FATTY ACID AND GLYCERIDE GLYCEROL SYNTHESIS FROM GLUCOSE DURING HIGH RATES OF GLUCOSE UPTAKE IN THE INTACT RAT

Abstract

The extent of incorporation of glucose carbon into total lipids and component fatty acid, neutral glyceride glycerol, and phosphoglyceride glycerol moieties of carcass, liver, and epididymal tissue has been measured in 20 rats under conditions of constant plasma glucose concentration and specific activity. Rates of fatty acid synthesis from glucose and absolute rates of synthesis have also been estimated. Each rat received 750 mg glucose per hour by continuous infusion. The incorporation of glucose carbon into carcass, liver, and epididymal fat was, respectively, 6.2, 0.75, and 0.06% of the total glucose carbon taken up by the rat tissues. Fifty percent of the C14found in total lipids of carcass and liver was in the fatty acid fraction. Corresponding glyceride glycerol moieties contained approximately 40% of the total activity. The low level of incorporation of glucose carbon into fatty acids and glyceride glycerol indicates that lipogenesis from glucose can only account for a small proportion of the total glucose taken up by the tissues, even at high rates of glucose uptake. Rates of synthesis from glucose of carcass and liver fatty acids were estimated as 1.5 and 0.11 mmoles fatty acid per tissue per day respectively, with corresponding half-lives of 57 and 7.6 days. Absolute rates of fatty acid synthesis were estimated as 2.6 and 0.55 mmoles fatty acid per day for carcass and liver tissue respectively, with corresponding half-lives of 34 and 4.6 days.