[Comparative morphological properties of different hepatoid glands: histological variants and the morphofunctional unit].

Three groups can be recognized in the type of hepatoid glands: glands synthesizing protein alone, glands synthesizing protein and hydrophobic lipids and/or melanin, and intermediate glands. Histological variants (seven in total) can be recognized within each group. Different possible combinations of hepatoid glands with other derivatives of hair follicles are considered. The first definition of the morphofunctional unit of the hepatoid land is proposed.

[Unknown hepatoid glands of some species of cats and deer]. / Neizvestnye gepatoidnye zhelezy nekotorykh koshach'ikh i olen'ikh.

Our histological description of the fourth type of mammalian skin glands--hepatiod glands--allowed us to revise the obtained and published data mistaking the alveolar glands of the anal sacs in cats and the limb glands in deers as sebaceous. Large clusters of hepatiod glands were discovered in the anal sacs of the cat, lynx, and tiger, interdigital gland of elk, and the tarsal gland of reindeer. These glands secrete considerable amounts of protein to the clearance of the intercellular canaliculi and contain hydrophobic lipids. The available data substantiate revision of the data on the structure of many skin glandular organs with atypical sebaceous glands.

[Contradictions in modern data on the structure and function of dog hepatoid circumanal glands]. / Protivorechiia sovremennykh dannykh otnositel'no stroeniia i funktsii gepatoidnykh tsirkumanal'nykh zhelez sobaki.

Since the 1950s, an erroneous viewpoint has gained a foothold in the special and reference literature that dog hepatoid circumanal glands have an abortive nature, lack efferent ducts, and show no signs of secretory activity. Nevertheless, most modern researchers indicate that these glands are actively functioning structures differentiated to exercise some function according to their histological pattern; however, no one has managed to define this function. The latest international publication (Atoji et al., 1998) considers dog circumanal hepatoid glands as a "circumanal body" similar to epidermis rather than glands. We discuss strong and weak points of the data on dogs hepatoid circumanal glands published in 1950s-1990s in comparison with those obtained in our purposeful long-term investigation of various hepatoid glands. We strongly disagree with the viewpoint of Atoji et al. (1998); hepatoid circumanal glands of dog and other canids should be considered as odor glands, their abundant protein secretion covers the skin surface in the circumanal region, it is preserved on fecal marks, and its smell is perceived during mutual nosing of the anal region.

[Once more about hepatoid circumanal glands of dogs. History of their discovery and reasons for revision the structural and functional data]. / Eshche raz o gepatoidnykh tsirkumanal'nykh zhelezakh sobaki. Istoriia ikh otkrytiia i prichiny peresmotra svedenii ob ikh stroenii i funktsii.

In the skin surrounding the anus in dogs and other Canidae, there is a glandular sheet consisting of strongly developed hepatoid glands, as well as single apocrine glands and a certain number of sebaceous glands, which are much smaller and occur less frequently than the hepatoid glands. All three circumanal glands have excretory ducts connecting with the hair bags (hair funnels). The hepatoid glands of some Canidae and Bovidae were extensively studied in the 1920s-1930s, but from the beginning of the 1950s until the present, as a result of the often repeated mistake passing from one book to another, old information about the hepatoid glands was fully lost, while the new information does not answer the question about the function of this complex and well developed structure. We were successful in repeating the data of the discoverers of the hepatoid glands and proved that these glands are exocrine and that their cells excrete protein to intercellular channels and then to ducts and hair funnels. According to the published data, the odor of the secretory substance of the circumanal hepatoid glands is essential for communication in wolves and dogs.

[Detection of hepatoid glands and distinctive features of hepatoid acinus]. / Obnaruzhenie gepatoidnykh zhelez i otlichitel'nye cherty gepatoidnogo atsinusa.

In the 1920s-1930s, skin glands of a new type, hepatoid glands, were described in 13 mammal species (Rodentia, Canidae, and Bovidae). The hepatoid glands resemble sebaceous glands in their morphology, bur radically differ from them in specific structure of the acinus and another type of secretion. Later, these data either could not be confirmed or were considered insignificant and the hepatoid glands were described as modified sebaceous glands, glands with uncertain function, or modifications of epidermis. Based on the studies of various hepatoid glands in 22 species of Carniviora and Artiodactyla, the authors described in detail the characteristic features of the hepatoid acinus, which allow a precise discrimination of hepatoid and sebaceous glands. Extracellular secretory canaliculi have been described in the hepatoid glands, as well as the richness of hepatoid glands in protein, distribution of hydrophobic lipids in certain hepatoid glands, and formation of excretory ducts and cysts. The hepatoid glands are a source of great amounts of protein secreted in the merocrine way; the secretory substance of some of these glands has a strong odor.

[The caudal gland in the cat is a hepatoid gland]. / Khvostovaia zheleza koshki--gepatoidnaia.

The cat supracaudal gland is usually considered as a conglomeration of massive sebaceous glands, although the author of the only detailed description of its structure stated that it is a hepatoid gland (HG) of lower order. Investigation of the supracaudal gland in adult cats of both sexes showed that it is a massive layer of HGs opening either into dilated follicles of coarse hairs or into large cisterns. These glands possess all features specific for HGs: polyhedral cells, a network of intracellular canaliculi, abundant cytoplasmic protein granules, release of protein structures from the cells to adjacent canaliculi. The reasons for misinterpreting certain structural properties are discussed. It was shown that the cat caudal gland is a typical "embryonal" HG previously described in dogs and certain hollow-horned ruminants. They secrete protein and hydrophobic lipids, have wide excretory ducts, are connected with coarse hairs, are devoid of cysts, and have no sexual dimorphism. Formation of cisterns, special secretion receptacles of the cat supracaudal gland, was monitored. It begins with stagnation of the lipid-protein secretion in the hair follicle and progresses until transformation of the whole glandular lobe to the cistern and dissolving of the hair shaft in it.

