Differentiation between myenteric plexus and longitudinal muscle of the rat jejunum as the site of action of putative enteric neurotransmitters.

The contribution of the myenteric plexus in the mechanical responses of rat jejunal longitudinal muscle produced by several enteric nerve substances was evaluated. The myenteric plexus of a segment of rat jejunum was destroyed by serosal application of benzalkonium chloride (BAC). Fifteen days after BAC treatment, both the BAC-treated and an orad control jejunal segment were removed and the mechanical responses of the longitudinal muscle produced by the following substances were examined: substance P, acetylcholine (ACh), 5-hydroxytryptamine (5-HT), cholecystokinin octapeptide (CCK-8), norepinephrine, vasoactive intestinal peptide (VIP), bombesin, [Leu5]enkephalin and somatostatin. Our results indicate that: substance P and norepinephrine produce their mechanical responses by acting predominantly on the longitudinal smooth muscle; 5-HT, CCK-8, ATP, VIP and neurotensin act predominantly through the myenteric plexus; ACh possesses both direct and indirect actions; and because the responses to [Leu5]enkephalin, bombesin and somatostatin were equivocal, a conclusion as to their site of action could not be made with this preparation.