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Year : 2014  |  Volume : 16  |  Issue : 73  |  Page : 416--421

Morphological changes of adrenal gland and heart tissue after varying duration of noise exposure in adult rat

Noura Gannouni1, Abada Mhamdi2, Michèle El May3, Olfa Tebourbi4, Khémais Ben Rhouma4,  
1 Department of Biological Sciences, Laboratory of Integrated Physiology, Faculty of Sciences of Bizerte, Bizerte; Department of Occupational Medicine, Laboratory of Toxicology, Ergonomics and Occupational Environment, Faculty of Medicine of Tunis, Tunis, Tunisia
2 Department of Occupational Medicine, Laboratory of Toxicology, Ergonomics and Occupational Environment, Faculty of Medicine of Tunis, Tunis, Tunisia
3 Department of Histology, Embryology and Cell Biology, Recherch Unit 01/UR/08-07, Faculty of Medicine of Tunis, Tunisia
4 Department of Biological Sciences, Laboratory of Integrated Physiology, Faculty of Sciences of Bizerte, Bizerte, Tunisia

Correspondence Address:
Noura Gannouni
Imm Elezz J11 Radès Méliane, Radès 2040, Tunis


Noise was considered an environmental stressor causing a wide range of health effects such as acoustic, cardiovascular, nervous, and endocrine systems. The present study was performed to examine the effects of a repeated noise exposure on adrenal gland and heart tissue. The results showed that exposure to moderate intensity sound (70 dB[A]) causes time-dependent changes in the morphological structure of the adrenal cortex that involve disarrangement of cells and modification in thickness of the different layers of the adrenal gland. The experiment revealed important changes depending on exposure duration in the morphological structure of heart tissue that causes irreversible cell damage leading to cell death or necrosis.

How to cite this article:
Gannouni N, Mhamdi A, El May M, Tebourbi O, Rhouma KB. Morphological changes of adrenal gland and heart tissue after varying duration of noise exposure in adult rat.Noise Health 2014;16:416-421

How to cite this URL:
Gannouni N, Mhamdi A, El May M, Tebourbi O, Rhouma KB. Morphological changes of adrenal gland and heart tissue after varying duration of noise exposure in adult rat. Noise Health [serial online] 2014 [cited 2022 Dec 1 ];16:416-421
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Noise can have a more global effect on human physiology and act upon multiple non-auditory systems such as cardiovascular, neuroendocrine, and psychological. [1] The World Health Organization document, Guidelines for Community Noise, indicates that noise exposure may lead to many detrimental effects, including auditory and non-auditory effects. [2]

In addition to lesions to the hearing function [3],[4] noise may be deleterious to internal organs due to vibration that is strong enough to be transmitted to human body tissues. [5],[6],[7] Several studies have demonstrated a correlation between exposure to noise and the development of alterations and/or pathologies in organs and apparatus, apart from the auditory one.

Long-term exposure to a chronic noise stressor can lead to chronic stress, defined as long-term overstimulation of coping mechanisms. This in turn can lead to less predictable changes in the hypothalamic-pituitary-adrenal (HPA) axis. One possible impact of introduced noise was the induction of stress, the negative effects of noise on cell structure and function were supposed by increase of reactive oxygen species. The study of Frenzilli et al. [8] has shown that the exposure to loud noise caused a significant increase of DNA damage in the adrenal gland, the imbalance of redox cell status was responsible for the induction and persistence of noise-induced cellular damage.

Exposure to noise causes changes in morphological structure of the adrenal gland. Moreover, most studies on the effects of noise investigated the relationship between noise and myocardial damage. [9],[10]

The purpose of the present study was to investigate whether prolonged exposure to noise at moderate intensity will be able to produce time-dependent changes in the morphological structure of adrenal cortex and heart tissue.


Animals and experimental procedures

Male Wistar rats are weighing 200-250 g were used for the experiments (n = 6 per group). Animals were housed in the animal facility, fed ad libitum and kept under closely controlled environmental conditions (12 h light: Dark cycle, lights on between 07:00 and 19:00 h; room temperature 21°C). Animals were treated in accordance with the European Convention (1986) for the protection and use of vertebrate animals. All possible efforts were made to reduce animal suffering and minimize the number of animals used.

