Nighttime Melatonin Production Research Articles

Thyroid hormone receptors are required for the melatonin-dependent control of Rfrp gene expression in mice.

Mammals adapt to seasons using a neuroendocrine calendar defined by the photoperiodic change in the nighttime melatonin production. Under short photoperiod, melatonin inhibits the pars tuberalis production of TSHβ, which, in turn, acts on tanycytes to regulate the deiodinase 2/3 balance resulting in a finely tuned seasonal control of the intra-hypothalamic thyroid hormone T3. Despite the pivotal role of this T3 signaling for synchronizing reproduction with the seasons, T3 cellular targets remain unknown. One candidate is a population of hypothalamic neurons expressing Rfrp, the gene encoding the RFRP-3 peptide, thought to be integral for modulating rodent's seasonal reproduction. Here we show that nighttime melatonin supplementation in the drinking water of melatonin-deficient C57BL/6J mice mimics photoperiodic variations in the expression of the genes Tshb, Dio2, Dio3, and Rfrp, as observed in melatonin-proficient mammals. Notably, we report that this melatonin regulation of Rfrp expression is no longer observed in mice carrying a global mutation of the T3 receptor, TRα, but is conserved in mice with a selective neuronal mutation of TRα. In line with this observation, we find that TRα is widely expressed in the tanycytes. Altogether, our data demonstrate that the melatonin-driven T3 signal regulates RFRP-3 neurons through non-neuronal, possibly tanycytic, TRα.

Structure of Rhythms of Blood Pressure, Heart Rate, Excretion of Electrolytes, and Secretion of Melatonin in Normotensive and Spontaneously Hypertensive Rats Maintained under Conditions of Prolonged Daylight Duration.

We studied the structure of rhythms of BP, HR (by telemetric monitoring), electrolyte excretion (by capillary electrophoresis), and products of epiphyseal melatonin (by the urinary concentration of 6-sulfatoxymelatonin measured by ELISA) in normotensive Wistar-Kyoto rats and spontaneously hypertensive SHR rats maintained at 16/8 h and 20/4 h light-dark regimes. In Wister-Kyoto rats exposed to prolonged daylight, we observed changes in the amplitude, rhythm power (% of rhythm), and range of oscillations of systolic BP; HR mezor decreased. In SHR rats, mezor of HR also decreased, but other parameters of rhythms remained unchanged. Changes in electrolyte excretion were opposite in normo- and hypertensive rats. Under conditions of 20/4 h light-dark regime, daytime melatonin production tended to increase in normotensive rats and significantly increased in SHR rats. At the same time, nighttime melatonin production did not change in both normotensive and hypertensive animals. As the secretion of melatonin has similar features in animals of both lines, we can say that the epiphyseal component of the "biological clock" is not the only component of the functional system that determines the response of the studied rhythms to an increase in the duration of light exposure.

Melatonin profiles during the third trimester of pregnancy and health status in the offspring among day and night workers: A case series

Successful pregnancy requires adaptation in maternal physiology. During intrauterine life the mother's circadian timing system supports successful birth and postnatal development. Maternal melatonin is important to transmit circadian timing and day length to the fetus. This study aims to describe the third trimester of pregnancy among day (n = 5) and night (n = 3) workers by assessing their melatonin levels in a natural environment. Additionally, we describe the worker's metabolic profiles and compare the health status of the newborns between groups of day and night working mothers. Our results indicate an occurrence of assisted delivery (cesarean and forceps) among night workers. Moreover, the newborns of night workers showed lower Apgar index and breastfeeding difficulty indicating a worse condition to deal with the immediate outside the womb environment. Additionally, there was lower night-time melatonin production among pregnant night workers compared to day workers. These findings may be related to light-induced suppression of melatonin that occurs during night work. We conclude that night work and consequent exposure to light at unconventional times might compromise the success of pregnancy and the health of the newborn. Further studies need to be carried out to monitor pregnancy and newborn health in pregnant night workers.

Circadian rhythms and mood disorders: a guide for the perplexed.

