Abstract
Initially, morphological and endocrinological features of the thyroid gland are reviewed in view of the recent progress in thyroidology. The second part of this article deals with morphology and hormone measurement in the rat following drug-induced alteration in thyroid function. Single and short-term injection of hypothalamic thyrotropin-releasing hormone (TRH) resulted in an increase in serum TSH concentration but not in thyroid hormone concentration. Electron microscopic observation revealed that augmented TSH stimulation after administration of TRH, induced follicular exocytosis, followed by endocytosis. The increase in colloid droplet counts after TRH-treatment differed between follicles as well as between follicular cells in the same thyroid. Treatment with the antithyroid drug, propylthiouracil (PTU) caused a progressive decrease in serum thyroid hormone levels and an elevation of serum TSH. The earliest morphological changes in follicular cells after short-term administration of PTU were the appearance of subapical vesicles and colloid droplet formation in response to the elevated level of serum TSH. Conversely, prolongation of goitrogen-treatment led to the disappearance of exocytotic and endocytotic vesicles. Substained decrease of serum TSH after thyroxine (T4) treatment led to colloid and thyroglobulin (Tg) accumulation in the follicular lumen and to the disappearance of exocytotic and endocytotic vesicles. In the T4-treated rats hypothalamic stimulation (TRH injection) resulted in a rise in the serum level of TSH, accompanied by apparent colloid droplet formation in the follicular cells.
