Biphasic protective effect of oxytocin on cardiac ischemia/reperfusion injury in anaesthetized rats

Oxytocin: A Shield against Radiation-Induced Lung Injury in Rats

BACKGROUND

Radiation-induced lung injury (RILI), a serious side effect of thoracic radiotherapy, can lead to acute radiation pneumonitis (RP) and chronic pulmonary fibrosis (PF). Despite various interventions, no effective protocol exists to prevent pneumonitis. Oxytocin (OT), known for its anti-inflammatory, antiapoptotic, and antioxidant properties, has not been explored for its potential in mitigating RILI.

MATERIALS AND METHODS

This study involved 24 female Wistar albino rats, divided into three groups: control group, radiation (RAD) + saline, and RAD + OT. The RAD groups received 18 Gy of whole-thorax irradiation. The RAD + OT group was treated with OT (0.1 mg/kg/day) intraperitoneally for 16 weeks. Computerizing tomography (CT) imaging and histopathological, biochemical, and blood gas analyses were performed to assess lung tissue damage and inflammation.

RESULTS

Histopathological examination showed significant reduction in alveolar wall thickening, inflammation, and vascular changes in the RAD + OT group compared to the RAD + saline group. Biochemical analysis revealed decreased levels of TGF-beta, VEGF, and PDGF, and increased BMP-7 and prostacyclin in the RAD + oxytocin group (p < 0.05). Morphometric analysis indicated significant reductions in fibrosis, edema, and immune cell infiltration. CT imaging demonstrated near-normal lung parenchyma density in the RAD + oxytocin group (p < 0.001).

CONCLUSION

Oxytocin administration significantly mitigates radiation-induced pneumonitis in rats, implying that is has potential as a therapeutic agent for preventing and treating RILI.

Oxytocin: A Multi-Functional Biomolecule with Potential Actions in Dysfunctional Conditions; From Animal Studies and Beyond

Oxytocin is a hormone secreted from definite neuroendocrine neurons located in specific nuclei in the hypothalamus (mainly from paraventricular and supraoptic nuclei), and its main known function is the contraction of uterine and/or mammary gland cells responsible for parturition and breastfeeding. Among the actions of the peripherally secreted oxytocin is the prevention of different degenerative disorders. These actions have been proven in cell culture and in animal models or have been tested in humans based on hypotheses from previous studies. This review presents the knowledge gained from the previous studies, displays the results from oxytocin intervention and/or treatment and proposes that the well described actions of oxytocin might be connected to other numerous, diverse actions of the biomolecule.

Oxytocin: An Old Hormone, A Novel Psychotropic Drug And Possible Use In Treating Psychiatric Disorders

BACKGROUND

Oxytocin is a nonapeptide synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Historically, this molecule has been involved as a key factor in the formation of infant attachment, maternal behavior and pair bonding and, more generally, in linking social signals with cognition, behaviors and reward. In the last decades, the whole oxytocin system has gained a growing interest as it was proposed to be implicated in etiopathogenesis of several neurodevelopmental and neuropsychiatric disorders.

METHODS

With the main goal of an in-depth understanding of the oxytocin role in the regulation of different functions and complex behaviors as well as its intriguing implications in different neuropsychiatric disorders, we performed a critical review of the current state of art. We carried out this work through PubMed database up to June 2021 with the search terms: 1) "oxytocin and neuropsychiatric disorders"; 2) "oxytocin and neurodevelopmental disorders"; 3) "oxytocin and anorexia"; 4) "oxytocin and eating disorders"; 5) "oxytocin and obsessive-compulsive disorder"; 6) "oxytocin and schizophrenia"; 7) "oxytocin and depression"; 8) "oxytocin and bipolar disorder"; 9) "oxytocin and psychosis"; 10) "oxytocin and anxiety"; 11) "oxytocin and personality disorder"; 12) "oxytocin and PTSD".

RESULTS

Biological, genetic, and epigenetic studies highlighted quality and quantity modifications in the expression of oxytocin peptide or in oxytocin receptor isoforms. These alterations would seem to be correlated with a higher risk of presenting several neuropsychiatric disorders belonging to different psychopathological spectra. Collaterally, the exogenous oxytocin administration has shown to ameliorate many neuropsychiatric clinical conditions.

CONCLUSION

Finally, we briefly analyzed the potential pharmacological use of oxytocin in patient with severe symptomatic SARS-CoV-2 infection due to its anti-inflammatory, anti-oxidative and immunoregulatory properties.

The Importance of Experimental Investigation of the Peripheral Oxytocin System

Oxytocin and oxytocin receptors are synthesized in the periphery where paracrine/autocrine actions have been described alongside endocrine actions effected by central release of oxytocin from the posterior pituitary. In the female reproductive system, classical actions of uterine contraction and milk ejection from mammary glands are accompanied by actions in the ovaries where roles in steroidogenesis, follicle recruitment and ovulation have been described. Steroidogenesis, contractile activity, and gamete health are similarly affected by oxytocin in the male reproductive tract. In the cardiovascular system, a local oxytocinergic system appears to play an important cardio-protective role. This role is likely associated with emerging evidence that peripheral oxytocin is an important hormone in the endocrinology of glucose homeostasis due to its actions in adipose, the pancreas, and the largely ignored oxytocinergic systems of the adrenal glands and liver. Gene polymorphisms are shown to be associated with a number of reported traits, not least factors associated with metabolic syndrome.

Can intravenous oxytocin infusion counteract hyperinflammation in COVID-19 infected patients?

OBJECTIVES

Based on its well-documented anti-inflammatory and restorative properties we propose trials with the natural hormone oxytocin for treatment of hospitalised Covid-19 patients.

METHODS

We searched for, retrieved, and commented on specific literature regarding multiple functions of oxytocin with a special focus on its modulation of inflammatory, immune, and restorative functions.

RESULTS

Available data gathered in animals and humans support the anti-inflammatory properties of oxytocin. The multiple anti-inflammatory effects of oxytocin have been demonstrated in vitro and in vivo in various animal models and also in humans in response to intravenous infusion of oxytocin. Furthermore, oxytocin has been documented to activate several types of protective and restorative mechanisms and to exert positive effects on the immune system.

CONCLUSIONS

In addition, to being anti-inflammatory, it may be hypothesised, that oxytocin may be less suppressive on adaptive immune systems, as compared with glucocorticoids. Finally, by its restorative effects coupled with its anti-stress and healing properties, oxytocin may shorten the recovery period of the Covid-19 patients.

