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Lack of Specificity of Polyunsaturated Fats in the Inhibition of Rat Liver Glucose-6-Phosphate Dehydrogenase

Bela Szepesi^*, A. Kalla Kamara and Steven D. Clarke

^* Carbohydrate Nutrition Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705, Human Nutrition & Food, School of Human Ecology, Howard University, Washington, D.C. 20059 The Upjohn Company, Kalamazoo, MI 49001

The mechanism of the effect of polyunsaturated fatty acids (PUFA) on glucose-6-phosphate dehydrogenase (EC 1.1.1.49) (G6PDH) was studied in young, male Wistar rats. Starvation-refeeding increased G6PDH level above that seen in ad libitum-fed animals (enzyme overshoot). A second episode of starvation-refeeding produced even higher levels of G6PDH activity (induction increment). Interposing a high fat diet (containing PUFA) between starvation and feeding the inducer diet abolished one-half to two-thirds of the overshoot. Feeding a high fat diet between the two starvations abolished the induction increment. Inhibitors of arachidonic acid metabolism were not able to reverse the PUFA effect. In another set of experiments it was shown that both linoleic and linolenic acid are equally effective in either reducing the overshoot or abolishing the induction increment. The evidence was interpreted as supporting a hypothesis that the PUFA effect does not require the formation of a specific end product of arachidonic metabolism in a direct way.

KEY WORDS: • glucose-6-phosphate dehydrogenase • linoleic acid • linolenic acid • metabolic inhibitors • enzyme induction • starvation-refeeding

Manuscript received 9 March 1988. Revision accepted 11 October 1988.