Pharmacological Concentrations Of Melatonin Research Articles

Механизмы взаимодействия мелатонина c лимфоцитами

Melatonin is an indoleamine synthesized from the essential amino acid tryptophan. At the system level, it is produced mainly by the pineal gland, and at the local level, by most organs and tissues, including the gastrointestinal tract, liver, kidneys, lungs, skin, tissues of the reproductive system, and many others. The hormone regulates a wide range of biological reactions in health and diseases, and has a pronounced antioxidant, anti-inflammatory and antitumor activity. Along with this, melatonin is an effective regulator of the immune system, however, the data available to date on the problem are extremely contradictory, especially for the main effectors of adaptive immunity - T-lymphocytes. On the one hand, under physiological conditions or under immunodeficiency conditions, the effects of melatonin are usually stimulatory: it enhances the proliferative response of T- and B-lymphocytes, increases the production of Th1-cytokines, and inhibits apoptosis of lymphocytes induced by various stimuli. On the other hand, there are no fewer works demonstrating the immunosuppressive activity of melatonin, in particular, suppression of the production of pro-inflammatory cytokines. The resolution of these contradictions is the goal of this review. At the same time, the work focuses on two fundamental points. First, the main part of immunostimulating effects was obtained in experiments in vitro, while immunosuppressive effects were obtained in vivo, and since melatonin controls the synthesis of a number of other hormones of the hypothalamic-pituitary-adrenal and / or gonadal axes, many of which are effective immunomodulators themselves, it direct effects in vivo can be mediated and offset by other hormones. Second, lymphocytes express three high-affinity melatonin receptors: two membrane receptors, MT1 and MT2, and a nuclear one, RORα, as well as a number of low-specific targets, all with varying affinities for melatonin. Binding of different receptors apparently triggers different signaling mechanisms. Accordingly, physiological, pathological and pharmacological concentrations of melatonin can have different immunomodulating effects, and when evaluating the effect of melatonin on the immune system, it is important to correlate the hormone concentrations with the state of the receptor apparatus of the cells under study.

Melatonin MT2 receptor is expressed and potentiates contraction in human airway smooth muscle.

Nocturnal asthma is characterized by heightened bronchial reactivity at night, and plasma melatonin concentrations are higher in patients with nocturnal asthma symptoms. Numerous physiological effects of melatonin are mediated via its specific G protein-coupled receptors (GPCRs) named the MT1 receptor, which couples to both Gq and Gi proteins, and the MT2 receptor, which couples to Gi. We investigated whether melatonin receptors are expressed on airway smooth muscle; whether they regulate intracellular cyclic AMP (cAMP) and calcium concentrations ([Ca2+]i), which modulate airway smooth muscle tone; and whether they promote airway smooth muscle cell proliferation. We detected the mRNA and protein expression of the melatonin MT2 but not the MT1 receptor in native human and guinea pig airway smooth muscle and cultured human airway smooth muscle (HASM) cells by RT-PCR, immunoblotting, and immunohistochemistry. Activation of melatonin MT2 receptors with either pharmacological concentrations of melatonin (10-100 µM) or the nonselective MT1/MT2 agonist ramelteon (10 µM) significantly inhibited forskolin-stimulated cAMP accumulation in HASM cells, which was reversed by the Gαi protein inhibitor pertussis toxin or knockdown of the MT2 receptor by its specific siRNA. Although melatonin by itself did not induce an initial [Ca2+]i increase and airway contraction, melatonin significantly potentiated acetylcholine-stimulated [Ca2+]i increases, stress fiber formation through the MT2 receptor in HASM cells, and attenuated the relaxant effect of isoproterenol in guinea pig trachea. These findings suggest that the melatonin MT2 receptor is expressed in ASM, and modulates airway smooth muscle tone via reduced cAMP production and increased [Ca2+]i.

Physiological and pharmacological effects of melatonin on remote ischemic perconditioning after myocardial ischemia-reperfusion injury in rats: Role of Cybb, Fas, NfκB, Irisin signaling pathway.