Oxytocin promotes hepatic regeneration in elderly mice

Liver aging impairs the ability of hepatocyte regeneration. Recent studies have found that oxytocin (OT) plays an important role in promoting tissue repair and maintaining differentiation and regeneration of stem cells. Here, we reported that OT receptors, which are specifically located in hepatocytes, decrease with aging in human and mice. Interestingly, the level of serum OT also decline with age. Notably, OT promotes hepatocyte regeneration only in aged mice but not in young mice in vitro and in vivo. Further studies reveal that OT promotes autophagy in either AML12 mouse hepatocytes or aged mice after partial hepatectomy or with CCl4-induced acute liver injury. In conclusion, OT promotes liver regeneration, especially in aged mice, which may be achieved by promoting autophagy. All these results support the possibility of OT and its analog being a potent anti-aging drug and promote liver rejuvenation.

Engineering a Potent, Long-Acting, and Periphery-Restricted Oxytocin Receptor Agonist with Anorexigenic and Body Weight Reducing Effects

The effects of oxytocin on food intake and body weight reduction have been demonstrated in both animal models and human clinical studies. Despite being efficacious, oxytocin is enzymatically unstable and thus considered to be unsuitable for long-term use in patients with obesity. Herein, a series of oxytocin derivatives were engineered through conjugation with fatty acid moieties that are known to exhibit high binding affinities to serum albumin. One analog (OT-12) in particular was shown to be a potent full agonist at the oxytocin receptor (OTR) in vitro with good selectivity and long half-life (24 h) in mice. Furthermore, OT-12 is peripherally restricted, with very limited brain exposure (1/190 of the plasma level). In a diet-induced obesity mouse model, daily subcutaneous administration of OT-12 exhibited more potent anorexigenic and body weight reducing effects than carbetocin. Thus, our results suggest that the long-acting, peripherally restricted OTR agonist may offer potential therapeutic benefits for obesity.

Oxytocin maintains lung histological and functional integrity to confer protection in heat stroke

Oxytocin (OT) has been reported to have a protective effect in lipopolysaccharide-induced experimental acute lung injury (ALI). However, its role in heat stroke-related ALI has never been investigated. Herein, we aimed to explore the therapeutic effects and potential mechanism of action of OT on heat-induced ALI. Rats were treated with OT 60 min before the start of heat stress (42 °C for 80 min). Twenty minutes after the termination of heat stress, the effects of OT on lung histopathological changes, edema, acute pleurisy and the bronchoalveolar fluid levels of inflammatory cytokines and indicators of ischemia, cellular damage, and oxidative damage were assessed. We also evaluated the influence of OT pretreatment on heat-induced hypotension, hyperthermia, ALI score, and death in a rat model of heat stroke. The results showed that OT significantly reduced heat-induced lung edema, neutrophil infiltration, hemorrhage score, myeloperoxidase activity, ischemia, and the levels of inflammatory and oxidative damage markers in bronchoalveolar lavage fluid. The survival assessment confirmed the pathophysiological and biochemical results. An OT receptor antagonist (L-368,899) was administered 10 min before the OT injection to further demonstrate the role of OT in heat-induced ALI. The results showed that OT could not protect against the aforementioned heat stroke responses in rats treated with L-368,899. Interestingly, OT treatment 80 min after the start of heat shock did not affect survival. In conclusion, our data indicate that OT pretreatment can reduce the ischemic, inflammatory and oxidative responses related to heat-induced ALI in rats.

Puerarin pre-conditioning on the expression levels of CK-MB, cTnI and inflammatory factors in patients undergoing cardiac valve replacement

Effect of puerarin preconditioning on the expression levels of nuclear factor κB (NF-κB), interleukin 6 (IL-6), interleukin 8 (IL-8), troponin I (cTnI), and creatine kinase isoenzyme MB (CK-MB) in the neutrophils of patients undergoing cardiac valve replacement under cardiopulmonary bypass (CPB) was evaluated. We enrolled 50 patients scheduled for cardiac valve replacement and assigned them randomly divided into either a puerarin or a control group. Puerarin was dissolved in 10 ml normal saline before CPB, and administered by intravenous infusion to patients in the puerarin group. The control group was administered an equivalent amount of saline. We used flow cytometry to determine the expression levels of NF-κB, IL-6 and IL-8 in neutrophils and an auto chemistry analyzer to determine the serum levels of cTnI and CK-MB before anesthesia induction (T0), 30 min after aortic declamping (T1), 4 h after aortic declamping (T2), and 8 h after aortic declamping (T3). We found the mean serum cTnI and CK-MB levels of the puerarin group tended to decrease with time. The positive rates of NF-κB, IL-6 and IL-8 at different time-points were lower in patients of the puerarin group than in those of the control group (and the differences at T3 were statistically significant). The clinical manifestations of patients in the puerarin group after operation were better than those in the control group (P<0.05). We found that the expression levels of NF-κB, IL-6 and IL-8 were positively correlated with the levels of CK-MB and cTnI (P<0.05). Puerarin preconditioning can reduce the NF-κB activation and the overexpression of IL-6 and IL-8 in neutrophils, and it inhibits the release of myocardial enzyme cTnI and CK-MB reflecting myocardial cell protection. Puerarin seems to improve safety and efficacy of valvular replacement operations.

Protective effect of oxytocin on LPS-induced acute lung injury in mice

Oxytocin (OT), a neurohypophyseal hormone synthesized in the paraventricular and supraoptic nuclei of the hypothalamus, has been reported to have an anti- inflammatory effect. However, its role in acute lung injury (ALI) has never been investigated. The aim of this study was to explore the therapeutic effects and potential mechanism action of OT on lipopolysaccharide (LPS)-induced ALI. Mice were treated with OT 30 min before the intraperitoneal injection of LPS. After 2 h, the effects of OT on lung histopathological changes, lung wet/dry (W/D) ratio, myeloperoxidase (MPO) activity, levels of inflammatory cytokines in the bronchoalveolar lavage fluid (BALF), and expression of inflammation proteins were detected. The results showed that OT significantly reduced LPS-induced pathological injury, W/D ratio, MPO activity, and the levels of interleukin (IL)-1β, IL-18 and IL-6. Further, OT also inhibited LPS-induced Toll-like receptor 4 expression and NLR family pyrin domain containing 3 inflammasome activation. OT receptor antagonist (L-368,899) was given 90 min before injecting OT to further demonstrate the role of OT in LPS-induced ALI. The results showed OT could not alleviate the aforementioned inflammatory reactions after administering L-368,899. In conclusion, the present results indicated that OT could reduce inflammatory responses of LPS-induced ALI.

Taxifolin protects rat against myocardial ischemia/reperfusion injury by modulating the mitochondrial apoptosis pathway

Background

Taxifolin (TAX), is an active flavonoid, that plays an underlying protective role on the cardiovascular system. This study aimed to evaluate its effect and potential mechanisms on myocardial ischemia/reperfusion (I/R) injury.

