The role of nitric oxide, reactive oxygen species, and protein kinase C in oxytocin-induced cardioprotection in ischemic rat heart

The Heart as a Target of Vasopressin and Other Cardiovascular Peptides in Health and Cardiovascular Diseases

The automatism of cardiac pacemaker cells, which is tuned, is regulated by the autonomic nervous system (ANS) and multiple endocrine and paracrine factors, including cardiovascular peptides. The cardiovascular peptides (CPs) form a group of essential paracrine factors affecting the function of the heart and vessels. They may also be produced in other organs and penetrate to the heart via systemic circulation. The present review draws attention to the role of vasopressin (AVP) and some other cardiovascular peptides (angiotensins, oxytocin, cytokines) in the regulation of the cardiovascular system in health and cardiovascular diseases, especially in post-infarct heart failure, hypertension and cerebrovascular strokes. Vasopressin is synthesized mostly by the neuroendocrine cells of the hypothalamus. There is also evidence that it may be produced in the heart and lungs. The secretion of AVP and other CPs is markedly influenced by changes in blood volume and pressure, as well as by other disturbances, frequently occurring in cardiovascular diseases (hypoxia, pain, stress, inflammation). Myocardial infarction, hypertension and cardiovascular shock are associated with an increased secretion of AVP and altered responsiveness of the cardiovascular system to its action. The majority of experimental studies show that the administration of vasopressin during ventricular fibrillation and cardiac arrest improves resuscitation, however, the clinical studies do not present consisting results. Vasopressin cooperates with the autonomic nervous system (ANS), angiotensins, oxytocin and cytokines in the regulation of the cardiovascular system and its interaction with these regulators is altered during heart failure and hypertension. It is likely that the differences in interactions of AVP with ANS and other CPs have a significant impact on the responsiveness of the cardiovascular system to vasopressin in specific cardiovascular disorders.

Oxytocin-induced endothelial nitric oxide dependent vasorelaxation and ERK1/2-mediated vasoconstriction in the rat aorta

Oxytocin is a neuropeptide produced primarily in the hypothalamus and plays an important role in the regulation of mammalian birth and lactation. It has been shown that oxytocin has important cardiovascular protective effects. Here we investigated the effects of oxytocin on vascular reactivity and underlying the mechanisms in human umbilical vein endothelial cells (HUVECs) in vitro and in rat aorta ex vivo. Oxytocin increased phospho-eNOS (Ser 1177) and phospho-Akt (Ser 473) expression in HUVECs in vitro and the aorta of rat ex vivo. Wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), inhibited oxytocin-induced Akt and eNOS phosphorylation. In the rat aortic rings, oxytocin induced a biphasic vascular reactivity: oxytocin at low dose (10^-9–10^-8 M) initiated a vasorelaxation followed by a vasoconstriction at high dose (10^-7 M). L-NAME (a nitric oxide synthase inhibitor), endothelium removal or wortmannin abolished oxytocin-induced vasorelaxation, and slightly enhanced oxytocin-induced vasoconstriction. Atosiban, an oxytocin/vasopressin 1a receptor inhibitor, totally blocked oxytocin-induced relaxation and vasoconstriction. PD98059 (ERK1/2 inhibitor) partially inhibited oxytocin-induced vasoconstriction. Oxytocin also increased aortic phospho-ERK1/2 expression, which was reduced by either atosiban or PD98059, suggesting that oxytocin-induced vasoconstriction was partially mediated by oxytocin/V1aR activation of ERK1/2. The present study demonstrates that oxytocin can activate different signaling pathways to cause vasorelaxation or vasoconstriction. Oxytocin stimulation of PI3K/eNOS-derived nitric oxide may participate in maintenance of cardiovascular homeostasis, and different vascular reactivities to low or high dose of oxytocin suggest that oxytocin may have different regulatory effects on vascular tone under physiological or pathophysiological conditions.

Oxytocin and vasopressin in the hippocampus

Oxytocin (OXT) and vasopressin (AVP) are related neuropeptides that exert a wide range of effects on general health, homeostasis, development, reproduction, adaptability, cognition, social and nonsocial behaviors. The two peptides are mainly of hypothalamic origin and execute their peripheral and central physiological roles via OXT and AVP receptors, which are members of the G protein-coupled receptor family. These receptors, largely distributed in the body, are abundantly expressed in the hippocampus, a brain region particularly vulnerable to stress exposure and various lesions. OXT and AVP have important roles in the hippocampus, by modulating important processes like neuronal excitability, network oscillatory activity, synaptic plasticity, and social recognition memory. This chapter includes an overview regarding OXT and AVP structure, synthesis, receptor distribution, and functions, focusing on their relationship with the hippocampus and mechanisms by which they influence hippocampal activity. Brief information regarding hippocampal structure and susceptibility to lesions is also provided. The roles of OXT and AVP in neurodevelopment and adult central nervous system function and disorders are highlighted, discussing their potential use as targeted therapeutic tools in neuropsychiatric diseases.

