@article {LAN96, author = {SHIH-JUNG LAN and THEODORE J. CHANDO and ERIC C. SCHREIBER}, title = {HYDROXYLATION OF 14C-NIFLUMIC ACID BY PHENOBARBITAL-INDUCED RAT LIVER MICROSOMES}, volume = {3}, number = {2}, pages = {96--103}, year = {1975}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {Hydroxylation of niflumic acid to 4{\textquoteright}-hydroxyniflumic acid and 5-hydroxyniflumic acid by rat liver microsomes from untreated animals or phenobarbital-pretreated animals has been demonstrated. Pretreatment of rats with phenobarbital (50 mg/kg) increased the 4{\textquoteright}-hydroxylase activity 53\%, whereas the 5-hydroxylase activity was increased 205\%. Niflumic acid inhibited both the 4{\textquoteright}- and 5-hydroxylases at concentrations greater than 1 mM. Competitive inhibition of 4{\textquoteright}- or 5-hydroxylase was observed with SKF 525-A. WIN 13099 inhibited both hydroxylases noncompetitively. With freshly prepared microsomes, acetone, at concentrations up to 10\% (v/v), enhanced 4{\textquoteright}-hydroxylase markedly but had little effect on 5-hydroxylase. With frozen and aged microsomes, maximum enhancement of 4{\textquoteright}-hydroxylase was obtained at 5\% acetone: little or no effect on 5-hydroxylase was observed at the same concentration. At 10\% acetone, the 4{\textquoteright}- and 5-hydroxylases were inhibited 33 and 73\%, respectively. The data indicate that at least two different enzyme systems are involved in the hydroxylation of niflumic acid by the microsomes of rat liver. Copyright {\textcopyright} 1975 by The American Society for Pharmacology and Experimental Therapeutics}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/3/2/96}, eprint = {https://dmd.aspetjournals.org/content/3/2/96.full.pdf}, journal = {Drug Metabolism and Disposition} }