STEROLS WITH 29, 28 AND 27 CARBON ATOMS METABOLICALLY RELATED TO CHOLESTEROL, OCCURRING IN DEVELOPING AND MATURE BRAIN1

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Abstract
—: Brain sterols from chick embryos (11 and 18 days of incubation) and mature rats, previously injected with [2‐14C]mevalonate, were analysed.Acetate derivatives of the sterols were chromatographed on Silica Gel:Celite:AgNO3 columns. Sterol fractions were assayed for radioactivity and the amounts determined by gas chromatography. Sterol structures were elucidated by gas chromatography‐mass spectrometry. The method used allowed the identification of some sterols representing no more than 0‐01 per cent of the total mixture.The following brain sterols were identified: cholesterol, cholestanol, cholest‐5,24‐dien‐3β‐ol (desmosterol); 4,4′‐dimethyl‐cholest‐8‐en‐3β‐ol, 4α‐methyl‐cholest‐8‐en‐3β‐ol, cholest‐8‐en‐3β‐ol, 4,4′‐dimethyl‐choIest‐8,24‐dien‐3β‐ol, 4α‐methyl‐cholest‐8,24‐dien‐3β‐ol, cholest‐8,24‐dien‐3β‐ol and cholest‐7,24‐dien‐3β‐ol. Small amounts of other sterols including polyhydroxy sterols, were also detected. There were no qualitative differences in the sterols detected in developing and mature brain. In the developing chick brain, cholesterol represented approximately 90 per cent of the total sterols. In the mature rat brain, cholesterol accounted for 98 per cent of the sterols.The adult rat brain, as well as the embryonic chick brain, demonstrated the capacity to incorporate mevalonate into cholesterol precursors and cholestanol. The sterols retaining the double bond in the lateral chain, that is, those of the Δ8,24 series with 29, 28 and 27 carbon atoms and desmosterol, were highly labelled compared with the other identified intermediates. The possibility, supported by our data, that a preferential biosynthetic route for cholesterol exists in brain, is discussed.

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