Effects of indomethacin on thyroid iodine metabolism

Several alterations of thyroid function parameters have been reported in animals treated with indomethacin, and we have studied the effect of this drug on the intrathyroidal iodine metabolism in Wistar rats. Indomethacin was administered by an esophagic tube in two doses (total = 6 mg) given at 0 and 5 hours in experiment I and three doses (total = 9 mg) given at 0, 10 and 23 hours in experiment II. No significant differences in thyroid weight, thyroidal 131I uptake and (131I) iodoaminoacids distribution was observed between the controls and indomethacin treated rats in experiments I and II. In experiment II the intrathyroidal protein bound 131I was not affected by indomethacin, but the extrathyroidal protein bound 131I was markedly affected by the drug, with 72% inhibition. Thyroid peroxidase activity was scarcely affected by the action of the drug. In experiment I indomethacin produced a reduction in serum total thyroxine (T4) of 52%, with a significant elevation in serum total triiodothyronine (T3) of 37%. In experiment II the serum total T4 and T3 levels in indomethacin treated rats were significantly reduced when compared to those of the control rats (77% and 56%, respectively). Serum thyrotropin (TSH) levels did not change in any of the two experiments. In summary, we have found that administration of indomethacin to rats causes an inhibition of thyroid function, measured by decreased thyroid hormone blood levels, without any change in the iodine organification process in these glands.