The circadian variation of hepatic microsomal drug and steroid metabolism in the golden hamster.

Rhythmic variations in a number of parameters of hepatic microsomal drug and steroid metabolism and binding were observed in the adult male golden hamster. With an illumination schedule of a light phase between 06.30 and 18.30 h, maximal activities were encountered between 04.00 and 08.00 h with corresponding minima between 16.00 and 18.00 h. In addition, kinetic changes were observed in both the metabolism and spectral interaction of aniline and biphenyl at times of maximal and minimal activities. Possible mechanisms responsible for the circadian variation in hamster hepatic microsomal xenobiotic metabolism are discussed.