bluuebunny/crossref_metadata_2025 huggingface dataset:
Exogenous melatonin modifies the circadian rhythm but does not increase the level of some immune parameters in the chicken
Authors: Skwarto‐Sołta Krystyna , Thaela Mary‐Jane , Midura Monika , Lech Beata , Głuchowska Boźna , Drela Nadzieja , Kozłowska Ewa , Kowalczyk Renata
Published: February 2007

Abstract: The effect of daily injections of the pineal hormone melatonin and naltrexone, an opioid antagonist, on the circadian rhythm and the level of immune parameters (plaque forming cell [PFC] number, serum agglutinin titer, lymphoid gland weight, total white blood cells (WBC) and their fraction number, and serum lysozyme [LZ] content) was examined in White Leghorn cockerels and female BALB/c mice kept in LD 12:12. Animals were immunized ip with sheep red blood cells (SRBC) to stimulate their immune system. Subcutaneous injections of melatonin, naltrexone, or both drugs together were made 2 hr before the end of light, for 4 or 5 days, beginning on the day of immunization. The day following the fifth injection, chickens were sacrificed over a 24 hr period every 4 hr (experiment I) or twice daily, i.e., at the beginning of light and dark phases (experiment II). Mice were killed on the day following the fourth injection at the beginning of light, and splenic PFC number was determined (experiment III). In experiment I, the existence of the diurnal rhythm was evaluated by cosinor analysis. Melatonin injections entrained the circadian rhythm in anti‐SRBC serum agglutinins, but it did not influence circadian rhythmicity in other parameters examined. The circadian rhythm in total WBC number and their fractions was entrained by naltrexone treatment. Melatonin injections did not affect either the diurnal mean of parameters examined or the weight of lymphoid organs. Splenic PFC number in chickens was diminished by both melatonin and naltrexone injections, whereas in mice it was increased by melatonin, and naltrexone antagonized that effect. It is concluded that melatonin in chickens, at least in the dose range used, is not an immunoenhancing agent, as in mice. Possible reasons for this difference are discussed.
Serotonin content and melatonin production in the pineal gland of the male Djungarian hamster (Phodopus sungorus)
Authors: Lerchl Alexander , Schlatt Stefan
Published: February 2007

Abstract: Diurnal variations in serum melatonin levels and pineal concentrations of serotonin (5‐HT), N‐acetylserotonin (NAS), 5‐hydroxyindole acetic acid (5‐HIAA), and melatonin were estimated in adult male Djungarian hamsters kept under long‐day (LD 16:8) or short‐day (LD 8:16) photoperiods. The nocturnal increase in melatonin production was accompanied by a marked drop in pineal serotonin concentrations. Serotonin levels, however, decreased approximately 4 hr before pineal melatonin increased. Correlations of the mean values for pineal serotonin and pineal melatonin indicated significant correlations at both LD 16:8 (r = ‐0.92, P < 0.001) and LD 8:16 (r = ‐0.85, P < 0.001). The mean levels of pineal serotonin and serum melatonin were correlated as well (LD 16:8, r = ‐0.91, P < 0.001; LD 8:16, r = ‐0.81, P < 0.01). The levels of pineal serotonin declined at approximately the same time as serum melatonin levels increased. These data suggest that the drop in pineal serotonin is primarily a consequence of melatonin production (as reflected by increasing serum concentrations). Consequently, pineal concentrations of melatonin may not be the best estimate of actual melatonin production, but a measure of how much melatonin is accumulated within the pineal due to high synthesis rates while the release of the hormone from the gland is limited.
Diurnal changes in cyclic nucleotide response to pineal indoles in murine mammary glands
Authors: Cardinali Daniel P. , Bonanni Rey Roberto A. , Mediavilla M. Dolores , Sánchez‐Barceló E.
Published: February 2007

Abstract: The aim of this study was to determine whether pineal indoles affect cyclic nucleotide levels in mammary gland slices of BALB/c adult mice. Melatonin at 0.1 nM ‐ 10 μM concentrations decreased cAMP and augmented cGMP concentration in murine mammary gland slices in the presence of a phosphodiesterase inhibitor (1 mM theophylline), an index of cyclic nucleotide synthesis. Melatonin‐induced changes in cyclic nucleotide levels were significantly larger at the end of the light period (2000) than in the morning (at 1000). Indole‐induced inhibition of cyclic AMP levels by mammary slices exhibited the following order of potency: 5‐methoxytryptamine > melatonin > 6‐hydroxymelatonin > serotonin, N‐acetylserotonin > 5‐hydroxytryptophol. The order of potency for indole‐induced augmentation of cyclic GMP levels was: 5‐methoxytryptamine > melatonin > 6‐hydroxymelatonin > serotonin, N‐acetylserotonin, 5‐hydroxytryptophol. When melatonin or 5‐methoxytryptamine (10 nM) were examined for their effects on cAMP and cGMP levels in mammary glands of mice killed at six different time intervals during the 24‐hr cycle, the activity was maximal during night. The data demonstrate that 5‐methoxytryptamine and melatonin decreased cAMP and increased cGMP levels in mammary gland slices. Methoxyindole‐induced changes in cyclic nucleotide synthesis in murine mammary glands exhibit the time‐dependency known to occur in several other melatonin‐influenced responses.
Antiproliferative effect of pineal indoles on cultured tumor cell lines
Authors: Sze S.F. , Ng T.B. , Liu W.K.
Published: February 2007

