Effects of tributyltin on the cytochrome P450 monooxygenase system and sex steroid metabolism in the clam Ruditapes decussata

Abstract

The effects of tributyltin (TBT) on the cytochrome P450 monooxygenase system of the clam Ruditapes decussata have been evaluated. Digestive gland microsomes were observed to catalyze the oxidative metabolism of testosterone. The metabolites detected were androstenedione, dihydrotestosterone, dihydroandrostenedione, 6β-, 6α-, 2α-, and 2β-hydroxytestosterone, estrone and 17β-estradiol. The effect of 0.1 and 1 mM TBT in the incubation mixture led to a significant reduction in the total metabolic rate and changes in the metabolite profile. Clams were also exposed to different concentrations of TBT in water (0.1, 0.45, 2.27 μgl −1 of TBT as Sn) for seven days. A significant increase in testosterone levels was found in the TBT exposed organisms. When digestive gland microsomes of control and exposed organisms were assayed for their ability to metabolize testosterone, a dose-responsive decrease in aromatization of testosterone to estrone and estradiol was observed ( p < 0.05). These changes indicated a significant interaction of TBT with androgen metabolism in the clam Ruditapes decussata and they may contribute to masculinization of clam physiology.