PT  - JOURNAL ARTICLE
AU  - J A Augustine
AU  - M A Zemaitis
TI  - The effects of cyclosporin A (CsA) on hepatic microsomal drug metabolism in the rat.
DP  - 1986 Jan 01
TA  - Drug Metabolism and Disposition
PG  - 73--78
VI  - 14
IP  - 1
4099  - http://dmd.aspetjournals.org/content/14/1/73.short
4100  - http://dmd.aspetjournals.org/content/14/1/73.full
SO  - Drug Metab Dispos1986 Jan 01; 14
AB  - The effects of cyclosporin A (CsA), a powerful immunosuppressant, on the hepatic microsomal mixed function oxidase (MFO) system was studied in male rats. Difference spectroscopy studies indicated that CsA binds to cytochrome P-450 producing a type I spectral change. To investigate potential interactions with the MFO system, CsA was administered orally at doses of either 25 mg/kg or 50 mg/kg once daily for 9 days. Various metabolic parameters were examined, including: levels of microsomal protein, cytochrome P-450, and cytochrome b5, NADPH-cytochrome c reductase activity, N-demethylation of ethylmorphine (ETM), and p-hydroxylation of aniline (ANL). Rats treated with 50 mg/kg showed a 25% or greater decrease over controls in all parameters examined except microsomal protein and cytochrome b5 levels. Rats treated with 25 mg/kg showed a 28% or greater decrease in all parameters except microsomal protein, cytochrome b5, and cytochrome P-450. Kinetic studies of ETM-N-demethylase and ANL-hydroxylase activities were conducted either with microsomes prepared from CsA-treated animals (50 mg/kg/day for 5 days) or with pooled microsomes prepared from untreated animals to which CsA was added directly. Enzyme reaction velocities were measured and apparent KM and apparent Vmax were determined. Studies with CsA-treated animals revealed a 57% decrease in both KM and Vmax for ETM-N-demethylase, and a 46% decrease in KM and a 32% decrease in Vmax for ANL-hydroxylase. Studies involving direct addition of CsA to microsomes at final concentrations of 0.01 mM and 0.10 mM revealed no significant changes in apparent KM or Vmax for either enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)