Polymeric nanoparticles in the diagnosis and treatment of myocardial infarction: Challenges and future prospects

Myocardial infarction (MI) is the leading cause of morbidity and mortality worldwide. Despite extensive efforts to provide early diagnosis and adequate treatment regimens, detection of MI still faces major limitations and pathological MI complications continue to threaten the recovery of survivors. Polymeric nanoparticles (NPs) represent novel noninvasive drug delivery systems for the diagnosis and treatment of MI and subsequent prevention of fatal heart failure. In this review, we cover the recent advances in polymeric NP-based diagnostic and therapeutic approaches for MI and their application as multifunctional theranostic tools. We also discuss the in vivo behavior and toxicity profile of polymeric NPs, their application in noninvasive imaging, passive, and active drug delivery, and use in cardiac regenerative therapy. We conclude with the challenges faced with polymeric nanosystems and suggest future efforts needed for clinical translation.

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.

The Gasotransmitter Hydrogen Sulfide and the Neuropeptide Oxytocin as Potential Mediators of Beneficial Cardiovascular Effects through Meditation after Traumatic Events

Trauma and its related psychological and somatic consequences are associated with higher cardiovascular morbidity. The regulation of both the gasotransmitter hydrogen sulfide (H2S) and the neuropeptide oxytocin (OT) have been reported to be affected during physical and psychological trauma. Both mediators are likely molecular correlates of trauma-induced cardiovascular complications, because they share parallel roles and signaling pathways in the cardiovascular system, both locally as well as on the level of central regulation and the vagus nerve. Meditation can alter the structure of specific brain regions and can have beneficial effects on cardiovascular health. This perspective article summarizes the evidence pointing toward the significance of H2S and OT signaling in meditation-mediated cardio-protection.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

H2S and Oxytocin Systems in Early Life Stress and Cardiovascular Disease

Today it is well established that early life stress leads to cardiovascular programming that manifests in cardiovascular disease, but the mechanisms by which this occurs, are not fully understood. This perspective review examines the relevant literature that implicates the dysregulation of the gasomediator hydrogen sulfide and the neuroendocrine oxytocin systems in heart disease and their putative mechanistic role in the early life stress developmental origins of cardiovascular disease. Furthermore, interesting hints towards the mutual interaction of the hydrogen sulfide and OT systems are identified, especially with regards to the connection between the central nervous and the cardiovascular system, which support the role of the vagus nerve as a communication link between the brain and the heart in stress-mediated cardiovascular disease.

Oxytocin Receptor Signaling in Vascular Function and Stroke

The oxytocin receptor (OXTR) is a G protein-coupled receptor with a diverse repertoire of intracellular signaling pathways, which are activated in response to binding oxytocin (OXT) and a similar nonapeptide, vasopressin. This review summarizes the cell and molecular biology of the OXTR and its downstream signaling cascades, particularly focusing on the vasoactive functions of OXTR signaling in humans and animal models, as well as the clinical applications of OXTR targeting cerebrovascular accidents.

The Interaction of the Endogenous Hydrogen Sulfide and Oxytocin Systems in Fluid Regulation and the Cardiovascular System

The purpose of this review is to explore the parallel roles and interaction of hydrogen sulfide (H2S) and oxytocin (OT) in cardiovascular regulation and fluid homeostasis. Their interaction has been recently reported to be relevant during physical and psychological trauma. However, literature reports on H2S in physical trauma and OT in psychological trauma are abundant, whereas available information regarding H2S in psychological trauma and OT in physical trauma is much more limited. This review summarizes recent direct and indirect evidence of the interaction of the two systems and their convergence in downstream nitric oxide-dependent signaling pathways during various types of trauma, in an effort to better understand biological correlates of psychosomatic interdependencies.

Oxytocin ameliorates ischemia/reperfusion-induced injury by inhibiting mast cell degranulation and inflammation in the rat heart

BACKGROUND

Oxytocin (OT) has shown a cardioprotective effect on myocardial ischemia/reperfusion injury (MIRI). This study aimed to investigate whether the cardioprotective effect of OT is associated with the inhibition of mast cell degranulation and inflammation.

METHODS

The left anterior descending coronary artery of rats was ligated for 30 min and reperfused for 120 min to establish an ischemia and reperfusion (I/R) injury model. A preliminary experiment was conducted to evaluate the optimal dose of OT (0.01, 0.1, 1 μg/kg via intraperitoneal). The mast cell secretagogue compound 48/80 (C48/80) was used to promote the degranulation of mast cells with or without I/R injury, while rats were pretreated with OT to determine whether this compound suppresses mast cell degranulation. The expression of the inflammatory factors HMGB1 and NF-κB p65 was evaluated. A cell experiment was performed for verification.

