Studies on the enzyme inducing effect of polychlorinated biphenyls

Abstract

Aroclor 1260 was fed to weanling male and female rats in the diet at levels of 1, 5, 25 and 50 ppm to determine its enzyme inducing capacity over various feeding periods. Dose-dependent increases in the activity of 3 hepatic microsomal enzymes were observed; maximal induction occurred in the first 3 weeks of the feeding period. Among the 3 enzyme systems studied, N-demethylase was the most sensitive to the inducing effect of Aroclor 1260. The enzyme induction was more pronounced in male rats than in females. An age difference in susceptibility of male rats to the enzyme inducing effect was also noted, young rats being more susceptible than adults. Data obtained by simultaneously feeding PCB and DDT to rats showed that these compounds have additive inducing effects on N-demethylase activity. However, PCB and DDT were not, when combined, additive on the O-demethylase and EPN-detoxification systems under the test conditions employed. Comparison of enzyme inducing effects of three Aroclor compounds, Aroclor 1221, 1254 and 1260, clearly indicates that both microsomal N-demethylase and EPN detoxification activity were increased in proportion to the chlorine content of the Aroclor compounds. Maximal induction of O-demethylase occurred at 54% chlorination.