N-acetyltransferase activity and indole contents of the male Syrian hamster Harderian gland: changes during the light:dark cycle

Pineal Calcification, Melatonin Production, Aging, Associated Health Consequences and Rejuvenation of the Pineal Gland

The pineal gland is a unique organ that synthesizes melatonin as the signaling molecule of natural photoperiodic environment and as a potent neuronal protective antioxidant. An intact and functional pineal gland is necessary for preserving optimal human health. Unfortunately, this gland has the highest calcification rate among all organs and tissues of the human body. Pineal calcification jeopardizes melatonin's synthetic capacity and is associated with a variety of neuronal diseases. In the current review, we summarized the potential mechanisms of how this process may occur under pathological conditions or during aging. We hypothesized that pineal calcification is an active process and resembles in some respects of bone formation. The mesenchymal stem cells and melatonin participate in this process. Finally, we suggest that preservation of pineal health can be achieved by retarding its premature calcification or even rejuvenating the calcified gland.

Melatonin modulates autophagy through a redox-mediated action in female Syrian hamster Harderian gland controlling cell types and gland activity

The Syrian hamster Harderian gland exhibits sexually dimorphic porphyrin biosynthesis, wherein the female glands display an extraordinarily high concentration of porphyrins. Damage derived from this production of porphyrins, mediated by reactive oxygen species, causes the glands to develop autophagic processes, which culminate in detachment-derived cell death; these cells normally play a central role in the secretory activity of the gland. The main aim of this study was to analyze how a change in the redox state impacts autophagy. Female Syrian hamsters were treated daily with melatonin (25 μg, subcutaneously) at ZT 10 for 1-2 months (N-acetyl-5-methoxytryptamine), an endogenous antioxidant that ameliorates the deleterious effects of free radicals via a variety of mechanisms. The length of treatment affected the redox balance, the autophagy machinery, and the activation of p53 and NF-κB. One-month treatment displaces redox balance to the antioxidant side, promotes autophagy through a p53-mediated mechanism, and increases cell detachment. Meanwhile, 2-month treatment restores redox balance to the oxidant side, activates NF-κB reducing autophagy to basal levels, increases number of type II cells, and reduces number of detached cells. Our results conclude that the redox state can modulate autophagy through redox-sensitive transcriptions factors. Additionally, these findings support a hypothesis that ascribes differences in the autophagic-lysosomal pathway to epithelial cell types, thereby restricting detachment-induced autophagic cell death to epithelial cell type I.

Melatonin synthesis in the rat harderian gland: age- and time-related effects

The Harderian gland is considered as an extrapineal source of melatonin. In the pineal gland, melatonin is known to present a circadian rhythm with high concentration during nighttime in all species studied. We determined in Wistar male rats the effects of age and time of day on melatonin synthesis in the Harderian gland. We compared Harderian gland melatonin content and the hormone synthesizing enzymes, serotonin N-acetyltransferase and hydroxyindole-O-methyltransferase, in young (4 months) and old (22 months) animals at six circadian stages and found that melatonin synthesis in the Harderian gland was unaffected by age. We also studied the Wistar rat Harderian gland at ten different circadian stages and found that the Harderian gland did not exhibit a daily rhythm in its melatonin content. This study shows that, by contrast to the pineal gland, melatonin in Wistar rat Harderian gland does not exhibit daily variations and that aging does not affect the melatonin content of the gland.

