SUMMARY 1. The incorporation of 131I into the thyroid and the secretion of labelled thyroid hormones from the gland have been studied in living animals and in vitro in rats of both sexes from the Maudsley Reactive and Non-reactive strains, selectively bred for emotional defecation. 2. The rate of uptake of 131I in living animals differed significantly in the two strains, being slower in the high defecating strain than in the low defecating one. 3. The rate of excretion of thyroid hormones from the gland was also different in these rats both in vivo and in vitro; it was slower in the high defecating than in the low defecating strain. 4. The size of the thyroids differed significantly; the wet weights of the gland of the rats of the high defecating strain were higher than those of the low defecating strain. 5. The water content of the thyroids of the high defecating strain was higher than in the low defecating strain. 6. Histology of the thyroids showed that the glands of the high defecating rats contained proportionately less secretory epithelium and more colloid and intercellular tissue than the glands of the low defecating rats. 7. The thyrotrophic hormone (TSH) content of the serum and the pituitary differed in the two strains. In the high defecating strain the level of TSH in the serum was lower and in the pituitary higher than that in the low defecating animals.
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Feuer et al. (1962) studied this question.