The Harderian gland: Endocrine function and hormonal control.

The Harderian gland (HG) is an exocrine gland located within the eye socket in a variety of tetrapods. During the 1980s and 1990s the HG elicited great interest in the scientific community due to its morphological and functional complexity, and from a phylogenetic point of view. A comparative approach has contributed to a better understanding of its physiology. Whereas the chemical nature of its secretions (mucous, serous or lipids) varies between different groups of tetrapods, the lipids represent the more common component among different species. Indeed, besides being an accessory to lubricate the nictitating membrane, the lipids may have a pheromonal function. Porphyrins and melatonin secretion is a feature of the rodent HG. The porphyrins, being phototransducers, could modulate HG melatonin production. The melatonin synthesis suggests an involvement of the HG in the retinal-pineal axis. Finally, StAR protein and steroidogenic enzyme activities in the rat HG suggests that the gland contributes to steroid hormone synthesis. Over the past twenty years, much has become known on the hamster (Mesocricetus auratus) HG, unique among rodents in displaying a remarkable sexual dimorphism concerning the contents of porphyrins and melatonin. Mainly for this reason, the hamster HG has been used as a model to compare, under normal conditions, the physiological oxidative stress between females (strong) and males (moderate). Androgens are responsible for the sexual dimorphism in hamster and they are known to control the HG secretory activity in different species. Furthermore, HG is a target of pituitary, pineal and thyroid hormones. This review offers a comparative panorama of the endocrine activity of the HG as well as the hormonal control of its secretory activity, with a particular emphasis on the sex dimorphic aspects of the hamster HG.

Functional Morphology of the Upper and Lower Eyelids, Third Eyelid, Lacrimal Gland and Superficial Gland of the Third Eyelid in the Red Kangaroo (Macropus rufus).

A study concerning the upper (UE) and lower (LE) eyelids, lacrimal gland (LG), superficial gland of the third eyelid (SGTE) and third eyelid (TE) was conducted on 4 sexually mature red kangaroos (2 males and 2 females). Gross anatomical, histological, histometrical, histochemical and ultrastructural (TEM) components were compared. Tissue sections were stained with haematoxylin and eosin, azan-trichrome, van Gieson, Masson-Goldner trichrome, methyl green-pyronin Y, periodic acid-Schiff, alcian blue pH 2.5, aldehyde fuchsin and Hale's dialysed iron. The location of the LG, SGTE, TE, UE and LE was similar to that of other mammals. Organized lymphoid follicles were also found in the LE. The TE resembled the letter T and was composed of cartilage (hyaline tissue). The LG was relatively larger than the SGTE. The LG and SGTE were multilobar tubuloacinar glands. The LG had more plasma cells than the SGTE. The SGTE and LG secretions were mucoserous in composition. The TEM study showed that the secretory cells of the LG and SGTE have a similar ultrastructural appearance. Two types of secretory vesicles were detected in the cytoplasm in acini and one type of secretory vesicle was found in the tubules of these glands.

Analysis of constant tissue remodeling in Syrian hamster Harderian gland: intra-tubular and inter-tubular syncytial masses.

The Syrian hamster Harderian gland (HG) has a marked sexual dimorphism and exhibits an extraordinary rate of porphyrinogenesis. The physiological oxidative stress, derived from constant porphyrin production, is so high that the HG needs additional survival autophagic mechanisms to fight against this chronic exposure, provoking the triggering of a holocrine secretion in female glands that forms two types of secretory masses: intra-tubular-syncytial and inter-tubular-syncytial masses. The aim of this work was to study the development of this inter-tubular holocrine secretion. To approach this task, we have considered that the steps developed during the formation of the so-called invasive masses consist of the growth of epithelial cells, cell detachment from the basal lamina and invasion of surrounding tissues. The presence of these masses, particularly in the female HG, are closely linked to sexual dimorphism in redox balance and to alterations in the expression of certain factors such as cytokeratins, P-cadherin, matrix metalloproteinases, cathepsin H, proliferating cell nuclear antigen, p53, CD-31 and vascular endothelial growth factor, which seem to be involved in tissue remodeling. The results document unusual mechanisms of secretion in Syrian hamster HG: an extraordinary system of massive secretion through the conjunctive tissue, disrupting the branched structure of the gland.

