Phthalate exposure impairs testis development and function, however whether phthalates affect non-reproductive functions is not well understood. To investigate this, C57Bl/6J mice were fed 1-500 mg di-n-butyl phthalate (DBP) in corn oil, or vehicle only, daily from 4-14 days, after which tissues were collected (prepubertal study). Another group was fed 1-500 mg DBP/kg/day from 4-21 days then maintained untreated until 8 weeks for determination of adult consequences of prepubertal exposure. Bones were assessed by micro-computed tomography and dual energy X-ray absorptiometry, and testosterone by radioimmunoassay. DBP exposure decreased prepubertal femur length, marrow volume and mean moment of inertia. Adult animals exposed prepubertally to low DBP doses had lower bone mineral content (BMC) and bone mineral density (BMD) and less lean tissue mass than vehicle-treated animals. Altered dynamics of the emerging Leydig population were found in 14 day old animals fed 100-500 mg DBP/kg/day. Adult mice had variable testicular testosterone and serum testosterone and luteinizing hormone concentrations following prepubertal exposure, and dose-dependent reduction in CYP11A1. INSL3 was detected in Sertoli cells of adult mice administered the highest dose of 500 mg DBP/kg/day prepubertally, a finding supported by the induction of INSL3 expression in TM4 cells exposed to 50 μ M, but not 5 μ M, DBP. We propose that low dose DBP exposure is detrimental to bone but that normal BMD/BMC following high dose DBP exposure reflects changes in testicular somatic cells that confer protection to bones. These findings will fuel concerns that low dose DBP exposure impacts health beyond the reproductive axis.
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