Effects of fluoro-dopamines on dopamine receptors (D1, D2, D3 sites)

The ring-fluorinated compounds, 2-, 5- and 6-fluoro-derivatives of dopamine, were tested on three dopamine-sensitive receptor sites in striatal tissue of rat and calf brain. Although the D₁ site (dopamine-sensitive adenylate cyclase) was stimulated by micromolar concentrations of both dopamine and the fluoro-dopamines, the latter were considerably weaker. The D₂ receptor, as measured by the binding of [³H]spiperone, was occupied by similar concentrations of dopamine and the fluoro-dopamines, with ic₅₀ values ranging from 17,000 to 63,000 nM. The D₃ receptor site, as measured by the highaffinity binding of [³H]dopamine, was also occupied by similar concentrations of these compounds. Since it is primarily the D₂ receptor that is related to various dopaminergic behaviours, the similar potencies of dopamine and the fluoro-dopamines at this receptor site further validate the use of ¹⁸F-compounds to study dopamine function by non-invasive means.