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.