Characteristics of the muscularis mucosae in the acid-secreting region of the rabbit stomach

It has been suggested that muscularis mucosae excitation may augment gastri c acid secretion, implying that this muscle should contract to secretagogue s or stimulation of its motor innervation. The aim of this study was to cha racterize in vitro the responses of the muscularis mucosae in the rabbit ga stric corpus to substances that modulate acid release and to intrinsic nerv e stimulation. Muscularis mucosae from both fundic and antral ends of the c orpus had identical mechanical properties, contracted to ACh, ADP, ATP, and histamine but relaxed to vasoactive intestinal polypeptide. Fundic but not antral muscularis mucosae contracted to bombesin and PGE(2) and PGF(2 alph a), whereas adenosine, AMP, CCK, gastrin, secretin, and somatostatin were w ithout effect on any preparation. In both regions electrical field stimulat ion evoked TTX-sensitive responses consisting of an atropine-resistant cont raction followed by an N-G-nitro-L-arginine methyl ester- and indomethacin- resistant relaxation. It is concluded from the regional variability in the pharmacological properties of the gastric muscularis mucosae that if its mo tor activity is linked to acid secretion this would be achieved by a neural ly mediated relaxation rather than a paracrine- and/or endocrine-induced al teration in tone.