Analysis of tamoxifen and 4-hydroxytamoxifen levels in immature rat uterine cytoplasm and KCl-nuclear extracts by gas chromatography-mass spectrometry (GC-MS) using selected ion monitoring (SIM).

A GC-MS (SIM) method has been developed which allows the measurement of tamoxifen and its metabolites in uterine cytosol and 0.5 M KCl-extracts of uterine nuclei from groups of immature rats. The method was shown to be specific, precise and accurate. Using this procedure tamoxifen and 4-hydroxytamoxifen were tentatively identified and measured in uterine extracts after tamoxifen administration. When tamoxifen and 4-hydroxytamoxifen levels in uterine cytosol and 0.5 M KCl nuclear extracts were compared a relative enrichment in the nuclear fraction of 4-hydroxytamoxifen (relative to tamoxifen) was consistently seen. These observations are supportive of a role for 4-hydroxytamoxifen in mediating the antiestrogenic actions of tamoxifen in the immature rat uterus. In some of the uterine cytosolic fractions desmethyltamoxifen and metabolite Y could also be detected.