The effect of sex hormones on lipid content and mast cell number in the harderian gland of the female toad, Bufo viridis

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.

Neuroendocrine-immune interaction: Evolutionarily conserved mechanisms that maintain allostasis in an ever-changing environment

It has now become accepted that the immune system and neuroendocrine system form an integrated part of our physiology. Immunological defense mechanisms act in concert with physiological processes like growth and reproduction, energy intake and metabolism, as well as neuronal development. Not only are psychological and environmental stressors communicated to the immune system, but also, vice versa, the immune response and adaptation to a current pathogen challenge are communicated to the entire body, including the brain, to evoke adaptive responses (e.g., fever, sickness behavior) that ensure allocation of energy to fight the pathogen. This phenomenon is evolutionarily conserved. Hence it is both interesting and important to consider the evolutionary history of this bi-directional neuroendocrine-immune communication to reveal phylogenetically ancient or relatively recently acquired mechanisms. Indeed, such considerations have already disclosed an extensive "common vocabulary" of information pathways as well as molecules and their receptors used by both the neuroendocrine and immune systems. This review focuses on the principal mechanisms of bi-directional communication and the evidence for evolutionary conservation of the important physiological pathways involved.

A new sex dimorphism in the Harderian gland of the frog Rana esculenta

The Harderian gland (Hg), the only gland found in the orbit of the frog Rana esculenta L., 1758, probably plays a role in orbital lubrication. The secretory activity of the Hg is seasonal, showing the highest activity in summer. There is little information on Hg gene expression; previously, we identified a mRNA named harderin, whose deduced protein has no homology with other proteins. Differential expression of the harderin transcript between the sexes expressed during the annual cycle implies sexual dimorphism. RT–PCR (reverse transcription – polymerase chain reaction) analysis, revealed that harderin is expressed during the entire year in the Hg of both sexes. It shows a higher level of expression in the female glands than that of male glands. Two peaks of expression, in February and in June, were observed in the female glands, while only the February peak was observed in those of males. These observations were supported by in situ hybridization. Experiments involving gonadectomy and (or) hormonal replacement therapy showed a significant decrease in harderin in the Hg of females; this effect is prevented by estradiol (testosterone had no effect), while ICI (antiestrogen) counteracts the hormonal prevention, suggesting that this sexual dimorphism is under estradiol control. The constant expression of harderin mRNA during the year suggests a probable constitutive role for this molecule.

Hematopoietic prostaglandin D2 synthase in the chicken Harderian gland

The Harderian gland (HG), a sero-mucous secreting organ in the eye orbit, has long been recognized as immunologically important in chickens. During experimentation to characterize immune components of the gland, proteomics analysis revealed the presence of hematopoietic prostaglandin D synthase (H-PGDS). Extraction of total RNA followed by RT-PCR produced cDNA of 597 base pairs. DNA sequencing revealed nucleic acid and predicted amino acid sequences that were 99% aligned with the one published sequence for chicken H-PGDS of the spleen. Alignment with murine, rat, and human H-PGDS were 69, 69, and 66%, respectively. Ocular vaccination of chickens with a Newcastle Disease/Infectious Bronchitis vaccine (Mass.-Ark. Strain) induced an increase in H-PGDS expression determined by real-time PCR. Furthermore, immunohistochemistry of frozen HG sections showed positive stained cells for both H-PGDS and mast cell tryptase in the sub-epithelial cell layers of the HG ducts. Based on the potent vasoactive role of PGD(2), it appears that the chicken HG is a site of active mucosal immunity partially mediated by PGD(2) synthesized by H-PGDS in the gland.

Morphology of the Harderian gland of the Gecko, Tarentola mauritanica

The Harderian gland of the gecko, Tarentola mauritanica, was studied at the histological, histochemical, and ultrastructural levels. It is a nonlobate compound acinar gland surrounded by a thin capsule of connective tissue. Numerous connective tissue-type mast cells, ultrastructurally similar to those described in other higher vertebrates, were identified in the interstitial tissue between the acini. Pyramidal or columnar-shaped secretory glandular cells were observed in the acini. In the glandular cells, two types of structures could be distinguished on the basis of their high or low electron density. Lipid droplets were found in the cytoplasm of the Harderian gland of both sexes. Histochemical tests showed that the Harderian gland of the gecko is a seromucous gland. The secretion is essentially merocrine, although an apocrine type of secretion is sometimes observed.

