ANP Secretion Research Articles

Thrombin receptor protease-activated receptor 1 (PAR1) related cytotoxic CD8+ T cell activity is associated with atrial myopathy and pro-inflammatory immune response in early atrial fibrillation

Abstract Background and aims Cytotoxic CD8+ T cells mediate myocardial damage in patients with virus induced myocarditis, plaque erosion during acute coronary syndrome, and promote adverse post-ischemic cardiac remodeling. There is emerging evidence to support a link between inflammation and atrial fibrillation (AF). Protease-activated receptor 1 (PAR1) is the thrombin receptor expressed on platelets, but it is also expressed in endothelial cells, vascular smooth muscle cells, cardiac fibroblasts, and CD8+ T cells. The role of CD8+ T cells and PAR1 in atrial myopathy and early AF have not been studied. Methods In 80 non-anticoagulated patients with a first documented episode of AF, and 20 control subjects without AF but with a comparable cardiovascular risk profile (e.g. SCORE2, CHA2DS2-VASc, p>0.05), we studied PAR1-related cytotoxic T cell activity in the first hours (up to 24 h) of AF clinical manifestation. The Apolipoprotein E–knock out (ApoEko) mouse is a commonly used model of metabolic syndrome that develops atrial myopathy (structural correlate of AF). ApoEko male mice (Apoetm1Unc with a C57BL/6 genetic background) were fed for six weeks with a standard chew, western-type diet (high fat and high sucrose = WD) ± the specific PAR1 inhibitor vorapaxar. Results High levels of circulating, activated CD8+ T cells (CD8+CD57+ T cells with pro-inflammatory and high cytotoxic properties) were present in patients with early AF (flow cytometry). Stimulation of cytotoxic T cells, that expressed the thrombin receptor PAR1, that were isolated from patients with new onset of AF, released pro-inflammatory cytokines (e.g. IFN-γ, TNF-α). Enhanced cytotoxic activity of CD8+ T cells was suggested by elevated plasma levels of effector molecules (e.g. granulysin and granzyme). In ApoEko mice fed a WD, atrial myopathy as the structural correlate for AF, was paralleled by increased expression of effector molecules that were associated with CD8+ T cell activity (like perforin, granzyme A, granzyme B, IFN-γ). Cytotoxic T cell activity disrupted the release of the potective atrial natriuretic peptide, ANP, and increased signaling pathways associated with atrial fibrosis (e.g. TGF-β, cTGF, TGF-β receptor). The specific PAR1 inhibitor, vorapaxar, reduced inflammatory T cell activity, transcription of fibrotic mediators, and reconstituted ANP secretion in atria of ApoEko mice. Conclusions Targeting the FXa/FIIa-PAR1-CD8+ axis might be a promising approach to reduce atrial fibrosis and inflammation. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): BIH Charité Clinician Scientist Program

Oryeongsan (Wulingsan) ameliorates impaired ANP secretion of atria from spontaneously hypertensive rats

Oryeongsan (ORS), a herbal medicine formula, has long been used for the treatment of impaired body water balance in Asian countries. Recently, it was shown that ORS administration modulates the renin-angiotensin system (RAS). Purpose of the present study was to determine characteristics of atrial ANP secretion and effects of ORS on the secretion in the atria from spontaneously hypertensive rats (SHR). Normotensive WKY groups (WKY-V, WKY-ORS, WKY-LOS) and hypertensive SHR groups (SHR-V, SHR-ORS, SHR-LOS) treated with vehicle, ORS, and losartan as a positive control group, respectively, were used. Experiments were performed in perfused beating atria (1.3 Hz) allowing atrial distension, acetylcholine (ACh) stimulation, and serial collection of atrial perfusates. The secreted ANP concentration was measured using radioimmunoassay. Interstitial fluid (ISF) translocation was measured using [3H]inulin clearance. Stepwise increase in atrial distension by 1.1, 2.0, and 2.7 cmH2O above basal distension further increased ANP secretion proportionally in the atria from WKY-V, but the response was significantly suppressed in the atria from SHR-V. Cardiomyocyte ANP release, the first step of atrial ANP secretion, was suppressed in the atria from SHR-V compared to those from WKY-V (−8.02 ± 2.86, −15.86 ± 2.27, and −20.09 ± 3.62%; n = 8, for SHR-V vs. 8.59 ± 2.81, 15.65 ± 7.14, and 38.12 ± 8.28%; n = 8, for WKY-V; p < 0.001 for all stepwise distension, respectively). Chronic treatment with ORS reversed the suppressed ANP release in atria from SHR-ORS group (6.76 ± 3.92, 9.12 ± 2.85, and 28.79 ± 1.79% for SHR-ORS; n = 5 vs. SHR-V; n = 8; p = 0.01, p < 0.001, p < 0.001, respectively). The effects of ORS were comparable to those of losartan. Trans-endocardial translocation of ISF, the second step of atrial ANP secretion was similar in the atria from the hypertensive SHR-V and normotensive WKY-V. ACh-induced ANP secretion and cardiomyocyte ANP release were also suppressed in the atria from SHR-V compared to WKY-V and ORS reversed the suppression. These findings were accompanied with accentuation of the AT1 receptor expression and suppression of the AT2/Mas receptor, M2 mACh receptor and GIRK4, a molecular component of KACh channel, expression in the atria from SHR-V. Further, treatment with ORS or losartan reversed the expressions in the groups of SHR-ORS and SHR-LOS. These results show that ANP secretion is suppressed in the atria from SHR in association with accentuation of AT1 receptor and suppression of AT2/Mas receptor and KACh channel expression. Treatment with ORS ameliorates impaired ANP secretion through improving cardiomyocyte ANP release with modulation of the cardiac RAS and muscarinic signaling. These findings provide experimental evidence which supports the effect of ORS on the regulation of atrial ANP secretion in the atria from SHR.

