The use of a monoclonal antibody to measure plasma atriopeptins in rat

Interaction of a neutral endopeptidase inhibitor with an ANP-C receptor ligand in anesthetized dogs

Inhibition of important degradative pathways of atrial natriuretic peptide (ANP) in vivo could be a valuable therapeutic tool for regulating endogenous levels of ANP. The aim was to investigate the in vivo effects of both blockade of atrial natriuretic peptide clearance receptor and inhibition of neutral endopeptidase 24.11, an enzyme shown to be involved in ANP breakdown. Therefore, we infused a specific neutral endopeptidase inhibitor ((S)-thiorphan) and an ANP-C receptor ligand (AP 811) alone or in combination into anaesthetized beagle dogs. Compared with vehicle controls, coadministration of (S)-thiorphan and AP 811 (100 micrograms/kg/min and 10 micrograms/kg/min, resp.) had greater effects on endocrine and renal parameters than administration of either substance alone. Coadministration of both compounds increased urinary excretion of volume and sodium, cGMP and ANP. We found also increased plasma cGMP, plasma ANP and decreased plasma renin activity. No effects were observed with respect to blood pressure, left ventricular pressure or heart rate during the infusion period of 2 h. We conclude from these investigations, that blocking both degrading pathways of ANP with the ANP-C receptor ligand AP 811 and the neutral endopeptidase inhibitor (S)-thiorphan is more effective than inhibition of either system alone. Such a combination might therefore be a useful therapeutic tool in cardiovascular diseases.

Big ANF: large-molecular-weight ANF in rabbit plasma. II. Acid dissociation and HPLC of dissociated irANF

A large-molecular-weight form of atrial natriuretic factor (ANF) was found in rabbit plasma. When extraction of plasma utilizing octadecylsilane cartridges is employed, this big ANF is not retained by the cartridge. When this material is dissociated with acid, immunoreactive ANF (irANF) is released. Of the acids tested, formic and acetic acid (0.05 M) were indicated as the most effective in causing the dissociation. High-performance liquid chromatography analysis of dissociated ANF, confirmed by coelution with synthetic peptides, disclosed the presence of ANF-(99-126) and ANF-(103-126) in a ratio of approximately 2:1. Atriopeptin I was detected in most of the samples analyzed, but atriopeptin II was only detected in one analysis. Despite the wide spectrum of the antiserum used for detection of irANF in the eluent fractions, only immunoreactive peaks coeluting with the four standards were detected. We therefore conclude that big ANF is a bound form of atrial peptides found in normal circulation.

Big ANF: large-molecular-weight ANF in plasma. I. Gel filtration and affinity chromatography studies

A large molecular form of immunoreactive atrial natriuretic factor (irANF) was demonstrated in plasma of rabbit and rat on the basis of gel filtration experiments. This big ANF was not retained by octadecylsilane cartridges and cross-reacted with four anti-ANF antisera of different specificities. Gel filtration in acid, but not in 8 M urea, resulted in material with elution characteristics of irANF. Affinity chromatography and gel electrophoresis of big ANF suggested that the material was similar to albumin. However, high concentrations of big ANF were found in analbuminemic rats, with characteristics similar to those seen in rabbit and normal rats (affinity and gel chromatography and gel electrophoresis). We thus conclude that big ANF represents a bound form of ANF in circulation and that the carrier is similar to but not identical with albumin.

Role of endogenous ANP on endocrine function investigated with a monoclonal antibody

Substantial volume expansion in conscious rats induces a strong natriuresis, cyclic GMP excretion, increase in cyclic GMP in plasma and kidney tissue, decrease in plasma renin activity and plasma aldosterone concentration. These effects are directly related to an increase in plasma levels of atrial natriuretic peptides. The renal response and the changes in plasma and kidney cyclic GMP, plasma renin activity and aldosterone could be totally blocked by simultaneous administration of monoclonal antibodies directed against ANP. From this study it seems to be clear that the rise in cyclic GMP and the inhibition of the renin-aldosterone system is not a direct effect of volume expansion but is specifically mediated by the released ANP. The great importance of ANP in acute volume expansion made us wonder about the role of ANP in chronic volume expansion and under basal conditions without volume loading. Chronic volume loading was induced pharmacologically by the sodium retaining vasodilatator minoxidil. Under both chronic volume expansion and basal conditions the neutralization of the circulation ANP by antibody administration leads to reduced plasma cyclic GMP levels. No alterations in urinary sodium excretion, plasma renin activity and plasma aldosterone concentration could be observed: In conclusion, the monoclonal antibody directed against ANP is a useful tool for the investigation of the physiological role of endogenous ANP.

