Atrial natriuretic peptide regulation of endothelial permeability is mediated by cGMP

Association of Empagliflozin Treatment With Albuminuria Levels in Patients With Heart Failure: A Secondary Analysis of EMPEROR-Pooled

Importance

Albuminuria, routinely assessed as spot urine albumin-to-creatinine ratio (UACR), indicates structural damage of the glomerular filtration barrier and is associated with poor kidney and cardiovascular outcomes. Sodium-glucose cotransporter-2 (SGLT2) inhibitors have been found to reduce UACR in patients with type 2 diabetes, but its use in patients with heart failure (HF) is less well studied.

Objective

To analyze the association of empagliflozin with study outcomes across baseline levels of albuminuria and change in albuminuria in patients with HF across a wide range of ejection fraction levels.

Design, Setting, and Participants

This post hoc analysis included all patients with HF from the EMPEROR-Pooled analysis using combined individual patient data from the international multicenter randomized double-blind parallel-group, placebo-controlled EMPEROR-Reduced and EMPEROR-Preserved trials. Participants in the original trials were excluded from this analysis if they were missing baseline UACR data. EMPEROR-Preserved was conducted from March 27, 2017, to April 26, 2021, and EMPEROR-Reduced was conducted from April 6, 2017, to May 28, 2020. Data were analyzed from January to June 2022.

Interventions

Randomization to empagliflozin or placebo.

Main Outcomes and Measures

New-onset macroalbuminuria and regression to normoalbuminuria and microalbuminuria.

Results

A total of 9673 patients were included (mean [SD] age, 69.9 [10.4] years; 3551 [36.7%] female and 6122 [63.3%] male). Of these, 5552 patients had normoalbuminuria (UACR <30 mg/g) and 1025 had macroalbuminuria (UACR >300 mg/g). Compared with normoalbuminuria, macroalbuminuria was associated with younger age, races other than White, obesity, male sex, site region other than Europe, higher levels of N-terminal pro-hormone brain natriuretic peptide and high-sensitivity troponin T, higher blood pressure, higher New York Heart Association class, greater HF duration, more frequent previous HF hospitalizations, diabetes, hypertension, lower eGFR, and less frequent use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers and mineralocorticoid receptor antagonists. An increase in events was observed in individuals with higher UACR levels. The association of empagliflozin with cardiovascular mortality or HF hospitalization was consistent across UACR categories (hazard ratio [HR], 0.80; 95% CI, 0.69-0.92 for normoalbuminuria; HR, 0.74; 95% CI, 0.63-0.86 for microalbuminuria; HR, 0.78; 95% CI, 0.63-0.98 for macroalbuminuria; interaction P trend = .71). Treatment with empagliflozin was associated with lower incidence of new macroalbuminuria (HR, 0.81; 95% CI, 0.70-0.94; P = .005) and an increase in rate of remission to sustained normoalbuminuria or microalbuminuria (HR, 1.31; 95% CI, 1.07-1.59; P = .009) but not with a reduction in UACR in the overall population; however, UACR was reduced in patients with diabetes, who had higher UACR levels than patients without diabetes (geometric mean for diabetes at baseline, 0.91; 95% CI, 0.85-0.98 and for no diabetes at baseline, 1.08; 95% CI, 1.01-1.16; interaction P = .008).

Conclusions and Relevance

In this post hoc analysis of a randomized clinical trial, compared with placebo, empagliflozin was associated with reduced HF hospitalizations or cardiovascular death irrespective of albuminuria levels at baseline, reduced progression to macroalbuminuria, and reversion of macroalbuminuria.

Trial Registration

ClinicalTrials.gov Identifiers: NCT03057977 and NCT03057951.

Progress and prospects of Sacubitril/Valsartan: Based on heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is present in nearly half of patients with heart failure. The prevalence of heart failure with normal or near-normal ejection fractions increases more rapidly than in patients with reduced ejection fractions. Angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blocker (ARB), aldosterone antagonist, β-blocker, and calcium channel blocker have not shown significant efficacy in HFpEF clinical trials. Sacubitril/Valsartan, combined angiotensin receptor blocker (Valsartan) with neprilysin inhibitor (Sacubitril), was the first-of-its-kind angiotensin receptor-neprilysin inhibitor (ARNI) to be developed. It has shown significant efficacy on HFpEF in recent studies. It is considered that most of the current Sacubitril/Valsartan studies are still concentrated in the field of heart failure, especially heart failure with reduced ejection fraction (HFrEF). This review discusses the latest advances in cardiovascular, renal, and metabolic aspects of Sacubitril/Valsartan, mainly in HFpEF, providing more evidence for further future research on Sacubitril/Valsartan and raising issues that should be paid attention. At the same time, this review will introduce the academic consensus on Sacubitril/Valsartan in treating HFpEF in China.

Effect of Sacubitril/Valsartan on renal function in patients with chronic kidney disease and heart failure with preserved ejection fraction: A real-world 12-week study

Patients with chronic kidney disease (CKD) are often complicated with heart failure with preserved ejection fraction (HFpEF). However, several drugs, including angiotensin-converting enzyme inhibitor (ACEI) and angiotensin receptor blocker (ARB), have not shown apparent benefits in terms of morbidity and mortality of HFpEF. PARAMOUNT and other studies have shown the potential benefits of Sacubitril/Valsartan on patients with HFpEF, but its effects on renal function and the effect of low-dose Sacubitril/Valsartan in actual clinical conditions have not been thoroughly evaluated. In our longitudinal and observational research, 353 patients were followed up for 12 weeks. We evaluated renal function [urinary protein, serum creatinine and estimated glomerular filtration rate (eGFR)] and cardiac function [NT-proBNP (brain natriuretic peptide), New York Heart Association (NYHA) classification, left ventricular ejection fraction (LVEF), left atrial width and left ventricular end-diastolic width] at baseline and during follow-up. Worsening renal function (WRF) was defined as an increased serum creatinine≥26.5umol/L or decreased eGFR≥20%. The decline of eGFR in the Sacubitril/Valsartan group was slower than that in the control group (p = 0.021). The outcome of proteinuria in the ACEI/ARB group was significantly better than that in the Sacubitril/Valsartan group (p = 0.001). In terms of echocardiogram, the average left atrial width in Sacubitril/Valsartan group decreased by 1.38 ± 3.02 mm, which was significantly lower than that in the ACEI/ARB group (p = 0.02). The increase of urine protein class in the ACEI/ARB group increased the risk of WRF with statistical significance (OR = 2.36, 95%CI 1.01-5.49, p = 0.047), but no statistical significance was found in all the patients or Sacubitril/Valsartan group. In conclusion, Sacubitril/Valsartan could more effectively slow down renal function decline and reverse myocardial remodeling in patients with CKD and HFpEF than ACEI/ARB, even at low doses, though its protective effect on urinary protein is not as good as that of ACEI/ARB.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

