Background: Phthalates are plasticizers with widespread industrial, domestic and medical applications. Epidemiological data indicating increased incidence of testicular dysgenesis in boys exposed to phthalates in utero are supported by studies demonstrating phthalates impair fetal testis development in rodents^{1 2}. Humans are continually exposed to phthalates from gestation through adulthood. It is thus imperative to determine whether phthalates pose a threat to testis development and function at other life stages. To address this, we have developed a mouse model of phthalate exposure to assess effects on the postnatal testis.

Methods: Wildtype (C57Bl/6J) mice were fed 1-500 mg/kg/day di-n-butyl phthalate (DBP) in corn oil vehicle, or vehicle only, from 4-14 days post partum.At 14 days, mice were culled, blood was taken for hormone analyses and body and testis weights and anogenital distance were measured.  One testis was fixed for histology/immunohistochemistry and the other used for gene expression analysis by quantitative RTPCR.

Results: Testis weight and testis:body weight ratios, but not body weights, were significantly lower in mice fed 10-500 mg/kg/day DBP. DBP-fed animals had defective seminiferous epithelium development, with delayed lumen formation, mis-localization of Sertoli cells to the centre of the cord/tubule and germ cell loss, including absence of germ cells in some areas. Anogenital distance, an indicator of androgen action, was reduced in mice fed 50-500 mg/kg/day.  Serum testosterone levels were similar between groups, however, indicating impaired androgen action at earlier timepoints.  DBP-treated mice had elevated circulating inhibin, suggesting DBP may suppress activin signalling, which is consistent with several features indicating impaired activin signalling in testes of these mice.

Significance: This study demonstrates the sensitivity of the prepubertal mouse testis to di-n-butyl phthalate, with effects measured at much lower concentrations than reported for rats. We are now using this approach in transgenic mice to identify the genetic basis of phthalate susceptibility.