Melatonin Infusion Research Articles

The Effect of Melatonin on Incretin Hormones: Results From Experimental and Randomized Clinical Studies.

Glucose homeostasis is under circadian control through both endocrine and intracellular mechanisms, with several lines of evidence suggesting that melatonin affects glucose homeostasis. To evaluate the acute in vivo and in situ effects of melatonin on secretion of the incretin hormones, glucagon-like-peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), and their impact on β-cell insulin secretion. A human randomized, double-blinded, placebo-controlled crossover study combined with a confirmatory in situ study of perfused rat intestines. Aarhus University Hospital. Fifteen healthy male participants were examined 2 × 2 times: an oral glucose tolerance test (OGTT) was performed on day 1 and an isoglycemic IV glucose infusion replicating the blood glucose profile of the OGTT day was performed on day 2. These pairs of study days were repeated on treatment with melatonin and placebo, respectively. For the in situ study, 6 rat intestines and 4 rat pancreases were perfused arterially with perfusion buffer ± melatonin. The intestines were concomitantly perfused with glucose through the luminal compartment. In humans, melatonin treatment resulted in reduced GIP secretion compared with placebo (ANOVA P = 0.003), an effect also observed in the perfused rat intestines (ANOVA P = 0.003), in which GLP-1 secretion also was impaired by arterial melatonin infusion (ANOVA P < 0.001). Despite a decrease in GIP levels, the in vivo glucose-stimulated insulin secretion was unaffected by melatonin (P = 0.78). Melatonin reduced GIP secretion during an oral glucose challenge in healthy young men but did not affect insulin secretion. Reduced GIP secretion was confirmed in an in situ model of the rat intestine.

The Circadian Hormone Melatonin Inhibits Morphine-Induced Tolerance and Inflammation via the Activation of Antioxidative Enzymes.

Opioids are commonly prescribed for clinical pain management; however, dose-escalation, tolerance, dependence, and addiction limit their usability for long-term chronic pain. The associated poor sleep pattern alters the circadian neurobiology, and further compromises the pain management. Here, we aim to determine the correlation between constant light exposure and morphine tolerance and explore the potential of melatonin as an adjuvant of morphine for neuropathic pain treatment. Methods: Wistar rats were preconditioned under constant light (LL) or a regular light/dark (LD) cycle before neuropathic pain induction by chronic constriction injury. An intrathecal (i.t.) osmotic pump was used for continued drug delivery to induce morphine tolerance. Pain assessments, including the plantar test, static weight-bearing symmetry, and tail-flick latency, were used to determine the impact of the light disruption or exogenous melatonin on the morphine tolerance progression. Results: constant light exposure significantly aggravates morphine tolerance in neuropathic rats. Continued infusion of low-dose melatonin (3 μg/h) attenuated morphine tolerance in both neuropathic and naïve rats. This protective effect was independent of melatonin receptors, as shown by the neutral effect of melatonin receptors inhibitors. The transcriptional profiling demonstrated a significant enhancement of proinflammatory and pain-related receptor genes in morphine-tolerant rats. In contrast, this transcriptional pattern was abolished by melatonin coinfusion along with the upregulation of the Kcnip3 gene. Moreover, melatonin increased the antioxidative enzymes SOD2, HO-1, and GPx1 in the spinal cord of morphine-tolerant rats. Conclusion: Dysregulated circadian light exposure significantly compromises the efficacy of morphine’s antinociceptive effect, while the cotreatment with melatonin attenuates morphine tolerance/hyperalgesia development. Our results suggest the potential of melatonin as an adjuvant of morphine in clinical pain management, particularly in patients who need long-term opioid treatment.

Melatonin inhibits GABAergic neurons in the hypothalamus consistent with a reduction in wakefulness.

