In vitro and in vivo irreversible blockade of cortical S2 serotonin receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline: a technique for investigating S2 serotonin receptor recovery.

N-Ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) treatment, both in vitro and in vivo, results in an irreversible blockade of cortical S2 5-hydroxytryptamine (serotonin) receptors. Incubation of rat cortical homogenates with EEDQ in vitro results in a concentration-dependent (EC50 approximately 5 microM) and time-dependent decrease in the Bmax of [3H]ketanserin-labeled S2 serotonin receptors. Extensive washing of the homogenate following in vitro or in vivo EEDQ treatment does not result in an increase in the amount of [3H]ketanserin binding, indicating that EEDQ acts to modify irreversibly cortical S2 serotonin receptors. That the modification of S2 receptor binding by EEDQ occurs at the recognition site of the receptor is indicated by the finding that coincubation with the S2 receptor antagonist ketanserin, but not the D2 3,4-dihydroxyphenylethylamine (dopamine) receptor antagonist domperidone, selectively protects against the irreversible blockade of S2 serotonin receptors. Peripheral administration of EEDQ results in a dose-dependent reduction in cortical S2 serotonin receptors with maximal effects (approximately 90% reduction) observed following 10 mg/kg (i.p.). Seven days following peripheral administration of EEDQ there is a recovery of S2 serotonin receptors back to 74% of the original receptor population. These data demonstrate that EEDQ in vitro and in vivo acts as an irreversible antagonist of S2 serotonin receptors and that it can be used to investigate the recovery rate of these receptors.