Melatonin reduces oxidative stress in erythrocytes and plasma of senescence-accelerated mice

It has been suggested that oxidative stress is a feature of aging. The goal of the present study was to assess the oxidant effects related to aging and the protective role of exogenous melatonin in senescence-accelerated mice (SAMP8). Two groups of SAMP8 mice (males and females) were compared with their respective control groups of SAMR1 mice (senescence-resistant inbred strain) to determine their oxidative status without melatonin treatment. Four other groups of the same characteristics were treated with melatonin (10 mg/kg/day) in their drinking water. The melatonin concentration in the feeding bottles was titrated according to water consumption and body weight (i.e. 0.06 mg/mL for 30 g of body weight and 5 mL/day of water consumption). The treatment began when animals were 1-month old and continued for 9 months. When mice were 10-month old, they were anesthetized and blood was obtained. Plasma and erythrocytes were processed to examine oxidative stress markers: reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferase (GST), thiobarbituric acid reactive substances (TBARS), and hemolysis. The results showed greater oxidative stress in SAMP8 than in SAMR1, largely because of a decrease in GSH levels and to an increase in GSSG and TBARS with the subsequent induction of the antioxidant enzymes GPX and GR. Melatonin, as an antioxidant molecule, improved the glutathione-related parameters, prevented the induction of GPX in senescent groups, and promoted a decrease in SOD and TBARS in almost all the groups.     

Melatonin reduces uranium-induced nephrotoxicity in rats

The protective role of exogenous melatonin on U-induced nephrotoxicity was investigated in rats. Animals were given single doses of uranyl acetate dihydrate (UAD) at 5 mg/kg (subcutaneous), melatonin at 10 or 20 mg/kg (intraperitoneal), and UAD (5 mg/kg) plus melatonin (10 or 20 mg/kg), or vehicle (control group). In comparison with the UAD-treated group only, significant beneficial changes were noted in some urinary and serum parameters of rats concurrently exposed to UAD and melatonin. The increase of U excretion after UAD administration was accompanied by a significant reduction in the renal content of U when melatonin was given at a dose of 20 mg/kg. Melatonin also reduced the severity of the U-induced histological alterations in kidney. In renal tissue, the activity of the superoxide dismutase (SOD) and the thiobarbituric acid reactive substances (TBARS) levels increased significantly as a result of UAD exposure. Following UAD administration, oxidative stress markers in erythrocytes showed a reduction in SOD activity and an increase in TBARS levels, which were significantly restored by melatonin administration. In plasma, reduced glutathione (GSH) and its oxidized form (GSSG) were also altered in UAD-exposed rats. However, only the GSSG/GSH ratio was restored to control levels after melatonin treatment. Oxidative damage was observed in kidneys. Melatonin administration partially restored these adverse effects. It is concluded that melatonin offers some benefit as a potential agent to treat acute U-induced nephrotoxicity.     

Melatonin provides neuroprotection by reducing oxidative stress and HSP70 expression during chronic cerebral hypoperfusion in ovariectomized rats

Abstract:  Oxidative stress is believed to contribute to functional and histopathologic disturbances associated with chronic cerebral hypoperfusion (CCH) in rats. Melatonin has protective effects against cerebral ischemia/reperfusion injury. This effect has mainly been attributed to its antioxidant properties. In the present study, we evaluate the effects of melatonin on chronic cerebral hypoperfused rats and examined its possible influence on oxidative stress, superoxide dismutase (SOD) activity, reduced glutathione (GSH) levels, and heat shock protein (HSP) 70 induction. CCH was induced by permanent bilateral common carotid artery occlusion in ovariectomized female rats. Extensive neuronal loss in the hippocampus at day 14 following CCH was observed. The ischemic changes were preceded by increases in malondialdehyde (MDA) concentration and HSP70 induction as well as reductions in GSH and SOD. Melatonin treatment restored the levels of MDA, SOD, GSH, and HSP70 induction as compared to the ischemic group. Histopathologic analysis confirmed the protective effect of melatonin against CCH-induced morphologic alterations. Taken together, our results document that melatonin provides neuroprotective effects in CCH by attenuating oxidative stress and stress protein expression in neurons. This suggests melatonin may be helpful for the treatment of vascular dementia and cerebrovascular insufficiency.     

