THE ANTITHYROID ACTIVITY OF THE ANTICOAGULANT PHENYLINDANEDIONE

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Abstract
SUMMARY 1. The anticoagulant drug phenylindanedione (PID) reduced the uptake of 131I by the rat thyroid as effectively as propylthiouracil (PTU) in a dosage of 0·3 m-mole/kg body weight. The effect of PID lasted for a shorter time, and at smaller doses PTU was much more effective than PID. 2. Chromatography of digested thyroid tissue showed that PID exerts its antithyroid action by blocking the organic binding of iodine. 3. Vitamin K1 did not overcome the antithyroid action of PID. Among other anticoagulants and chemically related compounds tested only phthiocol was found to have an antithyroid effect. 4. In five out of seven patients receiving PID the 48 hr thyroid 131I uptake was at or below the lower limit of the normal range. Three of these patients were retested after stopping PID, in each case the thyroid uptake was markedly increased. 5. The chemical grouping was noted to be common to phthiocol, PID, and various other antithyroid compounds. The anticoagulant action of PID has also been attributed to this configuration, and the suggestion is made that this is the active grouping in the antithyroid action of PID and phthiocol, and that a vitamin K-like substance may be concerned in thyroxine as well as prothrombin synthesis.