Methods

Healthy rat heart was subjected to I/R using the Langendorff apparatus. Hemodynamic parameters, including heart rate, left ventricular developed pressure (LVDP), maximum/minimum rate of the left ventricular pressure rise (+dp/dt_max and −dp/dt_min) and rate pressure product (RPP) were recorded during the perfusion. Histopathological examination of left ventricular was measured by hematoxylin-eosin (H&E) staining. Creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) activities in the effluent perfusion, and the levels of malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX) in the tissue were assayed. Apoptosis related proteins, such as B-cell lymphoma-2 (Bcl-2), Bcl2-associated X (Bax), and cytochrome c (Cyt-c) were also assayed by ELISA. Western blot was employed to determine apoptosis-executive proteins, including caspase 3 and 9. Transferase-mediated dUTP-X nick end labeling assay was performed to evaluate the effect TAX on myocardial apoptosis.

Results

Taxifolin significantly improved the ventricular functional recovery, as evident by the increase in LVDP, +dp/dt_max, −dp/dt_min and RPP, the levels of SOD, GSH-PX were also increased, but those of LDH, CK-MB, and MDA were decreased. Furthermore, TAX up-regulated the Bcl-2 protein level but down-regulated the levels of Bax, Cyt-c, caspase 3 and 9 protein, thereby inhibits the myocardial apoptosis.

Discussion

Taxifolin treatment remarkably improved the cardiac function, regulated oxidative stress and attenuated apoptosis. Hence, TAX has a cardioprotective effect against I/R injury by modulating mitochondrial apoptosis pathway.

The SAFE pathway is involved in the postconditioning mechanism of oxytocin in isolated rat heart

Oxytocin (OT) has a postconditioning effect against the ischemia-reperfusion (I/R) injury. However, its precise cardioprotection mechanism at the early reperfusion phase remains under debate. Our previous study revealed that OT postconditioning (OTpost) is cardioprotective by activating the Reperfusion Injury Salvage Kinase (RISK) pathway. Therefore, the present study is aimed to determine the biological effects of OTpost via the OT receptor and the activation of the JAK/STAT3 signaling pathway, mitochondrial adenosine triphosphate-dependent potassium channel (mitoKATP), nitric oxide (NO) release, and its anti-apoptotic effects against I/R injury in an isolated rat heart model. Sixty-three rats were randomly allocated to one of nine groups. OT was perfused 40 min prior to the regional ischemia or 15 min at the early reperfusion phase. AG490 (a JAK/STAT3 inhibitor), 5HD (a mitoKATP blocker), atosiban (an OT receptor antagonist), L-NAME (a nonspecific nitric oxide synthase inhibitor) were applied either alone or in combination with OT during the pre-ischemia phase and/or in the early reperfusion phase. Myocardial infarct size, hemodynamic factor, ventricular arrhythmia, coronary flow, cardiac biochemical marker, and the apoptosis index were determined at the end of reperfusion. Oxytocin postconditioning reduced infarct size, lactate dehydrogenase activity, arrhythmia score, ventricular fibrillation, and apoptosis. Moreover, AG490, 5HD, atosiban, and L-NAME abrogated the cardioprotective effects of OT. Our results demonstrated that the cardioprotective effects of OT are mediated by NO release, and the activation of mitoKATP and the SAFE pathway through the JAK/STAT3 signaling cascade that finally lead to decrease in the apoptosis index during the early reperfusion phase.

The psychoneuroimmunology of pregnancy

Pregnancy is associated with a number of significant changes in maternal physiology. Perhaps one of the more notable changes is the significant alteration in immune function that occurs during pregnancy. This change in immune function is necessary to support a successful pregnancy, but also creates a unique period of life during which a female is susceptible to disease and, as we'll speculate here, may also contribute to mental health disorders associated with pregnancy and the postpartum period. Here, we review the known changes in peripheral immune function that occur during pregnancy and the postpartum period, while highlighting the impact of hormones during these times on immune function, brain or neural function, as well as behavior. We also discuss the known and possible impact of pregnancy-induced immune changes on neural function during this time and briefly discuss how these changes might be a risk factor for perinatal anxiety or mood disorders.

Protective effects of cinnamon bark extract against ischemia-reperfusion injury and arrhythmias in rat

Cinnamomum zeylanicum (cinnamon) is a plant with potent antioxidant activity and has been used in traditional medicine for improvement of heart function. The effects of cinnamon bark ethanolic extract were investigated against ischemia-induced arrhythmias and heart injury in an in vivo rat model of regional heart ischemia. The extract was also standardized, and its antioxidant activity was evaluated. Adult male Sprague-Dawley rats were subjected to 30 min of ischemia by occlusion of the left anterior descending coronary artery followed by 5 days of reperfusion. Thirty-two animals were randomized to receive daily oral administration of vehicle or C. zeylanicum bark extract (intragastric, 50, 100, or 200 mg/kg) 14 days before ischemia. C. zeylanicum was standardized through HPLC analysis. Administration of cinnamon bark extract significantly improved ischemia/reperfusion-induced myocardial injury as evidenced by reduction of the infarct size. Also, during the ischemic period, ventricular tachycardia and ventricular ectopic beats episodes decreased as compared with that of the control group. The extract stabilized the ST segment changes and QTc shortening, decreased R-wave amplitude, and increased heart rate during ischemia. The extract also caused significant elevations in serum superoxide dismutase and glutation proxidase activities as well as a significant decrease in serum cardiac troponin I, lactate dehydrogenase, and malondialdehyde levels, 5 days after reperfusion. In HPLC analysis, the amounts of Cinamic acid, Methyl eugenol, and Cinnamaldehyde were 8.99 ± 0.5, 13.02 ± 1.8, and 14.63 ± 1.1 mg/g, respectively. The results show that the ethanolic extract of cinnamon bark is able to protect the heart against ischemia-reperfusion injury probably due to its antioxidant properties. Hence, it might be beneficial in these patients and this remedy might be used for preparation of new drugs.

An examination of changes in maternal neuroimmune function during pregnancy and the postpartum period

There is strong evidence that the immune system changes dramatically during pregnancy in order to prevent the developing fetus from being "attacked" by the maternal immune system. Due to these alterations in peripheral immune function, many women that suffer from autoimmune disorders actually find significant relief from their symptoms throughout pregnancy; however, these changes can also leave the mother more susceptible to infections that would otherwise be mitigated by the inflammatory response (Robinson and Klein, 2012). Only one other study has looked at changes in microglial number and morphology during pregnancy and the postpartum period (Haim et al., 2016), but no one has yet examined the neuroimmune response following an immune challenge during this time. Therefore, in this study, we investigated the impact of an immune challenge during various time-points throughout pregnancy and the postpartum period on the expression of immune molecules in the brain of the mother and fetus. Our results indicate that similar to the peripheral immune suppression measured during pregnancy, we also see significant suppression of the immune response in the maternal brain, particularly during late gestation. In contrast to the peripheral immune system, immune modulation in the maternal brain extends moderately into the postpartum period. Additionally, we found that the fetal immune response in the brain and placenta is also suppressed just before parturition, suggesting that cytokine production in the fetus and placenta are mirroring the peripheral cytokine response of the mother.

