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Oxidative stress, a central mediator of cardiovascular disease, results in loss of the prosthetic haem group of soluble guanylate cyclase (sGC), preventing its activation by nitric oxide (NO). Here we introduce Apo-sGC mice expressing haem-free sGC. Apo-sGC mice are viable and develop hypertension. The haemodynamic effects of NO are abolished, but those of the sGC activator cinaciguat are enhanced in apo-sGC mice, suggesting that the effects of NO on smooth muscle relaxation, blood pressure regulation and inhibition of platelet aggregation require sGC activation by NO. Tumour necrosis factor (TNF)-induced hypotension and mortality are preserved in apo-sGC mice, indicating that pathways other than sGC signalling mediate the cardiovascular collapse in shock. Apo-sGC mice allow for differentiation between sGC-dependent and -independent NO effects and between haem-dependent and -independent sGC effects. Apo-sGC mice represent a unique experimental platform to study the in vivo consequences of sGC oxidation and the therapeutic potential of sGC activators.

Introduction: Because of their nitric oxide (NO)-donating capacities, oxime derivatives have shown to offer some therapeutic perspective for the treatment of erectile dysfunction (ED) as well as cardiovascular diseases. However, to date the in vivo effect of these oximes on erectile function remains unknown. In many disease states oxidative stress occurs, impairing NO-mediated relaxations. Hence the influence of oxidative stress on oxime-induced effects is also of interest., Aims: This study aimed to evaluate the in vivo effect of formaldoxime (FAL) and formamidoxime (FAM) on blood pressure and intracavernosal pressure (ICP); and to examine the role of soluble guanylyl cyclase (sGC) and the influence of oxidative stress on the FAL and FAM responses., Methods: Blood pressure and ICP were monitored in vivo after resp. intravenous or intracavernosal injection of FAL and FAM. Moreover isometric tension was measured in vitro on isolated mice corpora cavernosa (CC), thoracic aorta, and femoral artery in organ baths. The role of sGC was investigated using transgenic mice lacking the alpha 1 subunit of sGC., Main Outcome Measures: Mean arterial pressure (MAP) and ICP were measured after FAL/FAM injection. In vitro relaxation of CC strips was evaluated in response to addition of FAL/FAM., Results: In vivo both FAL and FAM elicit a dose-dependent lowering of blood pressure (maximal ΔMAP: 33.66 ± 4.07 mm Hg [FAL] and 20.43 ± 2.06 mm Hg [FAM] ) as well as an increase of ICP (maximal increase of ICP/MAP: 70.29 ± 2.88% [FAL] and 52.91 ± 8.61% [FAM] ). The FAL/FAM effect is significantly lower in knockout vs. wild-type mice. Oxidative stress has an inhibitory effect on corporal NO-mediated relaxations induced by electrical field stimulation, acetylcholine, and sodium nitroprusside whereas the responses to 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate sodium salt, FAL and FAM were not influenced., Conclusions: Oximes induce erection which is mediated by sGC. The oxime-induced relaxations are resistant to oxidative stress, which increases their therapeutic potential for the treatment of ED., (© 2015 International Society for Sexual Medicine.)

