Further evidence that methergoline is a central 5-hydroxytryptamine receptor blocking agent.

The effects of methergoline were studied on [5-(3)H]hydroxytryptamine ([5-(3)H]HT) and [d-(3)H]lysergic acid diethylamide ([d-(3)H]LSD) binding in rat cerebral cortex and on a behaviour dependent upon 5-HT receptor activity. Methergoline had a high affinity for both d-LSD binding sites and 5-HT binding sites, the affinity being 5 times higher for the d-LSD binding site. Methergoline also blocked the 5-hydroxytryptophane (5-HTP) and d-LSD induced head twitches in mice being 4 times more efficient in blocking 5-HTP induced head twitches than d-LSD induced head twitches. The present results give evidence that methergoline is a postsynaptic 5-HT receptor blocking agent, an action probably related to its ability to bind to the antagonist site of the postsynaptic 5-HT receptor.