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Effect of Potassium Iodide and Duodenal Powder on the Growth and Organ Weights of Goitrogen-fed Rats¹

Department of Biochemistry and Nutrition, Virginia Polytechnic Institute, Blacksburg, Virginia

Two factors which modify the thyroid hormone deficiency produced by the ingestion of thiouracil or sulfaguanidine were studied and certain observations indicate that the mode of action of these two goitrogens are different.

1. The addition of 10 µg of KI/gm of diet markedly inhibited growth, and 30 µg of KI/gm of diet resulted in growth arrest of rats fed 1.0% sulfaguanidine. Growth arrest occurred after 28 days in thiouracil-fed rats when 10 µg of KI/gm were added to the diet. With either goitrogen, growth arrest was accompanied by an increase in the relative weights of the thyroid, adrenals, testes, and the pituitary, and a decrease in that of the thymus gland. The uptake of I¹³¹ and its incorporation into protein by the thyroid gland was markedly reduced. Prolonged feeding of either goitrogen with 30 µg of KI/gm of diet was fatal to some of the rats.

2. Growth and organ weights were maintained at or near normal values when 4% duodenal powder was added to those diets capable of producing growth arrest. Under such conditions, duodenal powder decreased the uptake of I¹³¹ by the thyroid gland but increased the incorporation of thyroidal I¹³¹ into protein. The pattern of response to duodenal powder suggests that this tissue contains thyroid hormone-active material. Since growth arrest could not be induced in rats fed thiouracil plus 30 µg of KI/gm of commercial laboratory chow, it was inferred from these experiments that this diet contains thyroid hormone-active material in the meat meal which is a component of this chow.

3. The relative weights of the thyroid glands from growth-arrested, sulfaguanidine-fed rats were consistently less than that of growth-arrested, thiouracil-fed rats indicating that the mechanism which compensates for low levels of circulating thyroid hormones was inhibited by the sulf-aguanidine under the conditions of these experiments.

Manuscript received 13 August 1962.