Although melatonin is necessary for circadian regulation of sleep, the mechanisms underlying this effect of melatonin are still unclear. In the present study, we showed that melatonin suppressed the activity of GABAergic neurons in the lateral hypothalamus, which has been reported to play a crucial role in maintaining wakefulness. The inhibitory effect of the melatonin was mediated by activation of melatonin 1 receptors and depended on the inhibition of hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels. At behavioral levels, infusion of melatonin into the lateral hypothalamus significantly decreased the locomotor and exploratory activities and increased the time of immobility in open filed. Additionally, using electroencephalogram (EEG) and electromyogram (EMG) recordings, we found that infusion of melatonin into the lateral hypothalamus decreased the time spent in wakefulness and increased the amount of sleep. Overall, these results suggest that melatonin inhibits GABAergic neurons in the lateral hypothalamus via melatonin 1 receptor-dependent inhibition of the HCN channels, which is consistent with a decrease in wakefulness. These findings provide a new mechanism underlying the hypnotic effect of the melatonin.

Investigating ovine placentome blood perfusion using power flow Doppler ultrasonography

Abstract Increasing ovine placentome blood perfusion improves placental efficiency while increasing the likelihood of healthier birth weights and lower mortality rates in offspring. Invasive surgical techniques have been used to examine uteroplacental blood flow; however, non-invasive Doppler ultrasonography has recently been observed as a reliable alternative method. Even so, smaller tissues, such as placentomes, do not permit reliable measurements of vessel diameter and subsequently blood flow calculations. Objectives were to validate Doppler ultrasonography techniques for examining placentome blood perfusion in ewes administered vasoactive compounds. Ewes (n = 28) were bred to a single ram, with pregnancy being confirmed prior to experimentation. For experiment 1, placentome blood perfusion was determined pre-infusion (PRE1; n = 8) and 3–5 minutes post i.v. infusion with sodium nitroprusside at 5 μg/kg of body weight (SN5; n = 4) or 10 ug/kg of body weight (SN10; n = 4). Immediately after ultrasonography all ewes were administered N(G)-Nitro- l -arginine methyl ester (L-NAME) at 12.5 mg/kg of body weight (n = 8) and imaged for placentome perfusion 30 min post i.v. infusion. For experiment 2, ewes (n = 15) were first imaged for placentome perfusion prior to the administration of antioxidants (min 0; PRE2) and then 30 min following i.v. infusion of melatonin (MEL; 100 ug/kg of body weight), ascorbate (ASC; 10 mg/kg of body weight), or vehicle (VEH; 50% ethanol solution). Data for experiment 1 and 2 were analyzed separately by ANOVA with least significant difference test. For experiment 1, the percent area of placentome perfusion was not different (P > 0.05) between SNP and l -NAME infusions. However, the summation and average integrated pixel density of placentomes were increased (P l -NAME. For experiment 2, the percent area of placentome perfusion was increased (P

Infusion of Melatonin Into the Paraventricular Nucleus Ameliorates Myocardial Ischemia-Reperfusion Injury by Regulating Oxidative Stress and Inflammatory Cytokines.

:Melatonin, the receptors for which are abundant in the hypothalamic paraventricular nucleus (PVN), can protect the heart from myocardial ischemia–reperfusion (MI/R) injury. The aim of this study was to determine whether the infusion of melatonin into the PVN protects the heart from MI/R injury by suppressing oxidative stress or regulating the balance between proinflammatory cytokines and anti-inflammatory cytokines in MI/R rats. Male Sprague–Dawley rats were treated with a bilateral PVN infusion of melatonin. MI/R operation was performed 1 week after infusion. At the end of the third week after the infusion, all the rats were euthanized. This was followed by immunohistochemistry and immunofluorescence studies of the rats. MI/R rats showed larger infarct size, increased left ventricular (LV) end-diastolic volume, and decreased LV ejection fraction and LV fractional shortening. Moreover, MI/R rats had a higher level of norepinephrine in the plasma, heart, and PVN; higher PVN levels of reactive oxygen species, NOX2, NOX4, IL-1β, and NF-κB activity; and lower PVN levels of copper/zinc superoxide dismutase (Cu/Zn-SOD) and IL-10 compared with the sham group. Melatonin infusion in PVN reduced LV end-diastolic volume, norepinephrine, reactive oxygen species, NOX2, NOX4, IL-1β, and NF-κB activity, and increased LV ejection fraction, LV fractional shortening, Cu/Zn-SOD, and IL-10. Overall, these results suggest that the infusion of melatonin ameliorates sympathetic nerve activity and MI/R injury by attenuating oxidative stress and inflammatory cytokines in the PVN of MI/R rats.

