A COMPARISON OF THE EFFECT OF THIOURACIL AND OF INJECTED THYROTROPIC HORMONE ON THE COLLECTION OF RADIOACTIVE IODINE AND THE ANATOMIC CHANGES INDUCED IN THE THYROID OF THE CHICK12

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Abstract
Following adm. of thiouracil to the chick, no anatomic change was observed for 5 days, after which rapid development of hypertrophy and hyperplasia as measured by comparison of thyroid wt. and mean acinar cell height took place. Except for the lag in onset, the histologic changes following adm. of thiouracil were identical with those which follow the daily inj. of thyrotrophic hormone and developed in a similar manner. The thyroid of the chick made goitrous with thiouracil showed a greatly diminished capacity to collect radioactive I. When thiouracil was withdrawn, such thyroids rapidly acquired a capacity to collect radioactive I in much larger quantities than controls and in quantities similar to those collected by thyroids made hyperplastic by the inj. of thyrotrophic hormone. The capacity of thiouracil to inhibit the collection of I by the thyroid may be its essential and primary effect. The development of thyroid hyperplasia which follows occurs later and appears histologically and functionally identical with that resulting from the inj. of thyrotrophic hormone.