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

Abstract

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 ACh, ADP, ATP, and histamine but relaxed to vasoactive intestinal polypeptide. Fundic but not antral muscularis mucosae contracted to bombesin and PGE2and PGF2α, whereas adenosine, AMP, CCK, gastrin, secretin, and somatostatin were without effect on any preparation. In both regions electrical field stimulation evoked TTX-sensitive responses consisting of an atropine-resistant contraction 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 motor activity is linked to acid secretion this would be achieved by a neurally mediated relaxation rather than a paracrine- and/or endocrine-induced alteration in tone.

Muscularis mucosae - the forgotten sibling

“…Since the neuronally-mediated relaxation of the gastric muscularis mucosae seems to facilitate acid release by opening the gastric glands (Synnerstad et al, 1998), dysfunction of VIPergic nerve-muscularis mucosae transmission may contribute to peptic ulcer (Percy et al, 1999).…”

“…This indicates that pathological changes in the transduction pathway between mucosal endocrine cells and primary afferent nerve terminals may lead to decreased motility and secretion in irritable bowel diseases. A number of studies by Percy and his colleagues Percy et al, 1992;Percy et al, 1993a;Percy et al, 1993b;Percy and Warren, 1994;Percy et al, 1997;Percy et al, 1998;Percy et al, 1999;Percy et al, 2001) have revealed that contractility of the muscularis mucosae closely linked with mucosal secretory function and its abnormal motility was concerned in inflammatory bowel diseases. As this physiological transduction mechanism, muscularis mucosae motor activity is translocated into mucosal secretion via the contraction-related PG synthesis and stimulation of non-cholinergic secretomotor neuron (Lawson and Powell, 1987;Percy et al, 2003).…”

“…Rat gastric muscularis mucosae contracted to acetylcholine and adrenaline, but not to 5-HT or histamine (Horn and Zweifach, 1963). The responsiveness to drugs showed a greater regional difference in gastric body, where fundic but not antral muscularis mucosae contracted to bombesin, PGE2 and PGF2α (Percy et al, 1999).…”

“…In contrast to human, dog gastric muscularis mucosae possessed both contractile H1 and relaxant H2 receptors (Muller et al, 1993). Rabbit gastric muscularis mucosae contracted to acetylcholine, ATP and histamine, but relaxed to VIP (Percy et al, 1999). Adenosine, cholecystokinin, gastrin, secretin and somatostatin were without effect (Muller et al, 1994).…”

“…Electrical field stimulation of the muscularis mucosae evoked a biphasic response, consisting of an initial contraction followed by a sustained relaxation. Although both components were abolished by the pretreatment with tetrodotoxin, neither initial contraction nor following relaxation were inhibited with atropine, propranolol or L-NAME (Percy and Warren, 1994;Percy et al, 1999). The rabbit gastric muscularis mucosae is presumably innervated by excitatory non-cholinergic nerves and inhibitory non-adrenergic and non-nitrergic nerves, but each neurotransmitter is still unclear.…”