Cholinergic control of canine antral immunoreactive gastrin release and motility

We used acute anesthetized dogs to investigate the role of cholinergic receptors in the relationship between antral immunoreactive (I) gastrin release and antral motility. Electrical stimulation of extrinsic nerves via the cervical vagus or the nerve of Latarjet appeared to increase I gastrin release and antral motility by separate pathways as blockade of muscarinic receptors, i.e., atropinization inhibited motility but did not alter I gastrin release. On the other hand, blockade of nicotinic receptors by hexamethonium treatment obliterated I gastrin release induced by stimulation of the extrinsic nerves but only reduced motility. Field stimulation of intrinsic nerves via serosal electrodes also increased both I gastrin release and local motility. Since hexamethonium treatment only slightly reduced both I gastrin release and motility and atropinization eliminated both during field stimulation, the presence of a muscarinic receptor in the final pathway for each is proposed. Atropine eliminated carbachol-induced I gastrin release and motility increases, even in the presence of nerve blockade by tetrodotoxin. This suggests that this muscarinic receptor is on the smooth muscle cell itself and possibly on the gastrin cell. However a proposed role of the somatostatin cell in controlling gastrin release is also consistent with these data. Thus, both an intrinsic cholinergic and a separate extrinsic noncholinergic pathway are involved in antral release of I gastrin but initiation of motility appears to involve a final common pathway terminating in a muscarinic receptor on the smooth muscle cell.