Certain dopamine agonists increase dopamine synthesis in the striatum of rat brain

N,N-Dipropylamino-5,6-dihydroxytetrahydronaphthalene (DP-5,6-ADTN) induced a rapid and dose-related rise in dopamine (DA) levels in the striatum of rat brain. The increase of DA was less pronounced in the tuberculum olfactorium and there was no change in the frontal cortex. DP-5,6-ADTN and DP-6,7-ADTN also caused a rapid increase in striatal DA synthesis (evaluated from the rise of 3,4-dihydroxyphenylalanine after decarboxylase inhibition) which lasted about 20 min and was followed by a decrease. The increase in DA synthesis rate after the DP-ADTNs was restricted to the striatum, only a decrease was observed in mesolimbic areas and frontal cortex. Dose-effect curves showed that the ED 50% for the stimulation of DA synthesis was somewhat higher (approx. 0.2 mumol/kg) than the ED 50% for the decreasing effect (approx. 0.01 mumol/kg). The increase in striatal DA biosynthesis was not seen after the DA agonists piribedil, TL-99 or apomorphine. Pretreatment of rats with gamma-hydroxybutyrolactone or haloperidol prevented the DP-5,6-ADTN-induced increase in DA synthesis.