Iodine is an essential nutrient for the normal growth and development of humans and animals and is necessary for normal metabolism and regulation of thyroid hormones. Iodine excess can produce thyrotoxicosis but not cancer. However, radioiodine is carcinogenic for the thyroid gland. Dietary iodine deficiency is associated with goiter in humans and animals. The goiter develops because of a feedback system between thyroid hormones, the pituitary gland, and the hypothalamus, and it regulates the synthesis and release of thyroid-stimulating hormone. Chronic hypersecretion of thyroid-stimulating hormone causes profound goiter (diffuse thyroid hyperplasia)‚ which appears to be related to carcinogenesis. Chronic dietary iodine deficiency in rats leads to thyroid follicular adenomas by 12 months and follicular carcinomas by 18 months. An increased risk of thyroid cancer has been reported in humans with goiter and those living in some iodine-deficient areas of the world. In very recent animal studies, iodine deficiency, chemical goitrogens, and thyroid toxins have been shown to have potent tumor-promoting effects. In rats, iodine deficiency is a much more effective tumor promoter than it is a carcinogen, suggesting that a similar relationship may exist in human populations. These studies suggest that a major role of iodine is to prevent the formation of thyroid tumors in humans and animals.

The role of iodine in carcinogenesis.

Effects of dietary iodine on the induction of thyroid carcinoma using N-nitrosobis(2-hydroxypropyl)amine (BHP) were studied. Male Wistar rats were fed with an iodine-adequate diet (IAD group), an iodine-rich diet (IRD group) and an iodine-deficient diet (IDD group), respectively, until the time of sacrifice. From the 2nd experimental month, animals were injected with BHP once a week for 10 weeks. In the IAD and IRD groups, benign nodules and papillary carcinoma were found. The incidence of rats with benign nodules was 100% in both groups and animals with papillary carcinoma in the IAD and IRD groups comprised 33% and 29%, respectively. The area of the thyroid gland occupied by nodular lesions was much narrower in the IRD group than in the IAD group. In the IDD group, the thyroid showed marked enlargement due to multiple nodular proliferation of follicle cells. The incidence of rats with carcinoma was 100%, and not only papillary but also follicular carcinoma and one pulmonary metastasis were found. As the iodine content of the diet decreased, the nodular lesions increased in width and number, and the incidence of carcinoma in rats became higher. These effects of dietary iodine are probably related to the goitrogenic and/or promoting effects of TSH.

Effects of dietary iodine on chemical induction of thyroid carcinoma.

In vitro formation of a triazene compound by reaction of sulphadimidine and nitrite.

The total weight of both lobes of the goitrous thyroids of rats after receiving amitrole is between 1.0 and 2.5 g (Fig. 202). The surface is usually smooth, but the tissue may adhere to the adjacent fatty or muscular tissue. Occasionally, the enlarged thyroid is surrounded by a mass of coagulated blood, due to the rupture of blood vessels in hypertrophied thyroid tissue. In rats given amitrole after partial thyroidectomy, goiters of various sizes develop from the residual tissue and often have fibrous adhesions to adjacent tissue. In rats subjected to partial thyroidectomy only, the thyroid regenerates to almost the same size and weight as the controls.

Goiter, Adenoma, and Carcinoma of the Thyroid Induced by Amitrole and Ethylenethiourea, Rat

The greatly enlarged thyroid lobes of surviving rats that have received amitrole (0.25% in drinking water) have a combined weight of as much as 1.0-2.5g. The affected thyroids usually appear whitish in color because of their thickened fibrous capsule. Their surface is usually smooth, but the capsule may adhere to the adjacent fatty or muscular tissue. Occasionally the enlarged thyroid is surrounded by a mass of coagulated blood due to the rupture of subcapsular blood vessels in hypertrophied thyroid tissue (Fig. 304).

道人高橋

Papers

Effect of 3-amino-1h-1,2,4-triazole of low iodine diet on rat thyroid carcinogenesis induced by ethylenethiourea

Chronic effects of 1,3-di(4-sulfamoylphenyl)triazene on male icr mice

道人 高橋

Papers

Effect of 3-amino-1h-1,2,4-triazole of low iodine diet on rat thyroid carcinogenesis induced by ethylenethiourea

Chronic effects of 1,3-di(4-sulfamoylphenyl)triazene on male icr mice

道人高橋