Forms Of BNP Research Articles

Abstract 15838: Atrial Natriuretic Peptide Compensatory Response is Impaired in Human Acute Decompensated Heart Failure

Atrial and B-type natriuretic peptides (ANP and BNP) are cardiac hormones secreted as compensatory measures to preserve cardiorenal homeostasis. Treating heart failure (HF) with sacubitril/valsartan increased ANP and not BNP, suggesting the ANP system may confer therapeutic benefit. Thus, the presence of an ANP deficient subgroup of HF patients possibly posing higher risk for HF severity, underscores a need to characterize both, the biologically active and inactive (NT-proANP and NT-proBNP) natriuretic peptides (NPs)(latter resistant to degradation), to highlight the extent of NP production in HF. Characterizing neprilysin (NEP) activity may also provide insights into the degree of NP degradation in HF. This study aims to both highlight the cardiac NP response in acute decompensated HF(ADHF) by measuring molecular forms of ANP and BNP together with defining circulating soluble NEP activity as to assess mechanisms impairing the NP response in HF. We recruited 47 healthy individuals with neither cardiovascular nor metabolic disease and compared ANP, BNP, NT-proANP, NT-proBNP, and NEP activity levels with 107 recruited ADHF patients. In ADHF, compared to a healthy setting, median ANP, BNP, NT-proANP, and NT-proBNP were all elevated (15.7 vs. 118.1 pg/mL , p<0.0001; 23 vs. 515 pg/ml, p<0.0001; 60.1 vs. 651.6 pg/mL, p<0.0001; 46 vs. 3330 pg/mL, p<0.0001, respectively). However, circulating NEP activity was significantly lower in ADHF than in healthy circulation (32 vs. 12.3 nM/mL/min, p<0.0001). NPs did not correlate with NEP activity in healthy circulation. However, only ANP (r = 0.4788, p<0.0001) and NT-proANP (r = 0.6819, p<0.0001) correlated with NEP activity in ADHF. The presence of an impaired ANP response in ADHF, underscored by insufficient increases in NT-proANP than NT-proBNP, suggests decreased ANP production may induce not only an ANP deficient ADHF state, but be characteristic of ADHF. The presence of NEP activity in ADHF circulation, despite lower NEP activity compared to healthy individuals, suggests ANP degradation may second impaired production, further lowering ADHF ANP levels. Our studies support augmenting the ANP system in ADHF through either endogenous stimulation or exogenous supplementation as optimal therapeutic strategies.

Superiority of proatrial natriuretic peptide in the prognostic power in patients with acute decompensated heart failure on hospital admission: comparison with B-type natriuretic peptide and other natriuretic peptide forms

AimsThere are significant differences in how atrial (A-type) and B-type natriuretic peptide (ANP and BNP) are secreted and metabolised, but there is little information available about the relative clinical significance...

4934Circulating molecular forms of ANP and BNP in human acute decompensated Heart Failure: evidence for a relative ANP deficiency state

4934Circulating molecular forms of ANP and BNP in human acute decompensated Heart Failure: evidence for a relative ANP deficiency state

Natriuretic peptides: degradation, circulating forms, dosages and new therapeutic approaches.

Testing for natriuretic peptides (BNP, NT-proBNP or MR-proANP) is recommended by the European Society of Cardiology (ESC) since 2005 for the exclusion diagnosis of acute and chronic heart failure because of very high predictive values. Natriuretic peptides are produced by the heart in response to high transmural pressure and/or myocardial ischemia. These peptides circulate in blood of both healthy subjects and heart failure patients. Mass spectrometry methods allowed identifying a collection of circulating and degraded forms of BNP, NT-proBNP and proBNP. Glycosylated forms of NT-proBNP and proBNP have also been identified. Current immunoassays are lacking analytical specificity due to high cross-reactivities between circulating forms. Moreover, glycosylation has been found to interfere with the capacity of antibodies to bind correctly to analytes. These elements have been taken into account to propose strategies for the development of new standardized and improved immunoassays. More recently, the better understanding of the degradation pathways of natriuretic peptides allowed the raise of new therapeutic approaches for heart failure patients. All these elements are detailed in this review.

