Effects of an epiphyseal peptide preparation epithalamin on serotonin metabolism in the pineal gland of rats]

5-day morning injections to pubertal male rats of polypeptide epithalamin preparation obtained from cattle epiphysis, in dose of 0.25 mg/100 g body mass induced the increase of serotonin epiphyseal concentration night peak, N-acetylserotonin and melatonin and didn't produce any essential influence on 5-methoxytryptamine, 5-oxy- and 5-methoxyindoleacetic acid level. It has been concluded, that epiphyseal peptides and indoles interact according to ultrashort connection, epiphyseal peptides point of application is the reaction of tryptophan transformation into serotonin and its further metabolism in N-acetylserotonin and melatonin. It has been suggested that the increase of epiphyseal melatonin production is on the basis of epithalamin therapeutic action.     

Modulation of the Circadian Rhythm of the Renal Function upon the Action of a GABA<Subscript>A</Subscript> Receptor Agonist and Melatonin

We studied the effects of injections of an activator of GABA-ergic cerebral systems, aminalone, and an epiphyseal hormone, melatonin, on the circadian rhythm of the excretory activity of the kidneys; the experiments were carried out on rats under conditions close to natural. Introduction of exogenous melatonin resulted in significant intensification of excretory renal activity within both day and night periods. Injections of aminalone suppressed the effects of melatonin; in the case of combined injections of these agents, the circadian rhythm of the activity of the kidneys became noticeably smoothed. These findings are interpreted as proof of the important role of reciprocal interactions between the GABA-ergic neuronal systems (first of all, in the main central circadian pacemaker, i.e., in the suprachiasmatic nuclei of the hypothalamus) and melatonin-producing units of the brain epiphysis in the regulation of the above rhythm.     

Melatonin synthesis by rabbit platelets

Platelets of reserpinized rabbits, incubated in buffer containing tritiated 5-hydroxytryptamine (³H-5HT), have the ability to convert ³H-5HT into labelled compound (s) extractable with alkaline-chloroform. The bulk of the chloroform-extractable radioactivity showed a Rf value similar to authentic melatonin on silicagel thin-layer chromatography.The labelled product eluted with ethanol from the silicagel area where melatonin was suspected to reside was indentified as melatonin by mass spectrometry and radioimmunoassay.Our in vitro experiments demonstrate that rabbit platelets are capable of converting 5-HT into melatonin apparently because they possess the enzymatic equipment necessary for this biosynthesis i.e. serotonin N-acetyltransferase and hydroxyindole-O-methyltransferase.     

Role of melatonin in the control of depth distribution of <Emphasis Type="Italic">Daphnia magna</Emphasis>

Previous studies confirmed the presence of melatonin in Daphnia magna and demonstrated diurnal fluctuations in its concentration. It is also known that in several invertebrate species, melatonin affects locomotor activity. We tested the hypothesis that this hormone is involved in the regulation of Daphnia diel vertical migration (DVM) behaviour that is well recognized as the adaptive response to predation threat. Using ‘plankton organs’, we studied the effect of three concentrations of exogenous melatonin (10⁻⁵, 10⁻⁷, 10⁻⁹ M) on DVM of both female and male D. magna in the presence or absence of chemical cue (kairomone) of planktivorous fish. Depth distribution was measured six times a day, using infrared-sensitive closed circuit television cameras. Our results showed a significant effect of melatonin on the mean depth of experimental populations, both males and females, but only when melatonin was combined with fish kairomone. Females stayed, on average, closer to the surface than males, both responding to the presence of kairomone by descending to deeper strata. In the presence of exogenous melatonin and with the threat of predation, Daphnia stayed closer to the surface and their distribution was more variable than that of individuals, which were exposed to the kairomone alone. Approaching the surface in the presence of predation threat seems to be maladaptive. We postulate the role of melatonin as a stress signal inhibitor in molecular pathways of response to predation threat in Cladocera.     