Effect of different doses of oxytocin on cardiac electrophysiology and arrhythmias induced by ischemia

The onset of acute myocardial ischemia (MI) is accompanied by a rapid increase in electrical instability and often fatal ventricular arrhythmias. This study investigated that whether oxytocin (OT) can modulate ischemia-induced arrhythmias and considered relationships between the severity of arrhythmia and the electrocardiogram parameters during ischemia. OT (0.0001–1 μg) was administrated intraperitoneally 30 min before ischemia. To examine receptor involved, a selective OT-receptor antagonist, atosiban (ATO), was infused 10 min before OT. OT caused a significant and biphasic dose-dependent reduction in ectopic heart activity and arrhythmia score. OT doses that reduced ventricular arrhythmia elicited significant increase in QT interval. OT attenuated the electrophysiological changes associated with MI and there was significant direct relationship between QRS duration and arrhythmia score. ATO treatment reduced beneficial effects of OT on arrhythmogenesis. Nevertheless, ATO failed to alter OT effects on premature ventricular contractions. We assume that the ability of OT to modulate the electrical activity of the heart may play an important role in the antiarrhythmic actions of OT.

RISK pathway is involved in oxytocin postconditioning in isolated rat heart

The reperfusion injury salvage kinase (RISK) pathway is a fundamental signal transduction cascade in the cardioprotective mechanism of ischemic postconditioning. In the present study, we examined the cardioprotective role of oxytocin as a postconditioning agent via activation of the RISK pathway (PI3K/Akt and ERK1/2). Animals were randomly divided into 6 groups. The hearts were subjected under 30minutes (min) ischemia and 100min reperfusion. OT was perfused 15min at the early phase of reperfusion. RISK pathway inhibitors (Wortmannin; an Akt inhibitor, PD98059; an ERK1/2 inhibitor) and Atosiban (an OT receptor antagonist) were applied either alone 10min before the onset of the ischemia or in the combination with OT during early reperfusion phase. Myocardial infarct size, hemodynamic factors, ventricular arrhythmia, coronary flow and cardiac biochemical marker were measured at the end of reperfusion. OT postconditioning (OTpost), significantly decreased the infarct size, arrhythmia score, incidence of ventricular fibrillation, Lactate dehydrogenase and it increased coronary flow. The cardioprotective effect of OTpos was abrogated by PI3K/Akt, ERK1/2 inhibitors and Atosiban. Our data have shown that OTpost can activate RISK pathway mostly via the PI3K/Akt and ERK1/2 signaling cascades during the early phase of reperfusion.

Microbes and Oxytocin: Benefits for Host Physiology and Behavior

It is now understood that gut bacteria exert effects beyond the local boundaries of the gastrointestinal tract to include distant tissues and overall health. Prototype probiotic bacterium Lactobacillus reuteri has been found to upregulate hormone oxytocin and systemic immune responses to achieve a wide array of health benefits involving wound healing, mental health, metabolism, and myoskeletal maintenance. Together these display that the gut microbiome and host animal interact via immune-endocrine-brain signaling networks. Such findings provide novel therapeutic strategies to stimulate powerful homeostatic pathways and genetic programs, stemming from the coevolution of mammals and their microbiome.

Oxytocin inhibits lipopolysaccharide-induced inflammation in microglial cells and attenuates microglial activation in lipopolysaccharide-treated mice

Background

Overactivated microglia is involved in various kinds of neurodegenerative diseases. Suppression of microglial overactivation has emerged as a novel strategy for treatment of neuroinflammation-based neurodegeneration. In the current study, anti-inflammatory effects of oxytocin (OT), which is a highly conserved nonapeptide with hormone and neurotransmitter properties, were investigated in vitro and in vivo.

Methods

BV-2 cells and primary microglia were pre-treated with OT (0.1, 1, and 10 μM) for 2 h followed by LPS treatment (500 ng/ml); microglial activation and pro-inflammatory mediators were measured by Western blot, RT-PCR, and immunofluorescence. The MAPK and NF-κB pathway proteins were assessed by Western blot. The intracellular calcium concentration ([Ca²⁺]i) was determined using Fluo2-/AM assay. Intranasal application of OT was pre-treated in BALB/C mice (adult male) followed by injected intraperitoneally with LPS (5 mg/kg). The effect of OT on LPS-induced microglial activation and pro-inflammatory mediators was measured by Western blot, RT-PCR, and immunofluorescence in vivo.

Results

Using the BV-2 microglial cell line and primary microglia, we found that OT pre-treatment significantly inhibited LPS-induced microglial activation and reduced subsequent release of pro-inflammatory factors. In addition, OT inhibited phosphorylation of ERK and p38 but not JNK MAPK in LPS-induced microglia. OT remarkably reduced the elevation of [Ca²⁺]_i in LPS-stimulated BV-2 cells. Furthermore, a systemic LPS-treated acute inflammation murine brain model was used to study the suppressive effects of OT against neuroinflammation in vivo. We found that pre-treatment with OT showed marked attenuation of microglial activation and pro-inflammatory factor levels.

Conclusions

Taken together, the present study demonstrated that OT possesses anti-neuroinflammatory activity and might serve as a potential therapeutic agent for treating neuroinflammatory diseases.

Body temperature and cardiac changes induced by peripherally administered oxytocin, vasopressin and the non-peptide oxytocin receptor agonist WAY 267,464: a biotelemetry study in rats

BACKGROUND AND PURPOSE

There is current interest in oxytocin (OT) as a possible therapeutic in psychiatric disorders. However, the usefulness of OT may be constrained by peripheral autonomic effects, which may involve an action at both OT and vasopressin V1A receptors. Here, we characterized the cardiovascular and thermoregulatory effects of OT, vasopressin (AVP) and the non-peptide OT receptor agonist WAY 267,464 in rats, and assessed the relative involvement of the OT and V1A receptors in these effects.

EXPERIMENTAL APPROACH

Biotelemetry in freely moving male Wistar rats was used to examine body temperature and heart rate after OT (0.01 - 1 mg kg(-1); i.p.), AVP (0.001 - 0.1 mg kg(-1); i.p.) or WAY 267,464 (10 and 100 mg kg(-1); i.p.). The actions of the OT receptor antagonist Compound 25 (C25, 5 and 10 mg kg(-1)) and V1A receptor antagonist SR49059 (1 and 10 mg kg(-1)) were studied, as well as possible V1A receptor antagonist effects of WAY 267,464.

KEY RESULTS

OT and AVP dose-dependently reduced body temperature and heart rate. WAY 267,464 had similar, but more modest, effects. SR49059, but not C25, prevented the hypothermia and bradycardia induced by OT and AVP. WAY 267,464 (100 mg·kg(-1)) prevented the effects of OT, and to some extent AVP.