Two groups were exposed in this study of 3 and 5 months, the acoustic exposure was done using the audio software Audacity 1.3.12 (Unicode). It is free software for manipulating digital audio data. It allows editing noise on multiple tracks and is accompanied by various filters and effects (noise reduction, equalizer, increased frequencies, compression, amplification…). The noise level generated by the software was set at 70 dB(A) to an octave-band noise (8-16 kHz) by the use of two loudspeakers installed at a distance of 10 cm to each cage. The noise level was monitored using an Integrating Sound Level Meter with Class 1 accuracy-type 2238 Bruel and Kjaer. The exposure duration was 6 h/day and repeated automatically after selecting start and end of noise. During noise exposure, noise levels were controlled using a sound level meter, a preamplifier and a condenser microphone positioned at the level of the animal's head. The stimulus intensity varied by 1 dB across the cages. Control rats underwent same periods without noise stimulation when the background sound level was 32-35 dB(A).

Qualitative analysis of heart tissue and adrenal gland: Light microscopy

In order to avoid circadian variation, all animals were sacrificed by decapitation and the tissues were rapidly removed. Formalin-fixed, paraffin-embedded tissue samples were used for histological analyses. Briefly, 5 μm thick sections were cut with a microtome, stained with hematoxylin and eosin dye or Masson's trichrome. The preparation was dried at room temperature and observed by light microscopy. Many sections (n = 3) of each animal was observed.

Measurement of the thickness of the adrenal cortex

The different layers of the adrenal cortex were measured using ImageJ software in the research unit UR-01-08-07 in the Faculty of Medicine of Tunis. The value of each layer was calculated according to the length of a cell Mallasses at the same magnification as the picture taken by the camera's optical microscope. Each blade (×6 blades) was measured on the entire surface of cutting organ.

Statistical analysis

The results were expressed as mean ± standard error of mean the data collected statistically analyzed using Two-way analysis of variance using Statview Software. P ≤ 0.05 was considered as significant.


Action on the adrenal architecture

In order to know if noise exposure at moderate intensity was accompanied by histological changes of the adrenal gland, we performed a histological study comparing the adrenal gland of the control animals and those exposed to noise.

Adrenal gland of control animals was comprised of two distinct structures [Figure 1]a, the outer part of the adrenal glands was called the adrenal cortex, and the inner region was known as the adrenal medulla. The cortex has three zones. The zona glomerulosa was the outermost zone and consisted of cells arranged in rounded or arched clusters. The zona fasciculata, was the easiest layer to spot as it was a broad zone of cells arranged in straight cords. The zona reticularis was the third area, and their cells were arranged as anastomosing cords.{Figure 1}

In the adrenal cortex of animals exposed to 70 dB(A) for 3 months, there was a cellular disorganization of both glomerulosa and fasciculata zona. In fact, the cells of the zona glomerulosa lose their disposal in ovoid clusters. Part of the zona fasciculata crossed the zona glomerulosa and raised the capsule of the organ [Figure 1]b. On the other hand, the cells of the zona fasciculata were no longer arranged in parallel cords, but showed a random disposal [Figure 1]c. The first layer of the zona fasciculata showed in [Figure 1]c presented small eosinophilic cells similar to glomerulosa cells, an aspect that was absent in controls.

Histological study of animals that have undergone a noise exposure for 5 months revealed a structural alteration of the adrenal cortex compared to control animals.

[Figure 2]a showed that the zona fasciculata of control rats had a frothy appearance. Exposed animals to noise exposure for 5 months showed that the zona fasciculata has lost cord appearance [Figure 2]b; the cytoplasm also has lost its foamy appearance and becomes more eosinophilic. [Figure 2]c showed that the fasciculata cells were dilated and their nuclei were irregular, which is related to necrosis.{Figure 2}

In the adrenal medulla, no major structural change was observed in animals exposed to noise.

