Dose/action and time/action relationships of some biological molecules evaluated on the cerebral enzymatic activities

Dose/action and time/action relationships relative to the effect of the in vivo treatment with some biological molecules (cytidine, uridine and glutamine) on several enzymatic activities connected with cerebral metabolism (lactate dehydrogenase, malate dehydrogenase, total NADH cytochrome c reductase, cytochrome oxidase and citrate synthase) were studied in the normal rat brain. While time/action curves were found to be in agreement with classical pharmacodynamic descriptions, dose/action curves exhibited a varying behavior according to the biological substrate tested (brain homogenate in toto or crude mitochondrial fraction from brain in toto). Often enzymatic activity changes as a function of dose failed to show linear correlations, a parabolic pattern being observed. At any rate, the changes affecting several cerebral enzymatic activities may account for some pharmacodynamic properties of the biological molecules tested.