In previous papers, we reported that the activity of drug-metabolizing enzymes was higher in young female rats than in old female rats and that the duration of hexo barbital anesthesia was shorter in the young females than in the old females (1-3). More over, it was observed that the induction of microsomal drug-metabolizing enzymes by phenobarbital was more effective in young rats than in old rats (4,5).In the present communication, we wish to report the evidence that, in contrast to the results obtained with rats, clear age difference was not observed in the activity of drug-metabolizing enzymes in mice and there was no clear age difference in the induc tion of drug-metabolizing enzymes by phenobarbital.
MATERIALS AND METHODSMale mice of ICR strain were used, unless otherwise specified. Phenobarbital (80 mg/kg) was given intraperitoneally 48 and 24 hours before sacrifice. Pooled liver from 3 mice was used for the preparation of each homogenate. Preparation of post mitochondrial and microsomal fractions was carried out as described in a previous paper (6). The activity of drug-metabolizing enzymes of liver microsomes was assayed as described in the previous paper (6). The hydroxylation of hexobarbital was determined by measuring the disappearance of the substrate according to the method of Cooper and Brodie (7). The N-demethylation of aminopyrine was determined by the forma tion of 4-aminoantipyrine (La Du et al.) (8). The hydroxylation of aniline was deter mined by the formation of p-aminophenol according to the method described by Kato and Gillette (9). The nitroreduction of p-nitrobenzoic acid was determined by measur ing the p-aminobenzoic acid formed according to the method of Fouts and Brodie (10). NADPH-cytochrome c reductase was determined according to the method of Williams and Kamin (11). NADPH-neotetrazolium reductase was assayed as described in the previous paper (2). The contents of microsomal protein and cytochrome P-450 were determined by the method of Lowry et al. (12) and Omura and Sato (13), respective ly. The duration of hexobarbital anesthesia and zoxazolamine paralysis was determined by the loss of the righting reflex. Strychnine toxicity was evaluated by the convulsion rate and mortality.