Vasodilatory action of endogenous atrial natriuretic factor in a rat model of chronic heart failure as determined by monoclonal ANF antibody

Elucidation of the role of (elevated) endogenous atrial natriuretic factor (ANF) in chronic heart failure has been hampered by a lack of specific inhibitors. We used a newly developed monoclonal antibody that has been shown to specifically block both exogenously and endogenously released ANF in vivo. For assessment of the vasodilatory action of ANF in chronic heart failure, either this antibody against ANF or ascites (control serum) was injected in rats with myocardial infarction and failure and in sham animals. Ascites did not alter central hemodynamics in either the sham or infarcted group. Antibody significantly increased right atrial pressure, left ventricular end-diastolic pressure, and systemic vascular resistance (SVR) in the infarction group but did not affect these variables in the sham group. Because renal blood flow, as measured by radioactive microspheres, decreased significantly in all four groups, probably due to nonspecific renal vasoconstrictor effects of the ascites, a separate group of infarcted animals was treated with purified ANF antibody (devoid of nonspecific effects) or mouse IgG as a control injection. In these animals, right atrial pressure increased from 1.1 +/- 0.7 to 2.6 +/- 0.7 mm Hg (p less than 0.001). Although SVR, renal blood flow velocity (measured by Doppler probe), and renal vascular resistance did not change in the infarcted animals after administration of purified ANF antibody, a significant correlation was found between baseline plasma ANF values and the change in SVR exerted by purified ANF antibody (r = 0.758, p less than 0.02, n = 9); that is, SVR increased in rats with high baseline plasma ANF (greater than 350 pg/ml), but decreased in animals with plasma ANF less than 200 pg/ml. These results suggest that moderately elevated endogenous plasma ANF levels in chronic heart failure do affect central hemodynamics, primarily by reducing venous pressure (e.g., by decreasing intravascular volume or by venous dilation). Arterial vasodilation, however, appears to emerge when plasma ANF is greatly increased.

ANP concentrations of atria, plasma and brain in Dahl S (DS) and Dahl R (DR) rats

In order to investigate the possible involvement of ANP in the salt dependent hypertension of the DS rats the concentrations of immunoreactive atrial natriuretic peptides (ANP-IR) in atria, plasma and brain of salt loaded and control fed DS and DR rats were determined. On a low salt diet the ANP-IR concentrations in atria, hypothalamus and basal ganglia of DS rats were higher versus DR rats. Salt loading results in a decrease of ANP-IR in left DS atria and an increase in plasma and brain stem of DS rat versus control and DR rat. The data are compared with other studies about ANP performed in Dahl rats, SHR and WKY rats. The possible reasons for the found distribution of ANP-IR are discussed.

Effects of nisoldipine on atrial natriuretic peptides, blood pressure and cardiac hypertrophy in Dahl rats

The role of the calcium antagonist nisoldipine and the arteriolar vasodilator minoxidil on plasma levels of atrial natriuretic peptides (ANP), systolic blood pressure and heart weight was estimated in inbred Dahl salt sensitive (S) rats and inbred Dahl resistant (R) rats in long-term experiments. S rats develop quickly malignant hypertension, cardiac hypertrophy and have increased ANP plasma levels when fed a high salt diet (8% NaCl), while R rats on a high salt stay normotensive. In S rats 5 weeks on a high salt diet, therapeutic treatment with nisoldipine for 5 weeks not only decreased blood pressure but also produced a regression in cardiac hypertrophy and a reduction in elevated ANP plasma levels in comparison to the untreated salt-loaded S controls. Similar results were achieved in a preventive trial. In contrast with nisoldipine, therapeutic treatment with minoxidil in salt-loaded S rats lead to no reduction in cardiac hypertrophy and produced an additional increase in plasma ANP despite a reduction in blood pressure. The increase in plasma ANP level in this model of hypertension and its modulation by antihypertensive treatment with a calcium antagonist or an arteriolar vasodilator show that the changes in ANP plasma levels are probably secondary to hypertensive disease and the associated cardiac volume overload.

