Kinetics of mixed function oxygenase induction and retene excretion in retene-exposed rainbow trout (Oncorhynchus mykiss)

The polycyclic aromatic hydrocarbon 7-isopropyl-1-methylphenanthrene (reten e) induces mixed function oxygenase (MFO) activity of fish. Bile levels of retene and its metabolite(s) were measured in relation to exposure time, ex posure concentration, and induction of MFO activity. Synchronous fluorescen ce spectrometry provided a rapid means of measuring the amount of retene pr esent in the bile of exposed fish, whereas conventional fluorescence spectr ometry was used to quantify the amount of retene metabolites. Based on bile analysis, increased retene exposure resulted in an increased uptake of ret ene and a curvilinear increase in hepatic MFO activity. Retene was present in the bile within 6 h of initial exposure. However, retene metabolite(s) o nly appeared in the bile after MFO induction had occurred, 12 h after expos ure had commenced, suggesting that MFO activity is required for metabolism. Transfer of fish to clean water after 48 h of exposure resulted in a rapid decrease in the presence of retene and its metabolite(s) in the bile, with a calculated half-life of about 14 h. In vitro additions of retene directl y to the ethoxyresorufin O-deethylase assay demonstrated that retene is cap able of acting as a competitive inhibitor. Thus, retene contamination of po stmitochondrial supernatant (S9 fraction) could result in false-negative re sults in the MFO assay. The MFO activity in extrahepatic tissues (gills, he art, and kidney) was not significantly induced with retene exposure. Thus, the major site of retene metabolism seems to be in the liver. These results confirm that retene is rapidly taken up, metabolized, and excreted by rain bow trout, and that retene metabolism and excretion are linked to hepatic M FO induction.