CONCLUSIONS AND IMPLICATIONS

Peripherally administered OT and AVP have profound cardiovascular and thermoregulatory effects that appear to principally involve the V1A receptor rather than the OT receptor. Additionally, WAY 267,464 is not a simple OT receptor agonist, as it has functionally relevant V1A antagonist actions.

Role of atrial natriuretic Peptide in oxytocin induced cardioprotection

BACKGROUND

The purpose of this study was to determine whether endogenous atrial natriuretic peptide (ANP) contributes to the protective effect of neurohypophysial hormone oxytocin (OT) in heart preconditioning.

METHODS

Sprague-Dawley male rats were subjected to 25 min regional ischaemia and 120 min reperfusion and were divided into eight groups. Oxytocin or an equivalent volume of saline was administrated intraperitoneally, 30 min before ischaemia. The OT receptor antagonist (atosiban), ANP receptor antagonist (anantin) and nitric oxide synthase inhibitor (L-NAME) were injected 10 min before OT. In other groups, atosiban, anantin and L-NAME were only administered 40 min prior to ischaemia.

RESULTS

Compared with the ischaemia/reperfusion group (I/R), alterations in infarct size, biochemical parameters [LDH (lactate dehydrogenase), CK-MB (creatine kinase-MB), MDA (malondialdehyde) plasma levels] and severity of ventricular arrhythmia due to I/R injury were attenuated and VF was abolished by OT treatment. These OT effects were eliminated by OT and ANP receptor blockers and nitric oxide synthase inhibitor, but anantin did not reverse the effect of OT in lipid peroxidation.

CONCLUSIONS

These findings demonstrate an important contributory role of ANP in the OT induced protection in myocardial ischaemia reperfusion. OT also reduced lipid peroxidation with a NO-dependent mechanism.

Oxytocin is an age-specific circulating hormone that is necessary for muscle maintenance and regeneration

The regenerative capacity of skeletal muscle declines with age. Previous studies suggest that this process can be reversed by exposure to young circulation, but systemic age-specific factors responsible for this phenomenon are largely unknown. Here we report that oxytocin- a hormone best known for its role in lactation, parturition, and social behaviors - is required for proper muscle tissue regeneration and homeostasis, and that plasma levels of oxytocin decline with age. Inhibition of oxytocin signaling in young animals reduces muscle regeneration, whereas systemic administration of oxytocin rapidly improves muscle regeneration by enhancing aged muscle stem cell activation/proliferation throughactivation of the MAPK/ERK signalling pathway. We further show that the genetic lack of oxytocin does not cause a developmental defect in muscle, but instead leads to premature sarcopenia. Considering that oxytocin is an FDA approved drug, this work reveals a potential novel and safe way to combat or prevent skeletal muscle aging.

The protective effect of oxytocin on ischemia/reperfusion injury in rat urinary bladder

Oxytocin (OXY), a well-known nonapeptide, plays a crucial role in reproduction, and has effects on modulating the immune and inflammatory processes in living organisms as well. Recently it is also known as an antioxidant in several organs. The present study aims to demonstrate the protective effect of OXY against ischemia/reperfusion (I/R) injury in urinary bladder tissue. Abdominal aorta of rats, were clamped to perform urinary bladder ischemia. OXY (0.5 μg/kg) was injected intraperitoneally before ischemia in I/R+OXY group, whereas the vehicle solution was injected to I/R group. At the end of reperfusion, tissue samples from urinary bladder were processed for histochemical, ultrastructural and biochemical analysis. Tissue sections were stained by toluidine blue for mast cell counting and hematoxylin-eosin for histopathology. In addition, malondialdehyde (MDA) and glutathione (GSH) levels were determined biochemically. The results demonstrated that there was an extreme damage at urothelium, dilatation of intercellular junctions, inflammatory cell infiltration in I/R group. I/R+OXY group demonstrated a reduction in the severity of urinary bladder damage. According to mast cell counting results, both granulated and degranulated mast cells were decreased in I/R+OXY group compared to I/R group. The mean MDA level was higher in I/R group compared to control and lower in I/R+OXY group compared to I/R group. GSH level reduced in I/R group compared to the control and increased in I/R+OXY group compared to I/R group. In conclusion, oxytocin, as confirmed by histological evaluation and biochemical assays has a potential protective effect in the urinary bladder tissue against ischemia/reperfusion injury.

Oxytocin ameliorates cisplatin-induced nephrotoxicity in Wistar rats

BACKGROUND AND OBJECTIVES

The clinical use of cisplatin (CP) is highly limited because of its renal toxicity and the production of reactive oxygen species (ROS) that intensify the cytotoxic effects. Oxytocin (OT) was previously shown to have antioxidant activity.

DESIGN AND SETTING

Experimental study on male Wistar albino rats performed in the Faculty of Pharmacy, King Abdulaziz University, Jeddah, Saudi Arabia.

METHODS

Forty-eight male Wistar albino rats were classified into four equal groups: a control group, OT only-treated group which received OT twice (500 micro g/kg intraperitoneally (ip) 30 minutes and just before saline administration), a CP-induced nephrotoxicity group that received a single dose of CP (7.5 mg/kg ip) and treated with saline, and CP+OT group treated with the same previous doses. Seventy-two hours after CP administration, the rats were sacrificed and blood was withdrawn for determination of urea, creatinine, albumin and lactate dehydrogenase (LDH). The kidneys were extracted for histopathological examination and determination of the tissue levels of reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS) and nitric oxide end product nitrite (NO(2)). Glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and myeloperoxidase (MPO) activities were assessed.

RESULTS

CP-induced renal injury was evidenced histopathologically and manifested by a significant increase in serum LDH activity as well as urea and creatinine levels. Moreover, renal injury was associated with decreased renal tissue activities of CAT, SOD, GPx and GST as well as GSH level. On the other hand, renal tissue content of TBARS and NO(2) as well as the activity of MPO were increased. Alterations in these biochemical and histopathological indices due to CP were attenuated by OT.

CONCLUSION

OT protected rats from CP-induced nephrotoxicity. Such protection is attributed, at least in part, to its antioxidant activity.

Role of central oxytocin in stress-induced cardioprotection in ischemic-reperfused heart model

BACKGROUND AND PURPOSE

There is growing evidence that stress contributes to cardiovascular disease and triggers the release of oxytocin. Moreover previous studies confirmed oxytocin mimics the protection associated with ischemic preconditioning. The present study was aimed to assess the possible cardioprotective effects of the centrally released oxytocin in response to stress and intracerebroventricular (i.c.v.) administration of exogenous oxytocin in ischemic-reperfused isolated rat heart.