Abstract: The in vitro antiproliferative action of pineal indoles on several tumor cell lines including melanoma (B16), sarcoma (S180), macrophage‐like cell line (PU5), fibroblasts (3T3), and choriocarcinoma (JAr) was examined by measuring the incorporation of 3H‐thymidine by the tumor cells, and, in the case of melanoma cells, by also measuring the incorporation of 3H‐leucine and 3H‐uridine. Uptake of crystal violet was used to assess the viability of the tumor cells. The order of inhibitory potency of the indoles was found to be methoxytryptamine > melatonin, methoxytryptophol, hydroxytryptophol, and methoxyindoleacetic acid > serotonin and hydroxyindoleactic acid. The possibility of an adverse effect of the indoles on the viability of normal cells was also investigated by employing a primary culture of rat hepatocytes. The release of glutamate‐oxaloacetate transaminase by hepatocytes was not affected by the indoles, although the release of glutamate‐pyruvate transaminase was increased to a small extent and the uptake of crystal violet was slightly inhibited
Vasopressin and vasoactive intestinal peptide infused in the paraventricular nucleus of the hypothalamus elevate plasma melatonin levels
Authors: Kalsbeek A. , Rikkers M. , Vivien‐Roels B. , Pévet P.
Published: February 2007

Abstract: The connection between the suprachiasmatic nucleus (SCN) and the paraventricular nucleus of the hypothalamus (PVN) forms an important component of the melatonin rhythm‐generating system. However, the chemical identity of this projection is not known. To test the possible implication of the SCN peptides vasopressin (VP) and vasoactive intestinal peptide (VIP) in this projection, we performed microinfusions in the PVN during the first half of the dark period and subsequently monitored resulting plasma melatonin levels. Infusions for 7 hr of either VP or VIP, but not oxytocin, caused increased plasma melatonin levels in the middle of the dark period. These observations confirm the role of the PVN in the melatonin rhythm‐generating pathway and indicate that both VP and VIP released at the level of the PVN, and probably derived from the SCN, are able to influence peripheral plasma melatonin levels.
Distribution of melatonin in mammalian tissues: The relative importance of nuclear versus cytosolic localization
Authors: Menendez‐Pelaez Armando , Reiter Russel J.
Published: February 2007

Abstract: Besides its presence in the pineal gland, melatonin has been found in a variety of other tissues as well. The indoleamine also has been identified in invertebrates including an unicellular organism where it exhibits a diurnal rhythm. Although melatonin is mainly known for its effects on seasonal reproduction and endocrine physiology, there is evidence showing that this ubiquitously acting hormone is also a potent free radical scavenger, thereby providing protection from oxidative attack to DNA and other biomolecules. Through the years, melatonin was thought to be exclusively cytosolic. However, careful examination of some of these pioneering reports revealed a nuclear localization of melatonin in different tissues including the retina and Harderian glands. Using a very sensitive immunocytochemical method, we have also found that melatonin is located in the nucleus of many cells where it may bind to nuclear components. The use of cell fractionation studies followed by radioimmunoassay confirmed these results. The administration of exogenous melatonin resulted in a marked increase in the nuclear melatonin content without a concomitant change in the cytosolic fraction. In addition to its ability to scavenge free radicals, its location in the nucleus suggests possible genomic actions.
Nor epinephrine induces Ca2+ release from intracellular stores in rat pinealocytes
Authors: Sáez Juan C. , Moreno Alonso P. , Spray David C.
Published: February 2007

Sáez JC, Moreno AP, Spray DC. Nor epinephrine induces Ca 2+ release from intracellular stores in rat pinealocytes. J. Pineal Res. 1994: 16: 57–64.

In rat pinealocytes, an increase in intracellular Ca2+ concentration ([Ca2+]i) due to Ca2+ influx in response to nor epinephrine (NE) is a well recognized event involved in regulating several metabolic functions. Since NE also stimulates the metabolism of phosphatidyl inositols in rat pineal gland, it is conceivable that Ca2+ release from intracellular stores also contributes to the NE‐induced increase in [Ca2+]i. In this communication, we report that in rat pinealocytes loaded with fura‐2, a Ca2+ indicator, NE induced a transient increase in [Ca2+]i that preceded the known Ca2+ influx. This novel [Ca2+]i response to NE was detected in pinealocytes bathed with Ca2+‐free saline and prevented by TMB‐8, a blocker of Ca2+ release from intracellular stores, supporting the notion that the transient NE‐induced Ca2+ response was due to Ca2+ release from intracellular stores. In addition, after an extended exposure to NE a new addition of this neurotransmitter did not elicit the phasic Ca2+ response, and application of increasing amounts of NE induced a Ca2+ response that was progressively smaller, suggesting desensitization. Thus, NE is proposed to increase [Ca2+]i in rat pinealocytes by two mechanisms: (1) phasic release from intracellular stores and (2) tonic influx through a mechanism activated by larger applications of NE than required to evoke the phasic release.
Impact of light pulses on 6‐sulphatoxymelatonin rhythms in rats
Authors: Away David J. Ken , Rowe Shawn A.
Published: February 2007

Kennaway DJ, Rowe SA. Impact of light pulses on 6‐sulphatoxymelatonin rhythms in rats. J. Pineal Res. 1994: 16: 65–72.

