Effects of enhanced striatal dopamine turnover in vivo on glutathione oxidation

In Parkinson's disease (PD), a compensatory increase in dopamine (DA) turnover occurs in the remaining nigrostriatal dopaminergic neurons, resulting in greater exposure of each neuron to hydrogen peroxide (H2O2) derived from oxidative deamination of DA. The formation of oxyradicals from H2O2 is regarded as a mechanism that could contribute to the progression of PD, and incubation of rat striatal synaptosomes with levodopa (LD) results in an increase in oxidized glutathione (GSSG), indicative of oxidant stress. The present study was undertaken to determine whether striatal GSSG levels increase in response to administration of LD in vivo. Acute and repeated (3-week) treatment of normal rats with LD at doses of up to 100 mg/kg did not increase striatal GSSG despite marked increase in DA turnover. These results suggest that intact striatum may possess increased defense capacity against oxidant stress generated by increased DA turnover as compared with isolated synaptosomes.