Pro-B-type natriuretic peptide is cleaved intracellularly: impact of distance between O-glycosylation and cleavage sites.

We investigated the molecular mechanism underlying the processing of pro-B-type natriuretic peptide (proBNP). Rat neonatal atrial and ventricular myocytes were cultured separately. We examined the molecular forms of secreted and intracellular BNP in atrial and ventricular myocytes; levels of corin and furin mRNA in atrial and ventricular myocytes; the effect their knockdown on proBNP processing; plasma molecular forms of BNP from rats and humans with and without heart failure; and the impact of the distance between the glycosylation and cleavage sites in wild-type and mutant human proBNP, expressed in rat myocytes transfected with lentiviral vectors. BNP was the major molecular form secreted by atrial and ventricular myocytes. Transfection of furin siRNA reduced proBNP processing in both atrial and ventricular myocytes; however, transfection of corin siRNA did not reduce it. BNP was the major molecular form in rat plasma, whereas proBNP was the major form in human plasma. The relative fraction of human BNP in rat myocytes expressing human proBNP was about 60%, but increasing the distance between the glycosylation and cleavage sites through mutation, increased the processed fraction correspondingly. These results suggest that proBNP is processed into BNP intracellularly by furin. The level of proBNP processing is lower in humans than rats, most likely due to the smaller distance between the O-glycosylation and cleavage sites in humans.

Protease corin expression and activity in failing hearts.

Atrial and brain natriuretic peptides (ANP and BNP) regulate blood pressure and cardiac function. In patients with heart failure (HF), plasma levels of pro-ANP and pro-BNP, the precursor forms of ANP and BNP, are highly elevated, but the mechanism underlying the apparent deficiency in natriuretic peptide processing is unclear. Corin is a cardiac protease that activates natriuretic peptides. In this study, we examined corin protein expression and activity in mouse and human failing hearts. Tissue samples were obtained from a mouse model of HF induced by myotrophin overexpression and from human nonfailing, hypertrophic, and failing hearts. Corin protein levels in the membrane fraction and tissue lysate were measured by Western blotting and ELISA. Corin catalytic and biological activities were measured by fluorescent substrate and pro-ANP processing assays. In mice, corin protein levels did not change with age in normal hearts but increased significantly in failing hearts. In humans, corin protein levels were similar in the atrium from nonfailing and failing hearts but were increased in the ventricle in failing hearts compared with those in nonfailing or hypertrophic hearts. Unlike the protein level, however, corin activity did not increase in failing hearts, as measured by fluorogenic substrate and pro-ANP processing assays. Our results indicate that corin activation is a rate-limiting step in failing hearts. Insufficient corin activation is expected to prevent natriuretic peptide processing and may contribute to body fluid retention and impaired cardiac function in patients with HF.

Natriuretic Peptides in the Diagnosis and Management of Chronic Heart Failure

Circulating levels of the BNP system can help in the diagnosis of cardiovascular disease and provide prognostic information not only for patients who have HF but also for the general population and other patient groups. Changes over time also carry prognostic information, and studies are assessing BNP-guided treatment strategies. With the identification of circulating molecular forms of BNP, new insights regarding the biology of the BNP system are emerging that may improve the diagnostic and prognostic value of BNP. Likewise, accounting for rs198389 (a common single nucleotide polymorphism that increases BNP levels) may help to further refine the use of components of the BNP system as biomarkers.

