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Monosodium Glutamate (MSG) Promotes the Contraction of
Duodenal Visceral Smooth Muscle Ex Vivo in Rat
Suraiya Parvin, Sourapriya Mukherjee, Goutam Paul*
Molecular Neurotoxicology Laboratory, Department of Physiology, University of Kalyani, Kalyani -
741235, West Bengal, India
*Corresponding Author
DOI: https://doi.org/10.51244/IJRSI.2025.120800200
Received: 30 Aug 2025; Accepted: 05 Sept 2025; Published: 19 September 2025
ABSTRACT
Monosodium glutamate (MSG), popularly trading in the name of AJI-NO-MOTO, is one of the world’s most
extensively used taste enhancing food additive. It is used in cooking as a flavor enhancer with an umami taste
that intensifies the meaty and savory flavor of food. Thus, humans are often exposed to MSG through
consumption of MSG tainted food stuffs and the small intestine gets primarily exposed to it. In order to
examine any effect of MSG on the contractile activity of the small intestinal visceral smooth muscle (SiVSM),
the movement of the duodenum ex vivo in response to MSG in single dose experiments have been recorded
using an isotonic transducer (IT-2245) coupled with an RMS-Polyrite D machine (RMS, Chandigarh, India).
Significant increase in the amplitude and frequency of contraction of the duodenum in comparison with control
tracings in a dose-response manner were observed. From the results, it can be suggested that MSG potentiates
the contractile activity of duodenal visceral smooth muscle probably by increasing the amplitude and
frequency of the contractions of the visceral smooth muscle located in the wall structure of the duodenum,
probably by facilitating the activity of excitatory intrinsic cholinergic efferents and/or inhibiting the activity of
inhibitory adrenergic or nitrergic myenteric efferents. The MSG induced impairment in the contraction of the
dVSM results in impaired digestive and absorptive functions of the duodenum (small intestine).
Keywords: MSG, contractile activity, SiVSM, food additive, myenteric efferents
INTRODUCTION
Monosodium glutamate (MSG) is a hydrated sodium salt of naturally occurring L-glutamic acid. It is generally
used as a flavor-enhancing food additive to processed fast foods. It has been reported that MSG altered the
renal cortical structure and degenerative nephron structure in the kidney of MSG exposed groups of rats
(Eweka, 2007). It has also been reported that MSG significantly induced the weight gain of the animal feed
with MSG added diet as results of the induction in the appetite process (Moore, 1999). Endocrine disruptions
in MSG exposed laboratory animals have also been reported (Samuels, 1999). It has been also reported that
locomotion disorders were observed in MSG-exposed animals (Ali et al., 2000).
Humans are often exposed to MSG through consumption of MSG tainted food stuffs and the small intestine
gets primarily exposed to it. The small intestine helps in digestion and absorption with the help of the
contractions of the visceral smooth muscles located in the muscularis externa layer of the small intestine that
provides motility to it. Any impairment in the contractions of the SiVSM due to exposure to external agents
might impair the digestive and absorptive functions of the small intestine. So, the present study was carried out
to examine the effect of MSG on the contractile activity of the duodenal VSM ex vivo in male albino rats.
MATERIALS AND METHODS
Chemical and Reagents
Chemical used for this acute study was Monosodium glutamate (MSG) with 99% purity. It was purchased
INTERNATIONAL JOURNAL OF RESEARCH AND SCIENTIFIC INNOVATION (IJRSI)
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Sigma-Aldrich, USA. All the experimental reagents were of analytical grade. They were such as sodium
chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), calcium chloride (CaCl2), sodium
bicarbonate (NaHCO3), glucose, sodium dihydrogen phosphate (NaH2PO4) were obtained E- Merck, India, and
Sisco Research Laboratory (SRL), India respectively.
Animal Handling
Charles Foster male albino rats weighing 110-130 gm were used for this experimental study. Ethical clearance
regarding animal acclimatization was gained by the Kalyani University Animal Ethics Committee according to
national guidelines.
Experimental Set Up for the Post-treatment of the Animal
For this post-treatment experiment, animals were sacrificed by cervical dislocation after acclimatization
duration. The abdomen was opened, duodenal segments were taken off by transverse incision and were
prepared to record the contraction ofthe duodenum. For this acute study, a graded dosage of MSG was applied
directly in the 50 ml organ bath and the contraction of the duodenum was recorded.
Table 1.1: Experimental set up for Acute Study
Animal grouping Application of dosages (µM)
I Application of 2.1µM dose of MSG on isolated duodenal (n=10)preparation.
II Application of 4.2µM dose of MSG on isolated duodenal (n=10) preparation.
III Application of 8.5µM dose of MSG on isolated duodenal (n=10) preparation.
IV Application of 17µM dose of MSG on isolated duodenal (n=10) preparation.
V Application of 34µM dose of MSG on isolated duodenal (n=10) preparation.