IL-6 induced enhanced clearance of proANP and ANP by insulin-degrading enzyme in T1DM mice.

Cardiovascular disease (CVD) is a prevalent cause of morbidity and mortality in type I diabetes mellitus (T1DM). However, the pathophysiological mechanisms underlying the relationship between CVD, CVD risk factors, and T1DM have not yet been sufficiently explored. Here, we report that insulin-degrading enzyme (IDE) effectively degrades the precursor of atrial natriuretic peptide (proANP) in HEK293T cells. The pro-inflammatory cytokine IL-6 elicited a significant dose-dependent increase in IDE protein expression. Inhibition of the ERK/MAPK signaling pathway with selumetinib abolished the IL-6-stimulated increase in IDE protein levels and decreased ANP secretion in H9C2 cells. Importantly, the T1DM mouse model displayed lower proANP in the heart and ANP in serum, due to increased IDE expression and activity. Our results suggest a novel role of IL-6 in ANP metabolism via IDE and provide possibilities for new potential therapeutic strategies for diabetes-related cardiovascular complications.

B-PO03-154 METABOLIC EFFECTS OF THE LEFT ATRIAL APPENDAGE EXCLUSION (THE HEART HORMONE STUDY)

It is currently unknown whether the elimination of ANP and other neurohormone secretion from LAA in AF patients can have any consequences on long term physiological regulation of lipid and glucose metabolism, obesity, and insulin resistance. To investigate the lipid and glucose metabolism and acting on the metabolism of broader hormones and long-term follow-up covering 2 years in patients who undergone epicardial LAA closure procedure. In a single-center prospective observational study, 60 patients with longstanding persistent AF with cardiovascular risk factors had undergone an epicardial exclusion procedure. Anthropometric parameters and glucose, glycated hemoglobin (HbA1c), insulin, leptin, adiponectin, free fatty acids, beta-hydroxybutyrate, and total cholesterol levels were evaluated on fasting at baseline before the procedure and compared with levels at 24 hours, 7 days, 1 month, 3 months, 6 months, and 24 months after the procedure. Device implantation (LARIAT) was successful in all 60 patients. No complications were noted. Postprocedural transesophageal echocardiogram (TEE) showed complete LAA closure in all patients, no leak was observed. The group on average was insulin levels significantly increased at 7 days, 1 month, 3 months, 6 months, 12 months, and 24 months follow-up. The leptin levels showed a significant increase in 6 months, 12 months, and 24 months when compared to baseline. Whereas the adiponectin levels showed a significant decrease at 3 months, 6 months, 12 months, and 24 months when compared to baseline levels. In patients with the epicardial procedure, when compared to baseline, glucose, glycated hemoglobin, total cholesterol, and beta-hydroxybutyrate levels did not show any significant changes at baseline and 24 months follow up. The tendency of reduced weight was observed one year after the procedure (p = 0.084). The epicardial exclusion ligation in AF patients was associated with significant changes in insulin, leptin, and adiponectin over long follow up. It provides preliminary data that demonstrates the impact of LAA exclusion on various hormones or cytokines that can affect the insulin resistance, lipid, and glucose metabolism regulation in the body.

