Effects of age and substrate on the circadian rhythm of liver tryptophan pyrrolase of female rats.

The level of tryptophan pyrrolase does not change significantly throughout the 24 hr cycle of the day in rat liver. Young and adult rats show a similar trend in the activity pattern of this enzyme. However, the activity pattern is altered in the post-reproductive rats. L-tryptophan induces liver tryptophan pyrrolase in rats of all the ages. Maximum induction is observed in the post-reproductive rats as compared to the young and adult rats. Further, the degree of induction of this enzyme by its substrate is also affected by the age of the rat.