EFFECTS OF ACUTE EXERCISE ON HEPATIC LIPOGENIC ENZYMES IN FASTED AND REFED RATS

The effects of an acute bout of prolonged exhaustive exercise on the a ctivities of hepatic lipogenic enzymes have been investigated. Male Sp rague-Dawley rats were randomly divided into three groups: fasted for 48 h without refeeding (FA) and fasted for 48 h and refed a diet high in fructose (RF) or in cornstarch (RC). One-half of each group of rats exercised on a treadmill at 20 m/min, 5% grade, until exhaustion and the other half rested for the same amount of time without food. Dietar y intakes during refeeding were kept equal between the exercised and r ested control animals. Activities of all hepatic lipogenic enzymes mea sured, i.e., fatty acid synthase (FAS), L-type pyruvate kinase (L-PK), ATP citrate lyase, malic enzyme, and glucose-6-phosphate dehydrogenas e, were induced dramatically by fasting-refeeding and were significant ly higher in the RF than in the RC rats (P < 0.05). FAS activity was i ncreased 19- and 39-fold, respectively, in the RC and RF rats compared with the FA rats. Exercise decreased FAS activity to approximately on e-third of the resting control value in both RC and RF rats (P < 0.05) but not in FA rats. L-PK activity was elevated by 55% in RC and 100% in RF rats compared with FA rats (P < 0.05). FA and RF rats also showe d a reduction of L-PK activity with exercise. No significant alteratio n of other lipogenic enzymes was observed after exercise. Enzymatic do wnregulation of FAS and L-PK with exercise was associated with signifi cantly elevated plasma levels of glucagon and depressed levels of insu lin in the fasted-refed rats regardless of diet. Exercised rats also d emonstrated lower levels of hepatic pyruvate content and decreased blo od glucose concentration compared with the rested rats. It is conclude d that dietary induction of key hepatic lipogenic enzymes can be inhib ited by an acute bout of exhaustive exercise and that this enzymatic d ownregulation is most dramatic in rats receiving a high-fructose diet.