Hypoxia augments NaHS-induced ANP secretion via KATP channel, HIF-1α and PPAR-γ pathway

It has been reported that sodium hydrosulfide (NaHS) stimulated high stretch induced-atrial natriuretic peptide (ANP) secretion via ATP sensitive potassium (KATP) channel. KATP channel is activated during hypoxic condition as a compensatory mechanism. However, whether NaHS affects ANP secretion during hypoxia remains obscure. The purpose of the present study is to discover the impact of NaHS on ANP secretion during hypoxia and to unravel its signaling pathway. Isolated beating rat atria were perfused with buffer exposed to different O2 tension (to 100% O2, normoxia; to 20% O2, hypoxia). The ANP secretion increased negatively correlated with O2 tension. NaHS (50 μM) did not show any significant effect on low stretch induced-ANP secretion in normoxic condition but augmented low stretch induced-ANP secretion in hypoxic condition. The augmentation of NaHS-induced ANP secretion during hypoxia was blocked by the pretreatment with KATP channel blocker (glibenclamide) and was enhanced by the pretreatment with KATP channel activator (pinacidil). Hypoxia increased the expression of PPAR-γ protein but did not change the expression of HIF-1α protein and eNOS phosphorylation. The NaHS-induced ANP secretion during hypoxia was also blocked by the pretreatment with HIF-1α inhibitor (2-methoxy- estradiol), PPAR−γ inhibitor (GW9662) but not by NOS inhibitor (L-NAME) and endothelin receptor inhibitor (bosentan). The intravenous infusion of NaHS increased plasma ANP level in monocrotaline-treated rats but not in sham rats. These results suggest that hypoxia augmented NaHS-induced ANP secretion partly through KATP channel, HIF-1α, and PPAR−γ pathway.

Abstract 334: Temporal Regulation of Retinoic Acid Delineates First Heart Field Ventricular and Atrial Cardiac Differentiation of Human Pluripotent Stem Cells

Retinoic acid plays a pivotal role during the heart development. The mammalian heart is formed from cardiac progenitors in the first and second heart fields (FHF and SHF). FHF progenitors populate the left ventricle and the atria; SHF progenitors populate the right ventricle, outflow tract and parts of the atria. Loss of retinoic acid signaling leads to depletion of FHF progenitors and compensatory increase in SHF progenitors. Here we hypothesized that mimicking the in vivo retinoic acid signaling during human pluripotent stem cell differentiation could lead to FHF cardiomyocytes.Human pluripotent stem cells were differentiated to cardiac lineage by treatment with Activin A, BMP4 and bFGF (control) for the first three days (d0-3). This lead to &gt;70% Brachyury+ mesodermal cells, and &gt;90% of Brachyury+ cells became cTnT+ cardiac myocytes. Retinoic acid signaling activated with exogenous RA (1μM) from d5-8 (RA protocol). This RA protocol was compared to another protocol in which d5-8 retinoic acid activation was followed by initial inhibition with a pan-retinoic acid (RiRA protocol). At d14, both RA and RiRA cardiomyocytes expressed higher transcript and protein levels of the FHF markers, NKX2.5, TBX5and HCN4, but lower levels of the SHF markers, ISL1, MEF2c, FGF8/10, compared to control. RiRA cardiomyocytes showed highest expression of ventricular markers, IRX4 and HRT2 , lowest expression of an atrial specific marker CoupTFII, which were mirrored in RA cardiomyocytes. In line with their atrial/ventricular-specific gene expression profile, RA cardiomyocytes demonstrated higher beating rates, higher maximum shortening velocity, faster conduction velocity, higher atrial specific ANP secretion and higher sensitivity to atrial-selective sodium blocker, ranolazine compared to control. In contrast, RiRA cardiomyocytes generated higher force but shorter action potential duration compared to control.Taken together, the data demonstrate temporal regulation of retinoic acid signaling can not only accurately recapitulate ventricular to atrial cardiomyocyte differentiation by delineating FHF vs. SHF lineages.

Peroxisome proliferator-activated receptor γ is essential for secretion of ANP induced by prostaglandin D2 in the beating rat atrium.

Prostaglandin D2 (PGD2) may act against myocardial ischemia-reperfusion (I/R) injury and play an anti-inflammatory role in the heart. Although the effect of PGD2 in regulation of ANP secretion of the atrium was reported, the mechanisms involved are not clearly identified. The aim of the present study was to investigate whether PGD2 can regulate ANP secretion in the isolated perfused beating rat atrium, and its underlying mechanisms. PGD2 (0.1 to 10 µM) significantly increased atrial ANP secretion concomitantly with positive inotropy in a dose-dependent manner. Effects of PGD2 on atrial ANP secretion and mechanical dynamics were abolished by AH-6809 (1.0 µM) and AL-8810 (1.0 µM), PGD2 and prostaglandin F2α (PGF2α) receptor antagonists, respectively. Moreover, PGD2 clearly upregulated atrial peroxisome proliferator-activated receptor gamma (PPARγ) and the PGD2 metabolite 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2, 0.1 µM) dramatically increased atrial ANP secretion. Increased ANP secretions induced by PGD2 and 15d-PGJ2 were completely blocked by the PPARγ antagonist GW9662 (0.1 µM). PD98059 (10.0 µM) and LY294002 (1.0 µM), antagonists of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling, respectively, significantly attenuated the increase of atrial ANP secretion by PGD2. These results indicated that PGD2 stimulated atrial ANP secretion and promoted positive inotropy by activating PPARγ in beating rat atria. MAPK/ERK and PI3K/Akt signaling pathways were each partially involved in regulating PGD2-induced atrial ANP secretion.