Light and electron microscopic studies of the Gerbillus tarabuli (Thomas, 1902) Harderian gland.

The purpose of this investigation was to study the morphological aspects of the Harderian gland in Gerbillus tarabuli. Tissues were obtained from both male and female adult Gerbillus tarabuli and processed for light and electron microscopy. The Harderian gland in gerbil is large and well developed, covered by a thin capsule, from which thin septae extend, subdividing the gland into lobes and lobules. The endpieces of the gland are tubuloalveolar, which produce a secretion of lipid character. The glandular epithelium is pseudostratified with two types of secretory cells, the type C cells are columnar in shape with large lipid vacuoles, and type P cells pyramidal and serous, they are basally located with no luminal aspect. The epithelium possesses well-developed myoepithelial cells. The wide lumina are filled with lipid vacuoles, cellular debris, and porphyrins. The Harderian gland of the gerbil has no morphologically distinct duct system; a single extraglandular excretory duct is detected. Electron microscopic examination revealed that type C cells contain large electron-light lipid vacuoles, a well and extensive reticulum endoplasmic and a large number of mitochondria. The pyramidal cells are characterized by a small number of PAS-positive granules at the basal region; these cells exhibit one or two round nuclei, many electron-dense granules, crystalloid bodies, abundant mitochondria and many ribosomes in their cytoplasm. The three mechanism of secretion are seen in the Harderian gland of Gerbillus tarabuli. In its overall characteristics, the Harderian gland of Gerbillus tarabuli conforms to the general pattern observed in rodents. However, further research will be needed to correlate the presence of cytoplasmic slashes, crystalloids bodies and glycoproteins in epithelial cells with the biology of these animals and to their functional significance.

Molecular cloning and multifunctional characterization of host defense peptides from the bullfrog Harderian gland with special reference to catesbeianalectin.

The Harderian gland (HG) is an orbital gland found in many terrestrial vertebrates that possess a nictitating membrane. Using reverse-transcription polymerase chain reaction (RT-PCR), we cloned five cDNAs encoding antimicrobial peptide (AMP)-homologs, catesbeianalectin, ranacyclin-CBa, ranatuerin-1CBa, ranatuerin-2CBa, and ranatuerin-2CBb, from the bullfrog HG total RNA. Of these, catesbeianalectin has not been thoroughly studied in terms of its biological activities. We examined antimicrobial activities of the synthetic replicate of catesbeianalectin and its putative unprocessed precursor, catesbeianalectin-GK. Both peptides showed slight but significant growth inhibitory activity against the Gram-negative bacterium Escherichia coli. Subsequently, we tested catesbeianalectin and catesbeianalectin-GK for mast cell degranulation activity as a criterion of the release of N-acetyl-ß-D-glucosaminidase from the mouse-derived mastocytoma cell line P-815, followed by the standard MTT assay to assess cell survival and recovery after peptide treatment. We found that catesbeianalectin and catesbeianalectin-GK invariably exhibited mast cell degranulation activity without cytotoxic effects. Hemagglutination assay revealed the presence of lectin-like activity in both catesbeianalectin and catesbeianalectin-GK. Our findings strongly suggest that these multifunctional host defense peptides in the amphibian HG are involved in innate immunodefense of the eye of the host against pathogenic environmental microorganisms.

Investigations on the conjunctival goblet cells and the characteristics of the glands associated with the eye in chinchillas (Chinchilla Laniger).

