Daily fluctuation of 7-alkoxycoumarin O-dealkylase activities in the liverof male F344 rats under ad libitum-feeding or fasting condition

It has been reported that drug metabolizing enzyme activities in the liver fluctuate daily, though the daily fluctuation of 7-alkoxycoumarin O-dealkyl ase (ACD) activities catalyzed by P450 has not been examined. The ACD activ ities are known to be useful to clarify the extensive induction of P450-dep endent oxygenases. In the present study, the hepatic ACD activities, as wel l as P450 content, were investigated periodically in male F344 rats under a d libitum-feeding or fasting condition. The ACD activities in ad libitum-fe d rats were found to follow obvious daily fluctuations with high values dur ing dark periods and with low values during light periods. This agreed with the other previous results of drug metabolizing enzyme activities measured with other substrates. Because the daily fluctuation was also observed in fasted rats, the fluctuation in ACD activities was clearly not affected by feeding, an external factor. P450 content, however, showed different fluctu ation patterns from the ACD activities. This suggests that the fluctuation of ACD activities might not be related to the quantitative variation of P45 0 proteins. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.