Exposure to exogenous 17β-oestradiol disrupts P450aromB mRNA expression in the brain and gonad of adult fathead minnows ( Pimephales promelas)

Oestrogens are key regulators in sexual differentiation and development in higher vertebrates. P450 aromatase (P450arom) is the steroidogenic enzyme responsible for the synthesis of oestrogens from aromatisable androgens. Effects of endocrine disrupting chemicals on steroidogenic enzyme gene expression have received little attention so far, yet it is potentially a major pathway for sexual disruption. In this 14-day study the effects of exogenous 17β-oestradiol (E2) at environmentally relevant concentrations were assessed on gene expression of P450aromB in the gonad and brain of maturing male and female fathead minnows (FHM). Exposure to E2 resulted in an oestrogenic response as shown by a dose-dependent induction of plasma vitellogenin (VTG) in female and male fish and a dose-dependent inhibition of testis growth. There was an effect of exposure to E2 on P450aromB mRNA expression in the gonads; E2 up-regulated P450aromB mRNA expression in the testis and ovary in a dose-response manner after 14 days of exposure. In male brain, P450aromB mRNA concentrations were significantly reduced in fish exposed to 100 and 320 ng E2/l on day 4, but on day 14 were elevated in males exposed to both 32 and 100 ng E2/l. No effects of E2 on P450aromB mRNA expression occurred in the brain of females. The results of this study show that concentrations of E2 found in the environment can have disruptive effects on key steroidogenic enzyme pathways that control sexual development in fish.