Moyamoya is a cerebrovascular condition characterized by a progressive stenosis of the terminal part of the internal carotid arteries (ICAs) and the compensatory development of abnormal "moyamoya" vessels. The pathophysiological mechanisms of this condition, which leads to ischemic and hemorrhagic stroke, remain unknown. It can occur as an isolated cerebral angiopathy (so-called moyamoya disease) or in association with various conditions (moyamoya syndromes). Here, we describe an autosomal-recessive disease leading to severe moyamoya and early-onset achalasia in three unrelated families. This syndrome is associated in all three families with homozygous mutations in GUCY1A3, which encodes the α1 subunit of soluble guanylate cyclase (sGC), the major receptor for nitric oxide (NO). Platelet analysis showed a complete loss of the soluble α1β1 guanylate cyclase and showed an unexpected stimulatory role of sGC within platelets. The NO-sGC-cGMP pathway is a major pathway controlling vascular smooth-muscle relaxation, vascular tone, and vascular remodeling. Our data suggest that alterations of this pathway might lead to an abnormal vascular-remodeling process in sensitive vascular areas such as ICA bifurcations. These data provide treatment options for affected individuals and strongly suggest that investigation of GUCY1A3 and other members of the NO-sGC-cGMP pathway is warranted in both isolated early-onset achalasia and nonsyndromic moyamoya., (Copyright © 2014 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Rationale: Soluble guanylyl cyclase (sGC), a cyclic guanosine 5'-monophosphate-generating enzyme, regulates smooth muscle tone and exerts antiinflammatory effects in animal models of asthma and acute lung injury. In chronic obstructive pulmonary disease (COPD), primarily caused by cigarette smoke (CS), lung inflammation persists and smooth muscle tone remains elevated, despite ample amounts of nitric oxide that could activate sGC., Objectives: To determine the expression and function of sGC in patients with COPD and in a murine model of COPD., Methods: Expression of sGCα1, α2, and β1 subunits was examined in lungs of never-smokers, smokers without airflow limitation, and patients with COPD; and in C57BL/6 mice after 3 days, 4 weeks, and 24 weeks of CS exposure. The functional role of sGC was investigated in vivo by measuring bronchial responsiveness to serotonin in mice using genetic and pharmacologic approaches., Measurements and Main Results: Pulmonary expression of sGC, both at mRNA and protein level, was decreased in smokers without airflow limitation and in patients with COPD, and correlated with disease severity (FEV1%). In mice, exposure to CS reduced sGC, cyclic guanosine 5'-monophosphate levels, and protein kinase G activity. sGCα1(-/-) mice exposed to CS exhibited bronchial hyperresponsiveness to serotonin. Activation of sGC by BAY 58-2667 restored the sGC signaling and attenuated bronchial hyperresponsiveness in CS-exposed mice., Conclusions: Down-regulation of sGC because of CS exposure might contribute to airflow limitation in COPD.

Primary open angle glaucoma (POAG) is a leading cause of blindness worldwide. The molecular signaling involved in the pathogenesis of POAG remains unknown. Here, we report that mice lacking the α1 subunit of the nitric oxide receptor soluble guanylate cyclase represent a novel and translatable animal model of POAG, characterized by thinning of the retinal nerve fiber layer and loss of optic nerve axons in the context of an open iridocorneal angle. The optic neuropathy associated with soluble guanylate cyclase α1-deficiency was accompanied by modestly increased intraocular pressure and retinal vascular dysfunction. Moreover, data from a candidate gene association study suggests that a variant in the locus containing the genes encoding for the α1 and β1 subunits of soluble guanylate cyclase is associated with POAG in patients presenting with initial paracentral vision loss, a disease subtype thought to be associated with vascular dysregulation. These findings provide new insights into the pathogenesis and genetics of POAG and suggest new therapeutic strategies for POAG.

Nitric oxide (NO) plays an essential role in regulating hypertension and blood flow by inducing relaxation of vascular smooth muscle. Male mice deficient in a NO receptor component, the α1 subunit of soluble guanylate cyclase (sGCα1), are prone to hypertension in some, but not all, mouse strains, suggesting that additional genetic factors contribute to the onset of hypertension. Using linkage analyses, we discovered a quantitative trait locus (QTL) on chromosome 1 that was linked to mean arterial pressure (MAP) in the context of sGCα1 deficiency. This region is syntenic with previously identified blood pressure-related QTLs in the human and rat genome and contains the genes coding for renin. Hypertension was associated with increased activity of the renin-angiotensin-aldosterone system (RAAS). Further, we found that RAAS inhibition normalized MAP and improved endothelium-dependent vasorelaxation in sGCα1-deficient mice. These data identify the RAAS as a blood pressure-modifying mechanism in a setting of impaired NO/cGMP signaling.