RESULTS

C48/80 (0.5 mg/kg, intravenous) increased mast cell degranulation and tryptase release compared with I/R-treated alone (27.12 ± 3.52 % vs. 16.57 ± 2.23 %; 8.34 ± 1.66 ng/mL vs. 3.63 ± 0.63 ng/mL), but these effects could be decreased by OT (0.1 μg/kg, intraperitoneal) preconditioning (19.29 ± 0.74 %; 5.37 ± 0.73 ng/mL). Besides that, hemodynamic disorders, arrhythmias, cardiac edema, infarct size, histopathological damage, and the levels of cTnI, HMGB1 and NF-κB p65 were significantly increased in I/R-treated group compared with corresponding observations in the control group, and C48/80 exacerbated these injuries, but pretreatment with OT could ameliorate these effects. Furthermore, C48/80 (10 μg/mL) inhibited the viability and promoted the apoptosis of H9C2(2-1) and RBL-2H3 cells, and increased the release of cTnI and tryptase, all of which were reversed by prophylactic OT (0.01 ng/mL) treatment.

CONCLUSION

We concluded that OT pretreatment inhibits the degranulation of cardiac mast cells induced by I/R injury and downregulates the expression of the inflammatory factors HMGB1 and NF-κB p65.

Protective Effects of Hyperbaric Oxygen Therapy on Brain Injury by Regulating the Phosphorylation of Drp1 Through ROS/PKC Pathway in Heatstroke Rats

This study aimed to elucidate the neurotherapeutic effect of hyperbaric oxygen (HBO) on brain injury and the potential role of dynamin-related protein 1 (Drp1) and its regulatory pathway in heatstroke (HS) rats. In in vivo experiments, rats were exposed to HBO after the onset of HS, or the same pressure but normal air as a control. The results indicated that HBO decreased the mortality and thermoregulatory dysfunction and prolonged the survival time of HS rats. Neurological dysfunction induced by HS was attenuated by HBO through assessment of modified neurological severity score and Morris water maze. HBO also alleviated histopathologic changes and oxidative injury (malondialdehyde and 8-hydroxyguanine), increased activities of superoxide dismutase (SOD) and glutathione/oxidized glutathione and ameliorated apoptotic parameters (caspase-3/6 activities and the number of apoptotic cells) of the hippocampus, hypothalamus and brain stem in rats compared to the HS group. Phosphorylation of Drp^Ser616 was increased by HS but decreased by HBO in the brains of rats determined by Western blot and immunohistochemical staining. In experiments in vitro, rat hippocampal neurons were used as a heat stress (HS) cellular model to examine the effects of HBO. As the results, HBO attenuated HS-induced cytotoxicity, oxidative injury (malondialdehyde), reactive oxygen species (ROS) generation, decreasing SOD activity and apoptosis. Drp1 inhibitor (Mdivi-1) treatment produced the same effects and had a trend to decrease oxidative injury. But the difference is not statistically significant. HBO and Mdivi-1decreased the phosphorylation of Drp^Ser616 induced by HS and HBO decreased the phosphorylation of protein kinase C (PKC) induced by HS. Moreover, both PKC inhibitor and ROS scavenger inhibited HS-induced p-Drp^Ser616. In conclusion, HBO may alleviate the brain injury caused by HS by decreasing ROS/PKC-regulated p-Drp^Ser616.

Oxytocin may have a therapeutical potential against cardiovascular disease. Possible pharmaceutical and behavioral approaches

Based on the ancient role of oxytocin and its homologues as amplifiers of reproduction we argue for an evolutionary coupling of oxytocin to signaling pathway which support restorative mechanisms of cells and tissue. In particular, the survival and function of different categories of stem cells and primordial cells are enhanced by mitogen-activated protein kinase (MAPK) pathways. Furthermore, oxytocin stimulates the AMP-activated protein kinase pathway (AMPK) in numerous of cell types which promotes the maintenance of different cell structures. This involves autophagic processes and, in particular, may support the renewal of mitochondria. Mitochondrial fitness may protect against oxidative and inflammatory stress - a well-documented effect of oxytocin. The combined specific trophic and protective effects oxytocin may delay several degenerative phenomena including sarcopenia, type-2 diabetes and atherosclerosis. These effects may be exerted both on a central level supporting the function and integrity of the hypothalamus and peripherally acting directly on blood vessels, pancreas, heart, skeletal muscles and adipose tissue etc. Furthermore, in the capacity of being both a hormone and neuromodulator, oxytocin interacts with numerous of regulatory mechanisms particularly the autonomic nervous system and HPA-axis which may reduce blood pressure and affect the immune function. The potential of the oxytocin system as a behavioral and molecular target for the prevention and treatment of cardiovascular disease is discussed. Focus is put on the affiliative and sexual significance and the different options and limitations associated with a pharmaceutical approach. MeSH: Aging, Atherosclerosis, Heart, Hypothalamus, Inflammation, Love, Orgasm, Oxytocin.

