Aryl hydrocarbon hydroxylase (AHH) induction by polybrominated biphenyls (PBBs): Enhancement by photolysis

Irradiation of the commercial polybrominated biphenyl (PBB) mixture, fireMaster BP-6, in cyclohexane solution at 300 nm for 930 min resulted in a marked diminution of the major components of the mixture. Administration of the photolyzed PBB mixture or fireMaster BP-6 to immature mall Wistar rats caused dose-related decreases in thymus weight and increases in hepatic microsomal benzo[a]pyrene hydroxylase (AHH), 4-dimethylaminoantypyrine N-demethylase and NADPH-cytochrome c reductase activities and cytochrome P-450 content. The dose effecting half-maximal AHH induction for the photolyzed PBBs (9 mg · kg^-1) was approximately 6 times lower than that of fireMaster Bp-6 (50 mg · kg^-1). Futhermore, the concentration of photolyzed PBBs (2 μM) required to displace 50% of the specifically-bound [³H]TCDD from its high-affinity cytosolic Ah receptor was approximately 150 times lower than that required for fireMaster BP-6 (300 μM), as measured by sucrose density gradient centrifugation analysis. The results suggest that the photolysis of the commercial PBB mixture yields products which possess increased biologic activity.