METHODS AND SUBJECTS

Rats were divided in two main groups and all of them were subjected to i.c.v. infusion of vehicle or drugs: unstressed rats [control: vehicle, oxytocin (OT; 100 ng/5 μl), atosiban (ATO; 4.3 μg/5 μl) as oxytocin antagonist, ATO+OT] and stressed rats [St: stress, OT+St, ATO+St]. After anesthesia, hearts were isolated and subjected to 30 min regional ischemia and 60 min reperfusion (IR). Acute stress protocol included swimming for 10 min before anesthesia. Myocardial function, infarct size, coronary flow, ventricular arrhythmia, and biochemical parameters such as creatine kinase and lactate dehydrogenase were measured. Ischemia-induced ventricular arrhythmias were counted during the occlusion period.

RESULTS

The plasma levels of oxytocin and corticosterone were significantly elevated by stress. Unexpectedly hearts of stressed rats showed a marked depression of IR injury compared to control group. I.c.v. infusion of oxytocin mimicked the cardioprotective effects of stress, yet did not elevate plasma oxytocin level. The protective effects of both stress and i.c.v. oxytocin were blocked by i.c.v. oxytocin antagonist.

CONCLUSIONS

These findings suggest that i.c.v. infusion of exogenous oxytocin and centrally released endogenous oxytocin in response to stress could play a role in induction of a preconditioning effect in ischemic-reperfused rat heart via brain receptors.

Neurohypophyseal hormones protect against pentylenetetrazole-induced seizures in zebrafish: role of oxytocin-like and V1a-like receptor

Oxytocin (OT) and arginine-vasopressin (AVP) are involved in the physiological response to different stressors like the occurrence of seizures which is regarded as a severe stress factor. Zebrafish (Danio rerio) is recently featured as a model of epilepsy but the role of neurohypophyseal hormones on this teleost is still unknown. We attempted to determine whether non-mammalian homologues like isotocin (IT) and vasotocin (AVT) affected pentylenetetrazole (PTZ)-induced seizures in adult zebrafish in comparison with OT/AVP. The mechanism was studied using the most selective OT and AVP receptor antagonists. Zebrafish were injected i.m. with increasing doses (0.1-40 ng/kg) of the neuropeptides 10 min before PTZ exposure. DesGly-NH2-d(CH2)5-[D-Tyr2,Thr4]OVT (desglyDTyrOVT) for OT receptor and SR49059 for V1a subtype receptor, were injected together with each agonist 20 min before PTZ exposure. All the peptides significantly decreased the number of seizures, increased the mean latency time to the first seizure and decreased lethality. This protective effect led to a dose-response curve following a U-shaped form. IT was approximately 40 times more active than OT while AVT was 20 times more potent than AVP in reducing the number of seizures. DesglyDTyrOVT was more effective in antagonizing OT/IT, while SR49059 mainly blocked AVP/AVT-induced protection against PTZ-induced seizures. The present findings provide direct evidence of an important involvement of IT/OT and AVP/AVT as anticonvulsant agents against PTZ-induced seizures with a receptor-mediated mechanism in zebrafish. These data reinforce zebrafish as an emerging experimental model to study and identify new antiepileptic drugs.

The effect of acute stress exposure on ischemia and reperfusion injury in rat heart: role of oxytocin

Previous studies showed the protective effects of oxytocin (OT) on myocardial injury in ischemic and reperfused rat heart. Moreover, exposure to various stressors not only evokes sudden cardiovascular effects but also triggers the release of OT in the rat. The present study was aimed to evaluate the possible cardioprotective effects of endogenous OT released in response to stress (St), and effects of administration of exogenous OT on the ischemic-reperfused isolated heart of rats previously exposed to St. Wistar rats were divided into six groups: ischemia/reperfusion (IR); St: rats exposed to swim St for 10 min before anesthesia; St+atosiban (ATO): an OT receptor antagonist, was administered (1.5 mg/kg i.p.) prior to St; St+OT: OT was administered (0.03 mg/kg i.p.) prior to St; OT: OT was administrated prior to anesthesia; ATO was given prior to anesthesia. Isolated hearts were perfused with Krebs buffer solution by the Langendorff method and subjected to 30 min of regional ischemia followed by 60 min of reperfusion. The infarct size (IS) and creatine kinase MB isoenzyme (CK-MB) and lactate dehydrogenase (LDH) in coronary effluent were measured. Hemodynamic parameters were recorded throughout the experiment. The plasma concentrations of OT and corticosterone were significantly increased by St. Unexpectedly St decreased IR injury compared with the IR alone group. OT administration significantly inhibited myocardial injury, and administration of ATO with St abolished recovery of the rate pressure product, and increased IS and levels of CK-MB and LDH. These findings indicate that activation of cardiac OT receptors by OT released in response to St may participate in cardioprotection and inhibition of myocardial IR injury.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Is preconditioning by oxytocin administration mediated by iNOS and/or mitochondrial K(ATP) channel activation in the in vivo anesthetized rabbit heart?

AIMS

Oxytocin (OXT) pretreatment protects the heart during ischemia-reperfusion injury by activating ATP-dependent potassium (K(ATP)) channels. The aim of the current study was to elucidate the roles of nitric oxide synthaseNOS and myocardial biochemistry in the cardioprotective effects of OXT and ischemic preconditioning (IPC).

MAIN METHODS

Male New Zealand White anesthetized rabbits (13 groups) were subjected to 30 min of occlusion of the left coronary artery and 120 min of reperfusion with or without IPC.

KEY FINDINGS

IPC (1 cycle), OXT (0.03 μg/kg, i.p.) or IPC + OXT yield significant infarct size reductions (21.8±1.5%, 20.5±1.2% and 19.4±1.4%, respectively, versus 38.9±3.5% in the S-CONT group; P<0.01) and antiarrhythmic effects, including VF (0%, 0% and 0%, versus 50% in S-CONT group; P<0.05) sustained VT (13%, 13% and 13%, versus 100% in S-CONT group; P<0.005) and other arrhythmias (25%, 13% and 25%, versus 100% in S-CONT group; P<0.005, P<0.01 and P<0.005, respectively). Atosiban (ATO, a selective OXT receptor antagonist), 5-HD and L-NAME (a nonspecific NOS inhibitor) abolished the beneficial effects of IPC and OXT, suggesting that the benefits are achieved via selective activation of OXT receptors, mitochondrial K(ATP) channels and NO. An iNOS inhibitor (1400 W) blocked the beneficial effects of IPC but not OXT. The IPC, OXT, IPC + OXT and 1400 W + OXT interventions significantly preserved ATP levels in the heart.

SIGNIFICANCE

This study demonstrates similarities between acute OXT pretreatment and IPC in terms of infarct size reduction, antiarrhythmic activity, and metabolic status.