Therapeutic Potential of Oxytocin in Atherosclerotic Cardiovascular Disease: Mechanisms and Signaling Pathways

Coronary artery disease (CAD) is a major cardiovascular disease responsible for high morbidity and mortality worldwide. The major pathophysiological basis of CAD is atherosclerosis in association with varieties of immunometabolic disorders that can suppress oxytocin (OT) receptor (OTR) signaling in the cardiovascular system (CVS). By contrast, OT not only maintains cardiovascular integrity but also has the potential to suppress and even reverse atherosclerotic alterations and CAD. These protective effects of OT are associated with its protection of the heart and blood vessels from immunometabolic injuries and the resultant inflammation and apoptosis through both peripheral and central approaches. As a result, OT can decelerate the progression of atherosclerosis and facilitate the recovery of CVS from these injuries. At the cellular level, the protective effect of OT on CVS involves a broad array of OTR signaling events. These signals mainly belong to the reperfusion injury salvage kinase pathway that is composed of phosphatidylinositol 3-kinase-Akt-endothelial nitric oxide synthase cascades and extracellular signal-regulated protein kinase 1/2. Additionally, AMP-activated protein kinase, Ca²⁺/calmodulin-dependent protein kinase signaling and many others are also implicated in OTR signaling in the CVS protection. These signaling events interact coordinately at many levels to suppress the production of inflammatory cytokines and the activation of apoptotic pathways. A particular target of these signaling events is endoplasmic reticulum (ER) stress and mitochondrial oxidative stress that interact through mitochondria-associated ER membrane. In contrast to these protective effects and machineries, rare but serious cardiovascular disturbances were also reported in labor induction and animal studies including hypotension, reflexive tachycardia, coronary spasm or thrombosis and allergy. Here, we review our current understanding of the protective effect of OT against varieties of atherosclerotic etiologies as well as the approaches and underlying mechanisms of these effects. Moreover, potential cardiovascular disturbances following OT application are also discussed to avoid unwanted effects in clinical trials of OT usages.

Oxytocin administration prevents cellular aging caused by social isolation

Chronic stressors, such as chronic isolation in social mammals, can elevate glucocorticoids, which can affect cellular mechanisms of aging, including increased levels of oxidative stress and shortened telomere lengths. Recent work in the selectively social prairie vole (Microtus ochrogaster) suggests that oxytocin and social support may mitigate some of the negative consequences of social isolation, possibly by reducing glucocorticoid levels. We investigated the influences of isolation, social support, and daily oxytocin injections in female prairie voles. Glucocorticoid levels, oxidative damage, telomere length, and anhedonia, a behavioral index of depression, were measured throughout the study. We found that six weeks of chronic isolation led to increased glucocorticoid levels, oxidative damage, telomere degradation and anhedonia. However, daily oxytocin injections in isolated voles prevented these negative consequences. These findings demonstrate that chronic social isolation in female prairie voles is a potent stressor that results in depression-like behavior and accelerated cellular aging. Importantly, oxytocin can completely prevent the negative consequences of social isolation.

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.

Oxytocin is involved in steroid hormone-stimulated bovine satellite cell proliferation and differentiation in vitro

Sex steroid hormones are used in the meat industry due to their ability to regulate muscle hypertrophy. However, the mechanisms underlying their action are not fully elucidated. Recent reports demonstrate that steroid hormones increase oxytocin (OXT) expression in skeletal muscle, indicating that OXT may play a role in satellite cell activity. This hypothesis was tested using steroid hormones (17β-estradiol [E2]; trenbolone acetate [TBA]), tamoxifen (TAM), OXT, and atosiban (A: OXT receptor inhibitor) applied to bovine satellite cells (BSCs) to investigate BSC regulation by OXT. Oxytocin alone increased fusion index (P < 0.05) but not BSC proliferation. Oxytocin reduced (P < 0.05) apoptotic nuclei and stimulated migration rate (P < 0.05). Similarly, E2 and TBA increased (P < 0.05) BSC proliferation rate, fusion index, and migration and decreased (P < 0.05) apoptotic nuclei. 17β-Estradiol or TBA supplemented with A had lower (P < 0.05) BSC proliferation rate, fusion index, and migration and more (P < 0.05) apoptotic nuclei compared with E2 or TBA alone. Furthermore, OXT expression increased (P < 0.05) in E2 or TBA-treated proliferating BSC. Oxytocin, E2, and TBA increased (P < 0.05) MyoD and MyoG expression in proliferating BSC. During BSC differentiation, OXT expression increased (P < 0.05) with E2 or TBA treatments. MyoG expression increased (P < 0.05) in OXT, E2, and TBA compared with control. However, A, OXT + A, TAM, TAM + OXT, E2 + TAM, E2 + A, and TBA + A decreased (P < 0.05) MyoG expression during BSC differentiation. These results indicate that OXT is involved in steroid hormone-stimulated BSC activity.