Pro-B-Type Natriuretic Peptide: A Novel, Specific Biomarker for Detection of Left Ventricular Dysfunction in the General Community

Introduction: Pro-B-Type Natriuretic Peptide (ProBNP), from which biologically active BNP and inactive amino-terminal BNP (NT-proBNP) are processed, has been reported to be elevated in heart failure (HF). It remains to be shown in a large cohort study whether ProBNP circulates in normals, what factors influence ProBNP, and if it is a sensitive biomarker for left ventricular (LV) dysfunction. Hypothesis: We test whether a novel assay (BioRad) for ProBNP will be specific for ProBNP and not cross react with other forms of BNP. Furthermore, we hypothesize that ProBNP levels will be most determined by age and gender and that ProBNP will be a sensitive and specific biomarker for LV dysfunction in the general community. Methods: We used a large community cohort (n=2009; age=>45) from Olmsted County, MN. All subjects had detailed echocardiography, clinical phenotyping, and assessment of comorbidities. ProBNP was measured using BioRad assay. Univariable and multivariable analysis were used to determine which clinical factors best determine ProBNP levels in all subjects. ROC curves were generated by comparing ProBNP to 2-D Doppler Echo in detecting LV dysfunction. Assay specificity was assessed by adding 8 different forms of BNP to normal human plasma. Results: ProBNP was present in normals (median male=10 pg/ml, female=20; p<.001) and elevated in those with EF<40% (median male=195, female=188; n=36). Gender and age (Spearman>.3, p<.01) were strong predictors of ProBNP. ProBNP was a sensitive and specific marker for LV dysfunction based on ROC curves (AUC=.86). Finally, the BioRad assay did not cross react with any BNP forms that we added to normal human plasma. Conclusions: Using a novel ProBNP assay, we are the first to establish normal ProBNP levels in a large general adult population, suggesting that the normal human heart secretes ProBNP. We conclude that age and gender should be considered in interpretation of ProBNP values, similar to BNP and NT-proBNP. Importantly, in the entire population of randomly selected adults in the general community, ProBNP was a sensitive and specific biomarker for the detection of LV dysfunction. Thus, these studies establish the utility of ProBNP as a biomarker for HF, and we suggest further studies to better establish the biologic and pathophysiologic significance of ProBNP in humans. Introduction: Pro-B-Type Natriuretic Peptide (ProBNP), from which biologically active BNP and inactive amino-terminal BNP (NT-proBNP) are processed, has been reported to be elevated in heart failure (HF). It remains to be shown in a large cohort study whether ProBNP circulates in normals, what factors influence ProBNP, and if it is a sensitive biomarker for left ventricular (LV) dysfunction. Hypothesis: We test whether a novel assay (BioRad) for ProBNP will be specific for ProBNP and not cross react with other forms of BNP. Furthermore, we hypothesize that ProBNP levels will be most determined by age and gender and that ProBNP will be a sensitive and specific biomarker for LV dysfunction in the general community. Methods: We used a large community cohort (n=2009; age=>45) from Olmsted County, MN. All subjects had detailed echocardiography, clinical phenotyping, and assessment of comorbidities. ProBNP was measured using BioRad assay. Univariable and multivariable analysis were used to determine which clinical factors best determine ProBNP levels in all subjects. ROC curves were generated by comparing ProBNP to 2-D Doppler Echo in detecting LV dysfunction. Assay specificity was assessed by adding 8 different forms of BNP to normal human plasma. Results: ProBNP was present in normals (median male=10 pg/ml, female=20; p<.001) and elevated in those with EF<40% (median male=195, female=188; n=36). Gender and age (Spearman>.3, p<.01) were strong predictors of ProBNP. ProBNP was a sensitive and specific marker for LV dysfunction based on ROC curves (AUC=.86). Finally, the BioRad assay did not cross react with any BNP forms that we added to normal human plasma. Conclusions: Using a novel ProBNP assay, we are the first to establish normal ProBNP levels in a large general adult population, suggesting that the normal human heart secretes ProBNP. We conclude that age and gender should be considered in interpretation of ProBNP values, similar to BNP and NT-proBNP. Importantly, in the entire population of randomly selected adults in the general community, ProBNP was a sensitive and specific biomarker for the detection of LV dysfunction. Thus, these studies establish the utility of ProBNP as a biomarker for HF, and we suggest further studies to better establish the biologic and pathophysiologic significance of ProBNP in humans.

