Differences in thyroidal iodine concentration and T/S ratio among strains of mice and rats

¹ National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

The weight, stable iodine concentration and thyroid-to-serum (T/S) ratio of the thyroid gland was measured in 12 strains of mice and 4 strains of rats. Strain differences of as much as twofold in thyroidal iodine concentration usually increased with age. Mean thyroidal iodine concentration tended to vary inversely with T/S ratio in mice and directly in rats, but no intrastrain correlation was apparent, nor was there a consistent sex difference. The thyroidal iodine concentration was not consistently related to T/S among the strains of mice or rats on stock diet. Therefore, iodine concentration in the thyroid and genetic constitution are only two of many factors responsible for the level of the T/S ratio.