Oxytocin effects on the inhibition of the NF-κB/miR195 pathway in mice breast cancer

Oxytocin (OT) has the suppressive effects on breast tumor formation and development. We hypothesized that OT through the NF-κB inhibition can induce the miR-195 up-regulation which it can promote the cell apoptosis and inhibit the cell proliferation. Thirty-two BALB/c female mice were equally divided into four groups to study the effects of OT and atosiban (ATO) (an oxytocin receptor antagonist) on the mammary tumor growth. The animal weight, OT plasma concentration, and the tumor weight and volume were measured. Moreover, the tumor-related signaling pathways including NF-κB, miR-195, and Cyclin D1 were evaluated by qPCR assays, and Akt and ERK proteins were assessed by western blot at the end of the study. The volume and weight of tumors were significantly decreased after OT administration. The phosphorylated Akt and ERK expressions were significantly decreased in the OT group compared to the tumor group. In contrast, the dephosphorylated Akt and ERK expressions were significantly increased in the OT group in comparison with the tumor group. The mRNA expressions of miR-195, OTR, and Bax genes were significantly increased, and the mRNA expression of ERα, PI3K, NF-κB, cyclin D1 and Bcl-2 genes were decreased in the OT group in comparison with the tumor group. Interestingly, ATO administration reversed these effects. These results can exhibit a new therapeutic potential for OT on the down-regulation of the NF-κB and up-regulation of miR-195 and consequently, decrease of the tumor volume and weight in a mouse model of breast cancer.

Signaling mediators modulated by cardioprotective interventions in healthy and diabetic myocardium with ischaemia-reperfusion injury

Ischaemic heart diseases are one of the major causes of death in the world. In most patients, ischaemic heart disease is coincident with other risk factors such as diabetes. Patients with diabetes are more prone to cardiac ischaemic dysfunctions including ischaemia-reperfusion injury. Ischaemic preconditioning, postconditioning and remote conditionings are reliable interventions to protect the myocardium against ischaemia-reperfusion injuries through activating various signaling pathways and intracellular mediators. Diabetes can disrupt the intracellular signaling cascades involved in these myocardial protections, and studies have revealed that cardioprotective effects of the conditioning interventions are diminished in the diabetic condition. The complex pathophysiology and poor prognosis of ischaemic heart disease among people with diabetes necessitate the investigation of the interaction of diabetes with ischaemia-reperfusion injury and cardioprotective mechanisms. Reducing the outcomes of ischaemia-reperfusion injury using targeted strategies would be particularly helpful in this population. In this study, we review the protective interventional signaling pathways and mediators which are activated by ischaemic conditioning strategies in healthy and diabetic myocardium with ischaemia-reperfusion injury.

Treatment with oestrogen-receptor agonists or oxytocin in conjunction with exercise protects against myocardial infarction in ovariectomized rats

NEW FINDINGS

What is the central question of this study? Could the activation of oxytocin or oestrogen receptors be protective against myocardial injury after ovariectomy? If so, would exercising have an additional ameliorating effect? What is the main finding and its importance? The results revealed that when accompanied by exercise, both oestrogen receptor agonists and oxytocin improved cardiac dysfunction, inhibited the generation of pro-inflammatory cytokines and reduced myocardial injury in ovariectomized female rats, suggesting a new approach for protecting postmenopausal women against ischaemia-induced myocardial injury. To investigate the putative protective effects of oxytocin or oestrogen receptor agonists against myocardial injury of ovariectomized sedentary or exercised rats, female Sprague-Dawley rats assigned to sham-operated control and ovariectomized (OVX) groups were kept sedentary or undertook swimming exercise for 4 weeks and were treated with saline, an oestrogen receptor (ER) β (DPN) or ERα agonist (PPT) or oxytocin. Ovariectomy increased weight gain and anxiety in sedentary rats, whereas exercise prevented weight gain. When accompanied by exercise, both ER agonists and oxytocin inhibited weight gain and anxiety; oxytocin, in the absence or presence of exercise, increased the left ventricular diastolic dimensions and ejection fraction, whereas ER agonists also increased left ventricular diameter when given to exercised rats. Upon the induction of myocardial ischaemia-reperfusion in the OVX rats, plasma creatine kinase-(muscle-brain) was depressed by PPT and oxytocin, whereas DPN, PPT and OT reduced plasminogen activator inhibitor-1 concentrations. The increased tumour necrosis factor-α concentration in OVX rats was also suppressed by exercise or DPN, PPT or oxytocin treatments, whereas the interleukin-6 concentration was diminished by all the treatments when given in conjunction with exercise. Disorganization of cardiac muscle fibres was reduced in all exercised rats. Oestrogen receptor agonists, as well as oxytocin, in conjunction with exercise may be effective new therapeutics to protect against myocardial ischaemia in postmenopausal women.