Action on the thickness of the cortex

The histological examination of adrenal gland of rats exposed to noise has led us to identify the thickness of the adrenocortical zone. Animals exposed to 3 months showed that the thickness of the zona glomerulosa was almost similar to the controls [Figure 3]. There was no significant decrease in the thickness of zona fasciculata, but the zona reticularis showed a significant increase compared with the control animals [Figure 3].{Figure 3}

After noise exposure to 5 months at 70 dB(A), the animals showed more change in the thickness of their adrenal cortex than animals noise exposed for 3 months. [Figure 4] showed that changes occurred in animals exposed to noise were accompanied by decrease in thickness of the zona glomerulosa and a significant decrease in thickness of zona fasciculata. On the other hand, there was a significant increase in the thickness of zona reticularis.{Figure 4}

Spontaneous and continuous changes on the layer of the adrenal cortex induced by a moderate intensity of 70 dB(A) depending on the duration of exposure were found.

Action on cardiac structure

Histological study of the heart tissue of animals exposed to noise showed changes in heart tissue layers [Figure 5]. The control rats [Figure 5]a showed the normal structure of myocardium. It is the muscular layer of the heart and forms a thick middle layer between the outer epicardium layer and the inner endocardium layer. The cells that constitute cardiac muscle are called cardiomyocytes or myocardiocytes.{Figure 5}

The heart of animals exposed to 3 months had dilated veins in the pericardium and an artery with deposit in the myocardium [Figure 5]b. At high magnification, the endothelium of the veins was damaged [Figure 5]c. [Figure 5]d showed that the endocardium contains inflammatory cells with numerous dilated veins. These disturbances caused by noise testify the installation of cardiac ischemia.

Animals exposed to 5 months showed most important damage to their heart tissue. Control rats showed a normal structure of heart tissue [Figure 6]a. [Figure 6]b showed a disorganized myocardium with an inflammatory reaction in exposed rats, and the absence of myocardial structure or necrosis was properly installed in [Figure 6]c. A more advanced stage of necrosis was shown in [Figure 6]d where myocardial cells disappeared.{Figure 6}


The results of our study showed that chronic exposure to noise causes structural changes in the adrenal cortex, namely a decrease in the thickness of the zona glomerulosa and zona fasciculata accompanied, at least in part, by cells disorganization and depletion of lipid in the first layers of zona fasciculata. However, there was an increase in the thickness of the zona reticularis without cellular disorganization. Our findings were similar to the work of Oliveira et al. [11] showing that chronic exposure to industrial noise triggers cytological changes in the adrenal gland, and then a depletion of lipid droplet in zona fasciculata cells and an increase in the volume of the zona reticularis.

The noise-induced changes were located in the adrenal cortex zone, [11],[12] which is the most sensitive area to adrenocorticotropic hormone stimulation, known to increase during stress conditions that activate the HPA axis. [13]

Recent study demonstrated that exposure to long-term noise (3 month) for different intensities 70 and 85 dB(A) affected various parameters of the endocrine glands. [12] The results of Zheng et al. [14] have shown that chronic noise causes weight change of the adrenal gland. The vibrations, as the main element of noise, induced pathology changes in the morphological structure of suprarenal glands. [15]

It is evident that high noise levels above 95-100 dB(A) causes morphological changes in animals as in humans. Our data indicate that the repetitive noise at moderate intensity was able to induce structural changes in the adrenal gland. Prolonged exposure to noise at 70 dB(A) may result in health disorders. Furthermore, it was found that the structural changes and the variation in volumes of different layers of the adrenal cortex depend on the duration of exposure. Noise exposure induced time-dependent changes in the adrenal cortex that suggest the existence of a sustained stress response. [11] The duration of exposure to noise is thus a factor of harm. In fact, even a low-intensity noise can be annoying. [16]

Results of varying duration of noise exposure on rat indicate that each zona of the adrenal cortex and the two cell types of the adrenal medulla showed a differential reaction to noise stress. [17] These morphological changes were maybe due to an excessive release of catecholamines and corticosterone. [14],[18]

The prolonged stress causes the production and release of cortisol and adrenaline from adrenal glands. At the beginning of the period of stress, there is an adaptive response to mobilize the energy to deal with a critical situation. During this period, a negative feedback was exerted by cortisol on the secretion of corticotropin-releasing hormone to reduce cortisol levels. [19],[20] However, when stress becomes chronic, this action of negative feedback loses its effectiveness; cortisol rises to extremely dangerous levels causing the cardiovascular, neuroendocrine and immune disorders. [9],[21],[22] The noise is a real pollution that promotes stress when it comes to frequent and repeated exposure. It is considered as a source of disturbance of the endocrine balance whose persistence can cause a disease adaptation.

