H2S induces vasoconstriction of rat cerebral arteries via cAMP/adenylyl cyclase pathway

Clinical Applications for Gasotransmitters in the Cardiovascular System: Are We There Yet?

Ischemia is the underlying mechanism in a wide variety of acute and persistent pathologies. As such, understanding the fine intracellular events occurring during (and after) the restriction of blood supply is pivotal to improving the outcomes in clinical settings. Among others, gaseous signaling molecules constitutively produced by mammalian cells (gasotransmitters) have been shown to be of potential interest for clinical treatment of ischemia/reperfusion injury. Nitric oxide (NO and its sibling, HNO), hydrogen sulfide (H2S), and carbon monoxide (CO) have long been proven to be cytoprotective in basic science experiments, and they are now awaiting confirmation with clinical trials. The aim of this work is to review the literature and the clinical trials database to address the state of development of potential therapeutic applications for NO, H2S, and CO and the clinical scenarios where they are more promising.

Hydrogen sulfide in the experimental models of arterial hypertension

Hydrogen sulfide (H₂S) is the third member of gasotransmitter family together with nitric oxide and carbon monoxide. H₂S is involved in the regulation of blood pressure by controlling vascular tone, sympathetic nervous system activity and renal sodium excretion. Moderate age-dependent hypertension and endothelial dysfunction develop in mice with knockout of cystathionine γ-lyase (CSE), the enzyme involved in H₂S production in the cardiovascular system. Decreased H₂S concentration as well as the expression and activities of H₂S-producing enzymes have been observed in most commonly used animal models of hypertension such as spontaneously hypertensive rats, Dahl salt-sensitive rats, chronic administration of NO synthase inhibitors, angiotensin II infusion and two-kidney-one-clip hypertension, the model of renovascular hypertension. Administration of H₂S donors decreases blood pressure in these models but has no major effects on blood pressure in normotensive animals. H₂S donors not only reduce blood pressure but also end-organ injury such as vascular and myocardial hypertrophy and remodeling, hypertension-associated kidney injury or erectile dysfunction. H₂S level and signaling are modulated by some antihypertensive medications as well as natural products with antihypertensive activity such as garlic polysulfides or plant-derived isothiocyanates as well as non-pharmacological interventions. Modifying H₂S signaling is the potential novel therapeutic approach for the management of hypertension, however, more experimental clinical studies about the role of H₂S in hypertension are required.

The Role of Perivascular Adipose Tissue-Derived Hydrogen Sulfide in the Control of Vascular Homeostasis

Significance: Emerging evidence suggests that perivascular adipose tissue (PVAT) has a relevant role in the control of vascular tone in physiology and pathology. Healthy PVAT has anticontractile, anti-inflammatory, and antioxidative actions. Accumulating data from both human and experimental animal models indicate that PVAT dysfunction is conceivably coupled to cardiovascular diseases, and it is associated with vascular inflammation, oxidative stress, and arterial remodeling. Therefore, "healthy" PVAT may constitute a novel therapeutic target for the prevention and treatment of cardiovascular diseases. Recent Advances: Hydrogen sulfide (H₂S) has been recognized as a vascular anti-contractile factor released from PVAT. The enzymes deputed to H₂S biosynthesis are variously expressed in PVAT and strictly dependent on the vascular bed and species. Metabolic and cardiovascular diseases can alter the morphological and secretory characteristics of PVAT, influencing also the H₂S signaling. Here, we discuss the role of PVAT-derived H₂S in healthy conditions and its relevance in alterations occurring in vascular disorders. Critical Issues: We discuss how a better understanding may help in the prevention of vascular dysfunction related to alteration in PVAT-released H₂S as well as the importance of the interplay between PVAT and H₂S. Future Directions: We propose future directions to evaluate the contribution of each enzyme involved in H₂S biosynthesis and their alteration/switch occurring in vascular disorders and the remaining challenges in investigating the role of H₂S. Antioxid. Redox Signal. 37, 84-97.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

The effect of hydrogen sulfide on the contractility of cerebral arterioles. A pilot study

BACKGROUND AND AIMS

Endogenous gaseous substances, such as NO and CO have been found to be effective vasodilators earlier. H2S has been identified as an additional one, however, for that substance both vasodilatory and vasoconstrictor responses have been described in different vascular territories. Our aim was to examine the effect of hydrogen sulfide on the tone of cerebral arterioles and some aspects of its mechanism.

