Oxytocin: Old Hormone, New Drug

Microbes, oxytocin and stress: Converging players regulating eating behavior

Oxytocin is a peptide-hormone extensively studied for its multifaceted biological functions and has recently gained attention for its role in eating behavior, through its action as an anorexigenic neuropeptide. Moreover, the gut microbiota is involved in oxytocinergic signaling through the brain-gut axis, specifically in the regulation of social behavior. The gut microbiota is also implicated in appetite regulation and is postulated to play a role in central regulation of hedonic eating. In this review, we provide an overview on oxytocin and its individual links with the microbiome, the homeostatic and non-homeostatic regulation of eating behavior as well as social behavior and stress.

Relationship between oxytocin receptor gene polymorphism and hypertension in Turkish population

INTRODUCTION AND OBJECTIVES

Known to play a key role in uterine contraction and milk ejection, the neuropeptide, oxytocin, has cardiovascular effects. To date, the known cardiovascular effects of oxytocin are blood pressure lowering (caused by natriuresis and atrial natriuretic peptide release), negative inotropic and chronotropic effect caused by parasympathetic neuromodulation, anti-stress effect and vasodilation mediated by activation of the nitric oxide pathway. The clinical significance of the rs2268498 polymorphism in oxytocin receptors in these effects is controversial. Based on the known genetic inheritance of hypertension, our research aimed to determine whether the presence of the rs2268498 oxytocin receptor (OXTR) allele C affects hypertension in our region.

METHODS

This article is a case-control study conducted in the Turkish population. About 140 normotensive and 140 isolated hypertensive volunteers included in the research and genotyped with real-time PCR hybridization method via melt curve analysis.

RESULTS

Oxytocin receptor rs2268498 polymorphism was assessed in terms of the risk of hypertension and hypertensive individuals were compared to the control group. OXTR rs2268498 polymorphism was not found to be a significant risk factor for dominant, recessive and additive modeled hypertension (ORdominant: 0.966, 95% CI: 0.57-1.61, p: 0.9; ORrecessive: 1, 95% CI: 0.58-1.71, p: 1.0 and ORoverall: 0.98, chi2=0.01).

CONCLUSION

We concluded that rs2268498 single nucleotide polymorphism is not a risk factor for hypertension in our region.

Ameliorative Effect of Oxytocin on FBN1 and PEPCK Gene Expression, and Behavioral Patterns in Rats' Obesity-Induced Diabetes

Amelioration of hyperinsulinemia and insulin resistance associated with obesity is a cardinal target for therapeutics. Therefore, we investigated the relation of Fibrilln-1 (FBN1) mRNA expression and hepatic phosphoenolpyruvate caboxykinase (PEPCK) enzyme to the ameliorative impact of oxytocin on obesity-induced diabetes, suggesting glycogenolysis markers in diabetic models. Four groups of forty male Wistar rats were formed (n = 10): a control group fed basal diet and intraperitoneal injections of saline; an oxytocin-injected group; a diet-induced obese group fed a high-fat/high-sugar diet and injected with saline; a diet-induced obese group injected with oxytocin. Depending on blood glucose levels, obese groups were further sub-grouped into prediabetic, and diabetic rats, with 5 rats each, at the ninth and the 16th week of the feeding period, respectively. FBN1 expression and PEPCK activity were determined using the qPCR technique and some biochemical parameters (glycemic, lipid profile, kidney, and liver functions) were determined using kits. Obese groups showed an elevation of brain FBN1 expression, high serum lipid profile, high glucose level, and a deleterious impact on liver and kidney functions. Obese groups showed the stimulator effect of the PEPCK enzyme and time-dependent pathological changes in renal and hepatic tissues. The motor activities were negatively correlated with FBN1 gene expression in prediabetic and diabetic rats. In addition to our previous review of the crucial role of asprosin, here we showed that oxytocin could ameliorate obesity-induced diabetes and decrease FBN1 gene expression centrally to block appetite. Oxytocin caused decreases in PEPCK enzyme activity as well as glycogenolysis in the liver. Therefore, oxytocin has a potential effect on FBN1 expression and PEPCK enzyme activity in the obesity-induced diabetic-rat model.