It has been found that remote organ/limb temporary ischemia, known as remote ischemic conditioning, can provide protection against the formation of lethal ischemic outcome. Current evidence suggests that aging and age-releated comorbidities impair the cardioprotective effects of conditionings. In conjuction with aging, decrease in melatonin synthesis from pineal gland can have role in the pathogenesis of aging and age-related cardiovascular diseases. In this study, we investigated the effects of remote ischemic perconditioning (RIPerC) and physiological and pharmacological concentrations of melatonin on the infarct size, Fas gene, cytochrome b-245 beta chain (Cybb) gene, nuclear factor-kappa B (NfκB), and irisin using an in vivo model of myocardial ischemia/reperfusion (I/R) injury. Sprague-Dawley rats that were divided into two groups first as non-pinealectomized (Non-Px) and pinealectomized (Px), and then (a) Control; (b) I/R (30-minute ischemia, 120-minute reperfusion caused by left coronary artery ligation); (c) I/R+RIPerC (when myocardial ischemia initiated, three cycles of 5-minute occlusion followed by 5-minute reperfusion); (d) I/R+Mel; (e) Px; (f) Px+I/R; (g) Px+I/R+RIPerC; (h) Px+I/R+RIPerC+Mel groups. The infarct size was determined by TTC staining and analyzed by the ImageJ program. Molecular parameters were evaluated by qRT-PCR and Western blot. Results showed that increased infarct size in Non-Px groups decreased with RIPerC and melatonin. However, increased infarct size in Px groups was decreased minimally with RIPerC and significantly decreased with RIPerC+Melatonin. Fold change in Fas gene was associated with the infarct size. RIPerC and melatonin reduced expressions of Cybb, NfκB, and irisin genes. The physiological release and pharmacological concentration of melatonin may improve protective effect of RIPerC against I/R-induced infarct size by modulating Cybb, Fas, NfκB, Irisin signaling pathways.

Ischemic postconditioning reduced myocardial ischemia-reperfusion injury: The roles of melatonin and uncoupling protein 3.

Objective:Protective effects of ischemic postconditioning (PostC) decrease/disappear with age and chronic heart diseases. Similarly, low serum melatonin levels have been reported in the same risk groups. The aims of this study were to investigate the effects of melatonin on the protection of PostC in ischemia–reperfusion (I/R)-induced infarct size and roles of uncoupling protein (UCP) 3, irisin, and nuclear factor kappa B (NFkB) levels.Methods:Rats were pinealectomized (Px) or sham operated (non-Px) 2 months before the I/R studies. The left main coronary artery was occluded for 30 min followed by 120 min reperfusion. PostC was induced with three cycles of R/I (10 s each) after ischemia.Results:The infarct size was found to be significantly higher in Px rats (54.68±1.5%) than in the control group (35.1±2.5%). PostC and melatonin administrations to non-Px rats significantly reduced the infarct size. On the other hand, PostC did not create a significant effect in Px rats, but protection was provided when PostC was co-administrated with melatonin. While significant decreases were detected in the UCP3 levels, irisin and NFkB levels increased with I/R and Px. Treatment with PostC and melatonin in non-Px groups and their co-administration in Px groups were found to return all the genes close to normal levels.Conclusion:The physiological and pharmacological concentrations of melatonin may play a role in the protection of PostC. In cases when physiological melatonin is reduced, such as aging and heart diseases, this protection may decrease, and this effect may be restored by melatonin replacement. PostC and melatonin may regulate energy metabolism and inflammatory mediators and protect mitochondria by affecting the UCP3, irisin, and NFkB levels.

ERK MAPK activation mediates the antiapoptotic signaling of melatonin in UVB-stressed U937 cells

The pineal gland hormone melatonin has been recently described to downregulate the intrinsic (or damage-induced) pathway of apoptosis in human leukocytes. These properties appear to depend on a specific mitochondrial signaling of melatonin which is associated with a lower generation of reactive oxygen species and a better control of redox-sensitive components such as the antiapoptotic protein Bcl-2. Other elements upstream in this signaling are expected to contribute regulatory roles that remain unexplored. The aim of this study was to investigate whether the extracellular signal-regulated kinase (ERK), which controls the balance between survival and death-promoting genes throughout the MAPK pathway, is involved in the antiapoptotic signaling of melatonin. Human monocytic U937 cells irradiated with UVB light were used as a model of stress-induced apoptosis. In this model we found that pharmacological concentrations of melatonin (1 mM) were able to decrease superoxide anion production, mitochondrial damage, and caspase-dependent apoptosis by improved Bcl-2 levels and decreased Cyt c release in the cytoplasm. Moreover, melatonin increased the phosphorylative activation of ERK 1/2 independently from the presence of UVB stress, and decreased the UVB-mediated activation of the stress kinases p38 MAPK and JNK. The ERK 1/2 inhibitor PD98059, but not the p38 MAPK inhibitor SB203580, abolished to different extents the effects that melatonin had on the UVB-induced ROS generation, mitochondrial dysfunction, and apoptosis. Using these inhibitors, a cross-talk effect between stress and survival-promoting kinases was tentatively identified, and confirmed the hierarchical role of ERK MAPK phosphorylation in the signaling of melatonin. In conclusion, melatonin sustains the activation of the survival-promoting pathway ERK MAPK which is required to antagonize UVB-induced apoptosis of U937 cells. This kinase mediates also the antioxidant and mitochondrial protection effects of this hormonal substance that may find therapeutic applications in inflammatory and immune diseases associated with leukocyte oxidative stress and accelerated apoptosis.