Melatonin and chlorpromazine: thermal selection in the mudpuppy, Necturus maculosus.

Intraperitonel (IP) injections of melatonin (4 mg kg^?1) and chlorpromazine (25 mg kg^?1), which blocks the breakdown of endogenous melatonin, significantly decreased temperatures selected by salamanders in a linear thermal gradient and eliminated the normal diel cycle in behavioral thermoregulation shown by control animals. Both endogenous and exogenous melatonin may play a crucial role in both physiological and behavioral thermoregulation of vertebrates.     

Independent changes of thyroid hormones in blood plasma and cerebrospinal fluid after melatonin treatment in ewes

The authors measured the effects of exogenous melatonin treatment on the concentrations of total (T) and free (f) fractions of thyroxine (T4) and triiodothyronine (T3) in cerebrospinal fluid (CSF) and blood plasma as well as the expression of their binding/transporter protein, transthyretin (TTR), in the choroid plexus of ewes from May to August. Melatonin implantation in May and July mainly prevented the decrease in plasma for fT3 and TT3 exhibited in untreated group, and induced a limited decrease in TT4 in June. By contrast, melatonin implantation prevented the decrease in CSF fT3 observed in the untreated group. No effect of melatonin was found on the expression of TTR mRNA in the choroid plexus There were a correlations between blood fT4 and CSF TT4 concentrations in both control and melatonin treated group (r²−0.4; P < 0.01 vs. r²−0.14; P < 0.05), as well as between blood fT3 and CSF TT3 concentrations but only in the melatonin-treated group (r²−0.26; P < 0.02). We conclude that T3, the active form of the hormone within the brain, is regulated by melatonin independently of the peripheral changes within the blood. The lack of correlation between plasma fT3 and CSF TT3 in the control group suggests that an increase in local T3 conversion could contribute as an additional source of T3 in the CSF during the period of increasing day length. These data seem to confirm a local nature for recently discovered connections between the pineal melatonin signal and thyroid-dependent seasonal biology in mammals.     

褪黑素对水稻镉积累及其化学结合形态的影响

研究了添加外源褪黑素对水稻幼苗中Cd积累以及水稻体内Cd化学形态分布的影响.结果表明: Cd胁迫显著降低水稻幼苗地上部和根部的生物量,并且显著降低水稻叶片的叶绿素含量.适宜的外源褪黑素添加能明显提高Cd胁迫下水稻的地上部和根部生物量,降低水稻地上部和根部Cd含量.当Cd胁迫浓度为5 μmol·L^-1时,添加20 μmol·L^-1褪黑素使水稻地上部和根部Cd含量分别比对照处理降低48.4%和16.9%,添加100 μmol·L^-1褪黑素水稻地上部和根部Cd含量分别降低67.5%和47.9%.添加外源褪黑素也显著降低了水稻体内Cd的转运效率.当Cd胁迫浓度为20 μmol·L^-1时,添加20 和100 μmol·L^-1褪黑素使水稻Cd的转运效率分别比对照降低24.4%和46.8%.通过逐步提取法对水稻幼苗Cd的化学结合形态进行分析发现,添加外源褪黑素使水稻体内氯化钠提取态Cd的比例提高,而水溶态Cd、乙醇提取态Cd的比例明显降低,说明添加褪黑素可促进水稻体内移动性较强的Cd形态向移动性较弱的Cd形态转移,从而降低水稻对Cd的吸收和转运.     

