Pumosetrag delays liquid gastric emptying in association with the relaxation of the proximal stomach stimulates fasting antroduodenal migrating motor complex activity and accelerates small intestinal transit. Pumosetrag displays little to no response in the regions of the mouse intestine. Pumosetrag shows both regional and species specificities. Pumosetrag has lower efficacy than 5-HT in the rat jejunum, ileum, and distal colon. However, it has a similar efficacy and potency to 5-HT in the rat proximal colon. The activity profile of Pumosetrag is different in the guinea pig intestine where it exhibits greater potency and efficacy than 5-HT in all regions. Responses to Pumosetrag in the rat and guinea pig tissues are inhibited by ondansetron, confirming its action on 5-HT(3) receptors[1] [2].