Abstract
1. Whole body irradiation of rats with Co60-γ rays did not affect either the aminoazo dye N-demethylating activity or the hydro-xylating activity of rat-liver. It also had no significant effect on the induction of the enzymatic activities by methylcholanthrene. The ionizing irradiation, however, appeared to increase the reduction of enzymatic activity following partial hepatectomy.
2. The time course of the N-demethylat-ing activity of regenerating rat liver after partial hepatectomy or a sham operation (laparotomy) was studied. In both cases, a remarkable reduction (50%) in the enzymatic activity was observed within a few hours after the operation. In the case of sham operation, the activity returned to the normal level within one day. In the case of partial hepatectomy, however, the activity remained at a low level for 24 hours and then later gradually returned to the normal level over a period of four days and in parallel with liver regeneration.
3. Administration of cortisone had no significant effect on the N-demethylating activity of normal liver but partially prevent-ed the decrease in enzymatic activity caused by adrenalin injections or partial hepa-tectomy.
4. Administration of adrenalin caused a large and a rapid decrease in N-demethylat-ing activity. This was also observed in methylcholanthrene-treated rats.
5. Methylcholanthrene was shown to induce N-demethylating activity in partially hepatectomized rats. A large prior dose of methylcholanthrene appeared to prevent reduction in the enzymatic activity after partial hepatectomy.
The authors wish to express their sincere thanks to Mr. Mitsuo Matsumoto and Dr. Tokutaro Hishizawa for their co-operation and valuable discus-sions throughout the study.
