Cholesterol synthesis in the liver, kidneys and brain after injection of uniformly 14C-labeled oleic or linoleic acid to developing rats.

6-day-old suckling rats, born to females kept on a fat-free diet, were used to determine cholesterol and fatty acid specific radioactivity (SRA) in the liver, kidneys and brain, after injection of 3 microCi uniformly 14C-labeled linoleic acid (ULI) or oleic acid (UOL). 1 h after injection, cholesterol SRA was highest in the liver and kidneys, and then decreased when UOL was injected. Cholesterol SRA peaked 3 h after injection of ULI in liver and kidneys. The delay in appearance of the ULI (over UOL) peak of cholesterol SRA may be due to differences in the rates of oxidation of these two labeled fatty acids into acetyl-CoA ester, according to the structural role of ULI. In the period between 3 and 56 h, cholesterol was more radioactive in the three tissues after injection of ULI than after injection of UOL. The radioactivity of saturated fatty acids was low in the ULI and UOL groups of these very young animals. Therefore, cholesterol synthesis seemed to happen at a faster rate than the other lipid syntheses in liver and kidneys, where the rate of linoleic acid elongation into arachidonic acid was also slower than cholesterol synthesis. Different results were obtained in the brain, where arachidonic acid SRA increased rapidly after ULI injection.