The effect of vigorous treadmill exercise on plasma lipoproteins and hepatic lipoprotein production in Zucker rats

Chronic exercise has been shown to alter plasma lipids in man and animals, but the mechanism(s) responsible for this phenomenon have not been clarified. In the present study we have examined the role of the liver in the production of lipoproteins following an intensive exercise regimen in lean and obese Zucker rats. Four-week-old lean and obese male Zucker rats were subjected to a vigorous exercise regimen of running on a motor-driven treadmill for 10 weeks. Hepatic lipoprotein cholesterol production was then assessed using liver perfusion techniques. Plasma cholesterol concentration was significantly lower in both lean and obese runners versus appropriate non-exercised controls. This decrease was due to a decline in both chylomicron and HDL cholesterol. Exercise had no affect on plasma VLDL and LDL cholesterol concentrations. Hepatic VLDL cholesterol production was elevated in obese rats versus lean rats and was not affected by exercise in runners of either phenotype. Hepatic HDL cholesterol production was higher in lean runners but was unchanged in obese runners. Plasma triglyceride was reduced by 50% in exercised obese rats. In summary, intense exercise decreased plasma triglyceride, cholesterol, and HDL cholesterol concentrations in lean and obese Zucker rats. Since hepatic HDL cholesterol production was increased and hepatic VLDL cholesterol production was unaffected by exercise, the changes in plasma lipid levels observed following exercise appear to be mediated by extrahepatic mechanisms.