Melatonin ameliorates low‐grade inflammation and oxidative stress in young Zucker diabetic fatty rats

The aim of this study was to investigate the effects of melatonin on low‐grade inflammation and oxidative stress in young male Zucker diabetic fatty (ZDF) rats, an experimental model of metabolic syndrome and type 2 diabetes mellitus (T2DM). ZDF rats (n = 30) and lean littermates (ZL) (n = 30) were used. At 6 wk of age, both lean and fatty animals were subdivided into three groups, each composed of 10 rats: naive (N), vehicle treated (V), and melatonin treated (M) (10 mg/kg/day) for 6 wk. Vehicle and melatonin were added to the drinking water. Pro‐inflammatory state was evaluated by plasma levels of interleukin‐6 (IL‐6), tumor necrosis factor‐α (TNF‐α), and C‐reactive protein (CRP). Also, oxidative stress was assessed by plasma lipid peroxidation (LPO), both basal and after Fe²⁺/H₂O₂ inducement. ZDF rats exhibited higher levels of IL‐6 (112.4 ± 1.5 pg/mL), TNF‐α (11.0 ± 0.1 pg/mL) and CRP (828 ± 16.0 µg/mL) compared with lean rats (IL‐6, 89.9 ± 1.0, P < 0.01; TNF‐α, 9.7 ± 0.4, P < 0.01; CRP, 508 ± 21.5, P < 0.001). Melatonin lowered IL‐6 (10%, P < 0.05), TNF‐α (10%, P < 0.05), and CRP (21%, P < 0.01). Basal and Fe²⁺/H₂O₂‐induced LPO, expressed as malondialdehyde equivalents (µmol/L), were higher in ZDF rats (basal, 3.2 ± 0.1 versus 2.5 ± 0.1 in ZL, P < 0.01; Fe²⁺/H₂O₂‐induced, 8.7 ± 0.2 versus 5.5 ± 0.3 in ZL; P < 0.001). Melatonin improved basal LPO (15%, P < 0.05) in ZDF rats, and Fe²⁺/H₂O₂‐ induced LPO in both ZL (15.2%, P < 0.01) and ZDF rats (39%, P < 0.001). These results demonstrated that oral melatonin administration ameliorates the pro‐inflammatory state and oxidative stress, which underlie the development of insulin resistance and their consequences, metabolic syndrome, diabetes, and cardiovascular disease.     

Melatonin counteracts oxidative stress in rats fed an ochratoxin A contaminated diet

The mycotoxin ochratoxin A (OTA) is a widespread contaminant in human and animal food products. It induces a wide range of toxic effects including lipid peroxidation through the generation of free radicals. The aim of this work was to evaluate the antioxidant effects of melatonin against OTA-induced oxidative stress in liver and kidney in rats. Treated animals were fed OTA-contaminated diet (3 mg/kg) for 15 days before, during and after melatonin administration (20 mg/kg bw). The results indicate that OTA caused severe effects typical to those reported in the literature for ochratoxicosis. Melatonin alone was effective in the improving food intake, body weight gain, serum total protein, albumin, the activities of alkaline phosphatase, G-glutamyl transferase and creatinine kinase and liver and kidney glutathione peroxidase, superoxide dismutase and malondialdehyde. Rats fed OTA-contaminated diet before, during or after melatonin administration showed a significant improvement in all tested parameters toward the normal values of the controls. This improvement was most pronounced in the group pretreated with melatonin. It is concluded that melatonin exhibits a preventive effect against OTA-induced oxidative stress through its role in the scavenging of free radicals and/or the prevention of lipid peroxidation.     

