Immunohistochemical localization of thyroxine (T4) and triiodothyronine (T3) in the rat thyroid gland under various experimental conditions.

Detection of T4 and T3 in paraffin sections of the rat thyroid gland in various functional states was attempted by an immunoenzyme technique. Both hormones showed a similar localization, being detected mainly in the colloid in the follicular lumen, and sometimes in certain regions of the cytoplasm of the follicular epithelium. Following administration of TSH, their stainability was increased, and the localization within the cytoplasm became more remarkable. Decrease or disappearance of stainability was observed after hypophysectomy or administration of PTU. These findings support the view that the immunostainability of T4 and T3 is closely correlated with the functional state of the thyroid gland.