An impaired natriuretic peptide hormone system may play a role in COVID-19 severity in vulnerable populations

Advanced age, underlying cardiovascular disease (including hypertension), and obesity are associated with a higher risk of progression to severe hypoxemia, acute respiratory distress syndrome (ARDS), and death in COVID-19-infected patients. African Americans have a higher degree of COVID-19 mortality. The incidence of salt-sensitive hypertension is higher in older individuals and African Americans. Lower circulating levels of natriuretic peptides, key regulators of vascular tone and kidney function, have been associated with salt-sensitive hypertension and obesity. Evidence has accumulated that ANP administered to pulmonary endothelial cells, isolated lungs, and patients suffering from ARDS reduces endothelial damage and preserves the endothelial barrier, thereby reducing pulmonary edema and inflammation. Epidemiologic and pharmacologic data suggest that deficiencies in the natriuretic peptide hormone system may contribute to the development of severe lung pathology in COVID-19 patients, and treatments that augment natriuretic peptide signaling may have potential to limit progression to ARDS.

Disruption of a self-amplifying catecholamine loop reduces cytokine release syndrome

Cytokine release syndrome (CRS) is a life-threatening complication of several new immunotherapies used to treat cancers and autoimmune diseases^1-5. Here we report that atrial natriuretic peptide can protect mice from CRS induced by such agents by reducing the levels of circulating catecholamines. Catecholamines were found to orchestrate an immunodysregulation resulting from oncolytic bacteria and lipopolysaccharide through a self-amplifying loop in macrophages. Myeloid-specific deletion of tyrosine hydroxylase inhibited this circuit. Cytokine release induced by T-cell-activating therapeutic agents was also accompanied by a catecholamine surge and inhibition of catecholamine synthesis reduced cytokine release in vitro and in mice. Pharmacologic catecholamine blockade with metyrosine protected mice from lethal complications of CRS resulting from infections and various biotherapeutic agents including oncolytic bacteria, T-cell-targeting antibodies and CAR-T cells. Our study identifies catecholamines as an essential component of the cytokine release that can be modulated by specific blockers without impairing the therapeutic response.

Renal effects of the angiotensin receptor neprilysin inhibitor LCZ696 in patients with heart failure and preserved ejection fraction

BACKGROUND

Increases in serum creatinine with renin-angiotensin-aldosterone system (RAAS) inhibitors can lead to unnecessary discontinuation of these agents. The dual-acting angiotensin receptor neprilysin inhibitor LCZ696 improves clinical outcome patients with heart failure with reduced ejection fraction, and pilot data suggest potential benefit in heart failure with preserved ejection fraction (HFpEF). The effects of LCZ696 on renal function have not been assessed.

METHODS AND RESULTS

A total of 301 HFpEF patients were randomly assigned to LCZ696 or valsartan in the PARAMOUNT trial. We studied renal function [creatinine, estimated glomerular filtration rate (eGFR), cystatin C, and urinary albumin to creatinine ratio (UACR)] at baseline, 12 weeks, and after 36 weeks of treatment. Worsening renal function (WRF) was determined as an serum creatinine increase of >0.3 mg/dL and/or >25% between two time-points. Mean eGFR at baseline was 65.4 ± 20.4 mL/min per 1.73 m(2) . The eGFR declined less in the LCZ696 group than in the valsartan group (-1.5 vs. -5.2 mL/min per 1.73 m(2) ; P = 0.002). The incidence of WRF was lower in the LCZ696 group (12%) than in the valsartan group (18%) at any time-point, but this difference was not statistically significant (P = 0.18). Over 36 weeks, the geometric mean of UACR increased in the LCZ696 group (2.4-2.9 mg/mmol), whereas it remained stable in the valsartan group (2.1-2.0 mg/mmol; P for difference between groups = 0.016).

CONCLUSION

In patients with HFpEF, therapy with LCZ696 for 36 weeks was associated with preservation of eGFR compared with valsartan therapy, but an increase in UACR.

Atrial natriuretic peptide genetic variant rs5065 and risk for cardiovascular disease in the general community: a 9-year follow-up study

We analyzed the phenotype associated with the atrial natriuretic peptide (ANP) genetic variant rs5065 in a random community-based sample. We also assessed and compared the biological action of 2 concentrations (10(-10) mol/L, 10(-8) mol/L) of ANP and ANP-RR, the protein variant encoded by the minor allele of rs5065, on activation of the guanylyl cyclase (GC)-A and GC-B receptors, production of the second messenger 3',5'-cGMP in endothelial cells, and endothelial permeability. rs5065 genotypes were determined in a cross-sectional adult cohort from Olmsted County, MN (n=1623). Genotype frequencies for rs5065 were 75%, 24%, and 1% for TT, TC, and CC, respectively. Multivariate analysis showed that the C allele was associated with increased risk of cerebrovascular accident (hazard ratio, 1.43; 95% confidence interval, 1.09-1.86; P=0.009) and higher prevalence of myocardial infarction (odds ratio, 1.82; 95% confidence interval, 1.07-3.09; P=0.026). ANP-RR 10(-8) mol/L activated the GC-A receptor (83.07±8.31 versus no treatment 0.18±0.04 per 6 wells; P=0.006), whereas ANP-RR 10(-10) mol/L did not. Neither 10(-8) mol/L nor 10(-10) mol/L ANP-RR activated GC-B receptor (P=0.10, P=0.35). ANP 10(-8) mol/L and ANP-RR 10(-8) mol/L stimulated 3',5'-cGMP production in endothelial cells similarly (P=0.58). Both concentrations of ANP-RR significantly enhanced human aortic endothelial cell permeability (69 versus 29 relative fluorescence units [RFUs], P=0.012; 58 versus 39 RFUs, P=0.015) compared with ANP. The minor allele of rs5065 was associated with increased cardiovascular risk. ANP-RR activated the GC-A receptor, increased 3',5'-cGMP in endothelial cells, and when compared with ANP, augmented endothelial cell permeability.