OBJECTIVE: To investigate the density and distribution of conjunctival goblet cells (GC) and study the anatomy and microscopic characteristics of glands associated with the eye in chinchillas (Chinchilla Laniger). PROCEDURE: 12 chinchillas were included in the study. Conjunctiva (divided into four regions), eyelids, and glands were embedded in paraffin wax, sectioned, stained, and analyzed. RESULTS: Highest GC densities were found in the palpebral region of the nasal and temporal conjunctiva of both eyelids (GC index: 25.1-18.2%), and lowest densities, in the bulbar and marginal region of the nasal and temporal conjunctiva of both eyelids (GC index: 1.5-0.0%). Meibomian glands extend along the entire length of both eyelids, and the whole glandular complex broadens toward the temporal canthus. This is macroscopically visible through the conjunctiva. The openings of the Meibomian glands are macroscopically not discernible. The light pink, smooth, and crescent-shaped lacrimal gland lies next to the aforementioned broadened part of the Meibomian glands in the temporal canthus. The whitish, 0.9-cm-long, smooth Harderian gland is firmly attached to the posterior part of the globe and extends nasally from the optic nerve to the equator. Furthermore, chinchillas possess two lacrimal puncta, situated on the inner conjunctival surface of both eyelids near the medial canthus. A pigmented lacrimal canaliculus originates from each punctum. The vestigial nictitating membrane is supported by a hyaline cartilage and is pigmented at its free margin. CONCLUSIONS: Chinchillas possess a Harderian gland, a lacrimal gland, and Meibomian glands. The GC density in the nasal and temporal palpebral conjunctiva is higher than in guinea pigs.

The effect of autophagy and mitochondrial fission on Harderian gland is greater than apoptosis in male hamsters during different photoperiods.

Photoperiod is an important factor of mammalian seasonal rhythm. Here, we studied morphological differences in the Harderian gland (HG), a vital photosensitive organ, in male striped dwarf hamsters (Cricetulus barabensis) under different photoperiods (short photoperiod, SP; moderate photoperiod, MP; long photoperiod, LP), and investigated the underlying molecular mechanisms related to these morphological differences. Results showed that carcass weight and HG weight were lower under SP and LP conditions. There was an inverse correlation between blood melatonin levels and photoperiod in the order SP > MP > LP. Protein expression of hydroxyindole-O-methyltransferase (HIOMT), a MT synthesis-related enzyme, was highest in the SP group. Protein expression of bax/bcl2 showed no significant differences, indicating that the level of apoptosis remained stable. Protein expression of LC3II/LC3I was higher in the SP group than that in the MP group. Furthermore, comparison of changes in the HG ultrastructure demonstrated autolysosome formation in the LP, suggesting the lowest autophagy level in under MP. Furthermore, the protein expression levels of ATP synthase and mitochondrial fission factor were highest in the MP group, whereas citrate synthase, dynamin-related protein1, and fission1 remained unchanged in the three groups. The change trends of ATP synthase and citrate synthase activity were similar to that of protein expression among the three groups. In summary, the up-regulation of autophagy under SP and LP may be a primary factor leading to loss of HG weight and reduced mitochondrial energy supply capacity.

The primate Harderian gland: Does it really exist?

The Harderian gland, an anterior orbital structure, is either absent or vestigial in primates. This is based upon gross anatomical observations of scattered adult specimens. Though largely absent in the adult human, it is present in the fetal and neonatal stages. Thus, histological examination of the orbital region of neonatal material was undertaken in other primates. The orbital region of neonatal specimens of 12 species of strepsirrhines (Lemuriformes and Lorisiformes), and haplorhine (tarsiers and callitrichids) was examined. The Harderian gland is ensconced in either periorbital fat or connective tissue and thus was not readily identifiable gross anatomically. Thus, it may have been missed in the anatomical studies. Tarsal glands are present in all neonatal primate eyelids. The relative size of the neonatal primate Harderian gland can be subdivided into five separate categories, ranging from large to absent (tarsiers), with no apparent phylogenetic trends. Thus, the Harderian gland is present in numerous primates at birth, quite possibly all strepsirrhines. The positive findings on callitrichids question whether any anthropoids lack the Harderian gland postnatally. The enigmatic tarsier appears to possess another apomorphic trait in lacking a Harderian gland. Further study is required to determine the role of this gland and its relationship with the tarsal glands.

Circadian genes in a blind subterranean mammal III: molecular cloning and circadian regulation of cryptochrome genes in the blind subterranean mole rat, Spalax ehrenbergi superspecies.

