%0 Journal Article %A RAYMOND D. MAGUS %A JAMES R. FOUTS %T Inhibition of Tryptophan Pyrrolase Induction by Carbon Tetrachloride in Rats %D 1968 %J Molecular Pharmacology %P 465-470 %V 4 %N 5 %X 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. ACKNOWLEDGMENT This investigation was supported by Grants GM12675 and 5-T01-GM 01308 from the National Institute of General Medical Sciences. %U https://molpharm.aspetjournals.org/content/molpharm/4/5/465.full.pdf