The acute and residual entraining effects of a 15 min pulse of light on rat pineal function in individual animals were investigated using the excretion rate of the melatonin metabolite, 6‐sulphatoxymelatonin, as an index of melatonin production. In animals maintained in a 12‐hr L: 12‐hr D photoperiod (lights off 1800), 15 min light exposure at 2000 had no significant effect on the metabolite rhythm. Light pulses at 2200 (i. e., after the onset of excretion) decreased the melatonin metabolite excretion rate for 3 hr, after which the excretion rate increased to normal. In contrast, pulses at 2400 and 0200 suppressed 6‐

sulphatoxymelatonin for the rest of the night such that total excretion was 58 ± 8% and 66 ± 6% of the amount excreted on the night before the pulse. A light pulse at 0400 had no significant effect on the 6‐sulphatoxymelatonin excretion when compared with the first night collection. When the 6‐sulphatoxymelatonin rhythm was assessed on the night following light pulses at 2000 and 0400, the onset of metabolite excretion was unaffected (0.2 ± 0.75‐hr advance and 0.75 ± 0.15‐hr delay, respectively). In contrast, pulses at 2200, 2400, and 0200 resulted in significant delays in the onset of 2. 4 ± 0.2‐hr, 1.5 ± 0. 1‐hr, and 2.1 ± 0.3‐hr, respectively (P < 0.05). The offset of metabolite excretion was not significantly affected by a prior light pulse, except in animals receiving light treatment at 0400 when the offset was advanced by 1.5 ± 0.3 hr. In an associated experiment, the effect of constant darkness during the day after a 2200 light pulse was compared with our standard condition of light exposure from 0900 to 1800. The phase delay provoked by the light pulse was similar in both conditions (2.9 ± 0.4 hr and 2.2 ± 0.2 hr delays, respectively; P > 0.05). These results confirm the differential responsiveness of the pineal gland to light pulses during the night, both in terms of the acute suppression of melatonin production and the subsequent entraining effect of the melatonin rhythm, which had previously been assessed indirectly by serration‐N‐acetyltransferase (NAT) determinations.
Differential regulation of melatonin receptors by short‐ versus long‐term pinealectomy in the rat suprachiasmatic nuclei and pars tuberalis
Authors: Gauer François , Masson‐Pévet Murielle , Pévet Paul
Published: February 2007

Gauer F, Masson‐Pévet M, Pévet P. Differential regulation of melatonin receptors by short‐ versus long‐term pinealectomy in the rat suprachiasmatic nuclei and pars tuberalis. J. Pineal Res. 1994: 16: 73–76.

We have investigated the effects of short‐ and long‐term pinealectomy on the density of melatonin receptors in both the suprachiasmatic nuclei (SCN) and pars tubercles (PT) of the rat. Short‐term pinealectomy (conducted 3‐5 days before sacrifice) induced a significant increase in the density of melatonin receptors in both structures. This increase can be interpreted as an up‐regulation of melatonin receptors following the absence of plasma melanoma. In contrast, 7 days after pinelectomy, the receptor density began to decrease, reaching a low point 1. 5 months after pinealectomy. At this time, the decrease represents a 40‐45% reduction in binding sites as compared with values measured 3–5 days after pinealectomy. This slow decrease could be related to a slowdown of melatonin receptor synthesis. These results suggest that emblazoning has a stimulatory effect on its own receptor synthesis. However, at 1. 5 months after pinealectomy a novel equilibrium between synthesis and hydrolysis seems to be reached. Melanoma does not appear to be indispensable for the synthesis of its receptors.
Localization and characterization of [125I]iodomelatonin binding sites in duck gonads
Authors: Ayre Elizabeth A. , Wang Zheng Pin , Brown Gregory M. , Pang Shiu Fun
Published: February 2007

Ayre EA, Wang ZP, Brown GM, Pang SF. Localization and characterization of [125I]iodomelatonin binding sites in duck gonads. J. Pineal Res. 1994: 17: 39–47.

The characterization and localization of [125I]iodomelatonin binding sites in the gonads advances the understanding of possible regulatory sites of melatonin action. With the availability of [125I]iodomelatonin as a biologically active radioligand, our study utilized a combined approach of autoradiography for anatomical resolution together with an established radioligand binding assay to assess mid‐light [125I]iodomelatonin binding in the testes and ovaries of ducks. In the autoradiography study, specific [125I]iodomelatonin binding was shown to be homogeneous throughout the testes, while in the ovaries, specific [125I]iodomelatonin binding appeared to be concentrated around the follicle. Radioligand binding assay results indicated a single class of binding sites with the maximum number of [125I]iodomelatonin binding sites measured at 1. 91 ± 0. 70 fmol/mg protein in testicular membrane and 4. 54 ± 0. 64 fmol/mg protein in ovarian membrane. [125I]Iodomelatonin binding affinity, characterized by equilibrium dissociation constants of 29 ± 6 pmol/L in testicular membrane and 53 ± 9 pmol/L in ovarian membrane, was in accordance with circulating melatonin levels, suggesting an appropriate concentration for eliciting a physiological response. [I]Iodomelatonin binding in duck gonads satisfied all the criteria for a binding site, being rapid, stable, saturable, reversible, specific, and of high affinity, and may indicate a direct pineal‐gonadal connection.
Direct influence of melatonin on steroid, Nona peptide hormones, and cyclic nucleotide secretion by granulosa cells isolated from porcine ovaries
Authors: Sirotkin Alexander V.
Published: February 2007

Sirotkin AV. Direct influence of melatonin on steroid, nonapeptide hormones, and cyclic nucleotide secretion by granulosa cells from porcine ovaries. J. Pineal Res. 1994; 17: 112–117.

