The swine as a model for studying exercise-induced changes in lipid metabolism.

The swine has many similarities to humans, making it an excellent research model in which to study the role of exercise on lipid metabolism. Swine adapt to exercise-training by increasing muscle oxidative enzymes, maximal stroke volume, cardiac output, VO2max, and high density lipoprotein cholesterol levels, while decreasing total cholesterol levels and resting heart rate. The lipoprotein profile of swine and humans is also similar, and low density lipoprotein is the major cholesterol transporting lipoprotein in both species. Several studies in swine report conflicting results on the effect of exercise-training on lipoprotein profile and atherosclerotic lesion appearance. This may result from differences in total exercise time between the studies. With sufficient total exercise, atherosclerosis was reduced and high density lipoprotein cholesterol levels were increased. Exercise may also play a role in reducing obesity, a risk factor for cardiovascular disease, by enhancing lipid mobilization from adipocytes. Recent research suggests that swine adipocyte sensitivity to adenosine, a locally-produced antilipolytic agent, is reduced after exercise treatment. Cellular mechanisms responsible for this metabolic change include a reduction in adenosine A1 receptor number. Current studies are examining the transport of extracellular cyclic AMP from adipocytes and its role as a potential adenosine precursor.