The neuronal origin of bombesin-like immunoreactivity in the rat gastrointestinal tract.

Extracts of muscle and mucosal layers of the rat stomach contained material cross-reacting in radioimmunoassays for the amphibian skin peptide bombesin. In the intestine, immunoreactive bom-besin was confined to the muscle layers. Two molecular forms of immunoreactive bombesin were identified; one of these components was eluted in a similar position to tetradecapeptide bombesin on gel filtration and accounted for about 90% of the immunoreactivity in intestinal extracts, compared with about 40% in stomach. The two components were distinguishable from synthetic bombesin, and from the structurally related peptide substance P, on the basis of their pattern of immunochemical properties with three different antisera. Immunohistochemical studies using the same antisera revealed a rich distribution of nerve fibres in the mucosa of the rat stomach, but few fibres were seen in the intestinal mucosa. Abundant fibres with bombesin-like immunoreactivity were found surrounding nerve cell bodies in the myenteric plexus throughout the gut. Immunoreactivc nerve cell bodies were not identified, neither was convincing evidence obtained to indicate the presence of bombesin in mucosal endocrine cells.The results support the possibilities that bombesin-like peptides are neurotransmitters in the gut and that they could play a role in the modulation of gastrointestinal motility and in the release of gastrin.