Melatonin, lipid peroxidation, and age in heterophils from the ring dove (Streptopelia risoria)

Numerous recent studies have shown the ability of physiological as well as all pharmacological concentrations of melatonin to prevent oxidative stress. We have found that incubating avian heterophils from young birds with a pharmacological concentration of 100 μM (23 × 106 pg/ml) melatonin reduced superoxide anion levels by modulating the activity of superoxide dismutase while also enhancing phagocytosis. There was also a decline in lipid peroxidation levels with both physiological and pharmacological concentrations of this indolamine.In the present work, we evaluated malonaldehyde (MDA) levels as an indicator of lipid peroxidation (both basal and antigen-induced) in young and old animals (ring doves) at different times of day (16:00 and 00:00) and with two incubation times (15 and 60 min). The lipid peroxidation was also measured in heterophils from old animals, incubated with the physiological concentrations of melatonin measured in young animals (50 and 300 pg/ml, diurnal and nocturnal, respectively). The results, expressed as nmol MDA/mg protein, show that MDA levels were higher in heterophils of old animals than in the young birds in all the experimental groups studied at both 16:00 and 00:00 (00:00 is the time at which the lowest peroxidation levels were obtained). Incubation with melatonin was found to reduce MDA levels, with the maximum reduction being after the 60 min incubation time and the nocturnal melatonin concentration. At both concentrations (diurnal and nocturnal), melatonin also counteracted the enhancement of MDA levels caused by latex beads, with the effect being greater at the longer incubation time. In conclusion, the results are further evidence of the antioxidant effect of melatonin even at physiological concentrations, and suggest its utility as a therapeutic agent in some pathological processes associated with age.

Melatonin protects against myocardial doxorubicin toxicity in rats: role of physiological concentrations.

Doxorubicin (Dox) is a widely used antineoplastic drug. Oxygen radical-induced injury of membrane lipids is considered to be the most important factor responsible for the development of Dox-induced cardiotoxicity. The pineal secretory product, melatonin, is known to be a potent free radical scavenger and its pharmacological concentrations have been shown to reduce Dox-induced cardiac damage. However, the physiological role of melatonin in the prevention of this damage is unknown. We investigated physiological and pharmacological effects of melatonin on Dox-induced changes in the levels of malondialdehyde (MDA), a lipid peroxidation product, and morphological changes in heart. Rats were pinealectomized (Px) or sham-operated (control) 2 months before the studies. Melatonin was administered [4 mg/kg, intraperitoneally (i.p.)] 1 hr before or 24 hr after the administration of a single dose of Dox (20 mg/kg, i.p.) and continued for 2 days. The levels of MDA Dox was found to be significantly higher in the Px rats (55.9 +/- 0.6 nmol/g tissue) than intact control animals (42.6 +/- 0.4). Dox administration to Px and non-Px rats significantly increased the MDA levels. Pre- and post-treatment with melatonin in both Px and intact rats significantly reduced MDA levels. Morphological changes parallelled the MDA alterations. These findings strongly suggest that both physiological and pharmacological concentrations of melatonin are important in protecting the heart from Dox-induced damage in rats. It would seem valuable to test melatonin in clinical trials for prevention of possible heart damage associated with Dox.

The protective effects of physiological and pharmacological concentrations of melatonin on renal ischemia-reperfusion injury in rats.

Reactive oxygen species have been implicated in the pathophysiology of renal ischemia reperfusion (I/R) injury. The pineal secretory product melatonin is known to be a potent free radical scavenger and antioxidant. This study was designed to investigate the effects of physiological and pharmacological concentrations of melatonin on I/R injury. Rats were pinealectomized (Px) or sham-operated (control) 2 months before the I/R studies. There were eight groups of eight rats each. After a right nephrectomy to produce damage, left renal vessels were occluded for 60 min, followed by 24 h reperfusion, in rats. Malondialdehyde (MDA) levels resulting from I/R were significantly higher in the pinealectomized rats than in the control group. Melatonin administration (4 mg kg(-1) i.p. either before ischemia or reperfusion) to Px and sham-operated rats significantly reduced the MDA values and returned them to the control values. Morphological changes in the groups were similar to the MDA levels. Serum levels of blood urea nitrogen and creatine were unchanged. These results suggest that physiological and pharmacological melatonin concentrations are important for the reduction of I/R-induced damage. We also demonstrated that melatonin, even when administrated just before reperfusion, had a protective effect on I/R injury. It would seem valuable to test melatonin in clinical trials for the prevention of possible I/R injury.

