ABSTRACT
OBJECTIVES: Traffic noise, as one of the noise types, is a widespread feature of the urban environments. Traffic noise exposure can lead to hearing loss, hypertension, obesity and ischemic heart diseases. Thyroid hormones involved in the physiological and pathological conditions of the body. Therefore, this study was designed to aim the evaluation of traffic noise effects on thyroid hormones secretion and thyroid tissue structure. METHODS: Seventy two males and females wistar rats were used in this study. After one week adaptation, they divided randomly into 12 groups; the control, short term (one day) and long term (one, two, three and four weeks) groups. Traffic sound was recorded, adjusted and played (86 dB) for animals. Female rats' cycle estrus was matched. At the end of experiment, the animals were anesthetized and cardiac blood sample was drawn. Thyroid tissue was then removed. Levels of the T3, T4, TSH, corticosterone and H&E staining were measured. p<0.05 considered to be statistically significant. RESULTS: Findings showed that in the one-day group, T3 levels increased and T3 levels decreased in the long term groups (p<0.05). In the same way, concentration of TSH decreased in the one day, while they increased in the one, two, three and four weeks' groups (p<0.05). Histopathological evaluations showed that in the female and male animals, long-term traffic noise increased the full follicles and decreased empty follicles (p<0.05). CONCLUSIONS: This study revealed that traffic noise exposure led to increase of T3 plasma concentration and decrement of TSH level, although in the long term, they return to basal status. It may be due to adaptation to traffic noise.
