5HT-receptor antagonist properties of SCH 23390 in vascular smooth muscle and brain

The dopamine D1-receptor antagonist SCH 23390 was a potent competitive antagonist of 5HT-induced vasoconstriction in the isolated perfused rat tail artery preparation (pA2 8.17) but a very weak antagonist of phenylephrine-induced responses (pA2 5.94). In rat brain cerebral cortex, SCH 23390 inhibited 5-HT2-sensitive [3H]spiperone binding with an IC50 of 112 nM. Binding of [3H]5HT to 5HT1 receptors in the cortex was inhibited by SCH 23390 with an IC50 of 2.49 microM. SCH 23390 has significant affinity for 5HT receptors in addition to the reported selective dopamine D1-receptor antagonist properties.