5-Hydroxytryptamine and rat passive peritoneal anaphylaxis.

Antigen challenge of rats, sensitized by intraperitoneal injection with rat anti-serum, did not result in a detectable increase in the 5-hydroxytryptamine (5-HT) levels in their peritoneal fluids over the background level induced by sensitisation alone. The maximum amount of extravasation produced by intraperitoneal injection of 5-HT into passively sensitised rats was less than that produced by antigen or histamine, and the doses of 5-HT producing these levels of extravasation produced an produced an increase of 5-HT concentrations in the peritoneal fluids. Therefore, 5-HT is unlikely to make much direct contribution to the extravasation produced during rat passive peritoneal anaphylaxis. However, when given intraperitoneally to rats, 5-HT potentiates the extravasation produced by histamine.