Studies on the mucosal hyperaemia of the feline small intestine observed at endoluminal perfusion with substance P.

Substance P-like immunoreactivity (SPLI) was found in the luminal contents of the feline small intestine. A physiological role for endoluminal substance P (SP) was explored in in vivo experiments, where feline jejunal segments were endoluminally perfused with saline or a low concentration of SP. A jejunal segment was initially perfused with saline, followed by SP in saline, and finally perfused with saline alone. The regional blood flow to the small intestine was determined by the microsphere technique. Endoluminal perfusion with SP caused a selective mucosal/submucosal hyperaemia of the experimental jejunum, which was normalized upon subsequent saline perfusion. Since neither acute vagotomy, local neural blockade (TTX, lidocaine), adrenergic blockade (phenoxybenzamine, propranolol), cholinergic blockade (hexamethonium, atropine), histamine - nor prostaglandin blockade - could antagonize the hyperaemic effects of luminally administered SP, it is suggested that this effect is directly paracrine in nature. Substance P may be released from SP nerves on physiological stimulation, that is, augmented vagal tone by a meal, and act at the effector cell, that is, vascular smooth muscle.