METHODS

The work was performed on excised rat anterior cerebral artery segments in vitro (diameter range 150-250 µm), using a pressure myograph system. We used NaHS as exogenous H2S donor, propargylglycine (PAG) to abolish the endogenous synthesis of hydrogen sulfide and 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) to examine the potential role of Cl-/HCO3 - exchanger in the effects of H2S. The time course of the events after application of exogenous H2S was also evaluated.

RESULTS

Our findings revealed that in these pathologically important vessels (1) endogenously produced H2S is not a vasodilator, but a moderate vasoconstrictor; (2) H2S has a biphasic effect: low concentrations are moderate vasoconstrictors, while at higher concentrations the initial contraction is followed by dilatation; (3) that vasodilation is prevented by DIDS (4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid disodium, an inhibitor of the Cl-/HCO3 - exchanger).

CONCLUSION

These studies confirm that H2S should be taken into consideration as a modulator of cerebral arteriolar tone in mammals.

NIR Fluorescent Probe for In Situ Bioimaging of Endogenous H2S in Rice Roots under Al3+ and Flooding Stresses

Hydrogen sulfide (H₂S) is one of the typical reactive sulfur species, which exhibits an important role in regulating both physiological and pathological processes. Recent studies indicate that H₂S also serves as a key signaling molecule in a broad range of regulatory processes in plants. However, in situ imaging and detection of the levels of H₂S in plant tissues remains a challenge. In this work, a NIR fluorescent probe (HBTP-H₂S) was synthesized to achieve H₂S imaging in living plant tissues. HBTP-H₂S exhibited high sensitivity toward H₂S with a large Stokes shift (250 nm). HBTP-H₂S could be applied to HeLa cells to detect the fluctuation of endogenous H₂S levels in response to physiological stimulations. Importantly, HBTP-H₂S was utilized for direct H₂S imaging of rice roots and revealed the upregulation of H₂S signaling in response to aluminum ions and flooding stresses. Our work thus provides a new tool to investigate H₂S-involved signal interaction and protective resistance of crops under environmental stresses.

Minimally modified low-density lipoprotein upregulates mouse mesenteric arterial 5-HT1B receptor in vivo via activation of the JAK2/STAT3 pathway

OBJECTIVES

To explore whether minimally modified low-density lipoprotein (mmLDL) upregulates mesenteric arterial 5-hydroxytryptamine 1B (5-HT_1B) receptor expression by activating the JAK2/STAT3 signaling pathway.

METHODS

Mice were randomly divided into the following groups: the normal saline (NS), LDL, mmLDL, mmLDL+galiellactone (GL, a JAK2/STAT3 pathway inhibitor), and mmLDL+DMSO groups. The dose-response curve of mesenteric arterial ring constriction after administration of 5-carboxamidotryptamine (5-CT), an agonist of 5-HT_1B, was recorded with a microvascular tensiometer. JAK2, p-JAK2, STAT3, p-STAT3, and 5-HT_1B receptor protein expression levels were determined by Western blotting. 5-HT_1B receptor mRNA levels were measured by RT-PCR. 5-HT_1B receptor protein expression was determined by immunofluorescence.

RESULTS

Injection of mmLDL into the tail vein significantly increased the contractile dose-response curve after 5-CT stimulation, as the E_max was 82.15 ± 6.15% in the NS group and 171.88 ± 5.78% in the mmLDL group (P < 0.01); significantly elevated 5-HT_1B receptor mRNA and protein expression levels; and significantly increased p-JAK2 and p-STAT3 protein expression levels. After intraperitoneal injection of GL, the vasoconstrictive response was significantly reduced compared with that in the mmLDL group, as the E_max was decreased to 97.14 ± 1.20% (P < 0.01); 5-HT_1B receptor mRNA and protein expression levels were significantly reduced; STAT3 phosphorylation and p-JAK2 and p-STAT3 protein expression were not significantly changed; and 5-HT_1B receptor expression was altered via inhibition of p-STAT3 binding to DNA, which suppressed transcription.