The effect of melatonin and corticosterone on the phagocytic function of BALB/c mice macrophages

The hormones melatonin and corticosterone are able to modulate the immune response, with indications that melatonin may counteract the immunosuppressory action of the glucocorticoids. The aim of the present study is to evaluate the effects of pharmacological concentrations of melatonin and corticosterone, singly and together, on macrophage phagocytosis of antigen particles. To this end we performed an in vitro study using as phagocytes peritoneal macrophages from two groups of BALB/c mice, one in a basal situation and the other subjected to stress by swimming. The concentrations used were ten and one hundred times greater than the previously determined physiological levels. In particular, for incubations with macrophages from the basal group they were 0.9 pg/ml and 9 pg/ml of melatonin, and 2 μ g/ml and 20 μ g/ml of corticosterone, and for macrophages from the stressed group they were 0.7 pg/ml and 7 pg/ml of melatonin, and 5 μ g/ml or 50 μ g/ml of corticosterone. The results indicate that the immunomodulatory effect of the two hormones depends on the conditions of the study. Thus, melatonin led to increased phagocytic capacity in macrophages from both the basal and the stressed animals, while corticosterone only had an immunostimulatory effect with macrophages from the unstressed animals. With both hormones acting together, the macrophage phagocytic activity was stimulated at all the concentrations used and independently of whether or not the corresponding animals had been stressed, although the greatest activation was seen in the basal animal phagocytes incubated with the higher corticosterone concentration. In conclusion, while melatonin was definitely immunostimulatory at the concentrations tested, the immunoregulatory properties of corticosterone depended on the situation.

Myocardial ischemia-reperfusion in rats: reduction of infarct size by either supplemental physiological or pharmacological doses of melatonin.

Myocardial ischemia-reperfusion (I/R) represents a clinically relevant problem associated with thrombolysis, angioplasty and coronary bypass surgery. I/R injury is believed to be a consequence of free radical generation in the heart especially during the period of reperfusion. The pineal secretory product, melatonin, is known to be a potent free radical scavenger and pharmacological concentrations have been shown to reduce the I/R-induced cardiac damage in isolated rat hearts. However, the physiological role of melatonin in the prevention of this damage is unknown. Rats were pinealectomized or sham-operated (control) 2 months before the I/R studies. To produce cardiac damage, the left main coronary artery was occluded for 30 min, followed by 120 min reperfusion, in anesthetized rats. Infarct size, expressed as the percentage of the risk zone, was found significantly higher in pinealectomized rats (49+/-3.4%) than in the control group (34+/-3.6%). Melatonin administration (4 mg/kg, either before ischemia or reperfusion) to pinealectomized rats significantly reduced the infarct size values and returned them to the control values. On the other hand, melatonin administration (4 mg/kg) to sham-operated rats failed to attenuate significantly the I/R-induced infarct size. These results suggest that physiological melatonin concentrations are important in reducing the I/R-induced myocyte damage, while pharmacological concentrations of melatonin did not add to the beneficial effect. As melatonin levels have been reported to decrease with age, melatonin replacement therapy may attenuate I/R-induced myocardial injury, especially in older patients.

Effects of physiological and pharmacological concentrations of melatonin on ischemia–reperfusion arrhythmias in rats: can the incidence of sudden cardiac death be reduced?

