Present Status of Thiouracil*
It is now four years since Kennedy and Purves reported the effects of feeding Brassica seed diets to rats,1 the goitrogenic effects of which were later shown to be due to their content of allyl thiourea. Their early studies showed that this goiter-producing effect was absent in hypophysectomized animals.2 Since that time the work of the Mackenzies3 and Astwood4 has been followed by a flood of experimental and clinical literature on the subject.
Thiourea has been shown to produce cretinism in rats5 and to retard metamorphosis in tadpoles.6 Enlargement of the thyroid occurs in rats in a few days on thiouracil feeding and recedes rapidly when feeding is stopped.7 Such glands become highly vascular, with tall columnar cells lining their acini and with a marked decrease in colloid. In the pituitary gland thiourea causes a decrease in the number of acidophile cells and an increase in the basophiles, some of which are vacuolated. All of these changes apparently are due to a disappearance of thyroid hormone, since they can be prevented by giving thyroxin.3
Astwood found an almost complete disappearance of iodine from the thyroid gland of thiouracil-fed rats as early as five days,7 and Larson showed that the thyroid glands of thiouracil-fed chicks8 fail to take up radioactive iodine as well as do normal glands. The adrenal cortex atrophies under the effect of thiouracil,9 and the plasma proteins change with an increase in β globulin, as after thyroidectomy.10
The mechanism by which these actions take place is. . .