Regulation of skeletal muscle fatty acid metabolism following acute and chronic exercise
This thesis investigated the effects of acute and chronic exercise on skeletal muscle lipolysis, fatty acid transport and oxidative capacity. The first study examined the importance of acute hormonal stimulation of hormone sensitive lipase (HSL) activity during the onset of exercise at ~65% VO2peak and ~90% VO2peak. Arterial epinephrine (EPI) increased (p < 0.05) post-exercise at 65% and 90% VO2peak. HSL activity increased following 1 min of exercise at both intensities. Cyclic AMP content, which has been associated with hormonal regulation of HSL, was augmented following exercise. The results indicated that increases in arterial EPI concentration during the onset of moderate and high intensity exercise increase cyclic AMP content which is associated with the phosphorylation of Ser 660 activating HSL. The second study examined the potency of seven high intensity aerobic interval training (HIIT) sessions on skeletal muscle and whole body fat metabolism in women. Each session consisted of ten, 4-min bouts at ~90% VO2 peak with 2-min rest between intervals. Training increased VO2 peak by 13%, whole body fat oxidation during exercise increased 36% and muscle mitochondrial enzyme maximal activities by 20-32%. Total muscle FABPpm content increased (25%), while FAT/CD36 content was unchanged following training. HIIT appears to stimulate improvements in whole body and skeletal muscle fat metabolism with only seven hours of training in two weeks. The third study determined if training altered total skeletal muscle, sarcolemmal and mitochondrial fatty acid transport protein contents in women. Ten females completed six weeks of HIIT. Training resulted in (1) a 48% and 13% increase in total FABPpm and FAT/CD36 content, respectively. (2) a 23% increase in FABPpm content and no change in FAT/CD36 content on the sarcolemma, (3) and a 51% increase in mitochondrial FAT/CD36 content (per g mitochondria), with no change in FABPpm content. This is the first study to show that exercise training in humans can increase sarcolemmal and mitochondrial content of fatty acid transport proteins. These results suggest that adaptations in whole body fat oxidation following training are in part due to a redistribution of fatty acid transport proteins to the sarcolemma and mitochondria enhancing transport capacity.