Cardiac arrhythmias during ischemia-reperfusion (I/R) are believed to be related to free radicals generated in the heart especially during the period of reperfusion. The pineal secretory product, melatonin, is known to be a potent free radical scavenger and its pharmacological concentrations have been shown to reduce the I/R-induced arrhythmias in isolated rat hearts. However, the physiological role of melatonin in the prevention of these arrhythmias is unknown. Rats were pinealectomized (Px) or sham-operated (non-Px) (control) 2 months before the I/R studies. To produce arrhythmias, left main coronary artery was occluded for 7 min, followed by 7 min reperfusion, in anesthetized rats. The incidence of mortality resulted from irreversible ventricular fibrillation (VF) was found significantly higher in the Px rats (63%) than in the control group (25%). Melatonin administration (0.4 mg/kg, either before ischemia or reperfusion) to Px rats significantly reduced the incidence of total (irreversible plus reversible) and irreversible VF and returned them to control values. On the other hand, melatonin administration (0.4 and 4 mg/kg) to non-Px rats failed to attenuate the I/R arrhythmias, significantly. These results suggest that physiological melatonin concentrations are important to reduce the I/R-induced VF and mortality, while pharmacological concentrations of melatonin did not increase its beneficial effect on these arrhythmias. As melatonin levels have been reported to decrease with age, melatonin replacement therapy may attenuate the incidence of sudden cardiac death especially in older patients.

Circadian rhythm of melatonin, corticosterone and phagocytosis: effect of stress

Melatonin has a functional connection with the immune system. Phagocyte function is altered by extirpation of the pineal gland, one source of melatonin, or by in vitro incubation of phagocytes with pharmacological concentrations of melatonin. Given that its synthesis by pinealocytes is under the control of the noradrenaline released by the sympathetic postganglionaric nerve endings, the present work was aimed at evaluating the circadian rhythm of melatonin, corticosterone, and phagocytosis in BALB/c mice in basal and stress situations. Peritoneal macrophages were used as phagocytes, latex beads as the particles to be ingested, and forced swimming to exhaustion as the stress situation. Radioimmunoassay was used to determine the animals' serum hormone levels. Samples were taken every 3 hr in the period from 04:00 to 22:00 hr, and every 30 min during the remaining period from 22:00 to 04:00 hr. Control mice presented a short-term melatonin peak at 23:30 hr, while the maximum inert-particle ingestion capacity of the peritoneal macrophages also occurred during the night but at 03:30 hr. The corticosterone levels in control mice presented a circadian rhythm with a day-time maximum peak (16:00 hr). Compared with the controls, the animals subjected to stress maintained, although at lower values, the melatonin peak at 23:30 hr, but they presented a loss of the rhythm of serum corticosterone levels, and the corticosterone levels and the macrophage phagocytic capacity were greater at all hours of the day.

Potential involvement of mt1 receptor and attenuated sex steroid-induced calcium influx in the direct anti-proliferative action of melatonin on androgen-responsive LNCaP human prostate cancer cells.

Melatonin, a pineal secretory product, has been shown to exert a direct anti-proliferative action on the androgen-sensitive LNCaP prostate cancer cell line through hitherto undefined mechanisms. In this communication, expression of mt1 melatonin receptor protein in human prostate cancer tissues and LNCaP cells was demonstrated by immunohisto(cyto)chemistry and western blotting, hence supporting the use of LNCaP cell line as a model for the study of melatonin signaling in prostate cancer cell growth. Using 3H-thymidine incorporation assay, LNCaP cell proliferation was inhibited by 2-iodomelatonin, a high-affinity melatonin receptor agonist. Furthermore, melatonin inhibited 3H-thymidine incorporation into LNCaP cells and attenuated 5alpha-dihydrotestosterone (DHT) or 17beta-estradiol (E2)-induced stimulation of LNCaP cell proliferation at physiological and pharmacological concentrations. Similar concentration-dependent inhibition of sex steroid-induced stimulation of thymidine incorporation into LNCaP cells by 2-iodomelatonin was also observed. Interestingly, attenuation of sex steroid-stimulated calcium influx into LNCaP cells by pharmacological concentrations of melatonin was recorded, whereas 2-iodomelatonin had no effect on cytosolic calcium changes induced by sex steroids. In addition, proliferative and cytosolic calcium changes were associated with inhibition of total prostate-specific antigen (PSA) production by LNCaP cells at high physiological and pharmacological concentrations of melatonin. Our data suggest that activated mt1 receptor and attenuated sex steroid-induced calcium influx are two important mechanisms mediating the direct anti-proliferative action of melatonin on androgen-responsive human prostate cancer cells.

