EXERCISE DOWN-REGULATES HEPATIC LIPOGENIC ENZYMES IN FOOD-DEPRIVED AND REFED RATS

The effects of an acute bout of prolonged exercise on the activities o f several hepatic lipogenic enzymes and the abundance of fatty acid sy nthase (FAS) mRNA were evaluated using a food deprivation-refeeding pr otocol in which diets contained 50% of the energy from either fructose or cornstarch. Food was withheld from male rats for 48 h and refed fo r 0, 4, 8, 12, 24 or 48 h. At each time point, half of each dietary gr oup was subjected to a single bout of treadmill running until exhausti on and killed immediately. The other half of each group rested without food for the same amount of time before being killed. Exercise signif icantly decreased FAS activity by 57, 46, 10, 26 and 70% at 4, 8, 12, 24 and 48 h of refeeding, respectively, in the fructose-fed rats; and by 70 and 63% at 24 and 48 h of refeeding, respectively, in the cornst arch-fed rats. Activities of L-type pyruvate kinase and glucose 6-phos phate dehydrogenase were significantly decreased after exercise in the fructose-fed,bu starch-fed rats. In rested rats, FAS mRNA abundance i ncreased similar to fourfold above the unfed levels after 8 and 12 h o f refeeding. Exercise attenuated the diet-induced increases in FAS mRN A abundance. At 8 h of refeeding, both cornstarch- and fructose-fed ex ercised rats had 71% (P < 0.05) of the FAS mRNA levels of their rested counterparts; at 12 h, these exercised rats showed only 46 and 27% (P < 0.05) of FAS mRNA levels compared with rested rats fed the same die t. We conclude that dietary induction of FAS activity and mRNA abundan ce can be inhibited by prolonged exercise, suggesting that exercise ma y influence FAS transcription and/or mRNA stability.