Acute and chronic administration of alpha-methyldopa: regional levels of endogenous and alpha-methylated catecholamines in rat brain.
Acute administration of alpha-methyldopa (200 mg kg-1 s.c.) produced a short-lived decrease in dopamine levels in 5 regions of the rat brain. Maximal dopamine depletion was 55% in the corpus striatum and over 75% in other regions and occurred 4--6 h after alpha-methyldopa injection; dopamine levels recovered within 12 h. Maximal noradrenaline depletion of over 80% occurred in all regions 4--24 h after alpha-methyldopa and after 24 h noradrenaline levels were still significantly reduced from control values. In these acute studies alpha-methyldopamine accumulated rapidly in amounts equal to or greater than the depleted dopamine in all regions, reaching a peak at 4 h. By contrast, alpha-methylnoradrenaline accumulated more slowly reaching a peak at 6--24 h and was never present in amounts greater than the depleted noradrenaline. Following chronic administration of alpha-methyldopa (40 mg kg-1 s.c., twice daily 5 days) there was a similar depletion of noradrenaline and dopamine to that seen in the acute studies. The depletion was associated with a much smaller accumulation of alpha-methyldopamine. The striking feature of these results, however, was the large accumulation of alpha-methylnoradrenaline in all brain regions. This probably reflects the slow turnover and resistance to degradation by monoamine oxidase of alpha-methylnoradrenaline.
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D002395:Catecholamines / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D006207:Half-Life; D008297:Male; D008745:Methylation; D008750:Methyldopa / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D013997:Time Factors
D002395:Catecholamines; D008750:Methyldopa; D004298:Dopamine; D009638:Norepinephrine