Search NEL Online

Comparative Study 2004; 25(1-2): 102-108 PubMed PMID: 15159692 Citation  Keywords:  Adaptation, Physiological, Animals, Circadian Rhythm:radiation effects, Darkness, Light, Male, Photoperiod, Photoreceptor Cells:radiation effects, Pineal Gland:radiation effects, Rats, Rats, Wistar,.   

OBJECTIVE: This study was aimed to examine the pineal gland of rats exposed to constant light and darkness at light and electron microscopic level.

DESIGN: For this purpose 18 male Wistar rats were used. Animals were divided into three groups. Rats in group I (Control) were kept under 12 hrs light: 12 hrs dark conditions. Rats in group II were exposed to constant darkness, while rats in group III were exposed to constant light for 6 weeks. At the end of the experiment, all animals were killed by decapitation. The pineal glands of rats were removed, then processed for light and electron microscopy.

RESULTS: In our study, extensive number of pinealocytes was observed in the structure of pineal gland of rats exposed to constant darkness and some of the observed pinealocytes were determined to contain double nucleoli. Furthermore, mitochondria and lipid droplets in the cytoplasm of pinealocytes were increased and rough endoplasmic reticulum sacs were enlarged in this group. Whereas, in rats those exposed to the constant light, a decrease in pinealocyte intensity was associated with increase in the connective tissue between parenchymal cells. Additionally, mitochondria and lipid droplets in the cytoplasm of cells were decreased.

CONCLUSIONS: It was observed that the pinealocyte cell activity of rats exposed to constant darkness was increased but decreased in rats exposed to constant light....

Read abstract  Full text PDF

Comparative Study 2004; 25(1-2): 70-74 PubMed PMID: 15159686 Citation  Keywords:  Animal Feed, Animals, Antioxidants:physiology, Brain:metabolism, Dose-Response Relationship, Drug, Iodides:administration & dosage, Liver:metabolism, Lung:metabolism, Male, Melatonin:physiology, Oxidative Stress:physiology, Rats, Rats, Wistar, Schiff Base.   

OBJECTIVES: Administration of iodides to animals, living in iodine-deficient areas, can induce necrosis and fibrosis of the thyroid gland. It is believed that structural and functional changes of the thyroid may be related to oxidative processes. Increased lipid peroxidation levels were reported in murine thyroid glands after high doses of iodine. Melatonin (MEL) is believed to exert its effects via electron donation to directly detoxify free radicals, such as, e.g., the highly toxic hydroxyl radical. In numerous reports related to the antioxidative action of MEL, the authors have considered the protective ability of this hormone against peroxidation of lipids. The goal of the study was to evaluate oxidative processes and the protective role of MEL in three organs of the rat (the liver, the brain, and the lungs) during treatment with different doses of iodide.

MATERIAL AND METHODS: Schiff's bases (SB) concentrations (a parameter of oxidative stress) were measured in liver, lung and brain homogenates of male Wistar rats. The animals received iodides in their diet in the following concentrations, for 2 weeks: Group 1--Controls (standard normal-iodine diet, containing approx. 0.7 mg of kalium iodide per kg; KI/kg); Group 2--diet containing 0,25 mg KI/kg; Group 3--diet with 4,0 mg KI/kg; Group 4--diet with 8,0 mg KI/kg. Group 5--standard normal-iodine diet and MEL alone in a dose of 1 mg/kg BW i.p. at 3.00 pm, every day for two weeks. Subsequent three groups (6-8) received KI in their diet in doses as above, respectively, together with MEL.

RESULTS: We noted increased levels of SB in the lungs and in the liver, when compared to those observed in controls. We also found decreased SB concentrations in liver and lung homogenates after an administration of MEL but--unexpectedly--the level of SB increased in the group with the highest dose of iodine in diet in lung homogenates. Increased levels of Schiff's bases suggest that iodine is involved in oxidative processes not only in the thyroid but also in other tissues, and MEL protects against the iodine-induced oxidative stress.

CONCLUSION: Our results confirm the differences in lipid peroxidation among the examined organs. These alterations can possibly be related to different sensitivity rates of examined tissues to oxidative damage....

Read abstract  Full text PDF

Journal Article 2003; 24(6): 435-439 PubMed PMID: 15073571 Citation  Keywords:  2-Amino-5-phosphonovalerate:pharmacology, Age Factors, Animals, Dizocilpine Maleate:pharmacology, Excitatory Amino Acid Antagonists:pharmacology, Hypothalamus:drug effects, Injections, Intraventricular, Male, Prolactin:metabolism, Rats, Rats, Wistar, Rece.   

