PARTICIPATION OF A RAT-LIVER CYTOCHROME-P-450 INDUCED BY PREGNENOLONE 16-ALPHA-CARBONITRILE AND OTHER COMPOUNDS IN THE 4-HYDROXYLATION OF MEPHENYTOIN

  • 1 January 1985
    • journal article
    • research article
    • Vol. 28  (2) , 215-219
Abstract
Mephenytoin 4-hydroxylation, which was one of the reactions showing genetic polymorphism in humans, was studied using rat liver microsomes. Pregnenolone 16.alpha.-carbonitrile, dexamethasone, troleandomycin and phenobarbital (but not .beta.-naphthoflavone) induced the hydroxylation activity to various extents. Mephenytoin itself also increased 4-hydroxylation considerably. Liver microsomes prepared from male rats contained higher mephenytoin hydroxylation activity than preparations islated from females. A cytochrome P-450 which is inducible by pregnenolone 16.alpha.-carbonitrile is involved in the 4-hydroxylation of mephenytoin. Cytochrome P-450PCN-E were purified from pregneneolone 16.alpha.-carbonitrile-treated rats using modifications of previous methods and compared its 4-hydroxylase activity with other purified rat cytochromes P-450. P-450PCN-E had the highest activity among the 10 purified rat cytochromes P-450 tested and antibodies raised to P-450PCN-E completely inhibited mephenytoin 4-hydroxylase in rat liver microsomes, suggesting the involvement of P-450PCN-E in this reaction. The microsomal concentration of P-450PCN-E, estimated by immunoelectrophoretic blotting analysis, correlated well with the hydroxylase activity in rat liver microsomes (r = 0.906). Mephenytoin induced P-450PCN-E as well as other phenobarbital-inducible cytochromes P-450.