Strain differences in the metabolism and action of drugs in mice and rats.

It is well documented that there is clear relationship between the rate of drug me tabolism by liver microsomes and the intensity of the effect and toxicity of a variety of drugs (1-5). Recent studies indicated that the individual, strain, sex and species dif ferences in the rate of drug metabolism appear to be factors responsible for the individual, strain, sex and species differences in the effect and toxicity of a variety of drugs (2, 3, 6, 7). Jay (8) observed marked difference in the duration of hexobarbital anesthesia in mice of various strain and later Quinn et al. (2) studied the strain difference in the metabolism of hexobarbital by liver microsomes from different strain of rats. In the present communication, strain differences of rats and mice used commonly in Japan concerning the activity of microsomal drug-metabolizing enzymes were studied in relation to the effect and toxicity of drugs. Thus the studies on the nature of strain difference in the drug effect and toxicity are important for the evaluation of drug action.