Abstract-The in vitro metabolic fate of 7-alkoxycoumarin was studied using liver microsomes.Microsomal enzyme catalyzed dealkylation of 7 alkoxycoumarin to 7-hydroxycoumarin in the presence of NADPH and molecular oxygen as cofactors was found to be one of the metabolic pathways.The metabolite 7-hydroxycoumarin was further metabolized to unidentified metabolite (s) in the presence of NADPH and 02 at a very slow rate, while the formation of the conjugate of 7-hydroxycoumarin with glucuronic acid was observed in the presence of UDPGA.Microsomal 7 alkoxycoumarin 0-dealkylase activity was altered by the substitution of the alkyl group of the substrate, and the substitutions to either an 0-propyl or an 0-butyl group resulted in a decrease of the enzyme activity. Species differences were observed in the substrate specificity of microsomal 0 dealkylation.The 0-dealkylase activities in rat liver microsomes were stimulated by pretreatment of the animals with phenobarbital, regardless of the 0-alkyl substituent at the 7 position of the coumarin ring. On the other hand, pretreatment with 3-methylcholanthrene or (3-naphthoflavone resulted in marked increase of 0-deethylation, 0-depropylation and 0 debutylation activities, but not of 0-demethylation activity. Pretreatment of animals with ,3-naphthoflavone also resulted in remarkable stimulation of 7-hydroxycoumarin-glucuronide formation by the microsomal enzyme, while the conversion of 7-hydroxycoumarin to unidentified metabolite(s) was activated by the pretreatment of rats with only phenobarbital. The 0-dealkylation activities in liver microsomes from intact and phenobarbital pretreated rats were inhibited markedly by the addition of hexobarbital to the incubation mixture, but no inhibition was observed with a-naphthoflavone. On the other hand, the 0-dealkylation activities in microsomes from Q naphthoflavone-pretreated rats were inhibited remarkably by a-naphtho flavone.These results confirmed that several microsomal enzymes, in cluding the cytochrome P-450's and UDP-glucuronyltransferase, participate in the biotransformation of 7-alkoxycoumarin, and these enzymes are regulated differently by inducers.

The in vitro biotransformation of 7-alkoxycoumarin by rat liver microsomes was studied to develop a simple and accurate assay procedure for 7-alkoxycoumarin

Abstract-Liver microsomal 0-dealkylation activity was determined using 0-methyl, 0-ethyl and 0-propyl derivatives of p-nitrophenol, 7-hydroxycoumarin (umbelliferon) and 7-hydroxyphenoxazone (resorufin) as substrates. Microsomal 0-dealkylation activities of p-nitrophenol and 7-hydroxycoumarin 0-alkyl derivatives were of similar levels, but the activities of 7-hydroxyphenoxazone O-alkyl derivatives were very low compared with those of other substrates. Pretreatment of rats with (9-naphthoflavone resulted in the preferential increase of 0-deethylation and 0-depropylation activities regardless of the ring structure of the substrates, and the ratio of 0-deethylation and 0-depropylation activities to that of 0-demethylation increased markedly. On the other hand, the 0-dealkylase activity of all substrates increased generally upon pretreatment of the rats with phenobarbital, but the ratio of 0-deethylase or 0-depropylase activity to that of 0-demethylase in the pretreated rats was not very different from that of the untreated animals. Hexobarbital inhibited competitively the 0-dealkylation activity in control and phenobarbital-pretreated rat microsomes. On the other hand, the 0-dealkylase activity

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