Production of a monoclonal antibody against C terminus of atrial natriuretic factor by in vitro immunization

Spleen cells, sensitized in vitro with ANF-KLH conjugate, were fused with a non-producing mouse myeloma cell line, X63-Ag8.653. One of the isolated hybridomas secreted a monoclonal antibody which exhibited an association constant of 7.25 X 10(-9) M for ANF and recognized an epitope at the C-terminal of the synthetic rat ANF(101-126). Cross reactivity experiments with Auriculin B, Atriopeptin I and Atriopeptin II suggests Phe124-Arg125-Tyr126 in the epitope recognized by this antibody. The epitope appears to be similar to the portion of the hormone molecule essential for ANF binding to the B-receptor (high m.wt. receptor). This antibody may be useful for the generation of anti-idiotypic antibodies for the B-receptors.

Phylogenetic study on the immunoreactive atrial natriuretic peptide in the heart

Using two antisera against atriopeptin III (AP III) which had different characteristics in cross-reactivities with atrial natriuretic peptide (ANP) analogs, we have measured an immunoreactive ANP (ir-ANP) in the heart extracts of several species. ir-ANP in atrial extracts showed both high and low molecular weights. Serial dilutions of atrial extracts from chickens, turtles, frogs, and fish yielded competition curves which were parallel to the standard curve of AP III with antiserum No. 4. In comparison with two serial dilution curves of atrial extracts made using two antisera, No. 4 and No. 9, we suggest that the amino acid at position 12 of ir-ANP in the atrial extracts of chicken, turtle, frog, and fish is not isoleucine but is some other amino acid.

Human atrial natriuretic factor (ANF). Characterisation of a monoclonal antibody panel and its use in radioimmunoassay

The production of nine monoclonal antibodies to human atrial natriuretic factor (ANF 1-28) is described. All possible combinations of two antibodies failed to reveal any which could simultaneously bind ANF. Studies with ANF analogues and the antibodies having the three highest affinity values (KD = 5, 25 and 21 pM) indicated that the antibodies are directed to the central portion of the antigen molecule. The highest affinity antibody was able to replace polyclonal antisera in the radioimmunoassay of ANF in extracts of plasma.

Endothelin stimulates release of atrial natriuretic peptides in vitro and in vivo

The effect of endothelin (END) on the release of atrial natriuretic peptides (ANP) was studied in isolated rat atria and in conscious rats. END stimulates the ANP release in vitro in a dose-dependent manner. An increase in ANP plasma levels and cyclic GMP plasma levels was also observed in conscious rats after injection of END. When a monoclonal antibody directed against ANP was injected together with END the increase in cyclic GMP was completely blocked. From this study it is concluded that END is a potent secretagogue for ANP both in vitro and in vivo.

A two-site immunoradiometric assay of proatrial natriuretic factor. Application to tissue extracts

A "two-site" immunoradiometric assay (IRMA) was developed to specifically measure ANF (1-126), the precursor of ANF. This assay is based on the simultaneous use of antibodies against two different antigenic determinants: murine monoclonal antibody (2H2), which recognizes positions 101 through 103 of ANF, is linked to Immunobeads and employed to extract any ANF C-terminal; a second antibody, which is directed against positions 11 through 37, is radioiodinated and allows binding to any C-terminal-2H2-Immunobead material which bears the N-terminal antigenic site. A curvilinear relationship was obtained between radioactivity and the amount of proANF (1.5 to 400 fmol) added. Optimisation of IRMA was determined by the amount of 2H2-Immunobeads and labeled antibody used, incubation time as well as possible interference by both ANF (99-126) and ANF (1-98). Tissue extracts were used to validate the assay. proANF was detected in decreasing amounts in heart atria, heart ventricles, lungs, kidneys and adrenal glands. Its presence was further confirmed by reverse-phase HPLC followed by radioimmunoassay. IRMA is a simple and rapid method for the direct measurement of proANF in tissue extracts and chromatographic fractions. The presence of proANF in tissues strongly suggests local synthesis.

