Assessment of the developmental toxicity, metabolism, and placental transfer of Di-n-butyl phthalate administered to pregnant rats.

The developmental toxicity and placental transfer of di-n-butyl phthalate (DBP) were evaluated in Sprague-Dawley rats given a single oral dose of DBP on Gestational Day 14. In the developmental toxicity study, dams were dosed with 0, 0.5, 1, 1.5, or 2 g DBP/kg and were necropsied on GD21. Increased incidence of resorptions and reduced fetal body weight were observed at 1.5 and 2 g/kg. Higher incidences of skeletal variations were found at doses > or = at 1 g/kg. No embryotoxic or teratogenic effects were observed at a dose of 0.5 g/kg. In the placental transfer study, dams were dosed with 0.5 or 1.5 g [14C]DBP/kg. Maternal and embryonic tissues were collected at intervals from 0.5 to 48 h. Embryonic tissues accounted for less than 0.12-0.15% of the administered dose. Levels of radiocarbon in placenta and embryo were one-third or less of those in maternal plasma. No accumulation of radioactivity was observed in the maternal or embryonic tissues. From HPLC analyses, it was shown that unchanged DBP and its metabolites mono-n-butyl phthalate (MBP) and MBP glucuronide were rapidly transferred to the embryonic tissues, where their levels were constantly lower than those in maternal plasma. MBP accounted for most of the radioactivity recovered in maternal plasma, placenta, and embryo. Unchanged DBP was found only in small amounts. These findings support the hypothesis that MBP, a potent teratogen, largely contributes to the embryotoxic effects of DBP.