A light and electron microscopic study of the distribution and effects of water-soluble radiographic contrast medium after retrograde infusion into the rat submandibular gland.

For microscopic visualization, horseradish peroxidase (HRP; 10 mg/ml) was added to the contrast medium. Some glands were infused with saline solution containing HRP. During continuous infusion, the intraglandular pressure was recorded. Infusion was stopped at different phases of the pressure curve and the glands fixed by vascular perfusion. Morphological alterations, principally dilatation of the intralobular ducts, were most pronounced in the intercalated duct segment. HRP was first observed in the lumina of the intralobular ducts and acini but gained access to the intercellular spaces thought the apical junctional complexes and subsequently surrounded various cellular components. Eventually the tracer was found in blood and lymphatic vessels. Because of an uneven distribution of the tracer and variation in the degree of filling in different areas of the same gland, the development of the intraglandular pressure could not be directly correlated with specific morphological alterations but is thought to reflect all events occurring in the tissue at a particular time.