Circadian rhythms and mood disorders: a guide for the perplexed.

Editorial: Molecular Endocrinology Articles in the Spotlight for November 2013

Welcome to the November issue of Molecular Endocrinology. I am pleased to report that beginning with this issue, the editors will identify a single article each month to be made freely available upon publication. In addition, all minireviews will be freely available immediately upon publication effective with this issue. Our first freely available article is by Mao et al., “Circadian Gating of Epithelial-to-Mesenchymal Transition in Breast Cancer Cells via Melatonin-Regulation of GSK3 .” In this study, the authors investigated the connection between circadian/melatonin disruption and breast cancer risk in shift workers. Their studies used a unique xenograft model with human breast cancer cells maintained in nude rats. Disruption of nighttime melatonin production by exposure of the host to light at night has far-reaching biological consequences, including disruption and activation of key proliferative/survival pathways in the xenograft human breast cancer cells including MAPK/ERK and PI3K/AKT, which repress glycogen synthase kinase 3 (GSK3 ) activity and drive epithelial-tomesenchymal transition. Thus, this study identifies a molecular mechanism that could contribute to the increased risk of breast cancer incidence in industrialized nations characterized by excessive use of artificial light during the night. “20-HETE Induces Hyperglycemia through the cAMP/PKA-PhK-GP Pathway” by Lai et al. demonstrated that hyperglycemia and hypertension in CYP4F2 transgenic mice were ameliorated with HET0016 [a selective 20-hydroxyeicosatetraenoic acid (20-HETE) inhibitor] treatment. Furthermore, 20-HETE was shown to activate glycogen phosphorylase, which is a target for diabetes therapy. Therefore, through induction of glycogenolysis through the cAMP/protein kinase A-phosphorylase kinase-glycogen phosphorylase pathway, 20HETE could participate in the common pathogenesis of hypertension and hyperglycemia. This study implicates 20-HETE as a potential new target for hypertension and hyperglycemia therapy. Williams et al.’s “The microRNA (miR)-199a/214 Cluster Mediates Opposing Effects of Progesterone and Estrogen on Uterine Contractility during Pregnancy and Labor” investigates the role of the clustered miRNAs, miR-199a-3p and miR-214, as important mediators of the opposing action of progesterone (P4) vs. estradiol-17 (E2) on myometrial quiescence and contractility during pregnancy and labor. Specifically, P4 and E2 exert opposite effects on these clustered miRs with P4 triggering induction and E2 repression via differential effects on the zinc finger, E-box binding homeobox protein (ZEB1). Furthermore, miR199a-3p and miR-214 act to block TNF-induced myometrial contractility via an inhibition of cyclooxygenase-2, an enzyme that catalyzes the formation of proinflammatory cytokines. Their findings in mice and humans provide new insight into strategies to prevent preterm birth as specific targets are identified that respond differentially to endogenous steroid hormones during normal labor. These studies and others in this issue highlight the impact of endocrinology research in both prevention and treatment of many conditions. Congratulations to these researchers, as well as those who produced all of the excellent science in this issue, on broadening our knowledge in such diverse areas. We also hope you enjoy the new freely available articles that will hereafter be a monthly feature in Molecular Endocrinology. Donald B. DeFranco, Ph.D. Editor-in-Chief, Molecular Endocrinology

