Temperature-dependent effects of increased intraluminal pressure on serotonin release from the vascularly perfused guinea pig ileum.

Isolated segments of the guinea pig ileum were vascularly perfused and the release of endogenous serotonin into the portal effluent was measured. Peristalsis was induced by raising the intraluminal hydrostatic pressure by 500 Pa for 5 min. Serotonin release increased during peristalsis induced by fluid of 37 degrees C, but decreased when the temperature of the intraluminal fluid was between 13 degrees C and 22 degrees C. In the presence of naloxone (0.3 mumol/l) raising the intraluminal pressure with fluid of 37 degrees C caused an inhibition of the serotonin release which was blocked by scopolamine (0.1 mumol/l). Naloxone did not affect the inhibition of serotonin release during peristalsis caused by fluid of 19 degrees C, neither did indomethacin (1 mumol/l). In conclusion, liquid distension of the guinea pig isolated ileum elicits peristaltic activity, and affects the release of serotonin into the portal circulation. The changes in serotonin release depend on the temperature of the fluid passing through the intestinal lumen, whereas peristalsis is not affected by the temperature of the intraluminal fluid.