关键词: 低温, 运动, 肥胖, 大鼠, 白色脂肪, 肩胛间, 腹股沟, 解偶联蛋白1, 体脂率, 米色脂肪

Abstract: BACKGROUND: Cold exposure and exercise serve as two powerful physiological stimuli to change the type and function of fat, which has positive implications for the treatment of obesity and related metabolic diseases. So far, it remains to be unclear whether exercise in the different cold exposure can produce an addictive effect on fat change.
OBJECTIVE: To observe the browning effect of white fat and the expression of uncoupling protein 1 in obese rats after 5 weeks of exercise intervention under cold exposure.
METHODS: Sixty-four Sprague-Dawley rats were selected to establish animal models of nutritional obesity. They were randomly divided into four groups: normal control group (NTS), normal exercise group (NTE), acute cold control group (ACS), acute cold exercise group (ACE), intermittent cold control group (ICS) and intermittent cold exercise group (ICE), continuous cold control group (CES), and continuous cold exercise group (CEE). The normal temperature environment was 24-26 °C, the cold environment was 3-4 °C, and the relative humidity was 50%-60%. For acute cold exposure, the rats were exposed to low temperature for only 4 hours before the end of the experiment; for intermittent cold exposure, the rats were exposed to low temperature for 4 hours per day; for continuous cold exposure, the rats stayed in a cold environment all day. The protocol for treadmill running in exercise groups was as follows: 25 m/min (speed), 0 °C (slope), 30 minutes once, for two sections. Sampling was conducted after 5 weeks. The fat rate was measured by Micro-CT LCT200. The interscapular and inguinal fats were collected for hematoxylin-eosin staining to observe morphological changes, and the expression of uncoupling protein 1 in the inguinal fat was examined by western blot. 
RESULTS AND CONCLUSION: In the CES, ICE and CEE groups, the volume of interscapular fat cells decreased significantly and the cell number increased significantly; the lipid droplets gradually disappeared and the intercellular capillaries gradually increased. The white fat cells in the inguinal of the rats in the ICE and SEE groups were multilocular, with smaller and more uniform cell size and tighter tissue, showing an obvious browning trend. Compared with the CEE group, the visceral and body fat rate were significantly declined in the NTS, NTE, ACS, ACE, ICS and CES groups (P < 0.05). The subcutaneous fat rate of the NTS group was significantly declined compared with that of the ACS and ICS groups (P < 0.05), and that of the ACE group was significantly declined compared with that of the NTE group (P < 0.05). Compared with the NTS group, the brown fat rate was significantly higher in the ACS, ICS, CES and CEE groups (P < 0.05); compared with the ACE group, the brown fat rate was significantly higher in ACS group (P < 0.05); compared with the ICE group, the brown fat rate was significantly higher in ICS group (P < 0.05); compared with the ACE group, the brown fat rate was significantly declined in ICE and CEE groups (P < 0.05). The expression of uncoupling protein 1 in each exercise group was significantly up-regulated compared with the corresponding control group (P < 0.05). The expression of uncoupling protein 1 was lowest in the NTS group, and highest in CCE group, followed by the ICE group (P < 0.05). To conclude, exercises under continuous and intermittent cold exposure can induce the browning of subcutaneous inguinal white fat and reduce the body fat rate of obese body, which may be correlated with the morphological changes of inguinal fat as well as the changes of uncoupling protein 1. 

Key words: low temperature, exercise, obesity, rat, white fat, interscapular, inguinal, uncoupling protein 1, body fat rate, beige fat