Melatonin attenuates diabetes-induced oxidative stress in rabbits

Oxidative stress is considered to be the main cause of diabetic complications. As the role of antioxidants in diabetes therapy is still underestimated, the aim of the present investigation was to study the antioxidative action of melatonin in comparison with N-acetylcysteine (NAC) under diabetic conditions. Alloxan-diabetic rabbits were treated daily with either melatonin (1 mg/kg, i.p.), NAC (10 mg/kg, i.p.) or saline. Blood glutathione redox state and serum hydroxyl free radicals (HFR), creatinine and urea levels were monitored. After 3 wk of treatment animals were killed and HFR content, reduced glutathione/oxidized glutathione (GSH/GSSG) ratio as well as the activities of glutathione reductase, glutathione peroxidase and gamma-glutamylcysteine synthetase were estimated in both liver and kidney cortex. Diabetes evoked a several-fold increase in HFR levels accompanied by a significant decline in GSH/GSSG ratio in serum and the examined organs. In contrast to NAC, melatonin (at 1/10 the dose of NAC) attenuated diabetes-induced alterations in glutathione redox state and HFR levels, normalized creatinine concentration and diminished urea content in serum. Moreover, the indole resulted in an increase in glutathione reductase activity in both studied organs and in a rise in glutathione peroxidase and gamma-glutamylcysteine synthetase activities in the liver. In contrast to NAC, melatonin seems to be beneficial for diabetes therapy because of its potent antioxidative and nephroprotective action. The indole-induced increase in the activities of the enzymes of glutathione metabolism might be of importance for antioxidative action of melatonin under diabetic conditions.     

Melatonin reduces lipid peroxidation and nitric oxide during irradiation-induced oxidative injury in the rat liver

Radiation therapy is a popular and useful tool in the treatment of cancer. Melatonin participates in the regulation of a number of important physiological and pathological processes. Melatonin, a powerful endogenous antioxidant, plays a role in the reduction of oxidative damage. Thirty adult rats were divided into five equal groups. On the day of the experiment, groups I and II were injected with 5 or 10 mg/kg melatonin, respectively, while group III received isotonic NaCl solution. Thirty minutes later, groups I, II and III were exposed to 6.0 Gy whole body ionizing radiation in a single fraction. Group IV was injected with 5 mg/kg melatonin but was not irradiated. The final group was reserved as sham treated. Liver malondialdehyde (MDA) and nitric oxide (NO*) levels were measured in all groups. Whole body irradiation caused a significant increase in liver MDA and NO* levels. Hepatic MDA and NO* levels in irradiated rats that were pretreated with melatonin (5 or 10 mg/kg) were significantly decreased. Malondialdehyde and NO* levels were reduced in a dose-related manner by melatonin. The data show that melatonin reduces liver damage inflicted by irradiation when given prior to the exposure to ionizing radiation. The radioprotective effect of melatonin is likely achieved by its ability to function as a scavenger for free radicals generated by ionizing radiation.     

Melatonin inhibits oxidative stress and apoptosis in fetal brains of hyperhomocysteinemic rat dams

Moderate hyperhomocysteinemia is a risk factor for neurodegenerative diseases and complications during pregnancy. Increased homocysteine levels during pregnancy may elevate developmental risk on fetal brain structure and function. However, little is known about the mechanism of action of homocysteine on the degeneration of the fetal brain. Hence in this study, we examined the effects of maternal hyperhomocysteinemia on oxidative stress and apoptosis in brain tissues and investigated whether administration of melatonin to the mother would prevent homocysteine-induced oxidative cerebral damage in pups. Hyperhomocysteinemia was induced in female rats by administration of methionine at a dose of 1 g/kg body weight dissolved in drinking water during pregnancy. Some animals received methionine plus 10 mg/kg/day melatonin subcutaneously throughout pregnancy. After delivery, the level of lipid peroxidation (malondialdehyde + 4-hydroxyalkenals) was determined in different subfractions of pup brains. Furthermore, DNA fragmentation, levels of Bcl-2 protein and p53 mRNA expression were determined to evaluate apoptosis. Significant elevation was found in the levels of lipid peroxidation in subcellular fractions of the brain of pups of hyperhomocysteinemic dams. Increased DNA fragmentation and p53 mRNA expression was observed in the brain of pups of homocysteine-treated rats, while a significant reduction was seen in the levels of anti-apoptotic Bcl-2 levels. Melatonin administration prevented markers of oxidative stress and biochemical signs of apoptosis. In conclusion, therapeutic administration of melatonin protects against the induction of oxidative stress and neural tissue injury and might prevent congenital malformations of fetal brain caused by maternal hyperhomocysteinemia.     

