Influence of hypoxia on the metabolism and biliary excretion of trimetrexate by the isolated perfused rat liver

Effect of toremifene on antipyrine elimination in the isolated perfused rat liver

Toremifene is a triphenylethylene antioestrogen with significant antitumor activity. It is structurally very similar to tamoxifen. Both drugs undergo extensive hepatic metabolism, and tamoxifen is known to inhibit hepatic mixed-function oxidases (MFO). Using the isolated perfused rat-liver model, we investigated the effect of toremifene on the elimination of antipyrine, a standard marker of MFO activity. Perfusate consisted of 20% red cells in a modified Krebs-Henseleit buffer, and 80 ml was recirculated at 14 ml/min for 3 h. High but clinically relevant steady-state toremifene levels of 3 and 10 micrograms/ml were achieved using bolus plus constant infusion into the reservoir. Elimination of 2.5 mg antipyrine was not inhibited by steady-state toremifene, but methanol (maximal perfusate concentration, 1.29%), the vehicle used for toremifene administration, caused a statistically significant increase in the antipyrine elimination half-life (mean, 1.4 +/- 0.2 h for controls vs 2.2 +/- 0.3 h for methanol; P < 0.05, n = 4). Whereas the methanol had no apparent effect on liver viability as assessed by bile flow and perfusate back-pressure, toremifene at a steady-state concentration of 10 micrograms/ml caused a statistically significant decrease in bile flow (value at 180 min, 0.22 +/- 0.05 ml/h as compared with 0.52 +/- 0.06 ml/h in the methanol control; P < 0.05) and a statistically significant increase in perfusate back-pressure (value at 180 min, 17.5 +/- 1.8 cm vs 11.0 +/- 2.6 cm in the methanol control; P < 0.05). Therefore, toremifene used at high doses can impair liver function in the isolated perfused rat liver, but it does not have any effect on antipyrine elimination.