Some features of the structure and histochemistry of the rat parathyroid gland

Summary Some features of the structure and histochemistry of the rat parathyroid gland have been studied using a variety of histological and histochemical staining methods. The gland is composed of a compact parenchyma consisting essentially of a single cell type. The parenchyma is encapsulated by a connective tissue layer which extends into it and holds abundant branches of blood vessels. In the parenchymal cells four types of protein granules are demonstrated by the tetrazonium, DDD-diazo blue B, alkaline tetrazolium and HNAH-diazo blue B methods respectively. The DDD-diazo blue B reactive granules are considered to relate to the secretory activity of the parenchymal cells in view of their morphology and recent biochemical data on the nature of parathyroid hormone. The cytophysiological significance of the other three types of protein granules was discussed on the basis of their morphological features. Besides protein granules the parenchymal cells contain glycogen, RNA and DNA, and are reactive for alkaline phosphatase. The quantity of these substances and the enzyme activity seem to reflect to a certain extent different states of cellular activity. The parenchymal cells show scanty sudanophilic lipid content in paraffin sections and are devoid of basophilic mucopolysaccharides. Further, the cells are negative for acid phosphatase. In the connective tissue stroma of the gland the vascular endothelial cells show high alkaline phosphatase activity, and a hypothesis is presented as to the physiological significance of this high enzyme activity.