Expression of familial Alzheimer disease presenilin 1 gene attenuates vesicle traffic and reduces peptide secretion in cultured astrocytes devoid of pathologic tissue environment

In the brain, astrocytes provide metabolic and trophic support to neurones. Failure in executing astroglial homeostatic functions may contribute to the initiation and propagation of diseases, including Alzheimer disease (AD), characterized by a progressive loss of neurones over years. Here, we examined whether astrocytes from a mice model of AD isolated in the presymptomatic phase of the disease exhibit alterations in vesicle traffic, vesicular peptide release and purinergic calcium signaling. In cultured astrocytes isolated from a newborn wild-type (wt) and 3xTg-AD mouse, secretory vesicles and acidic endosomes/lysosomes were labeled by transfection with plasmid encoding atrial natriuretic peptide tagged with mutant green fluorescent protein (ANP.emd) and by LysoTracker, respectively. The intracellular Ca(2+) concentration ([Ca(2+)]i) was monitored with Fluo-2 and visualized by confocal microscopy. In comparison with controls, spontaneous mobility of ANP- and LysoTracker-labeled vesicles was diminished in 3xTg-AD astrocytes; the track length (TL), maximal displacement (MD) and directionality index (DI) were all reduced in peptidergic vesicles and in endosomes/lysosomes (P < 0.001), as was the ATP-evoked attenuation of vesicle mobility. Similar impairment of peptidergic vesicle trafficking was observed in wt rat astrocytes transfected to express mutated presenilin 1 (PS1M146V). The ATP-evoked ANP discharge from single vesicles was less efficient in 3xTg-AD and PS1M146V-expressing astrocytes than in respective wt controls (P < 0.05). Purinergic stimulation evoked biphasic and oscillatory [Ca(2+)]i responses; the latter were less frequent (P < 0.001) in 3xTg-AD astrocytes. Expression of PS1M146V in astrocytes impairs vesicle dynamics and reduces evoked secretion of the signaling molecule ANP; both may contribute to the development of AD.

Influence of estrogen and 5‐HT1A receptors in electrolyte balance and endocrine in ovariectomized rats

Thus, we examined in the present study the endocrine response in ovariectomized (OVX) rats submitted to oil or estrogen treatment (OVX‐E2 group estradiol cypionate, 100microg/kg, SC, during 14 days) and to treatment with the 8‐OH‐DPAT(8‐hydroxy‐di‐propilamino tetraline, 5‐HT1A receptor agonist, 250microg/kg, IP for 7 days) or vehicle (0.9% NaCl) during 7 days). We also investigated a possible correlation between serotonergic functional status and E2 replacement on the plasma levels of angiotensin I and II (ANG I, II), oxytocin (OT), natriuretic peptide (ANP) and corticosterone (CORT) in basal condition and after sodium depletion. The ANG I and ANG II release and respective mechanisms seem to be depending of the condition of the animal or 8‐OH‐DPAT treatment. Chronic 8‐OH‐DPAT in basal condition increased the ANG I plasma concentration while the E2 seems to attenuate this response following sodium depletion. The OT and CORT plasma levels at basal condition were enhanced by association of the two treatments. E2 replacement, both at baseline and depletion conditions, increased OT and CORT plasma levels. Additionally we did not observe estrogen influence on plasma CORT concentrations following sodium depletion; on the other hand, the 8‐OH‐DPAT seems to be critical to enhance the ANP secretion following sodium depletion. The serotonergic system seems to recruit different endocrine mechanisms regarding the homeostatic condition of the animal.