Inhibition of malignant trophoblastic cell proliferation in vitro and in vivo by melatonin

Melatonin inhibited thymidine incorporation into human choriocarcinoma JEG-3 cells at physiological and pharmacological concentrations in the present study. Gene expression of MT 2 receptor, but not that of mt 1 receptor, was detected in JEG-3 cells by reverse transcription-polymerase chain reaction (RT-PCR). The gene expression profile of the two human melatonin receptor subtypes in JEG-3 cells was identical to that previously reported for JAr cells, whose proliferation had also been shown to be similarly inhibited by physiological and pharmacological concentrations of melatonin. In contrast, melatonin had no effect on thymidine incorporation into 3A-Sub-E cells (a transformed trophoblast cell line), in which gene expression of both receptor subtypes could not be detected. The data suggest that in human placental trophoblasts, a correlation may exist between MT 2 receptor gene expression and the direct anti-proliferative action of melatonin. Although melatonin has been reported to induce G1/S delay in cell cycle progression of JAr cells, no significant changes in the percentages of JEG-3 cells in different cell cycle phases upon melatonin treatment was recorded by flow cytometric analysis. This indicates that G1/S transition delay is probably not an important cellular mechanism in the direct anti-proliferative action of melatonin on human JEG-3 cells in vitro. Furthermore, melatonin inhibited the growth of both JAr and JEG-3 xenograft tumors in athymic nude mice, and prolonged the survival of those animals that developed choriocarcinoma. While the number of apoptotic tumor cells was not increased by melatonin, the pineal hormone induced significant decreases in the numbers of JAr and JEG-3 cells expressing proliferating cell nuclear antigen (PCNA) and cyclin A in the tumors. Taking into account both the in vitro and in vivo findings, it is likely that the inhibitory effect of melatonin on choriocarcinoma JAr and JEG-3 cell proliferation in vivo is largely a direct action of the hormone on the tumor cells.

Melatonin-induced inhibition of proliferation and G1/S cell cycle transition delay of human choriocarcinoma JAr cells: possible involvement of MT2 (MEL1B) receptor.

Melatonin, the pineal neurohormone, is an evolutionarily conserved photoperiodic signaling molecule with diverse functions that include the entrainment of human circadian rhythms. Although evidence supporting a direct inhibitory action of melatonin on human cancer cell proliferation exists in the literature, the molecular and cellular signaling mechanisms involved are largely undefined. In our study, significant inhibition of human choriocarcinoma JAr cell proliferation at physiological and pharmacological concentrations of melatonin was observed. 2-Iodomelatonin, a high affinity melatonin receptor agonist, was more potent than melatonin in inhibiting JAr cell proliferation. In addition, the presence of putative melatonin receptors in choriocarcinoma was suggested by the demonstration of specific 2-[125I]iodomelatonin binding to the tumor. Interestingly, the selective MT2 melatonin receptor ligand, 4-phenyl-2-propionamidotetraline (4-P-PDOT), was found to exert not only concentration-dependent anti-proliferative actions on JAr cells, but also additive effects with melatonin in inhibiting JAr cell proliferation. Furthermore, MT2 melatonin receptor gene expression by JAr cells was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization (ISH). Taken together, our data suggest that the reported anti-proliferative action of melatonin on human choriocarcinoma JAr cells may be mediated, in part, by MT2 melatonin receptor. Moreover, analysis of melatonin effect on cell cycle kinetics indicated that G1/S transition delay may underlie the observed inhibition of choriocarcinoma cell proliferation by melatonin.

T-helper-2 lymphocytes as a peripheral target of melatonin.

In the past several years we demonstrated that the pineal neurohormone melatonin has immunoenhancing properties and can counteract the immunodepression that may follow acute stress, drug treatment, and viral diseases or aging. Several laboratories have subsequently confirmed and extended our findings. It soon appeared evident that T-derived cytokines constitute the main mediators of the immunological effect of melatonin. We have recently found a high affinity (Kd: 346 +/- 24 pM) binding site for 125I-melatonin on T-helper-type 2 lymphocytes in the bone marrow. Activation of this putative melatonin receptor, with both physiological and pharmacological concentrations of melatonin, resulted in an enhanced production of interleukin-4 (IL4), which in turn acted on bone marrow stromal cells and induced the release of hematopoietic growth factors. This melatonin-cytokine cascade showed the remarkable capacity of rescuing hematopoietic functions in mice treated with cancer chemotherapeutic compounds without interfering with the anticancer action of these agents. The very low concentration (0.1 nM) at which melatonin is active may well reflect a physiological function of endogenous melatonin. The pineal gland has been, in fact, reported to signal the blood forming system. The evidence of IL4 involvement is relevant to our understanding of many melatonin effects and may be part of a pineal-immune axis involving also Th1 cytokines. The ability of rescuing hematopoiesis against the toxic action of cancer chemotherapeutic compounds and the presence of high-affinity IL4 receptors on human tumors provide a further promising rationale for the clinical use of melatonin.