Melatonin mitigates oxidative damage and apoptosis in mouse cerebellum induced by high-LET 56Fe particle irradiation

Abstract:  Cerebellum is a vital organ responsible for the motor coordination and recently it has been reported to be involved in cognitive function. Reactive oxygen species are implicated in neurodegeneration and cognitive disorders because of higher vulnerability of neuronal tissues. Therefore, the present study aimed at investigating the role of melatonin against high-LET (linear energy transfer) ⁵⁶Fe particle irradiation-induced oxidative damage and apoptosis in the mouse cerebellum. Radiation-induced oxidative damage was examined using a neuronal-specific terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), quantitative histopathology, DNA damage (comet assay), carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of the cerebellum. Radiation exposure augmented the number of TUNEL positive cell, DNA migration in the comet tail and carbonyl and 4-HAE + MDA level in the cerebellum. Melatonin pretreatment significantly inhibited the oxidative damage to biomolecules as well as cerebellar apoptosis. Melatonin-treated irradiated mice showed higher counts of intact Purkinje cells as compared to vehicle-treated irradiated mice. In addition, radiation induced augmentation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and a decline in the total antioxidant capacity in serum; these changes were also ameliorated by melatonin pretreatment. The present results provide evidence supporting the antioxidant and neuroprotective function of melatonin.     

Melatonin attenuates kainic acid-induced hippocampal neurodegeneration and oxidative stress through microglial inhibition

The antioxidant and anti-inflammatory effects of melatonin on kainic acid (KA)-induced neurodegeneration in the hippocampus were evaluated in vivo. It has been suggested that the pineal secretory product, melatonin, protects neurons in vitro from excitotoxicity mediated by kainate-sensitive glutamate receptors, and from oxidative stress-induced DNA damage and apoptosis. In this study, we injected 10 mg/kg kainate intraperitoneally (i.p.) into adult male Sprague-Dawley rats. This results in selective neuronal degeneration accompanied by intense microglial activation and triggers DNA damage in the hippocampus. We tested the in vivo efficacy of melatonin in preventing KA-induced neurodegeneration, oxidative stress and neuroinflammation in the hippocampus. Melatonin (2.5 mg/kg, i.p.) was given 20 min before, immediately after, and 1 and 2 hr after KA administration. Rats were killed 72 hr later and their hippocampi were examined for evidence of DNA damage (in situ dUTP end-labeling, i.e. TUNEL staining), cell viability (hematoxylin and eosin staining), and microglial (isolectin-B4 histochemistry) and astroglial responses (glial fibrillary acidic protein immunohistochemistry), as well as lipid peroxidation (4-hydroxynonenal immunohistochemistry). A cumulative dose of 10 mg/kg melatonin attenuates KA-induced neuronal death, lipid peroxidation, and microglial activation, and reduces the number of DNA breaks. A possible mechanism for melatonin-mediated neuroprotection involves its antioxidant and anti-inflammatory actions. The present data suggest that melatonin is potentially useful in the treatment of acute brain pathologies associated with oxidative stress-induced neuronal damage such as epilepsy, stroke, and traumatic brain injury.     

Melatonin improves cerebrovascular function and decreases oxidative stress in chronically hypoxic lambs

Chronic hypoxia during gestation and delivery results in oxidative stress and cerebrovascular dysfunction in the neonate. We assessed whether melatonin, a potent antioxidant and potential vasodilator, improves the cerebral vascular function in chronically hypoxic neonatal lambs gestated and born in the highlands (3600 m). Six lambs received melatonin (1 mg/kg per day oral) and six received vehicle, once a day for 8 days. During treatment, biometry and hemodynamic variables were recorded. After treatment, lambs were submitted to a graded FiO₂ protocol to assess cardiovascular responses to oxygenation changes. At 12 days old, middle cerebral arteries (MCA) were collected for vascular reactivity, morphostructural, and immunostaining evaluation. Melatonin increased fractional growth at the beginning and improved carotid blood flow at all arterial PO₂ levels by the end of the treatment (P < 0.05). Further, melatonin treatment improved vascular responses to potassium, serotonin, methacholine, and melatonin itself (P < 0.05). In addition, melatonin enhanced the endothelial response via nitric oxide‐independent mechanisms in isolated arteries (162 ± 26 versus 266 ± 34 AUC, P < 0.05). Finally, nitrotyrosine staining as an oxidative stress marker decreased in the MCA media layer of melatonin‐treated animals (0.01357 ± 0.00089 versus 0.00837 ± 0.00164 pixels/μm², P < 0.05). All the melatonin‐induced changes were associated with no systemic cardiovascular alterations in vivo. In conclusion, oral treatment with melatonin modulates cerebral vascular function, resulting in a better cerebral perfusion and reduced oxidative stress in the neonatal period in chronically hypoxic lambs. Melatonin is a potential therapeutic agent for treating cerebrovascular dysfunction associated with oxidative stress and developmental hypoxia in neonates.     

