Concentrations of dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured in the striatum of rats after i.p. injection of apomorphine, N,N-dipropyldopamine and a series of alkylated and/or esterified dopamine analogues of the dihydroxyaminotetralin type.
All compounds tested caused a decrease in DOPAC- and HVA-concentrations. The N-alkylated derivatives had a rapid onset of action, showing a maximal HVA decrease after 15–45 min, after which time the metabolite concentrations slowly returned to control values. In addition, the dihydroxyaminotetralins, especially N,N-dipropylamino-5,6-dihydroxytetrahydronaphthalene (DiPr-5,6-ADTN), produced a rapid, short lasting elevation of DA concentrations. The esterified primary amines, dibenzoyl-5,6-and dibenzoyl-6,7-dihydroxyaminotetralin, had a delayed effect, causing a maximal HVA decrease after 4–6 h.
DiPr-5,6-ADTN was found to be the most potent compound, with a maximal effect at a dose of 0.33
mol/kg, it being 30 times more potent than apomorphine and DiPr-6,7-ADTN. The results corroborate reported behavioural data, and the relative potencies of the alkylated derivatives in this test system for dopaminergic activity are in agreement with those based on stereotyped behaviour.
Key words Dihydroxyaminotetralins - Apomorphine - Prodrugs - Striatum - Dopamine metabolism