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Comparative Study 2007; 28(2): 159-165 PubMed PMID: 17435669 Citation  Keywords:  Animals, Circadian Rhythm, Corticosterone:blood, Diabetes Mellitus, Experimental:metabolism, Gastrointestinal Tract:metabolism, Kidney:metabolism, Male, Melatonin:blood, Pancreas:metabolism, Pineal Gland:metabolism, Rats, Rats, Wistar, Spleen:metabolism, .   

OBJECTIVE: Exogenous melatonin was found to protect target organs under conditions of diabetes mellitus, however, concentrations of the hormone in peripheral tissues have not been determined. Therefore the aim of the present study was to measure the daily profile of melatonin levels in the pineal gland, plasma, pancreas, kidney, spleen, duodenum and colon of control and diabetic rats.

MATERIAL & METHODS: Diabetes was induced by a single injection of streptozotocin (STZ, 65 mg/kg of body weight) and samples were collected over a 24 hr cycle on day 17 after STZ treatment. Melatonin and corticosterone levels were measured directly in plasma and after extraction in the pineal gland and peripheral organs (pancreas, kidney, spleen, duodenum and colon).

RESULTS: A significant daily rhythm of melatonin concentrations was found not only in the pineal gland and plasma but also in the pancreas, kidney, spleen and duodenum. The daily pattern of melatonin levels in the colon was arrhythmic without a characteristic night-time increase of hormone concentration. Experimentally induced diabetes resulted in lower melatonin levels in the pancreas, kidney and duodenum as compared to control. No differences between STZ-treated and control rats were found in the spleen and colon. Plasma corticosterone levels were enhanced in diabetic rats in comparison with controls and the daily profile was not rhythmic.

CONCLUSION: Our data suggest that the lower amplitude of melatonin rhythm in target organs induced by experimental diabetes can contribute to desynchronization of daily rhythms and can lower the antioxidative capacity of tissues....

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Comparative Study 2005; 26(6): 795-798 PubMed PMID: 16380688 Citation  Keywords:  Animals, Antioxidants:metabolism, Brain:enzymology, Glutathione:metabolism, Hyperthyroidism:metabolism, Lipid Peroxidation:physiology, Liver:enzymology, Male, Malondialdehyde:metabolism, Myocardium:enzymology, Pineal Gland:physiology, Rats, Rats, Sprague-.   

OBJECTIVE: Thyroid hormones regulate energy metabolism and act on the mitochondria, which is an important source of free radicals in the cell. Reactive oxygen types play a significant role in physiological mechanisms, but in excessive amounts they can cause oxidative damage in molecules. The aim of the present study was to determine levels of lipid peroxidation caused by induced hyperthyroidism in cerebral, hepatic and cardiac tissues of pinealectomized rats.

METHODS: Experimental animals used in the study were allocated to three groups as general control group, hyperthyroidism-sham pinealectomy group and hyperthyroidism-pinealectomy group. GSH and MDA levels in cerebral, hepatic and cardiac tissues were evaluated at the end of the 3-week study period.

RESULTS: It was found that MDA levels in cerebral, hepatic and cardiac tissues were the highest in hyperthyroidism and pinealectomy group and that these values were higher in hyperthyroidism-sham pinealectomy group than in the control group (p<0.001). It was seen that tissue GSH levels significantly increased in hyperthyroidism-sham pinealectomy group (p<0.001) and that the increase in hyperthyroidism and pinealectomy group was higher than the increase in the control group only (p<0.001).

CONCLUSION: Results of our study show that MDA and GSH levels in cerebral, hepatic and cardiac tissues increased due to hyperthyroidism and that the increase in MDA levels became more evident and GSH levels were significantly suppressed after pinealectomy....

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Journal Article 2005; 26(5): 503-510 PubMed PMID: 16264410 Citation  Keywords:  Aging:physiology, Animals, Chickens:metabolism, Darkness, Female, Light, Male, Melatonin:metabolism, Organ Culture Techniques, Perfusion, Pineal Gland:metabolism, Temperature,.   

: The melatonin rhythm of cultured chicken pineal cells can be synchronized by cyclic environmental effects. Unlike the effects of light on the melatonin secretion, those of the temperature changes are much less known. Similarly, only a few data are available on the interactions between environmental illumination and periodic temperature changes and on the sensitivity of the pineal gland to temperature changes in different ages of animals. We monitored the effects of temperature on chicken pineals for several days in vitro, in a perifusion system under different illumination patterns. The effects of temperature on pineals from chicken of different age were also compared. The phase of the melatonin rhythm was controlled by periodic elevations of temperature under both constant darkness and continuous illumination. These results show that rhythmic changes of temperature prevent desynchronization induced by constant light. Following elevation of the temperature, the melatonin rhythm of pineals of young chickens (less, than 14 weeks old) was altered for 16 - 18 hours. Similar changes in melatonin rhythm were not found in older animals. It is concluded that the sensitivity for temperature changes of the pineal cells is varying with age....

