Endurance training leads to high levels of intramuscular triacylglycerol (IMTG). This includes a high capacity to recruit, store, and oxidize both endogenous and exogenous fatty acids during exercise. In recent years, lipid droplet associated proteins and their interactions with enzymes have been demonstrated to influence IMTG storage and breakdown capacity. This study investigates changes in expression of the primary proteins and enzymes in fatty acid uptake, lipid droplet storage and mobilisation for oxidation after very prolonged endurance exercise at moderate intensity. Methods: Six healthy (61+/-4 yrs), cycle-trained (VO2-max: 48+/-2 ml/kg/min) males completed a 2770 km bike ride in 14 days. A muscle biopsy (m. vastus lateralis) was obtained before and 30-34 hours after completing the bike ride. The biopsies were taken at rest and after overnight fasting. Muscle samples were analysed by Western-blotting for expression of: endothelial lipase (EL), lipoprotein lipase (LPL), fatty acid binding protein (FAPB), diglyceride acyltransferase 1 and 2 (DGAT 1 and 2), perilipin 2, 3, and 5, adipose triglyceride lipase (ATGL), and hormone-sensitive lipase (HSL). The Western-blots were normalised to the average arbitrary unit of a standard control homogenate. Results: Across the 14 days body weight remained unchanged (77.4+/-4.6 to 77.7+/-4.8 kg). The expression of EL, LPL, FABP, DGAT 1 & 2, Perilipin 2, 3 & 5, ATGL and HSL were unchanged after 14 days of prolonged (580+/-30 min/day) endurance exercise at moderate intensity (53+/-1% VO2-max). However, the expression of LPL tended (P=0.08) to be increased by two fold. Discussion: In the present study there was no adaptation in capacity for fatty acid recruitment, storage in lipid droplets and promotion for oxidation, after 14 days of very prolonged exercise. It is intriguing that the major increase in energy turnover was insufficient to induce changes in muscle lipid recruitment and storage pathways even though the body weight remained unchanged. The trend towards an increased muscle LPL expression implies that the exogenous supply of plasma derived triacylglycerol was important to generate the increased muscle substrate turnover during the 14 days.
© Copyright 2012 17th Annual Congress of the European College of Sport Science (ECSS), Bruges, 4. -7. July 2012. Published by Vrije Universiteit Brussel. All rights reserved.