Emodin accentuates atrial natriuretic peptide secretion in cardiac atria

Emodin, an active anthraquinone constituent isolated from the rhubarb, a traditional Chinese herbal medicine which is widely used in clinical treatment, has cardiovascular protective properties. However, it remains unclear whether the cardiovascular protective actions of emodin are related to an activation of cardiac natriuretic hormone secretion. The purpose of the present study was to explore the effect of emodin on the secretion of ANP, a member of the family of cardiac natriuretic hormones, and its mechanisms involved. Experiments were performed in isolated perfused beating rabbit atria allowing measurement of ANP secretion, atrial pulse pressure, and stroke volume. Emodin increased ANP secretion concomitantly with a decrease in atrial pulse pressure and stroke volume in a concentration-dependent manner. These effects were reversible. Inhibition of K+ channels with tetraethylammonium and glibenclamide attenuated the emodin-induced changes in ANP secretion and atrial dynamics. Furthermore, the emodin-induced changes in ANP secretion and atrial dynamics were attenuated by inhibition of L-type Ca2+ channels with nifedipine. Atropine, methoctramine, tertiapin-Q, and pertussis toxin had no significant effect on the emodin-induced changes in ANP secretion and mechanical dynamics. The present study demonstrates that emodin increases ANP secretion via inhibition of L-type Ca2+ channels through an activation of K+ATP channel in isolated beating rabbit atria. The results also provide a rationale for the use of emodin in the treatment of impairment of the regulation of the cardiovascular homeostasis.

RNA Sequencing Analysis and Atrial Natriuretic Peptide Production in Patients with Dilated and Ischemic Cardiomyopathy

BackgroundThe atrium is the major site of ANP synthesis, which has been said to increase in heart failure as a result of increased production in the left ventricular (LV) myocardium. This is a key issue related to its diagnostic and prognostic capabilities. We aimed to evaluate protein levels of proANP and ANP and the enzymes that cleave the natriuretic peptides, corin and furin, in the LV tissue of heart transplant patients with dilated (DCM) and ischemic (ICM) cardiomyopathy compared with control donors (CNT). We also evaluate mRNA levels of ANP gene (NPPA) by RNA sequencing in the same tissue.Methods and ResultsSeventy-three human LV tissue samples from ICM (n = 30) and DCM (n = 33) patients and CNT (n = 10) were analyzed by Western blot and RNA sequencing. Comparing protein levels according to etiology, neither DCM nor ICM showed levels of proANP or ANP different from those of CNT. However, NPPA was increased in both groups compared to CNT (DCM 32 fold, p<0.0001; ICM 10 fold, p<0.0001). Corin (but not furin) was elevated in the ICM group compared to CNT (112±24 vs. 100±7, p<0.05), and its level was inversely related with LV ejection fraction (LVEF) (r = −0.399, p<0.05).ConclusionsPatients present with elevated levels of NPPA but not of proANP or ANP proteins in LV tissue, which may be due to posttranscripcional regulation of NPPA or different pathways for ANP secretion between the atrium and ventricle. Moreover, there are differences between DCM and ICM in corin levels, indicating that a different molecular mechanism may exist that converge in this syndrome. Further, LV concentration of corin is inversely related to LVEF in ICM.

Impact of epicardial ablation of concomitant atrial fibrillation on atrial natriuretic peptide levels and atrial function in 6 months follow-up: does preoperative ANP level predict outcome of ablation?

BackgroundEpicardial ablation concomitant to cardiac surgery is an easy and safe approach to treat atrial fibrillation (AF), but its efficacy in longstanding persistent (LsPe) AF remains intermediate. Although larger left atrial size has been associated with worse outcome after ablation, biochemical predictors of success are not well established. The aim of this study was to evaluate relationship between biochemical marker, echo-characteristic and cardiac rhythm in 6 months follow-up after epicardial ultrasound (HIFU) ablation.MethodsWe included 78 consecutive patients, who underwent elective cardiac surgery. 42 patients with AF (11.9% paroxysmal, 23.8% persistent, 64.3% LsPeAF) underwent concomitant HIFU ablation (AF ablation group), 16 with AF underwent cardiac surgery without ablation (AF control) and 20 had preoperatively normal sinus rhythm (SR control). We measured plasma ANP secretion before, on postoperative day (POD) 1, POD 7 as well as 3 and 6 months after surgery. Moreover, we estimated cardiac rhythm and atrial mechanical function by Atrial Filling Fraction (AFF) and A-wave velocity in follow-up.ResultsBaseline ANP levels were higher in patients with LsPeAF, as compared to the paroxysmal and permanent AF and to the SR control group. Patients with LsPeAF (n = 27) who converted to SR had preoperatively smaller left atrial diameter (LAD) and LA area (p < 0.05) and higher ANP level (p = 0.009) than those who remained in AF at 6 months after ablation. Multivariate regression analysis revealed that only preoperative ANP level was an independent predictor of cardiac rhythm after ablation. Patients with LsPeAF and preoperative ANP >7.5 nmol/l presented with SR in 80%, in contrast to those with ANP <7.5 nmol/l who converted to SR in 20%. We detected gradual increase of AFF and A-velocity at 6 months after ablation (p < 0.05) solely in AF ablation group. ANP levels were increased on POD 1 in ablation group (p < 0.05), without changes in further follow-up.ConclusionOur results indicate that preoperative ANP levels may be a new biochemical predictor of successful epicardial ablation in patients with concomitant LsPeAF. HIFU ablation caused a significant improvement of atrial mechanical function and gradual increase of AFF and did not associate with alteration of atrial endocrine secretion at 6 months follow-up.

