Effects of hydrogen sulfide (H2S) on water intake and vasopressin and oxytocin secretion induced by fluid deprivation

Role of Sex and Early Life Stress Experience on Porcine Cardiac and Brain Tissue Expression of the Oxytocin and H2S Systems

Early life stress (ELS) significantly increases the risk of chronic cardiovascular diseases and may cause neuroinflammation. This post hoc study, based on the material available from a previous study showing elevated "serum brain injury markers" in male control animals, examines the effect of sex and/or ELS on the cerebral and cardiac expression of the H2S and oxytocin systems. Following approval by the Regional Council of Tübingen, a randomized controlled study was conducted on 12 sexually mature, uncastrated German Large White swine of both sexes. The control animals were separated from their mothers at 28-35 days, while the ELS group was separated at day 21. At 20-24 weeks, animals underwent anesthesia, ventilation, and surgical instrumentation. An immunohistochemical analysis of oxytocin, its receptor, and the H2S-producing enzymes cystathionine-β-synthase and cystathionine-γ-lyase was performed on hypothalamic, prefrontal cortex, and myocardial tissue samples. Data are expressed as the % of positive tissue staining, and differences between groups were tested using a two-way ANOVA. The results showed no significant differences in the oxytocin and H2S systems between groups; however, sex influenced the oxytocin system, and ELS affected the oxytocin and H2S systems in a sex-specific manner. No immunohistochemical correlate to the elevated "serum brain injury markers" in male controls was identified.

Hydrogen sulfide and its role in female reproduction

Hydrogen sulfide (H2S) is a gaseous signaling molecule produced in the body by three enzymes: cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). H2S is crucial in various physiological processes associated with female mammalian reproduction. These include estrus cycle, oocyte maturation, oocyte aging, ovulation, embryo transport and early embryo development, the development of the placenta and fetal membranes, pregnancy, and the initiation of labor. Despite the confirmed presence of H2S-producing enzymes in all female reproductive tissues, as described in this review, the exact mechanisms of H2S action in these tissues remain in most cases unclear. Therefore, this review aims to summarize the knowledge about the presence and effects of H2S in these tissues and outline possible signaling pathways that mediate these effects. Understanding these pathways may lead to the development of new therapeutic strategies in the field of women's health and perinatal medicine.

Decreased levels of hydrogen sulfide in the hypothalamic paraventricular nucleus contribute to sympathetic hyperactivity induced by cerebral infarction

Paroxysmal sympathetic hyperactivity (PSH) is a common clinical feature secondary to ischemic stroke (IS), but its mechanism is poorly understood. We aimed to investigate the role of H2S in the pathogenesis of PSH. IS patients were divided into malignant (MCI) and non-malignant cerebral infarction (NMCI) group. IS in rats was induced by the right middle cerebral artery occlusion (MCAO). H2S donor (NaHS) or inhibitor (aminooxy-acetic acid, AOAA) were microinjected into the hypothalamic paraventricular nucleus (PVN). Compared with the NMCI group, patients in the MCI group showed PSH, including tachycardia, hypertension, and more plasma norepinephrine (NE) that was positively correlated with levels of creatine kinase, glutamate transaminase, and creatinine respectively. The 1-year survival rate of patients with high plasma NE levels was lower. The hypothalamus of rats with MCAO showed increased activity, especially in the PVN region. The levels of H2S in PVN of the rats with MCAO were reduced, while the blood pressure and renal sympathetic discharge were increased, which could be ameliorated by NaHS and exacerbated by AOAA. NaHS completely reduced the disulfide bond of NMDAR1 in PC12 cells. The inhibition of NMDAR by MK-801 microinjected in PVN of rats with MCAO also could lower blood pressure and renal sympathetic discharge. In conclusion, PSH may be associated with disease progression and survival in patients with IS. Decreased levels of H2S in PVN were involved in regulating sympathetic efferent activity after cerebral infarction. Our results might provide a new strategy and target for the prevention and treatment of PSH.

