Ultrastructural studies on apical blebs of striated ducts in the rat submandibular gland.

Apical blebs of rat submandibular gland striated ducts were studied by electron microscopy. The glands were stimulated by starvation of the animals for 24 h whereafter they were fed 15 min before death and tissue removal. After stimulation most striated duct cells developed apical blebs, with various shapes and usually without granules and vesicles. A semi-separating filamentous structure separates the cell from the content of the bleb. Apparently only the vesicular and granular content can pass through this structure and enter the bleb. Following the appearance of small ruptures in the bleb membrane, the bleb is discarded into the lumen of the duct where it disintegrates. Typical wall-like protrusions on the luminal surface of the duct cell, are probably, rudiments of the ruptured bleb membrane. It is suggested that the apical blebs are manifestations of apocrine secretion.