Noise-induced adverse effects in human health, principally involving the cardiovascular and autonomic nervous systems and the endocrine apparatus. [23] Some studies have assessed the physiological and psychological effects of noise and its relation to quality-of-life. [24],[25]

The present findings indicate that a prolonged exposure to noise induced structural and functional modifications in the myocardium and adrenal gland. Histological heart tissue of animals exposed to moderate intensity (70 dB[A]) showed that the structure of the pericardium and myocardium was differently affected depending on the time.

There have been multiple studies that have investigated the relationship between noise, blood pressure, and myocardial damage. A comprehensive meta-analysis by van Kempen et al. [9] of 43 epidemiological studies looked for the correlation between noise exposure and elevated blood pressure and ischemic heart disease during the period of 1970 and 1999. They found that there was a significant association between occupational and air-traffic noise exposure and hypertension.

Noise activates the sympathetic and endocrine systems including cortical and sub-cortical structures. The disturbance in metabolic equilibrium causes chronic changes in values of biological risk factors, which increase the risk of cardiovascular diseases. [26] The results of Spreng [27] have shown that changes in the myocardium ultrastructure were associated with increased levels of corticosterone in rats after noise exposure for 7 days (6 h/day). According to our results, a moderate intensity and repeated over time induced a structural alteration of the different layers of the heart tissue, these effects cannot be neglected under any circumstances, they may be related to ischemia. Epidemiological studies suggest chronic noise stress to be a risk factor for cardiovascular disorders. Annoyance and disturbance due to road traffic noise was associated with a higher incidence of ischemic heart disease. [28] Other studies demonstrated a clear association between cardiovascular effects and environmental noise. [29],[30],[31],[32] An association has been reported between long-term exposure to noise and the risk of myocardial infarction, but the evidence was limited and inconclusive as there was no definitive relationship. [25],[33] Long-term exposure to road traffic noise with levels reaching 66-70 dB(A) was associated with a slightly increased risk of ischemic heart disease, taking into account the various confounding factors. On the other hand, it was reported that prolonged exposure to road traffic noise exposure increases the risk of myocardial infarction. [34] The hypothesis that long-term noise exposure can have an adverse effect on health has been supported by animal studies. [35],[36],[37] Experiments with rats have shown that chronic noise pollution alone or in combination with other stressors (e.g., magnesium deficient diet) can lead to high blood pressure, increased stress hormone secretion, as well as, an accelerated aging of the heart. [38] The results of Di and Zheng [39] have shown that high-speed railway noise for 90 days in 70 dB(A) exposed Sprague-Dawley rats were associated with abnormal ultrastructural synaptic plasticity and decreased levels of phosphorylated-CaMKII in the central nervous system. These effects may have resulted in impairments in learning and memory function.

Physiological changes seem to appear when a person was exposed to noise levels of 70-75 dB. [1],[40] These data might be potentially relevant in contributing to explain the effects induced in humans exposed to loud noise in a variety of environmental conditions.

Our study showed a model of structural disorders of the adrenal gland and heart caused by moderate and repeated sounds. The effects of noise were innumerable and difficult to apprehend, they depend on, in large part, on individual parameters.


The present study provides morphological evidence that exposure to repetitive noise at moderate levels of 70 dB(A) causes changes in the adrenal cortex and heart tissue. When this sound intensity is sufficiently severe by duration of exposure, some animals suffer irreversible cell damage leading to cell death. If exposure to uniform stimulation can lead to the hearing loss, it is rather exposure to the irregular stimulation may lead to more disorders due to repeated activation of neuro-endocrine system.

The association between noise exposure and manifestation of damage deserves more attention due to the long-term consequences in terms of serious risk to health.


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