In the heart, nitric oxide (NO) modulates contractile function; however, the mechanisms responsible for this effect are incompletely understood. NO can elicit effects via a variety of mechanisms including S-nitrosylation and stimulation of cGMP synthesis by soluble guanylate cyclase (sGC). sGC is a heterodimer comprised of a β(1)- and an α(1)- or α(2)-subunit. sGCα(1)β(1) is the predominant isoform in the heart. To characterize the role of sGC in the regulation of cardiac contractile function by NO, we compared left ventricular cardiac myocytes (CM) isolated from adult mice deficient in the sGC α(1)-subunit (sGCα(1)(-/-)) and from wild-type (WT) mice. Sarcomere shortening under basal conditions was less in sGCα(1)(-/-) CM than in WT CM. To activate endogenous NO synthesis from NO synthase 3, CM were incubated with the β(3)-adrenergic receptor (β(3)-AR) agonist BRL 37344. BRL 37344 decreased cardiac contractility in WT CM but not in sGCα(1)(-/-) myocytes. Administration of spermine NONOate, an NO donor compound, did not affect sarcomeric shortening in CM of either genotype; however, in the presence of isoproterenol, addition of spermine NONOate reduced sarcomere shortening in WT but not in sGCα(1)(-/-) CM. Neither BRL 37344 nor spermine NONOate altered calcium handling in CM of either genotype. These findings suggest that sGCα(1) exerts a positive inotropic effect under basal conditions, as well as mediates the negative inotropic effect of β(3)-AR signaling. Additionally, our work demonstrates that sGCα(1)β(1) is required for NO to depress β(1)/β(2)-AR-stimulated cardiac contractility and that this modulation is independent of changes in calcium handling.

Reperfusion injury limits the benefits of revascularization in the treatment of myocardial infarction (MI). Breathing nitric oxide (NO) reduces cardiac ischemia-reperfusion injury in animal models; however, the signaling pathways by which inhaled NO confers cardioprotection remain uncertain. The objective of this study was to learn whether inhaled NO reduces cardiac ischemia-reperfusion injury by activating the cGMP-generating enzyme, soluble guanylate cyclase (sGC), and to investigate whether bone marrow (BM)-derived cells participate in the sGC-mediated cardioprotective effects of inhaled NO. Wild-type (WT) mice and mice deficient in the sGC α(1)-subunit (sGCα(1)(-/-) mice) were subjected to cardiac ischemia for 1 h, followed by 24 h of reperfusion. During ischemia and for the first 10 min of reperfusion, mice were ventilated with oxygen or with oxygen supplemented with NO (80 parts per million). The ratio of MI size to area at risk (MI/AAR) did not differ in WT and sGCα(1)(-/-) mice that did not breathe NO. Breathing NO decreased MI/AAR in WT mice (41%, P = 0.002) but not in sGCα(1)(-/-) mice (7%, P = not significant). BM transplantation was performed to restore WT BM-derived cells to sGCα(1)(-/-) mice. Breathing NO decreased MI/AAR in sGCα(1)(-/-) mice carrying WT BM (39%, P = 0.031). In conclusion, these results demonstrate that a global deficiency of sGCα(1) does not alter the degree of cardiac ischemia-reperfusion injury in mice. The cardioprotective effects of inhaled NO require the presence of sGCα(1). Moreover, our studies suggest that BM-derived cells are key mediators of the ability of NO to reduce cardiac ischemia-reperfusion injury.

Purpose: Soluble guanylyl cyclase (sGC), which plays a pivotal role in penile erection, is a heterodimer build up by an α and a β subunit. For both subunits two isoforms have been characterized, but only the sGCα(1)β(1) and sGCα(2)β(1) isoforms seem to be functionally active. To elucidate the functional role of the sGCα(1)β(1) heterodimer in the mechanism of erection, experiments were performed in vivo and on isolated corpora cavernosa (CC) using sGCα(1)(-/-) mice., Materials and Methods: For the in vivo study sGC-dependent and -independent vasorelaxing agents were injected intracavernosally in sGCα(1)(-/-) and sGCα(1)(+/+) mice and the rise in intracavernosal pressure was recorded. For the in vitro study, isolated CC tissues from sGCα(1)(-/-) and sGCα(1)(+/+) mice were mounted in organ baths for isometric tension recording and concentration-dependent curves were obtained for sGC-dependent and -independent vasorelaxing agents. These experiments were performed on 2 different mice strains (129SvEvS7 and C57BL6/J) to determine potential strain differences., Results: The responses in sGCα(1)(-/-) after administration of the NO-donors, sodium nitroprusside (SNP) and spermine-NO, and to electrical stimulation are significantly reduced although not completely abolished. Responses to sGC-independent vasorelaxing agents are similar in sGCα(1)(-/-) and sGCα(1)(+/+) mice from both strains suggesting that the decreased potential of smooth muscle relaxation is not related to structural changes or changes in the pathway downstream sGC., Conclusion: This study illustrates the strain-independent importance of the sGCα(1)β(1) heterodimer, although remaining vasorelaxing responses in the sGCα(1)(-/-) mice suggest a complementary role for the sGCα(2)β(1) isoform or (an) sGC-independent mechanism(s).

