Comparison of effects of tiapride and sulpiride on D-1, D-2, D-3 and D-4 subtypes of dopamine receptors in rat striatal and bovine caudate nucleus membranes

To determine the affinity of tiapride to D-1, D-2, D-3 and D-4 subtypes of dopamine (DA) receptors, inhibitory effects of tiapride on [3H]-cis-flupenthixol, [3H]spiperone and [3H]N-propylapomorphine binding were examined in the rat striatum and bovine caudate nucleus membranes and compared to those of sulpiride and haloperidol. The IC50 values of tiapride, sulpiride and haloperidol were estimated as follows: 1440, 132 and 0.295 microM for D-1; 45.8, 8.8 and 0.004 microM for D-2; greater than 100, greater than 100 and 0.64 microM for D-3; 11.7, 2.88 and 0.0044 microM for D-4, respectively. It is suggested that the affinity of tiapride is high to D-2 and D-4, but is not high to D-1 and D-3. The affinity pattern of tiapride to each DA receptor subtype is similar to but lower than those of sulpiride and haloperidol. In the D-2 receptor assay, the IC50 values of tiapride and sulpiride were 1/22.7 and 1/19.1 of those in the presence of 100 mM NaCl, respectively, suggesting that benzamide drug binds to the D-2 subtype with higher affinity in the presence of Na+ than in the control.