Incorporation in vivo of 1-14C-acetate into lipids of rats fed threonine imbalanced diet

In order to investigate the mechanism of the fatty liver production in rats fed the thereonine imbalanced diet, time course of lipogenesis was followed after intraperitoneal injection of 1-14C-acetate into rats that had been reared on the imbalanced diet for 7 days. 1) The rate of the incorporation of 1-14C-acetate into hepatic triglyceride, estimated either on the base of unit weight of liver or of whole liver, in comparison with that of the control rats, did not increase by feeding the imbalanced diet under the condition where the extent of lipogenesis could be measured (30 min after the dose of the label). Also, the specific activity of triglyceride was by no means high at this point. The rate of disappearance of the radioactivity, between 60 min and 180 min after the label injection, from triglyceride was evidently slower in rats fed the imbalanced diet, thus the radioactivity of triglyceride in this animal being to some extent higher after 180 min. 2) The incorporation of radioactivity into phospholipid was not influenced by the imbalanced diet. 3) There was no difference in the incorporation of the radioactivity into kidney lipids between the control and imbalanced groups. 4) From the distribution of the radioactivity in the hepatic lipid fractions, it appeared that the relative incorporation into triglyceride tended to increase after feeding the imbalanced diet. 5) There were no demonstrable differences in the activity of plasma total lipids at any times after the injection of the label. The ratio of the label incorporation into whole plasma and liver total lipids tended to decrease in the imbalanced rat after 180 min. These results suggested that, although alternative explanations are possible, the decreased turnover in hepatic triglyceride, rather than the increased hepatic lipogenesis, would largely be responsible for the production of fatty liver in rats fed the threonine imbalanced diet. (auth.)