Angiotensin AT2 receptor agonist stimulates high stretch induced- ANP secretion via PI3K/NO/sGC/PKG/pathway

Angiotensin II (Ang II) type 1 receptor (AT1R) mediates the major cardiovascular effects of Ang II. However, the effects mediated via AT2R are still controversial. The aim of the present study is to define the effect of AT2R agonist CGP42112A (CGP) on high stretch-induced ANP secretion and its mechanism using in vitro and in vivo experiments. CGP (0.01, 0.1 and 1μM) stimulated high stretch-induced ANP secretion and concentration from isolated perfused rat atria. However, atrial contractility and the translocation of extracellular fluid did not change. The augmented effect of CGP (0.1μM) on high stretch-induced ANP secretion was attenuated by the pretreatment with AT2R antagonist or inhibitor for phosphoinositol 3-kinase (PI3K), nitric oxide (NO), soluble guanylyl cyclase (sGC), or protein kinase G (PKG). However, antagonist for AT1R or Mas receptor did not influence CGP-induced ANP secretion. In vivo study, acute infusion of CGP for 10min increased plasma ANP level without blood pressure change. In renal hypertensive rat atria, AT2R mRNA and protein levels were up-regulated and the response of plasma ANP level to CGP infusion in renal hypertensive rats augmented. The pretreatment with AT2R antagonist for 10min followed by CGP infusion attenuated an increased plasma ANP level induced by CGP. However, pretreatment with AT1R or Mas receptor antagonist unaffected CGP-induced increase in plasma ANP level. Therefore, we suggest that AT2R agonist CGP stimulates high stretch-induced ANP secretion through PI3K/NO/sGC/PKG pathway and these effects are augmented in renal hypertensive rats.

Stimulation of ANP secretion by Angiotensin‐(1–9) via Angiotensin Type 2 Receptor

Renin‐angiotensin system (RAS) plays an essential role in cardiovascular homeostasis. The peptide hormone angiotensin II (Ang II), generated by angiotensin converting enzyme (ACE), mainly regulates cardiovascular system via its receptors. More recently, we have reported that Ang‐(1–7) stimulates ANP secretion via Mas receptor. However, Ang‐(1–9), converted from Ang I by ACE 2, is still unknown. The aim of the present study is to determine whether Ang‐(1–9) stimulates ANP secretion using isolated perfused beating atria and to find out its signaling pathway. Ang‐(1–9) augmented ANP secretion and concentration in a dose‐dependent manner. Ang‐(1–9)‐induced ANP secretion (about 60% increase by 3 uM) was attenuated by the pretreatment with Ang II type 2 receptor (AT2R) antagonist but not by AT1R or Mas receptor antagonist. In addition, pretreatment with inhibitors of phosphatidylinositol 3 kinase(PI3K), protein kinase B (Akt), endothelial nitric oxide synthase (eNOS) or guanylyl cyclase (GC), blocked the attenuation of ANP secretion by Ang‐(1–9). However, Ang‐(1–9) did not influence atrial contractility and ECF translocation. These results suggest that Ang‐(1–9) stimulates ANP secretion via AT2R, PI3K, Akt, eNOs, GC pathway. We try to do further study to find out the signaling mechanism involved these responses.Supported by the National Research Foundation (2012–0009322 )

Ursolic acid potentiates muscarinic receptor‐induced ANP secretion in perfused beating rat atria

Ursolic acid has recently been reported to increase both atrial natriuretic peptide (ANP) secretion and mechanical dynamics in rabbit atria. The present study was designed to clarify the regulatory effects of ursolic acid on the ¥â‐adrenergic or muscarinic receptor‐mediated changes in ANP secretory and contractile function allowing measurement of atrial dynamics such as pulse pressure, stroke volume, and cAMP efflux in isolated perfused beating rabbit atria. Pretreatment with ursolic acid significantly attenuated the isoproterenol (¥â‐adrenergic agonist)‐ induced decrease in ANP secretion and increases in cAMP levels and atrial dynamics. Interestingly, ursolic acid concentration‐dependently accentuated the acetylcholine‐induced increase of ANP secretion and decrease of pulse pressure in the presence of isoproterenol (p &lt; 0.001). These findings indicate that acetylcholine‐induced increase of ANP secretion is potentiated by ursolic acid, furthermore, acetylcholine‐induced decrease of atrial dynamics is also potentiated by ursolic acid, suggesting that ursolic acid regulates muscarinic receptor‐mediated secretory and contractile responses in perfused beating rabbit atria. Thus, this implicates for the beneficial effects of ursolic acid in the regulation of cardiovascular and body fluid homeostasis.

