Effects of in utero exposure to finasteride on androgen-dependent reproductive development in the male rat

Finasteride is a specific inhibitor of type II 5alpha-reductase, the enzyme that converts testosterone (T) to the more potent androgen receptor agonist dihydrotestosterone (DHT). In utero exposure to androgen receptor antagonists and T biosynthesis inhibitors have induced permanent effects on androgen-sensitive end points such as anogenital distance (AGD), nipple retention, and malformations of the male rat reproductive tract. The objectives of this study were to (1) characterize the dose response of finasteride-mediated alterations in androgen-dependent developmental end points, (2) determine whether prenatal exposure to finasteride permanently decreases AGD or results in nipple retention, and (3) evaluate whether AGD or nipple retention is predictive of adverse alterations in the male reproductive tract. Pregnant Crl:CD(SD)BR rats (n = 5-6/group) were gavaged with either vehicle or finasteride at 0.01, 0.1, 1.0, 10, or 100 mg/kg/day on gestation days 12 to 21. All male offspring were monitored individually until necropsy on postnatal day (PND) 90. The present study design has been used previously for other antiandrogens and is sensitive to perturbations of the male rat reproductive tract. Decreases in AGD on PND 1 and increases in areolae-nipple retention on PND 13 were significantly different from controls in all finasteride-exposed male rats. Finasteride-induced changes in AGD and nipple retention were permanent in male rats exposed to finasteride at and above 0.1 mg/kg/day. On PND 90, dorsolateral and ventral prostate lobes were absent in 21 to 24% of rats exposed to 100 mg/kg/day finasteride and weighed significantly less at and above 10 mg/kg/day. In the highest dose group, 73% of animals had ectopic testes, much higher than previously reported. The most sensitive malformation other than decreased AGD and nipple retention was the dose-dependent increase in hypospadias. The lowest observed adverse effect level (LOAEL) for finasteride-induced permanent effects in this study was 0.1 mg/kg/day based on permanent changes in AGD and nipple retention. Finasteride-induced changes in AGD and retention of nipples were highly predictive of hypospadias, ectopic testes, and prostate malformations even though some animals with retained nipples or decreased AGD may not have had other reproductive tract malformations. In summary, prenatal exposure to finasteride specifically inhibited DHT-mediated development with little to no change in T-mediated development.