The Thyroid Axis and Brain 5'-Monodeiodination of Thyroxine in the Burned Rat Model of Nonthyroidal Illness

Rats with a cutaneous burn exhibited a burn-size-related depression of serum thyroid hormones 2 weeks after injury. Thyroidectomized rats had a marked rise in brain in vitro T4 deiodination to T3 and in serum TSH concentration compared to controls. These normal responses to depressed thyroid hormones were not seen in burned rats. The depression of serum thyronines and thyrotrophin suggests that the burned rat may be a model for human burn injury and other nonthyroidal illness. In this model it appears that the brain and pituitary do not respond as in thyroidectomy, suggesting lack of true hypothyroidism in burn injury.