The Influence of Hypothermia on Thyroid Function in Rats

He study was designed to investigate the influence of hypothermia on thyroid gland function and its role in metabolic balances.
Materials and Methods: Superficial hypothermia, bringing the body temperature to 25°C, was induced in ten rats (albino, Wistar race) with a mean age of 8 months. Serum levels of FT3, FT4, T3, T4, and TSH were determined before and just after hypothermia, repeated every 24hours for 4 days.
Results: Hormone levels, measured by radioimmunoassay, changed during the study. On different days of study, TSH levels altered, although not significantly, from basal values. Other hormones, decreased significantly after hypothermia, except for T3 that increased significantly on day 3 compared to basal levels. FT3 and FT4 showed the most decrease. Serum T4 level decreased significantly until 48 hours following hypothermia, after which the decrease was not significant and thereafter began to rise and return to basal levels. Although the body temperature of rats decreased significantly after hypothermia, it increased the day after hypothermia and reached closer to body basal temperature (37°c) after 96 hours.
Conclusion: Our findings indicate reduced activity of the thyroid gland and hypothalamus-pituitary axis during hypothermia, this being more prominent in the thyroid gland.