Oxytocin revisited: its role in cardiovascular regulation

Traditionally associated with female reproduction, oxytocin (OT) was revisited recently and was revealed to have several new roles in the cardiovascular system. Functional OT receptors have been discovered in the rat and human heart, as well as in vascular beds. The cardiovascular activities of OT include: (i) lowering blood pressure; (ii) negative cardiac inotropy and chronotropy; (iii) parasympathetic neuromodulation; (iv) vasodilatation; (v) anti-inflammatory; (vi) antioxidative; and (vii) metabolic effects. These outcomes are mediated, at least in part, by stimulating cardioprotective mediators, such as nitric oxide and atrial natriuretic peptide. OT and its extended form OT-Gly-Lys-Arg have been shown to be abundant in the foetal mouse heart. OT has the capacity to generate cardiomyocytes from various types of stem cells, including the cardiac side population. Mesenchymal cells transfected with OT-Gly-Lys-Arg, or preconditioned with OT, are resistant to apoptosis and express endothelial cell markers. OT increases glucose uptake in cultured cardiomyocytes from newborn and adult rats, in normal, hypoxic and even insulin resistance conditions. In rats with experimentally-induced myocardial infarction, continuous in vivo OT delivery improves the cardiac healing process, as well as cardiac work, reduces inflammation and stimulates angiogenesis. Therefore, in pathological conditions, OT exerts anti-inflammatory and cardioprotective properties, and improves vascular and metabolic functions. Thus, OT has potential for therapeutic use.

The administration of oxytocin during early reperfusion, dose-dependently protects the isolated male rat heart against ischemia/reperfusion injury

In our previous study, the administration of oxytocin (OT) could precondition the heart against ischemia/reperfusion injury. In this study, to investigate the cardiac postconditioning effect of oxytocin, isolated rat hearts were mounted on a Langendorff perfusion apparatus. In all groups, the hearts underwent 30 min of regional ischemia followed by 120 min of reperfusion. In the ischemia/reperfusion (IR) group, ischemia and reperfusion was induced. In the ischemic postconditioning (Ipost) group, hearts underwent 6 cycles of 10s reperfusion and 10s ischemia at the beginning of reperfusion. In the other groups (III-IX), OT was perfused 5 min before the onset of reperfusion and continued for 25 min with following doses (Molar): 10(-12), 5 × 10(-12), 8 × 10(-12), 10(-11), 2 × 10(-11), 5 × 10(-11), and 10(-10). The infarct size and coronary effluent levels of creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH) and malondialdehyde (MDA) were calculated at the end of reperfusion. The infarct size decreased considerably in Ipost group compared to IR group (P<0.05). Also, the infusion of oxytocin by doses of 8 × 10(-12)M, 10(-11)M and 2 × 10(-11)M dose-dependently reduced infarct size (P<0.05) significantly compared to the IR group. LDH level in coronary effluent was markedly decreased in Ipost group and treatment with oxytocin by doses of 8 × 10(-12)M, 10(-11)M, 2 × 10(-11)M and 5 × 10(-11)M (P<0.05) compared to IR group. Ipost, OT 2 × 10(-11)and 10(-11)M significantly decreased CK-MB level (P<0.05). Ipost, OT 8 × 10(-12), 10(-11) and 2 × 10(-11)M significantly decreased MDA level as compared to IR group. Our study shows that oxytocin dose-dependently exerts cardiac postconditioning.

The cardioprotective effect of different doses of vasopressin (AVP) against ischemia-reperfusion injuries in the anesthetized rat heart

The aim of the present study was to investigate the protective effect of various doses of exogenous vasopressin (AVP) against ischemia-reperfusion injury in anesthetized rat heart. Anesthetized rats were randomly divided into seven groups (n=4-13) and all of them subjected to prolonged 30 min regional ischemia and 120 min reperfusion. Group I served as saline control with ischemia, in treatment groups II, III, IV and V, respectively different doses of AVP (0.015, 0.03, 0.06 and 1.2 μg/rat) were infused within 10 min prior to ischemia, in group VI, an AVP-selective V1 receptor antagonist (SR49059, 1mg/kg, i.v.) was administrated prior to effective dose of AVP injection and in group VII, SR49059 (1 mg/kg, i.v.) was only administrated prior to ischemia. Various doses of AVP significantly prevented the decrease in heart rate (HR) at the end of reperfusion compared to their baseline and decreased infarct size, biochemical parameters [LDH (lactate dehydrogenase), CK-MB (creatine kinase-MB) and MDA (malondialdehyde) plasma levels], severity and incidence of ventricular arrhythmia, episodes and duration of ventricular tachycardia (VT) as compared to control group. Blockade of V1 receptors by SR49059 attenuated the cardioprotective effect of AVP on ventricular arrhythmias and biochemical parameters, but partially returned infarct size to control. AVP 0.03 μg/rat was known as effective dose. Our results showed that AVP owns a cardioprotective effect probably via V1 receptors on cardiac myocyte against ischemia/reperfusion injury in rat heart in vivo.

Oxytocin mediates social neuroprotection after cerebral ischemia

BACKGROUND AND PURPOSE

The reduced incidence, morbidity, and mortality of stroke among humans with strong social support have been well-documented; however, the mechanisms underlying these socially mediated phenomena remain unknown, but may involve oxytocin (OT), a hormone that modulates some aspects of social behavior in humans and other animals.

METHODS

In the present study, adult male mice were socially isolated (housed individually) or socially paired (housed with an ovariectomized female); social pairing increased hypothalamic OT gene expression. To determine whether a causal relationship exists between increased OT and improved stroke outcome, mice were treated with exogenous OT or OT receptor antagonist beginning 1 week before induction of experimental stroke via middle cerebral artery occlusion.

RESULTS

Relative to social isolation, social housing attenuated infarct size, neuroinflammation, and oxidative stress following experimental stroke; the neuroprotective effect of social housing was eliminated by receptor antagonist treatment. In contrast, administration of OT to socially isolated mice reproduced the neuroprotection conferred by social housing. We further report evidence for a direct suppressive action of OT on cultured microglia, which is a key instigator in the development of neuroinflammation after cerebral ischemia.

CONCLUSIONS

These findings support the hypothesis that OT mediates the neuroprotective effect of social interaction on stroke outcome.

