Characteristics of the muscularis mucosae in the acid secreting region of the rabbit stomach. W.H. Percy, J. M. Warren and J.T. Brunz. Am. J. Physiol. 276: G1213-1220, 1999. It has been suggested that muscularis mucosae excitation may augment gastric acid secretion, implying that this muscle should contract to secretagogues or stimulation of its motor innervation. The aim of this study was to characterize in vitro the responses of the muscularis mucosae in the rabbit gastric corpus to substances that modulate acid release and to intrinsic nerve stimulation. Muscularis mucosae from both fundic and antral ends of the corpus had identical mechanical properties, contracted to acetylcholine, adenosine diphosphate, adenosine triphosphate and histamine but relaxed to vasoactive intestinal polypeptide. Fundic, but not antral muscularis mucosae contracted to bombesin and prostaglandins E2 and F2a whereas, adenosine, adenosine monophosphate, cholecystokinin, gastrin, secretin and somatostatin were without effect on any preparation. In both regions electrical field stimulation evoked tetrodotoxin-sensitive responses consisting of an atropine-resistant contraction followed by an L-NAME and indomethacin-resistant relaxation. It is concluded from the regional variability in the pharmacologic properties of the gastric muscularis mucosae that, if its motor activity is linked to acid secretion, this would be achieved by a neurally-mediated relaxation rather than a paracrine/endocrine-induced alteration in tone.

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