The release of progesterone, estradiol‐173, oxytocin, arginine‐vasopressin, cAMP, and cGMP by cultured granulosa cells isolated from porcine ovaries without and in the presence of melatonin (0. 001, 0. 01, 0. 1, 1, 10, and 100 ng/ml medium) was analyzed. It was found that melatonin is able to inhibit progesterone and stimulate estuarial secretion. Melatonin treatments significantly inhibited oxytocin release. Some inhibition of vasopressin and cAMP and significant stimulation of cGMP also resulted from melatonin treatment. The present observations suggest a direct effect of melatonin on the steroid, nonapeptide hormone, and cyclic nucleotide release from porcine ovarian cells.
The enzymatic basis for the rat liver 6‐hydroxymelatonin sulfotransferase activity
Authors: Singer Sanford S. , Hagedorn Julie E. , Smith Dale M. , Williams Jennifer L.
Published: February 2007

Abstract: Understanding 6‐hydroxymelatonin (6HM) sulfation is deemed impor‐tant to explaining normal and oncostatic actions of the pineal gland. Here we identify the enzymatic basis for this sulfation in rats. First, a quantitative assay was designed for measuring hepatic 6HM sulfotransferase (6HMST) activity. The as‐say was then used to identify a male dominant sexual dimorphism wherein liver from males contains double the 6HMST per g or per 100 g body weight seen in fe‐males. Examination of other rat tissues showed that most in vivo 6HM sulfation was likely to occur in liver. In addition, DEAE‐Sephadex chromatography of liver cytosol indicated that 80–90% of the 6HMST activity in both sexes was due to an enzyme we named 6HMST II. A minor 6HM sulfotransferase (6HMST I) eluted from the columns prior to the main enzyme. 6HMST II, purified additionally, was shown to convert 6HM to a product that appeared to be 6HM sulfate (6‐sulfa‐toxymelatonin). The enzyme was inhibited by Na+, K+, Zn2+, and Cd2+. Its pH op‐timum was 7.80 ± 0.30. Comparisons are made between 6HMST II, dopamine sulfotransferase II, and aryl sulfotransferase IV.
On the primary functions of melatonin in evolution: Mediation of photoperiodic signals in a unicell, photooxidation, and scavenging of free radicals*
Authors: Hardeland Ruediger , Balzer Ivonne , Poeggeler Burkhard , Fuhrberg Birgit , Una Higinio , Behrmann Gudrun , Wolf Rupert , Meyer Torsten J. , Reiter Russel J.
Published: February 2007

Abstract: Melatonin is widely abundant in many eukaryotic taxa, including vari‐ous animal phyla, angiosperms, and unicells. In the bioluminescent dinoflagellate Gonyaulax polyedra, melatonin is produced in concentrations sometimes exceed‐ing those found in the pineal gland, exhibits a circadian rhythm with a pro‐nounced nocturnal maximum, and mimics the short‐day response of asexual encystment. Even more efficient as a cyst inducer is 5‐methoxytryptamine (5MT), which is also periodically formed in Gonyaulax. In this unicell, the photoperiodic signal‐transduction pathway presumably involves melatonin formation, its deace‐tylation to 5MT, 5MT‐dependent transfer of protons from an acidic vacuole, and cytoplasmic acidification. According to this concept, we observe that cyst forma‐tion can be induced by various monoamine oxidase inhibitors and protonophores, that 5MT dramatically stimulates H+‐dependent bioluminescence and leads to a decrease of cytoplasmic pH, as shown by measurements of dicyanohydroquinone fluorescence. Cellular components from Gonyaulax catalyze the photooxidation of melatonin. Its property of being easily destroyed by light in the presence of cel‐lular catalysts may have been the reason that many organisms have developed mechanisms utilizing this indoleamine as a mediator of darkness. Photooxidative reactions of melatonin, as studied with crude Gonyaulax extracts and, more in de‐tail, with protoporphyrin IX as a catalyst, lead to the formation of N1 ‐acetyl‐N ‐formyl‐5‐methoxykynuramine (AFMK) as one of the main products. Photochemical mechanisms involve interactions with a photooxidant cation radi‐cal leading to the formation of a melatonyl cation radical, which subsequently combines with a superoxide anion. Photooxidation of melatonin represents one of several possibilities of a more general, biologically highly important property of this indoleamine to act as an extremely efficient radical scavenger, including its feature of terminating radical reaction chains by a final combination with the su‐peroxide anion. Trapping of free radicals may reflect the primary and evolutionar‐ily most ancient role of melatonin in living beings.
Calbindin‐D28k, calretinin, and S‐100 immunoreactivities in rat pineal gland during postnatal development
Authors: Bastianelli Enrico , Pochet Roland
Published: February 2007

Abstract: Profound morphological modifications occur during postnatal development of the rat pineal gland. We have immunohistochemically followed those events from postnatal day 1 to 20 by using three cytoarchitectonic markers (S‐100, calbindin‐D28k, and calretinin) that belong to the calmodulin/troponin C calcium‐binding protein family. In the developing rat pineal, anticalbindin‐D28k antibody labels three cell types: immature and mature astrocytes and perivascular type II pinealocytes. During development, calbindin‐D28k positive cells migrate from the base of the pineal stalk into the superficial part of the pineal. Calbindin‐D28k, usually used as a neuronal marker in the central nervous system, recognizes in rat pineal precursor astrocytes 5 days before S‐100 and labels a subpopulation somewhat different from S‐100 positive astrocytes. Calretinin im‐munoreactivity appeared in the postero‐superior part of the pineal and was abundant until postnatal day 5, then its density dramatically felt to leave, after postnatal day 20, an occasional population of cells whose morphology is compatible with neuron‐like cells.
Distinct modes of melatonin secretion in normal men
Authors: Follenius M. , Weibel L. , Brandenberger G.
Published: February 2007

