Interstitial porphyrins and tubule degeneration in the hamster Harderian gland.

The Harderian glands of rodents manufacture and store porphyrins and are increasingly used as models for porphyrin biosynthesis. Although porphyrins are normally stored as solid intraluminal accretions, interstitial deposits also occur; in the Harderian gland of the female hamster these are found frequently in ovariectomised or aged animals. The present study (employing double-embedding techniques) suggests that interstitial porphyrin deposits are the result of degenerative processes which conform to an escalating pattern. Initially, tubule epithelial and myoepithelial cells become greatly attenuated and there is neutrophil invasion. Secondly, tubule walls disappear leaving previously intraluminal porphyrin stores free within the interstitium. Finally, large interstitial porphyrin accretions become surrounded by foreign body giant cells or are broken down into smaller deposits within free macrophages. These are often associated with plasma cells. Infiltration of the interstitium by lymphocytes may also occur. It may be that the abnormal localisation of porphyrin in the interstitium (i) evokes an immune response and (ii) is related to elevated blood porphyrin levels found in these animals.