Intragastric monosodiuml-glutamate stimulates motility of upper gut via vagus nerve in conscious dogs

Abstract

Monosodium l-glutamate (MSG) is a substance known to produce the umami taste. Recent studies indicate that MSG also stimulates a variety of activities in the gastrointestinal tract through its receptor in the gut, but no study has reported the activity in conscious large experimental animals. The aim of our study was to investigate whether direct intragastric MSG stimulates gut motility and to identify the mechanism in conscious dogs. Contractile response to intraluminal injection of MSG was studied in the fed and fasted states by means of chronically implanted force transducers. MSG (5, 15, 45, and 90 mM/kg) dissolved in water was injected into the stomach and duodenum in normal and vagotomized dogs. MSG solution was administered into the stomach before feeding, and gastric emptying was evaluated. Several inhibitors of gastrointestinal motility (atropine, hexamethonium, and granisetron) were injected intravenously before MSG administration to the stomach. The effect of MSG was investigated in Pavlov (vagally innervated corpus pouch), Heidenhain (vagally denervated corpus pouch), and antral pouch (vagally innervated) dogs. Upper gut motility was significantly increased by intragastric MSG but not significantly stimulated by intraduodenal MSG. Intragastric MSG (45 mM/kg) stimulated postprandial motility and accelerated gastric emptying. MSG-induced contractions were inhibited by truncal vagotomy, atropine, hexamethonium, and granisetron. Gut motility was increased by intrapouch injection of MSG in the Pavlov pouch, but it was not affected in the Heidenhain or antral pouch dogs. We conclude that intragastric MSG stimulates upper gut motility and accelerates gastric emptying. The sensory structure of MSG is present in the gastric corpus, and the signal is mediated by the vagus nerve.

Taste receptors of the gut: emerging roles in health and disease

“…Thus, once proteins such as wheat are digested, dietary Glu may stimulate Glu sensors (e.g TAS1R -TAS1R3, CaSR and metabotropic glutamate receptors (mGluR)) in the stomach and intestine producing local effects on gut function. For example, in dogs, intragastric, but not intraduodenal, administration of monosodium glutamate (MSG) stimulated gastric emptying and induced phasic non-propagating contractions in the upper gut which were blocked by vagotomy 125. Contradictory results have been reported concerning the effect of MSG on gastric emptying in humans 126 127…”

Luminal Amino Acid-Sensing Cells in Gastric Mucosa

“…This would provide a mechanism for the previously reported effects of glutamate in the stomach. Indeed, dietary glutamate reportedly stimulates gastric secretion and motility in dogs and humans [16,17,18]. Since somatostatin is an inhibitory regulator of gastric exocrine and endocrine secretion [12,13,14,15], it is reasonable to assume that the inhibition of somatostatin release via G i -protein-coupled mGluRs stimulation (i.e., inhibition of inhibitory effect) results in stimulation of gastric secretion.…”

Inhibitory effect ofSuaeda asparagoides(Miq.) extract on the motility of rat gastric antrum is mediated by β-adrenoceptor

“…Stimulating gastric motility agents also enhances gastric emptying [19-21]. On the other hand, higher concentrations SAWF may have a beneficial effect on symptoms associated with rapid gastric emptying.…”