Toxicological investigation of di(2-ethylhexyl)phthalate in rats. The determination of a no-observed-effect-level
Jansen EHJM, van den Ham WA, Dormans JAMA, van Apeldoorn ME, van Leeuwen FXR
RIVM Rapport 618902007
Two animal experiments are described in which male rats have been exposed to di(2-ethylhexyl)phthalate (DEHP) for 2 and 4 weeks. Besides morphometric analysis using both light and electron microscopy, a number of enzyme parameters in liver homogenates have been determined which have a relation with the proliferation of peroxisomes in hepatocytes, such as palmitoyl coenzyme-A oxidase (PCO), enoyl coenzyme-A hydratase (ECH), carnitine acetyl transferase (CAT), catalase (cat) and lauric acid hydroxylase (LAH). Glutamate dehydrogenase (GIDH) was measured as a control enzyme for mitochondria. For all enzymes, except GIDH, a dose-response relationship was observed. There were not many differences between the results of the parameters examined in the 2 and 4 weeks exposed animals. In the 2 weeks exposure experiment, the enzyme parameters appeared to be slightly more sensitive. Therefore the parameters from this experiment were taken for determination of the doses-without-effect (DWE). Also the morphometric analysis has been performed on the 2 weeks-experiment. Although CAT turned out the most sensitive parameter, this enzyme activity was not considered in the establishment of an overall no-observed-effect-level since it is not specific for peroxisome proliferation. The second most sensitive parameters were the morphometric analysis and the induction of LAH and ECH activity (DWE = 5 mg/kg b.w./day) followed by PCO (DWE = 18 mg/kg b.w./day). Catalase activity was not a very sensitive parameter (52 mg/kg b.w./day). An overall no-observed-effect-level for DEHP was established as 5 mg/kg b.w./day, based on the parameters mentioned for peroxisome proliferation.