The blind subterranean mole rat superspecies Spalax ehrenbergi is an extreme example of mammalian adaptation to life underground. Though this rodent is totally visually blind, harboring a drastically degenerated subcutaneous rudimentary eye, its daily activity rhythm is entrainable to LD cycles. This indicates that it confers light information to the clock, as has been previously shown by the authors in behavioral studies as well as by molecular analyses of its Clock/MOP3 and its three Per genes. The Cryptochrome (Cry) genes found in animals and plants act both as photoreceptors and as essential components of the negative feedback mechanism of the biological clock. To further understand the circadian system of this unique mammal, the authors cloned and characterized the open reading frame of Spalax Cry1 and Cry2. The Spalax CRY1 protein is significantly closer to the human homolog than to the mice one, in contrast to the evolutionary expectations. They have found two isoforms of Cry2 in Spalax, which differ in their 5' end of the open reading frame and defined their expression in Spalax populations. They found a large and significant excess of heterozygotes of sCry2 (sCry2L/S genotype). Both sCry1 and sCry2 mRNAs were found in the SCN, the eye, the harderian gland, as well as in a wide range of peripheral tissues. Their expression pattern under different LD conditions has also been analyzed. As was already shown for other circadian genes, despite being blind and living in darkness, the Cry genes of Spalax behave in a similar, though not identical, pattern as in sighted animals. Once again, the results indicate that the uniquely hypertrophied harderian gland of Spalax plays a key role in its circadian system.

Effects of constant bright illumination on reproductive processes in the female rat.

Physiological and behavioral reproductive changes in the female rat which occur under constant bright illumination (LL) are examined. The development of LL-induced persistent estrus (PE) is discussed first in relation to other conditions in which PE is displayed. Next, mechanisms are reviewed which may account for the LL-induced changes. These include: (1) role of the retina, the retinohypothalamic tract and the suprachiasmatic nucleus; (2) influence of adrenal, pineal and Harderian glands; and (3) disruptions in either the 4-day endocrine rhythms or circadian neural component of the estrous cycle. Additional topics which are examined include the ontogeny of age-induced PE and the effects of LL on hormone receptor binding, puberty, sexual receptivity and mating.

Thyroid hormone affects secretory activity and uncoupling protein-3 expression in rat harderian gland.

The effects of T(3) administration on the rat Harderian gland were examined at morphological, biochemical, and molecular levels. T(3) induced hypertrophy of the two cell types (A and B) present in the glandular epithelium. In type A cells, the hypertrophy was mainly due to an increase in the size of the lipid compartment. The acinar lumina were filled with lipoproteic substances, and the cells often showed an olocrine secretory pattern. In type B cells, the hypertrophy largely consisted of a marked proliferation of mitochondria endowed with tightly packed cristae, the mitochondrial number being nearly doubled (from 62 to 101/100 microm(2)). Although the average area of individual mitochondria decreased by about 50%, the total area of the mitochondrial compartment increased by about 80% (from 11 to 19/100 microm(2)). This could be ascribed to T(3)-induced mitochondrial proliferation. The morphological and morphometric data correlated well with our biochemical results, which indicated that mitochondrial respiratory activity is increased in hyperthyroid rats. T(3), by influencing the metabolic function of the mitochondrial compartment, induces lipogenesis and the release of secretory product by type A cells. Mitochondrial uncoupling proteins 2 and 3 were expressed at both mRNA and protein levels in the euthyroid rat Harderian gland. T(3) treatment increased the mRNA levels of both uncoupling protein 2 (UCP2) and UCP3, but the protein level only of UCP3. A possible role for these proteins in the Harderian gland is discussed.

Cloning of a Syrian hamster cDNA related to sexual dimorphism: establishment of a new family of proteins.

The clone FHG22, isolated from a female minus male subtracted cDNA library obtained from the sexually dimorphic Syrian hamster Harderian glands (HG) is 440 bp long with a 95 amino acids ORF, and hybridizes to a female HG-specific 0.6 kb mRNA. The FHG22 nucleotide and amino acid sequences are similar to the subunits from prostatein, uteroglobin, major cat allergen Fel dI (chain 1) and mouse salivary androgen binding proteins (subunit alpha). Therefore I propose that all those polypeptides belong to a common new family. The hamster genome has a single copy of the FHG22 gene, without homologous genes. FHG22 mRNA is also found in male and female parotid (higher levels in females) and submandibular glands, indicating a tissue and sex-dependent control of expression.