Thirst: neuroendocrine regulation in mammals

Animals can sense their changing internal needs and then generate specific physiological and behavioural responses in order to restore homeostasis. Water-saline homeostasis derives from balances of water and sodium intake and output (drinking and diuresis, salt appetite and natriuresis), maintaining an appropriate composition and volume of extracellular fluid. Thirst is the sensation which drives to seek and consume water, regulated in the central nervous system by both neural and chemical signals. Water and electrolyte homeostasis depends on finely tuned physiological mechanisms, mainly susceptible to plasma Na+ concentration and osmotic pressure, but also to blood volume and arterial pressure. Increases of osmotic pressure as slight as 1-2% are enough to induce thirst ("homeostatic" or cellular), by activation of specialized osmoreceptors in the circumventricular organs, outside the blood-brain barrier. Presystemic anticipatory signals (by oropharyngeal or gastrointestinal receptors) inhibit thirst when fluids are ingested, or stimulate thirst associated with food intake. Hypovolemia, arterial hypotension, Angiotensin II stimulate thirst ("hypovolemic thirst", "extracellular dehydration"). Hypervolemia, hypertension, Atrial Natriuretic Peptide inhibit thirst. Circadian rhythms of thirst are also detectable, driven by suprachiasmatic nucleus in the hypothalamus. Such homeostasis and other fundamental physiological functions (cardiocircolatory, thermoregulation, food intake) are highly interdependent.

Brain Histology and Immunohistochemistry After Resuscitation From Hemorrhagic Shock in Swine With Pre-Existing Atherosclerosis and Sodium Thiosulfate (Na2S2O3) Treatment

Background

The hydrogen sulfide (H₂S) and the oxytocin/oxytocin receptor (OT/OTR) systems interact in the central nervous and cardiovascular system. As a consequence of osmotic balance stress, H₂S stimulates OT release from the paraventricular nuclei (PVN) in the hypothalamic regulation of blood volume and pressure. Hemorrhagic shock (HS) represents one of the most pronounced acute changes in blood volume, which, moreover, may cause at least transient brain tissue hypoxia. Atherosclerosis is associated with reduced vascular expression of the main endogenous H₂S producing enzyme cystathionine-γ-lyase (CSE), and, hence, exogenous H₂S administration could be beneficial in these patients, in particular after HS. However, so far cerebral effects of systemic H₂S administration are poorly understood. Having previously shown lung-protective effects of therapeutic Na₂S₂O₃ administration in a clinically relevant, long-term, porcine model of HS and resuscitation we evaluated if these protective effects were extended to the brain.

Methods

In this study, available unanalyzed paraffin embedded brain sections (Na₂S₂O₃N = 8 or vehicle N = 5) of our recently published HS study were analyzed via neuro-histopathology and immunohistochemistry for the endogenous H₂S producing enzymes, OT, OTR, and markers for brain injury and oxidative stress (glial fibrillary acidic protein (GFAP) and nitrotyrosine).

Results

Neuro-histopathological analysis revealed uninjured brain tissue with minor white matter edema. Protein quantification in the hypothalamic PVN showed no significant inter-group differences between vehicle or Na₂S₂O₃ treatment.

Conclusions

The endogenous H₂S enzymes, OT/OTR co-localized in magnocellular neurons in the hypothalamus, which may reflect their interaction in response to HS-induced hypovolemia. The preserved blood brain barrier (BBB) may have resulted in impermeability for Na₂S₂O₃ and no inter-group differences in the PVN. Nonetheless, our results do not preclude that Na₂S₂O₃ could have a therapeutic benefit in the brain in an injury that disrupts the BBB, e.g., traumatic brain injury (TBI) or acute subdural hematoma (ASDH).

Localization of the hydrogen sulfide and oxytocin systems at the depth of the sulci in a porcine model of acute subdural hematoma

In the porcine model discussed in this review, the acute subdural hematoma was induced by subdural injection of autologous blood over the left parietal cortex, which led to a transient elevation of the intracerebral pressure, measured by bilateral neuromonitoring. The hematoma-induced brain injury was associated with albumin extravasation, oxidative stress, reactive astrogliosis and microglial activation in the ipsilateral hemisphere. Further proteins and injury markers were validated to be used for immunohistochemistry of porcine brain tissue. The cerebral expression patterns of oxytocin, oxytocin receptor, cystathionine-γ-lyase and cystathionine-β-synthase were particularly interesting: these four proteins all co-localized at the base of the sulci, where pressure-induced brain injury elicits maximum stress. In this context, the pig is a very relevant translational model in contrast to the rodent brain. The structure of the porcine brain is very similar to the human: the presence of gyri and sulci (gyrencephalic brain), white matter to grey matter proportion and tentorium cerebelli. Thus, pressure-induced injury in the porcine brain, unlike in the rodent brain, is reflective of the human pathophysiology.

