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Flutamide, when administered subcutaneously to female rats at doses of 3, 10, or 30 mg/kg/day during late pregnancy (gestational days 16-21), significantly and dose-dependently decreased anogenital distance (AGD) of the male offspring in each dose group compared to controls. Significant delays in preputial separation were found in males at a dose of 30 mg/kg, but body weight gain was not inhibited. Cryptorchidism and absence of the prostate gland and seminal vesicles were found in males at doses > or = 10 mg/kg, and testicular hypoplasia at a dose of 30 mg/kg. Hypospadias was noted in all dose groups and vaginal pouches at doses of > or =10 mg/kg. The effects on the accessory reproductive organs were severe, although the effects on the testes themselves were mild. However, those effects appeared to become more pronounced with growth, as evaluated on Days 30 and 42 and Weeks 16 to 18. Most of these affected animals displayed cryptorchidism. Male offspring exposed to flutamide in utero showed impairments of sexual behavior as adults in a dose-related manner. Number and frequency of mounts with intromissions was markedly decreased in all treated groups as compared to controls. At 10 mg/kg, no mounting with ejaculation was observed, and at a dose of 30 mg/kg, no mounting with intromission or ejaculation was observed. These changes in sexual behavior were closely associated with abnormalities of the external genitalia. Animals with hypospadias did not display mounts with ejaculation. However, F1 males that copulated at a dose of 3 mg/kg had a normal reproductive function. Histological examination of the reproductive organs revealed degeneration of the seminiferous tubules, hypospermatogenesis, and hypoplasia and inflammation of the seminal vesicles and prostate. Serum levels of FSH, LH, and testosterone in these animals were comparable between control and all dose groups. Therefore, the male reproductive dysfunction seen in the present study could not be attributed to abnormal sex hormone levels during maturation, but to possible demasculinization of the brain and progressively delayed dysmorphology of the male genitalia caused by fetal exposure to flutamide.