Effect of phenobarbital on the incorporation of 3H or 14C labeled precursors into fatty acids

The incorporation of various 3H or 14C labeled precursors into hepatic fatty acids was studied in control and phenobarbital-treated rats. In vitro, phenobarbital had no effect on fatty acid synthesis from the tritiated precursors 3H 2O, 1- 3H glucose, 2- 3H lactate, 2,3- 3H succinate and 2- 3H acetyl CoA or from the 14C labeled precursors 1- 14C acetate and 1,3- 14C malonyl CoA in liver supernatant or supernatant + microsomes preparations. In vivo, phenobarbital stimulated the incorporation of 1- 14C acetate, 3H 2O, 2- 3H lactate and 2,3- 3H succinate but had no stimulatory effect on the incorporation of 1- 3H glucose. The activities of lactic dehydrogenase, glucose 6-phosphate dehydrogenase and succinate cytochrome c reductase were not modified by administration of phenobarbital but that of NADPH-cytochrome c reductase was increased. These results indicate that the NADH and NADPH pools are not quite in equilibrium, and that the endoplasmic reticulum probably competes with the cytoplasm for NADPH utilization and thus may play a part in the regulation of fatty acid synthesis. The increased incorporation of 14C precursors observed in vivo in phenobarbital-treated rats was not due to stimulation of the synthesis of the key enzymes of fatty acid synthesis but could be related to an activation of these enzymes which, in vivo, are probably fixed on the endoplasmic reticulum.