The release of 5-hydroxytryptamine from the rat stomach in vitro.

1. 5-HT was released into the lumen of the intact isolated rat stomach and into the bath fluid surrounding a preparation of the body and antrum stretched mechanically.2. Release of 5-HT increased when the pressure inside the intact stomach was raised or when the body/antrum preparation was stretched.3. This increased release was not prevented by hexamethonium, atropine, hyoscine or procaine, and was probably due to distortion of cells containing 5-HT.4. During periods of peristalsis induced by transmural stimulation the pharmacological activity of the fluid in the stomach was usually increased owing to a greater release of 5-HT and also to the release of an unidentified substance.5. In reserpine-treated rats, 5-HT was released into the stomach but transmural stimulation did not produce true peristalsis and only rhythmic contractions occurred.6. Peristalsis was seldom reduced by methysergide, and it is concluded that 5-HT is not essential for gastric peristalsis in the rat.