Limited response to propylthiouracil in the tumor-bearing rat.

The accidental observation that the thyroid gland of the tumor-bearing rat was not enlarged after the oral administration of thiouracil was made while investigating the possible role of the thyrotrophic hormone (TSH) as a fat-mobilizing hormone (14). Further experiments were carried out to ensure that the effect was not limited to a particular strain of rat or type of tumor, or due to the action of inanition on the pituitary (10, 15). The results of these experiments are recorded in this paper, though the underlying mechanism is not understood.