Regulatory mechanisms in endoluminal release of serotonin and substance P from feline jejunum

The mechanisms controlling vagally induced 5-HT and SP release into the jejunal lumen were studied in the cat. In control animals, electrical vagal nerve stimulation doubled the rate of endoluminal secretion of 5-HT and SP. Propranolol pretreatment did not alter luminal secretion of these hormones. Atropine suppressed motor function and induced dose-related inhibition of vagal release of endoluminal 5-HT, but not of SP; the response to hexamethonium pretreatment was similar to that of atropine. In contrast, superior cervical ganglionectomy did not alter stimulated endoluminal 5-HT release but it completely abolished release into the portal vein. The portal 5-HT release was not affected by ganglionic blockade. The data suggest that (1) vagally mediated 5-HT release into the lumen and the portal circulation are mediated by different neural mechanisms, the former cholinergic, the latter presumably adrenergic; and (2) release of feline 5-HT and SP are independent, suggesting two intestinal sources, the EC cell for 5-HT and peptidergic neurons for SP.