A Comparative Study of the Harderian Gland in the Female Rat and Female Rabbit (A Histological, Histochemical, Scanning Electron Microscopic and Morphometric study)

Background: The Harderian gland (HG) is a large retrobulbar, tubuloalveolar organ. It is present in many animals possessing a nictitating membrane (third eye lid). Aim of the Work: Compare the microscopic features of the HG in the female rat (as n example of rodents) with those of the female rabbit (as an example of mammals). Materials and Methods: Using histological, histochemical and morphometric techniques on the HG in adult female rat (3 months old) and rabbit (4.5 months old). A total number of 6 adult animals were used in each species. Results: By gross inspection the Harderian gland is bilobed. In the rat, the two lobes are similar in colour and texture while in the rabbit, the small lobe is white and the large lobe is red (pink). The gland is covered by a thin C.T. capsule with species variations both in structure and auto fluorescence. In the rat the two lobes show a fundamentally similar histological structure and the secretory epithelium is formed of two types of cells, type A and type B. While in the rabbit the two lobes have different histological structure and each lobe is formed of a single type of cells that differs in both lobes. The contents of the lumina of the tubuloalveoli vary in the two species indicating different modes of secretion. Statistical difference in the arbitrary area of the tubuloalveoli between the large and small lobes of the gland is insignificant in the rat but it is significant in the rabbit. In both species a single extra glandular excretory duct is detected at the hilum of the gland. In the rat the wall of the duct possess diverticula and the lining epithelium comprises some serous/or mucous acini. While in the rabbit, the structure of the duct is simple and it is lined by a low columnar epithelium with some goblet cells. Conclusion: Further research will be needed to correlate the different histological structure between the female rat and rabbit HG with the biology of these animals and to their functional significance.