Nitrite (NO(2)(-)), previously viewed as a physiologically inert metabolite and biomarker of the endogenous vasodilator NO, was recently identified as an important biological NO reservoir in vasculature and tissues, where it contributes to hypoxic signaling, vasodilation, and cytoprotection after ischemia-reperfusion injury. Reduction of nitrite to NO may occur enzymatically at low pH and oxygen tension by deoxyhemoglobin, deoxymyoglobin, xanthine oxidase, mitochondrial complexes, or NO synthase (NOS). We show that nitrite treatment, in sharp contrast with the worsening effect of NOS inhibition, significantly attenuates hypothermia, mitochondrial damage, oxidative stress and dysfunction, tissue infarction, and mortality in a mouse shock model induced by a lethal tumor necrosis factor challenge. Mechanistically, nitrite-dependent protection was not associated with inhibition of mitochondrial complex I activity, as previously demonstrated for ischemia-reperfusion, but was largely abolished in mice deficient for the soluble guanylate cyclase (sGC) alpha1 subunit, one of the principal intracellular NO receptors and signal transducers in the cardiovasculature. Nitrite could also provide protection against toxicity induced by Gram-negative lipopolysaccharide, although higher doses were required. In conclusion, we show that nitrite can protect against toxicity in shock via sGC-dependent signaling, which may include hypoxic vasodilation necessary to maintain microcirculation and organ function, and cardioprotection.

Altered cGMP signaling has been implicated in myocardial depression, morbidity, and mortality associated with sepsis. Previous studies, using inhibitors of soluble guanylate cyclase (sGC), suggested that cGMP generated by sGC contributed to the cardiac dysfunction and mortality associated with sepsis. We used sGC(alpha)(1)-deficient (sGC(alpha)(1)(-/-)) mice to unequivocally determine the role of sGC(alpha)(1)beta(1) in the development of cardiac dysfunction and death associated with two models of inflammatory shock: endotoxin- and TNF-induced shock. At baseline, echocardiographic assessment and invasive hemodynamic measurements of left ventricular (LV) dimensions and function did not differ between wild-type (WT) mice and sGC(alpha)(1)(-/-) mice on the C57BL/6 background (sGC(alpha)(1)(-/-B6) mice). At 14 h after endotoxin challenge, cardiac dysfunction was more pronounced in sGC(alpha)(1)(-/-B6) than WT mice, as assessed using echocardiographic and hemodynamic indexes of LV function. Similarly, Ca(2+) handling and cell shortening were impaired to a greater extent in cardiomyocytes isolated from sGC(alpha)(1)(-/-B6) than WT mice after endotoxin challenge. Importantly, morbidity and mortality associated with inflammatory shock induced by endotoxin or TNF were increased in sGC(alpha)(1)(-/-B6) compared with WT mice. Together, these findings suggest that cGMP generated by sGC(alpha)(1)beta(1) protects against cardiac dysfunction and mortality in murine inflammatory shock models.

Nitric oxide (NO) activates soluble guanylate cyclase (sGC) to produce guanosine-3',5'-cyclic-monophosphate (cGMP). The aim of this study was to investigate the nitrergic regulation of jejunal motility in sGCalpha(1) knockout (KO) mice. Functional responses to nitrergic stimuli and cGMP levels in response to nitrergic stimuli were determined in circular muscle strips. Intestinal transit was determined. Nitrergic relaxations induced by electrical field stimulation and exogenous NO were almost abolished in male KO strips, but only minimally reduced and sensitive to ODQ in female KO strips. Basal cGMP levels were decreased in KO strips, but NO still induced an increase in cGMP levels. Transit was not attenuated in male nor female KO mice. In vitro, sGCalpha(1)beta(1) is the most important isoform in nitrergic relaxation of jejunum, but nitrergic relaxation can also occur via sGCalpha(2)beta(1) activation. The latter mechanism is more pronounced in female than in male KO mice. In vivo, no important implications on intestinal motility were observed in male and female KO mice.

