Evaluation of the 5α-reductase inhibitor finasteride on reproduction and gonadal development in medaka, Oryzias latipes

5-α reductase (5αR) inhibitors have an anti-androgenic effect in mammals because they inhibit the conversion of testosterone to the potent androgen, dihydrotestosterone. Finasteride is a type-2 5αR inhibitor that is used as a human pharmaceutical for the treatment of prostate cancer, benign prostate hyperplasia and male pattern baldness. This study evaluated the impacts of finasteride (50, 500 and 5000 μg/L) on the development and reproduction of medaka (Oryzias latipes) exposed continuously over multiple generations (F0, F1 and F2). The exposure was initiated with reproductively mature fish (F0 generation) and continued until the hatching of the F2 generation. There were no significant effects on survival, fecundity or fertility in the F0 (50, 500, 5000 μg/L) and F1 (50, 500 μg/L) generations. The F1 generation exposed to 5000 μg/L exhibited significant mortality. Histopathology of the gonads demonstrated that medaka and pre-clinical species respond similarly to finasteride exposure. Intersex condition and maldeveloped gonads were observed in F0 generation males exposed to 5000 μg/L and F1 generation males exposed to 500 μg/L. F1 generation males exposed to 500 μg/L displayed reduced gonadosomatic index with an increased incidence of testicular degeneration. Males in both generations exhibited an increased incidence of Leydig cell hyperplasia at concentrations ⩾500 μg/L. F0 generation females exposed to 5000 μg/L exhibited increased gonadosomatic index. An increased prevalence of accelerated post-ovulatory follicle involution was observed in females at concentrations ⩾500 μg/L in both generations. The gonadal changes induced by finasteride support the idea that 5-α reductase inhibition impacts androgen signaling in fish. Results from this study are discussed in the context of differential expression of the androgen receptor between species of fish.