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 activities of hepatic lipogenic enzymes have been investigated. Male Sprague- 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. Dietary intakes during refeeding were kept equal between the exercised and rested control animals. Activities of all hepatic lipogenic enzymes measured, i.e., fatty acid synthase (FAS), L-type pyruvate kinase (L-PK), ATP citrate lyase, malic enzyme, and glucose-6- phosphate dehydrogenase, were induced dramatically by fasting-refeeding and were significantly higher in the RF than in the RC rats (P < 0.05). FAS activity was increased 19- and 39-fold, respectively, in the RC and RF rats compared with the FA rats. Exercise decreased FAS activity to approximately one-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 showed a reduction of L-PK activity with exercise. No significant alteration of other lipogenic enzymes was observed after exercise. Enzymatic downregulation of FAS and L- PK with exercise was associated with significantly elevated plasma levels of glucagon and depressed levels of insulin in the fasted-refed rats regardless of diet. Exercised rats also demonstrated lower levels of hepatic pyruvate content and decreased blood glucose concentration compared with the rested rats. It is concluded that dietary induction of key hepatic lipogenic enzymes can be inhibited by an acute bout of exhaustive exercise and that this enzymatic downregulation is most dramatic in rats receiving a high-fructose diet.