CONCLUSIONS

mmLDL can upregulate 5-HT_1B receptor expression in mouse mesenteric arteries by activating the JAK2/STAT3 signaling pathway.

Circulating levels of hydrogen sulphide negatively correlate to nitrite levels in gestational hypertensive and preeclamptic pregnant women

Endothelial dysfunction is a hallmark of preeclampsia and the role of nitric oxide (NO) has been extensively studied in this pregnancy complication. In recent years, hydrogen sulphide (H₂ S) has arisen as a new gasotransmitter with an impact on endothelial function. However, the involvement of H₂ S in the pathophysiology of preeclampsia is not fully understood, and only a few studies with limited sample size have investigated circulating levels of H₂ S in preeclamptic patients. Moreover, H₂ S levels have not been previously evaluated in gestational hypertension. Furthermore, the relationship between H₂ S and NO in these hypertensive disorders of pregnancy has yet to be determined. We measured H₂ S levels in plasma of 120 healthy pregnant women, 88 gestational hypertensive and 62 preeclamptic women. We also measured plasma nitrite in a subset of patients and carried out correlation analysis between plasma H₂ S and nitrite in these three groups. We found that plasma H₂ S was elevated in preeclampsia and further increased in gestational hypertension compared to healthy pregnancy. Plasma nitrite was reduced in gestational hypertension and preeclampsia, and these levels were negatively correlated with H₂ S in both gestational hypertension and preeclampsia, but not in healthy pregnancy. Our results indicate that increases in H₂ S may represent a mechanism triggered as an attempt to compensate reduced NO in gestational hypertension and preeclampsia. Future studies are warranted to investigate the mechanisms underlying H₂ S/NO interaction on mediating endothelial dysfunction in these hypertensive disorders of pregnancy.

GYY4137 and Sodium Hydrogen Sulfide Relaxations Are Inhibited by L-Cysteine and KV7 Channel Blockers in Rat Small Mesenteric Arteries

Donors of H₂S may be beneficial in treating cardiovascular diseases where the plasma levels of H₂S are decreased. Therefore, we investigated the mechanisms involved in relaxation of small arteries induced by GYY4137 [(4-methoxyphenyl)-morpholin-4-yl-sulfanylidene-sulfido-λ5-phosphane;morpholin-4-ium], which is considered a slow-releasing H₂S donor. Sulfides were measured by use of 5,5′-dithiobis-(2-nitro benzoic acid), and small rat mesenteric arteries with internal diameters of 200–250 µm were mounted in microvascular myographs for isometric tension recordings. GYY4137 produced similar low levels of sulfides in the absence and the presence of arteries. In U46619-contracted small mesenteric arteries, GYY4137 (10⁻⁶–10^–3 M) induced concentration-dependent relaxations, while a synthetic, sulfur-free, GYY4137 did not change the vascular tone. L-cysteine (10⁻⁶–10^–3 M) induced only small relaxations reaching 24 ± 6% at 10^–3 M. Premixing L-cysteine (10^–3 M) with Na₂S and GYY4137 decreased Na₂S relaxation and abolished GYY4137 relaxation, an effect prevented by an nitric oxide (NO) synthase inhibitor, L-NAME (N^ω-nitro-L-arginine methyl ester). In arteries without endothelium or in the presence of L-NAME, relaxation curves for GYY4137 were rightward shifted. High extracellular K⁺ concentrations decreased Na₂S and abolished GYY4137 relaxation suggesting potassium channel-independent mechanisms are also involved Na₂S relaxation while potassium channel activation is pivotal for GYY4137 relaxation in small arteries. Blockers of large-conductance calcium-activated (BK_Ca) and voltage-gated type 7 (K_V7) potassium channels also inhibited GYY4137 relaxations. The present findings suggest that L-cysteine by reaction with Na₂S and GYY4137 and formation of sulfides, inhibits relaxations by these compounds. The low rate of release of H₂S species from GYY4137 is reflected by the different sensitivity of these relaxations towards high K⁺ concentration and potassium channel blockers compared with Na₂S. The perspective is that the rate of release of sulfides plays an important for the effects of H₂S salt vs. donors in small arteries, and hence for a beneficial effect of GYY4137 for treatment of cardiovascular disease.