Melatonin improves cardiovascular function and ameliorates renal, cardiac and cerebral damage in rats with renovascular hypertension

Abstract:  The effect of melatonin was investigated in an angiotensin II-dependent renovascular hypertension model in Wistar albino rats by placing a renal artery clip (two-kidney, one-clip; 2K1C), while sham rats did not have clip placement. Starting either on the operation day or 3 wk after the operation, the rats received melatonin (10 mg/kg/day) or vehicle for the following 6 wk. At the end of the nineth week, after blood pressure (BP) and echocardiographic recordings were obtained, plasma samples were obtained to assay lactate dehydrogenase (LDH), creatine kinase (CK), antioxidant capacity (AOC), asymmetric dimethylarginine (ADMA), and nitric oxide (NOx) levels. In the kidney, heart and brain tissues, malondialdehyde (MDA) and glutathione (GSH) levels, superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO) and Na⁺-K⁺ ATPase activities were determined. 2K1C caused an increase in BP and left ventricular (LV) dysfunction. In hypertensive animals LDH, CK, ADMA levels were increased in plasma with a concomitant reduction in AOC and NOx. Moreover, hypertension caused a significant decrease in tissue SOD, CAT, and Na⁺, K⁺-ATPase activities and glutathione content, while MDA levels and MPO activity were increased in all studied tissues. On the other hand, both melatonin regimens significantly reduced BP, alleviated oxidative injury and improved LV function. In conclusion, melatonin protected against renovascular hypertension-induced tissue damage and improved cardiac function presumably due to both its direct antioxidant and receptor-dependent actions, suggesting that melatonin may be of therapeutic use in preventing oxidative stress due to hypertension.     

Melatonin protects against Nickel‐induced neurotoxicity in vitro by reducing oxidative stress and maintaining mitochondrial function

Abstract: Nickel is a potential neurotoxic pollutant. Oxidative stress is supposed to be involved in the mechanism underlying nickel‐induced neurotoxicity. Melatonin has efficient protective effects against various oxidative damages in nervous system. The purpose of this study was to investigate whether melatonin could efficiently protect against neurotoxicity induced by nickel. Here, we exposed primary cultured cortical neurons and mouse neuroblastoma cell lines (neuro2a) to different concentrations of nickel chloride (NiCl₂) (0.125, 0.25, 0.5, and 1 mm ) for 12 hr or 0.5 mm NiCl₂ for various periods (0, 3, 6, 12, and 24 hr). We found that nickel significantly increased reactive oxygen species production and caused the loss of cell viability both in cortical neurons and neuro2a cells. In addition, nickel exposure obviously inhibited the mitochondrial function, disrupted the mitochondrial membrane potential (ΔΨm), reduced ATP production, and decreased mitochondrial DNA (mtDNA) content. However, each of these oxidative damages was efficiently attenuated by melatonin pretreatment. These protective effects of melatonin may be attributable to its roles in reducing oxidative stress and improving mitochondrial function in nickel‐treated nerve cells. Our results suggested that melatonin may have great pharmacological potential in protecting against the adverse effects of nickel in the nervous system.     