Role of oxytocin and c-Myc pathway in cardiac remodeling in neonatal rats undergoing cardiac apical resection

Oxytocin (OT) is a nonapeptide hormone that can improve cardiomyocyte proliferation, suggesting a potential heart regeneration function. Here, we investigated the role of oxytocin and the c-Myc pathway in cardiac remodeling in neonatal rats undergoing cardiac apical resection. We have utilized a knockout of oxytocin receptor (OTR) with OTR-shRNA. A neonatal rat model of cardiac resection (≈10%-15%) was first established. The protein levels of OTR and c-Myc and the expression of cyclin d1 and c-Myc genes were then evaluated in the cardiac tissues at 1, 7, and 21 days after cardiac resection. We also analyzed the proliferation of cardiomyocytes through α-actinin, BrdU, and ki-67 markers. At last, the hemodynamic and electrophysiologic functions were evaluated eight weeks after cardiac resection. At 21 days, the regeneration of cardiomyocytes was repaired among rats in the control and resection groups, while OTR-shRNA groups were failed to improve. Inhibition of OTR failed cardiac regeneration and reduced the number of proliferating cardiomyocytes. The c-Myc protein was significantly reduced in the OTR-shRNA injection hearts. Moreover, we have severely found a depressed heart function in the OTR-shRNA injection animals. These observations revealed that the OT must improve cardiac remodeling in neonatal rat hearts by regulating the c-Myc pathway.

Influence of the Type of Delivery, Use of Oxytocin, and Maternal Age on POU5F1 Gene Expression in Stem Cells Derived from Wharton's Jelly within the Umbilical Cord

The paper presents an evaluation of the POU5F1 gene expression in mesenchymal stem cells derived from Wharton's jelly within the umbilical cord, collected from 36 patients during labor. The study is the first one to show that the expression of POU5F1 in mesenchymal stem cells has been dependent on maternal age, birth order, route of delivery, and use of oxytocin. Our research proves that the POU5F1 gene expression in mesenchymal stem cells decreases with each subsequent pregnancy and delivery. Wharton's jelly stem cells obtained from younger women and during their first delivery, as well as patients treated with oxytocin, show higher POU5F1 gene expression when compared with the subsequent deliveries. This leads to a conclusion that they are characterized by a lower level of differentiation, which in turn results in their greater plasticity and greater proliferative potential. Probably, they are also clinically more useful.

The spiking and secretory activity of oxytocin neurones in response to osmotic stimulation: a computational model

KEY POINTS

A quantitative model of oxytocin neurones that combines a spiking model, a model of stimulus-secretion coupling and a model of plasma clearance of oxytocin was tested. To test the model, a variety of sources of published data were used that relate either the electrical activity of oxytocin cells or the secretion of oxytocin to experimentally induced changes in plasma osmotic pressure. To use these data to test the model, the experimental challenges involved were computationally simulated. The model predictions closely matched the reported outcomes of the different experiments.

ABSTRACT

Magnocellular vasopressin and oxytocin neurones in the rat hypothalamus project to the posterior pituitary, where they secrete their products into the bloodstream. In rodents, both vasopressin and oxytocin magnocellular neurones are osmoresponsive, and their increased spiking activity is mainly a consequence of an increased synaptic input from osmoresponsive neurons in regions adjacent to the anterior wall of the third ventricle. Osmotically stimulated vasopressin secretion promotes antidiuresis while oxytocin secretion promotes natriuresis. In this work we tested a previously published computational model of the spiking and secretion activity of oxytocin cells against published evidence of changes in spiking activity and plasma oxytocin concentration in response to different osmotic challenges. We show that integrating this oxytocin model with a simple model of the osmoresponsive inputs to oxytocin cells achieves a strikingly close match to diverse sources of data. Comparing model predictions with published data using bicuculline to block inhibitory GABA inputs supports the conclusion that inhibitory inputs and excitatory inputs are co-activated by osmotic stimuli. Finally, we studied how the gain of osmotically stimulated oxytocin release changes in the presence of a hypovolaemic stimulus, showing that this is best explained by an inhibition of an osmotically regulated inhibitory drive to the magnocellular neurones.

The Relationship between the Serum Oxytocin Levels, Disease Activity, the ADLs and the QOL in Patients with Rheumatoid Arthritis

Objective To investigate the factors associated with depression, including the serum oxytocin (OXT) levels, disease activity, activities of daily living (ADLs) and quality of life (QOL), and their effects on rheumatoid arthritis (RA). Methods This study included 42-RA-patients. We measured the following variables before and after 6 months of treatment with biological disease-modifying antirheumatic drugs (bDMARDs): the baseline characteristics (including age, sex, disease duration, smoking, and body mass index), the doses of prednisolone and methotrexate, the serum level of matrix metalloprotease-3, the erythrocyte sedimentation rate and the C-reactive protein level. The disease activity of RA was assessed using the Simplified Disease Activity Index (SDAI), depression was assessed using the Hamilton Depression Rating Scale (HAM-D), the ADLs were assessed using the Health Assessment Questionnaire disability index and the QOL was assessed using the Short Form (SF)-36. The serum OXT levels were determined using an enzyme-linked immunosorbent assay. Results The HAM-D score was significantly correlated with the SDAI, and the mental component summary score of the SF-36. However, the serum OXT levels were not correlated with the HAM-D score. The serum OXT levels before and after bDMARDs treatment did not differ to a statistically significant extent, regardless of the presence of depression. Although the differences in the serum levels of OXT were observed prior to the initiation of treatment, there was no gender difference after treatment. Conclusion Although RA complicated by depression may be related to the following high disease activity, a poor QOL and poor ADLs, the serum OXT levels were not directly correlated.

