Form Of Atrial Natriuretic Peptide Research Articles

Three molecular forms of atrial natriuretic peptides: quantitative analysis and biological characterization.

Atrial natriuretic peptide (ANP) is primarily produced in the heart tissue and plays a pivotal role in maintaining cardiovascular homeostasis in endocrine and autocrine/paracrine systems and has clinical applications as a biomarker and a therapeutic agent for cardiac diseases. ANP is synthesized by atrial cardiomyocytes as a preprohormone that is processed by a signal peptidase and stored in secretory granules as a prohormone. Subsequent proteolytic processing of ANP by corin during the secretion process results in a bioactive form consisting of 28 amino acid residues. Mechanical stretch of the atrial wall and multiple humoral factors directly stimulates the transcription and secretion of ANP. Secreted ANP elicits natriuretic and diuretic effects via cyclic guanosine monophosphate produced through binding to the guanylyl cyclase-A/natriuretic peptide receptor-A. Circulating ANP is subjected to rapid clearance by a natriuretic peptide receptor-C-mediated mechanism and proteolytic degradation by neutral endopeptidase. In humans, ANP is present as three endogenous molecular forms: bioactive α-ANP, a homodimer of α-ANP designated as β-ANP, and an ANP precursor designated as proANP (also referred to as γ-ANP). The proANP and especially β-ANP, as minor forms in circulation, are notably increased in patients with cardiac diseases, suggesting the utility of monitoring the pathophysiological conditions that result in abnormal proANP processing that cannot be monitored by inactive N-terminal proANP-related fragments. Emerging plate-based sandwich immunoassays for individual quantitation of the three ANP forms enables evaluation of diagnostic implications and net ANP bioactivity. This new tool may provide further understanding in the pathophysiology of cardiac diseases. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Effects of thyroid hormone withdrawal on natriuretic peptides during radioactive iodine therapy in female patients with differentiated thyroid cancer

Objective: We aimed to investigate the effects of thyroid hormone withdrawal on N-terminal prohormone forms of atrial natriuretic peptide (NT-proANP) and brain natriuretic peptide (NT-proBNP) during radioiodine therapy in female patients with differentiated thyroid cancer (DTC).Methods: Serum concentrations of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), NT-proANP and NT-proBNP were measured in 51 female patients with DTC (48.7 ± 4.2 years) at three time-points: day of radioiodine therapy (t1 – under acute hypothyroidism), 5 days after radioiodine (t2 – under acute hypothyroidism) and 3 months after radioiodine (t3 – under TSH suppression). Thirty healthy euthyroid women served as controls (42.8 ± 5.6 years).Results: At t1/t2/t3, median NT-proANP was 5.2/1.7/487 pmol/L vs. 297.7 pmol/L in control group (p < 0.001), median NT-proBNP was 50.1/36.5/79.5 pmol/L vs. 64.5 pmol/L (p < 0.001) and median NT-proANP/NT-proBNP ratios was 0.20/0.18/4.81 vs. 4.14 (p < 0.001). In acute hypothyroidism, FT3 levels were positively correlated with NT-proANP (r = 0.38, p = 0.005), NT-proANP/NT-proBNP ratios (r = 0.47, p = 0.001), heart rate (r = 0.39, p = 0.005), and negatively with mean arterial blood pressure (r = −0.58, p < 0.001).Conclusions: Our results indicate that NT-proANP reflects more accurately direct thyroid hormone effects than NT-proBNP. Thyroid hormone-dependent hemodynamic effects seem to be overlapped on the direct stimulatory effect of thyroid hormones on NT-proANP secretion by cardiac myocytes.