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.

Biological Connection of Psychological Stress and Polytrauma under Intensive Care: The Role of Oxytocin and Hydrogen Sulfide

This paper explored the potential mediating role of hydrogen sulfide (H2S) and the oxytocin (OT) systems in hemorrhagic shock (HS) and/or traumatic brain injury (TBI). Morbidity and mortality after trauma mainly depend on the presence of HS and/or TBI. Rapid "repayment of the O2 debt" and prevention of brain tissue hypoxia are cornerstones of the management of both HS and TBI. Restoring tissue perfusion, however, generates an ischemia/reperfusion (I/R) injury due to the formation of reactive oxygen (ROS) and nitrogen (RNS) species. Moreover, pre-existing-medical-conditions (PEMC's) can aggravate the occurrence and severity of complications after trauma. In addition to the "classic" chronic diseases (of cardiovascular or metabolic origin), there is growing awareness of psychological PEMC's, e.g., early life stress (ELS) increases the predisposition to develop post-traumatic-stress-disorder (PTSD) and trauma patients with TBI show a significantly higher incidence of PTSD than patients without TBI. In fact, ELS is known to contribute to the developmental origins of cardiovascular disease. The neurotransmitter H2S is not only essential for the neuroendocrine stress response, but is also a promising therapeutic target in the prevention of chronic diseases induced by ELS. The neuroendocrine hormone OT has fundamental importance for brain development and social behavior, and, thus, is implicated in resilience or vulnerability to traumatic events. OT and H2S have been shown to interact in physical and psychological trauma and could, thus, be therapeutic targets to mitigate the acute post-traumatic effects of chronic PEMC's. OT and H2S both share anti-inflammatory, anti-oxidant, and vasoactive properties; through the reperfusion injury salvage kinase (RISK) pathway, where their signaling mechanisms converge, they act via the regulation of nitric oxide (NO).

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.

ΔMST and the Regulation of Cardiac CSE and OTR Expression in Trauma and Hemorrhage

Genetic deletion of 3-mercaptopyruvate sulfurtransferase (MST) is known to result in hypertension and cardiac hypertrophy in older mice, and is associated with increased anxiety-like behaviors. Endogenous hydrogen sulfide (H2S) produced by MST in the mitochondria is also known to be involved in physiological and cellular bioenergetics, and its dysfunction associated with depressive behavior and increased cardiovascular morbidity. Interestingly, early life stress has been shown to lead to a significant loss of cystathionine-γ-lyase (CSE) and oxytocin receptor (OTR) expression in the heart. Thus, we were interested in testing the hypothesis of whether genetic MST mutation (ΔMST) would affect cardiac CSE and OTR expression and affect the mitochondrial respiration in a clinically relevant, resuscitated, mouse model of trauma and hemorrhagic shock. In ΔMST mice, we found a reduction of CSE and OTR in both the naive as well as injured state, in contrast to the wild type (wt) controls. Interestingly, the ΔMST showed a different complex IV response to injury than the wt controls, although our claims are based on the non-demonstrated assumption that naive wt and naive ΔMST mice have comparable complex IV activity. Finally, hemorrhagic shock led to a reduction of CSE and OTR, confirming previous results in the injured mouse heart. To date, the exact mechanisms of the cardiac interaction between H2S and OT are not clear, but they point the way to potential cardioprotective therapies.

Role of Hydrogen Sulfide in the Endocrine System

Hydrogen sulfide (H₂S), as one of the three known gaseous signal transduction molecules in organisms, has attracted a surging amount of attention. H₂S is involved in a variety of physiological and pathological processes in the body, such as dilating blood vessels (regulating blood pressure), protecting tissue from ischemia-reperfusion injury, anti-inflammation, carcinogenesis, or inhibition of cancer, as well as acting on the hypothalamus and pancreas to regulate hormonal metabolism. The change of H₂S concentration is related to a variety of endocrine disorders, and the change of hormone concentration also affects the synthesis of H₂S. Understanding the effect of biosynthesis and the concentration of H₂S on the endocrine system is useful to develop drugs for the treatment of hypertension, diabetes, and other diseases.