Evaluation of novel formulations of d-β-hydroxybutyrate and melatonin in a rat model of hemorrhagic shock

d-β-hydroxybutyrate and melatonin (BHB/MLT) infusion improves survival in hemorrhagic shock models. The original BHB/MLT formulation contains dimethyl sulfoxide (DMSO) to increase melatonin solubility. We formulated BHB/MLT solutions wherein DMSO was replaced either with 10% polyvinylpyrrolidone (BHB/MLT/PVP) or with 5% hydroxypropyl-β-cyclodextrin/2.5% PVP/2.5% polyethylene glycol 400 (BHB/MLT/CD). Safety and efficacy of the new and the original BHB/MLT solution were tested in a lethal rat hemorrhagic shock model, with seven groups: 1) sham, 2) shock, untreated, 3) shock, lactated Ringer’s solution (LR), 4) shock, 4 M BHB/MLT/DMSO, 5) shock, 2 M BHB/MLT/DMSO, 6) shock, BHB/MLT/PVP and 7) shock, BHB/MLT/CD. BHB/MLT/DMSO was given at full strength and 1:1 dilution to match the concentration of the novel formulations. Rats were anesthetized, instrumented, and 40% of the total blood volume was withdrawn in three steps, followed by four-hour long shock. Treatment boluses were infused half-way throughout hemorrhage. Survival was highest in BHB/MLT/CD-treated rats (8/10), followed by the BHB/MLT/PVP (6/10), 4 M BHB/MLT/DMSO (5/10) or 2 M BHB/MLT/DMSO (5/10), LR (3/10) and the untreated group (0/11). Survival did not differ significantly between BHB/MLT groups (p > 0.05), but was significantly higher in BHB/MLT/CD than in LR-treated animals (p = 0.018). BHB/MLT/PVP and BHB/MLT/CD constitute promising candidates for clinical hemorrhagic shock treatment.

Melatonin promotes sleep in mice by inhibiting orexin neurons in the perifornical lateral hypothalamus.

Melatonin promotes sleep. However, the underlying mechanisms are unknown. Orexin neurons in the perifornical lateral hypothalamus (PFH) are pivotal for wake promotion. Does melatonin promote sleep by inhibiting orexin neurons? We used C57BL/6J mice and designed 4 experiments to address this question. Experiment 1 used double-labeled immunofluorescence and examined the presence of melatonin receptors on orexin neurons. Second, mice, implanted with bilateral guides targeted toward PFH and sleep-recording electrodes, were infused with melatonin (500pmole/50nL/side) at dark onset (onset of active period), and spontaneous bouts of sleep-wakefulness were examined. Third, mice, implanted with bilateral guides into the PFH, were infused with melatonin (500pmole/50nL/side) at dark onset and euthanized 2hours later, to examine the activation of orexin neurons using c-Fos expression in orexin neurons. Fourth, mice, implanted with PFH bilateral guides and sleep-recording electrodes, were infused with melatonin receptor antagonist, luzindole (10pmol/50nL/side), at light onset (onset of sleep period), and spontaneous bouts of sleep-wakefulness were examined. Our results suggest that orexin neurons express MT1, but not MT2 receptors. Melatonin infusion into the PFH, at dark onset, site-specifically and significantly increased NREM sleep (43.7%, P=.003) and reduced wakefulness (12.3%, P=.013). Local melatonin infusion at dark onset inhibited orexin neurons as evident by a significant reduction (66%, P=.0004) in the number of orexin neurons expressing c-Fos. Finally, luzindole infusion-induced blockade of melatonin receptors in PFH at sleep onset significantly increased wakefulness (44.1%, P=.015). Based on these results, we suggest that melatonin may act via the MT1 receptors to inhibit orexin neurons and promote sleep.