Oxytocin mediates the beneficial effects of the exercise training on breast cancer

NEW FINDINGS

What is the central question of this study? We hypothesized that potential anti-tumour effects of exercise training might be mediated by oxytocin and explored the underlying mechanisms in a mouse model of breast cancer. What is the main finding and its importance? Interval exercise training, by inducing oxytocin secretion, may reduce the activity of the PI3K/Akt and ERK pathways, and consequently, results in a smaller tumour volume in a mouse model of breast cancer. Exercise training can affect the growth of breast tumours. We hypothesized that exercise training might reduce breast tumour growth by inducing oxytocin (OT) secretion and its related signalling pathways, such as PI3K/Akt and ERK. Therefore, 56 BALB/c mice were equally divided into seven groups to study the effects of OT and atosiban (an oxytocin receptor antagonist) together with interval exercise training on mammary tumour growth, as well as tumour-related signalling pathways, including PI3K/Akt and ERK. Animal weight, OT plasma concentration, tumour weight and volume were measured at the end of the study. PI3K/Akt and ERK were evaluated by Western blot and qPCR assays. The results showed that OT plasma concentration was significantly increased in trained animals. The volume and weight of tumours were decreased significantly after both exercise training and OT administration. The expression of genes involved in tumour cell proliferation, such as PI3KR2, Akt and mTOR, was notably lower in the exercise-trained and OT-treated groups. Furthermore, the expression of genes involved in cell apoptosis, such as caspase-3 and Bax, was significantly increased in the tumour tissues. In addition, Western blot results showed that phosphorylated Akt and ERK were significantly decreased in the exercise training and OT groups compared with the tumour group. Interestingly, atosiban reversed these effects. These results indicated that interval exercise training, acting via OT secretion, may reduce PI3K/Akt and ERK axis activities, and consequently, decrease tumour volume and weight in a mouse model of breast cancer.

Effect of Normal Pregnancy Followed by Lactation on Long-Term Maternal Health in a Mouse Model

Although it has been widely accepted that pregnancies with complications are associated with increased maternal cardiovascular risk later in life, there is no consensus if noncomplicated pregnancy followed by lactation plays a protective role or is a risk factor. The objective of this study was to investigate the effects of normal pregnancy and lactation on long-term maternal health in a mouse model. CD-1 mice were allocated to breeding (primigravid [PG]) and nonbreeding (nulligravid [NG]) groups. The PG group proceeded through normal pregnancy and delivery. Using a telemetry system, blood pressure (BP) was analyzed in the PG group at 6 months postpartum and in age-matched NG mice. Serum analytes, gene expressions, and protein levels were determined using appropriate analysis methods. Primigravid mice had significantly lower systolic and diastolic BP and fasting glucose levels. Circulating oxytocin (OXT) levels were significantly higher in PG mice. Oxt gene expression was significantly higher in the heart and aorta and lower in visceral adipose tissue (VAT) from PG mice. The oxytocin receptor ( Oxtr) gene expression was significantly higher in the heart, aorta, and VAT from PG animals. The level of Oxtr DNA hypermethylation and the expression of mmu-miR-29a were significantly lower in the hearts of PG mice. In PG VAT, glucose transporter-4 expression was significantly higher. Our study demonstrates that a history of normal pregnancy followed by lactation was associated with lower maternal cardiovascular risk factors later in life in female mouse.

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.

Increased Activity of the Intracardiac Oxytocinergic System in the Development of Postinfarction Heart Failure

Aim. The present study was designed to test the hypothesis that the development of postinfarction heart failure is associated with a change of activity of the intracardiac oxytocinergic system. Methods. Experiments were performed on male Sprague-Dawley rats subjected to myocardial infarction or sham surgery. Four weeks after the surgery, blood samples were collected and the samples of the left ventricle (LV) and right ventricle (RV) were harvested for evaluation of the mRNA expression (RT-PCR) of oxytocin (OT), oxytocin receptor (OTR), natriuretic peptides, and the level of OT and OTR protein (ELISA). The concentration of N-terminal B-type natriuretic peptide was measured to determine the presence of heart failure. Results. Plasma NT-proBNP concentration was higher in the infarcted rats. In the infarcted rats, the expression of OT mRNA and the OT protein level were higher in the RV. There were no significant differences between infarcted and noninfarcted rats in the expression of OT mRNA and in the OT protein level in the fragments of the LV. In both the left and the right ventricles, OTR mRNA expression was lower but the level of OTR protein was higher in the infarcted rats. Conclusions. In the present study, we indicate that postinfarction heart failure is associated with an increased activity of the intracardiac oxytocinergic system.

