Structure of the secretory cells of male and female adult guinea pigs Harderian gland.

The main objective of this study was to investigate the structure of the Harderian gland (HG) in male and female guinea pigs. A total number of sixteen animals of 4 months age were divided according to sex into two groups; eight animals each. Unfixed glands were weighed and their length and width were measured. Specimens from fixed glands were processed and examined using light, transmission electron microscopy and immunohistochemistry for the detection of the presence of chromogranin A (CgA). The gland consisted of a well-developed duct system which included both intra and extra parenchymal ducts and secretory end pieces lined by many types of cells of variable morphological features and modes of secretion. However, the holocrine mode of secretion was rare as mitotic figures were occasionally present. The interstitial cells included fibroblasts and immune cells (mast cells, lymphocyte, plasma cells and macrophages). The secretion produced by the gland included lipid, protein, neutral mucin and CgA which may be a newly identified constituent of biologically potent proteins stored in the cells of the guinea pig HG. Neutral mucin and CgA may function in photoprotection. The gland revealed sexual dimorphism in mast cells and blood capillaries number and chromogranin secretory activity.