Antioxidants Delay the Onset of Thyroiditis in Obese Strain Chickens*

Abstract

Dietary iodine has been shown to be important in the induction of thyroiditis in susceptible chicken strains although the underlying mechanism remains unknown. Iodine may exert its effects through the formation of reactive oxidative radicals which would cause thyroidal injury and initiate infiltration. We have tested this hypothesis by examining the ability of butylated hydroxyanisole (BHA), ethoxyquin, and other antioxidants to prevent thyroiditis in Obese strain (OS) chickens, a strain that develops severe disease by 4 weeks of age. BHA, when administered from hatching until death at 5 weeks of age, reduced thyroidal infiltration and serum levels of antibodies binding thyroglobulin, T3, T4. Similar effects were observed with the antioxidant ethoxyquin. Weaker antioxidants such as vitamins C and E and beta-carotene had only slight or negligible effects on these parameters. BHA reduced thyroiditis in OS chicks killed at 3 and 5 weeks of age, but not at 8 weeks. When BHA treatment was initiated after the development of severe disease, it did not reduce thyroglobulin antibody levels. To determine the mechanism by which BHA reduces thyroiditis, studies were performed to assess the effect of BHA on thyroid function and on the immune responses to exogenous antigens. BHA had no effect on thyroid function in normal strain chickens since thyroidal radioiodine uptake and organification and serum T3 and T4 levels were unaffected. BHA did not alter immune responses to exogenous antigens such as sheep red blood cells or Brucella abortus in OS chickens. In summary, potent antioxidant drugs delayed the onset of thyroiditis when treatment was initiated before the onset of disease, suggesting that reactive oxygen intermediates are involved in the early stages of pathogenesis. However, the site of action remains unknown since they had no detectable effects on thyroid function or general immune responses.