The Biosynthesis of Cholesterol and Other Sterols by Brain Tissue

The distribution of [14C]labelled material into subcellular fractions of 30‐day‐old rat brain was studied as a function of time, following intracerebral injection of [2‐14C] mevalonic acid. As in the adult and 15‐day‐old brain, the microsomal fraction was indicated as the site of sterol synthesis. Unlike the 15‐day‐old animal, the myelin fraction from the 30‐day‐old rat was the predominately labelled fraction at 2 weeks after injection of the animal. Significant amounts of [14C]cholesterol were not present until about 4 h after injection. In order to ascertain whether different populations of cholesterol were being labelled, depending on the age of the animal injected, we compared the labelling of myelin and non‐myelin components in animals injected at 15 or at 30 days of age, and sacrificed, respectively, from 14 to 29 days or from 1 to 28 days after injection. Our results indicated that there was an apparent shift of labelled sterol from non‐myelin to myelin fractions at about 37–44 days of age.