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Context: Mammary and placental 17b-hydroxysteroid dehydrogenase type 1 (17bHSD1). Objective: To assess the impact of testosterone, tibolone, and black cohosh on purified mammary and placental 17bHSD1. Materials and methods: 17bHSD1 was purified from human mammary gland and placenta by column chromatography, its activity was monitored by a radioactive activity assay, and the degree of purification was determined by gel electrophoresis. Photometric cofactor transformation analysis was performed to assess 17bHSD1 activity without or in presence of testosterone, tibolone and black cohosh. Results: 17bHSD1 from both sources displayed a comparable basal activity. Testosterone and tibolone metabolites inhibited purified mammary and placental 17bHSD1 activity to a different extent, whereas black cohosh had no impact. Discussion: Studies on purified enzymes reveal the individual action of drugs on local regulatory mechanisms thus helping to develop more targeted therapeutic intervention. Conclusion: Testosterone, tibolone and black cohosh display a beneficial effect on local mammary estrogen metabolism by not affecting or decreasing local estradiol exposure.

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