Effects of endogenous H2S production inhibition on the homeostatic responses induced by acute high-salt diet consumption

The gaseous modulator hydrogen sulfide (H₂S) is synthesized, among other routes, by the action of cystathionine-γ-lyase (CSE) and importantly participates in body fluid homeostasis. Therefore, the present study aimed to evaluate the participation of H₂S in behavioral, renal and neuroendocrine homeostatic responses triggered by the acute consumption of a high Na⁺ diet. After habituation, adult male Wistar rats were randomly distributed and maintained for seven days on a control [CD (0.27% of Na⁺)] or hypersodic diet [HD (0.81% of Na⁺)]. CD and HD-fed animals were treated with DL-Propargylglycine (PAG, 25 mg/kg/day, ip) or vehicle (0.9% NaCl in equivalent volume) for the same period. At the end of the experiment, animals were euthanized for blood and tissue collection. We demonstrated that a short-term increase in dietary Na⁺ intake, in values that mimic the variations in human consumption (two times the recommended) significantly modified hydroelectrolytic homeostasis, with repercussions in the hypothalamic-neurohypophysial system and hypothalamic-pituitary-adrenal axis function. These findings were accompanied by the development of a clear inflammatory response in renal tubular cells and microvascular components. On the other hand, the inhibition of the endogenous production of H₂S by CSE provided by PAG treatment prevented the inflammation induced by HD. In the kidney, PAG treatment induced the overexpression of inducible nitric oxide synthase in animals fed with HD. Taken together, these data suggest, therefore, that HD-induced H₂S production plays an important proinflammatory role in the kidney, apparently counter regulating nitric oxide actions in renal tissue.

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.

Cerebral Immunohistochemical Characterization of the H2S and the Oxytocin Systems in a Porcine Model of Acute Subdural Hematoma

The hydrogen sulfide (H₂S) and the oxytocin/oxytocin receptor (OT/OTR) systems interact in trauma and are implicated in vascular protection and regulation of fluid homeostasis. Acute brain injury is associated with pressure-induced edema formation, blood brain barrier disruption, and neuro-inflammation. The similarities in brain anatomy: size, gyrencephalic organization, skull structure, may render the pig a highly relevant model for translational medicine. Cerebral biomarkers for pigs for pathophysiological changes and neuro-inflammation are limited. The current study aims to characterize the localization of OT/OTR and the endogenous H₂S producing enzymes together with relevant neuro-inflammatory markers on available porcine brain tissue from an acute subdural hematoma (ASDH) model. In a recent pilot study, anesthetized pigs underwent ASDH by injection of 20 mL of autologous blood above the left parietal cortex and were resuscitated with neuro-intensive care measures. After 54 h of intensive care, the animals were sacrificed, the brain was removed and analyzed via immunohistochemistry. The endogenous H₂S producing enzymes cystathionine-ɤ-lyase (CSE) and cystathionine-β-synthase (CBS), the OTR, and OT were localized in neurons, vasculature and parenchyma at the base of sulci, where pressure-induced injury leads to maximal stress in the gyrencephalic brain. The pathophysiological changes in response to brain injury in humans and pigs, we show here, are comparable. We additionally identified modulators of brain injury to further characterize the pathophysiology of ASDH and which may indicate future therapeutic approaches.

Nitric oxide acutely modulates hypothalamic and neurohypophyseal carbon monoxide and hydrogen sulphide production to control vasopressin, oxytocin and atrial natriuretic peptide release in rats