Soluble guanylyl cyclase expression is reduced in LPS-induced lung injury

Soluble guanylyl cyclase (sGC) is a cGMP-generating enzyme implicated in the control of smooth muscle tone that also regulates platelet aggregation. Moreover, sGC activation has been shown to reduce leukocyte adherence to the endothelium. Herein, we investigated the expression of sGC in a murine model of LPS-induced lung injury and evaluated the effects of sGC inhibition in the context of acute lung injury (ALI). Lung tissue sGC alpha1 and beta1 subunit protein levels were determined by Western blot and immunohistochemistry, and steady-state mRNA levels for the beta1 subunit were assessed by real-time PCR. LPS inhalation resulted in a decrease in beta1 mRNA levels, as well as a reduction in both sGC subunit protein levels. Decreased alpha1 and beta1 expression was observed in bronchial smooth muscle and epithelial cells. TNF-alpha was required for the LPS-triggered reduction in sGC protein levels, as no change in alpha1 and beta1 levels was observed in TNF-alpha knockout mice. To determine the effects of sGC blockade in LPS-induced lung injury, mice were exposed to 1H-[1,2,4]oxodiazolo[4,3-a]quinoxalin-l-one (ODQ) prior to the LPS challenge. Such pretreatment led to a further increase in total cell number (mainly due to an increase in neutrophils) and protein concentration in the bronchoalveoalar lavage fluid; the effects of ODQ were reversed by a cell-permeable cGMP analog. We conclude that sGC expression is reduced in LPS-induced lung injury, while inhibition of the enzyme with ODQ worsens lung inflammation, suggesting that sGC exerts a protective role in ALI.

Natriuretic peptides differentially attenuate thrombin-induced barrier dysfunction in pulmonary microvascular endothelial cells

Previous studies have described a protective effect of atrial natriuretic peptide (ANP) against agonist-induced permeability in endothelial cells derived from various vascular beds. In the current study, we assessed the effects of the three natriuretic peptides on thrombin-induced barrier dysfunction in rat lung microvascular endothelial cells (LMVEC). Both ANP and brain natriuretic peptide (BNP) attenuated the effect of thrombin on increased endothelial monolayer permeability and significantly enhanced the rate of barrier restoration. C-type natriuretic peptide (CNP) had no effect on the degree of thrombin-induced monolayer permeability, but did enhance the restoration of the endothelial barrier, similar to ANP and BNP. In contrast, the non-guanylyl cyclase-linked natriuretic peptide receptor specific ligand, cyclic-atrial natriuretic factor (c-ANF), delayed the rate of barrier restoration following exposure to thrombin. All three natriuretic peptides promoted cGMP production in the endothelial cells; however, 8-bromo-cGMP alone did not significantly affect thrombin modulation of endothelial barrier function. ANP and BNP, but not CNP or c-ANF, blunted thrombin-induced RhoA GTPase activation. We conclude that ANP and BNP protect against thrombin-induced barrier dysfunction in the pulmonary microcirculation by a cGMP-independent mechanism, possibly by attenuation of RhoA activation.

Role of protein kinase G in barrier-protective effects of cGMP in human pulmonary artery endothelial cells

Increases in endothelial cGMP prevent oxidant-mediated endothelial barrier dysfunction, but the downstream mechanisms remain unclear. To determine the role of cGMP-dependent protein kinase (PKG)(I), human pulmonary artery endothelial cells (HPAEC) lacking PKG(I) expression were infected with a recombinant adenovirus encoding PKG(Ibeta) (Ad.PKG) and compared with uninfected and control-infected (Ad.betagal) HPAEC. Transendothelial electrical resistance (TER), an index of permeability, was measured after H(2)O(2) (250 microM) exposure with or without pretreatment with 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate (CPT-cGMP). HPAEC infected with Ad.PKG, but not Ad.betagal, expressed PKG(I) protein and demonstrated Ser(239) and Ser(157) phosphorylation of vasodilator-stimulated phosphoprotein after treatment with CPT-cGMP. Adenoviral infection decreased basal permeability equally in Ad.PKG- and Ad.betagal-infected HPAEC compared with uninfected cells. Treatment with CPT-cGMP (100 microM) caused a PKG(I)-independent decrease in permeability (8.2 +/- 0.6%). In all three groups, H(2)O(2) (250 microM) caused a similar approximately 35% increase in permeability associated with increased actin stress fiber formation, intercellular gaps, loss of membrane VE-cadherin, and increased intracellular Ca(2+) concentration ([Ca(2+)](i)). In uninfected and Ad.betagal-infected HPAEC, pretreatment with CPT-cGMP (100 microM) partially blocked the increased permeability induced by H(2)O(2). In Ad.PKG-infected HPAEC, CPT-cGMP (50 microM) prevented the H(2)O(2)-induced TER decrease, cytoskeletal rearrangement, and loss of junctional VE-cadherin. CPT-cGMP attenuated the peak [Ca(2+)](i) caused by H(2)O(2) similarly (23%) in Ad.betagal- and Ad.PKG-infected HPAEC, indicating a PKG(I)-independent effect. These data suggest that cGMP decreased HPAEC basal permeability by a PKG(I)-independent process, whereas the ability of cGMP to prevent H(2)O(2)-induced barrier dysfunction was predominantly mediated by PKG(I) through a Ca(2+)-independent mechanism.

Targets for pharmacological intervention of endothelial hyperpermeability and barrier function

Many diseases share the common feature of vascular leakage, and endothelial barrier dysfunction is often the underlying cause. The subsequent stages of endothelial barrier dysfunction contribute to endothelial hyperpermeability. Vasoactive agents induce loss of junctional integrity, a process that involves actin-myosin interaction. Subsequently, the interaction of leukocytes amplifies leakage by the leukocyte-derived mediators. The processes mainly occur at the postcapillary venules. The whole microvascular bed, including the capillaries, becomes involved in vascular leakage by the induction of angiogenesis. Plasma leakage results from gaps between endothelial cells as well as by the induction of transcellular transport pathways. Several mechanisms can improve endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockade of specific receptors and elevation of cyclic AMP (cAMP) by agents such as beta(2)-adrenergic agents. However, current therapies based on these principles often fail. Recent research has identified several new promising targets for pharmacological therapy. Endogenous compounds were also found with barrier-improving characteristics. Important insights were obtained in the different pathways involved in barrier dysfunction. Such insights regard the regulation of endothelial contraction and endothelial junction integrity: inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability reducing properties, and strategies to target vascular endothelial growth factor (VEGF)-mediated edema are under current investigation. In clinical practice, not only tools to improve an impaired endothelial barrier function are necessary. Sometimes, a controlled, temporal, and local increase in permeability can also be desired, for example, with the aim to enhance drug delivery. Therefore, vessel leakiness is also being exploited to enable tissue access of liposomes, viral vectors, and other therapeutic agents that do not readily cross healthy endothelium. This review discusses strategies for targeting signaling molecules in therapies for diseases involving altered endothelial permeability.

