5-HT3-receptor antagonist inhibits visceral pain differently in chemical and mechanical stimuli in rats.

The present study was designed to compare the effects of a selective 5-HT(3)-receptor antagonist, alosetron, on the glycerol-and colorectal distention (CRD)-induced visceral nociception as measured by changes in EMG of the external oblique muscle in conscious rats. Both glycerol and CRD evoked the EMG response, and these amplified EMG were attenuated by morphine, indicating that these responses might reflect visceral nociceptive responses. In the present study, we showed that alosetron significantly attenuated the glycerol-induced visceral pain, but not that of CRD. These results suggest that the mechanism of glycerol-induced visceral nociception are apparently different from that of CRD.