The Pineal Gland,but Not Melatonin,Is Associated with the Termination of Seasonal Testicular Activity in an Annual Reproductive Cycle in Roseringed Parakeet Psittacula krameri

The role of the pineal gland and its hormone melatonin in the regulation of annual testicular events was investigated for the first time in a psittacine bird, the roseringed parakeet (Psittacula krameri). Accordingly, the testicular responsiveness of the birds was evaluated following surgical pinealectomy with or without the exogenous administration of melatonin and the experimental manipulations of the endogenous levels of melatonin through exposing the birds to continuous illumination. An identical schedule was followed during the four reproductive phases, each characterizing a distinct testicular status in the annual cycle, namely, the phases of gametogenic quiescence (preparatory phase), seasonal recovery of gametogenesis (progressive phase), seasonal initiation of sperm formation (pre‐breeding phase), and peak gametogenic activity (breeding phase). In each reproductive phase, the birds were subjected to various experimental conditions, and the effects were studied comparing the testicular conditions in the respective control birds. The study included germ cell profiles of the seminiferous tubules, the activities of steroidogenic enzymes 17β‐hydroxysteroid dehydrogenase (17β‐HSD), and Δ⁵3β‐hydroxysteroid dehydrogenase (Δ⁵3β‐ HSD) in the testis, and the serum levels of testosterone and melatonin. An analysis of the data reveals that the pineal gland and its hormone melatonin may play an inhibitory role in the development of the testis until the attainment of the seasonal peak in the annual reproductive cycle. However, in all probability, the termination of the seasonal activity of the testis or the initiation of testicular regression in the annual reproductive cycle appears to be the function of the pineal gland, but not of melatonin.     

Melatonin synthesized by Jurkat human leukemic T cell line is implicated in IL-2 production

Human lymphocytes have recently been described as an important physiological source of melatonin (N-acetyl-5-methoxytryptamine), which could be involved in the regulation of the human immune system. On the other hand, stimulation of IL-2 production by exogenous melatonin has been shown in the Jurkat human lymphocytic cell line. Furthermore, both melatonin membrane and nuclear receptors are present in these cells. In this study, we show that the necessary machinery to synthesize melatonin is present and active in resting and stimulated Jurkat cells. Accordingly, we have found that cells synthesize and release melatonin in both conditions. Therefore, we investigated whether endogenous melatonin produced by Jurkat cells was involved in the regulation of IL-2 production. When melatonin membrane and nuclear receptors were blocked using specific antagonists, luzindole and CGP 55644, respectively, we found that IL-2 production decreased, and this drop was reverted by exogenous melatonin. Additionally, PHA activation of Jurkat cells changed the profile of melatonin nuclear receptor mRNA expression. A previous study showed that exogenous melatonin is able to counteract the decrease in IL-2 production caused by prostaglandin E2 (PGE2) in human lymphocytes via its membrane receptor. In our model, when we blocked the melatonin membrane receptor with luzindole, the inhibitory effect of PGE2 on IL-2 production was higher. Therefore, we have demonstrated the physiological role of endogenous melatonin in this cell line. These findings indicate that endogenous melatonin synthesized by human T cells would contribute to regulation of its own IL-2 production, acting as an intracrine, autocrine, and/or paracrine substance.     

Age- and sex-dependent effect of exogenous melatonin on expression pattern of melatonin receptor (MT1 and MT2) proteins in spleen of mice

Spleen is an important lymphoid organ which exerts immune activities throughout the life in mammals. In this study, we investigated the age- and sex-dependent effect of exogenous melatonin on expression pattern of MT1 and MT2 melatonin receptor proteins in spleen of laboratory Swiss albino mice in three different age-groups – 2, 4, and 8 months. The melatonin receptor expression patterns were studied by immunohistochemical localization and Western blot analysis. Immunohistochemical study showed reactivity of MT1 and MT2 melatonin receptors in spleen of both male and female mice. Exogenous melatonin significantly showed age- and sex-dependent expression pattern of MT1 receptor protein, while MT2 receptors showed only age-dependent differential expression patterns in both male and female mice. Therefore, this study may suggest that exogenous melatonin is modulating MT1 and MT2 receptor protein expression pattern in age- and sex-dependent manner in spleen of mice.     

