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-Glycerophosphate and Dihydroxyacetone Phosphate Metabolism in Rats Fed High-Fat or High-Sucrose Diets^1,2,3,

The Departments of Medicine and Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706

The concentrations of -glycerophosphate (GP) and dihydroxyacetone phosphate (DHAP) and the activities of the three participant enzymes, glycerokinase and the mitochondrial and cytosolic GP-dehydrogenases were determined in adipose tissue of rats after dietary treatment and in adipocytes from fed rats incubated in the presence of specific hormones and/or substrates. Fasting 48 hours decreased both the GP concentration and activities of cytosolic GP dehydrogenase and glycerokinase and increased the mitochondrial GP-dehydrogenase activity. These values were returned to control levels by refeeding. Feeding a high-fat diet increased both the GP concentration and glycerokinase activity. In adipose tissue obtained from rats fed a high-sucrose diet, the GP concentration was decreased while the activity of each participant enzyme was increased. The in vitro treatment effects on GP concentration were, in general, parallel with the results obtained from the feeding study. These results indicate that GP serves as the dominant precursor for glycerideglycerol synthesis in rat adipose tissue. Under all experimental conditions, the concentration of GP exceeded the K_m of GP-acyltransferase for this substrate and was sufficiently high to inhibit the acylation of DHAP. A more reduced cytosolic environment was observed in adipose tissue of rats fed the control and high-fat diets and in adipocytes incubated with insulin, glucose or glycerol. A more oxidized environment was associated with fasting. Paradoxically, the GP/DHAP ratio in adipose tissue of rats fed the high-sucrose diet approached the fasting value which favors the release rather than the uptake of fatty acids. This observation offers insight into the mechanism responsible for the hypertriglyceridemia associated with high-sucrose consumption.

KEY WORDS: • -glycerophosphate • dihydroxyacetone phosphate • -glycerophosphate-dehydrogenases • glycerokinase • adipose tissue • diet

¹ Supported by the College of Agricultural and Life Sciences, University of Wisconsin and USPHA Grant AM 15893.

² Reprint requests should be addressed to Dr. Charles Elson, Department of Nutritional Sciences. University of Wisconsin, Madison, Wisconsin 53706.

³ A preliminary report appears in Federation Proc. 36, 4695 (Abstr.) 1977.

Manuscript received 6 November 1978.