Editorial: Molecular Endocrinology Articles in the Spotlight for November 2012

Welcome to the November issue of Molecular Endocrinology. I am pleased to report that beginning with this issue, the editors will identify a single article each month to be made freely available upon publication. In addition, all minireviews will be freely available immediately upon publication effective with this issue. Our first freely available article is by Mao et al., “Circadian Gating of Epithelial-to-Mesenchymal Transition in Breast Cancer Cells via Melatonin-Regulation of GSK3 .” In this study, the authors investigated the connection between circadian/melatonin disruption and breast cancer risk in shift workers. Their studies used a unique xenograft model with human breast cancer cells maintained in nude rats. Disruption of nighttime melatonin production by exposure of the host to light at night has far-reaching biological consequences, including disruption and activation of key proliferative/survival pathways in the xenograft human breast cancer cells including MAPK/ERK and PI3K/AKT, which repress glycogen synthase kinase 3 (GSK3 ) activity and drive epithelial-tomesenchymal transition. Thus, this study identifies a molecular mechanism that could contribute to the increased risk of breast cancer incidence in industrialized nations characterized by excessive use of artificial light during the night. “20-HETE Induces Hyperglycemia through the cAMP/PKA-PhK-GP Pathway” by Lai et al. demonstrated that hyperglycemia and hypertension in CYP4F2 transgenic mice were ameliorated with HET0016 [a selective 20-hydroxyeicosatetraenoic acid (20-HETE) inhibitor] treatment. Furthermore, 20-HETE was shown to activate glycogen phosphorylase, which is a target for diabetes therapy. Therefore, through induction of glycogenolysis through the cAMP/protein kinase A-phosphorylase kinase-glycogen phosphorylase pathway, 20HETE could participate in the common pathogenesis of hypertension and hyperglycemia. This study implicates 20-HETE as a potential new target for hypertension and hyperglycemia therapy. Williams et al.’s “The microRNA (miR)-199a/214 Cluster Mediates Opposing Effects of Progesterone and Estrogen on Uterine Contractility during Pregnancy and Labor” investigates the role of the clustered miRNAs, miR-199a-3p and miR-214, as important mediators of the opposing action of progesterone (P4) vs. estradiol-17 (E2) on myometrial quiescence and contractility during pregnancy and labor. Specifically, P4 and E2 exert opposite effects on these clustered miRs with P4 triggering induction and E2 repression via differential effects on the zinc finger, E-box binding homeobox protein (ZEB1). Furthermore, miR199a-3p and miR-214 act to block TNF-induced myometrial contractility via an inhibition of cyclooxygenase-2, an enzyme that catalyzes the formation of proinflammatory cytokines. Their findings in mice and humans provide new insight into strategies to prevent preterm birth as specific targets are identified that respond differentially to endogenous steroid hormones during normal labor. These studies and others in this issue highlight the impact of endocrinology research in both prevention and treatment of many conditions. Congratulations to these researchers, as well as those who produced all of the excellent science in this issue, on broadening our knowledge in such diverse areas. We also hope you enjoy the new freely available articles that will hereafter be a monthly feature in Molecular Endocrinology. Donald B. DeFranco, Ph.D. Editor-in-Chief, Molecular Endocrinology

Retinal light input is required to sustain plasma melatonin rhythms in Nile tilapia Oreochromis niloticus niloticus

The aim of this work was to confirm previous findings suggesting that the eyes are required for night-time melatonin production in Nile tilapia and further characterise this divergent circadian organisation. To do so, melatonin levels were firstly measured in eyecups and plasma to determine circadian patterns of melatonin production. Secondly, the effect of partial ophthalmectomy on the suppression of melatonin production was determined in vivo as well as ex vivo pineal light/dark sensitivity. Finally, to investigate whether such findings could be related to post-surgery stress, melatonin analyses were performed in the subsequent 24 h and 7 days post-ophthalmectomy with cortisol levels assessed as an indicator of stress. Our results showed an inverse pattern of melatonin production in the eye cups of tilapia compared to blood circulating levels, suggesting different roles played by melatonin in these two tissues. Results then demonstrated that total or partial ophthalmectomy resulted in the suppression of night-time melatonin production. Furthermore, although pineals in culture were shown to be photosensitive, night-time melatonin levels were much lower than seen in other species. Finally, when performing sampling immediately or one week post-surgery, no difference in the melatonin profiles were observed. It is therefore unlikely that post-surgery stress would explain such suppression in melatonin production although all fish displayed high cortisol levels most probably due to social and handling stress. Taken together, these results provide further evidence of a new type of circadian organisation in a teleost species where the eyes are required to sustain night-time melatonin levels.

