| Summary: | The metabolism of Δ7-cholestenol, cholesterol, and cholestanol was examined in a patient with cerebrotendinous xanthomatosis after intravenous pulse-labeling with a mixture of dl-[2-14C]mevalonate and stereospecific 3S,4S,3R,4R-[4-3H]-mevalonate. Silver nitrate and reversed-phase thin-layer chromatography were used to purify the sterols isolated from the feces, and their identities were confirmed by gas–liquid chromatography–mass spectrometry. The specific activities were determined and plotted as a function of time. Isotope ratio measurements and specific activity decay curves showed that sterol synthesis proceeded in the following sequence: mevalonate, squalene, lanosterol, Δ7-cholestenol, cholesterol, cholestanol. Labeled cholesterol precursors might be advantageously used to measure changes in cholesterol synthesis because they appear to equilibrate rapidly and have very short turnover times.
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