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

Abstract

""-' Rats with a cutaneous burn exhibited a burn-size-related . depression of sertim thyroid hormones 2 weeks after Lnjury. Thyroidectomized rats had a marked rise in brain in vitro T4 f deiodination to T3 and in serum TSH concentration compared to controls. These normal responses to depressed thyroid hormones were S 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. Shirani et al. (1985) have reported depressed total and free concentrations of thyroxine (T4) and triiodothyronine (T3) in burned rats and suggested the burned rat as a model for human nonthyroidal illness (NTI). INTRODUCTIONIt is not yet known whether burn injury and other NTI represent conditions of hypothyroidism. We now assess whether serum thyrotrophin 'Sr) and brain T4 to T3 deiodinating capacity respond as expected for hypothyroidism in the burn model.

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