Possible Involvement of 5-HT4 Receptors, in Addition to 5-HT3 Receptors, in the Emesis Induced by High-Dose Cisplatin in Suncus murinus

To clarify the mechanism for the severe emesis concomitant with intensive chemotherapy, we investigated the effects of 5-HT3- and 5-HT4-receptor antagonists on the emesis induced by the high-dose of cisplatin in Suncus murinus. The emesis induced by 50 mg /kg of cisplatin was reduced by the oral pretreat-ment with tropisetron, which is known as a 5-HT3- and 5-HT4-receptor dual antagonist in vitro, with the ID50 value of 0.52 mg /kg. On the contrary, granisetron, a selective 5-HT3-receptor antagonist, did not markedly inhibit the emesis at up to 30 mg /kg. Moreover, GR125487, a selective 5-HT4-receptor antagonist, did not inhibit the emesis. However, co-administration of GR125487 and granisetron significantly reduced the number of emetic episodes. The study of the co-administration of GR125487 with tropisetron showed that GR125487 did not further enhance the inhibitory effect of tropisetron alone, suggesting that the anti-emetic effect of tropisetron is mediated via the blockade of both 5-HT3 and 5-HT4 receptors. These results suggest that both the 5-HT3 and 5-HT4 receptors are involved in the emesis induced by the high-dose of cisplatin in Suncus murinus.