Effect of dietary linoleate on synthesis and degradation of fatty acid synthetase from rat liver.

The induction of fatty acid synthetase activity in rat liver is markedly reduced by feeding a diet containing a source of linoleate. Within 48 h after changing from a fat-free, high carbohydrate diet to one containing 15% by weight of safflower oil, the specific activity of rat liver fatty acid synthetase is approximately 2-fold lower than that from rats fed a fat-free diet througout. In contrast, feeding a diet containing 15% hydrogenated coconut oil, a source of saturated fatty acids, or 5% methyl oleate for the same length of time has little effect on the activity of the enzyme. The rate of synthesis of the enzyme is reduced by safflower oil feeding from the fat-free (control) level and after 48 h is approximately one-half that of the control. The rate of degradation of fatty acid synthetase is markedly increased in the safflower oil-fed animals over the control; the half-lives are 1.8 days and 3.8 days, respectively. It is suggested that polyunsaturated fatty acids, or a product derived from them, may directly or indirectly regulate the transcription or translation (or both) of fatty acid synthetase messenger RNA.