Abstract: As for many hormones, melatonin levels in the blood suggest that it is discharged from the pineal gland in a pulsatile manner. Recently, the existence of short‐term episodes, superimposed on the circadian pattern of circulating melatonin, has been questioned. Because plasma melatonin levels reflect not only the secretory process, but also the effects of distribution and degradation, secretory rates were estimated from peripheral levels, using a deconvolution procedure. Fourteen healthy volunteers were studied during the night, while sleeping in the dark (2300–0700), and seven of them subsequently were used in a replicate study. Plasma melatonin levels were measured at 10‐min intervals by a direct, specific radioimmunoassay. Pulse analysis was performed using the computer program ULTRA. Approximately 30% more pulses were detected on the overall secretory profiles than on plasma profiles. The pulses occurred at random intervals and were often superimposed on tonic basal secretion. Their number, amplitude, and distribution over time were variable depending on subjects. Also the mean melatonin secretory rate varied more than threefold across individuals. Despite the large interindividual variability, the subjects, who were used in replicate experiment, displayed a rather similar secretory profile. We conclude that in normal adult men, melatonin secretion undergoes two distinct secretory modes, in which episodic secretion is superimposed on tonic secretion in subject‐dependent variable proportions.
Effects of the chemical denervation on the glial cells of the rat pineal gland: An immunocytochemical study during postnatal development
Authors: López‐Muñoz Francisco , Boya Jesús
Published: February 2007

Abstract: We have studied the postnatal evolution of the glial cells in the rat pineal gland after its chemical pre‐ and perinatal denervation, by the assessment of the immunocytochemical expression of three antigens characteristic of glial cells i.e., vimentin (VIM), glial fibrillary acidic protein (GFAP), and S‐100 protein. The neurotoxic agents we applied consisted of 6‐hydroxydopamine (6‐OHDA) administered during the first 5 postnatal days, and N‐(2‐chloroethyl)‐N‐ethyl‐2‐bro‐mobenzylamine (DSP‐4) injected to pregnant rats in the 15th gestational day. VIM immunoreactivity was detected in pineal glial cells from the first postnatal day, both in denervated and control groups. However, in denervated glands, the maturation process of the glial cells is considerably accelerated, since they appear completely detached of the connective tissue septa at day 15. From day 30, the number of VIM‐positive structures progressively increases until adulthood, when a large number of immunoreactive cell processes produces a reticular appearance to the denervated pineal gland. The first GFAP and S‐100 protein immunoreactive cells were observed earlier in denervated animals (5th postnatal day for S‐100 protein, and 10th postnatal day for GFAP) compared with controls. In the experimentally denervated groups, the population of positive cells, as well as their size and the number of their cell processes, is considerably higher and progressively increased. They were always characteristically located in the proximal half of the gland. From day 45, this region of the gland shows a notable amount of hypertrophic positive cells with thick processes, showing a gliotic aspect. This increase in the immunoreactive structures to the glial antigens we applied, and the acceleration of their expression in denervated animals, are interpreted as a functional reaction of the glial component of the gland that would enhance the synthesis and liberation of neurotrophic factors (such as nerve growth factor) to adapt to this particular experimental condition of lack of nerve supply.
Overnight human plasma melatonin, Cortisol, prolactin, TSH, under conditions of normal sleep, sleep deprivation, and sleep recovery
Authors: von Treuer Kathryn , Norman Trevor R. , Armstrong Stuart Maxwell
Published: February 2007

Abstract: Early investigations of the effect of sleep deprivation on plasma melatonin reported no major changes. Recently, 36 hrs of sleep deprivation was reported to elevate melatonin levels on the post‐sleep deprivation night. Given these contradictions melatonin, Cortisol, prolactin, and thyroid stimulating hormone before, during, and, after sleep deprivation were examined in nine healthy young males following one night of sleep deprivation. Hormone levels at hourly intervals, for each night, were statistically analyzed by a repeated measures, two‐way factorial ANOVA. ANOVA was also performed for measures of area under the curve (AUC). No significant differences were observed for melatonin levels. Cortisol was significantly higher on the sleep deprivation night presumably reflecting the aroused state accompanying being awake; however, there were several time points on the control night when it was elevated also. Prolactin was higher on the post‐sleep deprivation and control nights but did not rise on the deprivation night, indicating a useful nonpolysomnographic index for discriminating overnight sleep and awake states. TSH levels showed a similar rise during the control and sleep deprivation nights, but remained flat on the post‐sleep deprivation night. It appears that the pineal is insulated against feedback from changes to the level of arousal accompanying sleep and wakefulness. In comparison, Cortisol, prolactin, and TSH levels vary with these states and are, therefore, useful indices of arousal and sleep‐wake.
Dithiothreitol treatment permits measurement of melatonin in otherwise unusable saliva samples
Authors: Clemons Aaron A. , Geffen Jon F. , Otto Joanne M. , Pratt Katherine L. , Harker Christian T.
Published: February 2007

Abstract: Melatonin research has primarily utilized blood as the source of samples, but there is now increasing interest in measuring levels of the hormone found in saliva. One impediment to this approach is that several melatonin assays involve a column‐extraction step that can prove very time‐consuming or even impossible when salivary samples are excessively viscous. We have treated 67 samples with dithiothreitol to enhance their passage through the column. Following this treatment, all samples passed freely through the columns. The minimum and maximum values measured were 0.7–50.0 pg/ml for the untreated controls and 1.0–51.9 pg/ml for the treated samples. The means (± SEM) for these groups were 9.5 ± 1.6 and 9.9 ± 1.7, respectively, and were not significantly different from one another as assessed by Student's t‐test (P = 0.08). In summary, we have found that this technique permits us to obtain values on samples which would otherwise be unusable and that such treatment does not alter the melatonin values yielded by RIA analysis.
Twenty‐four hour urinary excretion of 6‐hydroxymelatonin sulfate in Down syndrome subjects
Authors: Reiter Russel J. , Barlow‐Walden Lornell , Poeggeler Burkhard , Heiden Sherry M. , Clayton Robert J.
Published: February 2007

