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In utero exposure to di(n)butyl phthalate reduces testicular testosterone and testis size in a dose-dependent manner in Harlan Sprague Dawley fetal rats
Citation:
HOWDESHELL, K., J. R. FURR, C. R. LAMBRIGHT, AND M. C. CARDON. In utero exposure to di(n)butyl phthalate reduces testicular testosterone and testis size in a dose-dependent manner in Harlan Sprague Dawley fetal rats. Presented at Society for the Study of Reproduction, 42nd Annual Meeting, Pittsburgh, PA, July 18 - 22, 2009.
Impact/Purpose:
To present to Society for the Study of Reproduction 42nd Annual Meeting
Description:
Phthalate esters are widely used to impart flexibility to plastics (e.g. plastic medical devices and children’s toys) as well as other uses in health and beauty products and some pharmaceuticals. Certain phthalate esters cause reproductive malformations and decrease androgen-dependent reproductive organ weights in male rats when exposure occurs during the period of sexual differentiation. A risk assessment of the potential human health effects of di(n)butyl phthalate (DBP) is currently in progress at the National Center for Environmental Assessment at the USEPA. Critical endpoints in this assessment include: fetal testosterone levels and postnatal reproductive tract malformations in male rats. Reduced testosterone levels are being considered as an adverse effect because they are causally linked to the induction of these malformations. Previous studies of phthalate effects on reproductive development have primarily been conducted in a variety of rat strains. However, the sensitivity of the Harlan Sprague Dawley (SD) rat during sexual differentiation to phthalates is not known. In response to the ongoing risk assessment and because the Harlan SD rat is the new strain of choice of the National Toxicology Program, we evaluated the effects of DBP on fetal endocrine and genomic parameters related to androgen-signaling and other pathways in the Harlan SD rat. Pregnant rat dams were orally dosed on gestation days (GD) 8-18 with 0, 33, 50, 100, 300, 600 or 900 mg DBP/kg/day, and fetuses were collected on GD18. In the first experiment, one testis from three males per litter was incubated and testosterone production was measured, while the remaining testes were stored for analysis of gene expression by qRT-PCR. In the second experiment, we recorded fetal body weights, testis weights, and fetal and maternal liver weights. Testes were ether extracted and testosterone was measured by radioimmunoassay. Livers were stored for analysis of gene expression by qRT- PCR. Gene expression analyses are measuring testicular expression levels of genes in the steroidogenic pathway (StAR and cyp11a) and PPAR isoforms, which may be a target for DBP-induced changes in testicular function. Fetal testosterone production was reduced in a dose-dependent manner by DBP, reaching a significant decrease at 100 mg/kg/d. Paired testes weight and extracted testicular testosterone levels were also decreased in a dose-dependent manner with significant reductions at 600 mg/kg/d and 300 mg/kg/d and above, respectively. Testosterone production and testis testosterone levels were not assessed at 900 mg/kg/d as fetal mortality at this dose was 50%; and maternal weight gain was also significantly decreased at this dose. In contrast, there were no treatment-related effects on maternal or fetal body weight or liver weights up to 600 mg/kg/d. These results indicate that DBP reduces fetal testosterone levels and testicular weights independent of any overt systemic fetal or maternal toxicity at dosage levels up to 600 mg/kg/d. These data demonstrate that DBP is a specific developmental reproductive toxicant that produces adverse effects on male rat sexual differentiation by reducing testosterone levels in utero. Study funded by EPA IAG # RW-75-92285501-0, NTP # Y1-ES-80124-01. This abstract does not necessary reflect USEPA policy.