Coupling of a vented column with splitless nanoRPLC-ESI-MS for the improved separation and detection of brain natriuretic peptide-32 and its proteolytic peptides

The circulating concentration of a biomarker for congestive heart failure, Brain (B-type) Natriuretic Peptide (BNP-32), is measured using ELISA based assays in order to rapidly diagnose and monitor disease progression. The lack of molecular specificity afforded by these assays has recently come into question as emerging studies indicate there are potentially multiple heterogeneous forms of BNP in circulation with immunoreactive capabilities. In order to better understand the molecular biology of BNP-32 as it relates to congestive heart failure, it would thus be advantageous to use a detection platform such as Fourier transform ion cyclotron resonance mass spectrometry. This high resolving power mass spectrometer can provide unparalleled molecular specificity and can facilitate identification and characterization of the various molecular forms across all disease states. Unfortunately, BNP circulates at low concentrations (as low as 3 fmol/mL). Thus, it will require a collaborative effort from a number of orthogonal front-end technologies to overcome the disconnect between the practical detection limits of this instrument platform and the physiological levels of BNP-32 and its alternative molecular forms. Herein, we begin optimization of these front-end techniques by first enhancing the conditions for online nanoLC-ESI-MS separations of BNP-32 and its proteolytic fragments. Through extensive analysis of various chromatographic parameters we determined that Michrom Magic C8 stationary phase used in conjunction with a continuous, vented column configuration provided advanced chromatographic performance for the nano-flow separations involving intact BNP-32 and its associated tryptic peptides. Furthermore, conditions for the tryptic digestion of BNP-32 were also studied. We demonstrate that the use of free cysteine as an alkylation quenching agent and a secondary digestion within the digestion scheme can provide targeted tryptic peptides with increased abundances. Combined, these data will serve to further augment the detection of BNP-32 by LC–MS.

Molecular Forms of BNP and ANP and gene expression of processing enzyme in atrium and ventricle in heart failure rat

Object: Recent studies suggest that there are several molecular forms of plasma BNP in patients with heart failure. However, precise mechanism remains unknown. Methods: The atrial and ventricular tissue levels of BNP1-45(alpha-BNP), BNP1-95(gamma-BNP), ANP1-28(alpha-ANP), and ANP1-126(gamma-ANP) were determined by radioimmunoassay following extraction with a Sep-Pak C18 cartridge and gel-filtration in control and Dahl salt-sensitive heart failure rat. We also measured mRNA levels of ANP, BNP, corin and furin, processing enzyme of ANP and BNP, in atrial and ventricular tissue by real-time PCR analysis.

Natriuretic Peptides

In the 25 years since de Bold et al demonstrated the existence of an atrial natriuretic factor, investigation of the cardiac natriuretic peptides has produced a maturing knowledge base1,2 identifying the cardiac peptides and addressing stimuli for secretion of atrial (ANP) and B-type (BNP) natriuretic peptides, the processing and release of the mature bioactive carboxy terminal peptides, together with their propeptides and amino terminal fragments, the nature of natriuretic peptide receptors, and the bioactivities of natriuretic peptides (including natriuresis, vasodilatation, suppression of renin–angiotensin–aldosterone and sympathetic nervous activity, and trophic effects inhibiting vascular and cardiac hypertrophy and fibrosis). Less is known of the more recently discovered C-type natriuretic peptide (CNP and its cosecreted amino-terminal peptide, NTproCNP).3,4 Increasingly, measurements of the B-type peptides have found diagnostic and prognostic application in cardiovascular disease.5–7 The genes for ANP and BNP are in tandem on human chromosome 1.8 Upstream regulatory regions identified for the BNP gene include an AP1 binding site, serum response elements, M-CAT and GATA sites.9,10 Translation results in pre-pro BNP from which a 26 amino acid signal peptide is cleaved to produce the 108 amino acid precursor proBNP. This in turn is processed between amino acid residues 76 and 77 resulting in a 32 amino acid biologically active peptide (BNP) from its carboxy terminal plus the remaining amino terminal peptide sequence (NTproBNP 1 to 76). ANP is synthesized as a 126 amino acid precursor and is stored in granules within atrial tissue.11 During or shortly after secretion, the precursor is processed to an active 28 amino acid carboxy terminal peptide (ANP) and amino terminal ANP (proANP 1 to 98). The amino terminal propeptides NTproANP, NTproBNP, and NTproCNP have no known biological actions. The mature bioactive human forms of ANP, BNP, and CNP all contain a 17 …

