Inhibition of 5 alpha-reductase does not simulate the effects of androgen deprivation on porphyrin metabolism by harderian glands from the male Syrian hamster

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.

Sexual differences in 5'-deiodinase activity in the Harderian gland of Syrian hamsters and the effect of pinealectomy: regulation by androgens

Sexual differences on thyroxin 5'-deiodinase (5'-D) in the Harderian gland of Syrian hamsters were investigated. We compared the 24-h profile of 5'-D activity in male and female hamsters, observing a clear rhythm in males but not in females. Female values were always significantly higher than male ones. After pinealectomy day/night variations in male 5'-D activity at the time points studied were abolished, results that are in correlation with serum thyroid hormones. We also studied the regulation by androgen of the enzyme activity. Basal 5'-D activity increased in castrated males and levels fell when animals were implanted with testosterone or its product 5 alpha-dihydrotestosterone (DHT). Female 5'-D activity was also inhibited by androgens. As only the addition of DHT in the presence of epitestosterone, an inhibitor of the conversion of testosterone on DHT, in castrated males was able to decrease 5'-D activity to the control animal levels, we suggest a probable direct effect of DHT by itself.

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.

Androgen receptor in the harderian glands of the golden hamster: characterization and the effects of androgen deprivation, the pituitary, and gender

The harderian glands of the golden hamster were found, by a competitive binding assay using [3H]mibolerone as the ligand, to have a high affinity androgen receptor. In intact male hamsters, this receptor was present in both cytosolic and nuclear KCl-extractable fractions. Castration or hypophysectomy led to 3- to 5-fold increases in the concentrations of cytosolic receptor with decreased dissociation constants. Hypophysectomy with maintenance of prolactin levels (by removal of pituitaries and their implantation either in the sella turcica or under the kidney capsule) had no effect on androgen receptor binding, compared to hypophysectomy alone. Female hamsters had androgen receptor levels which were 2 to 4 times higher than those of intact males. Hypophysectomy led to elevated receptor binding in ovariectomized female hamsters and this rise was prevented by maintaining prolactin levels. Binding of [3H]mibolerone in male glands was effectively inhibited by 5 alpha-dihydrotestosterone, whereas the parent molecule, testosterone, required approximately a 10-fold greater molar excess to achieve the same amount of inhibition. Estradiol and progesterone were relatively poor inhibitors of the observed binding of [3H]mibolerone, while dexamethasone was ineffective. Sucrose gradient studies indicated that the harderian androgen receptor migrated to the 8S region, as expected for this receptor in molybdate-containing gradients. These results indicate that the androgen receptor in the hamster harderian gland is a 5 alpha-dihydrotestosterone receptor.