Annual differences in daily variations in hepatic drug metabolizing enzyme activity and plasma hormone levels in the...

Daily variations in hepatic drug metabolism and in plasma corticosterone and insulin levels were examined at monthly intervals over the duration of 1 year. Annual differences were observed in the basal levels of all parameters. Consistent daily variations were observed only in plasma corticosterone levels, whereas daily variations in each of the other parameters occurred inconsistently over the year with significant variations being found in ethylmorphine metabolism and insulin levels only five times, and in aniline metabolism, six times. These data show that daily variations in the parameters examined do not occur in a regular manner.