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Journal Article 2013; 34(2): 143-153 PubMed PMID: 23645312 Citation  Keywords:  Animals, Circadian Rhythm:physiology, Male, Photoperiod, Pineal Gland:metabolism, Pituitary Gland:metabolism, Rats, Rats, Sprague-Dawley, Seasons, Testis:metabolism, Testosterone:metabolism,.   

BACKGROUND: Photoperiodic changes mediate certain physiological or pathological alterations in organisms. Solstices represent either the longest or shortest photoperiod of a year.

OBJECTIVES: Intact and pinealectomized rats were used to investigate the potential changes of reproductive hormones in the hypothalamus-pituitary-testis (HPT) axis including GnRH, FSH, LH, testosterone and melatonin, and their receptors at summer solstice (SS) and winter solstices (WS).

METHODS: The levels of reproductive hormones in HPT axis and the binding characteristics of their receptors were examined using radioimmunoassay and radioreceptor assay techniques, respectively.

RESULTS: The results indicate that in the intact male rat, GnRH, LH and testosterone are higher at the SS than at the WS. However, FSH exhibited no significant seasonal changes. In the testis, Bmax and Kd of LH receptors are higher at the WS than at the SS while those of FSH receptors are higher at the SS than at the WS. In addition, the melatonin in HPT axis appeared significant differences between WS and SS. Bmax and Kd of melatonin receptors in the hypothalamus and pituitary also showed higher at the WS than at the SS. Moreover, reproductive hormone production lost their seasonal rhythms after pinealectomy.

CONCLUSION: The most important discovery in this study is that we first reported that pinealectomy had profound effects on the binding characteristics of melatonin with its subtype receptors. Especially at the hypothalamus, the dominated melatonin receptors shifted from MT1 to MT2 after pinealectomy at the two solstices....

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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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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): 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 2002; 23(Suppl 1): 92-96 PubMed PMID: 12019360 Citation  Keywords:  Diagnosis, Humans, Melatonin:blood, Neoplasms:blood, Pineal Gland:metabolism, Prognosis, Tissue Distribution,.   

: During the last decade, attention was concentrated on melatonin -- one of the hormones of the diffuse neuroendocrine system, which has been considered only as a hormone of the pineal gland, for many years. Currently, melatonin has been identified not only in the pineal gland, but also in extrapineal tissues -- retina, harderian gland, gut mucosa, cerebellum, airway epithelium, liver, kidney, adrenals, thymus, thyroid, pancreas, ovary, carotid body, placenta and endometrium as well as in non-neuroendocrine cells like mast cells, natural killer cells, eosinophilic leukocytes, platelets and endothelial cells. The above list of the cells storing melatonin indicates that melatonin has a unique position among the hormones of the diffuse neuroendocrine system, which is present in practically all organ systems. Functionally, melatonin-producing cells are certain to be part and parcel of the diffuse neuroendocrine system as a universal system of response, control and organism protection. Taking into account the large number of melatonin-producing cells in many organs, the wide spectrum of biological activities of melatonin and especially its main property as a universal regulator of biological rhythms, it should be possible to consider extrapineal melatonin as a key paracrine signal molecule for the local coordination of intercellular relationships. Analysis of our long-term clinical investigations shows the direct participation and active role of extrapineal melatonin in the pathogenesis of tumor growth and many other non-tumor pathologies such as gastric ulcer, immune diseases, neurodegenerative processes, radiation disorders, etc. The modification of antitumor and other specific therapy by the activation or inhibition of extrapineal melatonin activity could be useful for the improvement of the treatment of illness....

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Journal Article 2002; 23(1): 49-53 PubMed PMID: 11880862 Citation  Keywords:  Aging:physiology, Animals, Circadian Rhythm, Freund's Adjuvant:administration & dosage, Hydroxyindoleacetic Acid:metabolism, Injections, Subcutaneous, Male, Melatonin:metabolism, Norepinephrine:metabolism, Pineal Gland:metabolism, Rats, Rats, Wistar, Sero.   

OBJECTIVES: This study was performed to search for changes in rat pineal function attributed to age and immunization with Freund's adjuvant.

METHODS: Young (2 months) and old (18-20 months) Wistar rats were injected s.c. with Freund's adjuvant or its vehicle. Eighteen days later, at the acute phase of arthritis, pineal concentration of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE) and melatonin was measured by high pressure liquid chromatography at 4 different time intervals throughout the nocturnal activity span.

RESULTS: Old rats had the lowest pineal 5-HT and 5-HIAA content, the decrease in 5-HIAA exceeding that of 5-HT; consequently, old rats had the lowest 5-HIAA/5-HT ratio, an index of pineal 5-HT turnover. Although immunization did not affect globally pineal 5-HT or 5-HIAA levels, significant interactions "immunization x age" and "immunization x time" were found, i.e., immunization augmented pineal 5-HT content at the beginning of the activity span in young rats and at second half of the activity span in young and old rats, and increased pineal 5-HIAA concentration in young rats at the second part of the activity span only. Freund's adjuvant treatment increased pineal 5-HT turnover exclusively in old rats, an effect mainly seen during the second part of the activity span. Old rats exhibited the lowest pineal NE and melatonin levels, immunization further depressing them.

CONCLUSION: The effect of immunization with Freund's adjuvant on a number of pineal pre- and postsynaptic parameters are age-dependent....

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Journal Article 2001; 22(6): 449-452 PubMed PMID: 11781543 Citation  Keywords:  Animals, Body Weight, Circadian Rhythm:physiology, Leptin:blood, Male, Melatonin:metabolism, Pineal Gland:metabolism, Rats, Rats, Wistar,.   

OBJECTIVES: Exogenous and endogenous melatonin decrease leptin release. It is not known whether melatonin also has an effect on circadian release pattern of leptin. So, this study was planned to investigate the possible changes in the circadian release of leptin following pinealectomy.

METHODS: A group of rats were surgically pinealectomized while some others were exposed to sham operation. The animals were decapitated at 13.30 p.m. and 01.30 a.m. Serum leptin levels were measured by radioimmunoassay.

RESULTS: Serum leptin levels at 13.30 p.m. were lower than the values at 01.30 a.m. in both pinealectomized (P<0.002) and sham rats P<0.001). Serum leptin levels measured at 13.30 p.m. and 01.30 a.m. were significantly elevated (P<0.05 and P<0.01, respectively) in the pinealectomized rats in comparison to sham animals.

CONCLUSION: The circadian release of leptin does not seem to be regulated by melatonin release from the pineal gland whereas melatonin, physiologically released, may have a decreasing effect on leptin release....

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