Abstract
Objective: The objective of the present study was to examine the effects of monosodium glutamate (MSG) on the contraction of visceral smooth muscle (VSM) of the duodenum in a rat model to understand the MSG-induced impairment of the function of the small intestine.
 Methods: Male albino rats of Charles Foster strain were exposed with MSG at three different dosages (632, 1264, and 2528 mg/kg BW/day) for 30-day duration. The records of the contraction of the duodenum were achieved with isotonic transducer (IT-2245) coupled with RMS-Polyrite D by our standard laboratory protocol.
 Results: We have observed potentiation of contraction of duodenum ex vivo dose-dependently in MSG exposed groups of rats compared to control. Furthermore, the enzymatic activity of acetylcholinesterase (AChE) in VSM tissue homogenate and expression of AChE protein in fixed duodenal muscle cell layers have been decreased in a dosage response manner comparing to control rats. We have found a significant decrease in the activities of some antioxidant enzymes such as Cu-Zn superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-s-transferase, and increase in the level of malondialdehyde in MSG exposed VSM tissue homogenate of the duodenum. We have also observed thickening of muscularis externa layer and increase in the number of muscle cells in circular and longitudinal muscle layers of the duodenal wall in transverse duodenal wall sections stained with eosin-hematoxylin.
 Conclusion: MSG potentiates the contraction of VSM of duodenum by augmenting the activity of intrinsic cholinergic efferents predominantly, and inducing oxidative stress and proliferating smooth muscle cells.
Highlights
Monosodium glutamate (MSG), marketed as Ajinomoto, is one of the world’s most extensively used taste enhancing food additive, which is ingested as part of commercially processed foods
Effects of monosodium glutamate on acetylcholinesterase enzyme activity of visceral smooth muscle of duodenum A significant decrease in AChE enzyme activity in the VSM tissue homogenate was observed in the MSG exposed (0.632, 1.264, and 2.528 gm MSG kg−1 BW day−1) groups of rats dosedependently compared to control group of rats (Fig. 3)
Effects of monosodium glutamate on acetylcholinesterase enzyme activity of visceral smooth muscle found in the wall structure of duodenum We have found a significant decrease in the deposition of aggregates of the thiocholine iodide conjugate in the muscularis externa layer of the duodenal wall of the exposed groups of rats dose-dependently compared to a control group of rats
Summary
Monosodium glutamate (MSG), marketed as Ajinomoto, is one of the world’s most extensively used taste enhancing food additive, which is ingested as part of commercially processed foods. Oladipo et al observed MSG-induced considerable structural changes including degenerated follicles, oocytes, and medulla with vacuoles having congested blood vessels in the ovaries of Sprague–Dawley rats. Due to these reasons, female infertility may happen in case of the increased amount of consumption of MSG [7]. Mohamed IK reported that MSG produces deleterious effects on the spermatogenic cells in case of long-term daily exposure compared to short-term treatment. Both short-term and long-term treatments may lead to infertility problem in experimental rats [11]. Our laboratory reported that MSG impairs the contraction of uterine visceral smooth muscle (VSM) ex vivo of the rat through augmentation of acetylcholine and nitric oxide signaling pathways [12]
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