XENOBIOTIC AND STEROID BIOTRANSFORMATION ENZYMES IN ATLANTIC SALMON (SALMO-SALAR) LIVER TREATED WITH AN ESTROGENIC COMPOUND, 4-NONYLPHENOL

Hepatic microsomal biotransformation reactions with xenobiotic and ste roid substrates have been investigated in 4-non-ylphenol (NP; 1, 5, 25 , and 125 mg/kg body weight)-treated juvenile Atlantic salmon (Salmo s alar), in addition to control and estradiol-17 beta (5 mg/kg, positive control)-treated fish. Treatment of juvenile salmon with NP caused an initial increase and an apparent dose-dependent decrease in progester one 6 beta-, 16 alpha, and 17 alpha-hydroxylase activities in liver mi crosomes. 7-Ethoxyresorufin O-deethylase and UDP-glucuronosyltransfera se activities were also reduced. Plasma levels of estradiol-17 beta (E -2) were lowered 24-43% as a result of NP treatment. Immunochemical an alysis of CYP1A, CYP2K-like, and CYP3A like proteins showed 18%, 47%, and 30% reductions in enzyme-linked immunosorbent assay absorbance lev els, respectively, in the groups treated with 125 NP/kg fish. The grou p treated with E, also showed similar reductions. In summary, the pres ent study has demonstrated variations in steroid hydroxylases, cytochr ome P450 isozymes, and conjugating enzyme levels in NP-treated juvenil e salmon. These results represent a novel aspect of NP effects not pre viously demonstrated with an environmental estrogen in any fish specie s or lower vertebrate.