FEATURES OF INTRACELLULAR (METABOLITHOTROPIC) MECHANISMS OF NEURORETINOPROTECTIVE ACTIVITY OF MELATONIN IN THE THERAPY OF EXPERIMENTAL CONTUSION OF THE VISUAL ANALYZER

Therapy of rabbits with an experimental contusion of the eye, caused by the action of the flow of carbon dioxide under pressure, by intravenous infusion of melatonin in dose 10 mg / kg, contributes to the realization of its positive adjustment effects on energy and nitrogen monoxide metabolisms, the glutamate excitotoxicity phenomenon and eliminates signs of oxidative stress due to the saving activity of its own fermentation links of antioxidant system. Melatonin significantly exceeds the effectiveness of corvitin or citicoline by the studied indicators (markers) of metabolism. The leading intracellular mechanisms of neuroretinoprotective effect of melatonin in experimental eye contusion can be attributed to its anti-excitotoxiciting and energy-modulating effect, antioxidant activity and the ability of the drug to normalize the metabolism of nitrogen monoxide.

Effects of antenatal melatonin therapy on lung structure in growth-restricted newborn lambs.

Oxidative stress arising from suboptimal placental function contributes to a multitude of pathologies in infants compromised by fetal growth restriction (FGR). FGR infants are at high risk for respiratory dysfunction after birth and poor long-term lung function. Our objective was to investigate the contribution of oxidative stress to adverse lung development and the effects of melatonin administration, a powerful antioxidant, on lung structure in FGR lambs. Placental insufficiency and FGR was surgically induced in 13 fetal sheep at ∼105 days of gestation by ligation of a single umbilical artery. Maternal intravenous melatonin infusion was commenced in seven of the ewes 4 h after surgery and continued until birth. Lambs delivered normally at term and lungs were collected 24 h after birth for histological assessment of lung structure and injury and compared with appropriately grown control lambs (n = 8). FGR fetuses were hypoxic and had lower glucose during gestation compared with controls. Melatonin administration prevented chronic hypoxia. Within the lung, FGR caused reduced secondary septal crest density and altered elastin deposition compared with controls. Melatonin administration had no effect on the changes to lung structure induced by FGR. We conclude that chronic FGR disrupts septation of the developing alveoli, which is not altered by melatonin administration. These findings suggest that oxidative stress is not the mechanism driving altered lung structure in FGR neonates. Melatonin administration did not prevent disrupted airway development but also had no apparent adverse effects on fetal lung development.NEW & NOTEWORTHY Fetal growth restriction (FGR) results in poor respiratory outcomes, which may be caused by oxidation in utero. We investigated the contribution of oxidative stress to adverse lung development and the effects of melatonin administration, a powerful antioxidant, on lung structure in FGR lambs. FGR disrupted septation of the developing alveoli, which is not altered by melatonin administration. Oxidative stress may not be the mechanism driving altered lung structure in FGR neonates.

Melatonin inhibits hypothalamic gonadotropin-releasing hormone release and reduces biliary hyperplasia and fibrosis in cholestatic rats.

