Effect of phthalate esters on drug metabolizing enzyme activities in rat liver.

Dibutyl-, di(2-ethylhexyl)-, di(3, 3, 5-trimethylhexyl)- and didecylphthalate (DBP, DEHP, TMHP, DDP) all caused an increase in the amount of hepatic cytochrome P=450, when administered intragastrically to rats. No statistically significant increase could be detected in the catalytic activities dependent on cytochrome P-450 (Benzo(a)pyrene hydroxylation, ethoxycoumarin deethylation). Dibutylphthalate inhibited these reactions, when added to the incubation in vitro. Phthalates caused an increase in the activities of epoxide hydratase, and glutathione-S-transferase. Conjugation of 0-aminophenol and 4-methylumbelliferone with glucuronic acid was increased after phthalate administration.