Nitric oxide (NO) negatively modulates the secretion of vasopressin (AVP), oxytocin (OT) and atrial natriuretic peptide (ANP) induced by the increase in extracellular osmolality, whereas carbon monoxide (CO) and hydrogen sulphide (H₂ S) act to potentiate it; however, little information is available for the osmotic challenge model about whether and how such gaseous systems modulate each other. Therefore, using an acute ex vivo model of hypothalamic and neurohypophyseal explants (obtained from male 6/7-week-old Wistar rats) under conditions of extracellular iso- and hypertonicity, we determined the effects of NO (600 μmol L^-1 sodium nitroprusside), CO (100 μmol L^-1 tricarbonylchloro[glycinato]ruthenium [II]) and H₂ S (10 mmol L^-1 sodium sulphide) donors and nitric oxide synthase (NOS) (300 μmol L^-1 N_ω -methyl-l-arginine [LNMMA]), haeme oxygenase (HO) (200 μmol L^-1 Zn(II) deuteroporphyrin IX 2,4-bis-ethylene glycol [ZnDPBG]) and cystathionine β-synthase (CBS) (100 μmol L^-1 aminooxyacetate [AOA]) inhibitors on the release of hypothalamic ANP and hypothalamic and neurohypophyseal AVP and OT, as well as on the activities of NOS, HO and CBS. LNMMA reversed hyperosmolality-induced NOS activity, and enhanced hormonal release by the hypothalamus and neurohypophysis, in addition to increasing CBS and hypothalamic HO activity. AOA decreased hypothalamic and neurohypophyseal CBS activity and hormonal release, whereas ZnDPBG inhibited HO activity and hypothalamic hormone release; however, in both cases, AOA did not modulate NOS and HO activity and ZnDPBG did not affect NOS and CBS activity. Thus, our data indicate that, although endogenous CO and H₂ S positively modulate AVP, OT and ANP release, only NO plays a concomitant role of modulator of hormonal release and CBS activity in the hypothalamus and neurohypophysis and that of HO activity in the hypothalamus during an acute osmotic stimulus, which suggests that NO is a key gaseous controller of the neuroendocrine system.

Interaction of the hydrogen sulfide system with the oxytocin system in the injured mouse heart

Background

Both the hydrogen sulfide/cystathionine-γ-lyase (H₂S/CSE) and oxytocin/oxytocin receptor (OT/OTR) systems have been reported to be cardioprotective. H₂S can stimulate OT release, thereby affecting blood volume and pressure regulation. Systemic hyper-inflammation after blunt chest trauma is enhanced in cigarette smoke (CS)-exposed CSE^−/− mice compared to wildtype (WT). CS increases myometrial OTR expression, but to this point, no data are available on the effects CS exposure on the cardiac OT/OTR system. Since a contusion of the thorax (Txt) can cause myocardial injury, the aim of this post hoc study was to investigate the effects of CSE^−/− and exogenous administration of GYY4137 (a slow release H₂S releasing compound) on OTR expression in the heart, after acute on chronic disease, of CS exposed mice undergoing Txt.

Methods

This study is a post hoc analysis of material obtained in wild type (WT) homozygous CSE^−/− mice after 2-3 weeks of CS exposure and subsequent anesthesia, blast wave-induced TxT, and surgical instrumentation for mechanical ventilation (MV) and hemodynamic monitoring. CSE^−/− animals received a 50 μg/g GYY4137-bolus after TxT. After 4h of MV, animals were exsanguinated and organs were harvested. The heart was cut transversally, formalin-fixed, and paraffin-embedded. Immunohistochemistry for OTR, arginine-vasopressin-receptor (AVPR), and vascular endothelial growth factor (VEGF) was performed with naïve animals as native controls.

Results

CSE^−/− was associated with hypertension and lower blood glucose levels, partially and significantly restored by GYY4137 treatment, respectively. Myocardial OTR expression was reduced upon injury, and this was aggravated in CSE^−/−. Exogenous H₂S administration restored myocardial protein expression to WT levels.

Conclusions

This study suggests that cardiac CSE regulates cardiac OTR expression, and this effect might play a role in the regulation of cardiovascular function.

A single episode of high intensity sound inhibits long-term potentiation in the hippocampus of rats

Exposure to loud sounds has become increasingly common. The most common consequences of loud sound exposure are deafness and tinnitus, but emotional and cognitive problems are also associated with loud sound exposure. Loud sounds can activate the hipothalamic-pituitary-adrenal axis resulting in the secretion of corticosterone, which affects hippocampal synaptic plasticity. Previously we have shown that long-term exposure to short episodes of high intensity sound inhibited hippocampal long-term potentiation (LTP) without affecting spatial learning and memory. Here we aimed to study the impact of short term loud sound exposure on hippocampal synaptic plasticity and function. We found that a single minute of 110 dB sound inhibits hippocampal Schaffer-CA1 LTP for 24 hours. This effect did not occur with an 80-dB sound exposure, was not correlated with corticosterone secretion and was also observed in the perforant-dentate gyrus synapse. We found that despite the deficit in the LTP these animals presented normal spatial learning and memory and fear conditioning. We conclude that a single episode of high-intensity sound impairs hippocampal LTP, without impairing memory and learning. Our results show that the hippocampus is very responsive to loud sounds which can have a potential, but not yet identified, impact on its function.