Melatonin is a hormone produced by the pineal gland with increased circulating levels shown to inhibit biliary hyperplasia and fibrosis during cholestatic liver injury. Melatonin also has the capability to suppress the release of hypothalamic gonadotropin-releasing hormone (GnRH), a hormone that promotes cholangiocyte proliferation when serum levels are elevated. However, the interplay and contribution of neural melatonin and GnRH to cholangiocyte proliferation and fibrosis in bile duct-ligated (BDL) rats have not been investigated. To test this, cranial levels of melatonin were increased by implanting osmotic minipumps that performed an intracerebroventricular (ICV) infusion of melatonin or saline for 7 days starting at the time of BDL. Hypothalamic GnRH mRNA and cholangiocyte secretion of GnRH and melatonin were assessed. Cholangiocyte proliferation and fibrosis were measured. Primary human hepatic stellate cells (HSCs) were treated with cholangiocyte supernatants, GnRH, or the GnRH receptor antagonist cetrorelix acetate, and cell proliferation and fibrosis gene expression were assessed. Melatonin infusion reduced hypothalamic GnRH mRNA expression and led to decreased GnRH and increased melatonin secretion from cholangiocytes. Infusion of melatonin was found to reduce hepatic injury, cholangiocyte proliferation, and fibrosis during BDL-induced liver injury. HSCs supplemented with BDL cholangiocyte supernatant had increased proliferation, and this increase was reversed when HSCs were supplemented with supernatants from melatonin-infused rats. GnRH stimulated fibrosis gene expression in HSCs, and this was reversed by cetrorelix acetate cotreatment. Increasing bioavailability of melatonin in the brain may improve outcomes during cholestatic liver disease.NEW & NOTEWORTHY We have previously demonstrated that GnRH is expressed in cholangiocytes and promotes their proliferation during cholestasis. In addition, dark therapy, which increases melatonin, reduced cholangiocyte proliferation and fibrosis during cholestasis. This study expands these findings by investigating neural GnRH regulation by melatonin during BDL-induced cholestasis by infusing melatonin into the brain. Melatonin infusion reduced cholangiocyte proliferation and fibrosis, and these effects are due to GNRH receptor 1-dependent paracrine signaling between cholangiocytes and hepatic stellate cells.

Effects of Antenatal Melatonin Treatment on the Cerebral Vasculature in an Ovine Model of Fetal Growth Restriction

Chronic moderate hypoxia, such as occurs in fetal growth restriction (FGR) during gestation, compromises the blood-brain barrier (BBB) and results in structural abnormalities of the cerebral vasculature. We have previously determined the neuroprotective and antioxidant effects of maternal administration of melatonin (MLT) on growth-restricted newborn lambs. The potential of maternal MLT therapy for the treatment of cerebrovascular dysfunction-associated developmental hypoxia has also been demonstrated in newborn lambs. We assessed whether MLT had an effect on the previously reported structural and cerebral vascular abnormalities in chronically hypoxic FGR lambs. Single umbilical-artery ligation surgery was performed in fetuses at approximately 105 days of gestation (term: 147 days) to induce placental insufficiency and FGR, and treatment with either saline or an MLT infusion (0.1 mg/kg) was started 4 h after surgery. Ewes delivered naturally at term and lambs were euthanased 24 h later. We found a significant reduction in the number of laminin-positive blood vessels within the subcortical and periventricular white matter (SCWM and PVWM) and the subventricular zone (SVZ) in FGR (p < 0.0005) and FGR + MLT brains (p < 0.0005 vs. controls), with no difference found between FGR and FGR + MLT animals. This was associated with a significant decrease in VEGF immunoreactivity in FGR and FGR + MLT brains versus controls (p < 0.0005; SCWM and PVWM) and in the SVZ in FGR brains versus controls (p < 0.005) and also with significantly lower levels of proliferating blood vessels versus controls (p < 0.0005). Glucose transporter-1 immunoreactivity (vascular endothelium) was decreased in FGR versus control lambs (p < 0.0005) in SCWM, PVWM, and the SVZ; it was significantly increased in FGR + MLT lambs compared with FGR lambs in SCWM and PVWM (p < 0.005) and even more markedly in the SVZ (p < 0.0005). FGR brains showed a 72% reduction in pericyte coverage versus control lambs and 68% versus FGR + MLT in PVWM. In SCWM, we found a 77 and 73% reduction compared with control and FGR + MLT lambs, respectively, while in the SVZ, we observed a 68% reduction versus controls and a 70% reduction in FGR versus FGR + MLT lambs. Astrocyte end-feet coverage in the SCWM showed a significant 24% reduction in FGR versus control levels, a 42% decrease within the PVWM, and a 35% decrease within the SVZ versus controls. MLT normalized astrocyte attachment to blood vessels, with no difference seen between controls and FGR + MLT animals in any of the brain regions examined. We also observed a decrease in albumin extravasation and microhemorrhage in controls and FGR + MLT brains versus FGR lambs. Our results demonstrate that umbilicoplacental insufficiency is associated with FGR-produced vascular changes in the white matter and SVZ of FGR newborn brains and that maternal MLT prevented disruption of the BBB by protecting perivascular cells essential for the maintenance of vascular homeostasis and stability.

