus, extensor digitorum longus (EDL), as well as heart were removed. The fatty acid composition of their PL and TG was determined by a combination of thin-layer chromatography and gas chromatography and was expressed as both concentrations and percentages. The activities of citrate synthase (CS) and phosphofructokinase (PFK) were measured spectrophotometrically in these tissues as markers of their oxidative and glycolytic capacity, respectively. Differences between untrained and trained animals were examined by two-tailed indipendent Student’s t tests. To determine the meaningfulness of the effect of exercise on fatty acid composition, effect sizes were calculated as the difference between means divided by the SD of the untrained group.

Results

We found several significant differences between untrained and trained animals in the fatty acid profile of PL and TG in all three tissues. Both skeletal muscles exhibited markedly but borderline non-significantly lower TG concentrations in the trained animals. Monounsaturated fatty acids of muscle PL were significantly lower in the trained rats. Estimated fatty acid elongase activity was significantly higher, whereas Δ9-desaturase activity was significantly lower in the trained muscles. Monounsaturated fatty acids of PL were also significantly lower in the trained hearts. The fatty acid composition of PL in the skeletal muscles and the heart adapted to training in a comparable manner, whereas most of the changes in the fatty acid profile of TG were tissue-dependent. Wheel running did not change CS and PFK activities in any of the tissues studied significantly, even though both activities increased slightly in soleus and EDL.

Discussion/Conclusions

Judging from the magnitude of the effect sizes and the percentage differences between trained and untrained animals, there were many large effects of chronic exercise on the fatty acid composition of the tissues examined. In addition, the magnitude of the adaptive capacity of the fatty acid profile of skeletal muscle TG to wheel running was comparable to that of PL. In conclusion, long-term wheel running modified the fatty acid profile of PL and TG in rat skeletal muscle and heart, and could thus be considered as a modulator of tissue fatty acid composition.