3種の心房性ナトリウム利尿ペプチド(ANP)分泌刺激時における血漿ANPの分子型の検討

This study analyzed by high performance gel permeation chromatography (HPGC) molecular forms of atrial natriuretic peptide (ANP) in plasma from anesthetized dogs stimulated by balloon inflation at the main pulmonary artery (Group A, n = 4), right atrial pacing (Group B, n = 4) and low-molecular dextran injection to right atrium (Group C, n = 4). Mean pulmonary arterial (PA) pressure, mean right atrial (RA) pressure, mean arterial pressure, heart rate and ECG were monitored by polygraph system Mean PA pressure in Group A, heart rate in Group B and mean RA pressure in Group C increased significantly by the stimulation (p less than 0.01, p less than 0.001 and p less than 0.05 respectively). Other parameters were not changed significantly in the three groups. There were significant increases in ANP concentration after the three stimulations (Group A: 52.4 +/- 5.4 (SD) pg/ml----86.4 +/- 12.2 (SD) pg/ml, Group B: 43.8 +/- 6.7 (SD) pg/ml----72.0 +/- 14.1 (SD) pg/ml, Group C: 42.7 +/- 8.8 (SD) pg/ml----69.3 +/- 10.0 (SD) pg/ml; each p less than 0.01). Gel filtration profiles showed that the increased form of plasma ANP in the three groups was alpha-ANP. These results suggest that alpha-ANP may be a main molecular form in plasma from dogs stimulated by the stretch of pulmonary arterial wall and right atrial wall, and atrial pacing.

Current biochemistry, molecular biology, and clinical relevance of natriuretic peptides

The mammalian natriuretic peptide family consists of atrial (ANP), brain [B-type; BNP] and C-type natriuretic peptide (CNP) and three receptors, natriuretic receptors-A (NPR-A), -B (NPR-B) and -C (NPR-C). Both ANP and BNP are abundantly expressed in the heart and are secreted mainly from the atria and ventricles, respectively. By contrast, CNP is mainly expressed in the central nervous system, bone and vasculature. Plasma concentrations of both ANP and BNP are elevated in patients with cardiovascular disease, though the magnitude of the increase in BNP is usually greater than the increase in ANP. This makes BNP is a clinically useful diagnostic marker for several pathophysiological conditions, including heart failure, ventricular remodeling and pulmonary hypertension, among others. Recent studies have shown that in addition to BNP-32, proBNP-108 also circulates in human plasma and that levels of both forms are increased in heart failure. Furthermore, proBNP-108 is O-glycosylated and circulates at higher levels in patients with severe heart failure. In this review we discuss recent progress in our understanding of the biochemistry, molecular biology and clinical relevance of the natriuretic peptide system.

Peptidylglycine-α-amidating monooxygenase and pro-atrial natriuretic peptide constitute the major membrane-associated proteins of rat atrial secretory granules

Peptidylglycine-α-amidating monooxygenase (PAM) is a bi-functional enzyme known to catalyze the post-translational bioactivation of signaling peptides. Although PAM is highly concentrated within the cardiac atrium, this tissue does not produce appreciable amounts of α-amidated peptides and thus, the function of PAM in atrium remains largely unknown. In this study, we demonstrate that PAM co-localizes in atrial secretory granules with the storage form of atrial natriuretic peptide (pro-ANP, amino acids 1–126), a hormone involved in the maintenance of blood pressure and fluid homeostasis. ANP is not amidated by PAM, but rather is processed to its active form (amino acids 99–126) by the proteolytic cleavage of pro-ANP. We demonstrate here by subcellular fractionation and biochemical analyses that PAM co-localizes with pro-ANP in secretory granules, where together they constitute the two most abundant membrane-associated proteins, accounting for approximately 95% of the total granular membrane protein. Respectively, light and electron microscopic immunohistochemistry show intense staining for PAM in atrial cardiomyocyctes and subcellular localization of PAM to secretory granules. Additionally, we demonstrate that while pro-ANP is readily found in the soluble contents of the granule lumen, significant amounts remain tightly associated with the membranes even after vigorous washing and estimate the molar ratio of pro-ANP to PAM to be approximately 30:1 in the membrane fraction. We postulate here that the primary function of PAM in the atrium is structural rather than enzymatic. In this regard, PAM may contribute to the packaging of pro-ANP within the secretory granule and possibly function in the presentation of pro-ANP for proteolytic processing.

Ectopic Expression of Active Processed Form of Atrial Natriuretic Peptide in Skeletal Myoblasts

Atrial natriuretic peptide (ANP) is a cardiac hormone that elicits a profound diuresis, natriuresis, and hypotension. As a preliminary study toward ANP gene therapy of cardiovascular disorders, we have cloned a cDNA for mouse preproANP and carried out expression studies in muscle cells. The expression cassette, which was flanked by ITRs from AAV-2, consisted of HCMV IE enhancer/promoter, preproANP gene, and polyadenylation signal from bovine growth hormone. We transfected this expression vector into primary skeletal myoblasts and examined the following points: (1) secretion of immunoreactive ANP, (2) biological activity, and (3) nature of secreted ANP(s). The conditioned media from cells transfected with ANP vector had significantly higher levels of irANP in comparison to mock control. The secreted irANP had biological activity as confirmed by the elevated level of intracellular cGMP in human umbilical vein endothelial cells. Reverse-phase HPLC analysis showed that the processed form of ANP was the predominant form. These results demonstrate that preproANP gene could be ectopically expressed and correctly processed in skeletal myoblasts, which has implications for development of muscle-based ANP gene therapy.

