Glucose contribution to in vivo synthesis of glyceride-glycerol and fatty acids in rats adapted to a high-protein, carbohydrate-free diet

Triacylglycerol (TAG) synthesis from all carbon sources and from glucose carbon was evaluated in rats fed a high-protein, carbohydrate-free (HP) diet or control diet by determining simultaneously in the same animal the rate of incorporation of (H2O)-H-3 and of C-14-glucose into the two TAG moieties in the carcass, liver, and retroperitoneal and epididymal adipose tissue. Incorporation rates of (H2O)-H-3 into TAG-fatty acids (FAs) in the two adipose tissues and in liver were reduced in HP rats to about 20% and 50%, respectively, of the rates in control rats. In the two experimental groups, glucose was a poor precursor for FA synthesis, contributing only 22.8% of whole-body (darcass plus liver) total FA synthesis in control rats and even less (14%) in HP rats. In contrast to the reduction in FA synthesis, incorporation of (H2O)-H-3 into TAG-glycerol in HP rats did not differ significantly or was even higher (in epididymal tissue) versus the control level. In all tissues of both HP and control rats, the rate of C-14-glucose incorporation into TAG-glycerol was much higher than the rate of incorporation into FA. Glyceroneogenesis, estimated by subtracting TAG-glycerol synthesis from glucose from the rate obtained with (H2O)-H-3, was significantly increased in adipose tissue from HP rats, with almost all of the glycerol formed by this route being used to esterify preformed FAs. It is suggested that the increased adipose tissue glyceroneogenesis is important for esterification of diet-derived FA and preservation of body fat stores in rats adapted to the HP diet. Copyright (C) 1998 by W.B. Saunders Company.