Evidence for melatonin synthesis in rodent Harderian gland: a dynamic in vitro study

Melatonin content and release from Harderian glands (HGs) has been measured by an in vitro perifusion technique in three rodent species: Wistar rat, Syrian hamster, and Siberian hamster. Melatonin immunoreactive concentrations in HGs of animals killed at 10.00 hr were 0.31 +/- 0.031 pg/mg gland in male Wistar rat, 0.54 +/- 0.026 pg/mg gland in male Siberian hamster, 0.17 +/- 0.070 and 0.20 +/- 0.059 pg/mg gland in male and female Syrian hamster, respectively. In all species examined, isolated HGs perifused for 9-15 hr released melatonin but did not stabilize their melatonin release rate. No sex-related difference could be noted in the HG melatonin release rate. The total amount of melatonin released over a 15 hr long perifusion was about 0.075 +/- 0.004 ng/15 h/mg gland and 0.063 +/- 0.010 ng/15 hr/mg gland in male and female Wistar rat, respectively; 0.155 +/- 0.019 ng/15 hr/mg gland and 0.141 +/- 0.006 ng/15 hr/mg gland in male and female Siberian hamster, respectively; 0.035 +/- 0.003 ng/15 hr/mg gland and 0.045 +/- 0.004 ng/15 hr/mg gland in male and female Syrian hamster, respectively. This amount, which is higher than the tissue levels, demonstrates the de novo melatonin synthesis. This is confirmed by the fact that infusion of the indoleamine precursor, tryptophan (TRP), stimulated melatonin secretion from HGs. The melatonin release is increased by 2.5-fold in male and female Wistar rat, 1.5-fold in male and female Siberian hamster, and 2.0- and 3.0-fold in male and female Syrian hamster, respectively. Treatment with a TRP hydroxylase inhibitor, para-chlorophenylalanine, reduced basal melatonin release and inhibited the TRP-induced melatonin stimulation. Kinetics and amounts of melatonin released were not affected by pinealectomy, ruling out a possible plasmatic origin of the HG melatonin. Isoproterenol, a beta-adrenergic agonist, and dibutyryl cyclic AMP, a cyclic AMP analogue, failed to stimulate HG melatonin secretion. In conclusion, these results confirm the presence of melatonin in the HGs and demonstrate that melatonin is synthesized in and released from isolated rodent HGs.

Hormones and the control of porphyrin biosynthesis and structure in the hamster harderian gland

The hamster Harderian gland seems to present both an excellent model for the control of porphyrin biosynthesis and an unusually robust example of the interrelationship between structure and function. It has been known for some time that 1) the capacity for manufacturing and storing porphyrins and 2) gland histology and ultrastructure are controlled by androgens. Thus, in intact males as well as in gonadectomised animals of either sex treated with androgens, porphyrin synthesis by the Harderian gland is suppressed and the gland tubules characteristically possess two cell types, the cytoplasm of both containing polytubular complexes. By contrast, the Harderian glands of intact females and castrated males synthesise and store large amounts of protoporphyrin, while their tubules possess only one cell type which lacks a polytubular complexes. So overarching is the effect of androgens that they have been described as a "coarse tuning" effect on the gland. By contrast, the role of the ovary is both less dramatic and less well understood. In female hamsters, ovariectomy leads to degenerative changes in Harderian gland tubules and (probably) a release of stored porphyrin; at the same time there is a reduction in enzyme levels and new synthesis. The causative hormone in this "fine tuning" is unclear at present. There is now clear evidence that the Harderian gland is also controlled directly by pituitary hormones. In particular, the use of continuous infusion osmotic minipumps has allowed us to demonstrate not only 1) that the expected rise in porphyrins and feminisation of gland morphology does not occur in castrated males receiving the dopamine agonist bromocriptine, but that 2) the simultaneous administration of prolactin does permit these changes; furthermore, 3) the administration of prolactin alone increases porphyrin synthesis above the levels found in untreated castrates. Similarly, bromocriptine administration to ovariectomised females markedly reduces porphyrin synthesis and masculinises gland structure; again, this is reversed by the simultaneous administration of prolactin. Prolactin must therefore be seen as equipotent with androgens in determining gland structure and activity.

