Hepatic de novo fatty acid synthesis in the rat

Generally, the rate of hepatic de novo fatty acid (FA) synthesis (lipogenesis) in vivo is determined by measuring the amount of newly synthesized FA present in the liver 1 h or less after injection of label (3H2O) for FA synthesis (1-hour value of labelled FA). Since this value may well be affected by momentary conditions, our objective was to investigate whether the amount of labelled FA present in the liver 24 h after injection of 3H2O can be used as a parameter of lipogenesis (24-hour value of labelled FA). To this end, effects of the amounts of dietary fat, sucrose and linoleic acid and the effect of meal feeding versus d libitum feeding on this 24-hour value were investigated. The 24-hour value decreased with the dietary fat level and was higher in rats fed a diet in which starch was partly replaced by sucrose [20% of metabolizable energy (E%)]. This is in accordance with literature data on the 1-hour value of labelled FA. No effect of meal feeding versus ad libitum feeding on the 24-hour value of labelled FA was found. Furthermore, no significant effect of the dietary linoleic acid level (1-10 E%) on the 24-hour value of labelled FA was found, although when lipogenesis was stimulated by feeding a diet containing 20 E% sucrose, the 24-hour value tended to be higher at 1 E% linoleic acid than at 2.5 E% linoleic acid or higher.