OBJECTIVE: To investigate the effects of N-methyl-D-aspartate (NMDA) receptor antagonists on restraint-induced release of prolactin (PRL) in male Wistar rats of different ages.

DESIGN: Rats were implanted with a brain ventricular for icv injection, and with a jugular vein cannula for iv injection. Competitive NMDA receptor antagonist AP-5 and noncompetitive NMDA receptor blocker MK-801 was injected via brain cannula or vein cannula and was restrained for 3 hours. The blood sample was collected through vein cannula during the restraint. The plasma concentration of prolactin was measured by RIA.

RESULTS: The restraint-induced PRL release in the adult rat (12-weeks) was significantly suppressed by MK-801 (50 microg/rat, icv; or 5 mg/kg, iv) and was partially inhibited by pretreatment of AP-5 (50, 100 microg/rat, icv), but was not changed by systemic administration of AP-5 (10 mg/kg, iv). MK-801 (5 mg/kg, iv) prevented the restraint-induced PRL release in the peripuberal rat (45-days) and in the middle-aged rat (16-months).

CONCLUSION: Central NMDA receptors mediate restraint-induced PRL release in the male rat....

Read abstract  Full text PDF

Journal Article 2003; 24(6): 397-400 PubMed PMID: 15073563 Citation  Keywords:  Angiotensin II:analogs & derivatives, Animals, Antihypertensive Agents:pharmacology, Cell Division:drug effects, Female, Losartan:pharmacology, Pituitary Gland, Anterior:cytology, Rats, Rats, Wistar, Receptor, Angiotensin, Type 1:metabolism, Vasoconstrict.   

OBJECTIVES: The purpose of this study was to investigate the effect of angiotensin II (AII) and angiotensin IV (AIV, 3-8 fragment of AII) on the cell proliferation in the anterior pituitary of rat in vivo.

MATERIALS AND METHODS: The female adult Wistar rats, ovariectomized 10 days before experiment were injected intraperitoneally with saline, AII, AIV and AII or AIV together with losartan--the specific AT1 receptor subtype antagonist. Bromodeoxyuridine (BrDU) incorporation into anterior pituitary cell nuclei was used as the index of cell proliferation.

RESULTS: We observed the increased BrDU-labeling index (LI) in the anterior pituitary of rat treated with either AII or AIV. The proliferogenic effect of neither AII nor AIV was reversed by AT1 specific antagonist losartan.

CONCLUSIONS: AII and AIV stimulate the rat anterior pituitary cell proliferation in vivo. This action of both angiotensin peptides is connected with activation of receptor different from AT1 subtype....

Read abstract  Full text PDF

Journal Article 2003; 24(6): 392-396 PubMed PMID: 15073562 Citation  Keywords:  Animals, Circadian Rhythm, Male, Melatonin:blood, Models, Animal, Pineal Gland:secretion, Postoperative Complications:metabolism, Pressure, Rats, Rats, Sprague-Dawley, Surgical Instruments,.   

OBJECTIVES: Pineal gland hormone, melatonin, is a current issue of interest for accumulating data concerning its diverse physiological functions. The disturbances in melatonin secretion are observed in different pathological conditions involving pineal regions, but it is not ascertained if those disturbances present any clinical implications. The aim of this work was to examine whether pineal gland compression changes melatonin secretion.

SETTING AND DESIGN: The experiment was carried out on adult rats, divided into four equal groups: (i) control (no surgery was performed), (ii) sham-operated, (iii) with sham pineal gland compression and (iv) with pineal gland compression performed by cotton piece application.

METHODS: The profile of melatonin secretion was assessed in blood samples collected five times daily, every second day, starting from 8 to 14 day following surgery.

RESULTS: We found that surgery itself significantly increased night melatonin secretion in comparison to controls. By contrast, in pineal-gland compressed rats, melatonin secretion was lower than in control group, suggesting that the influence of pineal compression overcame that induced by operation stress.

CONCLUSIONS: In conclusion, we presume that pineal gland compression (like in case of some tumors) results in decrease of the concentration of blood melatonin, that may possibly result in decreased protective action of the indoleamine....

Read abstract  Full text PDF

Journal Article 2003; 24(5): 350-354 PubMed PMID: 14647012 Citation  Keywords:  Animals, Anti-Bacterial Agents:pharmacology, Antioxidants:pharmacology, Female, Graft Survival, Malondialdehyde:blood, Melatonin:pharmacology, Necrosis, Ovary:metabolism, Oxytetracycline:pharmacology, Peritoneal Cavity, Rats, Rats, Wistar,.   

OBJECTIVES: To comparatively investigate the effects melatonin and oxytetracycline as antioxidants on autologous intraperitoneal ovary transplantation in rats.