Effects of angiotensin II type 2 receptor agonist on stretch‐induced ANP secretion via PI 3K/PKG/NO pathway

Angiotensin II (Ang II) is well‐known a major peptide of renin‐angiotensin system (RAS) as regulating blood pressure and body fluid volume. It is already known that the AT1 receptor mediates the major cardiovascular effects of Ang II. However, effects mediated via AT2 receptor are still controversial. The aim of the present study is to define the effect of AT2 receptor agonist, CGP 42112A on high stretch‐induced ANP secretion and its mechanism using in vitro and in vivo experiments. CGP 42112A stimulated high stretch‐induced ANP secretion and concentration from isolated perfused rat atria. The augmented effect of CGP42112A (0.1 μM) on high stretch‐induced ANP secretion was attenuated by the pretreatment with AT2 receptor antagonist or inhibitor for phosphoinositol 3‐kinase (PI3K), nitric oxide (NO), soluble guanylyl cyclase (sGC), or protein kinase G (PKG). However antagonist for AT1 or Mas receptor tended to augment the effect of CGP 42112A on high stretch‐induced ANP secretion. In vivo study, acute infusion of CGP 42112A for 10 min increased plasma ANP level without blood pressure change and pretreatment with losartan for 10 min followed by CGP 42112A infusion increased plasma ANP level more than CGP 42112A alone. In hypertensive atria, AT2 receptor mRNA and protein level were up‐regulated. The response of plasma ANP level by acute infusion of CGP 42112A in hypertensive rat augmented. Therefore, we suggest that AT2 receptor agonist stimulates high stretch‐induced ANP secretion through PI3K/NO/sGC/PKG pathway.Supported by the National Research Foundation (2012–0009322)

NTproBNP: An Important Biomarker in Cardiac Diseases

Natriuretic neuropeptides (ANP, BNP, CNP) are produced primarily in the cardiac atria under normal conditions. The main stimulus for ANP and BNP peptide synthesis and secretion is cardiac wall stress. Cardiac ventricular myocytes constitute the major source of BNP-related peptides. Ventricular NT-proBNP production is upregulated in cardiac failure and locally in the area surrounding a myocardial infarct. NT-proBNP is cleared passively by organs with high rate of blood flow (muscle, liver, kidney). It has a longer half life than BNP and higher plasma concentration. BNP and NTproBNP tend to be higher in women and lower in obese individuals. They are also higher in elderly, in left ventricular tachycardia, right ventricular overload, myocardial ischemia, hypoxaemia, renal dysfunction, liver cirrhosis, sepsis and infection. NT-proBNP is useful both in the diagnosis and prognosis of heart failure and is considered to be a gold standard biomarker in heart failure similar to BNP. A cut-off point 300 pg/ml has 99% sensitivity, 60%specificity and NPV 98%for exclusion of acute heart failure. NT proBNP has also a strong prognostic value of death in acute and chronic heart failure and also predicts short and long term mortality in patient with suspected or confirmed unstable CVD. Natriuretic peptides are also prognostic markers for the RV (Right Ventricular) Dysfunction. Their release is due to myocardial stretch from right ventricular pressure overload.Finally, there are data supporting that NT-proBNP might be useful to put a time frame on atrial fibrillation of unknown onset.

Effects of natriuretic peptides upon hypothalamo-pituitary-adrenocortical system activity and anxiety behaviour.