Abstract: Because of the overexpression of the enzyme superoxide dismutase, individuals with Down syndrome (DS) are believed to suffer from increased oxidative stress as a result of the excessive production of oxygen‐based free radicals; their exposure to higher than normal free radical production may account in part for signs of premature aging, early onset of cataracts, and of Alzheimer's disease. Free radicals are normally neutralized by free radical scavengers and other antioxidants. The pineal hormone melatonin is a potent scavenger of both the hydroxyl and peroxyl radicals, both of which are highly toxic, and a stimulator of the antioxidative enzyme glutathione peroxidase. Considering this, we deemed it important to define the day/night rhythm and levels of melatonin production in DS subjects. To do this, we assessed the urinary excretion of the chief melatonin metabolite, 6‐hydroxymelatonin sulfate, throughout a 24 hr period in DS subjects; comparisons were made with the metabolite levels in the urine of non‐Down siblings and parents of the DS subjects. All 8 non‐Down subjects exhibited what was classified as normal urinary excretion of 6‐hydroxymelatonin sulfate with the usual low daytime and high night‐time levels of the melatonin metabolite. Of 12 DS subjects studied, 10 exhibited the normal day/night rhythm in urinary 6‐hydroxymelatonin sulfate levels; 2 subjects were devoid of a rhythm. However, when all the data from each group were averaged, there were no noticeable differences in the absolute levels or 24 hr variations in urinary 6‐hydroxymelatonin sulfate excretion between DS and non‐Down subjects.
Comparative aspects of the pineal/melatonin system of poikilothermic vertebrates
Authors: Filadelfi Ana Maria Caliman , Castrucci Ana Maria de Lauro
Published: February 2007

Abstract: The pineal gland of poikilothermic vertebrates originates as an evagination from the diencephalic roof between the habenular and the posterior commissures, and associates with a parapineal organ to form the so‐called pineal complex. The pinealocytes may be photosensitive, secretory or intermediate cells between both. Melatonin, the indoleamine secreted by the pineal, exhibits a circadian secretory rhythm that conveys environmental information to the organism. The peak melatonin secretion occurs during the night, although there are a few examples of an increase in indoleamine secretion during the day. Melatonin is also synthesized in other sites such as the retina, and it has been found in many invertebrates and unicellular organisms. The rhythmic secretory pattern of melatonin is responsible for many biological rhythms exhibited by lower vertebrates. These rhythms are abolished by pinealectomy in some species, but not in others, suggesting the existence of an extra‐pineal pacemaker. The photoperiod and the temperature (especially in reptiles) are the main environmental factors affecting the secretory rhythm of melatonin. Poikilothermic vertebrates exhibit a circadian rhythmic color change, with nocturnal blanching, usually related to melatonin secretion. In amphibians, melatonin exhibits a potent skin lightening activity. However, in fishes and reptiles the melatonin effects vary with the species, the developmental stage, and the pigment cell location. Melatonin also exerts inhibitory or excitatory activity on the amphibian reproductive system, regulation of circadian locomotory activity in reptiles, and modulation of the amphibian metamorphosis. Melatonin has also a modulatory effect on the response of target cells to different hormones and high concentrations or prolonged exposure to the indoleamine may cause autodesensitization in various tissues. Binding sites of melatonin have been detected in the central nervous system and peripheral tissues of various vertebrates. The relative potencies of melatonin analogues demonstrated two subtypes of melatonin receptors (ML‐1 and ML‐2). A transmembrane melatonin receptor has been cloned from Xenopus laevis melanophores; it belongs to the family of the G protein‐coupled receptors and exhibits 85% homology with the mammalian nervous system receptor. Melatonin binding sites in the nucleus of many cell types and its potent intracellular anti‐oxidant action suggest mechanisms of action other than through the G‐protein coupled receptor.
A molecular perspective of the genetic relationships of G‐protein coupled melatonin receptor subtypes
Authors: Shiu S.Y.W. , Ng N. , Pang S.F.
Published: February 2007

Abstract: Successful cloning of melatonin receptors from various target tissues in the past few years has increased our understanding of the molecular signal transduction mechanisms of G‐protein coupled melatonin receptors, of which three subtypes (MEL‐1A, MEL‐1B, and MEL‐1C) have been reported in different vertebrates. Based upon melatonin receptor sequences available in the Genbank database, we have performed phylogenetic analyses of the nucleotide and encoded amino acid sequences of G‐protein‐coupled melatonin receptors, and determined the range of amino acid identities between melatonin receptors of the same and different subtypes. Besides the three well‐known subtypes, a potential novel subtype of MEL‐1D, as exemplified by unique separation of Xenopus X2.0 sequence (Genbank accession No. U31826) from the others in the protein phylogenetic tree, possibly exists. In addition, one of the chicken brain melatonin receptor sequences has been identified as belonging to the MEL‐1B subtype. Our analyses showed that melatonin receptors of the same subtype and different subtypes are likely to share >75% and <65% amino acid identities, respectively. Phylogenetic analysis based on amino acid comparisons will be needed to determine the subtype status of any pair of melatonin receptor sequences that exhibit ≥65% to <75% amino acid identity. Despite the usefulness of genetic relatedness in the subtype classification of G‐protein‐coupled melatonin receptors, functional correlation of molecular structure may ultimately prove the most comprehensive approach in melatonin receptor classification.
Effects of exposure to 16.7 Hz magnetic fields on urinary 6‐hydroxymelatonin sulfate excretion of Swiss railway workers
Authors: Pfluger Dominik H. , Minder Christoph E.
Published: February 2007

Abstract: The aim of our study was to examine the effects of 16.7 Hz electromagnetic‐field exposure on pineal melatonin production in healthy humans. The study was based on comparing urinary 6‐hydroxymelatonin sulfate (6‐OHMS) levels of 108 male railway workers between leisure periods and days following the start of service on electrically powered engines (66 engineers) or working beneath transmission lines (42 railway employees such as train attendants and station managers; controls). A repeated measures design was used, i.e., each volunteer served as his own control. The exposure averaged 20 μTesla in the most exposed workers and around 1 μTesla in the least exposed. Apart from magnetic exposure the workers were subject to a shift work schedule with daily advances between 15 min and 1 hr. Melatonin was assessed by sampling urinary 6‐OHMS both in the morning and the early evening.

