Exercise Training Down-Regulates Hepatic Lipogenic Enzymes in Meal-Fed Rats: Fructose versus Complex-Carbohydrate Diets

Manuscript received 30 September 1996. Initial reviews completed 5 December 1996. Revision accepted 23 December 1997.

Russ Fiebig, Margaret A. Griffiths^*, , Mitchell T. Gore, David H. Baker^*, Lawrence Oscai, Denise M. Ney, and Li Li Ji

Departments of Kinesiology and Nutritional Sciences, University of Wisconsin-Madison, Madison, WI; ^* Departments of Animal Science and Food and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL; and  Department of Kinesiology, University of Illinois at Chicago, Chicago, IL

The maximal activity and mRNA abundance of hepatic fatty acid synthase (FAS) and other lipogenic enzymes were investigated in rats meal-fed either a high fructose (F) or a high cornstarch (C) diet. The diet contained 50% F or C (g/100 g), casein (20%), cornstarch (16.13%), corn oil (5%), minerals (5.37%), vitamins (1%) and Solka-floc (2%). Female Sprague-Dawley rats (n = 44) were randomly divided into C or F groups that were meal-fed for 3 h/d; each group was subdivided into exercise-trained (T) and untrained (U) groups. Treadmill training was performed 4 h after the initiation of the meal at 25 m/min, 10% grade for 2 h/d, 5 d/wk, for 10 wk. Rats were killed 9 h after the meal and 27 h after the last training session. F-fed rats had significantly higher activities of all lipogenic enzymes assayed and mRNA abundance of FAS and acetyl-coenzyme A carboxylase (ACC) than C rats (P < 0.05). Concentrations of plasma insulin and glucose and liver pyruvate were not altered by F feeding. Proportions of the fatty acids 18:2 and 20:4 were lower, whereas those of 16:0 and 16:1 were higher, in livers of F than of C rats (P < 0.05). Training decreased FAS activity by 50% (P < 0.05), without affecting FAS mRNA level in C rats; this down-regulation was absent in the F rats. ACC mRNA abundance tended to be lower in CT than in CU rats (P < 0.075). L-Type pyruvate kinase activity was lower in FT than in FU rats (P < 0.05), whereas other lipogenic enzyme activities did not differ between T and U rats of each diet group. We conclude that hepatic lipogenic enzyme induction by high carbohydrate meal feeding may be inhibited by exercise training and that a fructose-rich diet may attenuate this training-induced down-regulation.

The Journal of Nutrition Vol. 128 No. 5 May 1998, pp. 810-817
Copyright ©1998 by the American Society for Nutritional Sciences

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