[Hypospadias induced by maternal exposure to di-n-butyl phthalate and its mechanisms in male rat offspring , , , , ,].

Objective To induce hypospadias in male rat offspring by maternal exposure to di-n-butyl phthalate (DBP) during late pregnancy and further investigate its mechanisms. METHODS We randomly divided 20 pregnant rats into a DBP exposure and a control group, the former treated intragastrically with DBP while the latter with soybean oil at 750 mg per kilogram of the body weight per day from gestation days (GD) 14 to 18. On postnatal day (PND) 1, we recorded the incidence rate of hypospadias and observed the histopathological changes in the genital tubercle of the hypospadiac rats. We also measured the level of serum testosterone (T) by radioimmunoassay and determined the mRNA and protein expressions of the androgen receptor (AR), sonic hedgehog (Shh), bone morphogenetic protein 4 (Bmp4) and fibroblast growth factor 8 (Fgf8) in the genital tubercle by real-time PCR and Western blot. RESULTS No hypospadiac male rats were found in the control group. The incidence rate of hypospadias in male offspring was 43.6% in the DBP-treatment group. Histological analysis confirmed hypospadiac malformation. The serum testosterone concentration was decreased in the hypospadiac male rats as compared with the controls (［0.49 ± 0.05］ vs ［1.12 ± 0.05］ ng/ml, P <0.05). The mRNA expressions of AR, Shh, Bmp4 and Fgf8 in the genital tubercle were significantly lower in the hypospadiac male rats than in the controls (AR: 0.50 ± 0.05 vs 1.00 ± 0.12, P <0.05; Shh: 0.65 ± 0.07 vs 1.00 ± 0.15, P <0.05; Bmp4: 0.42 ± 0.05 vs 1.00 ± 0.13, P <0.05; Fgf8: 0.46 ± 0.04 vs 1.00 ± 0.12, P <0.05), and so were their protein expressions (AR: 0.34 ± 0.05 vs 1.00 ± 0.09, P <0.05; Shh: 0.51 ± 0.07 vs 1.00 ± 0.12, P <0.05; Bmp4: 0.43 ± 0.05 vs 1.00 ± 0.11, P <0.05; Fgf8: 0.57 ± 0.04 vs 1.00 ± 0.13, P <0.05). CONCLUSIONS Maternal exposure to DBP during late pregnancy can induce hypospadias in the male rat offspring. DBP affects the development of the genital tubercle by reducing the serum T concentration and expressions of AR, Shh, Bmp4 and Fgf8 in the genital tubercle, which might underlie the mechanism of DBP inducing hypospadias.