NADPH and oxygen consumption in isoflurane-facilitated 2-chloro-1,1- difluoroethene metabolism in rabbit liver microsomes.

ABSTRACT

2-Chloro-1,1-difluoroethene (CDE) metabolism can be facilitated by isoflurane in microsomes. In an effort to elucidate the mechanisms of increased CDE metabolism, NADPH and oxygen consumption during CDE metabolism were measured in the absence and presence of isoflurane in rabbit liver microsomes. In microsomes from phenobarbital-treated rabbits, isoflurane (1-4 mumol, 0.6-2.3%) enhanced CDE (2 mumol, 1.1%) metabolism, increasing fluoride release up to 2.5 times compared with CDE alone. Fluoride release increased with increasing amounts of CDE (1-4 mumol). Isoflurane alone strongly increased NADPH consumption (3.78 +/- 0.4 to 9.65 +/- 0.23 nmol/mg/min +/- SD) and oxygen consumption (3.27 +/- 0.03 to 6.62 +/- 0.75 nmol/mg/min) compared with control when incubated for 5 min at 30 degrees C. No isoflurane metabolism was detected by fluoride release. Incubation of CDE alone resulted in CDE metabolism (0.70 +/- 0.15 nmol/mg/min) and lesser, but significant increases in NADPH (4.79 +/- 0.14) and oxygen consumption (4.44 +/- 0.24) compared with control. Incubation of isoflurane with CDE at 30 degrees C for 5 min caused a 3-fold increase of CDE metabolism (2.18 +/- 0.25 nmol/mg/min); however, no more NADPH (8.59 +/- 0.95) or oxygen (7.22 +/- 0.16) was consumed compared with isoflurane incubation. No significant changes in H2O2 production were observed between all groups. These data indicate that isoflurane is an efficient uncoupler of cytochrome P-450, and suggests that increased CDE metabolism by isoflurane may result from a coupling of isoflurane-stimulated cytochrome P-450 activity to CDE oxidation.