Alternate Circulating Pro-B-Type Natriuretic Peptide and B-Type Natriuretic Peptide Forms in the General Population

This study was designed to determine whether alternate pro-B-type natriuretic peptide (proBNP) and BNP forms circulate in the general population. Bioactive BNP(1-32) and NT-proBNP(1-76) are derived from a precursor molecule, proBNP(1-108). Recent data suggest that aminodipeptidase-processed forms of BNP(1-32) (BNP(3-32)) and of proBNP(1-108) itself (proBNP(3-108)) may circulate and have additional diagnostic potential. Residents (age > or =45 years) of Olmsted County, Minnesota, underwent medical review, echocardiography, and phlebotomy for 2 novel assays specific for proBNP(3-108) and BNP(3-32) and 2 commercial assays (Triage BNP and Roche NT-proBNP). Groups included normal subjects (n = 613), cardiovascular disease with normal ventricular function (n = 1,043), preclinical ventricular dysfunction (ALVD, n = 130), and chronic heart failure (HF, n = 52). ProBNP(3-108) levels were above assay detection limits in 68% of normal subjects (50th; 25th to 75th percentiles: 7.85; 3.00 to 22.45 pmol/l) and correlated with age, gender, body size, and renal function and with results of commercial assays. ProBNP(3-108) levels were higher in ALVD (17.88; 6.07 to 42.76 pmol/l) or HF (42.75; 20.51 to 65.73 pmol/l), where they correlated more strongly with commercial assays. BNP(3-32) was above assay detection limits in 22% of normal subjects; levels were not correlated with age, body size, or renal function but were higher in HF. Neither novel assay was superior to commercial assays for the detection of ALVD or HF. The presence of alternate circulating proBNP and BNP forms provides evidence for diverse proBNP and BNP processing in the general population. The physiologic consequences of these observations, both in terms of assay performance and endogenous BNP bioactivity, deserve further study.

Lack of activation of molecular forms of the BNP system in human grade 1 hypertension and relationship to cardiac hypertrophy

We evaluated relationships among two circulating molecular forms of brain natriuretic peptide (BNP32 and NT-proBNP), severity of hypertension (HTN), and cardiac hypertrophy in subjects with mild, moderate, and severe HTN. We prospectively studied 78 patients (43 males; mean age 51.4 +/- 11 yr) with essential HTN and 28 age- and sex-matched controls. BNP32 and NT-proBNP were measured by radioimmunoassay. In grade 1 HTN, BNP32 was not elevated and NT-proBNP was reduced (P = 0.030) compared with controls. However, log-transformed values of BNP32 and NT-proBNP were both increased with severity of HTN from grade 1 to 3 (P <0.0001 and P = 0.003, respectively). By multivariate analysis, log BNP32 was independently predicted by age (beta = 0.210, P = 0.026) and HTN grade (beta = 0.274, P = 0.004), whereas log NT-proBNP was independently predicted by sex (beta = 0.235, P = 0.012) and HTN grade (beta = 0.218, P = 0.0023). Two forms of BNP were measured in normal subjects and patients with essential HTN. In grade 1 HTN, BNP32 was unchanged and NT-proBNP was significantly reduced compared with controls. As severity increased in humans with grade 1 to 3 HTN, both BNP32 and NT-proBNP levels were increased while not being affected by the presence of left ventricular hypertrophy. The lack of activation of BNP32 together with the reduction of NT-proBNP in grade 1 HTN may represent an impaired response of the BNP system in the early phase of HTN. The later activation of both forms of BNP may be a late compensatory effect, because it correlates with severity of HTN rather than cardiac hypertrophy/remodeling.