Inhibition of p38 MAPK activation via induction of MKP-1: atrial natriuretic peptide reduces TNF-alpha-induced actin polymerization and endothelial permeability

The atrial natriuretic peptide (ANP) is a cardiovascular hormone possessing antiinflammatory potential due to its inhibitory action on the production of inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha). The aim of this study was to determine whether ANP is able to attenuate inflammatory effects of TNF-alpha on target cells. Human umbilical vein endothelial cells (HUVECs) were treated with TNF-alpha in the presence or absence of ANP. Changes in permeability, cytoskeletal alterations, phosphorylation of p38 MAPK and HSP27, and expression of MKP-1 were determined by macromolecule permeability assay, fluorescence labeling, RT-PCR, and immunoblotting. Antisense studies were done by transfecting cells with MKP-1 antisense oligonucleotides. Activation of HUVECs with TNF-alpha lead to a significant increase of macromolecule permeability and formation of stress fibers. Treatment of cells with ANP (10(-8) to 10(-6) mol/L) significantly reduced the formation of stress fibers and elevated permeability. Both TNF-alpha-induced effects were shown to be mediated via the activation of p38 using SB203580, a specific inhibitor of p38. ANP significantly reduced the TNF-alpha-induced activation of p38 and attenuated the phosphorylation of HSP27, a central target downstream of p38. ANP showed no effect on p38 upstream kinases MKK3/6. However, a significant induction of the MAPK phosphatase MKP-1 mRNA and protein could be observed in ANP-treated cells. Antisense experiments proved a causal role for MKP-1 induction in the ANP-mediated inhibition of p38. These data show the inhibitory action of ANP on TNF-alpha-induced changes in endothelial cytoskeleton and macromolecule permeability involving an MKP-1-induced inactivation of p38 MAPK. These effects point to an antiinflammatory and antiatherogenic potential of this cardiovascular hormone.

Role of vasodilator-stimulated phosphoprotein in PKA-induced changes in endothelial junctional permeability

At sites of ongoing inflammation, polymorphonuclear leukocytes (PMN, neutrophils) migrate across vascular endothelia, and such transmigration has the potential to disturb barrier properties and can result in intravascular fluid loss and edema. It was recently appreciated that endogenous pathways exist to dampen barrier disruption during such episodes and may provide an important anti-inflammatory link. For example, during transmigration, PMN-derived adenosine activates endothelial adenosine receptors and induces a cAMP-dependent resealing of endothelial barrier function. In our study reported here, we sought to understand the link between cyclic nucleotide elevation and increased endothelial barrier function. Initial studies revealed that adenosine-induced barrier function is tightly linked to activation of protein kinase A (PKA). Because PKA selectively phosphorylates serine and threonine residues, we screened zonula occludens-1 (ZO-1) immunoprecipitates for the existence of such phosphorylated proteins as targets for barrier regulation. This analysis revealed a dominantly phosphorylated band at 50 kDa. Microsequencing identified this protein as vasodilator-stimulated phosphoprotein (VASP), an actin binding protein with multiple serine/threonine phosphorylation sites. Immunofluorescent microscopy revealed that VASP localizes to endothelial junctional complexes and colocalizes with ZO-1, occludin, and junctional adhesion molecule-1 (JAM-1). To address the role of phospho-VASP in regulation of barrier function, we generated a phosphospecific VASP antibody targeting the Ser157 residue phosphorylation site, the site preferred by PKA. Immunolocalization studies with this antibody revealed that upon PKA activation, phospho-VASP appears at cell-cell junctions. Transient transfection of truncated VASP fragments revealed a parallel increase in barrier function. Taken together, these studies reveal a central role for phospho-VASP in the coordination of PKA-regulated barrier function, such as occurs during episodes of inflammation.

Nitric oxide attenuates H(2)O(2)-induced endothelial barrier dysfunction: mechanisms of protection

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated injury in porcine pulmonary artery endothelial cells (PAECs) and modulates intracellular levels of cGMP and cAMP. We hypothesized that.NO attenuates H(2)O(2)-induced PAEC monolayer barrier dysfunction through cyclic nucleotide-dependent signaling mechanisms. To examine this hypothesis, cultured PAEC monolayers were treated with H(2)O(2), and barrier function was measured as transmonolayer albumin clearance. H(2)O(2) caused significant PAEC barrier dysfunction that was attenuated by intracellular as well as extracellular.NO generation.NO increased PAEC cGMP and cAMP levels, but treatment with inhibitors of soluble guanylate cyclase or protein kinase G did not abrogate.NO-mediated barrier protection. In contrast, H(2)O(2) decreased protein kinase A activity, and inhibiting protein kinase A abrogated the protective effect of.NO. H(2)O(2)-induced barrier dysfunction was not associated with decreased levels of cGMP or cAMP. 3-Isobutyl-1-methylxanthine and the cGMP analog 8-bromo-cGMP had little effect on H(2)O(2)-mediated endothelial barrier dysfunction, whereas 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine was protective. These results indicate that.NO modulates vascular endothelial barrier function through cAMP-dependent signaling mechanisms.

Both inhalant and intravenous uroguanylin inhibit leukotriene C4-induced airway changes

Uroguanylin, a well-known ligand of guanylyl cyclase C receptor in the gastrointestinal tissue, has recently been reported to have pulmonary effects. We investigated the inhibitory effects of uroguanylin against leukotriene C4-induced bronchoconstriction and airway microvascular leakage. Anesthetized guinea pigs, ventilated via a tracheal cannula in a plethysmograph box, were measured by pulmonary mechanics for 10 min after i.v. administering 2 microg/kg leukotriene C4. Airway microvascular leakage was assessed by extravasation of Evans blue dye into airway tissues. Both inhalant and i.v. pretreatment of uroguanylin significantly inhibited leukotriene C4-induced pulmonary changes in a dose-dependent manner, suggesting its effectiveness against an asthmatic condition.

Serotonin-induced protein kinase C activation in cultured rat heart endothelial cells

This study examined whether serotonin can activate protein kinase C in rat heart endothelial cells. Protein kinase C isozyme translocation was examined by Western blot analysis with isozyme-specific anti-protein kinase C antibody. In this study, only alpha protein kinase C isozyme was found to be translocated from the cytosolic to the particulate fractions after serotonin stimulation. The effect of serotonin on the incorporation of 32P from [gamma-32P]ATP into peptide substrate was studied as another indicator of protein kinase C activation. The experiments in this study demonstrated that the Ca(2+)-phospholipid-dependent protein kinase, protein kinase C, was activated by serotonin. By investigating [3H]phorbol 12,13-dibutyrate binding to protein kinase C and trypsin-treated protein kinase C activity, we demonstrated that the site of action of serotonin is probably the regulatory domain of protein kinase C. Finally, we also demonstrated that serotonin had no effect on the intracellular concentration of cyclic nucleotides (cAMP, cGMP). These findings support the hypothesis that protein kinase C may be an important participant in serotonin-induced endothelial cell contraction and barrier dysfunction.