Evidence for differential photic regulation of pineal melatonin synthesis in teleosts

The aim of this study was to compare the circadian control of melatonin production in teleosts. To do so, the effects of ophthalmectomy on circulating melatonin rhythms were studied along with ex vivo pineal culture in six different teleosts. Results strongly suggested that the circadian control of melatonin production could have dramatically changed with at least three different systems being present in teleosts when one considers the photic regulation of pineal melatonin production. First, salmonids presented a decentralized system in which the pineal gland responds directly to light independently of the eyes. Then, in seabass and cod both the eyes and the pineal gland are required to sustain full night-time melatonin production. Finally, a third type of circadian control of melatonin production is proposed in tilapia and catfish in which the pineal gland would not be light sensitive (or only slightly) and required the eyes to perceive light and inhibit melatonin synthesis. Further studies (anatomical, ultrastructural, retinal projections) are needed to confirm these results. Ex vivo experiments indirectly confirmed these results, as while the pineal gland responded normally to day-night rhythms in salmonids, seabass and cod, only very low levels were obtained at night in tilapia and no melatonin could be measured from isolated pineal glands in catfish. Together, these findings suggest that mechanisms involved in the perception of light and the transduction of this signal through the circadian axis has changed in teleosts possibly as a reflection of the photic environment in which they have evolved in.

Melatonin as a potential antihypertensive treatment

The number of patients with well-controlled hypertension is alarmingly low worldwide and new approaches to treatment of increased blood pressure (BP) are being sought. Melatonin has a role in blood pressure regulation. The nighttime production of melatonin is found to be reduced in hypertensive individuals. Administration of melatonin decreased BP in several animal models of hypertension, in healthy men and women, and in patients with arterial hypertension. Most promising results were achieved in patients with non-dipping nighttime pressure, in which the circadian rhythm of BP variation is disturbed. Several potential mechanisms of BP reduction are considered. Melatonin can, via its scavenging and antioxidant nature, improve endothelial function with increased availability of nitric oxide exerting vasodilatory and hypotensive effects. Melatonin seems to interfere with peripheral and central autonomic system, with a subsequent decrease in the tone of the adrenergic system and an increase of the cholinergic system. Melatonin may act on BP also via specific melatonin receptors localized in peripheral vessels or in parts of central nervous system participating in BP control. With a large clinical trial using melatonin in hypertension treatment, many important questions could be answered, such as the dose of melatonin and regimen of its application, the choice of patients with greatest possible benefit from melatonin treatment, the potential of anti-remodeling effect of melatonin and the interaction of melatonin with other antihypertensive drugs.

No association between occupational exposure to ELF magnetic field and urinary 6‐sulfatoximelatonin in workers

A suppression in melatonin secretion is one of the mechanisms proposed to explain the possible adverse effects of extremely low frequency magnetic fields (ELF-MF), but the results of research are inconclusive. This study investigated the effect of occupational ELF-MF exposure on 6-sulfatoximelatonin (6-OHMS). Exposure was monitored for three complete work shifts in 59 workers using personal exposure meters. Environmental exposure was also evaluated. Urinary 6-OHMS in morning samples, an indicator of night-time melatonin production, was measured. Urine was collected twice on Friday and the following Monday. Workers were classified according to ELF exposure as low exposed (<or=0.2 microT) or higher exposed (>0.2 microT): 6-OHMS did not differ between groups (P > .05) in either Friday or Monday urine samples. In addition, 6-OHMS was not related to exposure under multivariate analysis. The ratio between 6-OHMS in Monday versus Friday samples was also calculated to test the hypothesis of a possible variation in pineal function after 2 days, interruption of occupational ELF-MF exposure: again no exposure-related difference was observed. Our results do not support the hypothesis that occupational exposure to ELF-MF significantly influences melatonin secretion.

Generation of the melatonin endocrine message in mammals: a review of the complex regulation of melatonin synthesis by norepinephrine, peptides, and other pineal transmitters.

Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

Decreased melatonin synthesis in patients with coronary artery disease.

