It is proposed that the Harderian glands are those ocular glands that have tubuloalveolar endpieces with wide lumina and secrete lipid by a merocrine mechanism.The Harderian gland occurs in various mammals, not only in eutherias but also in marsupials. However, as the gland has hereto-fore been studied almost exclusively in rodents and lagomorphs, it should be studied more in other groups of mammals, especially primitive mammals such as marsupials and insectivores.The secretory duct of the mammalian Harderian gland, as a rule, is single and opens near the third eyelid in the inner canthus. The whale Harderian gland is an exception as it is present as two masses and each of which has multiple excretory ducts. In rodents and lagomorphs, the orbital venous sinus is very well developed and surrounds almost all the orbital contents. Therefore, the surface of the gland is macroscopically smooth.Histologically, the gland has branched tubuloalveolar endpieces with wide lumina, and rarely has a duct system. It is quite difficult to detect a duct in usual histological sections. In rodents, the alveoli often contain two types of glandular cells, however, the significance of the difference between these two types is quite uncertain.The Harderian gland is the sole example in which glandular cells secrete lipid by a merocrine mechanism. The formation process of the secretory vacuoles within glandular cells is not known.In rodents and lagomorphs, the lipid of the gland is mainly either glyceryl ether diesters or wax esters, and similar to sebum. In rodents, the gland often contains porphyrin, but its significance is quite uncertain.The function of the Harderian gland probably varies among mammals. In aquatic mammals, the glandular secretion is thought to protect the eye from sea water. In rodents and lagomorphs, the gland may serve either as a sebaceous or a pheromonal gland.It appears most probable that phylogenetically the mammalian Harderian gland originated from the lacrimal gland of ancestral mammals from which all marsupials and eutherias have descended.

The Mammalian Harderian Gland: Morphology, Biochemistry, Function and Phylogeny

Hiroshi Nikaido Department of Microbiology and Immunology University of California, Berkeley Berkeley, California 94720 Gram-negative bacteria including Esherichia coli and Salmonella typhimurium produce outer membranes that serve as an effective permeability barrier. In order to shut out noxious sUbstances as much as possible, which include the bile salts in the case of enteric organisms, yet allow the rapid influx of nutrients, these bacteria have evolved porins, proteins with channels that are ideally suited for this purpose. Furthermore, the enteric organisms contain multiple species of porins, and have developed an elaborate mechanism of regulating the production of different species of porins so that their chances of survival would be maximized under different environmental conditions, providing us with a remarkable example of ecological adaptation at the molecular level. These porins are also of interest because analogous proteins occur in the outer membranes of organelles of eukaryotic cells, such as mitochondria.

The Cell Membrane

Oleoyl-CoA Is the Major de Novo Product of Stearoyl-CoA Desaturase 1 Gene Isoform and Substrate for the Biosynthesis of the Harderian Gland 1-Alkyl-2,3-diacylglycerol

The Harderian gland.

The harderian gland is an orbital gland of the majority of land vertebrates. It is the only orbital gland in anuran amphibians since the lacrimal gland develops later during phylogenesis in some reptilian species. Perhaps because it is not found in man, little interest was paid to this gland until about four decades ago. In recent years, however, the scientific community has shown new interest in analyzing the ontogenetic and morphofunctional aspects of the harderian gland, particularly in rodents, which are the preferred experimental model for physiologists and pathologists. One of the main characteristics of the gland is the extreme variety not only in its morphology, but also in its biochemical properties. This most likely reflects the versatility of functions related to different adaptations of the species considered. The complexity of the harderian gland is further shown in its control by many exogenous and endogenous factors, which vary from species to species. The information gained so far points to the following functions for the gland: (1) lubrication of the eye and nictitating membrane, (2) a site of immune response, particularly in birds, (3) a source of pheromones, (4) a source of saliva in some chelonians, (5) osmoregulation in some reptiles, (6) photoreception in rodents, (7) thermoregulation in some rodents, and (8) a source of growth factors.

Cell Biology of the Harderian Gland

Biochemical and morphological properties of the Harderian gland of the mouse were examined by combining autoradiographic, biochemical, and electron microscopic techniques. Autoradiographs show that the radioactive carbon from [U-14C]glucose injected into the abdominal cavity is completely incorporated into the acid-insoluble substances within 30 minutes. The results of chemical analysis show that the main components of this gland are glyceryl ether diesters and phospholipids. Scanning electron microscopy shows numerous lipid droplets in the secretory cells and alveolar lumina. Myoepithelial cells lie between the secretory cell base and the basement membrane and have a basket-like distribution of processes as confirmed by hydrochloric acid and collagenase digestions. Myofilaments are demonstrated in the cytoplasm. Two types of secretory cells (A and B) comprise the alveolar epithelium and can be differentiated under the electron microscope. The cytoplasm of both contains numerous vacuoles. The vacuoles are almost empty in A cells, which are a more numerous constituent of the alveolar epithelium than B cells. However, the vacuoles of the B cells contain densely osmiophilic material. In both, cell types show a merocrine mode of secretion. Unmyelinated nerve cell endings occur in the interstices of the connective tissue, and contain clear or cored vesicles.

Masahito Watanabe

Papers

An autoradiographic, biochemical, and morphological study of the harderian gland of the mouse.