Impact of Chronic Noise Stress on Thyroid Health: A Comparative Histomorphological and Endocrine Study in Adult Male and Female Rats.

Objective: To compare the effect of varying durations of noise exposure on the histomorphological and endocrine profile of the thyroid gland in male and female adult rats.

Study design: An experimental study. Place and Duration of the Study: Department of Anatomy, Army Medical College, Rawalpindi / NUMS, from January to December 2020.

Methodology: Thirty Sprague-Dawley rats (15 males and 15 females) were divided into three groups each having 10 rats with equal male- to-female ratio. Group A was the control group. Group B and Group C were exposed to 100 dB noise for 4 hours daily and 100 dB noise for 6 hours daily for 4 months, respectively. Thyroid histomorphological parameters such as follicular epithelial cells' height, follicular diameter, and thyroid stimulating hormone (TSH) levels were evaluated at the end of the study.

Results: Both male and female rats exposed to noise stress exhibited reduced follicular diameter (p <0.001) and increased epithelial cells' height (p <0.001) as compared to the control group. The experimental groups showed significantly higher TSH levels compared to the control group (p <0.001) among female rats, while no significant difference was observed among male rats (p 0.47). No significant differences in histological and serum parameters were noted between the experimental groups (Group B and C).

Conclusion: Chronic noise exposure induces hyperactivity of thyroid follicles in both male and female adult rats as evidenced by the thyroid histology, whereas only female rats showed raised TSH levels, suggesting a potential disruption in the hypothalamic-pituitary-thyroid axis.

Key words: Thyroid gland, Chronic noise stress, Follicular epithelial cells, Thyroid stimulating hormone, Thyroid follicles.