Effects of dibutyl phthalate as an environmental endocrine disrupter on gonadal sex differentiation of genetic males of the frog Rana rugosa

To examine the effects of dibutyl phthalate (DBP) on gonadal sex differenti ation, genetically male tadpoles of Rana rugosa were exposed to dilute solu tions of DBP at concentrations of 0.1, 1, or 10 muM during days 19-23 after fertilization, which is the critical period of gonadal sex differentiation in R. rugosa. Tadpoles were necropsied on day 40. The genetically male tad poles were produced from crossings between males (ZZ) of one local populati on, in which females are the heterogametic sex, and females (XX) of another local population, in which males are the heterogametic sex. As positive co ntrol groups, tadpoles were exposed to dilute solutions of 17 beta -estradi ol (E-2) at concentrations of 0.01, 0.1, or 1 muM during the same period. T he internal structure of the gonads was histologically examined in a total of 30 control tadpoles, 86 E-2-treated tadpoles, and 90 DBP-treated tadpole s. The gonads of the control tadpoles all showed the typical structure of t estes. In contrast, 0.01, 0.1, and 1 muM E-2 treatments caused the undiffer entiated gonads of 18, 63, and 100% of the tadpoles, respectively, to devel op into gonads of complete or partial ovarian structure. After 0.1, 1, and 10 muM DBP treatment, 0, 7, and 17% of tadpoles, respectively, were similar ly affected. These findings suggest that DBP was about 1,000-fold less pote nt than E-2. Nevertheless, DBP is an environmentally dangerous hormone that disrupts the pathways of testicular differentiation in genetically male an imals.