The biosynthesis of cholesterol and other sterols by brain tissue: II. A comparison of in vitro and in vivo methods

When microsomal + soluble preparations of adult or 15‐day‐old rat brains were incubated with 2‐14C‐mevalonic acid,14C‐squalene accumulated. A metabolic block at the squalene to cholesterol stage was indicated. This prompted a comparison of all methods currently used to study cholesterol biosynthesis by brain tissue. Brain cell‐free preparations from newborn, 15‐day‐old or adult rats accumulated14C‐squalene in a similar manner, with either 2‐14C‐acetate or 2‐14C‐mevalonic acid as substrates. Homogenates and minced preparations from newborn or 15‐day‐old rats accumulated some 4,4‐dimethyl sterols, but considerable conversion to free 4‐desmethyl sterols (cholesterol) was evident. Sterol esters were also present in all the in vitro studies. In general, increased disruption of tissue resulted in decreased free 4‐desmethyl sterol formation in vitro. Intraperitoneal injection of labeled acetate or mevalonate to newborn or 15‐day‐old rats produced labeled brain 4‐desmethyl sterol with little accumulation of squalene or 4,4‐dimethyl sterols, but the yields in brain were small compared to total amount of labeled material administered. At all ages intracerebral injection produced the best yield of labeled cholesterol for the amount of nonsaponifiable material formed.