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Response of Glucose-6-Phosphate Dehydrogenase and Malic Enzyme in Rat Liver and Adipose Tissue to Dietary Medium and Long Chain Triglycerides¹

Nutrition Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705

The responses of glucose-6-phosphate dehydrogenase (G6PD) (EC 1.1.1.49) and malic enzyme (ME) (EC 1.1.1.40) in liver and adipose tissue and of total liver lipid were studied in rats fed a fat-free diet for 2 days, then fed diets containing 12% synthetic triglyceride for 3 days, or fed a fat-free diet for 5 days. Triglycerides of the following fatty acids were used: caprylic (8:0), capric (10:0), palmitic (16:0), stearic (18:0), oleic (18:1) or linoleic (18:2). Enzyme activities and total liver lipids were statistically adjusted for differences in fat absorption to determine the theoretical effects of the different triglycerides if they all had been absorbed equally. Liver G6PD activity was highest in the group fed the 8:0 diet and lowest in the group fed the 18:2 diet; the response of liver ME was similar, but the differences were smaller among groups. The levels of both G6PD and ME in liver were greater in the groups fed saturated triglycerides (8:0, 10:0, 16:0, 18:0) than in the groups fed unsaturated triglycerides (18:1, 18:2). Total liver lipids were highest in the group fed the 8:0 diet, intermediate in the groups fed the 10:0, 18:2 and fat-free diets, and lowest in the groups fed the 16:0, 18:0 and 18:1 diets. When adjusted for differences in fat absorption, however, total liver lipids were generally highest in the groups fed saturated triglycerides (8:0, 10:0, 16:0, 18:0) or the fat-free diet, and lowest in the groups fed unsaturated triglycerides (18:1, 18:2). Adipose tissue G6PD and ME levels varied among the groups fed different triglycerides, but adjusted values for G6PD were greater in the groups fed the long-chain saturated triglycerides (16:0, 18:0) than in any other group.

KEY WORDS: • adipose tissue • glucose-6-phosphate dehydrogenase • malic enzyme • total liver lipid • dietary triglycerides

¹ The data from this study were presented in part at the 1976 meeting of the Federation of American Societies for Experimental Biology, Anaheim, California, Federation Proc. 35, 520 (Abstract). The data are from a dissertation by the first author to be submitted to the Graduate School, University of Maryland, in partial fulfillment of the requirement for the Ph.D. degree.

Manuscript received 18 October 1976.