The Potential Role of Hydrogen Sulfide in the Regulation of Cerebrovascular Tone

A better understanding of the regulation of cerebrovascular circulation is of great importance because stroke and other cerebrovascular diseases represent a major concern in healthcare leading to millions of deaths yearly. The circulation of the central nervous system is regulated in a highly complex manner involving many local factors and hydrogen sulfide (H₂S) is emerging as one such possible factor. Several lines of evidence support that H₂S takes part in the regulation of vascular tone. Examinations using either exogenous treatment with H₂S donor molecules or alterations to the enzymes that are endogenously producing this molecule revealed numerous important findings about its physiological and pathophysiological role. The great majority of these studies were performed on vessel segments derived from the systemic circulation but there are important observations made using cerebral vessels as well. The findings of these experimental works indicate that H₂S is having a complex, pleiotropic effect on the vascular wall not only in the systemic circulation but in the cerebrovascular region as well. In this review, we summarize the most important experimental findings related to the potential role of H₂S in the cerebral circulation.

Role of Hydrogen Sulfide in Chronic Diseases

In the past, hydrogen sulfide (H₂S) was considered as a poisonous gas or waste of the body. Later, researchers found that H₂S-producing enzymes exist in mammals. Moreover, their findings indicated that endogenous H₂S was associated with the occurrence of many diseases. Therefore, endogenous H₂S is able to participate in the regulation of physiological and pathological functions of the body as a gas signaling molecule. In this review, we summarize the regulation mechanism of endogenous H₂S on the body, such as proliferation, apoptosis, migration, angiogenesis, as well as vasodilation/vasoconstriction. Furthermore, we also analyze the relationship between H₂S and some chronic diseases, including hypoxic pulmonary hypertension, myocardial infarction, ischemic perfusion kidney injury, diabetes, and chronic intestinal diseases. Finally, we discuss dietary restriction and drugs that target for H₂S. Hence, H₂S is expected to become a potential target for treatment of these chronic diseases.

Erythromycin relaxes BALB/c mouse airway smooth muscle

AIMS

Bitter taste receptor (TAS2R) agonists have bronchodilatory potentials. Erythromycin is a ligand of TAS2R10, but its relaxant profile is unknown. This study was performed to understand the relaxant effects of erythromycin and its potential mechanism.

MAIN METHODS

Airway resistance was tested by the whole body plethysmography in the ovalbumin-aluminum hydroxide induced asthma model mice. Tracheal ring segment myography was used to investigate the isometric tension of the smooth muscle. The cyclic adenosine monophosphate (cAMP) concentration was measured by enzyme immunoassay kit. Changes in the calcium influx in airway smooth muscle cells (ASMCs) were surveyed using a real-time confocal microscopy.

KEY FINDINGS

Erythromycin significantly relieved airway hyperreactivity in asthma model mice. Erythromycin relaxed mouse tracheal segments precontracted with carbachol, KCl, 5-hydroxytryptamine and U46619, and further dilated the tracheal rings relaxed by isoprenaline or atropine. Epithelium removal, indomethacin or NS-398 partially reduced the relaxation. U73122, 2-APB, iberiotoxin or ouabain did not change the concentration-relaxation curves of erythromycin on tracheal segments. Erythromycin didn't elevate cAMP level. CaCl₂-induced contraction in the K⁺-rich solution was impaired by erythromycin in the Ca²⁺-free solution. The intercellular Ca²⁺ level in the ASMCs was decreased by erythromycin, which was partly inhibited by Bay K8644 but not gallein.

SIGNIFICANCE

Erythromycin had marked bronchodilatory effect. The relaxation might be related to the L-type voltage-dependent calcium channel, but not the gustducin-associated βγ/phospholipase-Cβ/inositol 1,4,5-tri-phosphate receptor/large conductance Ca²⁺-activated K⁺ channel pathway or a cAMP-dependent way.

