| Abstract: | Thyroxine (T4)-UDP-glucuronosyltransferase (UGT) activity was measured directly in cultured male Sprague–Dawley rat and OF-1 mouse hepatocyte monolayers. The activity of T4-UGT (pmol/min/g liver) in vitro in hepatocyte cultures was, after 24 hr in culture, equivalent to that previously measured in vivo in rat and mouse liver microsomes (Viollon-Abadie et al., 1999). A progressive decline in T4-UGT activity occurred over time in both rat and mouse hepatocyte cultures. Treatment of cultures with various model inducers such as phenobarbital (PB), β-naphthoflavone (NF) and clofibric acid (CLO) induced a strong increase in T4-UGT activity in rat hepatocyte monolayers. In addition, and as expected from available in vivo data, treatment of rat hepatocyte cultures with NF also increased p-nitrophenol (PNP)-UGT activity and treatment with PB or CLO increased bilirubin (Bili)-UGT activity. In contrast, T4-UGT activity in mouse hepatocyte monolayers was not affected by the treatments, neither were PNP- and Bili- UGT activities. These in vitro data confirm our previous in vivo observations that these inducers increase rat but not mouse liver T4-UGT activities (Viollon-Abadie et al., 1999). The present study thus demonstrates that hepatocyte monolayers are appropriated for the evaluation and inter-species comparison of the effects of xenobiotics on T4-UGT activities. |