Natriuretic peptides (ANP, BNP and CNP) comprise a family of structurally related peptides, which are derived from three different genes and which share a 17-amino acid internal ring. Besides their peripheral involvement in diuresis and blood pressure regulation these peptides, their bioactive fragments and their corresponding receptors (natriuretic peptide receptors NPR-A, NPR-B and NPR-C) are found throughout the central nervous system (CNS): NPR-A and NPR-C are found on neurons and astrocytes, while NPR-B is located mainly on neurons and partially colocalizes with NPR-A. In the CNS of man and rodents NPR-A is found mainly in cortex and hippocampus, whereas NPR-B is present in the amygdala and several brainstem regulatory sites. NPR-C is found widely within the CNS i.e. in neocortex, limbic cortex, the hippocampal area and the amygdala. These peptides and their receptors represent an important neuromodulatory system within the CNS, which is involved not only in the regulation of fluid homeostasis but also directly influences emotional behaviour, such as anxiety and arousal, and the sequelae of stress hormone release and autonomic nervous system activation. Natriuretic peptides are specifically involved in the regulation of the hypothalamo-pituitary-adrenocortical (HPA) system: in man and rodents ANP inhibits the HPA system at all regulatory levels, while CNP stimulates the release of cortisol. Complementarily, the anatomic structure of natriuretic peptide systems within the CNS supports an important role for these in normal and pathologic emotional behaviour (e.g. anxiety and panic): in rodents ANP was found to reduce anxiety levels, whereas CNP induced the opposite effect. In patients with panic disorder basal ANP plasma levels are lower in comparison to healthy volunteers, but ANP secretion is faster and more pronounced during experimentally induced panic attacks. The inhibitory potency of ANP could explain the unexpected and so far unresolved failure of autonomic and HPA system activation during panic attacks. Moreover, panic anxiety and concomitant ACTH and cortisol secretion elicited by stimulation with the panicogen cholecystokinin-tetrapeptide were also attenuated by ANP infusions in patients as well as in healthy volunteers. Hence, it may be surmised that in man and rodents ANP reduces anxiety and terminates panic attacks and their neuroendocrine sequelae.

Ectopic Excretion of Atrial Natriuretic Peptide (ANP) in Acute Lymphoblastic Leukaemia (ALL)

<h3>Background</h3> Hyponatraemia is an infrequent complication in ALL. It is reported to affect 10% of patients and is usually caused by hypovolaemia following gastrointestinal losses complicating chemotherapy. The syndrome of inappropriate antidiuretic hormone (SIADH) has been reported to complicate malignancy, however hyponatraemia secondary to excessive secretion of ANP in ALL has not been reported. We report a case of ALL in which hyponatraemia is presumed to be caused by ectopic excretion of ANP by leukaemic cells. <h3>Case</h3> A 10 year old boy presented with a 10 day history of pain in right lower shin, weight loss and reduced appetite. Examination revealed pallor, bruises on arms and legs, lymphoadenopathy and hepatosplenomegaly. A high white cell count with blast cells was noted. After bone marrow confirmation of ALL, chemotherapy was commenced. Lumber puncture ruled out CNS involvement. Mild hyponatraemia (130-135 mmol/L) was detected at admission and continued for the first two weeks but later declined further to 117 mmol/L in third week. Urinary sodium was noted to be significantly high with fractional excretion of sodium being more than 1%. His sodium requirement was up to 700 mmol/day. ANP was noted to be exceptionally high (106 pg/ml) when severely hyponatraemic. Hyponatraemia resolved over the period of 8 weeks with normalisation of ANP during remission (10 pg/ml). <h3>Discussion and conclusion</h3> Our case is an example of severe hyponatraemia in ALL with massive sodium requirement in the presence of a significantly high level of ANP. Common causes of hyponatraemia such as hypovolaemic dehydration were ruled out. SIADH was excluded by the absence of fluid overload and normal urine concentration. Renal function was normal with no evidence of glomerular or tubular damage. Normal echocardiogram ruled out the possibility of cardiotoxicity. Significantly high ANP levels were present with marked hyponatraemia and high urinary sodium losses in the absence of other causes suggesting ectopic excretion of ANP by leukaemic cells; this has not reported in the literature. We suggest considering measuring ANP in unexplained hyponatraemia in ALL.

Natriuretic Peptides Synthesis and Secretion Profiles during the Evolution of Cardiac Hypertrophy in DOCA-Salt Hypertensive Rats

The interactions between pressure and volume overload that occur in hypertension lead to different patterns of cardiac hypertrophy and to increase in natriuretic peptides (NPs). The profiles of ANP and BNP synthesis and secretion have been investigated in models of hypertension; however, the different evolution of these profiles during the acute and chronic periods of pressure overload-induced cardiac hypertrophy is still unknown. For this reason, we studied DOCA-salt treated Sprague-Dawley rats at weeks 2, 4, 6 and 12 and correlated the evolution of these profiles with cardiac hypertrophy and hypertension. Cardiac hypertrophy had a positive correlation with ANP expression in the left ventricle and with ANP plasma levels. BNP expression increased after 4 weeks of treatment while ANP increased significantly after 6 weeks. In addition, BNP plasma levels increased only in the group treated for 12 weeks, while ANP plasma levels increased from week 2. NP secretion has a differential response in the early stages of the development of cardiac hypertrophy induced by the DOCA-salt model, with an early increase in ANP. As ANP levels were exceeded to those of BNP in all the DOCA-salt groups, ANP might be considered a more specific marker of volume overload.