Identification and quantitation of cholest-5-ene-3 beta,4 beta-diol in rat liver and human plasma.

Cholest-5-ene-3 beta,4 beta-diol (4 beta-hydroxycholesterol) was identified in human plasma and rat liver by gas-liquid chromatography-mass spectrometry. An assay based on isotope dilution-mass spectrometry with a deuterium-labeled internal standard was developed for quantitation of this compound. The concentration of cholest-5-ene-3 beta,4 beta-diol in plasma from healthy subjects was 36 +/- 4.3 ng/ml (mean +/- SD, n = 8). The concentration in rat liver was 0.62 +/- 0.19 microgram/g wet weight (mean +/- SD, n = 6). These levels are of the same order of magnitude as other common oxysterols.