Increases in placental nitric oxide, but not nitric oxide-mediated relaxation, underlie the improvement in placental efficiency and antihypertensive effects of hydrogen sulphide donor in hypertensive pregnancy

Dysregulation of hydrogen sulphide (H₂ S) producing enzymes has been related to hypertensive pregnancy, and H₂ S donor, sodium hydrosulphide (NaHS) exerts antihypertensive effects, modulates angiogenic factors production and acts as an antioxidant. Moreover, reduction in nitric oxide (NO) bioavailability is related to hypertensive pregnancy and H₂ S may interact with NO, modulating its production. We aimed to investigate the NaHS effects in hypertension-in-pregnancy and also in feto-placental parameters. Female Wistar rats (200-250 g) were mated and desoxycorticosterone acetate injections followed by replacement of water by 0.9% saline solution were used to induce hypertensive pregnancy. Rats were divided into four groups: normal pregnant (Norm-Preg), pregnant + NaHS (Preg+NaHS), hypertensive pregnant (HTN-Preg) and HTN-Preg+NaHS. Systolic blood pressure was increased in HTN-Preg and this increase was blunted in HTN-Preg+NaHS. Fetal and placental weights were decreased in HTN-Preg animals, while fetal growth restriction was improved in HTN-Preg+NaHS. Placental weight was lower in HTN-Preg+NaHS than in HTN-Preg; however, placental efficiency was re-established in HTN-Preg+NaHS rats. We observed that a partial contribution of placental NO, but not changes in anti-angiogenic factors may mediate the increases in placental efficiency in HTN-Preg+NaHS. HTN-Preg presented thoracic aorta hyperreactivity to phenylephrine while NaHS treatment blunted this hyperreactivity, which seems not to be related to NO-mediated relaxation induced by acetylcholine. Therefore, changes in vascular responsiveness promoted by NaHS treatment may underlie the beneficial effects in systolic blood pressure and feto-placental parameters in our study.

The role of hydrogen sulfide in cyclic nucleotide signaling

Hydrogen sulfide (H₂S) is recognized as an endogenous gaseous transmitter alongside nitric oxide (NO) and carbon monoxide (CO). By integrating into multiple signaling pathways, H₂S elicits biological functions in various mammalian systems. Among these pathways, cyclic nucleotide signaling has gradually gained attention in the past decade. Based on current evidence, it seems that H₂S may differentially affect the activity of resting adenylyl cyclases (ACs) and activated ACs, therefore playing a dual role in the regulation of cyclic adenosine monophosphate (cAMP) mediated signaling. However, how H₂S achieves the differential regulation on ACs remains unknown at molecular level. In the context of cyclic guanosine monophosphate (cGMP) regulation, H₂S augments its downstream signaling at least through three different mechanisms: (1) H₂S potentiates the response of soluble guanylyl cyclases (sGCs) to NO; (2) H₂S inhibits activity of phosphodiesterases (PDEs); and (3) H₂S enhances the production of NO. By regulating cyclic nucleotide signaling, H₂S possesses therapeutic potentials particularly for hypertension and cardiac injury which have also been discussed in the current review. Nevertheless, a detailed portrayal of H₂S mediated interaction with target proteins is still required for a better understanding of the role of this important gaseous mediator in regulating cyclic nucleotide signaling.

The mechanism of action and role of hydrogen sulfide in the control of vascular tone

Our knowledge about hydrogen sulfide (H₂S) significantly changed over the last two decades. Today it is considered as not only a toxic gas but also as a gasotransmitter with diverse roles in different physiological and pathophysiological processes. H₂S has pleiotropic effects and its possible mechanisms of action involve (1) a reversible protein sulfhydration which can alter the function of the modified proteins similar to nitrosylation or phosphorylation; (2) direct antioxidant effects and (3) interaction with metalloproteins. Its effects on the human cardiovascular system are especially important due to the high prevalence of hypertension and myocardial infarction. The exact molecular targets that affect the vascular tone include the K_ATP channel, the endothelial nitric oxide synthase, the phosphodiesterase of the vascular smooth muscle cell and the cytochrome c oxidase among others and the combination of all these effects lead to the final result on the vascular tone. The relative role of each effect depends immensely on the used concentration and also on the used donor molecules but several other factors and experimental conditions could alter the final effect. The aim of the current review is to give a comprehensive summary of the current understanding on the mechanism of action and role of H₂S in the regulation of vascular tone and to outline the obstacles that hinder the better understanding of its effects.