Objectives: Despite advances in resuscitation methods, survival after out-of-hospital cardiac arrest remains low, at least in part, due to postcardiac arrest circulatory and neurologic failure. To elucidate the role of nitric oxide (NO) in the recovery from cardiac arrest and cardiopulmonary resuscitation (CPR), we studied the impact of NO synthase (NOS3)/cGMP signaling on cardiac and neurologic outcomes after cardiac arrest and CPR., Design: Prospective, randomized, controlled study., Setting: Animal research laboratory., Subjects: Mice., Interventions: Female wild-type (WT) mice, NOS3-deficient mice (NOS3-/-), NOS3-/- mice with cardiomyocyte-specific overexpression of NOS3 (NOS3-/-CSTg), and mice deficient for soluble guanylate cyclase alpha1 (sGCalpha1-/-) were subjected to potassium-induced cardiac arrest (9 min) followed by CPR. Cardiac and neurologic function and survival were assessed up to 24 hrs post-CPR., Measurements and Main Results: Cardiac arrest and CPR markedly depressed myocardial function in NOS3-/- and sGCalpha1-/- but not in WT and NOS3-/-CSTg. Neurologic function score and 24 hrs survival rate was lower in NOS3-/- and sGCalpha1-/- compared with WT and NOS3-/-CSTg. Detrimental effects of deficiency of NOS3 or sGCalpha1 were associated with enhanced inflammation of heart and liver and increased cell death in heart, liver, and brain that were largely prevented by cardiomyocyte-restricted NOS3 overexpression., Conclusions: These results demonstrate an important salutary impact of NOS3/sGC signaling on the outcome of cardiac arrest. Myocardial NOS3 prevented postcardiac arrest myocardial dysfunction, attenuated end-organ damage, and improved neurologic outcome and survival. Our observations suggest that enhancement of cardiac NOS3 and/or sGC activity may improve outcome after cardiac arrest and CPR.

Carbon monoxide (CO) has been shown to cause enteric smooth muscle relaxation by activating soluble guanylyl cyclase (sGC). In gastric fundus, the sGCalpha1beta1 heterodimer is believed to be the most important isoform. The aim of our study was to investigate the role of the sGCalpha1/alpha2 subunits in the relaxant effect of CO and CORM-2 in murine gastric fundus using wild-type (WT) and sGCalpha1 knock-out (KO) mice. In WT mice, CO (bolus)-induced relaxations were abolished by the sGC inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), while CORM-2- and CO (infusion)-induced relaxations were only partially inhibited by ODQ. In sGCalpha1 KO mice, relaxant responses to CO and CORM-2 were significantly reduced when compared with WT mice, but ODQ still had an inhibitory effect. The sGC sensitizer 1-benzyl-3-(5'-hydroxymethyl-2'-furyl-)-indazol (YC-1) was able to potentiate CO- and CORM-2-induced relaxations in WT mice but lost this potentiating effect in sGCalpha1 KO mice. Both in WT and sGCalpha1 KO mice, CO-evoked relaxations were associated with a significant cGMP increase; however, basal and CO-elicited cGMP levels were markedly lower in sGCalpha1 KO mice. These data indicate that besides the predominant sGCalpha1beta1 isoform, also the less abundantly expressed sGCalpha2beta1 isoform plays an important role in the relaxant effect of CO in murine gastric fundus; however, the sGC stimulator YC-1 loses its potentiating effect towards CO in sGCalpha1 KO mice. Prolonged administration of CO-either by the addition of CORM-2 or by continuous infusion of CO-mediates gastric fundus relaxation in both a sGC-dependent and sGC-independent manner.

In distal colon, both nitric oxide (NO) and ATP are involved in non-adrenergic non-cholinergic (NANC) inhibitory neurotransmission. The role of the soluble guanylate cyclase (sGC) isoforms alpha(1)beta(1) and alpha(2)beta(1), and of the small conductance Ca(2+)-dependent K(+) channels (SK(Ca) channels) in the relaxation of distal colon by exogenous NO and by NANC nerve stimulation was investigated, comparing wild type (WT) and sGCalpha(1) knockout (KO) mice. In WT strips, the relaxation induced by electrical field stimulation (EFS) at 1 Hz but not at 2-8 Hz was significantly reduced by the NO-synthase inhibitor L-NAME or the sGC inhibitor ODQ. In sGCalpha(1) KO strips, the EFS-induced relaxation at 1 Hz was significantly reduced and no longer influenced by L-NAME or ODQ. The SK(Ca) channel blocker apamin alone had no inhibitory effect on EFS-induced relaxation, but combined with ODQ or L-NAME, apamin inhibited the relaxation induced by EFS at 2-8 Hz in WT strips and at 8 Hz in sGCalpha(1) KO strips. Relaxation by exogenous NO was significantly attenuated in sGCalpha(1) KO strips, but could still be reduced further by ODQ. Basal cGMP levels were lower in sGCalpha(1) KO strips but NO still significantly increased cGMP levels versus basal. In conclusion, in the absence of sGCalpha(1)beta(1), exogenous NO is able to partially act through sGCalpha(2)beta(1). NO, acting via sGCalpha(1)beta(1), is the principal neurotransmitter in EFS-evoked responses at 1 Hz. At higher stimulation frequencies, NO, acting at sGCalpha(1)beta(1) and/or sGCalpha(2)beta(1), functions together with another transmitter, probably ATP acting via SK(Ca) channels, with some degree of redundancy.