Evening 6‐OHMS values appeared to be lowered by a factor of 0.81 (95%CI: 0.73–0.90) during work days compared to leisure days among engine drivers, but not in the controls. The lowering was not confined to certain types of shift work such as early, normal, or late shifts. During subsequent leisure periods evening values recovered significantly, mean ratio=1.27 (95%CI: 1.03–1.56), i.e., the effects appeared to be reversible. In contrast, morning 6‐OHMS samples of engineers and controls did not differ much between work and leisure days. There was, however, a tendency for a rebound of morning values in a leisure period following a work period both for engineers and controls. The observed pattern appears to be in line with predictions of the “phase response curve.” No evidence for a dose‐response relation was found. The results support the hypothesis that 16.7 Hz magnetic fields alter 6‐OHMS excretion in humans exposed to magnetic fields. An alternative explanation that cannot be excluded in this study is that the difference between engineers and controls is due to differential exposure to day light at work.
Retinal melatonin is not involved in corneal mitotic rhythms in the Japanese quail: Effects of formoguanamine hydrochloride and eye‐lid suture
Authors: Oishi Tadashi , Mohri Yayoi , Kaneko Tomoko , Sasaki Motoko , Hattori Atsuhiko , Obara Yoshihiko , Masuda Atsuko
Published: February 2007

Abstract: Relation between retinal melatonin and corneal mitotic rhythms in the Japanese quail was investigated in experiments manipulating the ocular physiology by treatments with formoguanamine hydrochloride (FG) and eye‐lid suture. In experiment 1, we investigated the effects of FG, which is known to induce photoreceptor degeneration, on retinal melatonin and corneal mitotic rhythms. FG‐treatment completely abolished the retinal melatonin rhythms in both LD 12: 12 and constant darkness (DD), but the corneal mitotic rhythm was maintained with high mitotic rate in darkness under a LD cycle and subjective night under DD. The result suggests that 1) the photoreceptor cells in the retina are the site for melatonin production and/or for the oscillator which drives the circadian rhythm in retinal melatonin, and 2) melatonin is not involved in generation of the corneal mitotic rhythm. In experiment 2, we investigated the effects of eye‐lid suture, which is known to induce eye enlargement and bulgy cornea, on the retinal melatonin and corneal mitotic rhythms. Eye‐lid suture abolished the corneal mitotic rhythm in both LD and DD, with a high mitotic rate being maintained throughout 24 hr. But retinal melatonin maintained its rhythm with high levels in darkness under a LD cycle and in subjective night under DD. The result suggests that 1) bulgy cornea in the sutured eye was induced by the increase in mitotic rate in the light period, and 2) disappearance of the corneal mitotic rhythm does not have a relation to retinal melatonin. These results suggest that retinal melatonin is not involved in generation of the corneal mitotic rhythm and that there are two circadian clock systems in the eye.
Melatonin concentrations in serum and tissues of porcine gastrointestinal tract and their relationship to the intake and passage of food
Authors: Bubenik G.A. , Pang S.F. , Hacker R.R. , Smith P.S.
Published: February 2007

Abstract: Melatonin concentrations were determined in serum and 10 segments of the gastrointestinal tract (GIT) of 48 pigs (100 kg weight). The animals were fasted for 30 hr and then sacrificed 0, 1,2, 5, 10, and 20 hr after refeeding. Peak amount of gastric digesta (2,428 g) and ileum digesta (850 g) were observed 1 hr and 5 hr, after refeeding, respectively. Conversely, colon content reached a minimal weight (726 g) at 2 hr after refeeding. Serum levels of melatonin increased from 3.4 pg/ml to 15.5 pg/ ml (peak 5 hr after refeeding). Melatonin levels in GIT tissues before refeeding varied from 23.8 pg/g (stomach‐fundus) to 62.1 pg/g (rectum). Increasingly higher levels of melatonin were detected in the distal segments of the GIT. Higher melatonin levels after refeeding were observed in most GIT tissues except the rectum. In most tissues, peak melatonin values were detected 5 hr after refeeding. A significant change in weight of digesta across time (P<0.05) was detected in the stomach, ileum, and cecum. Similar changes in melatonin levels across time were found in most tissues except the esophagus, stomach (cardia and pylorus), and rectum. Adjacent GIT tissues exhibited similar (P<0.05) melatonin levels. The GIT melatonin levels correlated best with the variation of digesta weight in the ileum. In addition, the increase of serum melatonin levels correlated best with the increase of GIT melatonin levels in the distal part of the GIT. Our results suggest that melatonin produced in the ileum, cecum, and colon may contribute significantly to the short‐term increase of serum melatonin levels observed after refeeding.
The amplitude of endogenous melatonin production is not affected by melatonin treatment in humans
Authors: Matsumoto Miki , Sack Robert L. , Blood Mary L. , Lewy Alfred J.
Published: February 2007

Matsumoto M, Sack RL, Blood ML, Lewy AJ. The amplitude of endogenous melatonin production is not affected by melatonin treatment in humans. J. Pineal Res. 1997; 22:42–44. © Munksgaard, Copenhagen