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Journal Article 2005; 26(5): 511-514 PubMed PMID: 16264409 Citation  Keywords:  Aging:physiology, Animals, Animals, Newborn, Cell Count, Colon:pathology, Hyperplasia, Male, Neurosecretory Systems:pathology, Paraffin Embedding, Pineal Gland:physiology, Rats, Rats, Wistar,.   

OBJECTIVES: The diffuse neuroendocrine system (DNES) participates in the systemic homeostasis and may work as a unified system with integrated functions but anatomically disperse. However, the mechanisms that are involved in the integration of the distant parts of the DNES are poorly known. This study is aimed on the effects of a pinealectomy on the population of the neuroendocrine cells (NECs) in the colon of rats.

METHODS: A group of seven newborn rats and one of adult rats were submitted to a pinealectomy. The animals were sacrificed after 15 days and 90 days, respectively. The control groups of adult and newborn rats were subjected to a 'sham surgery' and then sacrificed after similar periods of time. Paraffin-included sections of the colon samples were stained by the Churukian-Schenk method in order to selectively stain the NECs. The NEC index was estimated by the expression: iNEC = NECs population per crypt/Total cell population of the crypt. The results were expressed as median and absolute range, and the statistical significance was demonstrated by the Mann-Whitney (U) test.

RESULTS: The morphometric analysis showed a significant increase in the number of colonic NECs of the adult rats subjected to a pinealectomy when compared to the controls. No statistical difference was observed between the iNECs of the newborn groups of rats.

CONCLUSION: This finding suggests the existence of regulatory mechanisms that integrate distant parts of the DNES, by adapting the population of the endocrine cells after the ablation of an important component of the system. Further studies on the mechanisms involved in the integration of the DNES may be facilitated by the simple experimental model that we propose....

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Journal Article 2005; 26(5): 575-580 PubMed PMID: 16264398 Citation  Keywords:  Acetylserotonin O-Methyltransferase:metabolism, Animals, Arylalkylamine N-Acetyltransferase:metabolism, Female, Melatonin:blood, Microscopy, Electron, Pineal Gland:metabolism, Pregnancy, Pregnancy, Animal:metabolism, Rabbits, Radioimmunoassay,.   

OBJECTIVES: The morphological and biochemical aspects of the pineal gland of pregnant and non-pregnant female vizcachas were investigated to examine whether there is a relationship between the pregnancy and this gland.

METHODS: Pregnant and non-pregnant adult female vizcachas were used. The ultrastructure of type I cell (dark and light pinealocytes) was studied. Pineal and serum melatonin were investigated by radioimmunoassay. Radiometric methods were applied to investigate the arylalkylamine-N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities.

RESULTS: The morphological study showed the existence of dark and light pinealocytes. The differences between both cells are slight. However, the appearance of dark pinealocytes suggests that they have a high activity. These cells were more abundant in the pineal gland of pregnant females. The pineal melatonin levels and the AA-NAT activity were higher in the pregnant females. Serum melatonin and HIOMT activity did not show significant differences.

CONCLUSION: Our results suggest that the morphological and biochemical changes in the pineal gland of pregnant vizcachas are associated with the gestation. However, the relation between the pineal gland and the pregnancy is complex and further studies are necessaries to clearly establish it....

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Journal Article 2005; 26(5): 581-592 PubMed PMID: 16264397 Citation  Keywords:  Animals, Arylalkylamine N-Acetyltransferase:antagonists & inhibitors, Data Interpretation, Statistical, Depression, Chemical, Female, In Vitro Techniques, Melatonin:metabolism, Norepinephrine:antagonists & inhibitors, Perfusion, Pineal Gland:cytology, Rad.   

OBJECTIVES: Cell-permeable and specific inhibitors of melatonin secretion are sill lacking among tools of the pineal research. Recently, a large effort has been made in the development of arylalkylamine N-acetyltransferase inhibitors, but in most cases the new drugs were tested exclusively using cell-free assays or non-pineal cells. The aim of the present study was to characterize the effect of N-bromoacetyltryptamine (BAT), the first synthesized cell-permeable inhibitor of arylalkylamine N - acetyltransferase, on melatonin secretion from rat and pig pineal glands.

