Primary changes in rat brain metabolism at the outset of increased psychomotor activity induced by pemoline.

triphosphatase specific activities were decreased in all subcellular fractions during liver growth induced by both ‘toxic’ and ‘non-toxic’ compounds; however, the content of these enzymes in the whole liver did not change. These changes were due to the fact that proteins having no such enzymic activities were synthesized at a relatively higher rate and accumulated in the endoplasmic reticulum. However, both the specific activity and the total amount of ribonuclease together with nucleoside diphosphatase activities increased after a longer exposure of liver to the inducers. Disproportionate synthesis of the proteins of the fibrinolysis system was also observed during ‘non-toxic’ hepatomegaly. The synthesis of fibrinogen was induced but that of plasminogen was inhibited. Our observations, made during chemically induced hepatomegaly, are in contrast with those occurring in compensatory hypertrophy or liver regeneration. From ultrastructural analysis and studies on the control of macromolecular synthesis and turnover of various proteins of liver cytoplasm, however, it appears that during induction of both ‘toxic’ and ‘non-toxic’ hepatomegaly some common mechanism may operate. The characteristic feature of drug-induced ‘non-toxic’ hepatomegaly, i.e. stimulation of the metabolism of various foreign compounds, represents an enhanced synthesis of the drugmetabolizing system in proportion with all other induced protein components of the endoplasmic reticulum, each of them having a similar turnover rate.