Number of mast cells in the Harderian gland of the lizard Podarcis sicula sicula (Raf): the annual cycle and its relation to environmental factors and estradiol administration

The Harderian gland of the lizard Podarcis sicula sicula (Raf) contains connective tissue type mast cells whose numbers vary during the year showing two peaks, one in spring the other in winter. No sex differences are found throughout the year. Thermal and photoperiodic manipulations indicate that only temperature influences mast cell number (MCN) both in winter and in summer but not in spring. In animals exposed to high temperatures in February (but not in May) MCN declined, while exposure to low temperature in July had the opposite effect. Estradiol treatment of the February and April lizards increased MCN, an effect counteracted by the synthetic antiestrogen tamoxifen; in July lizards, this did not occur. In animals exposed to a high temperature in February, estradiol had no effect, as in animals exposed to low temperatures in July. These data suggest that in spring MCN seems to be more responsive to hormonal stimuli rather than external cues (temperature), while in summer MCN is more sensitive to temperature than to hormonal stimuli (estradiol). Both humoral and external factors are concluded to influence mast cell numbers in the Harderian gland of the lizard P. sicula sicula.

Oestrogen control of the sexual dimorphism in the Harderian gland of Xenopus laevis

Xenopus laevis shows a sexual dimorphism of the electrophoretic pattern of Harderian gland (HG) proteins. The male pattern displays three protein fractions whose molecular sizes are approx. 205, 180 and 78 kDa, respectively, and which are absent in the female pattern. Conversely, the female pattern displays two protein fractions of approx. 190 and 76 kDa, respectively. This sexual dimorphism led us to hypothesize a sex steroid control of the HG. Administration of 17beta-oestradiol to male Xenopus converts the male protein pattern into the female one, while the administration of testosterone to the female has no effect. In this respect neither Northern analysis nor the RNase-protection assay performed using a 213 bp encoding for the androgen-binding domain reveals the presence of an androgen receptor mRNA in Xenopus HG. Conversely, Northern analysis has shown an oestrogen receptor mRNA whose size is approx. 6.5 kb and the RNase-protection assay performed by using a 197 bp encoding for the oestrogen-binding domain has also displayed the presence of an oestrogen receptor mRNA in the female HG but not in the male one. In addition, the oestrogen administration to male Xenopus induces the appearance of an oestrogen receptor mRNA. Androgen administration to female toad is ineffective. Taken together, all these findings suggest that in Xenopus laevis oestrogens are involved into the HG physiology. The appearance of an oestrogen receptor mRNA in the oestradiol treated males supports the hypothesis of the occurrence of autoinduction of oestrogen receptor mRNA expression in the HG.

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.

Cell biology of 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.

The effects of testosterone and estradiol on mast cell number in the harderian gland of the frog, Rana esculenta

The Harderian gland (HG) of the frog Rana esculenta contains mast cells in the interstitial tissue. The mast cell number (MCN) is influenced by sex hormones. Gonadectomy in both sexes provoked a decrease in MCN in January, while no effect was observed in September. Sex hormone-replacement therapy gave different results; estradiol treatment in castrated males and females always increased MCN, while testosterone did not. Acute estradiol treatment provoked an increase in MCN on days 2 and 4 of treatment and the morphology of the glandular compartment appeared normal. On days 8, 10 and 12 of treatment the MCN drastically decreased. The majority of glandular acini appeared strongly disorganized and the interstitial tissue became hypertrophic in concomitance with an increased vascularization. Our results suggest that estradiol acts by stimulating mast cells and acute estradiol treatment provokes proliferation of interstitial connective tissue together with glandular cells damage.

Mast cell-Leydig cell relationships in the testis of the lizard Podarcis s. sicula Raf: thermal manipulation, ethane 1,2-dimethane sulphonate (EDS) and sex hormone treatment

Mast cells of connective tissue type are scattered in the interstitial compartment of the lizard Podarcis s. sicula. Their number varies during the year, showing peaks in spring and in winter, respectively. Thermal manipulation affects mast cell number (MCN): high temperature decreased MCN in both January and May, while low temperature increased MCN only in January. Ethane dimethane sulphonate, a toxin which specifically destroys Leydig cells, induced an increase in MCN on days 3 and 7 of treatment. Oestradiol treatment provoked a strong increase in MCN that was blocked by tamoxifen. Blocking androgen receptors with cyproterone acetate resulted in an increase in MCN, while testosterone injection provoked a strong decrease. These results suggest a relationship between the presence of mature Leydig cells and mast cell proliferation and/or differentiation.