Phosphorylation of vasodilator-stimulated phosphoprotein: a consequence of nitric oxide- and cGMP-mediated signal transduction in brain capillary endothelial cells and astrocytes

There is contradictory information on the relevance of nitric oxide (NO) and cGMP for the function of brain capillary endothelial cells (BCEC) forming the blood-brain barrier (BBB). Therefore, NO/cGMP-mediated signal transduction was investigated in cell cultures of BCEC and of astrocytes (AC) inducing BBB properties in BCEC. Constitutive, Ca2+-activated isoforms of NO synthase (NOS) were found in BCEC (endothelial NOS: eNOS) and in AC (neuronal NOS: nNOS), leading to increased NO release after incubation with the Ca2+-ionophore A23187. Both cell types expressed inducible NOS (iNOS) after incubation with cytokines. Soluble guanylate cyclase (sGC) was detected in both cell types. NO-dependent cGMP formation were observed in BCEC and, less pronounced, in AC. Furthermore, both cell types formed cGMP independently of NO via stimulation of particulate guanylate cyclase (pGC). cGMP-dependent protein kinase (PKG) type Ibeta, but not type II, was expressed in BCEC and AC. In BCEC, vasodilator-stimulated phosphoprotein (VASP) was detected, an established substrate of PKG and associated with microfilaments and cell-cell contacts. Phosphorylation of VASP was intensified by increased intracellular cGMP concentrations. The results indicate that BCEC and, to a smaller degree, AC can form NO and cGMP in response to different stimuli. In BCEC, NO/cGMP-dependent phosphorylation of VASP is demonstrated, thus providing a possibility of influencing cell-cell contacts.

Neutral endopeptidase 3.4.24.11 inhibition potentiates the inhibitory effects of type-C natriuretic peptide on leukotriene D4-induced airway changes

1. Microvascular leakage, a primary feature of inflammation, is well known for worsening the asthmatic condition. Gene expression of and a specific receptor for type-C natriuretic peptide (CNP), initially considered a neuropeptide, have been detected in the human vascular wall and secretion of CNP from vascular endothelial cells has recently been demonstrated. These facts suggest the presence of a vascular natriuretic peptide system and led us to expect that CNP may act beneficially on airway microvascular leakage in asthma. In the present study, we investigated the effects of CNP against leukotriene (LT) D4-induced airway microvascular leakage and bronchoconstriction and how these effects were potentiated by thiorphan, a potent neutral endopeptidase 3.4.24.11 (NEP) inhibitor. 2. Anaesthetized male guinea-pigs, ventilated via a tracheal cannula, were placed into a plethysmograph for 10 min, in order to measure pulmonary mechanics and mean blood pressure, after challenge with 2 micrograms/kg LTD4 and then the extravasation of 20 mg/kg Evans blue dye into airway tissue was investigated to indicate and evaluate microvascular leakage. 3. Intravenous administration of CNP (100, 300 and 1000 micrograms/kg) significantly inhibited the LTD4-induced microvascular leakage and bronchoconstriction in a dose-dependent manner. These inhibitory effects were enhanced by pretreatment with 20 mg/kg thiorphan, suggesting the important role of NEP in the pulmonary metabolism of CNP. 4. We believe that these results are encouraging for the further investigation of the therapeutic applications of exogenous CNP in asthma.

Decreased protein kinase C activation mediates inhibitory effect of norathyriol on serotonin-mediated endothelial permeability

We examined the mechanisms of norathyriol on the serotonin-induced increased permeability of rat heart endothelial cell monolayers. The present study showed that the activation of rat heart endothelial cell protein kinase C by phorbol myristate acetate led to the dose-dependent increase in endothelial permeability to albumin, an effect that was inhibited by staurosporine (a protein kinase inhibitor). Staurosporine also attenuated the serotonin-induced increase in permeability. Norathyriol abolished both serotonin- and phorbol myristate acetate-induced permeability. We investigated whether norathyriol, by inhibiting protein kinase C activation, attenuated the serotonin-induced permeability. Immunofluorescence studies demonstrated that norathyriol prevented the redistribution of protein kinase C isozymes following stimulation with serotonin. Western blot analysis showed that norathyriol significantly inhibited the serotonin-induced translocation of the alpha protein kinase C isozyme from the cytosolic to the particulate fraction. In conclusion, norathyriol attenuates the serotonin-induced permeability of rat heart endothelial cells to macromolecules in association with inhibition of protein kinase C activation. This decrease in endothelial cell permeability may be one of the mechanisms for the protective effects of norathyriol against edema formation in response to inflammatory agonists in vivo.

Effects of uroguanylin and guanylin against antigen-induced bronchoconstriction and airway microvascular leakage in sensitized guinea-pigs

Uroguanylin and guanylin are isolated mainly from the gastrointestinal tract and are activators of guanylyl cyclase C receptor (GC-C), which mediates the production of intracellular cyclic guanosine 3',5'-monophosphate (cyclic GMP). The bronchodilator effects of agents that raise cyclic GMP levels, such as atrial natriuretic peptide, have been reported, and uroguanylin mRNA has recently been detected in extra-gastrointestinal tissues, including the lung, suggesting their role in pulmonary activity. In the first step of this study, we examined the relaxant effects of uroguanylin and guanylin on isolated tracheal smooth muscle of guinea-pigs, and measured tissue cyclic GMP levels by means of enzymeimmunoassay. Uroguanylin produced concentration-dependent relaxant effects on resting tone and significant elevated cyclic GMP levels. Guanylin produced the same, but less potent, effects. In this study, we first investigated the effects of uroguanylin and guanylin on antigen-induced bronchoconstriction and airway microvascular leakage in actively sensitized guinea-pigs. Anesthetized male guinea-pigs, ventilated via a tracheal cannula, were placed in a plethysmograph to measure pulmonary mechanics for 10 min after challenging with 1 mg/kg of ovalbumin. Evans blue dye was then extravasated into their airway tissues to measure microvascular leakage. Intravenous pretreatment with uroguanylin significantly inhibited ovalbumin-induced bronchoconstriction and microvascular leakage in a dose-dependent manner. These inhibitory effects were mimicked by 8-bromoguanosine 3', 5'-cyclic monophosphate. This study is the first to show that uroguanylin not only had a potent bronchodilatory effect but also inhibited microvascular leakage. These results encouraged us to continue the above experimental and clinical studies in bronchial asthma.

