Critical Developmental Periods for Effects on Male Rat Genitalia Induced by Finasteride, a 5α-Reductase Inhibitor

The study investigated the effects of finasteride, a 5α-reductase inhibitor, on male rat genitalia during critical developmental periods. The critical period for inducing the effects of finasteride on male rat development, including hypospadias with cleft prepuce, decreased anogenital distance, presence of nipples, and decreased prostate weight, is during gestational days 16 to 17. Finasteride prevented the formation of the medial mesenchymal plate, which is responsible for separating the urethral plate from the ventral surface of the genital tubercle to form the penile urethra. The study concludes that finasteride could also likely cause hypospadias in male human fetuses considering the known effects of congenital 5α-reductase deficiency in humans.