The effect of phenytoin on testosterone metabolism in vitro.

We recently encountered a male newborn with ambiguous genitalia who had been exposed to the anticonvulsant phenytoin in utero. In an attempt to investigate a possible teratogenic connection between phenytoin exposure and genital anomalies, the effect of phenytoin on the conversion of testosterone to dihydrotestosterone by human skin slices was studied. Neonatal foreskins obtained at circumcision were incubated for two hours with testosterone-4-14C and various concentrations of phenytoin. The incubation mixture was then assayed for testosterone, dihydrotestosterone, androstanedione, androstenedione, androstanediol, and androsterone using thin-layer chromatography and liquid scintillation spectrometry. The amounts of testosterone metabolites formed with phenytoin added were compared to values obtained under control conditions without phenytoin. There was a significant decrease in the amounts of 5 alpha reduced metabolites formed with increasing amounts of phenytoin added. Implications for male phenotypic sexual differentiation of the fetus exposed to phenytoin in utero are discussed.