Tu1613 Cranial Infusion of Melatonin in a Rat Model of Extrahepatic Cholestasis Reduces Biliary Proliferation and Liver Fibrosis

Tu1613 Cranial Infusion of Melatonin in a Rat Model of Extrahepatic Cholestasis Reduces Biliary Proliferation and Liver Fibrosis

Subcellular distribution of melatonin receptors in rat parotid salivary glands: effect of melatonin intravenous infusion

The ultrastructural localization of melatonin receptors Mt1 and Mt2 in human salivary glands has previously been reported (Isola el al, 2013). In the acinar cells, the intragranular distribution of these receptors suggested to us that they may serve as a transcytotic system for melatonin. In an attempt to verify our working-hypothesis we currently exposed anaesthetized rats to the intravenous infusion of melatonin for 2 hrs. After another 30 min, the parotid gland on the right side was removed to be compared with prestimulation removed pieces of the left parotid gland serving as control specimens. Parotid gland tissues from 5 rats were cut into small pieces and fixed with a mixture of paraformaldehyde and glutaraldehyde. They were dehydrated, and embedded in Epon Resin. The ultrathin sections were collected on nickel grids and incubated overnight at 4oC with an antibody specific for Mt1 and Mt2, respectively. The grids were then incubated for 1 hr with the appropriate secondary antibody conjugated to gold particles and, finally examined using electron transmission microscopy. In all sections, the immunoreactivity to Mt2 and, with less intensity, to Mt1 was principally expressed in secretory granules of acinar cells. Occasionally, plasma membranes were also stained, although slightly. Statistical analysis showed that, in response to melatonin, the immunogold particles reactive for Mt1, but not those for Mt2, increased. To conclude, in line with our hypothesis, melatonin stimulates an acinar carrier system, which seems predominantly to involve the Mt1 receptor, in order to delivery this hormone into saliva.

Melatonin suppresses markers of inflammation and oxidative damage in a human daytime endotoxemia model

PurposeMelatonin used as an exogenous drug has been documented to have potent antioxidant and anti-inflammatory effects in animal model. We aimed to examine the effect of melatonin in an experimental human sepsis model. Materials and MethodsTwelve healthy males were enrolled in a randomized, placebo-controlled, double-blinded cross-over trial. They received lipopolysaccharide endotoxin 0.3 ng/kg of body weight intravenously at 12:00. Before endotoxemia, an 8-hour infusion of melatonin (100 mg) or placebo (saline) was initiated. Blood samples were drawn before and at 2, 4, 6, and 8 hours after lipopolysaccharide administration. Proinflammatory (tumor necrosis factor α [TNF-α], interleukin [IL] 1β, IL-6, and YKL-40), anti-inflammatory markers (IL-1Ra, IL-10, soluble tumor necrosis factor receptor I, and soluble tumor necrosis factor receptor II), a marker for oxidative damage (malondialdehyde), and antioxidants (ascorbic acid and dehydroascorbic acid) were analyzed in plasma. ResultsMelatonin significantly reduced proinflammatory markers IL-1β (P < .01) and YKL-40 (P < .05) but not TNF-α and IL-6. None of the anti-inflammatory markers (IL-1Ra, IL-10, soluble tumor necrosis factor receptor I, and soluble tumor necrosis factor receptor II) were lowered by melatonin. Melatonin reduced the levels of ascorbic acid (P < .05) but not dehydroascorbic acid or malondialdehyde. ConclusionsMelatonin administration before endotoxemia resulted in reduction of certain markers of inflammation and oxidative stress. Further studies are needed to clarify the role of melatonin in clinical setting.