Extraocular muscle and Harderian gland degeneration and regeneration after exposure of rats to continuous fluorescent illumination.

Exposure of adult albino rats to continuous cool-white fluorescent illumination caused extensive destruction to the extraocular skeletal muscles (EOM's) and Harderian glands. After 1 day of exposure, leukocytes and macrophages invaded the damaged area and were found among and within the myofibers. After 48 hr of exposure, myoblasts and short myotubes extending from the damaged fibers indicated that regeneration had begun. In spite of constant illumination of the animals, the EOM's continued to reconstitute, and by the seventh day of exposure, regeneration was almost complete. At this time, small loci of degeneration and leucocytic infiltration resembling those seen in the 1-day stage again occurred. Results supported the speculation that differentiated myofibers were susceptible to the damaging effects of continuous fluorescent illumination, but that myoblasts myotubes, and early undifferentiated myofibers were not. Although the tubular epithelium proliferated in damaged Harderian glands, very few other regenerative changes were observed during the 7-day exposure period. When animals with one eye occluded with a plastic contact lens and the other unoccluded were exposed to continuous illumination, the pattern of tissue destruction in unoccluded eyes was identical to that described in the above series. However, EOM's in occluded eyes were unaffected, and Harderian glands had minimal damage limited to unshielded areas at the conjunctival fornix. Glands apparently were more susceptible to injury than EOM's. Orbital tissue destruction in these animals seemingly was due directly to a radiant energy-dependent mechanism.

Investigation of the role of prolactin in the development and function of the lacrimal and harderian glands using genetically modified mice.

PURPOSE: To determine whether prolactin receptor is essential for normal development and function of the lacrimal gland and whether hyperprolactinemia can alter lacrimal development. METHODS: Lacrimal gland morphology and function were examined in two genetic mouse models of prolactin action: a prolactin receptor knockout model that is devoid of prolactin action and a transgenic model of hyperprolactinemia. RESULTS: Image analysis of lacrimal and Harderian gland sections was used to quantify glandular morphology. In females, lacrimal acinar area decreased by 30% and acinar cell density increased by 25% over control subjects in prolactin transgenic animals, but prolactin receptor knockout mice showed no changes. In males, transgenic animals showed no changes, but prolactin receptor knockout mice showed a 5% reduction in acinar area and an 11% increase in acinar cell density, which was lost after castration. The morphology of the Harderian glands underwent parallel changes but to a lesser degree. A complete loss of porphyrin accretions was seen in the Harderian glands of male and female knockout animals. No differences in tear protein levels were seen in knockout animals by two-dimensional gels. Enzyme-linked immunosorbent assay (ELISA) and Western blot analysis showed that the level of secretory component and IgA in knockout mouse tears remained unchanged. There was no change in the predisposition of the 129 mouse strain to conjunctivitis in the knockout animals. CONCLUSIONS: Prolactin plays a small role in establishing the sexual dimorphism of male lacrimal glands. In females, hyperprolactinemia causes a hyperfemale morphology, suggesting a role in dry eye syndromes. Prolactin is required for porphyrin secretion by the Harderian gland but plays no essential role in the secretory immune function of the lacrimal gland.

Hormonal regulation of FHG22 mRNA in Syrian hamster harderian glands: role of estradiol.

The regulation of the FHG22 gene by sex steroids has been studied in Syrian hamster Harderian gland, an organ with sexual dimorphism in which the FHG22 mRNA is female-specific. Testosterone treatment of females caused irregular inhibitory effects on the FHG22 mRNA levels, whereas male castration originated transitory increases during less than 2 weeks. Treatment of 15 day-castrated males for 1 or 2 days with beta-estradiol-3-benzoate caused a marked stimulation in the FHG22 mRNA levels. The results found in vivo may be explained considering those found in female Harderian gland serum-free primary cell cultures. In the absence of hormones, the FHG22 mRNA levels decreased along the time and neither progesterone, testosterone, or 5 alpha-dihydrotestosterone affected the expression. However, estradiol stimulated the FHG22 mRNA expression in a time and dose-dependent manner: increasing effects were detected between 8-96 h of treatment and the EC50 was about 10(-9) M. The estradiol effect was reverted by the antiestrogen ICI 164,384 or by cycloheximide. We conclude that estradiol stimulates FHG22 mRNA expression in Harderian gland, although other agents may also control the expression in vivo.

