17-alpha-ethinylestradiol affects reproduction, sexual differentiation and aromatase gene expression of the medaka (Oryzias latipes).

Juvenile medaka (Oryzias latipes) of the d-rR strain were exposed for 2 months to 1, 10 and 100 ng/l of the environmental estrogen 17-alpha-ethinylestradiol (EE(2)). The exposure period was followed by a 6 week recovering period in order to detect long-lasting effects on sexual differentiation. Survival rate, sex ratio, gonadal growth, spawning, fecundity, histology as well as the ovarian gene expression of aromatase were monitored. At 100 ng/l EE(2), all XY medaka were sex reversed and had developed an ovary. At lower EE(2) concentrations, which did not result in sex reversal, no alteration of testicular structure was detected and male fertility appeared to be unchanged. In XX females, reduced production of eggs was reflected in a significantly reduced gonadal weight at 10 and 100 ng/l EE(2). Aromatase, which in gonads is normally only expressed in ovaries, was detectable in testis of XY males exposed to 10 ng/l EE(2). The results indicated that a combination of different biological endpoints provide a suitable set of parameters for the biological evaluation of xenoestrogens, since the expression of molecular marker genes was not always paralleled by morphological deficiencies.