Afferent signaling drives oxytocinergic preautonomic neurons and mediates training-induced plasticity

We showed previously that oxytocinergic (OTergic) projections from the hypothalamic paraventricular nucleus (PVN) to the dorsal brain stem mediate training-induced heart rate (HR) adjustments and that beneficial effects of training are blocked by sinoaortic denervation (SAD; Exp Physiol 94: 630-640; 1103-1113, 2009). We sought now to determine the combined effect of training and SAD on PVN OTergic neurons in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Rats underwent SAD or sham surgery and were trained (55% of maximal capacity) or kept sedentary for 3 mo. After hemodynamic measurements were taken at rest, rats were deeply anesthetized. Fresh brains were frozen and sliced to isolate the PVN; samples were processed for OT expression (real-time PCR) and fixed brains were processed for OT immunofluorescence. In sham rats, training improved treadmill performance and increased the gain of baroreflex control of HR. Training reduced resting HR (-8%) in both groups, with a fall in blood pressure (-10%) only in SHR rats. These changes were accompanied by marked increases in PVN OT mRNA expression (3.9- and 2.2-fold in WKY and SHR rats, respectively) and peptide density in PVN OTergic neurons (2.6-fold in both groups), with significant correlations between OT content and training-induced resting bradycardia. SAD abolished PVN OT mRNA expression and markedly reduced PVN OT density in WKY and SHR. Training had no effect on HR, PVN OT mRNA, or OT content following SAD. The chronic absence of inputs from baroreceptors and chemoreceptors uncovers the pivotal role of afferent signaling in driving both the plasticity and activity of PVN OTergic neurons, as well as the beneficial effects of training on cardiovascular control.

Role of endogenous oxytocin in cardiac ischemic preconditioning

BACKGROUND

The aim of the present study is to assess the role of endogenous oxytocin (OT) in cardioprotective effects of ischemic preconditioning (IPC) in anesthetized rat.

MATERIALS AND METHODS

Animals were divided into five groups: 1) ischemia-reperfusion (IR); (n=6), hearts were subjected to 25 min regional ischemia and 60 min reperfusion, 2) OT; (n=6), oxytocin was administered (0.03 μg/kg i.p) 10 min prior to ischemia, 3) IPC; (n=7), IPC was induced via a 5 min regional ischemia followed by 5 min of reperfusion before IR, 4) IPC+ATO (Atosiban); (n=6), atosiban (1.5 μg/kg i.p) was used as OT receptor selective antagonist in the beginning of IPC and 5) IR+ATO; (n=6), atosiban was injected 10 min prior to ischemia-reperfusion.

RESULTS

In our experiment, Infarct size was decreased significantly in OT and IPC groups compared to IR (23 ± 1.5% and 19 ± 0.6% vs. 45 ± 2.9% in IR group, P<0.05). Administration of atosiban in IPC+ATO group increased infarct size to 39 ± 0.9% in comparison with OT and IPC groups (P<0.05). The use of OT and IPC prior to ischemia significantly declined ventricular arrhythmias severity in compared to IR group (1.2 ± 0.4 and 1 ± 0.5 respectively, vs. 4 ± 0.4 in IR group, P<0.05). Blockade of OT receptor by atosiban abolished the cardiopreconditioning effects of IPC.

CONCLUSION

This study shows that, in part, the cardioprotective effects of IPC can be induced by endogenous OT.

Cardiac oxytocin receptor blockade stimulates adverse cardiac remodeling in ovariectomized spontaneously hypertensive rats

An increasing amount of evidence demonstrates the beneficial role of oxytocin (OT) in the cardiovascular system. Similar actions are attributed to genistein, an isoflavonic phytoestrogen. The treatment with genistein activates the OT system in the aorta of ovariectomized (OVX) Sprague-Dawley (SD) rats. The objective of this study was to determine the effects of low doses of genistein on the OT-induced effects in rat hypertension. The hypothesis tested was that treatment of OVX spontaneously hypertensive rats (SHRs) with genistein improves heart structure and heart work through a mechanism involving the specific OT receptor (OTR). OVX SHRs or SD rats were treated with genistein (in microg/g body wt sc, 10 days) in the presence or absence of an OT antagonist (OTA) [d(CH(2))(5), Tyr(Me)(2), Orn(8)]-vasotocin or a nonspecific estrogen receptor antagonist (ICI-182780). Vehicle-treated OVX rats served as controls. RT-PCR and Western blot analysis demonstrated that left ventricular (LV) OTR, downregulated by ovariectomy, increased in response to genistein. In SHRs or SD rats, this effect was blocked by OTA or ICI-182780 administration. The OTR was mainly localized in microvessels expressing the CD31 marker and colocalized with endothelial nitric oxide synthase. In SHRs, the genistein-stimulated OTR increases were associated with improved fractional shortening, decreased blood pressure (12 mmHg), decreased heart weight-to-body weight ratio, decreased fibrosis, and lowered brain natriuretic peptide in the LV. The prominent finding of the study is the detrimental effect of OTA treatment on the LV of SHRs. OTA treatment of OVX SHRs resulted in a dramatic worsening of ejection fractions and an augmented fibrosis. In conclusion, these results demonstrate that cardiac OTRs are involved in the regulation of cardiac function of OVX SHRs. The decreases of OTRs may contribute to cardiac pathology following menopause.

Oxytocin protects rat heart against ischemia-reperfusion injury via pathway involving mitochondrial ATP-dependent potassium channel

Cardiac preconditioning represents the most potent and consistently reproducible method of rescuing heart tissue from undergoing irreversible ischemic damage. One of the major goals of the current cardiovascular research is to identify a reliable cardioprotective intervention that can salvage ischemic myocardium. The aim of the present study is to evaluate the oxytocin (OT)-induced cardioprotection and the signaling pathway involved with mitochondrial ATP-dependent potassium (mitoKATP) channel in the anesthetized rat heart. Animals were divided into six groups (n=6): (1) IR; hearts were subjected to 25 min ischemia and 120 min reperfusion, (2) OT; oxytocin was administered (0.03 microg/kg i.p.) 25 min prior to ischemia, (3) ATO+OT; atosiban (ATO) was used as an OT-selective receptor antagonist (1.5 microg/kg i.p.) 10 min prior to OT administration, (4) ATO; atosiban was used 35 min prior to ischemia, (5) 5HD+OT; 5-hydroxydecanoic acid (5HD) was used as a specific inhibitor of mitoKATP channel (10mg/kg i.v.) 10 min prior to OT administration, (6) 5HD; 5HD was used 35min prior to ischemia. Then infarct size, ventricular arrhythmia and creatine kinase-MB isoenzyme (CK-MB) plasma level were measured. Hemodynamic parameters were recorded throughout the experiment. OT administration significantly decreased infarct size, CK-MB plasma level, severity and incidence of ventricular arrhythmia as compared to IR group. Administration of atosiban and 5HD abolished the cardiopreconditioning effect of OT. This study demonstrates that cardioprotective effects of OT are mediated through opening the mitoKATP channels.

Oxytocin as feeding inhibitor: maintaining homeostasis in consummatory behavior

Initial studies showed that the anorexigenic peptide oxytocin (OT) regulates gastric motility, responds to stomach distention and to elevated osmolality, and blocks consumption of toxic foods. Most recently, it has been proposed to act as a mediator of general and carbohydrate-specific satiety and regulator of body weight. In the current review, we discuss the function of OT as a homeostatic inhibitor of consumption, capable of mitigating multiple aspects of ingestive behavior and energy metabolism.