Effects of ovariectomy and ageing on the structure and ultrastructure of the female Syrian hamster Harderian gland: a stereological analysis

The effects of ovariectomy and ageing on the structure and ultrastructure of the Syrian hamster Harderian gland were investigated by techniques of quantitative stereology. Tissues were obtained from intact 6-month-old, sham-operated 6-month-old, ovariectomized 6-month-old, intact 18-month-old and ovariectomized 18-month-old female hamsters. Glands from both ovariectomized and aged hamsters showed comparable qualitative and quantitative characteristics. They showed histological alterations that included thinning of the tubule walls, lowering of luminal porphyrins, invasion of lumina by neutrophils and the occurrence of interstitial porphyrins. Glands from both ovariectomized and aged hamsters showed statistically significant differences from control animals in relation to numerical density and cellular size. Finally, quantitative studies with the electron microscope revealed significant decreases in the volume densities of the cytoplasmic organelles concerned with secretion. These results support the hypotheses that the secretory activity of the female hamster Harderian gland is influenced, directly or indirectly, by ovarian hormones, and that many of the age-related modifications of the Harderian gland reflect alterations in ovarian function.

Immunohistochemical demonstration of melatonin in the female mink harderian gland

In the Harderian gland of the female mink, either intact or killed after a bilateral ablation of the cervical superior ganglion, almost all of the cells of the alveoli were immunolabeled with anti-melatonin antiserum. Animals were killed during the day or during the night. The immunolabelling was observed only in the cytoplasm, while the nucleus remained unstained. Using successive dilutions of the antiserum on serial sections of the Harderian gland to qualitate the melatonin content, a circadian rhythm of melatonin immunoreactivity was observed. The intensity of immunofluorescence labelling was higher in intact animals killed during the day than in those killed during the night. These results could be explained by the inhibitory or stimulatory influence of pineal melatonin released during the night on melatonin synthesis or release in the Harderian gland, respectively. In the Harderian gland of ganglionectomized animals, the intensity of melatonin immunofluorescence was lower than in intact animals killed during the day. It is concluded that the Harderian gland might be involved in the perception of the day/night cycle and that melatonin synthesis/secretion was likely controlled by the cervical superior ganglion in this organ.

Postnatal development of the harderian gland in the Syrian golden hamster (Mesocricetus auratus): a light and electron microscopic study

The main objective of the present investigation was to study the morphological and chronological aspects of the development of the Harderian gland in the Syrian golden hamster. Tissues were obtained from male and female hamsters at days 1,3,5,7,10,12,15,17,20,27,37,46, and 90 after birth and processed for light and transmission electron microscopy. The present observations indicate that a well-defined temporal sequence in microscopic and ultrastructural modification is recognizable in the development of the hamster Harderian gland. Four stages of development were proposed. Between days 1-5 (first stage), the gland shows characteristics of an immature structure. The glandular cells contain many free ribosomes, few and small organelles, and large irregular-shape nuclei. Between days 7-17 (second stage), there is a marked increase of organelles involved in synthesis and secretion. The gland begins the secretion of lipids and porphyrins, but no morphological differences between male and female glands are observed. Between days 20-36 (third stage), the morphological differences between the two sexes appear and progressively develop. In 45-day-old hamsters, the Harderian gland possesses the structural characteristics of adult glands, and further developmental changes are essentially quantitative in nature (fourth stage). At all stages of development, the population of secretory cells has a uniform appearance. The morphological results are discussed as well as the possible relationship of this temporal sequence with hormonal changes.

Attenuated nocturnal rise in pineal and serum melatonin in a genetically cardiomyopathic Syrian hamster with a deficient calcium pump