Body temperature and grooming in the Mongolian gerbil.

The Mongolian gerbil, Meriones unguiculatus, like many other rodents, releases a complex mixture of pigments and lipids from the Harderian gland during a self-groom. The material exits from the external nares of the nose, is mixed with saliva, and spread widely over the pelage. Cold temperatures, especially, are effective in initiating grooming. A self-groom is associated with an increase in body temperature (compensatory thermogenesis in the cold). In addition to acting as a chemosignal, the Harderian material serves two major homeostatic functions: (1) the lipids on the pelage act to insulate the animal against cold and wetness, and (2) the lipids and pigments darken the pelage and increase radiant absorption. Body temperature is thus maintained at a higher level than would otherwise be the case. The amount of Harderian material found on the pelage varies with Harderianectomy, sandbathing, and ambient temperatures. Animals prevented from sandbathing accumulate excess lipids on the pelage, and cold temperatures facilitate the acquisition of lipids on the pelage. Under hot temperatures the grooming of Harderian substances is repressed and the frequency of sandbathing is increased. Thus pelage lipids are reduced in two ways. The amount of Harderian material released during an autogroom is inversely related to the ambient temperature, whereas the amount of saliva used for evaporative cooling is positively related to ambient temperature. The net effect is that pelage lipids are increased and maintained during cold conditions, and are reduced during hot conditions. In hot environments the gerbil switches from the spread of Harderian material for insulation to the spread of saliva for evaporative cooling. The gerbil optimizes its body temperature by varying the frequency of grooming and sandbathing, and by altering the amount of Harderian material and saliva released. Other species living in arid environments may use similar mechanisms to stabilize body temperature. Self-grooming is a critical behavior for meeting thermal needs, and is complexly integrated with related processes.

The Harderian gland: perspectives.

This is the three-hundred and second anniversary of the first description of Harderian glands by Johann Jakob Harder. Despite more than three centuries of study, many features of these glands, including their definition and function, are not yet established to everyone's satisfaction. Some topics of Harderian biology will be reviewed. Morphology, ontogeny: Mammalian Harderian glands secrete largely by exocytosis, which is unusual in a lipid-secreting exocrine gland. Polytubular complexes are features of male hamster glands; their significance is unknown. Porphyrins: High levels of porphyrin in rodent Harderian glands have made this an attractive organ for research on the control of porphyrin synthesis. Attempts to use it as a model of human porphyria, however, have been disappointing. We do not know the function of Harderian porphyrin. The golden (hamster) age: Syrian (golden) hamster Harderian glands show marked sexual differences, including porphyrin levels. This has made them a very useful experimental animal for endocrine studies. The pineal connection: Rodent Harderian glands contain melatonin. Pinealologists often also study Harderian glands, and Harderianologists also often study the pineal. This relationship has contributed valuable insights to our knowledge of both systems. Lipids: Rodent Harderian glands are about 20% lipid by wet weight, and the main secretory product is lipid. The main lipid in many animals is 1-alkyl-2, 3-diacylglycerol. Harderian gland lipid is extensively studied for insights into lipid biochemistry; less has been done on understanding the function of lipids in the physiology of the glands. Behavior: Lipids may function as vehicles for pheromone secretion. In addition, the possible use of Harderian secretion during cold temperatures by gerbils has been noted. Immunology: Bird Harderian glands are probably lymphoid organs. This does not seem to be true of mammals, though the female Syrian hamster shows large numbers of mast cells. Harderian glands of amphibians and reptiles: Research on nonmammalian Harderian glands has been limited, though important insights continue to emerge from these studies.

Sexual dimorphism in the harderian gland of the Syrian hamster is controlled and maintained by hormones, despite seasonal fluctuations in hormone levels: functional implications.