Enzymatic inactivation of major circulating forms of atrial and brain natriuretic peptides

We compared the enzymatic inactivation of major circulating forms of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). Both ANP and BNP induced a significant increase in cyclic GMP (cGMP) formation in cultured epithelial cell line derived from porcine kidney, LLC-PK 1. The cGMP formation stimulated by ANP in LLC-PK 1 cells was significantly decreased by pre-treatment of the peptide with rat renal brush-border membranes, and the inactivation of ANP was inhibited by neutral endopeptidase inhibitors, phosphoramidon and S-thiorphan. BNP exhibited greater resistance to enzymatic inactivation than did ANP. In addition, phosphoramidon potentiated the natriuresis with a low dose (7.5 pmol min −1 kg −1) of ANP but not of BNP in rats. These results suggest that enzymatic degradation of natriuretic peptides is highly dependent on peptide structure, and that the affinity of BNP to neutral endopeptidase is less than that of ANP.

Molecular forms of atrial natriuretic peptide in atria and plasma from fetal and adult female rats.

Molecular forms of atrial natriuretic peptide (ANP) were determined by chromatography on Sephadex G50 fine coupled with a radioimmunoassay for rANP(1-28) in left and right atrial extracts and acidified plasmas from 17-, 19- and 21-day-old fetuses and adult female rats. Chromatographic analyses revealed two immunoreactive peaks of rANP with an apparent molecular weight of about 25 and 12 kD, respectively, in all atrial extracts from fetal and adult rats. Only one immunoreactive peak of rANP with an apparent molecular weight of about 3 kD was detected in all fetal plasmas. The 25- and 12-kD ANP molecular forms isolated from fetal atrial tissue and incubated with thrombin for 30 min at 37 degrees C were converted to ANP material with a molecular weight of about 3 kD. These results suggest that the two high molecular weight forms stored in fetal atrial tissue should be precursors of circulating rANP molecules, and the rat fetus should possess the same posttranslational processing of the precursor molecule as the adult rat as early as day 17 of gestation.

Changes in molecular pattern of atrial natriuretic peptide in hemodialysis patients

An attempt was made to clarify whether the molecular forms of atrial natriuretic peptide (ANP) in the plasma of stable hemodialysis patients differ from those of healthy volunteers, and whether the ANP molecular forms in plasma might change during hemodialysis treatment. Ten stable hemodialysis patients with no clinical signs of cardiac disease were treated for 4 hours by a hollow fiber-type dialyzer. Plasma ANP concentrations before dialysis were 210 +/- 101.6 pg/ml (mean +/- SD), which were significantly higher than that of volunteers (59.2 +/- 37.2 pg/ml, n = 25). They were significantly decreased to 71.6 +/- 60.1 pg/ml after dialysis. Molecular patterns of ANP were measured by gel permeation chromatography and reverse-phase high performance liquid chromatography. Immunoreactive alpha-ANP peaks of GPC, which co-migrated with authentic alpha-, beta-, and gamma-ANP, were supposed to be alpha-, beta-, and gamma-ANP. The plasma of four patients contained a beta-ANP peak before dialysis, and three of the four still contained a beta-ANP peak after dialysis. These results showed that the middle-molecular-weight ANP, which co-migrated with authentic beta-ANP and is supposed to be beta-ANP, may particularly be secreted in clinically stable hemodialysis patients.

Generation of Atrial Natriuretic Peptide (ANP) in perfused lungs of Spontaneously Hypertensive Rats (SHR). comparison to Wistar-Kyoto (WKY) and Wistar (W) rat strains

1. Lungs can take up from the vasculature, circulating forms of atrial natriuretic peptide (Turrin and Gillis, 1986, 1987) and also to synthesize ANP. 2. The lung peptide directly delivered by lungs into the lung vasculature could play a role in the local water/electrolytic balance. 3. Using Spontaneously Hypertensive Rats (SHR), isogenic normotensive controls, the Wistar-Kyoto strain (WKY), and the regular Wistar strain as second control (W), and using a highly sensitive RIA, we measured the immunoreactive IR-ANP content of extracted plasma, lung homogenate and lung perfusate, since there are references of altered ANP levels in this kind of hypertension. 4. The IR-ANP measured in the lung vasculature effluent collected throughout 32 min of Krebs perfusion, was significantly different in all of the three analyzed strains (SHR > WKY > W). 5. The results support the idea of a local function for the peptide hormone directly delivered into the lung vasculature of SHR, which could represent a local adaptation to haemodynamics SHR characteristics besides a genetic characteristic distinguishing WKY from W strains.

