Biosynthesis of Fatty Acids and Cholesterol in Isolated Rat‐Liver Parenchymal Cells

The fatty acid and cholesterol synthesis in isolated rat‐liver parenchymal cells was studied with tritiated water as the radioactive precursor. In cells from rats fed a diet containing 3% fat the rate of fatty acid biosynthesis was 1.25 and the cholesterol biosynthesis 0.68 nmol/mg protein per h. This means that the rate of cholesterol biosynthesis was in the same range as in earlier studies with perfused rat livers, whereas the fatty acid synthesis was about ten times lower than in the intact organ. Addition of palmitic or oleic acid to the medium caused up to 81% inhibition of the fatty acid synthesis, whereas the cholesterogenesis was either unaffected or inhibited to a lesser extent. The data therefore provide direct evidence for a feedback inhibition of hepatic lipogenesis, caused by the uptake of long‐chain fatty acids. Octanoic and dodecanoic acid were not as efficient inhibitors of the fatty acid biosynthesis. Instead the addition of these fatty acids to the medium in increasing concentrations caused an increasing inhibition of the cholesterol biosynthesis.