Subcutaneous administration of biologically active novel conjugates of human BNP in normal conscious dogs

BNP mediates vasorelaxation, natriuresis, and anti-renin-aldosterone activity through generation of cGMP. Currently the therapeutic use of BNP is limited to acute intravenous administration in congestive heart failure (CHF). However, CHF is a chronic diseases requiring long-term therapy. Proprietary technology (Nobex, Durham NC) has resulted in the development of amphiphilic oligomers covalently attached to peptides. The resulting conjugated peptide possesses improved pharmacokinetic and pharmacodynamic profiles. The current study evaluated four conjugated forms of human BNP (hBNP) to determine if these modified peptides would have sustained biological activity when administered subcutaneously (SQ). As all had significant biological actions and no significant differences were noted between conjugates the results are presented in aggregate. We hypothesized that these novel and potentially sustained acting modified peptides of BNP would be absorbed and result in an increase in plasma hBNP, cGMP, together with a sustained reduction in mean arterial pressure (MAP). Methods: Conjugates were administered SQ in 10 conscious dogs after baseline measurements of MAP and blood sampling for canine BNP (cBNP), hBNP and cGMP. MAP and blood sampling was repeated at 10, 30, 60, 120, 180, and 240 minutes after SQ administration. Results: Plasma hBNP was significantly elevated compared to baseline at 10 and 30 minutes (p<0.01). Plasma cGMP was elevated compared to baseline at 10 minutes and remained elevated through 180 minutes (p<0.01). MAP decreased at 10 minutes and remained decreased through 120 minutes (p<0.01). Plasma cBNP was unchanged compared to baseline throughout the protocol. Conclusions: These novel conjugated forms of human BNP are absorbed and present in the circulation when administered SQ. Importantly, they activate cGMP and induce significant reductions of MAP. These results suggest the importance of pursuing further studies with long-term administration of these modified forms of hBNP employing SQ administration in cardiovascular disease.

N-terminal pro-atrial natriuretic peptide as a biochemical marker of long-term interventional success after radiofrequency catheter ablation of paroxysmal supraventricular tachyarrhythmias

Radiofrequency (RF) catheter ablation has been shown to be highly effective in the treatment of supraventricular tachycardias. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (B-type natriuretic peptide; BNP) are secreted by the heart mainly in response to myocardial stretch induced by volume load. The aim of the present study was to determine the time course of the N-terminal prohormone forms of ANP (NT-proANP) and BNP (NT-proBNP) in patients undergoing radiofrequency (RF) catheter ablation for paroxysmal supraventricular tachycardias. Serial blood samples were taken from 13 patients with symptomatic paroxysmal supraventricular tachycardias undergoing RF ablation and from 13 age- and gender-matched healthy controls. Blood was taken before ablation (day 0, baseline), and at day one and day 120 after ablation. Levels of NT-proANP were significantly higher before RF ablation (4862+/-726 pmol/l) as compared to day one (2021+/-220 pmol/l) and day 120 after RF ablation (2470+/-349 pmol/l) (with p<0.01 on day one and p<0.05 on day 120; n=13). The size of the left atrium decreased from 41.0+/-5.5 mm before ablation to 34.9+/-5.9 mm (n=13; p<0.05) on day 120 as measured by M-mode echocardiography. Levels of NT-proBNP showed comparable values before and on day one and day 120 after ablation and were not significantly elevated as compared to healthy controls. NT-proANP levels are increased in patients presenting with paroxysmal supraventricular tachycardias and decrease one day after radiofrequency catheter ablation, possibly reflecting a transient reduction of ANP secretion from injured myocardial cells. Lower NT-proANP levels in the long-term time course may result from reduction of atrial volume load and reconstitution of atrial architecture after successful treatment of supraventricular tachycardias. NT-proANP may serve as a useful laboratory marker to describe the long-term interventional success after RF ablation.