Partial Neural Protection with Prophylactic Low-Dose Melatonin after Asphyxia in Preterm Fetal Sheep

Melatonin is a naturally occurring indolamine with mild antioxidant properties that is neuroprotective in perinatal animals. There is limited information on its effects on preterm brain injury. In this study, 23 chronically instrumented fetal sheep received 25 minutes of complete umbilical cord occlusion at 101 to 104 days gestation (term is 147 days). Melatonin was administered to the ewe 15 minutes before occlusion (0.1 mg/kg bolus followed by 0.1 mg/kg per hour for 6 hours, n=8), or the equivalent volume of vehicle (2% ethanol, n=7), or saline (n=8), or maternal saline plus sham occlusion (n=8). Sheep were killed after 7 days recovery in utero. Fetal blood pressure, heart rate, nuchal activity, and temperature were similar between groups. Vehicle infusion was associated with improved neuronal survival in the caudate nucleus, but greater neuronal loss in the regions of the hippocampus, with reduced proliferation and increased ameboid microglia in the white matter (P<0.05). Maternal melatonin infusion was associated with faster recovery of fetal EEG, prolonged reduction in carotid blood flow, similar neuronal survival to vehicle, improved numbers of mature oligodendrocytes, and reduced microglial activation in the white matter (P<0.05). Prophylactic maternal melatonin treatment is partially protective but its effects may be partly confounded by ethanol used to dissolve melatonin.

Uterine Infusion of Melatonin or Melatonin Receptor Antagonist Alters Ovine Feto-Placental Hemodynamics During Midgestation1

Dietary melatonin supplementation from mid- to late gestation increases umbilical artery blood flow and causes disproportionate fetal growth. Melatonin receptors have been described throughout the cardiovascular system; however, there is a paucity of data on the function of placental melatonin receptors. The objectives of the current experiment were to determine fetal descending aorta blood flow, umbilical artery blood flow, and placental and fetal development following a 4-wk uterine infusion of melatonin (MEL), melatonin receptor 1 and 2 antagonist (luzindole; LUZ), or vehicle (CON) from Day 62 to Day 90 of gestation. After 4 wk of infusion, umbilical artery blood flow and umbilical artery blood flow relative to placentome weight were increased (P < 0.05) in MEL- versus CON- and LUZ-infused dams. Fetal descending aorta blood flow was increased (P < 0.05) in MEL- versus CON- and LUZ-infused dams, while fetal descending aorta blood flow relative to fetal weight was increased in MEL- versus CON-infused dams and decreased in LUZ- versus CON-infused dams. Following the 4-wk infusion, we observed an increase in placental efficiency (fetal-placentome weight ratio) in MEL- versus LUZ-infused dams. The increase in umbilical artery blood flow due to chronic uterine melatonin infusion is potentiated by an increased fetal cardiac output through the descending aorta. Moreover, melatonin receptor antagonism decreased fetal descending aorta blood flow relative to fetal weight. Therefore, melatonin receptor activation may partially mediate the observed increase in fetal blood flow following dietary melatonin supplementation.

