Origin and Early Development of Canine Circumanal Glands

Abstract

SUMMARY Integument taken from the canine circumanal region was serially sectioned (for light microscopy) to study the circumanal glands which have hepatocyte-like cells (HCG). Primordial HCG, located in a circular zone around the anus between the inner and the outer zones of sebaceous glands, were present in pups at birth as distinct entities. The HCG were not present in fetuses at gestational day 38. The first set of HCG developed from ducts that originated from the inner and the outer perianal sides of the external root sheath of hair follicles. After pups were born, growth of HCG was rapid within 60 days; the ducts branched considerably, but remained solid, and acini were organized. Each acinus consisted of a lining basal cell layer and polyhedral inner cells. After 60 days, growth slowed and cysts appeared in the ducts. A second set of glands, termed transitional (TrHCG), was seen in pups at 20 days after birth; cells had developed within the deep poles of sebaceous glands located on either side of the HCG gland region. By 152 days after birth, cysts were evident within ducts of the TrHCG. These cysts were interpreted as unsuccessful attempts to form a lumen for an exocrine duct. The HCG which had a more highly developed connective tissue stroma than TrHCG, contained an extensive capillary bed similar to the stroma of endocrine glands. Cytoplasmic granules were observed, and their presence suggested that HCG cells might function to release a secretion into the vascular bed. These observations led to the conclusion that HCG do not result from abortive attempts to form sebaceous glands. Instead, the HCG developed directly from hair follicle sheath cells, and the TrHCG developed later within the deep poles of sebaceous glands. Thus, the hepatocyte-like cells are distinct entities closely related to sebaceous glands in their development. In addition, these cells do not fit into the exocrine gland category because they do not have patent ducts to the skin surface.