A physiological dose of melatonin (0.5 mg) or placebo was given at bedtime to night shift workers (n=21) for seven days, and endogenous melatonin profiles were measured on the eighth day. The amplitude of endogenous melatonin secretion was unchanged by treatment. Also, a melatonin treatment trial using a 50 mg daily bedtime dose for 37 days to a blind subject resulted in no change in the endogenous melatonin profile. We conclude that circulating melatonin can shift the phase, but does not alter the amplitude, of pineal melatonin secretion.
Estrogenic effects on urinary 6‐sulphatoxymelatonin excretion in the female rat
Authors: White Rehema M. , Kennaway David J. , Seamark Robert F.
Published: February 2007

ABSTRACT: The pattern of melatonin production during the estrous cycle of the rat was measured by monitoring urinary 6‐sulphatoxymelatonin (aMT.6S) excretion. Adult rats were maintained under a 14L: 10D photoperiod and urine was collected at hourly intervals over a 5‐day period using an automated collection system; the concentration of aMT.6S was assayed by RIA and hourly outputs were calculated. Each nightly collection of urine was assigned to an estrous cycle stage as determined by the vaginal smear of the preceding morning. Total aMT.6S excretions (mean ± SEM) during estrous, metestrous, diestrous, and proestrous stages were 493 ± 49, 539 ± 44, 562 ± 40, and 646 ±51 pmol/night, respectively (n = 7). The excretion of aMT.6S was significantly higher on the night of proestrus compared to each of the other stages (P < 0.05). To determine whether estrogen was responsible for the increased aMT.6S excretion during proestrus, rats were studied before and after ovariectomy and following implantation with estradiol implants. Total overnight aMT.6S excretion was reduced by 31 % in ovariectomized animals relative to the intact state (P < 0.05) and restored to the intact levels by administration of estradiol (P < 0.05). It was concluded that estradiol can modulate melatonin production in adult rats, and that the changing pattern of aMT.6S excretion throughout the estrous cycle may provide a basis for a functional relationship between pineal activity and reproduction in this species.
Immunohistochemical and tracer studies of macrophages/microglia in the pineal gland of postnatal rats
Authors: Kaur C. , Wu C.H. , Ling E.A.
Published: February 2007

ABSTRACT: The pineal gland of rats of various ages (1‐21 days old) was examined by immunohistochemistry and electron microscopy. Numerous widely distributed cells identified as macrophages/microglia were immunoreactive with the monoclonal antibodies OX‐42, OX‐18, OX‐6, and EDI, indicating that they expressed complement type 3 (CR3) receptors, major histocompatibility complex class I and II antigens, and antigens of monocyte/macrophage lineage as detected by the antibodies, respectively. Following an intraperitoneal injection of rhodamine isothiocyanate (RhIC) in all age groups, the cells emitted a bright fluorescence. They were also labeled by horseradish peroxidase (HRP), as demonstrated in both light and electron microscopy. An HRP reaction was observed in vesicles and lysosomes at the ultrastructural level. A remarkable feature was the uptake of these tracers by pinealocytes. In light microscopy, the pinealocytes showed a punctate reaction product 3–24 hours after HRP injection. By electron microscopy, the reaction product was observed in vesicles, lysosomes, and some rod‐like structures in the cytoplasm. On the basis of their immunophenotypic features, it is suggested that the macrophages/microglia in the pineal gland are active phagocytes which are also probably involved in the immunoregulatory function in the gland. The avid uptake of RhIC and HRP from the circulation by these cells suggests that serum‐derived substances that may gain access to the parenchyma of the gland are being constantly monitored. The labeling of pinealocytes with HRP suggests that the functional activities of these cells are being modulated by serum‐derived substances.
Melatonin inhibits vasopastic action of hydrogen peroxide in human umbilical artery
Authors: Okatani Yuji , Watanabe Kazushi , Hayashi Kazutoshi , Wakatsuki Akihiko , Sagara Yusuke
Published: February 2007

ABSTRACT: We evaluated the antioxidant property of melatonin as it relates to the vasospastic effect of hydrogen peroxide (H2O2) on the human umbilical artery. Helical sections of umbilical arteries were obtained from healthy pregnant women who were delivered between weeks 37 and 39 of gestation. Changes in maximal potassium chloride (KCl)‐induced tension were measured in arterial segments with intact endothelium. Segments were treated with H2O2 alone, or were pretreated either with an H2O2scavenger (catalase, 2000 IU), a hydroxyl radical scavenger (mannitol, 10−2M), a nitric oxide‐synthesis inhibitor (L‐NG‐monomethyl arginine, LNMA, 2 × 10−4M), or melatonin (10−6M to 10−4M). The effect of H2O2(10−4M) on the relaxation induced by the calcium ionophore A23187 was also determined in arterial segments, with or without pretreatment with melatonin (10−6M, 10−4M). H2O2 (10−6 M to 10−4 M) potentiated vascular tension in a concentration‐dependent manner (P < 0.0001). Pretreatment with LNMA significantly suppressed the vasospastic effect of H2O2 (P < 0.0001). Pretreatment with either catalase or mannitol significantly reduced the vasospastic effect of H2O2 (P < 0.005, P < 0.002, respectively). Melatonin also significantly reduced the vasospastic effect of H2O2 in a concentration‐dependent manner (H2O2 10−6 M, P < 0.0001: H2O2 10−5 M, P<0.0001: H2O2 10−4M, P < 0.00001). Pretreatment with H2O2 significantly inhibited the relaxation induced by the calcium ionophore A23187 (P < 0.005). Treatment with melatonin prior to exposure to H2O2 significantly restored the relaxation induced by A23187 (P < 0.005). Results suggest that H2O2 potentiates vascular tension in the human umbilical artery, perhaps by suppressing the endothelial synthesis of nitric oxide. Melatonin significantly suppressed the vasospastic effect of H2O2, possibly due to its ability to scavenge the hydroxyl radical.