A monoclonal antibody to alpha-human atrial natriuretic polypeptide

A monoclonal antibody to alpha-human atrial natriuretic polypeptide (alpha-hANP), KY-ANP-I, has been produced by fusion of a nonproducing mouse myeloma cell line, X63-Ag8.653, with spleen cells from BALB/c mice immunized with synthetic alpha-hANP conjugated to bovine thyroglobulin using the carbodiimide coupling procedure. Hybridomas were screened for antibody production by radioimmunoassay using culture media and 125I-alpha-hANP. They were cloned by the limiting dilution technique, expanded in culture, and injected intraperitoneally into BALB/c mice. The obtained antibody belonged to the immunoglobulin G1 subclass. Analysis by a Scatchard plot revealed a high affinity for alpha-hANP, with an association constant of 3.1 x 10(10) M-1. With this monoclonal antibody, a specific radioimmunoassay for alpha-hANP has been established. The antibody in mouse ascites was available for radioimmunoassay at a final dilution of 1:10(6). Values of IC10 and IC50 in this radioimmunoassay were 3 and 30 fmol/tube, respectively. The radioimmunoassay showed a cross-reactivity of 0.9% with alpha-rat ANP. alpha-hANP-(8-22) and alpha-ANP-(1-6) exhibited less cross-reactivity than alpha-rat ANP on a molar basis. There was no cross-reaction with alpha-ANP-(17-28). Thus, the recognized epitope must be located in the N-terminal half of the ring structure of alpha-hANP including Met12 residue. This radioimmunoassay could detect gamma-hANP and beta-hANP as well as alpha-hANP. The monoclonal antibody was also useful for immunohistochemical studies. ANP-positive cells were finely stained in the human atrium using the avidin-biotin-peroxidase complex technique.(ABSTRACT TRUNCATED AT 250 WORDS)

The reduction of renin and aldosterone as a response to acute hypervolemia is blocked by a monoclonal antibody directed against atrial natriuretic peptides

We have previously reported that the strong diuresis, natriuresis and urinary cyclic GMP excretion after acute volume loading in rats are caused by ANP and can be blocked by additionally given monoclonal antibodies directed against ANP. The present report describes that in contrast to the changes in ANP and cyclic GMP, the plasma renin activity and aldosterone concentration are decreased after volume loading. This decrease is completely blocked by simultaneous administration of the monoclonal antibodies. Plasma cyclic AMP levels are not affected. From this study it seems to be clear that the inhibition of the renin-aldosterone system is not a direct effect of volume expansion but is specially mediated by the released ANP.

Increased tubuloglomerular feed-back mediated suppression of glomerular filtration during acute volume expansion in rats

1. Volume expansion is currently believed to change the intrinsic properties of the juxtaglomerular apparatus such that the sensitivity of the tubuloglomerular feedback (TGF) mechanism is reduced, thus allowing glomerular filtration rate, and hence salt and water excretion, to rise. Recent studies conflict with this view and indeed the older literature reveals that the rise in glomerular filtration rate (GFR) under these conditions is far more modest than would be expected if TGF control were eliminated. 2. To investigate this problem, TGF control of filtration rate was examined by measuring single-nephron glomerular filtration rate (SNGFR) during loop of Henle perfusion at varying rates in rats under control conditions, after acute, moderate (4% of body weight), iso-oncotic volume expansion and in rats treated with antibodies to atrial natriuretic peptide (ANP) prior to the acute volume expansion. 3. With TGF control of filtration interrupted by filtrate collection from the proximal tubule, SNGFR in the expanded rats was massively increased compared with controls, although SNGFR measured in the distal tubule, and hence with TGF control intact, was only modestly increased, as was whole-kidney filtration rate. Loop perfusion at increasing rates up to 30 nl min-1 progressively decreased SNGFR in controls, and in the expanded rats the range over which control was exerted extended up to 60-80 nl min-1. For changes in loop flow around the spontaneous operating point, the sensitivity of the TGF mechanism, defined as delta SNGFR/delta loop flow, was similar in both groups. Treatment of rats with ANP antibodies prior to volume expansion substantially blunted the changes in renal salt and water excretion and the increase in SNGFR seen in the absence of loop perfusion. 4. These results are not consistent with a diminution of TGF function after volume expansion, rather with an enhancement. The latter is best accounted for by vasodilation of preglomerular resistance vessels on volume expansion, a result predicted by calculations from a model based on the serial arrangement of preglomerular and TGF-controlled vascular resistance elements and the established pharmacological actions of ANP.

Modulation of ANP receptor-mediated cGMP accumulation by atrial natriuretic peptides and vasopressin in A10 vascular smooth muscle cells

ANP receptor binding and desensitization were demonstrated in the A10 vascular smooth muscle cell (VSMC) line. Concomitantly, the ANP receptor coupled guanylate cyclase activity was reduced by the receptor down-regulation with ANP. The ANP stimulated cGMP accumulation is modulated by arginine-vasopressin, while the arginine-vasopressin mediated cAMP system remained unaffected by ANP. Results suggest negative coupling of arginine-vasopressin receptors to the guanylate cyclase activity, and indicate that the vasorelaxant activity of ANP might be regulated in part by arginine-vasopressin via specific receptor sites.

