REGULATION OF SUPEROXIDE ANION RADICAL-SUPEROXIDE DISMUTASE SYSTEM INTHE AVIAN THYROID BY TSH WITH REFERENCE TO THYROID HORMONOGENESIS

This study shows that superoxide dismutase is present in the thyroid g land of pigeons as a constitutive enzyme serving as an antioxidant aga inst oxygen toxicity. Exogenous administration of thyrotropin induced thyroidal superoxide dismutase with a simultaneous burst in superoxide anion radical levels during the initial phase of hormone treatment. T he superoxide radical generated was completely scavenged by SOD during the late phase of TSH-treatment, presumably as an adaptive measure to check the oxygen burst. TSH failed to augment serum T-3 levels, altho ugh the thyroxine level in the serum was elevated. The peak level of S OD activity profile in the thyroid gland correlated very well with the peak level of thyroxine concentrations in the serum of pigeon. It is reasonable to postulate that the thyroidal SOD in homeotherms serves a dual role, firstly as a strategic antioxidant enzyme to protect the t hyroid gland against the degenerative influence of toxic oxyradicals a nd secondly to provide H2O2 for thyroid hormone biosynthesis. Our resu lts confirm the previous observations that TSH is mainly thyrotropic i n birds and that it has no influence on the peripheral activation of t hyroxine to triiodothyronine by stimulating the extra thyroidal 5'-dei odinase activity. (C) 1997 Academic Press.