Ultrastructural localization of thyrocyte acid phosphatase in the presence of thyrocyte hyperfunction in rats

Acid phosphatase was found by electron microscopy in the lysosomes which appeared in great numbers in the follicular cells of rat hyperplastic thyroid gland. The other types of granules (mature secretory granules and lipids) whose amounts were also greatly increased in cases of functional thyrocyte strain were also nonreactive. The lysosomes were subdivided into three main groups according to distribution of the reaction product: the lysosomes with dense homogeneous deposit and with deposit in the form of densely or loosely packed dark round granules. The lysosome heterogeneity was apparently connected with their different functions also found within the colloid droplets in the form of inclusions of rarely located dark granules. The authors believe such granules to be the result of the merging of the colloid droplets and lysosomes. The acid phosphatase of the latter participated in the hydrolysis of the product of cell secretion with the formation of active substances.