PT  - JOURNAL ARTICLE
AU  - RAYMOND D. MAGUS
AU  - JAMES R. FOUTS
TI  - Inhibition of Tryptophan Pyrrolase Induction by Carbon Tetrachloride in Rats
DP  - 1968 Sep 01
TA  - Molecular Pharmacology
PG  - 465--470
VI  - 4
IP  - 5
4099  - http://molpharm.aspetjournals.org/content/4/5/465.short
4100  - http://molpharm.aspetjournals.org/content/4/5/465.full
SO  - Mol Pharmacol1968 Sep 01; 4
AB  - 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.