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The effect of hypothermia on thyroid function in rats

Introduction: Hypothermia has biological and physiological effects on the endorine system. The present study was undertaken to evaluate the effects of hypothermia on the thyroid function of rats. Material and Methods: Serum total T4, total T3, TSH, free T4 (FT4) and free T3 (FT3) were investigated in ten male albino Wistar rats (with an average age of 8 months) The rats were exposed to hypothermia for two hours. The body temperature was kept constant at 25°C. Serum thyroid hormone levels were measured before and immediately after hypothermia and then it was measured every 24 hours for four days. Results: The data showed variations of thyroid hormone during hypothermia. In comparison to basal level (before hypothermia) TSH level changed during the period of hypothermia but it was not statistically significant. T4, FT4 and FT3 decreased after hypothermia and it was statistically significant (p<0.002), while T3 increased significantly (p<0.005) during exposure to hypothermia after 48 hrs. The largest decrease was in FT4 and FT3. The decreasing level of FT4 did not reach the basal level even 96 hours after hypothermia. The concentration of T4 was statistically significant until 48 hours postexposure. it increased after 72 hours but did not reach the basal level. Conclusions: Hypothermic exposure had opposite effects on total thyroid hormones and their free fractions. The results of this study showed a decrease in thyroid gland activity and hypothalamo -hypophyseai axis, with a more pronounced effect on the thyroid gland.