Decreased night-time plasma levels of melatonin were recently reported in patients with coronary artery disease, and it was postulated that melatonin production may be impaired, due to a lack of synthesizing enzymes. However, since artefacts possibly influencing the release pattern were not taken into account, this interpretation was strongly criticized. We therefore carefully investigated night-time melatonin production in patients with coronary artery disease using an appropriate experimental approach. Furthermore, we examined the effect of beta-blockers, a frequently used drug in coronary artery disease therapy. Forty-eight male patients with angiographically documented severe coronary artery disease, 24 of them taking beta-blockers daily in therapeutic dosages, were included. Eighteen age-matched men, with no evidence of coronary sclerosis, served as controls. To determine melatonin production, 6-sulfatoxymelatonin (aMT6s) was measured radioimmunologically from overnight urine. Urinary aMT6s concentration was significantly decreased in patients, and beta-blocker treatment did not further suppress melatonin production. The data obtained using this investigative approach provide clearcut evidence that melatonin production in patients with coronary artery disease is decreased. Whether a decreased melatonin level may be a predisposing factor for coronary artery disease, or whether the occurrence of coronary artery disease decreases melatonin synthesis remains to be determined.

A 0.5 G, 60 Hz magnetic field suppresses melatonin production in pinealocytes

The objective of this study was to develop a model for testing various hypotheses concerning possible mechanisms whereby electromagnetic fields might induce suppression of nighttime melatonin production in rodents. A published method for digesting freshly obtained pineal glands to the single cell level was modified, yielding better than 95% viability. An in vitro exposure facility developed for the Food and Drug Administration was used for 12-h overnight exposures of primary pinealocyte cultures to 0.05 mT, 60 Hz, vertical AC and 0.06 microT, DC fields. After exposure, cells were separated from the supernatant by centrifugation. Supernatant melatonin was measured by ELISA assays. Data from 10 experiments demonstrated an average 46% reduction in norepinephrine-induced production of melatonin in the pinealocytes. The results support the hypothesis that EM exposure can produce pineal gland melatonin suppression by affecting individual cells.

Oxygen radical detoxification processes during aging: the functional importance of melatonin.

That free radical destruction of macromolecules is a basis of aging and age-related diseases has considerable experimental support. Melatonin, a hormone produced in organisms as diverse as algae and humans, is believed to have evolved coincident with aerobic metabolism. In all organisms melatonin is produced primarily during the daily period of darkness, with only small amounts being synthesized during the day. In mammals including man, melatonin is produced by and secreted from the pineal gland during the night; however, the night-time production of melatonin falls markedly with aging such that in senescent animals a night-time melatonin rise is barely measurable. This may be significant in terms of aging in the light of recent observations which show that melatonin is a highly efficient free radical scavenger and antioxidant both in vitro and in vivo. In vitro, melatonin has been shown to directly scavenge both the hydroxyl and peroxyl radical, and it does so more efficiently than other known antioxidants. Furthermore, melatonin greatly potentiates the efficiency of previously-discovered endogenous and exogenous antioxidants. In vivo, both physiological and pharmacological levels of melatonin reportedly counteract the devastatingly destructive actions of free radical generating chemicals. For example, melatonin effectively combats DNA damage in rats given massive doses of the chemical carcinogen safrole, and the indole overcomes much of the genomic damage inflicted by ionizing radiation. Also, lipid peroxidation induced by either paraquat, bacterial lipopolysaccharide or H2O2 is highly significantly reduced by concurrent melatonin administration. Finally, cataracts produced in newborn rats by the depletion of the endogenous antioxidant glutathione are prevented by melatonin. These findings provide evidence that melatonin is operative in the cell nucleus, in the aqueous cytosol and in lipid-rich cellular membranes as an antioxidant. Considering this, the loss of this potent antioxidant during aging may be consequential in terms of cellular and organismal aging as well as the onset of age-related diseases. These experimental results from a variety of sources suggest that a more determined approach to the study of melatonin as an anti-aging factor is warranted.

