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 as readily recognized with the FNAB method might be a useful marker in the attempt to characterize hepatocarcinogenic substances in rats.