Oxytocin's role on the cardiorespiratory activity of endotoxemic rats

BACKGROUND

Recent findings concerning oxytocin indicate its anti-inflammatory, cardioprotective and parasympathetic modulating properties. In this study, we investigated the effects of systemically applied oxytocin on the cardiorespiratory activity in a rodent model of moderate endotoxemia.

METHODS

Telemetrically recorded electrocardiogram (ECGs) from animals which received lipopolysaccharide (LPS); oxytocin (Ox); lipopolysaccharide+oxytocin (LPS+Ox), or vehicle (V) were analyzed using the ECG-derived respiration (EDR) technique to estimate the respiratory rate. The mean R-R interval and the spectral parameters of heart rate variability (HRV), such as the natural logarithm of the high frequency (lnHF) and low frequency (lnLF) components were also estimated up to 24h after treatment.

RESULTS

The endotoxemic animals (LPS) showed an elevated respiratory rate as well as a reduced mean R-R interval, lnHF and lnLF components compared to controls (V) from +5 to +12h after the treatment. The administration of oxytocin significantly attenuated the hyperventilation produced by the LPS-induced endotoxemia (LPS+Ox) and restored the values of the mean R-R interval and such spectral parameters at different time points.

CONCLUSIONS

Our results support the existence of a link among the respiratory, cardiovascular, and immune systems in which oxytocin seems to act as a potential cardioprotective peptide by favoring cardiac cholinergic autonomic coupling. As a result, oxytocin diminished animal's endotoxemic tachypnea and restored the cardiorespiratory interactions, which was indicated by the spectral components of HRV.

Prolonged Subcutaneous Administration of Oxytocin Accelerates Angiotensin II-Induced Hypertension and Renal Damage in Male Rats

Oxytocin and its receptor are synthesised in the heart and blood vessels but effects of chronic activation of this peripheral oxytocinergic system on cardiovascular function are not known. In acute studies, systemic administration of low dose oxytocin exerted a protective, preconditioning effect in experimental models of myocardial ischemia and infarction. In this study, we investigated the effects of chronic administration of low dose oxytocin following angiotensin II-induced hypertension, cardiac hypertrophy and renal damage. Angiotensin II (40 μg/Kg/h) only, oxytocin only (20 or 100 ng/Kg/h), or angiotensin II combined with oxytocin (20 or 100 ng/Kg/h) were infused subcutaneously in adult male Sprague-Dawley rats for 28 days. At day 7, oxytocin or angiotensin-II only did not change hemodynamic parameters, but animals that received a combination of oxytocin and angiotensin-II had significantly elevated systolic, diastolic and mean arterial pressure compared to controls (P < 0.01). Hemodynamic changes were accompanied by significant left ventricular cardiac hypertrophy and renal damage at day 28 in animals treated with angiotensin II (P < 0.05) or both oxytocin and angiotensin II, compared to controls (P < 0.01). Prolonged oxytocin administration did not affect plasma concentrations of renin and atrial natriuretic peptide, but was associated with the activation of calcium-dependent protein phosphatase calcineurin, a canonical signalling mechanism in pressure overload-induced cardiovascular disease. These data demonstrate that oxytocin accelerated angiotensin-II induced hypertension and end-organ renal damage, suggesting caution should be exercised in the chronic use of oxytocin in individuals with hypertension.

Balance of nitric oxide and reactive oxygen species in myocardial reperfusion injury and protection

Depending on their concentrations, both nitric oxide (NO) and reactive oxygen species (ROS) take part either in myocardial ischemia reperfusion injury or in protection by ischemic and pharmacological preconditioning (Ipre) and postconditioning (Ipost). At the beginning of reperfusion, a transient release of NO is promptly scavenged by ROS to form the highly toxic peroxynitrite, which is responsible for a further increase of ROS through endothelial nitric oxide synthase uncoupling. The protective role of NO has suggested the use of NO donors to mimic Ipre and Ipost. However, NO donors have not always given the expected protection, possibly because they are responsible for the production of different amounts of ROS that depend on the amount of released NO. This review is focused on the role of the balance of NO and ROS in myocardial injury and its prevention by Ipre and Ipost and after the use of NO donors given with or without antioxidant compounds to mimic Ipre and Ipost.

Catestatin increases the expression of anti-apoptotic and pro-angiogenetic factors in the post-ischemic hypertrophied heart of SHR

Background

In the presence of comorbidities the effectiveness of many cardioprotective strategies is blunted. The goal of this study was to assess in a hypertensive rat model if the early reperfusion with anti-hypertensive and pro-angiogenic Chromogranin A-derived peptide, Catestatin (CST:hCgA_352–372; CST-Post), protects the heart via Reperfusion-Injury-Salvage-Kinases (RISK)-pathway activation, limiting infarct-size and apoptosis, and promoting angiogenetic factors (e.g., hypoxia inducible factor, HIF-1α, and endothelial nitric oxide synthase, eNOS, expression).

