ISOFLURANE INCREASES THE ANAEROBIC METABOLITES OF HALOTHANE

The effect of isoflurane on the anaerobic metabolism of halothane to chlorodifluoroethene (CDE) and chlorotrifluoroethane (CTE) was studied with microsomes of guinea pig liver by gas chromatography. The reaction mixture used to measure the end products of anaerobic metabolism consisted of a microsomal suspension, 3 mM NADPH, halothane and isoflurane (except in control groups) in 0.1 M potassium phosphate buffer solution (pH 7.4). The K-m values for CDE formation were 601.61 +/- 266.91, 254.22 +/- 86.58, 257.92 +/- 129.11, 268.55 +/- 125.66 and 319.22 +/- 86.76 mu M (mean +/- SD, n = 5) at 0 mM (0%), 0.12 mM (0.26%), 0.29 mM (0.64%), 0.58 mM (1.30%) and 1.16 mM (2.59%) isoflurane, respectively. The K-m values for CTE formation were 1204.74 +/- 551.64, 553.75 +/- 177.89, 521.14 +/- 249.77, 560.67 +/- 229.61 and 711.05 +/- 317.13 mu M (n = 5) at 0 mM (0%), 0.12 mM (0.26%), 0.29 mM (0.64%), 0.58 mM (1.30%) and 1.16 mM (2.59%) isoflurane, respectively. In contrast, the V-max values for CDE and CTE formation at these isoflurane concentrations were not significantly different than in the control groups. In this study the production of CDE and CTE was significantly (P < 0.05) increased by isoflurane, at concentrations up to 0.58 mM (1.30%).