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THE TOXICOLOGICAL INFLUENCE OF NO₂ AND SO₂ GASES ON MAJOR
SALIVARY GLANDS: AN EXPERIMENTAL RAT MODEL
G’ulomova Madinabonu G’iyosiddin kizi
Kokand University Andijan Branch Faculty of Medicine
2nd year student of the medical field
[For correspondence: madinabonug092@gmail.com]
Abstract:
This study explores the morphological and morphometric changes in the major
salivary glands (parotid, submandibular, and sublingual) of laboratory rats subjected to chronic
exposure to nitrogen dioxide (NO₂) and sulfur dioxide (SO₂). A total of 30 Wistar rats were
divided into control and experimental groups. The experimental group was exposed to a 0.2 ppm
gas mixture for 6 hours daily over 90 days. Histological and morphometric analyses revealed
substantial degenerative, inflammatory, and atrophic alterations in the salivary glands of exposed
animals. Quantitative measurements showed significant reductions in acinar diameter, nuclear
volume, capillary density, and the number of secretory cells. These findings suggest that
prolonged inhalation of NO₂ and SO₂ compromises glandular structure and function, highlighting
the critical need for environmental pollution control strategies.
Keywords:
Salivary glands, NO₂ exposure, SO₂ toxicity, Morphological changes, Morphometric
analysis, Oxidative stress, Environmental pollution
Introduction
The rapid pace of industrialization and increasing vehicular emissions have intensified the
problem of atmospheric air pollution. Among the most harmful pollutants are nitrogen dioxide
(NO₂) and sulfur dioxide (SO₂), both of which have been shown to adversely impact the
respiratory system and oral tissues. Despite their known toxicological effects, the influence of
chronic exposure to these gases on the structural and functional integrity of major salivary glands
remains underexplored. Salivary glands, particularly the parotid, submandibular, and sublingual
glands, play a fundamental role in maintaining oral and systemic health through saliva
production, mucosal protection, and immunological defense. Thus, understanding how air
pollutants affect these glands is of substantial clinical and environmental significance. This study
aims to investigate the comparative morphological and morphometric effects of chronic NO₂ and
SO₂ exposure on the major salivary glands of rats.
Materials and Methods
Animal Subjects Thirty healthy male Wistar rats (180–220 g) were used in this study. The rats
were randomly assigned to two groups:
Control Group (n = 15): Maintained under standard laboratory conditions with clean air.
Experimental Group (n = 15): Exposed to a gas mixture of NO₂ and SO₂ (0.2 ppm each) for 6
hours per day over a 90-day period.
Tissue Sampling and Processing
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At the end of the exposure period, all animals were euthanized under deep anesthesia. Parotid,
submandibular, and sublingual glands were excised and fixed in 10% neutral-buffered formalin.
The tissues were embedded in paraffin, sectioned at 5 μm thickness, and stained with
hematoxylin and eosin for histological assessment.
Morphometric Evaluation
Microscopic images were analyzed using ImageJ software. The following parameters were
measured:
Acinus diameter (μm)
Nuclear volume (μm³)
Number of secretory cells per field
Capillary density (per 100 μm²)
Data from 10 random fields per sample were averaged to obtain representative values.
Statistical Analysis
Results were expressed as mean ± standard deviation (M ± SD). Differences between groups
were assessed using Student's t-test. A p-value of <0.05 was considered statistically significant.
Results
Morphological Findings
Parotid Glands: The control group exhibited normal histoarchitecture with well-organized,
densely packed acini. In contrast, the experimental group displayed cytoplasmic vacuolization,
nuclear pyknosis, lymphocytic infiltration, and fibrosis in the stromal regions. Submandibular
Glands: This gland demonstrated the most pronounced pathological changes, including marked
acinar degeneration, stromal fibrosis, and disrupted microcirculation. Sublingual Glands:
Degenerative changes included nuclear deformation, cytoplasmic vacuolization, and necrosis of
secretory epithelium, along with perivascular inflammation.
Morphometric Data
Indicator Control Group (M ± SD) Experimental Group (M ± SD) Difference (%) p-value
Acinus diameter (μm) 56.2 ± 3.1 42.8 ± 2.7 −23.9% <0.01
Nuclear volume (μm³) 112.5 ± 5.4 89.3 ± 4.9 −20.6% <0.01
Capillary density 7.4 ± 0.8 5.1 ± 0.7 −31.1% <0.01
Secretory cells 34.5 ± 2.6 25.2 ± 2.1 −27.0% <0.01
Discussion
The study confirmed that chronic exposure to NO₂ and SO₂ leads to significant morphological
and morphometric deterioration of major salivary glands. Cytoplasmic vacuolization, nuclear
pyknosis, and stromal fibrosis are indicative of cellular degeneration and inflammatory stress.
The marked decrease in acinar diameter and nuclear volume suggests diminished cellular activity
and secretory function. The submandibular gland showed the highest sensitivity to gas exposure,
which may be attributed to its mixed serous-mucous nature, making it more susceptible to
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oxidative and metabolic stress. These observations are consistent with previous findings
indicating environmental pollutants disrupt epithelial and vascular integrity in exocrine glands.
Morphometric analysis provided quantitative support to the histological findings, with
statistically significant reductions in all measured parameters in the experimental group. These
objective markers can be used to assess the functional impairment of salivary glands due to
chronic toxic exposure.
Conclusion
Chronic inhalation of NO₂ and SO₂ gases induces profound morphological and morphometric
changes in major salivary glands, including degenerative and inflammatory damage, vascular
impairment, and decreased secretory cell function. These findings highlight the vulnerability of
oral tissues to air pollution and underscore the importance of implementing stringent
environmental regulations and preventive health strategies to mitigate exposure risks.
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