| Purpose: Many athletes will appear obese after stopping the training, in which the body fat increase of swimming athlete is more remarkable. The consistent viewpoint of its reason is energy consumption reduction after stopping the training and the energy balance is destroyed to make the lipid accumulate, finally appears obese. Expansion of adipose tissue mass results from increased number and size of adipose cells, both take adipocyte differentiation as the precondition. In human body, the fatty cell differentiation peak exists in juvenile's growth and development period, which in accordance with the initial training age of swimming athlete. In this period, swimming may be a stimulus to accelerate the adipocyte differentiation and induce obesity. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma modulates the expression of numerous genes involved in lipid homeostasis and plays a critical role in adipocyte differentiation. During the sports, many changes may affect the PPAR gamma gene expression, even the fat metabolism. To study the relation of PPAR gamma and adipocyte differentiation, it is helpful to understand the molecular mechanism and provide the essential theory basis for reliable and effective methods to prevent the obesity after stopping training. The purpose of this research is to study the effect of aerobic exercise on the expression PPAR gamma and discuss whether can affect the adipocyte differentiation in order to provide the theory basis for prevention and treatment of obesity.Methods: 30 male SD rats were randomly assigned to a control (C), exercise-trained (Ex), combined exercise-trained for 8 weeks and stop exercises for 4 weeks(SE) group. Animals in the exercise-trained group were swimming for 8-12 weeks (90min/day, 5days/week).The epididymal and retroperitoneal adipose tissues were dissected and weighed. The level of PPAR gamma protein and the percent of adipose cell multiplication were detected by flow cytometric analysis. Still, the number and size of adipose cell wasmeasured.Results: The results shows that: (1) Swimming exercise of 8-12 weeks could suppress the accumulation of visceral fat, including epididymal and retroperitoneal fat. But after the exercise, the fat accumulation restart;(2) Swimming exercise of 8-12 weeks may increase PPAR gamma protein expression and then promote adipose cell multiplication and differentiation. The number of exercise group's adipose cell increase, although the performance did not represent obese, still had high potential to develop obesity;(3) After 4weeks stopping training, the PPAR gamma protein expression also showed the increase tendency and cell multiplication and differentiation presented high, the same time, cardinal number of original adipose cell is high quantity, so the body represented obese;(4) The change tendency of PPAR gamma protein expression and cell multiplication was consistent and PPAR gamma affect the cell multiplication in part. And this effect operate with other factors. Through the correlation analysis, we can see the relation of PPAR gamma and adipose multiplication is 0.40(P<0.05). And the relation of the number of adipose cells and visceral fat is -0.567(P<0.05), small and big adipose cells are -0.4O(P<0.05)and -0.37(P<0.05) respectively.Conclusion: From the results above, we can draw a conclusion that swimming exercise of 8-12 weeks could up-regulate PPAR gamma expression, while the adipose cell multiplication did not change distinctly. It may suggest that PPAR gamma in adipose tissue may play a certain effect in adipose differentiation, but not the only influencing factor. In addition, stopping exercise can promote the fat accumulation and this effect may be induced by the change of PPAR gamma expression, suggesting that once the exercise stop, the available influence of exercise will disappear. It is thought that the obesity represented after stopping training may arouse by adipose cell differentiation via PPAR gamma, suggesting it should carry the experiment on the human for confirmation.
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