Thyroid calorigenesis and oxidative stress: modification of the respiratory burst activity in polymorphonuclear leukocytes.

1. Recent research on experimental animals indicates that thyroid hormone administration is associated with greater electron flow through the microsomal, mitochondrial, and peroxisomal electron transport systems of the liver, as indicated by the enhanced production of superoxide radicals (O2.-) and/or hydrogen peroxide (H2O2). 2. Hyperthyroidism induces an increased respiratory burst activity in rat and human polymorphonuclear leukocytes, an effect that seems to be related to changes in the myeloperoxidase-H2O2 system of the cell, rather than to the direct actions of the hormone or changes in the opsonic capacity of plasma. 3. These findings indicate that thyroid calorigenesis involves an elevated prooxidant activity in target cells, which may be relevant in determining toxic effects within the tissue or in neighboring cells.