Aim: The effects of nitric oxide (NO) in the cardiovascular system are attributed in part to cGMP synthesis by the alpha1beta1 isoform of soluble guanylate cyclase (sGC). Because available sGC inhibitors are neither enzyme- nor isoform-specific, we generated knockout mice for the alpha1 subunit (sGCalpha1(-/-) mice) in order to investigate the function of sGCalpha1beta1 in the regulation of blood pressure and cardiac function., Methods and Results: Blood pressure was evaluated, using both non-invasive and invasive haemodynamic techniques, in intact and gonadectomized male and female sGCalpha1(-/-) and wild-type (WT) mice. Cardiac function was assessed with a conductance catheter inserted in the left ventricle of male and female sGCalpha1(-/-) and WT mice. Male sGCalpha1(-/-) mice developed hypertension (147 +/- 2 mmHg), whereas female sGCalpha1(-/-) mice did not (115 +/- 2 mmHg). Orchidectomy and treatment with an androgen receptor antagonist prevented hypertension, while ovariectomy did not influence the phenotype. Chronic testosterone treatment increased blood pressure in ovariectomized sGCalpha1(-/-) mice but not in WT mice. The NO synthase inhibitor Nomega-nitro-L-arginine methyl ester hydrochloride raised blood pressure similarly in male and female WT and sGCalpha1(-/-) mice. The ability of NO donor compounds to reduce blood pressure was slightly attenuated in sGCalpha1(-/-) male and female mice as compared to WT mice. The direct sGC stimulator BAY 41-2272 reduced blood pressure only in WT mice. Increased cardiac contractility and arterial elastance as well as impaired ventricular relaxation were observed in both male and female sGCalpha1(-/-) mice., Conclusion: These findings demonstrate that sGCalpha1beta1-derived cGMP signalling has gender-specific and testosterone-dependent cardiovascular effects and reveal that the effects of NO on systemic blood pressure do not require sGCalpha1beta1.

The principal target of the relaxant neurotransmitter nitric oxide (NO) is soluble guanylate cyclase (sGC). As the alpha(1)beta(1)-isoform of sGC is the predominant one in the gastrointestinal tract, the aim of this study was to investigate the role of sGC in nitrergic regulation of gastric motility in male and female sGCalpha(1) knock-out (KO) mice. In circular gastric fundus muscle strips, functional responses and cGMP levels were determined in response to nitrergic and non-nitrergic stimuli. sGC subunit mRNA expression in fundus was measured by real-time RT-PCR; in vivo gastric emptying of a phenol red meal was determined. No changes were observed in sGC subunit mRNA levels between wild-type (WT) and KO tissues. Nitrergic relaxations induced by short trains of electrical field stimulation (EFS) were abolished, while those by long trains of EFS were reduced in KO strips; the latter responses were abolished by 1H[1,2,4,]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The relaxations evoked by exogenous NO and the NO-independent sGC activator BAY 41-2272 were reduced in KO strips but still sensitive to ODQ. Relaxations induced by vasoactive intestinal peptide (VIP) and 8-bromo-cGMP were not influenced. Basal cGMP levels were decreased in KO strips but NO, long train EFS and BAY 41-2272 still induced a moderate ODQ-sensitive increase in cGMP levels. Gastric emptying, measured at 15 and 60 min, was increased at 15 min in male KO mice. sGCalpha(1)beta(1) plays an important role in gastric nitrergic relaxation in vitro, but some degree of nitrergic relaxation can occur via sGCalpha(2)beta(1) activation in sGCalpha(1) KO mice, which contributes to the moderate in vivo consequence on gastric emptying.