&lt;b&gt;PUTATIVE LIGAND-BINDING SITES OF THE TYPE C ATRIAL NATRIURETIC PEPTIDE &lt;/b&gt;&lt;b&gt;RECEPTOR &lt;/b&gt;

Based on the assumption that there is conservation of sequences in the functionally important regions among the various forms of atrial natriuretic peptide (ANP) receptor, and in hopes of learning about the structure of the ligand-binding sites of the ANP receptors, we selected two highly homologous regions in the extracellular domain of the type C ANP receptor, synthesized a series of overlapping peptides covering these regions, and examined their abilities to interact with ANP. The synthetic peptides Pro 74 -Leu 80 and Leu 146 -Pro 153 showed very weak but significant affinities for ANP, suggesting that these regions may constitute the ligand-binding site

Cardiovascular and renal effects of eel and rat atrial natriuretic peptide in rainbow trout, Salmo gairdneri.

The renal and in vitro vascular effects of atrial natriuretic peptides have been examined in several species of fish. However, comparatively few investigations have described the effects of these peptides on the cardiovascular system in vivo. In the present experiments the dorsal aorta and urinary bladder were cannulated and the effects of atrial natriuretic peptides from rat and eel were monitored in conscious trout during bolus injection or continuous atrial natriuretic peptide infusion. The results show that the initial pressor effect of atrial natriuretic peptides is independent of environmental salinity adaptation (fresh or seawater) and the chemical form of atrial natriuretic peptide injected, but it is affected by the rate of atrial natriuretic peptide administration. This pressor response, and the accompanying diuresis, are mediated through alpha-adrenergic activation. Continuous infusion of either rat or eel atrial natriuretic peptide produces a steady fall in mean arterial blood pressure, which is temporally preceded by an increase in heart rate and a decrease in pulse pressure. Diuresis induced by atrial natriuretic peptides is only partially sustained during continuous infusion. Propranolol partially blocks the increase induced in heart rate by atrial natriuretic peptides, but does not affect either pulse pressure or mean arterial pressure. Propranolol significantly increases urine flow in saline-infused animals but has no apparent effect on animals subjected to infusions of atrial natriuretic peptides. These results indicate that there are multiple foci for the action of atrial natriuretic peptides in trout and that in many instances the effects of atrial natriuretic peptides are mediated through secondary effector systems.

Preferential Increase in the Free Form of Atrial Natriuretic Peptide in Adriamycin-Induced Nephrotic Rats

In order to evaluate the pathophysiologic role of a free form of atrial natriuretic peptide (ANP) in the nephrotic syndrome, the plasma concentration of immunoreactive ANP was measured by radioimmunoassay using direct (unextracted) and extraction methods in adriamycin-induced nephrotic and normal control rats. The ir-ANP levels measured using unextracted or extracted plasma were representative of total and the free form of ANP, respectively. The plasma levels of total and the free form of ANP were significantly higher in nephrotic rats than in controls (p less than 0.01, p less than 0.001). However, plasma levels of the bound form of ANP, calculated by subtracting the free form of ANP from total ANP, were comparable between the two groups. The free form of ANP was inversely correlated with the daily urinary sodium excretion (r = -0.71, p less than 0.001) and plasma albumin (r = -0.83, p less than 0.001), and positively correlated with the daily urinary protein excretion (r = -0.85, p less than 0.001) in both control and nephrotic groups. Based on these results, the preferential increase in the free form of ANP in nephrotic rats is considered to be a compensatory phenomenon induced by the decreased renal ability to eliminate sodium and water. An increase in the free form of ANP may have some role in urinary protein excretion in the nephrotic syndrome.