Pineal perifusion with calcium channel blockers inhibits differently daytime and nighttime melatonin production in rat

In a previous study we have shown that the response of perifused pineal glands to calcium was different according to the circadian stage at which the glands were removed. This difference may be explained by circadian changes in calcium channel function. Therefore in the present study we documented the effects of calcium channel blockers in perifused rat pineal glands removed in the middle of the light and dark spans (7 and 19 HALO (hours after light onset), in a L/D 12:12 regimen). Moreover, we have studied the effect of calcium channel blockers on adrenergically stimulated pineal glands removed 7 HALO. Inorganic (Co 2+ and Cd 2+) and organic (nifedipine and diltiazem) calcium channel blockers at 10 −4 mol/1 all significantly reduced melatonin production and this inhibition was more effective with the glands removed 7 HALO. In a concentration of 10 −5 mol/1, only Cd 2+ and diltiazem reduced melatonin production significantly in pineal glands removed 7 HALO. Verapamil at 10 −4 and 10 −5 mol/1 showed no significant effect on melatonin production in glands removed both during the light and dark spans. Mn 2+ at 10 −4 mol/1 (but not at 10 −5 mol/1) appeared to stimulate melatonin production in glands removed both during the light and the dark (significant increase only with glands removed during the dark). Cobalt showed an immediate short inhibitory effect on both isoproterenol and norepinephrine-stimulated melatonin release, whereas nifedipine showed a significant inhibition only on isoproterenol-stimulated melatonin release. These results strongly suggest a circadian stage dependence of the pineal gland response to some calcium channel blockers and the involvement of calcium in the release of melatonin from pinealocytes.

Attenuated nocturnal rise in pineal and serum melatonin in a genetically cardiomyopathic Syrian hamster with a deficient calcium pump

Day and nighttime melatonin production in the pineal gland was compared in normal and cardiomyopathic (polydystrophic) adult male Syrian hamsters. These strains of hamsters were selected for comparison because the cardiomyopathetic hamster displays a deficient transmembrane Ca(2+)-pump in a number of tissues, and intracellular CA2+ concentrations ([Ca2+]i) play a central role in the nocturnal increase in pineal melatonin synthesis. Daytime levels of all constituents measured, i.e., pineal N-acetyltransferase (NAT) activity, pineal and serum melatonin levels, and pineal 5-hydroxytryptophan (5-HTP), serotonin, and 5-hydroxyindole acetic acid (5-HIAA) contents, were comparable in control and dystrophic hamsters. In contrast, the nighttime rises in pineal NAT activity and pineal and serum melatonin levels were significantly attenuated in the dystrophic hamsters. By comparison, the pineal contents of 5-HTP, serotonin, and 5-HIAA were essentially the same in both groups of hamsters with both pineal serotonin and 5-HIAA values exhibiting the usual nighttime drop. It is presumed that the alterations in nocturnal melatonin production in the pineal gland of the cardiomyopathic hamster may relate to a generalized deficiency in the Ca(2+)-pump in pinealocyte plasma membranes, which leads to unusually high [Ca2+]i, causing a depression of NAT activity; this leads to the commensurate decline in pineal and serum melatonin levels. Harderian gland NAT activity and melatonin levels were essentially similar in the two groups of animals, although NAT activity was slightly depressed in the dystrophic hamsters killed during the day. The reduced amounts of intrascapular brown fat in the cardiomyopathic hamster is speculated to be a result of the diminished amount of melatonin produced in these animals.

Antidepressant and circadian phase-shifting effects of light.

Bright light can suppress nighttime melatonin production in humans, but ordinary indoor light does not have this effect. This finding suggested that bright light may have other chronobiologic effects in humans as well. Eight patients who regularly became depressed in the winter (as day length shortens) significantly improved after 1 week of exposure to bright light in the morning (but not after 1 week of bright light in the evening). The antidepressant response to morning light was accompanied by an advance (shift to an earlier time) in the onset of nighttime melatonin production. These results suggest that timing may be critical for the antidepressant effects of bright light.