Melatonin and childbearing: Part 1. Preimplantation period and implantation

Melatonin is a hormone produced in terrestrial vertebrates and humans in the pineal organ, an endocrine gland. It was established that one of the major functions of melatonin is the synchronization of the function of all organs and the regulation of seasonal and diurnal rhythms of their physiological activity. The synchronization function and rhythm regulation are performed in accordance with the circadian rhythm of melatonin expression, depending on the length of day and night. Melatonin is able to influence the growth, development, and physiological activity of different types of cells, affecting the mechanisms of signaling pathways and cascades similarly to growth factors. It was confirmed that the processes of conception, pregnancy, and childbirth directly depend on the rhythm and secretion profile of the epiphyseal hormone melatonin in the body. In this review, we attempt to combine the available published data on the involvement of melatonin in various physiological processes during the preimplantation and postimplantation periods of life of the organism and its positive and negative effects at the stages of puberty.     

Daily melatonin administration synchronizes circadian patterns of brain metabolism and behavior in pinealectomized house sparrows,Passer domesticus

Recent research in our laboratory has indicated that in sparrows the visual suprachiasmatic nucleus (vSCN) is metabolically rhythmic such that 2-deoxy[¹⁴C]glucose (2DG) uptake and specific binding of 2[¹²⁵I]iodomelatonin (IMEL) are high during subjective day for up to 10 circadian cycles in constant darkness (DD). These rhythms damp to arrhythmicity in pinealectomized birds (PINX). The present study was designed to test the hypothesis that exogenous melatonin rhythmically applied can restore disrupted behavioral and cerebral rhythmicity. Pinealectomized house sparrows were placed in constant dim light and allowed to become arrhythmic. Experimental birds received 0.86 mM melatonin in 0.01% ethanol (ETOH) to drink for 12 of every 24 h for 14 days. Control birds received 0.01% ETOH only. Behavioral rhythmicity was restored by melatonin but not by ETOH. Birds were injected with 2DG 6 or 18 h following the beginning of melatonin (for experimental birds: MT06 and MT18 respectively) or ETOH (for control birds: ET06 and ET18 respectively) administration, allowed to survive 1 h and killed for 2DG and IMEL autoradiography. The data indicated 2DG rhythmicity such that uptake was high at MT18 in vSCN and several visual, auditory and limbic system structures in birds receiving melatonin but not in birds receiving ETOH. Similarly, IMEL binding rhythms were restored in vSCN and other visual, auditory and limbic system structures in birds receiving melatonin but not in those receiving ETOH. These data indicate that melatonin cycles are responsible for generating and/or driving a wide array of cerebral metabolic rhythms and that this influence is inhibitory.     

Effect of exogenous melatonin and plane of nutrition after weaning on estrous activity, endocrine status and ovulation rate in Salz ewes lambing in the seasonal anestrus

Forty-nine Spanish Salz ewes lambing in the second fortnight of March (20 March +/- 1.5 d) were used to determine the effects of exogenous melatonin and postweaning nutrition on endocrine status, date of first estrus and ovulation rate. Experimental design was a factorial defined by 2 postweaning planes of nutrition, 1.80 (high) and 1.35 (low) times the maintenance requirements, and treatment with a single 18-mg subcutaneous implant of melatonin (M) 32 d after lambing or no treatment control (C). Mean weaning to first estrus interval was shorter in treated than in control ewes (50.8 +/- 4.2 vs 87.6 +/- 6.3 d; P < 0.01). Considering both the treated and control animals together, the ratio between mean night and daytime plasma melatonin levels was significantly correlated with the implant insertion-first estrus interval on Day 5 (0.67; P < 0.01) and Day 35 (0.63; P < 0.05) after implantation. Melatonin implants induced a significant increase of mean LH concentrations at Days 14 and 33 after implantation (P < 0.01) without any significant influence of plane of nutrition. Ovulation rate was higher for treated than control ewes in the second estrus (P < 0.05). An interaction between plane of nutrition and exogenous melatonin on ovulation rate at the second cycle after weaning was detected (P < 0.01), being close to the significance in the first, fourth and fifth cycles (P < 0.1). These results suggest that exogenous melatonin in April may be an effective way of advancing the breeding season and enhancing ovulation rate associated with a low rather than a high plane of nutrition.     

