Mitochondrial deformation and apocrine secretory mechanism in the rabbit submandibular organ as revealed by electron microscopy

Summary The submandibular organ (a sort of apocrine sweat glands) of the rabbit was observed with the electron microscope. The cell structure of glandular tubules varies depending upon the secretory activity; there are three functional stages. The secretory cells at the resting stage are characterized by low height, absence of secretory substance, and presence of small and slender mitochondria.In the synthesizing stage, enlargement and peculiar deformation of mitochondria are observed. Secretory substance always occurs near the deformed mitochondria. The part of a mitochondrion closely abutting on the secretion mass is extremely thin, and contains longitudinally oriented cristae. Sometimes a direct continuity is observed between the thinned portion of the deformed mitochondria and the mass of secretory substance. It is presumed that the secretion is initially produced in the mitochondria and then discharged from them. The Golgi apparatus and the rough surfaced endoplasmic reticulum may be involved indirectly. Smooth surfaced vesicles, probably related to the transport of raw material, are extremely abundant in the cells of this stage.The development of a generally homogeneous projection into the gland lumen is characteristic of the stage of secretion discharge. The mitochondria are again small and slender, and the secretion is liquefied. At the base of the full-grown projection, cytoplasm is condensed to form a demarcation zone from which the projection may become detached. This mechanism of release of secretory product is quite the same as the so-called apocrine secretory process long postulated by light microscopists.