Nitric Oxide Modulates HCN Channels in Magnocellular Neurons of the Supraoptic Nucleus of Rats by an S-Nitrosylation-Dependent Mechanism

The control of the excitability in magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus has been attributed mainly to synaptic inputs from circunventricular organs. However, nitric oxide (NO), a gaseous messenger produced in this nucleus during isotonic and short-term hypertonic conditions, is an example of a modulator that can act directly on MNCs to modulate their firing rate. NO inhibits the electrical excitability of MNCs, leading to a decrease in the release of vasopressin and oxytocin. Although the effects of NO on MNCs are well established, the mechanism by which this gas produces its effect is, so far, unknown. Because NO acts independently of synaptic inputs, we hypothesized that ion channels present in MNCs are the targets of NO. To investigate this hypothesis, we used the patch-clamp technique in vitro and in situ to measure currents carried by hyperpolarization-activated and nucleotide-gated cation (HCN) channels and establish their role in determining the electrical excitability of MNCs in rats. Our results show that blockade of HCN channels by ZD7288 decreases MNC firing rate with significant consequences on the release of OT and VP, measured by radioimmunoassay. NO induced a significant reduction in HCN currents by binding to cysteine residues and forming S-nitrosothiol complexes. These findings shed new light on the mechanisms that control the electrical excitability of MNCs via the nitrergic system and strengthen the importance of HCN channels in the control of hydroelectrolyte homeostasis.

SIGNIFICANCE STATEMENT

Cells in our organism live in a liquid environment whose composition and osmolality are maintained within tight limits. Magnocellular neurons (MNCs) of the supra optic nucleus can sense osmolality and control the synthesis and secretion of vasopressin (VP) and oxytocin (OT) by the neurohypophysis. OT and VP act on the kidneys controlling the excretion of water and sodium to maintain homeostasis. Here we combined electrophysiology, molecular biology, and radioimmunoassay to show that the electrical activity of MNCs can be controlled by nitric oxide (NO), a gaseous messenger. NO reacts with cysteine residues (S-nitrosylation) on hyperpolarization-activated and nucleotide-gated cation channels decreasing the firing rate of MNCs and the consequent secretion of VP and OT.

Adropin acts in the rat paraventricular nucleus to influence neuronal excitability

Adropin is a peptide hormone with cardiovascular and metabolic roles in the periphery, including effects on glucose and lipid homeostasis. Central administration of adropin has been shown to inhibit water intake in rats; however, the site at which central adropin acts has yet to be elucidated. The hypothalamic paraventricular nucleus (PVN), a critical autonomic control center, plays essential roles in the control of fluid balance, energy homeostasis, and cardiovascular regulation, and is, therefore, a potential target for centrally acting adropin. In the present study, we used whole cell patch-clamp techniques to examine the effects of adropin on the excitability of neurons within the PVN. All three neuronal subpopulations (magnocellular, preautonomic, and neuroendocrine) in the PVN were found to be responsive to bath-application of 10 nM adropin, which elicited responses in 68% of cells tested (n = 57/84). The majority of cells (58%) depolarized (5.2 ± 0.3 mV; n = 49) in response to adropin, whereas the remaining responsive cells (10%) hyperpolarized (-3.4 ± 0.5 mV; n = 8), effects that were shown to be concentration-dependent. Additionally, responses were maintained in the presence of 1 μM TTX in 75% of cells tested (n = 9/12), and voltage-clamp analysis revealed that adropin had no effect on the amplitude or frequency of excitatory or inhibitory postsynaptic currents (EPSCs and IPSCs) in PVN neurons, suggesting the peptide exerts direct, postsynaptic actions on these neurons. Collectively, these findings suggest central adropin may exert its physiological effects through direct actions on neurons in the PVN.