The Harderian gland of the Syrian hamster (Mesocricetus auratus) is unusual amongst rodents in the degree of dimorphism present. Other types of hamsters have Harderian glands which are apparently identical in male and female animals. Laboratory populations of Syrian hamsters are derived from very limited genetic stock, which makes one concerned lest they not be representative of wild populations; however, until wild stocks of M. auratus become available, we should assume that insights derived from studies of dimorphism in Syrian hamsters represent important considerations for the life of these animals. Two dimorphic features are the histology and the porphyrin content of the Harderian glands. About 95% of the lipid droplets in female glands are small (type 1), whereas only about 65% of those in males in type 1, with the other 35% being type 2 (large droplets). Five weeks of castration of males led to an increase in type 1 droplets to 90%. On the other hand, 2 weeks treatment of females with testosterone led to a reduction in type 1 droplets to about 82%. Short day photoperiods led to a large increase in type 2 droplets in both males and females (to 52% in males, 35% in females after 8 weeks). These results suggest that the lipid contained in type 2 droplets is important to hamsters of both sexes during the winter. Porphyrin concentrations are 100-1,000 times higher in females than males, and this is largely controlled by testosterone as orchidectomy leads to increased male levels and testosterone treatment leads to reduced female levels. However, a number of treatments which also lead to reduced testosterone levels do not lead to increased porphyrins and may, in fact, prevent the rise which would normally follow orchidectomy. One of these antiporphyrinogenic treatments is exposure to short day photoperiods. Thus, the sexual differences in porphyrin, levels in Syrian hamsters are maintained, despite seasonal fluctuations in hormone levels. This suggests that this dimorphism is important for the function of the gland.

Harderian gland function of Indian tropical palm squirrel, Funambulus pennanti.

The Harderian gland (HG) of the Indian palm squirrel, F. pennanti, is composed of acini of a single type of simple columnar cells with uniform-sized lipid droplets and porphyrin (P) in the lumen. Morphologically it presented no sexual dimorphism except for the HG weight which revealed that males are acyclic. Circadian study of Harderian gland porphyrin (HG-P), plasma melatonin, (aMT) and testosterone showed a characteristic two peak cyclicity. In females, HG, HG-P and pineal gland weight, and plasma aMT presented an annual inverse relation. Circadian study in females only exhibited a two peak cyclicity of HG-P, plasma aMT, and estradiol. Pinealectomy (PX) and harderianectomy (HGX) revealed increased HG weight and gonad weight in males. Gonadectomy (GX), on the other hand, had no effect on HG in males. PX in females brought almost a similar effect as noted for males, but HGX had no effect on ovarian weight. GX, interestingly, reduced HG weight and P concentration. Daily evening (4:30-5:00) administration of aMT and 5-methoxytryptamine (5-MT) in males reduced HG weight and HG-P content only in aMT-treated male and female squirrels, thereby suggesting that HG-P is perhaps negatively regulated by pineal gland production and vice versa. Injections of gonadotropin and steroids during the sexually inactive phase showed no effect on HG-P content in both sexes. Short photoperiod (SP) in both sexes stimulated pineal weight without affecting HG weight, while long photoperiod (LP) increased HG-P but reduced the plasma aMT level again without affecting HG-P content. Continuous dark (CD) decreased HG-P, whereas continuous light was ineffective without effecting HG weight in both sexes. In conclusion, HG in this rodent is functionally an important gland having diverse physiological effect in both sexes sometimes with a very clear HG-pineal-gonad relationship.

A day/night rhythm of vasopressin and oxytocin in rat retina, pineal and harderian gland.

Arginine vasopressin (AVP), oxytocin (OT) and neurophysins (Np) have been found in the pineal gland and the retina of the rat. Because the retina, pineal gland and Harderian gland (HG) serve analogous functions, we undertook a study to determine the presence of these peptides in these three organs of rats. They were detected by two specific methods: HPLC and specific radioimmunoassays. For Np, total neurophysins (NpT) were measured. To determine a 24 hr rhythm, the animals were maintained under a light/dark cycle of 12 hr/12 hr for 3 weeks. The pineal glands, retinae and HG were collected. Day/night rhythms of AVP, OT and NpT were demonstrated in the retina and HG; but the pineal gland had only AVP rhythm. A significant decrease in the rhythms at 4 a.m. was demonstrated in the retina and HG. The 24 hr variation of AVP in the retina seemed parallel to that of the HG.