Compared effects of natriuretic peptides on ovalbumin-induced asthmatic model

We compared the effects of natriuretic peptides on antigen-induced bronchoconstriction and airway microvascular leakage in sensitized guinea pigs. Anesthetized male guinea pigs, ventilated via a tracheal cannula, were placed in a plethysmograph to measure pulmonary mechanics for 10 min after challenge with 1 mg/kg of ovalbumin, and then Evans blue dye was extravasated into airway tissue in order to indicate and evaluate microvascular leakage. Three separate intravenous pretreatments using atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) significantly inhibited the ovalbumin-induced bronchoconstriction and microvascular leakage in a dose-dependent manner. These inhibitory effects were mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate. We showed that the rank order of inhibitory potencies, which were mediated by cyclic guanosine 3',5'-monophosphate, was BNP > or = ANP > or = CNP. These results gave us some clues for the clinical application of the natriuretic peptides.

Inhibitory effect of 2-phenyl-4-quinolone on serotonin-mediated changes in the morphology and permeability of endothelial monolayers

The integrity of endothelial cell monolayers, a critical requirement for barrier maintenance, is needed for the prevention of edema formation. To investigate the mechanisms by which 2-phenyl-4-quinolone (YT-1) provided protection against serotonin-induced exudation, rat heart endothelial cell cultures were used. In this study, serotonin and phorbol myristate acetate (PMA) caused endothelial cells to became permeable to macromolecules by causing cell contraction and intercellular gap formation. These responses were attenuated by staurosporine, a protein kinase C inhibitor. Further experiments showed that YT-1 (1) did not alter serotonin-mediated early signal events such as protein kinase C activation, (2) protected against serotonin-induced endothelial barrier dysfunction by increasing intracellular cAMP levels, (3) played a role in regulating adenylate cyclase activity, (4) reversed serotonin-induced permeability to macromolecules, an effect which did not correlate with intracellular cGMP concentrations. This study demonstrates a possible mechanism by which YT-1 protects endothelial function and preserves the microvasculature from pharmacologic injury by vasoactive agents.

Cyclic GMP accumulation in pulmonary microvascular endothelial cells measured by intact cell prelabeling

Cyclic GMP accumulation in cultured rat pulmonary microvascular endothelial cells (RPMVEC) was studied with a new prelabeling method developed using intact platelets and smooth muscle cells (1). [3H]-hypoxanthine was used to radiolabel the cellular guanine nucleotide pool. Neutral alumina and Dowex-50 double column chromatography was used to purify and quantitate the levels of [3H]-cyclic GMP. Changes in cyclic GMP metabolism in short and long term RPMVEC cultures were studied using rat atrial naturetic factor 8-33 (ANF) and sodium nitroprusside (SNP) in the presence and absence of cyclic nucleotide (CN) phosphodiesterase (PDE) inhibitors. In RPMVEC exogenous hypoxanthine was incorporated into both low (65% uptake) and high (34% uptake) passage cells in a time-dependent manner reaching maximum incorporation near 8 hours. Basal cyclic GMP values in both groups were 0.003% of the total cellular tritium (9 x 10(6) and 4 x 10(6) cpm/10(6) cells, respectively). ANF treatment of prelabeled RPMVEC resulted in a 10- to 12-fold increase in [3H]-cyclic GMP in the absence of CN PDE inhibitors (EC50 = 5.4 nM). However, incubation with SNP showed no changes in cellular cyclic GMP accumulation. Several relatively selective CN PDE inhibitors had no effect on ANF or SNP induced cyclic GMP accumulation in RPMVEC. The ANF induced cGMP accumulation was verified by radioimmunoassay. These studies confirm the utility of the hypoxanthine prelabeling technique to monitor intact microvascular EC cyclic GMP accumulation. Cultured RPMVEC show little or no functional soluble guanylate cyclase or cyclic GMP PDE activity.

Role of nitric oxide and phosphodiesterase isoenzyme II for reduction of endothelial hyperpermeability

Regulation of endothelial permeability is poorly understood. Previous studies have shown that endothelial cells contain phosphodiesterase (PDE) isoenzymes II-IV and that simultaneous adenylate cyclase activation and/or PDE inhibition blocked endothelial hyperpermeability (J.Clin.Invest. 91: 1421-1428, 1993). We now focused on a possible role for guanosine 3',5'-cyclic monophosphate (cGMP)-dependent mechanisms and studied H2O2-exposed porcine pulmonary artery endothelial cell monolayers. Pretreatment of cells with different nitric oxide (NO) donors or atrial natriuretic peptide (ANP) increased endothelial cGMP-content severalfold and blocked H2O2-related effects on permeability; opposite results were obtained with a NO synthase inhibitor. Determination of cGMP degradation in nitroprusside-exposed endothelial cells identified PDE II as the major cGMP metabolizing pathway, whereas PDE III and IV contributed little or nothing. Inhibition of PDE II reduced H2O2-related endothelial hyperpermeability, an effect that could be enhanced synergistically by simultaneous guanylate cyclase activation. In summary, these studies indicate that cGMP-dependent mechanisms (NO donors, ANP, and dibutyryl-cGMP) blocked H2O2-related increases in endothelial permeability. The major cGMP degrading pathway in endothelial cells was PDE II, thereby substituting the missing PDE V in these cells. Simultaneous guanylate cyclase activation and/or PDE II inhibition may be a valuable approach to treat endothelial hyperpermeability.

Endothelial cell expression of vasoconstrictors and growth factors is regulated by smooth muscle cell-derived carbon monoxide

CO is produced in vascular smooth muscle cells (VSMC) by heme oxygenase-1 (HO-1). CO increases cGMP levels in VSMC; however, its possible additional roles in the vasculature have not been examined. We report that a product of HO, released from VSMC and inhibited by hemoglobin, has paracrine effects on endothelial cells: it increases endothelial cGMP content and decreases the expression of the mitogens, endothelin-1 (ET-1) and platelet-derived growth factor-B (PDGF-B). This product has the characteristics of CO, and its production is increased sevenfold under hypoxia. The VSMC-derived CO caused a fourfold rise in endothelial cell cGMP. In addition, it inhibited the hypoxia-induced increases in mRNA levels of the ET-1 and PDGF-B genes. Inhibitors of HO, and hemoglobin, a scavenger of CO, prevented the rise in cGMP and also restored the hypoxic response of these genes. The inhibition of ET-1 and PDGF-B mRNA by CO resulted in decreased production of these endothelial-derived mitogens, and in turn, inhibition of VSMC proliferation. These findings suggest an important physiologic role for VSMC-derived CO in modulating cell-cell interaction and cell proliferation in the vessel wall during hypoxia.