Role of nisoldipine on blood pressure, cardiac hypertrophy, and atrial natriuretic peptides in spontaneously hypertensive rats

The effect of long-term treatment with the calcium antagonist nisoldipine on development of hypertension, cardiac hypertrophy, and plasma levels of atrial natriuretic peptides (ANP) was determined in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) of the same age. Measurement of immunoreactive ANP in plasma provided a sensitive marker for the severity of hypertension and the associated cardiac overload. Long-term treatment with nisoldipine prevented the development of hypertension, the associated heart failure, and the increase of plasma levels of ANP in SHR but had no effect on systolic blood pressure, heart weight, and plasma levels of ANP in WKY. In addition, nisoldipine had a therapeutic effect in old SHR with manifest cardiac failure in end-stage hypertension, as evidenced not only by the reduction of blood pressure but also by the reduction of cardiac hypertrophy, of elevated immunoreactive ANP in plasma, and of increased plasma renin activity.

Production and characterization of monoclonal antibodies against amino-terminus of human alpha-atrial natriuretic polypeptide

Monoclonal antibodies directed against human, alpha-atrial natriuretic polypeptide (alpha-ANP; Human, 1-28) were obtained by somatic cell fusion between P3-X63-Ag8.653 myeloma cells and spleen cells from a BALB/c mouse immunized with human, alpha-ANP selectively coupled to keyhole limpet hemocyanin. From the analysis of polyclonal sera with respect to determinant specificity before the fusion, the strategy was primarily used to pick up monoclonal antibody specific for the N-terminal residues of human, alpha-ANP. Screening of antibodies in the hybridoma culture supernatants were performed by binding to iodinated synthetic human, alpha-ANP. Two stable clones producing anti-human, alpha-ANP antibodies, designated 13A1 and 10B1, were obtained by the limiting dilution technique. The ability of ANP(Rat, 1-28) to inhibit binding of 125I-human, alpha-ANP to these antibodies was almost equipotent to ANP(human, 1-28). However, ANP fragments (Human, 7-28) and (18-28) did not compete the binding completely. These results suggest that both 13A1 and 10B1 monoclonal antibodies can specifically recognized N-terminus of human, alpha-ANP, and may be a useful tool to investigate receptor binding of human, alpha-ANP by the antagonizing effect.

The use of a monoclonal antibody for the determination of atrial natriuretic peptides in human plasma

A monoclonal antibody (mab) directed against alpha-human atrial natriuretic peptides (alpha-hANP) was produced. Using this mab a radioimmunoassay for the determination of hANP-like immunoreactivity in human plasma was established. To demonstrate the possible application of this radioimmunoassay for clinical diagnosis, plasma levels were measured in healthy subjects and in patients with renal failure before and after hemofiltration or hemodialysis. Plasma levels in healthy subjects ranged between less than 30 and 124 pg/ml. Mean plasma concentrations of hANP-IR in uremic subjects were 324 pg/ml before and 113 pg/ml after hemofiltration or hemodialysis.

Receptor binding, cGMP stimulation and receptor desensitization by atrial natriuretic peptides in cultured A10 vascular smooth muscle cells

Receptor characteristics for atrial natriuretic peptides (ANP) were demonstrated in the permanent tissue culture system of vascular smooth muscle cell (VSMC) line. 125I-ANP exhibited reversible and saturable binding to A10 rat VSMC, and the equilibrium dissociation constant, Kd was 157 pM and maximal binding capacity, Bmax amounted to 115 fmol/mg of protein. Binding of the 125I-ligand was highly specific for certain potently displacing ANP analogues with inhibition constants (Ki values) in the nano- or even subnanomolar concentration range. Pretreatment of VSMC with ANP yielded receptor desensitization to one half of the ANP receptor density, and supports the conclusion of receptor autoregulation by ANP in A10 VSMC. The receptor coupled intracellular cGMP system was stimulated, and thus demonstrates the application of A10 cells as a model for the study of ANP receptor interaction involved in vascular smooth muscle relaxation.

The elevation of cyclic GMP as a response to acute hypervolemia is blocked by a monoclonal antibody directed against atrial natriuretic peptides

Substantial volume expansion in conscious rats induces a strong diuresis and natriuresis that is caused by the increase in plasma levels of atrial natriuretic peptides (ANP) as measured by a radioimmunoassay. This renal response could be blocked by monoclonal antibodies directed against ANP. Parallel to the change in ANP, the cyclic GMP levels in plasma, urine and kidney tissue were increased after volume loading and reduced after additionally given antibodies. From this study it seems to be clear that the cyclic GMP rise is not a direct effect of volume expansion but is specifically mediated by the released ANP.