Methods and Results

The effects of CST-Post on infarct-size, apoptosis and pro-angiogenetic factors were studied in isolated hearts of spontaneously hypertensive rats (SHR), which underwent the following protocols: (a) 30-min ischemia and 120-min reperfusion (I/R); (b) 30-min ischemia and 20-min reperfusion (I/R-short), both with and without CST-Post (75 nM for 20-min at the beginning of reperfusion). In unprotected Wistar-Kyoto hearts, used as normal counterpart, infarct-size resulted smaller than in SHR. CST-Post reduced significantly infarct-size and improved post-ischemic cardiac function in both strains. After 20-min reperfusion, CST-Post induced S-nitrosylation of calcium channels and phosphorylation of RISK-pathway in WKY and SHR hearts. Yet specific inhibitors of the RISK pathway blocked the CST-Post protective effects against infarct in the 120-min reperfusion groups. Moreover, apoptosis (evaluated by TUNEL, ARC and cleaved caspase) was reduced by CST-Post. Importantly, CST-Post increased expression of pro-angiogenetic factors (i.e., HIF-1α and eNOS expression) after two-hour reperfusion.

Conclusions

CST-Post limits reperfusion damages and reverses the hypertension-induced increase of I/R susceptibility. Moreover, CST-Post triggers antiapoptotic and pro-angiogenetic factors suggesting that CST-Post can be used as an anti-maladaptive remodeling treatment.

Oxytocin has therapeutic effects on cancer, a hypothesis

Oxytocin (OT) is the first peptide hormone structurally assessed and chemically synthesized in biologically active form. This hormone acts as an important factor in a human reproductive system particularly during pregnancy and lactation in women. So far, different therapeutic roles for OT have been identified as a spectrum from central and peripheral actions on male and female reproductive systems, circulatory system, musculoskeletal system, etc. Some in vitro and in vivo studies also revealed that OT is responsible for bivariate biological functions involved in cancer as following. By activating OT receptor in tumoral cells, OT enacts as a growth regulator, whether activator or inhibitor. Regarding the increase of OT in some conditions such as breastfeeding, exercise, and multiparity, we can relate the effect of these conditions on cancer with OT effects. Based on this hypothesis, we present a review on the effects of this neuropeptide on various types of cancer and also the influence of these conditions on the same cancer.

Oxytocin improves follicular reserve in a cisplatin-induced gonadotoxicity model in rats

Cisplatin (CP), an antitumor agent, has been shown to cause ovarian injury and dysfunction in both animal and human studies. The present study was conducted to investigate the protective effect of oxytocin (OT) on CP-induced ovarian toxicity in rats. Twenty-one adult female rats were included in the study. Fourteen rats were administered intraperitoneally CP (2 mg/kg/day) twice a week for 5 weeks. Control group (n = 7) did not receive any treatment. Following treatment, CP-received rats were randomly divided into two groups and treated with either saline (1 mL/kg/day, n = 7) or OT (160 μg/kg/day, n = 7) for 5 weeks. Then, ovarian toxicity and effects of OT were evaluated by histomorphological and biochemical analysis. Our findings revealed a significant reduction in the number of follicles at each grade in saline-treated group. AMH level was significantly lower in saline group compared to control (P < 0.0005). OT treatment significantly attenuated CP toxicity in ovaries and increased AMH levels compared to saline group (P < 0.005). Also, administration of OT lessened lipid peroxidation and prevented glutathione depletion in CP-treated rats (P < 0.05). These results indicated that OT could lessen the CP-induced ovarian damage and improve follicular reserve by preventing oxidative damage.

Is oxytocin a therapeutic factor for ischemic heart disease?

Ischemic heart disease (IHD) is among the most important and top ranked causes of death in the world, and its preventive and interventional mechanisms are actively being investigated. Preconditioning may still be beneficial in some situations such as IHD. Development of cardioprotective agents to improve myocardial function, to decrease the incidence of arrhythmias, to delay the onset of necrosis, and to limit the total extent of infarction during IHD is of great clinical importance. In order to reduce morbidity, a new treatment modality must be developed, and oxytocin may indeed be one of the candidates. There is increasing experimental evidence indicating that oxytocin may have cardioprotective effects either by decreasing the extent of reperfusion injury or by pharmacologic preconditioning activity. This review shows that in the presence of oxytocin, the cardioprotective effects may be increased to some extent. The presented board of evidence focuses on the valuable effects of oxytocin on myocardial function and candidates it for future clinical studies in the realm of ischemic heart diseases.