[Functional ultrastructure of the thyroid gland in rats].

Thyroid gland from normal and hormonally influenced rats (by application of exogenous Triiodothyronine and Thyroid stimulating Hormone), were investigated by means of classical electron microscopy. Dense granules, micropinocytotic and macropinocytotic structures were observed similarly as was already published. Triiodothyronine and Thyroglobulin were localized by affinity cytochemistry on ultrathin cryosections from normal rat thyroid gland. These method showed, that particular endocytotic and exocytotic structures can't be distinguish only by simple morphology and that functional status of these structures can be evaluated only by detection of contained molecules. Triioodthyronine was observed by affinity cytochemistry in multivesicular bodies and in lateral intercellular spaces. That findings indicate, that Triiodothyronine is internalized (transcytosed) by Receptor-mediated endocytosis. Affinity cytochemistry is useful for study of triiodothyronine and thyroglobulin movement in the thyroid gland.