Sex-related dimorphism of the morphofunctional characteristics of the epiphysis in newborn children subjected to hypoxic impairment and asphyxia

In 72 newborn children (37 boys and 35 girls) who suffered from prenatal hypoxia and were born in an asphyxic state, we measured the level of melatonin in the umbilicial blood and observed clinical manifestations of the adaptation/stress syndrome. These data were compared with the results of morphological examination of the epiphyses from 27 stillborns (15 boys and 12 girls) who perished because of heavy prenatal hypoxia. The level of melatonin in the blood of ill newborn girls was much higher than that in boys, and both these indices were about two times higher than those in respective groups of healthy newborn children. At the same time, the pathomorphological examination showed that active epiphyseal cell units in the male fetuses were much more numerous. The results show that the epiphysis plays a significant role in determination of the sex-related dimorphism of the adaptation/stress syndrome in newborn children suffering from hypoxia- and asphyxia-evoked heavy CNS damage. The reasons and consequences of more intensive morphofunctional loading of the epiphyseal system in the male fetuses are discussed.     

Pineal control of immune status and hematological changes in blood and bone marrow of male squirrels (Funambulus pennanti) during their reproductively active phase

In addition to pineal control of reproduction in seasonal breeders, melatonin is also known to influence various immune parameters. In the present experiment, we assessed the effect of exogenous melatonin treatment on different hematological parameters of peripheral blood and bone marrow cells, together with histological observations of spleen and thymus blastogenic response and stimulation ratio, and hormonal assays (melatonin and testosterone) of Indian palm squirrel (Funambulus pennanti) during their reproductively active phase when endogenous melatonin levels are low. Daily subcutaneous injection of melatonin (25 microg/100 g body mass.) at 17.30-18.00 h to adult male squirrels for 60 consecutive days during May-June significantly increased the lymphocyte count of blood and bone marrow and the blastogenic response/percent stimulation ratio of spleen and thymus. Histological observation showed densely packed thymocytes and splenocytes. During this period, peripheral testosterone level was high and melatonin was low establishing an inverse relationship as noted earlier for this squirrel. In pinealectomized squirrels, decreased total leukocyte count and percent lymphocyte count in peripheral blood and bone marrow, along with a decreased cell density in spleen and thymus was observed histologically. Further, melatonin treatment of pinealectomized squirrels resulted in restoration of the immune parameters in line with a normal control level. We suggest that during the reproductively active period of male Indian palm squirrels the lymphoid organs were sensitive to melatonin; hence, the exogenous melatonin treatment had an immuno-enhancing effect.     

Dose-dependent disruptive effects of melatonin,light and temperature on regeneration in the planarian Phagocata gracilis

Many critical cellular processes, including cell proliferation and tissue repair, exhibit melatonin sensitivity. We examined the effects of exogenous melatonin, photoperiod and temperature on regeneration in Phagocata gracilis, a common North American turbellarian. Planarian regeneration involves the proliferation and migration of pluripotent stem cells capable of replacing missing body components. A characteristic mass of cells (blastema) forms during planarian regeneration, and its formation, growth and differentiation provide reliable endpoints for the study of regenerative processes. We tested the effects of exogenous melatonin at two concentrations and three photoperiods on both head and tail regenerates under seasonal diurnal temperature regimes. High temperatures and melatonin treatment increased mortality in P. gracilis, and surviving melatonin-treated subjects exhibited delayed regeneration. Asymmetrical and deficient regeneration was more common in melatonin-treated, high temperature and dark treated subjects. Additionally, high temperature and melatonin induced a novel locomotor dysfunction.     