Recording of Contraction of Duodenal Movement
Segments of the duodenum were used for this study. After overnight fasting, each rat was sacrificed by
cervical dislocation. The abdomen of the sacrificed rat was then opened immediately, and the duodenal
segments were collected by transverse incision. After dissecting out the segment of the duodenal muscle, it
was kept in Tyrode’s solution made up of NaCl, KCl, MgCl2, NaH2PO4, Na2HPO4, glucose. The lower hook
was fixed at the bottom of the organ bath and the upper hook was connected to a lever connecting to an
isotonic transducer (IT-2245). They were blotted dry and after that, placed in the 50 ml organ bath containing
Tyrode’s solution. The temperature of the bath was maintained (37˚C±0.5) and 95% CO2, 5% O2 were
supplied continuously (2-3 bubbles/second). The initial preparations were allowed to equilibrate for at least 40
mins by applying an initial load of 0.1 gm. During this period, the experimental preparations underwent
repeated and continuous washes with Tyrode’s solution to avoid an accumulation of metabolites in the organ
bath. Contraction of the duodenum was carried out by isotonic transducer (IT-2245) coupled to RMS Polyrite-
D. Recording was taken at sweep speed= 0.937 mm/sec, deflection= 1000 mm, low filter= 0.2 Hz, high filter=
DC and sensitivity= 10 µV (Mondal et al., 2018).
Statistical Analysis
The data were presented as Mean ± SEM of the value of exposed groups and control group of rats. The values
of the data of the experimental groups were represented as percent changes of the values of a control group of
rats. Statistical analysis of the results was evaluated using students’‘t’ test or analysis of variance (ANOVA) in
the Graph Pad Prism 5.03 (Graph Pad Software, Inc). The level of significance was applied at p≤0.05. In the
results, the number of treated preparations of the duodenum was considered by ‘n’.
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RESULTS AND DISCUSSION
To examine the response produced by MSG on the contractions of duodenal VSM, the movement of
duodenum has been recorded ex vivo in response to application of graded doses of MSG. In this experiment, a
significant increase in the amplitude and frequency of contraction of the duodenum in comparison with control
tracings in a dose-response manner have been observed (Fig. 1.1: Tracings A-F; 1.2 and Table 1.2).
Fig. 1.1: Representative records show the effects of control and single graded dosages of MSG (i.e. 2.1, 4.2,
8.5,17, 34 µM) on the contraction of duodenum ex vivo, n=10.A) Tracings of the record of the duodenum in
absence of MSG, B) Tracings of the effect of a 2.1µM dose of MSG, C) Tracings of the effect of a 4.2 µM
dose of MSG, D) Tracings of the effect of an 8.5 µM dose of MSG, E) Tracings of the effect of a 17 µM dose
of MSG. F) Tracings of the effect of a 34 µM dose of MSG. BC indicates a basal contraction of the duodenum.
Arrowheads indicate the point of MSG application.
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Fig. 1.2: Diagrammatic representations of the changes in frequency (A) and amplitude (B) of the contraction in
absence of MSG and presence of MSG at single different dosages (i.e. 2.1, 4.2, 8.5,17, 34 µM) ex vivo. Data
are expressed as Mean ± SEM, ***p<0.001 vs. control, n=10.
Table 1.2: Tabular presentation of percent changes in the amplitude and frequency of the contraction of
duodenum ex vivo of rat in response to the graded dosages of MSG application. Data are expressed as
Mean±SEM, ***p<0.001 vs. control, n=10.
Graded dosages of MSG (µM) Amplitude of contraction Frequency of contraction
Control 76.125±7.273 99.257 ±1.728
2.1 119.980±6.826*** 115.921± 1.111***
4.2 123.400±5.017*** 120.735± 0.820***
8.5 128.718±7.194*** 129.993± 0.865***
17 172.075±4.679*** 133.329± 2.066***
34 185.975±7.216*** 140.736± 1.746***
In the present investigation, MSG potentiates the contraction of duodenal visceral smooth muscle (VSM) in
exposed rats. The MSG-induced potentiation of contraction of VSM, might be due to facilitation of the
contraction of duodenal visceral smooth muscle probably by augmenting the activity of cholinergic myenteric
efferents innervating the smooth muscle and/or inhibiting the activity of adrenergic or nitrergic myenteric
efferents as result of intoxication by MSG (Fig 1.3). Further, the increase in the frequency by MSG might be
due to facilitation in the propagation of slow waves (SWs) and basal electrical rhythm (BER) in the Interstitial
Cells of Cajal (ICCs) that determines the rhythmicity of the contraction of the dVSM. The MSG induced
hypermotility was characterized by increased, excessive movement of the small intestine, which can cause
diarrhea, nutrient malabsorption, bloating, and pain due to improper digestion or absorption. Improper
digestion would lead to several gastrointestinal problems; and malabsorption of nutrients will cause severe
deficiencies that could degrade the physical health.
CONCLUSION
In conclusion, it can be suggested that Monosodium glutamate is a potent toxicant and it impairs the basal
contractions of dVSM in rat by increasing the frequency and contractions of the dVSM. The MSG induced
INTERNATIONAL JOURNAL OF RESEARCH AND SCIENTIFIC INNOVATION (IJRSI)
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facilitation of the contractions of the dVSM might be due to promotion of the activity of cholinergic myenteric
efferents and/or facilitation of the activity of nitrergic and/or adrenergic myenteric efferents innervating the
dVSM. The results obtained from the study could be extrapolated in humans. Thus, alteration of the contractile
function of the dVSM on MSG exposure due to consumption of MSG tainted foods will result in the
impairment of the digestive and absorptive functions of the small intestine.
Fig1.3:Schematic representation showing probable neurocrine mechanism involved in MSG induced
potentiation of contraction of duodenal visceral smooth muscle.+ indicates stimulation, - indicates inhibition, ×
indicates no effect.
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