title: Endogenous melatonin protects L-DOPA from autoxidation in the striatal extracellular compartment of the freely moving rat: potential implication for long-term L-DOPA therapy in Parkinson's disease.
abstract: We previously showed, using microdialysis, that autoxidation of exogenous L-dihydroxyphenylalanine (L-DOPA) occurs in vivo in the extracellular compartment of the freely moving rat, with a consequent formation of L-DOPA semiquinone (L-DOPA-SQ). In the present study, intrastriatal infusion of L-DOPA (1.0 microm for 200 min) increased dialysate L-DOPA concentrations (maximum increases up to 116-fold baseline values); moreover, L-DOPA-SQ was detected in dialysates. Individual dialysate concentrations of L-DOPA were negatively correlated with those of L-DOPA-SQ. Co-infusion of N-acetylcysteine (100 microm) or melatonin (50 microm) increased L-DOPA (up to 151- and 246-fold, respectively) and decreased L-DOPA-SQ (by about 53% and 87%, respectively) dialysate concentrations. Systemic L-DOPA [25 mg/kg intraperitoneally (i.p.) twice in a 12-h interval] significantly increased striatal baseline dialysate concentrations of L-DOPA and decreased dopamine (DA) and ascorbic acid (AsAc) concentrations, when compared with controls. Following systemic L-DOPA, L-DOPA-SQ was detected in dialysates. Endogenous melatonin was depleted in rats maintained on a 24-h light cycle for 1 wk. In melatonin-depleted rats, systemic L-DOPA induced a smaller increase in dialysate L-DOPA, a greater increase in L-DOPA-SQ formation, and a greater reduction in DA and AsAc dialysate concentrations. Co-administration of melatonin (5.0 mg/kg, i.p., twice in a 12-h interval) with L-DOPA, in control as well as in light-exposed rats, significantly increased dialysate L-DOPA concentrations, greatly inhibited L-DOPA-SQ formation, and restored up to the control values dialysate DA and AsAc concentrations. These findings demonstrate that endogenous melatonin protects exogenous L-DOPA from autoxidation in the extracellular compartment of the striatum of freely moving rats; moreover, systemic co-administration of melatonin with L-DOPA markedly increases striatal L-DOPA bioavailability in control as well as in melatonin-depleted rats. These results may be of relevance to the long-term L-DOPA therapy of Parkinson's disease.
authors.affiliation: Department of Pharmacology, University of Sassari, Sassari, Italy.
authors.forename: Gaia
authors.initials: G
authors.lastname: Rocchitta
authors.forename: Rossana
authors.initials: R
authors.lastname: Migheli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Esposito
authors.forename: Bianca
authors.initials: B
authors.lastname: Marchetti
authors.forename: Maria S
authors.initials: MS
authors.lastname: Desole
authors.forename: Egidio
authors.initials: E
authors.lastname: Miele
authors.forename: Pier Andrea
authors.initials: PA
authors.lastname: Serra
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism* / Q000528:radiation effects; D004298:Dopamine / Q000378:metabolism; D007980:Levodopa / Q000378:metabolism* / Q000627:therapeutic use; D008027:Light; D008297:Male; D008550:Melatonin / Q000502:physiology*; D017551:Microdialysis; D009068:Movement; D010084:Oxidation-Reduction; D010300:Parkinson Disease / Q000188:drug therapy*; D011809:Quinones / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D011809:Quinones; D007980:Levodopa; D008550:Melatonin; D001205:Ascorbic Acid; D004298:Dopamine