H2S is a key antisecretory molecule against cholera toxin-induced diarrhoea in mice: Evidence for non-involvement of the AC/cAMP/PKA pathway and AMPK

Hydrogen sulphide (H₂S) is a gasotransmitter that participates in various physiological and pathophysiological processes within the gastrointestinal tract. We studied the effects and possible mechanism of action of H₂S in secretory diarrhoea caused by cholera toxin (CT). The possible mechanisms of action of H₂S were investigated using an intestinal fluid secretion model in isolated intestinal loops on anaesthetized mice treated with CT. NaHS and Lawesson's reagent and l-cysteine showed antisecretory activity through reduction of intestinal fluid secretion and loss of Cl^- induced by CT. Pretreatment with an inhibitor of cystathionine-γ-lyase (CSE), dl-propargylglycine (PAG), reversed the effect of l-cysteine and caused severe intestinal secretion. Co-treatment with PAG and a submaximal dose of CT increased intestinal fluid secretion, thus supporting the role of H₂S in the pathophysiology of cholera. CT increased the expression of CSE and the production of H₂S. Pretreatment with PAG did not reverse the effect of SQ 22536 (an AC inhibitor), bupivacaine (inhibitor of cAMP production), KT-5720 (a PKA inhibitor), and AICAR (an AMPK activator). The treatment with Forskolin does not reverse the effects of the H₂S donors. Co-treatment with either NaHS or Lawesson's reagent and dorsomorphin (an AMPK inhibitor) did not reverse the effect of the H₂S donors. H₂S has antisecretory activity and is an essential molecule for protection against the intestinal secretion induced by CT. Thus, H₂S donor drugs are promising candidates for cholera therapy. However, more studies are needed to elucidate the possible mechanism of action.

The role of hydrogen sulphide in blood pressure regulation

Cardiovascular studies have confirmed that hydrogen sulphide (H(2)S) is involved in various signaling pathways in both physiological and pathological conditions, including hypertension. In contrast to nitric oxide (NO), which has a clear vasorelaxant action, H(2)S has both vasorelaxing and vasoconstricting effects on the cardiovascular system. H(2)S is an important antihypertensive agent, and the reduced production of H(2)S and the alterations in its functions are involved in the initiation of spontaneous hypertension. Moreover, cross-talk between H(2)S and NO has been reported. NO-H(2)S interactions include reactions between the molecules themselves, and each has been shown to regulate the endogenous production of the other. In addition, NO and H(2)S can interact to form a nitrosothiol/s complex, which has original properties and represents a novel nitroso-sulphide signaling pathway. Furthermore, recent results have shown that the interaction between H(2)S and NO could be involved in the endothelium-regulated compensatory mechanisms that are observed in juvenile spontaneously hypertensive rats. The present review is devoted to role of H(2)S in vascular tone regulation. We primarily focus on the mechanisms of H(2)S-NO interactions and on the role of H(2)S in blood pressure regulation in normotensive and spontaneously hypertensive rats.

Vascular biology of hydrogen sulfide

Hydrogen sulfide (H₂S) is a ubiquitous signaling molecule with important functions in many mammalian organs and systems. Observations in the 1990s ascribed physiological actions to H₂S in the nervous system, proposing that this gasotransmitter acts as a neuromodulator. Soon after that, the vasodilating properties of H₂S were demonstrated. In the past decade, H₂S was shown to exert a multitude of physiological effects in the vessel wall. H₂S is produced by vascular cells and exhibits antioxidant, antiapoptotic, anti-inflammatory, and vasoactive properties. In this concise review, we have focused on the impact of H₂S on vascular structure and function with an emphasis on angiogenesis, vascular tone, vascular permeability and atherosclerosis. H₂S reduces arterial blood pressure, limits atheromatous plaque formation, and promotes vascularization of ischemic tissues. Although the beneficial properties of H₂S are well established, mechanistic insights into the molecular pathways implicated in disease prevention and treatment remain largely unexplored. Unraveling the targets and downstream effectors of H₂S in the vessel wall in the context of disease will aid in translation of preclinical observations. In addition, acute regulation of H₂S production is still poorly understood and additional work delineating the pathways regulating the enzymes that produce H₂S will allow pharmacological manipulation of this pathway. As the field continues to grow, we expect that H₂S-related compounds will find their way into clinical trials for diseases affecting the blood vessels.