Abstract
Histochemical properties of the pigment accumulated in Harderian gland of the rat closely resemble to those of lipofuscin. However, it should be assumed to be a unique type of pigment, for it is mainly composed of porphyrins. In fluorescent microscopy, not only a strong brightly red fluorescence is noted in the pigment in the glandular lumina and in the free margin of the glandular cells, but a weak diffuse red fluorescence is also observed in the cytoplasm. This fact indicates that porphyrins of this pigment are produced within the glandular cell and then retained in the glandular lumina. At the same time a large amount of fatty substances are demonstrated in both the glandular lumina and the cytoplasm, mixed with the pigment.
Electron microscopically, it is possible to differentiate two types of glandular cell, i. e. clear cells and dark cells. The cytoplasmic matrix of the dark cell is remarkably higher in electron density than that of the clear cell. The mode of secretion in this gland belongs to the apocrine type, and only dark cells take part in secretion. In the cytoplasm of the glandular cells a number of specific granules, 70-300Å in diameter, can be observed, which are very high in electron density, suggesting the complex salts of porphyrin and a certain metal. Most of the granules are attached to the endoplasmic reticulum and to the internal surface of the vacuoles within the cytoplasm. The glandular lumina are filled with degenerated organella, mainly consisted of crooked tubules, suggesting to be degenerated endoplasmic reticulum, but there is no electron dense granule as mentioned above.