Expression of cGMP-dependent protein kinase I and phosphorylation of its substrate, vasodilator-stimulated phosphoprotein, in human endothelial cells of different origin

Previous studies demonstrated that the thrombin-induced permeability of endothelial cell monolayers is reduced by the elevation of cGMP. In the present study, the presence of cGMP-dependent protein kinase (cGMP-PK) immunoreactivity and activity in various types of human endothelial cells (ECs) and the role of cGMP-PK in the reduction of thrombin-induced endothelial permeability was investigated. cGMP-PK type I was demonstrated in freshly isolated ECs from human aorta and iliac artery as well as in cultured ECs from human aorta, iliac vein, and foreskin microvessels. Addition of the selective cGMP-PK activator 8-(4-chlorophenylthio)-cGMP (8-pCPT-cGMP) to these ECs caused phosphorylation of the vasodilator-stimulated phosphoprotein (VASP), an established cGMP-PK substrate, which is localized at cell-cell contact sites of confluent ECs. cGMP-PK type I expression decreased during serial passage of ECs, which correlated with a diminished ability of 8-pCPT-cGMP to induce VASP phosphorylation. Preincubation of aorta and microvascular EC monolayers with 8-pCPT-cGMP caused a 50% reduction of the thrombin-stimulated permeability, as determined by measuring the peroxidase passage through EC monolayers on porous filters. Furthermore, the thrombin-induced rise in cytoplasmic [Ca2+]i was strongly attenuated by the cGMP-PK activator in fura 2-loaded aorta ECs. In contrast, cGMP-PK could not be demonstrated in freshly isolated and cultured human umbilical vein ECs. Incubation of umbilical vein ECs with 8-pCPT-cGMP did not cause VASP phosphorylation and had no effect on the thrombin-induced increases in cytoplasmic Ca2+ and endothelial permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Protamine does not affect the formation of cGMP or cAMP in pig vascular smooth muscle cells in response to vasodilators

OBJECTIVES

Protamine has recently been shown to have a direct vasodilator action in isolated vascular tissue. As one possible mechanism for this action, it has been hypothesized that protamine might increase the response of vascular smooth muscle to the endothelium-derived relaxing factor, nitric oxide. In this study, we tested this hypothesis and examined the effect of protamine on other guanosine 3'5'-cyclic monophosphate (cGMP)- and adenosine 3'5'-cyclic monophosphate (cAMP)-dependent processes.

DESIGN

Prospective, repeated measures analysis of concentration-response curves.

SETTING

Anesthesia research laboratory in an academic medical center.

SUBJECTS

Cultured coronary artery smooth muscle cells from pig heart.

INTERVENTIONS

Sodium nitroprusside was used to mimic the action of the endothelium-derived relaxing factor by stimulating the soluble guanylyl cyclase and increasing intracellular cGMP. Atrial natriuretic peptide was used to stimulate the particulate guanylyl cyclase. Isoproterenol and forskolin were used to increase intracellular cAMP. The responses to these agents were determined in the presence and absence of protamine.

MEASUREMENTS AND MAIN RESULTS

In cultured vascular smooth muscle cells, sodium nitroprusside increased cGMP, the second messenger for endothelium-derived relaxing factor, in a concentration-dependent manner. In cells treated with protamine (32 to 250 micrograms/mL), we could detect no effect of protamine on basal intracellular levels of cGMP until a concentration of 250 micrograms/mL of protamine was used. At this concentration, protamine increased basal cGMP concentrations from 4.2 +/- 0.3 to 9.0 +/- 0.6 pmol/mg protein (p < .001). The response of intracellular cGMP to sodium nitroprusside in cells treated with 250 micrograms/mL or other concentrations of protamine was not different from control. Likewise, we could detect no effect of protamine on intracellular cGMP stimulated with the atrial natriuretic peptide or on cAMP stimulated with the beta-adrenergic receptor agonist, isoproterenol, or with forskolin.

CONCLUSIONS

These experiments show that protamine does not alter the responses of the intracellular second messengers, cGMP and cAMP, to the vasodilators sodium nitroprusside, atrial natriuretic peptide, isoproterenol, and forskolin. These results do not support the hypothesis that protamine sensitizes vascular smooth muscle cells to the endothelium-derived relaxing factor, nitric oxide.

Atrial natriuretic peptide blocks hemorrhagic brain edema after 4-hour delay in rats

BACKGROUND AND PURPOSE

Atrial natriuretic peptide (ANP) and arginine vasopressin regulate brain water and electrolytes. Treatment with ANP at the onset of a hemorrhagic injury reduces edema. Clinically, however, hemorrhagic masses form too rapidly for preventive treatment. Therefore, we measured the effect of ANP on brain edema after the hemorrhagic mass was formed.

METHODS

Adult rats had hemorrhagic lesions produced by the intracerebral injection of 0.4 U bacterial collagenase. Four hours later, an infusion of ANP (120 or 700 ng/kg per 20 hours) was begun into the peritoneum using an implanted miniosmotic pump. Twenty-four hours after the injury, brain water and electrolyte values were measured. The mechanism of ANP action was explored in other groups of rats that either had osmolality increased with mannitol or were injected with the cyclic GMP analogue, 8-bromo-cGMP.

RESULTS

Atrial natriuretic peptide given after a 4-hour delay significantly reduced brain water and sodium 24 hours after the injury (P < .05). However, neither mannitol nor 8-bromo-cGMP affected brain edema.

CONCLUSIONS

Delayed administration of ANP reduces brain edema secondary to a hemorrhagic mass. Because it is effective after the mass has formed, ANP may be useful in treatment of edema secondary to intracranial bleeding.

cGMP and nitric oxide modulate thrombin-induced endothelial permeability. Regulation via different pathways in human aortic and umbilical vein endothelial cells