Investigation of the plasma concentrations and circulating forms of BNP and ANP in orthotopic cardiac transplant recipients.

Investigation of the plasma concentrations and circulating forms of BNP and ANP in orthotopic cardiac transplant recipients

Radioimmunoassay for Rat B-Type Natriuretic Peptide (BNP-45)

Rat BNP-45 is the main circulating form of BNP in rat plasma. To understand the role of BNP in physiological and pathophysiological conditions, a specific radioimmunoassay (RIA) for the quantitative determination of the peptide in plasma and tissues is necessary. An assay using rBNP-45 as the standard in conjunction with antisera directed against this peptide has not been described in the literature, though some investigators have reported values ranging from 0.73-2.0 pmol/L using either BNP-26 or BNP-32 as the standard peptide. Unfortunately, these forms of BNP do not exist in rat plasma. In our studies, we have developed a specific RIA for rBNP-45 using rBNP-45 as the standard peptide and Tyro-rBNP-45 as the radioligand. We have used two specific antisera for assay purposes; one against rBNP-45, and the second to a peptide composed of the first 20 amino acids of rBNP-45 (rBNP[1-20]). The recovery of various amounts of rBNP-45 added to control plasma was 50-80% depending on the method of extraction and purification. The interassay and intraassay coefficients of variation were 12% and 6% respectively. Values obtained were similar for blood sampled by either cardiac puncture, decapitation, or aortic puncture. The method was used to measure rBNP-45 in the plasma of normal (WKY) and Spontaneously Hypertensive (SHR) rats. The values obtained were 5.46 +/- 0.43 and 19.6 +/- 2.36 pmol/L respectively. The rat atrial natriuretic peptide (ANP[99-126]) values in the same extracts were 23.2 +/- 0.45 and 51.6 +/- 3.16 pmol/L.

Angiotensin II stimulates endothelin-1 secretion in cultured rat mesangial cells.

The present study was designed to test two hypotheses: (1) that angiotensin II (Ang II) stimulates endothelin-1 secretion in cultured rat mesangial cells and (2) that atrial and brain natriuretic peptides (ANP and BNP) inhibit the above-mentioned secretion in these cells. Ang II stimulated immunoreactive (ir) endothelin-1 secretion in a concentration-dependent manner between 10(-8) M and 10(-7) M. The protein kinase C (PKC) inhibitors from two chemical classes, H7 and staurosporine, inhibited secretion following such stimulation. The stimulatory effect of Ang II was also abolished in the PKC-depleted cells. Rat ANP(1-28) and rat BNP-45, which are the respective major circulating forms of ANP and BNP in rats, potently inhibited Ang II-stimulated endothelin-1 secretion in a concentration-dependent manner. Inhibition by ANP and BNP of Ang II-stimulated endothelin-1 secretion was paralleled by an increase in the cellular level of cyclic guanosine 5'-monophosphate (GMP). The addition of a cyclic GMP analogue, 8-bromo cyclic GMP, reduced the stimulated endothelin-1 secretion. Rat ANP(5-25) was less effective that rat ANP(1-28) with respect to inhibiting ir-endothelin-1 secretion and increasing cellular cyclic GMP. These findings indicate that Ang II stimulates endothelin-1 secretion in cultured rat mesangial cells by a mechanism probably involving activation of PKC, and that rat ANP and BNP inhibit this stimulated secretion through a cyclic GMP-dependent process.