SETTING AND DESIGN: 28 adult female Wistar rats with regular estrous cycles were randomly divided into four groups. Group 1 (n=7) was the control group; Group 2 (n=7) bilateral oophorectomy and intraperitoneal transplantation group; and Groups 3 (n=7) and 4 (n=7) firstly received 20 mg/kg/IP melatonin and 10 mg/kg/IP oxytetracycline., respectively and fifteen minutes after that, they had bilateral oophorectomy and intraperitoneal transplantation. Ovarian tissue and blood malondialdehyde (MDA) levels, superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) levels were determined. Vaginal cytology and ovarian necrosis were histopathologically investigated. Kruskall Wallis analysis of variance was used in the statistical analysis of data.

RESULTS: Ovarian necrosis, tissue MDA and plasma MDA levels were significantly higher in Group 2 compared to the Groups 1, 3 and 4 (p<0.03). SOD and GSHPx levels were significantly lower in group 2 compared to the groups 1, 3 and 4 (p<0.03). Melatonin was found to be more effective on ovarian necrosis and tissue MDA level than the use of oxytetracycline following autologous intraperitoneal ovary transplantation (p<0.03). There was a significant positive correlation between tissue MDA level and ovarian necrosis and a very strong negative correlation between tissue MDA and SOD level (rs = +/-0.9, n=28, p=0.000).

CONCLUSION: Although both melatonin and oxytetracycline were found to be effective in autologous intraperitoneal pelvic ovary transplantation, melatonin is more effective against both the ovarian necrosis and tissue MDA level in rats....

Read abstract

Journal Article 2003; 24(5): 345-347 PubMed PMID: 14647010 Citation  Keywords:  Animals, Antioxidants:pharmacology, Hyperthyroidism:drug therapy, Injections, Intraperitoneal, Male, Melatonin:pharmacology, Rats, Rats, Sprague-Dawley, Testis:drug effects, Testosterone:metabolism, Thyroid Gland:drug effects, Thyroid Hormones:metabolism,.   

OBJECTIVE: Melatonin has a general inhibitory effect on the reproductive system and thyroid functions. Testosterone secretion increases in parallel to thyroid hormones in hyperthyroidism. The aim of this study was to investigate the effects of melatonin application on total T3, T4 and testosterone in hyperthyroid rats.

METHODS: This study was performed on 4 groups each consisted of 6 male Spraque Dawley rats. Control group (G1); sham group (G2); applied 0.5 ml/day of serum physiologic intraperitoneally for 2 weeks, hyperthyroid group (G3); applied 0.3 mg/kg/day thyroxine intraperitoneally for 2 weeks, and hyperthyroid and melatonin supplemented group (G4); applied 0.3 mg/kg/day thyroxine and 3 mg/kg/day melatonin. Blood samples taken by way of decapitation were analysed for total T3, T4 and testosterone by RIA.

RESULTS: Serum total T3 and total testosterone levels were the highest in hyperthyroid group (G3), whereas in hyperthyroid and melatonin supplemented group (G4) were the lowest (P<0.001). Total T4 levels were higher in group 3 than group 1, 2 and 4 (P<0.001).

CONCLUSION: Results revealed that melatonin supplementation in hyperthyroidism suppress secretion of thyroid hormones and testosterone secretion....

Read abstract

Journal Article 2003; 24(5): 341-344 PubMed PMID: 14647009 Citation  Keywords:  3-Hydroxybutyric Acid:metabolism, Animals, Antioxidants:pharmacology, In Vitro Techniques, Malates:metabolism, Male, Melatonin:pharmacology, Mitochondria, Liver:drug effects, Oxygen Consumption:drug effects, Rats, Rats, Wistar, Succinic Acid:metabolism,.   

OBJECTIVE: To examine the in vitro effect of melatonin on rat mitochondrial liver respiration.

METHODS: Oxygen consumption by liver mitochondria was measured polarographically in the presence of one of the following Krebs' cycle substrates: Lsuccinate, DL-3- beta-hydroxybutyrate or L-malate. Respiratory velocities at rest (state 4) and during rapid respiration in the presence of substrate and adenosine diphosphate (state 3) were measured in the presence of 10 (-9)-10(-3) M concentrations of melatonin.

RESULTS: In vitro melatonin (10(-7)-10(-3) M) reduced state 3 mitochondrial respiration. Basal, state 4 respiration was not affected by melatonin. Consequently, control respiratory index (i.e., the ratio of state 3 to state 4 respiration) was inhibited by melatonin with a threshold at 10(-7) M concentration.

CONCLUSION: The ability of melatonin to curtail acutely the stimulation of oxygen consumption in liver mitochondria may protect the mitochondria from excessive oxidative damage....

Read abstract