Previous studies have demonstrated that cGMP and cAMP reduce the endothelial permeability for fluids and macromolecules when the endothelial permeability is increased by thrombin. In this study, we have investigated the mechanism by which cGMP improves the endothelial barrier function and examined whether nitric oxide (NO) can serve as an endogenous modulator of endothelial barrier function. Thrombin increased the passage of macromolecules through human umbilical vein and human aortic endothelial cell monolayers and concomitantly increased [Ca]2+ in vitro. Inhibition of these increases by the intracellular Ca2+ chelator BAPTA indicated that cytoplasmic Ca2+ elevation contributes to the thrombin-induced increase in endothelial permeability. The cGMP-dependent protein kinase activators 8-bromo-cGMP (8-Br-cGMP) and 8-(4-chlorophenylthio)cGMP (8-PCPT-cGMP) decreased the thrombin-induced passage of macromolecules. Two pathways accounted for this observation. Activation of cGMP-dependent protein kinase by 8-PCPT-cGMP decreased the accumulation of cytoplasmic Ca2+ in aortic endothelial cells and hence reduced the thrombin-induced increase in permeability. On the other hand, in umbilical vein endothelial cells, cGMP-inhibited phosphodiesterase (PDE III) activity was mainly responsible for the cGMP-dependent reduction of endothelial permeability. The PDE III inhibitors Indolidan (LY195115) and SKF94120 decreased the thrombin-induced increase in permeability by 50% in these cells. Thrombin treatment increased cGMP formation in the majority of, but not all, cell cultures. Inhibition of NO production by NG-nitro-L-arginine methyl ester (L-NAME) enhanced the thrombin-induced increase in permeability, which was restricted to those cell cultures that displayed an increased cGMP formation after addition of thrombin. Simultaneous elevation of the endothelial cGMP concentration by atrial natriuretic factor, sodium nitroprusside, or 8-Br-cGMP prevented the additional increase in permeability induced by L-NAME. These data indicate that cGMP reduces thrombin-induced endothelial permeability by inhibition of the thrombin-induced Ca2+ accumulation and/or by inhibition of cAMP degradation by PDE III. The relative contribution of these mechanisms differs in aortic and umbilical vein endothelial cells. NO can act in vitro as an endogenous permeability-counteracting agent by raising cGMP in endothelial cells of large vessels.

Atrial natriuretic peptide-like (ANP-LIR) and ANP prohormone immunoreactive astrocytes and neurons of human cerebral cortex

Atrial natriuretic peptide (ANP) represents a family of related peptides originally isolated from cardiac atria that have potent natriuretic, diuretic, and vasorelaxant properties. ANP has previously been localized in neurons of the rat brain in regions subserving cardiovascular functions and fluid/electrolyte balance and has been localized in astroglia of the canine brain. To determine whether ANP is present in astrocytes of the human brain and to validate the canine model for future studies, human brain tissue was obtained from autopsy cases with no brain damage or neurological or vascular disease. Human brains were obtained less than 3 h postmortem, and anterior cingulate and striate cortices were dissected following perfusion or immersion fixation. Immunohistochemical processing utilized antibodies against the processed form of ANP (ANP IV, ANP104-128) and against rat proANP (amino terminus) and the avidin-biotin-peroxidase technique. Isolated, strongly ANP-immunoreactive protoplasmic astrocytes were observed in all layers of the cingulate and striate cortex gray matter. ANP-positive fibrous astrocytes were observed in the white matter. Additionally, distinctive immunopositive astrocytes were found both within and immediately subjacent to the glia limitans. Antibody against the prohormone stained only protoplasmic astrocytes and sublimitans astrocytes and processes. In addition to the astroglia, ANP was detected in scattered multipolar neurons in the cerebral gray matter. These results provide additional evidence for diversity of peptide localization in astrocytes and suggest roles for ANP in the local regulation of cerebral blood flow, blood-brain barrier permeability, or cerebrospinal fluid volume.

Atrial natriuretic peptide improves pulmonary gas exchange in subjects exposed to hypoxia

Atrial Natriuretic Peptide (ANP) is secreted in response to hypoxia and pulmonary vasoconstriction. The hormone modulates pulmonary vascular tone in vivo and decreases pulmonary edema in isolated lungs exposed to several toxic agents. In addition, ANP improves the barrier function of endothelial cell monolayers in vitro. The plasma levels of ANP are elevated in patients with high-altitude pulmonary edema. We hypothesized that under these circumstances, ANP improves pulmonary gas exchange by attenuating the transvascular permeation of plasma (water). Therefore, we studied the effect of low-dose ANP in 11 healthy mountaineers exposed to hypoxia in a single-blind, placebo-controlled, cross-over design. During four 1-h periods, the subjects were stepwise exposed to decreasing barometric pressure, with a minimum of 456 mm Hg (simulated altitude, 4,115 m). Infusion of 5 ng/kg/min human-ANP increased the plasma ANP concentrations approximately twofold. The plasma concentrations of cyclic GMP, which is the second messenger of ANP, rose approximately threefold. Infusion of ANP did not affect the hemodynamic or ventilatory response to hypoxia. The hemoglobin concentration, however, rose from 9.0 +/- 0.1 to 9.4 +/- 0.1 mmol/L (p < 0.01) during ANP infusion but not during placebo infusion. The change in plasma volume calculated from this hemoconcentration indicated that approximately 10% of the plasma volume had permeated into the interstitium. Despite the observed whole-body hemoconcentration, oxygen saturation was significantly higher during ANP infusion than during placebo infusion (84.7 +/- 1.7 versus 79.6 +/- 1.8%, p < 0.05), and the alveolar-arterial oxygen difference was significantly lower (3.5 +/- 0.7 versus 7.3 +/- 0.8 mm Hg, p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-derived relaxing factor contributes to the regulation of endothelial permeability

To determine whether endothelium-derived relaxing factor (EDRF) contributes to the regulation of endothelial permeability, the transendothelial flux of 14C-sucrose, a marker for the paracellular pathway across endothelial monolayers (Oliver, J. Cell. Physiol. 145:536-548, 1990), was examined in monolayers of bovine aortic endothelial cells grown on collagen-coated filters. The permeability coefficient of 14C-sucrose was significantly decreased by 10(-3) M 8-Bromoguanosine 3',5'-cyclic monophosphate or by 5 x 10(-6) M glyceryl trinitrate, an activator of soluble guanylate cyclase. Depletion of L-arginine from endothelial monolayers increased 14C-sucrose permeability from 3.21 +/- 0.59 to 3.88 +/- 0.50 x 10(-5) cm.sec-1 (mean +/- SEM; n = 6; P < 0.05). The acute administration of 5 x 10(-4) M L-arginine to monolayers depleted of this amino acid decreased 14C-sucrose permeability from 2.91 +/- 0.27 to 2.52 +/- 0.26 x 10(-5) cm.sec-1 (n = 11; P < 0.05). 14C-sucrose permeability was increased by 10(-7) M bradykinin and this effect was enhanced by the presence of each one of the following compounds: 10(-5) M methylene blue, 4 x 10(-6) M oxyhemoglobin, 5 x 10(-4) M NG-methyl-L-arginine or 5 x 10(-4) M N omega-nitro-L-arginine. These results suggest that EDRF contributes to the sealing of the endothelial monolayer and that EDRF released by bradykinin acts as a feedback inhibitor attenuating the increase in endothelial permeability induced by this peptide. Because endothelial cells have the ability to contract and relax and possess guanylate cyclase responsive to nitric oxide, our results suggest that EDRF decreases 14C-sucrose permeability by relaxing endothelial cells, thereby narrowing the width of endothelial junctions.