METHODS: The studies were performed in the superfusion cultures of rat and pig pineal explants. Melatonin secretion was determined by radioimmunoassay (RIA).

RESULTS: BAT strongly inhibited the non-stimulated and norepinephrine - stimulated melatonin secretion from the pig and rat pineal explants, with ED50 0.3 - 0.7 microM. The adrenergic stimulation did not modify significantly the inhibitory potency of BAT on the melatonin release. The decline in melatonin secretion induced by the BAT - treatment was biphasic in both rat and pig pinealocytes, with an initial rapid phase followed by a slow one. The half-time of BAT-induced decline in the non - stimulated and norepinephrine-stimulated melatonin secretion was ca. 25 - 35 minutes. The inhibitory effect of BAT was reversible in pinealocytes of both investigated mammals.

CONCLUSIONS: The results show that BAT is a potent and reversible inhibitor of the melatonin secretion in the mammalian pineal gland and open the way for the use of this inhibitor in investigations on the pinealocyte physiology performed in vitro....

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Journal Article 2005; 26(4): 383-392 PubMed PMID: 16136004 Citation  Keywords:  Age Factors, Animals, Immunohistochemistry, Male, Methyltransferases:metabolism, Pineal Gland:cytology, Turkeys:anatomy & histology,.   

OBJECTIVE: The study was performed to analyze structural changes of the turkey pineal during the post-hatching development.

MATERIAL AND METHODS: The pineals were collected from male turkeys at the age of 1 day, 2, 8, 22, 56 weeks and subjected to histological investigations including morphometrical analyses. The pinealocytes were identified immunohistochemically using antiserum against hydroxyinolo-O-methyltransferase (HIOMT).

RESULTS AND CONCLUSIONS: Independently of age, the pineal consisted of a narrow proximal part and a club-shaped top. The narrow part extended into the stalk attached to the diencephalon. The pineal parenchyma was formed by the follicles, surrounded by the connective tissue. The caudal part of the organ contained the pineal lumen, which prolonged into the stalk lumen. Up to the age of two weeks the stalk lumen was open to the third ventricle, later--closed. The proximal part of the stalk showed age-dependent reduction. During the investigated period of life, the pineal increased in size due to creation of new follicles, enlargement of the follicles and development of the stroma. In immature turkeys, the follicular wall was formed by elongated cells bordering the lumen and sparse, peripherally localized, round cells. This pseudostratified organization was transformed during ontogenesis into thick, multilayer structure (characteristic for 22- and 56-week-old turkeys) composed by the layer of elongated cells and several layers of round cells, located peripherally. The rudimentary-receptor and secretory pinealocytes were demonstrated based on HIOMT-immunoreactivity. The secretory pinealocytes were sparse in young birds and predominated in mature turkeys. Intra-pineal calcified concrements occurred in 56-week-old turkeys....

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Comparative Study 2004; 25(4): 257-261 PubMed PMID: 15361813 Citation  Keywords:  Adrenergic beta-Agonists:pharmacology, Age Factors, Animals, Circadian Rhythm:drug effects, Isoproterenol:pharmacology, Male, Melatonin:biosynthesis, Organ Culture Techniques, Photoperiod, Pineal Gland:drug effects, Rats, Rats, Wistar, Time Factors,.   

OBJECTIVES: The purpose of this study was to investigate and compare the effects of the beta-adrenergic agonist, isoproterenol, on induced increase in melatonin production in the pineal gland of young and old rats, at different circadian stages.

MATERIALS AND METHODS: We report here the effects of 10(-6) M isoproterenol-stimulated melatonin production by perifused pineal glands obtained from young (55 day old) and old (21 month old) male Wistar rats acclimatised to light:dark cycles regimen of 12:12 for 3 weeks. Pineal glands were collected at different circadian stages: 3, 7, 11, 15, 19 and 23 hours after light onset (HALO), and perifused for 510 min.

RESULTS: The basal levels of melatonin production in the young rats were approximately twice greater than those of the old rats. Isoproterenol stimulated melatonin production in both young and old rat pineal glands, whatever the circadian stage. The intensity of the response to 10(-6) M isoproterenol infusion was greater in young than in old rat pineal glands (P<0.001), with a trend towards an increase during the light phase, at 7 HALO, in both young and old rat pineal glands, although this trend towards increased melatonin response did not reach statistical significance (P>0.05).

CONCLUSIONS: These results show that isoproterenol is able to stimulate both young and old rat pineal glands whatever the circadian stage. The magnitude of isoproterenol stimulation is greater in young than in old glands. Our results also suggest that the pineal gland response to isoproterenol is not dependent on circadian stage, at least, under our experimental conditions....

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