Dietary Glutamate Signal Evokes Gastric Juice Excretion in Dogs

Abstract

Background: Dietary-free L-glutamate (Glu) in the stomach interacts with specific Glu receptors (T1R1/T1R3 and mGluR1–8) expressed on surface epithelial and gastric gland cells. Furthermore, luminal Glu activates the vagal afferents in the stomach through the paracrine cascade including nitric oxide and serotonin (5-HT). Aim: To elucidate the role of dietary Glu in neuroendocrine control of the gastrointestinal phase of gastric secretion. Methods: In Pavlov or Heidenhain gastric pouch dogs, secretion was measured in the pouch while monosodium glutamate (MSG) was intubated into the main stomach alone or in combination with liquid diets. Results: In both experimental models, supplementation of the amino acid-rich diet with MSG (100 mmol/l) enhanced secretions of acid, pepsinogen and fluid, and elevated plasma gastrin-17. However, MSG did not affect secretion stimulated by the carbohydrate-rich diet and had no effect on basal secretion when applied in aqueous solution. Effects of MSG were abolished by denervation of the stomach and proximal small intestine with intragastrically applied lidocaine and partially suppressed with the 5-HT₃ receptor blocker granisetron. Conclusions: Supplementation of amino acid-rich liquid diets with MSG enhances gastrointestinal phase secretion through neuroendocrine pathways which are partially mediated by 5-HT. Possible mechanisms are discussed.

Monosodium glutamate stimulates secretion of glucagon‐like peptide‐1 and reduces postprandial glucose after a lipid‐containing meal

“…In general, lipids strongly inhibit gastric emptying, so the lipid content of the test meal in the present study might have overcome the potential of MSG to accelerate gastric emptying. The effect of MSG on gastric juice secretion has been reported to be dependent on the nutritional composition of the test meal in dogs . Thus, glutamate not only accelerates GI motility but also has the potential to regulate glycemic homeostasis in a manner dependent on the co‐existing nutrients in a meal.…”

Obesity and Diabetes

“…L-glutamate also potentiates gastric secretion via the vagus nerve after binding to glutamate receptors (T1R1/T1R3 and mGluRs) located in gastric glands (Khropycheva et al 2011;Nakamura et al 2011;San Gabriel et al 2007;Uneyama et al 2006). As a result, single AAs from the diet not only add flavor but may also increase protein digestion efficiency.…”

Role of Dietary Free Glutamate in Gastrointestinal Function

“…Recent reports have now shed new light on how free glutamate modulates gastric juice secretion. Khropycheva et al reported that the effect of dietary glutamate on the gastrointestinal phase of gastric secretion depended on the characteristics of the co-applied macronutrients [22,23]. Supplementation of glutamate to an amino acid-rich diet enhanced the secretion of acid, pepsinogen (inactive form of pepsin), and fluids in dogs with Pavlov pouches.…”