Motor responses to serotonin in isolated guinea pig fundus and antrum

The effects of serotonin on gut motility have been both excitatory and inhibitory. The purpose of the present study was to elucidate how serotonin influences motor activity in two functionally different parts of the stomach. Pressure recordings were made from fundic and antral pouches of isolated guinea pig whole stomach preparations. In the fundus serotonin induced relaxation, which developed gradually within 3 min. In the antrum serotonin initiated phasic contractions, which culminated within 3 min and then returned to near or below prestimulatory values. Whereas tetrodotoxin did not significantly reduce the fundic relaxation, the antral excitation was strongly inhibited by both atropine and tetrodotoxin, indicating different effect mechanisms in fundus and antrum.