Melatonin prevents peritoneal adhesions in rats

Background and Aim:  Intra-abdominal adhesions are important postoperative complications following abdominal surgery. The adhesions that develop form the basis of more advanced pathology such as intestinal obstruction or infertility. Melatonin is secreted from the pineal gland in a circadian pattern; this molecule has potent antioxidant characteristics and has beneficial effects in many models of inflammation. The aim of this study was to evaluate the effects of melatonin on peritoneal adhesions created in rats.
Methods:  A total of 28 Sprague–Dawley male rats were used and divided into four groups. In the first phase of the study, pinealectomy (PINX) was performed on half the animals. An incision was made and sutured in the cecum of all experimental animals in all groups 15 days after the PINX procedure. Some animals were given melatonin orally at a dose of 5 mg/kg daily following the adhesion operation and continued for 15 days. The rats were anesthetized and the abdomen opened after the 15th day (on day 30 of the study). After adhesion scoring based on macroscopic inspection, tissue samples were obtained from the sutured region of the cecum to measure malondialdehyde and hydroxyproline.
Results:  Peritoneal adhesion density was significantly higher in the PINX group compared to the control animals; exogenously administered melatonin significantly reduced adhesion formation. The degree of adhesion was also significantly lower in the intact rats given melatonin compared to the control group.
Conclusion:  Antioxidant activity increases in the oxidative process. We conclude that melatonin may be an important molecule in preventing peritoneal adhesions.     

Melatonin treatment improves blood pressure, lipid profile, and parameters of oxidative stress in patients with metabolic syndrome

Experimental studies have proven that melatonin has many beneficial pleiotropic actions. The aim of this study was to assess melatonin efficacy in patients with metabolic syndrome (MS). The study included 33 healthy volunteers (who were not treated with melatonin) and 30 patients with MS, who did not respond to 3-month lifestyle modification. Patients with MS were treated with melatonin (5 mg/day, 2 hr before bedtime) for 2 months. The following parameters were studied: systolic and diastolic blood pressure (SBP, DBP), levels of glucose, serum lipids, C-reactive protein, fibrinogen, activities of antioxidative enzymes: catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), thiobarbituric acid reactive substrates (TBARS). After 2-month therapy in comparison with baseline, the following significant changes were measured: systolic blood pressure (132.8±9.8 versus 120.5±11.0 mmHg, P<0.001), DBP (81.7±8.8 versus 75±7.4 mmHg, P<0.01), low-density lipoprotein cholesterol (LDL-C) (149.7±26.4 versus 139.9±30.2 mg/dL, P<0.05), TBARS (0.5±0.2 versus 0.4±0.1 μm/gHb, P<0.01), and CAT (245.9±46.9 versus 276.8±39.4 U/gHb). Melatonin administered for 2 months significantly improved antioxidative defense (increase in CAT activity, decrease in TBARS level) and lipid profile (decrease in LDL-C), and lowered blood pressure. We conclude that melatonin therapy may be of benefit for patients with MS, particularly with arterial hypertension. Further studies with higher doses of melatonin or prolonged supplementation are awaited.     

Melatonin reduces oxidative stress and improves vascular function in pulmonary hypertensive newborn sheep

Pulmonary hypertension of the newborn (PHN) constitutes a critical condition with severe cardiovascular and neurological consequences. One of its main causes is hypoxia during gestation, and thus, it is a public health concern in populations living above 2500 m. Although some mechanisms are recognized, the pathophysiological facts that lead to PHN are not fully understood, which explains the lack of an effective treatment. Oxidative stress is one of the proposed mechanisms inducing pulmonary vascular dysfunction and PHN. Therefore, we assessed whether melatonin, a potent antioxidant, improves pulmonary vascular function. Twelve newborn sheep were gestated, born, and raised at 3600 meters. At 3 days old, lambs were catheterized and daily cardiovascular measurements were recorded. Lambs were divided into two groups, one received daily vehicle as control and another received daily melatonin (1 mg/kg/d), for 8 days. At 11 days old, lung tissue and small pulmonary arteries (SPA) were collected. Melatonin decreased pulmonary pressure and resistance for the first 3 days of treatment. Further, melatonin significantly improved the vasodilator function of SPA, enhancing the endothelial‐ and muscular‐dependent pathways. This was associated with an enhanced nitric oxide‐dependent and nitric oxide independent vasodilator components and with increased nitric oxide bioavailability in lung tissue. Further, melatonin reduced the pulmonary oxidative stress markers and increased enzymatic and nonenzymatic antioxidant capacity. Finally, these effects were associated with an increase of lumen diameter and a mild decrease in the wall of the pulmonary arteries. These outcomes support the use of melatonin as an adjuvant in the treatment for PHN.