Further evidence that the tachycardiac response to 5-hydroxytryptamine in rats is not mediated via typical 5-HT2 receptors

Abstract 1. In pithed rats, the receptor type of cardiac tissue mediating the tachycardiac response to 5-hydroxytryptamine (5-HT) was analysed. 2. Ketanserin, mesulergine and methiothepin, administered in doses which antagonized the pressor response to 5-HT, slightly reduced, considerably reduced and antagonized, respectively, its tachycardiac response. 3. 8-OH DPAT and RU 24969 produced no significant tachycardia, while DOI neither mimicked nor blocked the 5-HT-induced tachycardia. 4. The tachycardia was not affected by MDL 72222, metoclopramide and cocaine. 5. The hypothesis is proposed that in rats the tachycardiac response to 5-HT is mediated via 5-HT receptors belonging to an yet unclassified subtype of 5-HT 1 or 5-HT 2 receptors.