Pharmacokinetics of Melatonin in Preterm Infants

Background: There is strong experimental evidence of a neuroprotective effect of melatonin in immature animals. However, pharmacokinetic (PK) data on melatonin in preterm infants is lacking. The aim was to examine the preterm pharmacokinetic profile.Methods: We conducted a multi centre, open label study in infants < 31 weeks and < 7 days of age. A single intravenous melatonin infusion was given to successive groups. Melatonin and its primary urinary metabolite aMT6s were analysed by radioimmunoassay. Dosage was adjusted in subsequent groups until adult physiological levels were achieved (34.5-1185.3 pmol/L).Results: 18 preterms were enrolled. The results are summarized in table/graph below. Pre-infusion median plasma melatonin levels were 0pmol/L (range-0-165pmol/L). Blood melatonin levels closest to adult levels were achieved with a 2 hour infusion of 0.1mcg/kg/hr; the half life was 15.99 hours and Area under the curve-7234.74. Lower doses resulted in widely variable PK data. Figure [Plasma Melatonin Profile] Table Table Full size table Conclusion: Preterms have none or minimal circulating plasma melatonin. Urinary aMT6s levels are negligible in this gestational age group, probably because of immature liver metabolism. This melatonin PK data will be used in future clinical studies to test the hypothesis that melatonin has a neuroprotective effect.

Treatment with beta-hydroxybutyrate and melatonin is associated with improved survival in a porcine model of hemorrhagic shock

IntroductionThe neuroprotective ketone β-hydroxybutyrate (BHB) and the antioxidant melatonin have been found at elevated levels in hibernating mammals. Previous studies in rat models of hemorrhagic shock have suggested a benefit. We compared infusion of 4M BHB and 43mM melatonin (BHB/M) to 4M sodium chloride and 20% DMSO (control solution) to evaluate for potential benefits in porcine hemorrhagic shock. MethodsHemorrhagic shock was induced to obtain systolic blood pressures <50mmHg for 60min. Pigs were treated with a bolus of either BHB/M (n=9) or control solution (n=8) followed by 4-h infusion of the either BHB/M or control solution. All animals were then resuscitated for 20h after shock. Physiological data were continually recorded, and blood samples were taken at intervals throughout the experiment. Serum samples were analyzed via high resolution NMR for metabolomic response. ResultsBHB/M treatment significantly increased 24-h survival time when compared to treatment with control solution (100% versus 62%; p=0.050), with a trend toward decreased volume of resuscitative fluid administered to animals receiving BHB/M. BHB/M-treated animals had lower base deficit and higher oxygen consumption when compared to animals receiving control solution. Serum metabolite profiles revealed increases in β-hydroxybutyrate (BHB), succinate, 2-oxovalerate and adipate with BHB/M treatment as compared with animals treated with control infusion. ConclusionInfusion of BHB/M conferred a survival benefit over infusion of control solution in hemorrhagic shock. BHB and its products of metabolism are identified in serum of animals subjected to shock and treated with BHB/M. Further preclinical studies are needed to clarify the mechanisms of action of this promising treatment strategy.

Improved neuroprotection with melatonin-augmented hypothermia versus hypothermia alone in a perinatal asphyxia model

BackgroundMelatonin (N-acetyl-5-methoxytryptamine) is a naturally occurring hormone, an anti-oxidant and cellular pro-survival factor. It is used safely in children with sleep disorders. Beneficial properties of melatonin following brain injury in...

No Effect of Melatonin to Modify Surgical-Stress Response after Major Vascular Surgery: A Randomised Placebo-controlled trial

Background A possible mechanism underlying cardiovascular morbidity after major vascular surgery may be the perioperative ischaemia–reperfusion with excessive oxygen-derived free-radical production and increased levels of circulating inflammatory mediators. We examined the effect of melatonin infusion during surgery and oral melatonin treatment for 3 days after surgery on biochemical markers of oxidative and inflammatory stress. Methods Patients received an intra-operative intravenous infusion of 50 mg melatonin or placebo. In addition, all patients received 10 mg melatonin or placebo orally the first 3 nights after surgery. Blood samples for analysis of malondialdehyde (MDA), ascorbic acid (AA), dehydroascorbic acid (DHA) and C-reactive protein (CRP) were collected preoperatively, and at 5 min, 6 h and 24 h after clamp removal (recirculation of the first leg). Results Twenty-six patients received melatonin and 24 patients received placebo. No significant differences were observed in any of the oxidative and inflammatory stress parameters. There were significantly more side effects in the melatonin group than in the placebo group. Conclusions Melatonin treatment in the perioperative period did not reduce the oxidative and inflammatory parameters measured in this study.