Cytochrome P-450 activity in human leiomyoma and normal myometrium

Variations in cytochrome P-450 levels may influence the responsiveness of uterine and breast tissue as well as carcinomas to endocrine therapy and may be of particular importance with agents such as tamoxifen (Nolvadex) where hydroxylation is known to alter therapeutic activities. Therefore, a sensitive spectrophotometric assay of cytochrome P-450 levels in reproductive tissue microsomes was developed to measure cyclohexane hydroxylase activity. Cyclohexane served as a substrate for several forms of cytochrome P-450. Human uterine leiomyomas (uterine fibroid tumor) contained significantly higher (p less than 0.01) cytochrome P-450 activity than adjacent normal myometrium. Specific activities for both leiomyomas (2.87 +/- 0.26 nmol/min/mg) and normal myometrium (1.60 +/- 0.11 nmol/min/mg) were in the range of those observed for untreated rabbit liver microsomes (1 to 3 nmol/min/mg). The contribution of smooth muscle in the specimen, the phase of the menstrual cycle, and the clinical diagnosis did not influence the level of cytochrome P-450 activity.