Effects of waterborne nitrite on phase I-II biotransformation in channel catfish (Ictalurus punctatus)

The effects of waterborne nitrite (3 mg/l NO2) on channel catfish were stud ied to evaluate changes in hematological parameters and phase I-II biotrans formation in liver slices. Nitrite-exposed fish had significantly higher me themoglobin, blood and liver nitrite, and significantly lower pO(2) than co ntrol fish. Total phase I-mediated metabolism of 7-ethoxycoumarin (EC) was not altered in nitrite-exposed fish compared with control fish (291+/-43 an d 312+/-20 pmol/ mg/h, respectively). However, phase II glucuronosyltransfe rase-mediated metabolism of 7-hydroxycoumarin (HC), both as a phase I metab olite of EC and as a parent substrate, was elevated in nitrite-exposed fish (204+/-17 and 1007+/-103 pmol/mg/h, respectively) as compared to control f ish (149+/-14 and 735+/-87 pmol/mg/h) (P< 0.05). Sulfotransferase-mediated metabolism of HC las a metabolite of EC and as a parent substrate) was not notably altered in nitrite-exposed fish (95+/-16 and 617+/-33 pmol/mg prote in/h, respectively) as compared with control fish (118+/-24 and 575+/-55 pm ol/mg/h, respectively). These studies indicate that in vivo nitrite exposur e and associated changes in hematological parameters do not appear to affec t hepatic phase I EC biotransformation in channel catfish. However, subtle but significant changes in phase II glucuronidation, but not sulfation acti vity, were observed. The mechanism of these alterations is unclear. However , the data suggest that environmentally realistic concentrations of nitrite may affect the dynamics of conjugative metabolism in exposed fish. (C) 200 0 Published by Elsevier Science Ltd.