Acute l-DOPA Effect on Hydroxyl Radical- and DOPAC-Levels in Striatal Microdialysates of Parkinsonian Rats

Abstract

The object of the current study was to determine the effect of l-3,4-dihydroxyphenylalanine (l-DOPA) on the in vivo striatal microdialysate levels of the respective dopamine and serotonin metabolites 3,4-dihydroxyphenlalanine (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) and hydroxyl radical level (HO^•; 2,3- and 2,5-dihydroxybenzoic acid, 2,3- and 2,5-DHBA) in adult rats made parkinsonian by treatment at 3 days after birth with the neurotoxin 6-hydroxydopamine (6-OHDA; 66.7 μg, base form, on each side; desipramine pretreatment, 1 h). Using HPLC/ED we found that in 6-OHDA-lesioned rats the basal striatal extraneuronal level of DOPAC was dramatically reduced and constituted only ~4.5% of referenced value (intact rats). Conversely, the striatal microdialysate level of 5-HIAA was elevated 2-fold in 6-OHDA-lesioned rats. Acute l-DOPA (60 mg/kg i.p.; S-carbidopa pretreatment, 12.5 mg/kg i.p., 30 min) produced a rapid rise in the extraneuronal DOPAC in both tested groups but to a much greater extent in intact rats (P < 0.05). Levels of HO^• (spin-trap products of salicylate, 2,3- and 2,5-DHBA) were elevated 2-fold in 6-OHDA-lesioned rats. However, l-DOPA did not enhance HO^• production; acute 6-OHDOPA treatment (60 mg/kg i.p.) also did not alter HO^• production. In summary, l-DOPA, an effective drug in ameliorating PD symptoms, did not acutely pose a risk for HO^• generation in parkinsonian rats. We conclude that l-DOPA is not likely to generate reactive oxygen species in humans nor is l-DOPA likely to accelerate PD in humans.