Hepta-, hexa-, tetra- and dichloronaphthalene congeners as inducers of hepatic microsomal drug-metabolizing enzymes.

Pretreatment of immature male Wistar rats with 1,2,3,4,5,6,7-hepta-, 1,2,3,4,5,6,8-hepta- and 1,2,3,4,5,6-hexachloronaphthalene resulted in the induction of several hepatic microsomal drug-metabolizing enzymes. The enzymic activities, reduced cytochrome P-450:CO and ethylisocyanide binding difference spectra and electrophoretic mobilities of the induced microsomal proteins were comparable to those observed after administration of the classical inducer of microsomal aryl hydrocarbon hydroxylase, 3-methylcholanthrene. The 1,2,3,4,5,6,7-heptachloronaphthalene congener, which is fully substituted in the lateral 2,3,6 and 7 positions, was more potent than the 1,2,3,4,5,6,8-hepta- and the 1,2,3,4,5,6-hexachloronaphthalene congeners which contain only 3 lateral chloro substituents. 1,2,3,4-Tetra- and several lower chlorinated naphthalenes were inactive as inducers of microsomal aryl hydrocarbon hydroxylase. The effects of structure on the induction activities of the polychlorinated naphthalenes were similar to those observed for other halogenated aryl hydrocarbons.