[The sex dimorphism of the hepatoid circumanal glands in the dog and the dynamics of its development]. / Polovoi dimorfizm gepatoidnykh tsirkumanal'nykh zhelez sobaki i dinamika ego razvitiia.

The histology of sexual dimorphism of the dog hepatoid circumanal glands has not been studied before. Studies of hepatoid and other skin glands of the circumanal region of adult dogs and puppies (1 and 38 days) of both sexes have shown striking differences in the structure of this region in adult males and females and complete qualitative similarity in puppies of the both sexes. The hepatoid glands of adult males form a massive glandular layer comprising 91% of the skin thickness and supplanting all other glandular types. In adult females these glands are reduced to widely spaced islets (12% of the skin thickness), and the apocrine glands are the prevailing glandular type (53%). The hepatoid glands of puppies of the both sexes develop according to the same structural scheme, approaching rapidly to the glands of adult males. In female puppies they develop more rapidly, and at the age of 38 days their absolute size (length of glandular lobes) is already thrice that of adult females. The hepatoid glands of adult females undergo a very significant regress and possess several structural features suggesting their degeneration.

[Cysts of the hepatoid glands]. / Tsisty gepatoidnykh zhelez.

Cysts are specific rounded closed structures characteristic of some hepatoid glands. They never occur in other cutaneous glands of mammals. The cysts of the circumanal hepatoid glands of the dog and polar fox, the violet gland of the polar and common red fox, and the groin pouches of three species of gazelles were studied. The cyst is enclosed in a cellular wall saturated with glycogen. The amorphous content of the cyst is rich in hydrophobic lipids and it also contains protein. The cysts of the dog and gazelle contain also carboxylated mucopolysaccharides. The amorphous masses of the cyst are surrounded by concentric fibers rich in sulfated mucopolysaccharides. It was shown, using the circumanal glands of adult male dogs, that cysts are permanently formed from single secretory cells capable of synthesizing hydrophobic lipids before their destruction. During the involution of the hepatoid cysts (circumanal glands of an old female dog), whole acini and glandular lobes transform into cysts.

[New data on histological variants of hepatoid cells: the succession of histological variants in the histogenesis of the circumanal glands in the dog]. / Novye dannye o gistologicheskikh variantakh gepatoidnykh zhelez: smena gistologicheskikh variantov v gistogeneze tsirkumanal'nykh zhelez sobaki.

Studies on the circumanal skin of a three-week-old puppy have shown that, contrary to the adult dogs, sebaceous glands are absent here (although they are well-developed in other skin sites of the puppy). Hepatoid glands accompany every hair follicle; they differ considerably from hepatoid glands of adult dogs. Hepatoid circumanal glands of the three-week old puppy are represented by two histological varieties of this glandular type which are capable of producing hydrophobic lipids, are rather poor in protein, and do not possess cysts--while in adult dogs they are represented by only one variety incapable of synthesizing lipids, extremely rich in protein, possessing numerous cysts. Discussion concerns histogenesis, distribution, and function of certain hepatoid gland varieties which were first described by the authors in their previous publication.

[Histological variants of the hepatoid glands in representative Canidae and Cavicornia: the structural and histochemical characteristics]. / Gistologicheskie varianty gepatoidnykh zhelez u predstavitelei volch'ikh i polorogikh: strukturnye i gistokhimicheskie kharakteristiki.

Both the original material and the data from literature collected in two previous papers, show a considerable diversity of structure and secretion of the glands which constitute the hepatoid gland type. According to the body of available histological (including morphometrical) and histochemical data, the authors distinguish: a) features characteristic of the hepatoid gland type only which do not appear in other types of skin glands; b) seven histological varieties within the hepatoid gland type. These seven varieties can be united, according to the laws of their structure and function, into two groups (1-3 and 5-7), with an intermediate variety (4) between them. The first group includes hepatoid glands of the "classical" structure which has been previously detaily exampled by circumanal glands of the dog: these glands possess cysts, produce a purely protein secretion; the secretion type is merocrine. The second group comprises mero-holocrine hepatoid glands which are characterized by the absence of cysts, broader excretion ducts, and a capability to produce, besides protein, considerable amounts of melanin and/or hydrophobic lipids.

[The histological and histochemical characteristics of the hepatoid circumanal glands in the dog: the features of similarity and difference with the skin glands of other types]. / Gistologicheskie i gistokhimicheskie kharakteristiki gepatoidnykh tsirkumanal'nykh zhelez sobaki: cherty skhodstva i razlichiia s kozhnymi zhelezami drugikh tipov.

Three types of skin glands, the derivatives of the outer root sheath of the hair follicle, have been compared, which are represented by hepatoid, sebaceous and apocrine sweat glands. There are three characteristic properties inherent to hepatoid glands, existence of a network of intercellular secretory tubules, lysis of some secretory cells during the duct formation which is not the fatty transformation and cyst formation.