Objective: Soluble guanylyl cyclase (sGC), the predominant receptor for nitric oxide (NO), exists in 2 active isoforms (alpha(2)beta(1) and alpha(1)beta(1)). In vascular tissue sGCalpha(1)beta(1) is believed to be the most important. The aim of our study was to investigate the functional importance of the sGCalpha(1)-subunit in vasorelaxation., Methods: Aortic and femoral artery segments from male and/or female sGCalpha(1)(-/-) mice and wild-type littermates were mounted in a small-vessel myograph for isometric tension recording. This was supplemented with biochemical measurements of the cGMP concentration and sGC enzyme activity., Results: The functional importance of sGCalpha(1)beta(1) was demonstrated by the significantly decreased relaxing effects of acetylcholine (ACh), sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), NO gas, YC-1, BAY 41-2272 and T-1032 in the sGCalpha(1)(-/-) mice of both genders. Moreover, the basal and SNP-stimulated cGMP levels and basal sGC activity were significantly lower in the sGCalpha(1)(-/-) mice. However, the relaxing effects of NO, BAY 41-2272 and YC-1 seen in blood vessels from sGCalpha(1)(-/-) mice indicate a role for an sGCalpha(1)beta(1)-independent mechanism. The increase in sGC activity after addition of BAY 41-2272 and the inhibition of the ACh-, SNP-, SNAP- and NO gas-induced response by the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) in the sGCalpha(1)(-/-) mice are observations suggesting that the sGCalpha(2)beta(1) isoform is also functionally active. However, the insignificant increase in cGMP in response to SNP and the non-upregulated sGCalpha(2) expression level in the sGCalpha(1)(-/-) mice suggest rather the involvement of (an) sGC-independent mechanism(s)., Conclusions: We conclude that sGCalpha(1)beta(1) is involved in the vasorelaxation induced by NO-dependent and NO-independent sGC activators in both genders. However, the remaining relaxation seen in the sGCalpha(1)(-/-) mice suggests that besides sGCalpha(1)beta(1) also the minor isoform sGCalpha(2)beta(1) and/or (an) sGC-independent mechanism(s) play(s) a substantial role.

Background: Nitric oxide (NO) activates soluble guanylate cyclase (sGC), a heterodimer composed of alpha- and beta-subunits, to produce cGMP. NO reduces pulmonary vascular remodeling, but the role of sGC in vascular responses to acute and chronic hypoxia remains incompletely elucidated. We therefore studied pulmonary vascular responses to acute and chronic hypoxia in wild-type (WT) mice and mice with a nonfunctional alpha1-subunit (sGCalpha1-/-)., Methods and Results: sGCalpha1-/- mice had significantly reduced lung sGC activity and vasodilator-stimulated phosphoprotein phosphorylation. Right ventricular systolic pressure did not differ between genotypes at baseline and increased similarly in WT (22+/-2 to 34+/-2 mm Hg) and sGCalpha1-/- (23+/-2 to 34+/-1 mm Hg) mice in response to acute hypoxia. Inhaled NO (40 ppm) blunted the increase in right ventricular systolic pressure in WT mice (22+/-2 to 24+/-2 mm Hg, P<0.01 versus hypoxia without NO) but not in sGCalpha1-/- mice (22+/-1 to 33+/-1 mm Hg) and was accompanied by a significant rise in lung cGMP content only in WT mice. In contrast, the NO-donor sodium nitroprusside (1.5 mg/kg) decreased systemic blood pressure similarly in awake WT and sGCalpha1-/- mice as measured by telemetry (-37+/-2 versus -42+/-4 mm Hg). After 3 weeks of hypoxia, the increases in right ventricular systolic pressure, right ventricular hypertrophy, and muscularization of intra-acinar pulmonary vessels were 43%, 135%, and 46% greater, respectively, in sGCalpha1-/- than in WT mice (P<0.01). Increased remodeling in sGCalpha1-/- mice was associated with an increased frequency of 5'-bromo-deoxyuridine-positive vessels after 1 and 3 weeks (P<0.01 versus WT)., Conclusions: Deficiency of sGCalpha1 does not alter hypoxic pulmonary vasoconstriction. sGCalpha1 is essential for NO-mediated pulmonary vasodilation and limits chronic hypoxia-induced pulmonary vascular remodeling.