Thyroid and Related Changes

Astwood, Sullivan, Bissell, and Tyslowitz (90) reported very similar results and reached somewhat similar conclusions. These investigators found sulfadiazine to be by far the most active sulfonamide tested although less active than thiourea. They postulated that a single hypophyseal factor is concerned with both hyperplasia and oversecretion of the thyroid, The sequence of events they consider to be as follows First, inability of the organism to synthesize thyroid hormone at a normal rate, with consequent reduction in the amount of circulating hormone second, a resultant production of excess thyrotropin by the pituitary which stimulates the thyroid to hyperplasia and to the release of the thyroid hormone stored therein and, third, a reduction of the BMR due to exhaustion of the stored thyroid hormone plus reduction in its rate of synthesis. 

Franklin and Chaikoff (91) have presented evidence which indicates that the mode of action of the sulfonamides in preventing the synthesis of thyroid hormone is by interfering directly with the conversion of inorganic iodide to diiodotyrosine and thyroxin. By means of in vitro experiments with radioactive iodine as indicator, they w ere able to demonstrate that sulfonamides do not interfere with the capacity of surviving thyroid slices to remove iodine from Ringer s solution but do interfere with its introduction into the benzene ring. 

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