Specificities compared for a radioreceptor assay and a radioimmunoassay of atrial natriuretic peptide

The main active form of atrial natriuretic peptide (ANP) in the circulation is alpha ANP(1-28) [gamma-ANP(99-126)], although some active and inactive metabolites are also though to be present. Some immunoassays for alpha ANP reportedly detect inactive metabolites, as determined by their comparison with results by receptor assay, which would lead to misleading results for alpha ANP(1-28) measurements. Here we compare a radioreceptor assay (RRA) and a radioimmunoassay (RIA) for alpha ANP and show that their results correlate very well with regard to specificity and that the RIA appears to detect only the active circulating form of alpha ANP(1-28).

Bovine atrial natriuretic peptide in heart failure

The present study describes the concentration and molecular form of atrial natriuretic peptide (ANP) in Holstein dairy cattle with mild (bacterial endocarditis; BEC) or severe (dilated cardiomyopathy; DCM) heart failure. Significant increases in plasma concentration of ANP were observed in cattle with DCM (73.3 +/- 16.02 pmol/l, n = 4, P less than 0.01) and BEC (20.6 +/- 3.45 pmol/l, n = 7, P less than 0.05), when compared with those in control cattle (14.5 +/- 1.84 pmol/l, n = 12). The concentration of ANP in cattle with DCM was significantly (P less than 0.01) higher compared with that in cattle with BEC. Plasma concentration of ANP correlated significantly with right atrial pressure (r = 0.95, P less than 0.01) and left ventricular end-diastolic pressure (r = 0.84, P less than 0.01). Gel-permeation chromatography of ANP in plasma and the right atrium from control and cattle with BEC revealed a single peak corresponding to the elution position of authentic human ANP(99-126) in plasma, and two peaks corresponding to those of authentic human ANP(99-126) and pro-ANP in the atrial extract. In cattle with DCM, however, peaks corresponding to the elution positions of authentic human beta-ANP and/or pro-ANP were detected in addition to the peak corresponding to ANP(99-126). The content of ANP in the right atrium of cattle with DCM was significantly (P less than 0.05) increased compared with that in control cattle and those with BEC. The present study therefore suggests that the synthesis and secretion of ANP might be stimulated by atrial distention induced by increased atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for Ecto-Protein Kinase Activity That Phosphorylates Kemptide in a Cyclic AMP-dependent Mode

The heptapeptide Leu-Arg-Arg-Ala-Ser-Leu-Gly (Kemptide) is a synthetic construct of a substrate for cAMP-dependent protein kinase (PK). In this work we show that Kemptide has all the properties of a cytophilic substrate, i.e. it is a molecule preserving cell membrane intactness when added to cultured cells. Kemptide thus satisfies the prerequisites for employment in assays for cell surface-located ecto-PK activity. Different types of intact cells catalyze the phosphorylation of Kemptide in the presence of extracellular ATP and cAMP with Km values of 3-4 microM for Kemptide. Kemptide phosphorylation was influenced by PKI, the inhibitory protein specific for cAMP-PK. The results of comparative experiments with intact cells and with cell extracts demonstrate the ectoenzyme nature of this cAMP-PK. Further, the possibility was ruled out of a transfer of enzyme activity from damaged cells to the surface of intact cells. The anchorage of the surface cAMP-PK activity to the plasma membrane appears to be relatively stable since (i) cell supernatants, obtained after preincubation of intact cells with cAMP or Kemptide, did not show Kemptide phosphorylation, and (ii) the cAMP-dependent PK activity remained with cells even after five consecutive washes with cAMP or Kemptide. This is in contrast to the ecto-cAMP-independent phosvitin/casein type PK (Kübler, D., Pyerin, W., Burow, E., and Kinzel, V. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 4021-4025) which is released from intact cells through the addition of substrate. Data are presented which show that both ectokinase activities are exhibited independently. In conjunction with published evidence for an active export of cAMP from cells as well as for the appearance of extracellular ATP the demonstration of an ecto-cAMP-PK further supports the potential of PK for intercellular regulation. The potential of ecto-cAMP-PK is demonstrated by its ability to phosphorylate biologically active forms of atrial natriuretic peptide, the atrial natriuretic peptide, which possesses the specific sequence for a cAMP-PK-catalyzed phosphorylation.

Changes of molecular forms of atrial natriuretic peptide after treatment for congestive heart failure.

