Epoxide hydrolase activity in small biopsy samples of preneoplastic and neoplastic rat liver

Epoxide hydrolase (EH) activity was measured in serial fine-needle aspiration biopsy (FNAB) samples of male rats chronically treated with the hepatocarcinogen, N-nitrosomorpholine (NNM, 10 mg/100 ml drinking water). The development of neoplasia was confirmed histopathologically at the end of the experiment. The enzyme activity was significantly increased after 2 days of NNM administration and reached a 3 to 4-fold increase after 2 weeks that remained stable throughout the experiment. Although EH is not related to the metabolism of NNM, the induction of enzyme activity as readily recognized with the FNAB method might be a useful marker in the attempt to characterize hepatocarcinogenic substances in rats.