Effect of irradiation on amino acid in vitro incorporation in the course of liver regeneration.

The in v itro incorporation o f 14C-leucine by rat liver microsomes is studied under four different physiological states: 1. Normal liver o f adult rats (NL), 2. irradiated (4 000 rads) liver (IL), 3. liver after partial hepatectomy (RL) and 4. regenerating liver in preirradiated rats (IRL) 2, 5, 12, and 24 hours after treatment. Both irradiation and partial hepatectomy, when applied separately, stimulate the endogenous activity of microsomes, whereas preirradiation abolishes the stimulatory effect in the early hours after partial hepatectomy. The results are in agreement with the concept that irradiation stimulates the operating synthe­ tic programme of the cell and inhibits cellular reprogramming.