In the present study, an attempt was made to clarify whether ANP molecular forms in the plasma of severe congestive heart failure patients differ from those in healthy persons and whether ANP molecular forms in the plasma of the patients were changed by successful treatment of cardiac disease. Twenty patients with congestive heart failure were treated at Kitasato University Hospital. They were classified as class III or IV by New York Heart Association criteria at the time of admission. Plasma ANP concentrations decreased after treatment from 356 +/- 58.2 to 72.3 +/- 14.8 pg/ml. The gel permeation chromatograms from the plasma of healthy persons showed low, or low and high molecular weight ANP peaks which correspond to the elution positions of authentic alpha-ANP or ribonuclease A (mol. wt., 13.7 kdalton). In patients with severe congestive heart failure at a severe stage, middle molecular weight ANP consisted with the elution position of authentic beta-ANP was particularly noted in addition of low and high molecular weight ANP peaks. This middle molecular weight peak disappears in most of cases by successful treatment. Molecular forms in the plasma obtained from the coronary sinus and the inferior or superior vena cava were essentially the same. These results indicate that the middle molecular weight ANP supposed as beta-ANP may particularly be secreted in severe congestive heart failure patients.

Free and bound forms of atrial natriuretic peptide (ANP) in rat plasma: Preferential increase of free ANP in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP)

Free and bound forms of atrial natriuretic peptide (ANP) in rat plasma were analysed by gel permeation chromatography combined with a radioimmunoassay (RIA) for rat ANP (rANP). Gel permeation chromatography showed two immunoreactive peaks in rat plasma, one corresponding to alpha-rANP, rANP(99-126), and the other eluted at a high molecular weight, clearly different from gamma-rANP, rANP(1-126). The chromatographic profile of rat plasma after incubation with synthetic alpha-rANP demonstrated that the high molecular immunoreactivity had ANP-binding capacity. This bound form of ANP was almost totally excluded following extraction procedure, therefore, the immunoreactive ANP (ir-ANP) measured with the extraction assay was mainly free ANP. On the other hand, direct RIA may detect not only the free but also the bound form of ANP. Using both direct RIA and the extraction method, bound forms of plasma ANP in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) were compared to normotensive Wistar Kyoto rats (WKY). Bound forms of plasma ANP in 20-week-old SHR and SHRSP were significantly higher than that in age-matched WKY. The ratio of free/bound form of plasma ANP in SHR and SHRSP also significantly increased compared to WKY, indicating a preferential increase in free ANP in the plasma of these hypertensive rats. These findings suggest that a bound form of ANP may be present in rat plasma and that it may play some pathophysiological role in the hypertension of SHR and SHRSP. Increased free ANP in plasma may indicate a compensatory increase in ANP release in these hypertensive rats.

Alpha-Form of Atrial Natriuretic Peptide Released from Dog Atrium During Atrial Distension

To assess the released form of atrial natriuretic peptide (ANP) during atrial distension, we compared the form of ANP before and during atrial distension in anesthetized dogs, using radioimmunoassay combined with high performance liquid chromatography (HPLC). When increasing the left atrial pressure (LAP) from 2.2 +/- 0.9 mmHg to 9.4 +/- 1.3 mmHg, the plasma ANP concentration in the coronary sinus was increased by 190% over the control, during left atrial distension. The major form of the released ANP extracted in the blood sample obtained from the coronary sinus was alpha-form. However other unidentified immunoreactive peaks, preceding and following the main peak were also discernible. These results suggest that the major form of ANP released during left atrial distension was the alpha-form.

Alpha-human atrial natriuretic peptide is a coronary vasodilator in the Langendorff-perfused guinea pig heart

The circulating form of atrial natriuretic peptide is now believed to be composed of 28 amino acids (1). Therefore, we studied the coronary vasoactivity of the 28 amino acid, alpha-human atrial natriuretic peptide (α-hANP) in five isolated guinea pig hearts Langendorff-perfused at constant pressure (46 mmHg) with Krebs-Henseleit solution. The reactivity of the coronary bed was assured in each heart with bolus injections of norepinephrine, adenosine, and the vasoconstrictor atrial natriuretic peptide, atriopeptin II (APII). APII was a coronary constrictor in each of these five hearts. Nineteen boluses of α-hANP were administered to the five hearts, spanning the range 1.6 to 64 nmol/g wet heart weight. α-hANP was vasodilator in all five hearts. The equation for the regression of y = flow, % increase, on x = dose, nmol/g, is y = 17.98 logx −4.11. The correlation coefficient, r, is 0.83, and the coefficient of determination, r 2, is 0.69. Analysis of variance of the regression of y and x yields an F statistic of 36.9, P<0.00001. These results indicate that coronary vasodilation is correlated with dose of α-hANP over much of the range 1.6 – 64 nmol/g.