Signaling through hepatocyte vasopressin receptor 1 protects mouse liver from ischemia-reperfusion injury

Terlipressin has been used extensively in the management of certain complications associated with end-stage liver diseases (ESLDs). In our pilot study, terlipressin treatment showed beneficial effects on liver function in patients with decompensated cirrhosis, however whether it plays a role in liver ischemia-reperfusion injury (IRI) remains unknown. Using a mouse nonlethal hepatic IR model, we found terlipressin administration significantly ameliorated IR-induced liver apoptosis, necrosis and inflammation. Furthermore, despite its known effect on visceral vasoconstriction, hemodynamic evaluation of murine hepatic tissue after IR revealed no change of overall hepatic blood flow after terlipressin treatment. Further studies identified the upregulation of vasopressin receptor 1 (V1R) expression on hepatocytes upon IR. In isolated hepatocyte hypoxia/reoxygenation model, the active component of terlipressin, lysine vasopressin, conferred hepatocytes resistant to oxidative stress-induced apoptosis. Mechanistic studies revealed the V1R engagement activated the Wnt/β-catenin/FoxO3a/AKT pathway, which subsequently circumvented the proapoptotic events, thus ameliorated hepatocyte apoptosis. Furthermore, genetic knockdown of V1R expression in hepatocyte cell lines or blockade of this signaling pathway abrogated such protective effect.

CONCLUSION

These data highlight the functional importance of the hepatocyte V1R/Wnt/β-catenin/FoxO3a/AKT pathway in protecting liver from oxidative stress-induced injury.

Brain Formaldehyde is Related to Water Intake behavior

A promising strategy for the prevention of Alzheimer’s disease (AD) is the identification of age-related changes that place the brain at risk for the disease. Additionally, AD is associated with chronic dehydration, and one of the significant changes that are known to result in metabolic dysfunction is an increase in the endogenous formaldehyde (FA) level. Here, we demonstrate that the levels of uric formaldehyde in AD patients were markedly increased compared with normal controls. The brain formaldehyde levels of wild-type C57 BL/6 mice increased with age, and these increases were followed by decreases in their drinking frequency and water intake. The serum arginine vasopressin (AVP) concentrations were also maintained at a high level in the 10-month-old mice. An intravenous injection of AVP into the tail induced decreases in the drinking frequency and water intake in the mice, and these decreases were associated with increases in brain formaldehyde levels. An ELISA assay revealed that the AVP injection increased both the protein level and the enzymatic activity of semicarbazide-sensitive amine oxidase (SSAO), which is an enzyme that produces formaldehyde. In contrast, the intraperitoneal injection of formaldehyde increased the serum AVP level by increasing the angiotensin II (ANG II) level, and this change was associated with a marked decrease in water intake behavior. These data suggest that the interaction between formaldehyde and AVP affects the water intake behaviors of mice. Furthermore, the highest concentration of formaldehyde in vivo was observed in the morning. Regular water intake is conducive to eliminating endogenous formaldehyde from the human body, particularly when water is consumed in the morning. Establishing good water intake habits not only effectively eliminates excess formaldehyde and other metabolic products but is also expected to yield valuable approaches to reducing the risk of AD prior to the onset of the disease.

A novel treatment for "morning sickness": Nausea of pregnancy could be induced by excess sulfite which molybdenum can help alleviate

Nausea and vomiting of pregnancy (NVP) remains difficult to treat. Last century, thalidomide was used to alleviate NVP, but it caused teratogenesis by interfering with angiogenesis. The gasotransmitters hydrogen sulfide (H2S) and nitric oxide are mutually dependent on each other for their angiogenesis-related functions. Pregnancy-related requirements for increased endogenous H2S could create a temporary excess of sulfite, an H2S catabolite, which is toxic and can induce nausea. Sulfite oxidase, a molybdenum-containing enzyme, catalyzes oxidation of sulfite to sulfate, which can then be excreted or reused by the body. Supplementation with molybdenum should facilitate enhanced sulfite oxidase activity, thus lowering gestationally-elevated sulfite levels in the gastrointestinal tract and easing NVP.

Gaseous modulators in the control of the hypothalamic neurohypophyseal system

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are gaseous molecules produced by the brain. Within the hypothalamus, gaseous molecules have been highlighted as autocrine and paracrine factors regulating endocrine function. Therefore, in the present review, we briefly discuss the main findings linking NO, CO, and H2S to the control of body fluid homeostasis at the hypothalamic level, with particular emphasis on the regulation of neurohypophyseal system output.