Abstract: BACKGROUND: Obesity is a multifactorial chronic disease. Regular exercise can improve lipid metabolism disorders and oxidative stress in obese groups, but the specific exercise intensity is unclear.
OBJECTIVE: To explore the effect of different-intensity exercises on lipid metabolism and oxidative stress in obese rats and to clarify the correlation of peroxisome proliferators-activated receptor α, liver X receptor α and related pathway proteins with lipid metabolism as well as the specific mechanism.
METHODS: Rats were randomly divided into five groups: normal control group (n=10), obesity model group (n=10), low-intensity exercise group (n=10), moderate-intensity exercise group (n=9) and high-intensity exercise group (n=8). The normal control group was given ordinary feed, and the other four groups were fed with high-fat diet for 16 weeks to prepare the obese rat model. After modelling, rats in each group were arranged to run on the treadmill 1 hour per day and 5 days per week. After 6 weeks of training, body mass, liver mass, heart mass, and body fat percentage, lipids, lipases and oxidative stress were tested, and adipose tissue were cut into sections for cell morphological and structural observations. The protein expression of apolipoprotein A5, peroxisome proliferators-activated receptor α, sterol regulatory element-binding protein 1c and liver X receptor α in liver tissue were detected by western blot assay. 
RESULTS AND CONCLUSION: Compared with the obesity model group, the levels of triacylglycerols, low-density lipoproteins, and free fatty acids were significantly reduced, while the activities of lipoprotein lipase and hepatic lipase increased significantly in the moderate-intensity exercise group (P < 0.01). Plasma malondialdehyde level showed a significant reduction in each exercise group (P < 0.01), but the activity of catalase increased significantly in all exercise groups (P < 0.01). Compared with the obesity model group, the protein expression of apolipoprotein A5 was significantly increased in each exercise group (P < 0.05, P < 0.01, P < 0.01) and the expression levels of sterol regulatory element-binding protein 1c (P < 0.01) and liver X receptor α (P < 0.01) were both decreased, whereas the expression of peroxisome proliferators-activated receptor α only increased significantly in the moderate-intensity exercise group (P < 0.05). Compared with the low- and high-intensity exercise groups, the expression of apolipoprotein A5 was significantly increased in the moderate-intensity exercise group (P < 0.01, P < 0.05). Compared with the low-intensity exercise group, the expression of sterol regulatory element-binding protein 1c was significantly lower in the moderate-intensity exercise group (P < 0.01). To conclude, lipid metabolism disorder and oxidative stress can be improved after different-intensity exercises. The moderate-intensity exercise has better effects, which may be related to the double regulation of exercise-dependent peroxisome proliferators-activated receptor α and liver X receptor α signaling pathways.

Key words: exercise, obesity, exercise intensity, high-fat diet, lipid metabolism, oxidative stress, animal model