Abstract
BackgroundEndurance exercise induces lipolysis, increases circulating concentrations of free fatty acids (FFA) and the uptake and oxidation of fatty acids in the working muscle. Less is known about the regulation of lipid metabolism in the liver during and post-exercise.Methodology/Principal FindingsWe performed an ultra fast liquid chromatography-mass spectrometry (UFLC-MS) based lipidomics analysis of liver tissue samples obtained from C57Bl/6J mice immediately after a 60 min treadmill run of moderate intensity, and after 3 h of recovery. The PLS-DA scores plot for 115 quantified lipid molecular species revealed a clear separation of the hepatic lipid profile of sedentary from recovering mice, but not from mice immediately after running. 21 lipid species were considered to be most responsible for the difference in the hepatic lipid profiles, including 17 triacylglycerides (TG), one lysophosphatidylcholine (LPC) and three phosphatidylcholines (PC). TG species were found to be more abundant in the recovery phase, while PC species were decreased. The degree of accumulation of individual TG species correlated well with the amount of theoretical energy stored whereas no increase was found for TG species containing only saturated or one monounsaturated fatty acid. Total liver TG content as assayed by an enzymatic method was increased to 163% in the recovery phase, while it was significantly decreased in skeletal muscle by the exercise bout and remained less in the recovery phase. Results from fasted and refed mice indicate that fasting-induced lipolysis was associated with a pronounced accumulation of hepatic TG, which is reversed by refeeding for 5 h. Thus food intake per se did not elevate hepatic TG.ConclusionThese data indicate that high availability of FFA induced by endurance exercise or fasting resulted in a transient hepatic TG accumulation, while muscle TG content was decreased during exercise presumably due to increased muscle fatty acid oxidation.
Highlights
Fatty acids are the major fuel during prolonged moderate intensity exercise
These data indicate that high availability of free fatty acids (FFA) induced by endurance exercise or fasting resulted in a transient hepatic TG accumulation, while muscle TG content was decreased during exercise presumably due to increased muscle fatty acid oxidation
The liver has a central function in lipid metabolism by repartitioning FFA derived from body fat stores and integrating dietary FFA into whole body fuel oxidation and energy storage via secretion of lipoproteins
Summary
Fatty acids are the major fuel during prolonged moderate intensity exercise. The availability of plasma free fatty acids (FFA) is markedly increased by the action of hormone-sensitive lipase and adipose tissue triacylglyceride (TG) lipase on the fat depots in adipose tissue and skeletal muscle [1,2]. Its role in the process of FFA supply and tissue redistribution during and after exercise is not well characterized Studies both in rodents and humans provide evidence that the hepatic tissue concentration of TG is influenced by regular exercise. Voluntary wheel running reduces the hepatic TG content in Otsuka Long-Evans Tokushima Fatty rats, a rodent model for obesity and type 2 diabetes [8]. These lipid-lowering effects of training could be absent in young, non-obese rodents [9]. Increases circulating concentrations of free fatty acids (FFA) and the uptake and oxidation of fatty acids in the working muscle. Less is known about the regulation of lipid metabolism in the liver during and post-exercise
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