Stereoselective interaction of mianserin with 5-HT3 receptors.

The interaction of the enantiomers of mianserin with the 5-HT3 receptor was determined. Using [3H]granisetron binding, (-)-mianserin was more potent than (+)-mianserin (pKi 8.46 and 6.95, respectively). The enantiomers competitively antagonized the depolarizing effect of 5-hydroxytryptamine in the rat vagus nerve preparation (pKapp: (-)-mianserin 8.13, (+)-mianserin 6.58). This stereoselectivity was maintained in-vivo as determined using ex-vivo inhibition of [3H]granisetron binding. Therefore, in contrast to its enantiomeric selectivity for the 5-HT1C and 5-HT2 receptors, where the (+)-isomer is more potent, the enantiomeric selectivity of mianserin for the 5-HT3 receptor was reversed. This differential selectivity of the enantiomers of mianserin may be useful in elucidating its utility in anxiety states.