Effect of Cold Exposure on Serum DBH and Interscapular Brown Adipose Tissue MAO Activity in Hypothyroid T3- and T4-Treated Rats
As the indicators of sympathetic nervous system (SNS) function, the activity of serum dopamine-?-hydroxylase (DBH) and interscapular brown adipose tissue (IBAT) monoamine oxidase (MAO) were examined in rats that were chemically thyroidectomized (TX), treated with thyroid hormones, and exposed to cold (4C). In TX animals, body temperature (bt) significantly decreased, and relative IBAT mass increased as compared with control, euthyroid animals, independent of the ambient temperature. The bt fall in TX cold-exposed animals was more severe, provoking hypothermia after 4 h. Under the same experimental conditions, the SNS function was enhanced as judged by the increased serum DBH and IBAT MAO activities. The treatment of TX animals with T4 and T3 re-established the temperature (bt was at the level of controls) and sympathetic homeostasis (DBH activity was at the level of controls) in animals maintained at room temperature but not in those kept under cold conditions. T4 and T3 did not affect IBAT MAO activity of TX rats
cold dbh mao t3 t4 ibat