Whereas serotonin and substance P stimulate in‐vivo and in‐vitro myoelectric activity in the small intestine, their effects on transit are unclear. We used a validated in‐vivo transit model in the chloral hydrate‐anaesthetized rat to study the effects of serotonin, substance P and motilin, three putative mediators of carcinoid diarrhoea, on transit through the upper digestive tract. Intra‐arterial serotonin accelerated gastric emptying of a radiolabeled liquid, while motilin accelerated overall upper gastrointestinal transit. Substance P slowed overall upper gastrointestinal transit without altering gastric emptying. The antagonists to serotonin receptor subtypes, R‐zacopride (5‐HT3) and ketanserin (5‐HT2), also accelerated rat gastric emptying of liquids; in contrast, a 5‐HT4 agonist, SC53116, resulted in a less pronounced effect on gastric emptying at the dose tested. We conclude that circulating substance P is unlikely to be an important accelerator of transit through the upper digestive tract; in contrast, hyperserotoninaemia significantly accelerates transit through the stomach, and 5‐HT2 and 5‐HT3 receptor subtypes may play a role in the motor effects of serotonin in the stomach.
|Number of pages
|Alimentary pharmacology & therapeutics
|Published - Feb 1993
ASJC Scopus subject areas
- Pharmacology (medical)