Day and nighttime melatonin production in the pineal gland was compared in normal and cardiomyopathic (polydystrophic) adult male Syrian hamsters. These strains of hamsters were selected for comparison because the cardiomyopathetic hamster displays a deficient transmembrane Ca(2+)-pump in a number of tissues, and intracellular CA2+ concentrations ([Ca2+]i) play a central role in the nocturnal increase in pineal melatonin synthesis. Daytime levels of all constituents measured, i.e., pineal N-acetyltransferase (NAT) activity, pineal and serum melatonin levels, and pineal 5-hydroxytryptophan (5-HTP), serotonin, and 5-hydroxyindole acetic acid (5-HIAA) contents, were comparable in control and dystrophic hamsters. In contrast, the nighttime rises in pineal NAT activity and pineal and serum melatonin levels were significantly attenuated in the dystrophic hamsters. By comparison, the pineal contents of 5-HTP, serotonin, and 5-HIAA were essentially the same in both groups of hamsters with both pineal serotonin and 5-HIAA values exhibiting the usual nighttime drop. It is presumed that the alterations in nocturnal melatonin production in the pineal gland of the cardiomyopathic hamster may relate to a generalized deficiency in the Ca(2+)-pump in pinealocyte plasma membranes, which leads to unusually high [Ca2+]i, causing a depression of NAT activity; this leads to the commensurate decline in pineal and serum melatonin levels. Harderian gland NAT activity and melatonin levels were essentially similar in the two groups of animals, although NAT activity was slightly depressed in the dystrophic hamsters killed during the day. The reduced amounts of intrascapular brown fat in the cardiomyopathic hamster is speculated to be a result of the diminished amount of melatonin produced in these animals.

Indole and porphyrin content of the Syrian hamster harderian glands during the proestrous and estrous phases of the estrous cycle

Porphyrin and indole metabolism was studied in the Harderian glands of Syrian hamsters during the proestrous and estrous stages of the estrous cycle. Porphyrins remained unaltered during these stages, but levels of different indoles (5-hydroxytryptophan, 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine, and 5-hydroxyindole acetic acid) exhibited pronounced changes during the dark:light period in both proestrous and estrous. There was a strong parallelism between 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine and 5-hydroxyindole acetic acid levels. Hydroxytryptophan rhythms appeared slightly shifted from those of the other indoles. Immunoreactive melatonin present in the Harderian glands did not show a significant day-night change during the stages studied.

Ultrastructure of the blood vessels in the Harderian gland of the hamster (Mesocricetus auratus): existence of sinusoids

The Harderian gland blood supply of female and male hamsters was studied using light and electron microscopy. A profuse vascularization surrounding secretory acini was observed. Among the blood vessels, the existence of large and irregular sinusoidal capillaries was apparent. These sinusoids appeared in close association to the basal aspect of the secretory cells. Typical, small, fenestrated capillaries were also observed within the connective tissue. The existence of this particular vascularization together with other morphological features of the secretory cell basal pole suggest a possible endocrine function of these orbital glands.

Androgenic control of N-acetyltransferase activity in the harderian glands of the Syrian hamster is mediated by 5 alpha-dihydrotestosterone

N-acetyltransferase (NAT) activity in the Harderian glands of intact and gonadectomized male and female Syrian hamsters was evaluated. The exogenous administration of 5 alpha-dihydrotestosterone (DHT) to castrated males and intact females produced an increase in NAT values, which reached the values present in the glands of intact males. The administration of a 5 alpha-reductase inhibitor to intact males led to a decrease in NAT activity, suggesting that testosterone is converted in DHT within the glands. It is concluded that NAT activity in the Syrian hamster Harderian glands is under androgenic control, the active steroid being DHT.

Melatonin and porphyrin in the harderian glands of the Syrian hamster: circadian patterns and response to autumnal conditions

1. Adult male Syrian hamsters were killed at nine intervals during a 24 hr period in the autumn, after 2 months either indoors in controlled conditions or in natural outdoor conditions. 2. Harderian glands were taken for determination of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities and melatonin and porphyrin concentrations. 3. Mean 24 hr Harderian NAT and melatonin values were lower outside than inside. 4. Twenty-four hour melatonin rhythms were detected with similar daytime (afternoon) acrophases in both environmental conditions. 5. An NAT rhythm was seen only in animals kept inside, with a circadian maximum in the late dark phase. 6. Mean 24 hr HIOMT activity was slightly higher outdoors than indoors, and 24 hr rhythms were not detected in either condition. 7. Mean porphyrin concentrations were higher outdoors, with 24 hr rhythms detected in both conditions and a significantly earlier nocturnal circadian maximum outdoors.