Influence of exogenous thyroxine on plasma melatonin in juvenile Atlantic salmon (Salmo salar)

One of the most clearly defined endocrine changes during the parr-smolt transformation of anadromous salmonids is an increase in plasma levels of thyroid hormones. The role of pineal hormone melatonin in timing and synchronisation of smoltification is widely discussed. The effect of administration of exogenous thyroxine (T4) on plasma melatonin was investigated in juvenile Atlantic salmon (Salmo salar) at the early stages of parr-smolt transformation. Fish were kept in fresh water under simulated-natural photoperiod and exposed to exogenous T4. Fish were sampled at 12.00 and 24.00 h from treatment and control tanks, 2 and 14 days after treatment started. Plasma melatonin and L-thyroxine were measured using RIA and competitive enzyme immunoassay, respectively. After 2 days of T4 treatment, marked difference in plasma melatonin concentration measured at 12.00 and 24.00 h was still observed in both groups. However, 2-week exposure to T4 caused a reduction in night-time plasma melatonin level and thus, probably, inhibited melatonin related time-keeping system in juvenile salmon. Additional studies are needed to clarify the mechanism of the described phenomenon.     

Ontogeny of heart rate responses to exogenous melatonin in Muscovy duck and chicken embryos

One of the major physiological effects of melatonin is coupling the internal clock with different organ functions. Despite the long list of functional responses to melatonin discovered in the past, it has been unclear when responsiveness to melatonin develops during ontogeny. The aim of the present study was therefore to investigate in Muscovy duck and chicken embryos, when they start to exhibit heart rate (HR) changes to exogenous melatonin. HR was recorded continuously in Muscovy duck embryos from day 24 of incubation (D24) and in chicken embryos from D17 until hatching. Every day four doses of 10 microg melatonin were injected into each egg at 30 min intervals. In Muscovy duck embryos HR responses to melatonin were first observed on D25; from D27 all embryos responded. In all cases HR decreased immediately after the injection. HR deviation from baseline values and duration of decreased HR period increased during the experimental period. Chicken embryos showed similar responses as Muscovy ducks from D17 onwards; from D18 the response rate was 100%. On D19 dose-response data revealed a partial responsiveness to exogenous melatonin at doses of 0.1 to 1 ng and full responsiveness from 10 ng to 10 microg. The time of the first occurrence of HR responses to melatonin coincides with published results on the start of periodic pineal melatonin secretion. These data suggest that the output signal of the avian internal clock, periodic plasma melatonin fluctuations, could result in periodic cardiac function already prenatally in these two avian species.     

Effects of melatonin and antagonists of MT1 and MT2 receptors on somatic pain induced within the fixed circadian rhythm

We studied behavioral pain-related reactions (PRRs) induced in mice by subcutaneous injections of 5% formalin within different phases of the fixed circadian illumination rhythm under conditions of administration of exogenous melatonin and of blocking of MT1 and MT2 melatonin receptors. It was demonstrated that modulation of experimentally induced somatic pain depends considerably on the phase of the preset circadian rhythm. In the norm, the duration of PRRs in the middle of the dark phase was 30% smaller than that in the middle of the light phase. Administration of exogenous melatonin in the middle of the light phase decreased the duration of episodes of noxious behavior by 43%, on average. Injections of melatonin within the dark phase resulted in no significant changes in the duration of PRRs. In the dark phase, the blockade of MT1 receptors by luzindole led to an increase in the duration of PRRs by 45%, as compared with the norm, while in the light phase we observed no significant alterations of this duration under conditions of blocking of the above-mentioned receptors. The blockade of MT2 receptors by prazocine in the middle of dark and light phases increased the durations of PRRs by 92 and 28%, respectively. Our data indicate that the analgesic effect of melatonin depends significantly on the level of this hormone in the organism; in turn, such a level is determined by the illumination conditions. The antinoxious effect of melatonin is mediated by MT receptors, in particular by MT2 receptors. Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 255–259, May–June, 2007.