Abstract

The inducing action of hydrocortisone and L-tryptophan on hepatic tryptophan pyrrolase in rats treated previously with CCl₄ was studied. CCl₄ exhibited a dose-dependent (and time-dependent) inhibitory action on the hematin-activated (apoenzyme) form of tryptophan pyrrolase but had no effect on basal holoenzyme activity. A low dose of CCl₄ (0.1 ml/kg) abolished induction of the holoenzyme by hydrocortisone but had little effect on the tryptophan-induced holoenzyme or total enzyme activity. This inhibitory action of CCl₄ required between 6 and 12 hr of exposure of the animal to CCl₄ in vivo, i.e., prior to administration of the inducing agents. A 10-fold increase in CCl₄ dose to 1.0 ml/kg did not abolish the inducing action of tryptophan; however, the enzyme response to tryptophan administration was appreciably reduced in rats receiving the higher CCl₄ dose.