EFFECT OF CYCLOPHOSPHAMIDE ADMINISTRATION ON THE ACTIVITY AND RELATIVE CONTENT OF HEPATIC P4502D1 IN RAT

1. The effects of the administration of the anticancer and immunosuppr essive drug, cyclophosphamide, to the rat on hepatic P4502D1 activity and content in the microsomal fraction have been examined. 2. Liver mi crosomes were obtained from male Hooded Wistar rats administered a sin gle dose (i.p.) of saline or cyclophosphamide (200 mg/kg). Rats receiv ing cyclophosphamide were killed 1, 4, 7, 10 or 14 days after cyclopho sphamide administration. The O-demethylation of dextromethorphan to de xtrorphan was used to monitor 2D1 activity. 3. The mean V-max, for dex trorphan formation was reduced significantly (p < 0.0001) 7, 10 and 14 days after cyclophosphamide administration compared with the control group (control, 0.32 +/- 0.07; 7-day, 0.20 +/- 0.08; 10-day, 0.11 +/- 0.02; and 14-day group, 0.15 +/- 0.02 nmol/mg/min). 4. Western blottin g revealed that there was a significant reduction (P < 0.0005) in the microsomal relative 2D1 content 10 days after cyclophosphamide adminis tration compared with the control group (control, 125 +/- 0.44; and 10 -day group, 0.65 +/- 0.14). 5. The activity of reduced nicotinamide ad enine dinucleotide phosphate P450 reductase was significantly reduced (p < 0.0001) 7, 10 and 14 days following cyclophosphamide administrati on (control, 215 +/- 24; 7-day, 102 +/- 20; 10-day, 59 +/- 4 and 14-da y group, 76 +/- 8 nmol/mg/min). Cytochrome bs content was significantl y reduced (P < 0.0001) 7 and 10 days following cyclophosphamide admini stration (control, 0.46 +/- 0.13; 7-day,0.28 +/- 0.07 and 10-day group , 0.20 +/- 0.03 nmol/mg). 6. The significant reductions in the activit y of rat hepatic microsomal 2D1 following cyclophosphamide administrat ion, as seen by the alterations in mean V-max for dextrorphan formatio n, do not appear to be due to a single factor, but may result from a c ombination of several events, including reductions in relative 2D1 con tent, reduced nicotinamide adenine dinucleotide phosphate P450-reducta se activity and cytochrome b(5) content.