The effect of exogenous oxytocin on streptozotocin (STZ)-induced diabetic adult rat testes

Oxytocin (OXY) plays a crucial role in reproduction. The aim of this study is to investigate the therapeutic and protective effects of oxytocin treatment on streptozotocin (STZ) induced diabetes in testicular tissue. The rats were randomly divided into four experimental groups: (I) Control Group, (II) STZ induced Diabetic Group (STZ Group), (III) STZ induced Diabetic Group with Pre-Oxytocin treatment (Pre-OXY Group) and (IV) STZ induced Diabetic Group with Post-Oxytocin treatment (Post-OXY Group); each group contains six animals. The rats whose blood glucose levels were more than 200mg/dl were included to the experiment. At the end of the 4th week, testes tissue samples were taken to be processed for light microscopy and transmission electron microscopy. Malondialdehyde (MDA), Glutathione (GSH) and Advanced Oxidation Protein Products (AOPP) levels were determined biochemically in blood samples. Testicular tissue samples stained with Hematoxylin and Eosin (H&E) and Periodic acid-Schiff (PAS) reaction were evaluated under light microscope. The histopathological damage score of testicular tissue, which was significantly increased in STZ group, was decreased by oxytocin treatment. According to biochemical data, MDA and AOPP levels have been increased in the blood of STZ Group compared to the Control Group whereas they decreased significantly in Oxytocin-treated Groups compared to STZ Group. GSH levels were significantly decreased in the blood of STZ Group and increased in the blood of Oxytocin-treated Groups compared to STZ Group. In conclusion, oxytocin has a potential protective effect on the testes tissue of STZ-induced diabetic rats.

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.

Amelioration of rotenone-induced dopaminergic cell death in the striatum by oxytocin treatment

Oxytocin (OT) is essentially associated with uterine contraction during parturition and milk ejection reflex. Although several studies implicate the role of OT in anti-inflammatory, anti-oxidative and anti-apoptotic pathways, there is a lack of data with regard to the protective effects of oxytocin in neurodegenerative models such as Parkinson's disease (PD). The present study was undertaken to investigate the neuroprotective effects of oxytocin (OT) on rotenone-induced PD in rats. Twenty adult Sprague-Dawley rats were injected with rotenone (3 μg/μl in DMSO) or vehicle (1 μl DMSO) into the left substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) under stereotaxic surgery, and PD model was assessed by rotational test ten days after drug infusion. The valid PD rats were randomly divided into two groups; Group 1 (n=7) and Group 2 (n=7) were administered saline (1 ml/kg/day, i.p.) and oxytocin (160 μg/kg/day, i.p.) through 20 days, respectively. The effects of OT treatment were evaluated by behavioral, histological and immunohistochemical parameters. Apomorphine-induced stereotypic rotations in PD rats were significantly inhibited by OT treatment (p<0.05). In addition, immunohistochemical studies clearly demonstrated the suppression of Bax, caspase-3, caspase-8 and elevation of Bcl-2 and tyrosine hydroxylase immunoexpression in OT-treated rats compared to saline group. Our findings suggest that oxytocin may have cytoprotective and restorative effects on dopaminergic neurons against rotenone-induced injury. The underlying mechanism may be associated with the inhibition of apoptotic pathways.

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

Ischemia-reperfusion injury is a common complication of heart disease that is the leading cause of death worldwide. Here, we plan to elucidate oxytocin cardioprotection effects against ischemia-reperfusion via nitric oxide (NO), reactive oxygen species (ROS), and protein kinase C (PKC) in anesthetized rat preconditioned myocardium. Forty-eight Sprague-Dawley rats were equally divided into eight groups. All animals were subjected to 25 min ischemia and 120 min reperfusion. Oxytocin (OT), L-NAME (LNA, a nitric oxide synthase inhibitor), chelerythrine (CHE, a PKC enzyme inhibitor), and N-acetylcysteine (NAC, a ROS scavenger) were used prior to ischemia. Results showed that mean arterial pressure significantly reduced during the first 10 min of ischemia and reperfusion in IR, LNA, CHE, and NAC groups (p<0.05). OT prevented mean arterial pressure decline during early phase of ischemia and reperfusion. Cardioprotective effects of OT in infarct size, plasma levels of creatine kinase-MB and lactate dehydrogenase, severity and incidence of ventricular arrhythmias were abolished by L-NAME, chelerythrine, and N-acetylcysteine (p<0.05). The present study showed that OT pretreatment reduces myocardial infarct size and ventricular arrhythmias, and improves mean arterial pressure via NO production, PKC activation, and ROS balance. These findings provide new insight into therapeutic strategies for ischemic heart disease.

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.