Alpha-atrial Natriuretic Polypeptide Research Articles

Distribution of alpha-ANP in the cochlea and the vestibular organs.

The distribution of rat alpha-atrial natriuretic polypeptide (ANP) was studied in the adult inner ear of the Sprague-Dawley rat using immunohistochemical methods. Immunostaining, in particular of the subepithelial stroma cells of the spiral ligament, the spiral prominence and below neuroepithelial areas of all five vestibular organs, was identified. We hypothesize that alpha-ANP is involved in perilymphatic dynamics rather than generating endolymph. The strong staining for alpha-ANP of outer hair cells indicates specific mechanisms for volume control as compared with inner hair cells and vestibular hair cells which all lack this immunostaining. The functional significance of the specific staining of nerve calyces in only the three cristae ampullaris but not in the two maculae remains to be clarified. The positivity of epithelial cells in the endolymphatic sac supports a previous hypothesis which looks upon this organ as a pressure regulation system in the inner ear.

Rat brain natriuretic peptide (BNP) reduces water intake following dehydration

The effect of rat brain natriuretic peptide (BNP) on drinking behaviour was examined in dehydrated and well-hydrated rats. Following dehydration for 18h, intracerebroventricular injections of 5 μg of rat BNP significantly reduced water consumption 0–2 h after the injections, but not 2–4 h afterwards. Rat BNP failed to decrease water intake in animals given water ad libitum. Thus, rat BNP is similar to alpha-atrial natriuretic polypeptide in that it only affects drinking in dehydrated rats. Following dehydration, plasma vasopressin levels were decreased by BNP, but BNP did not affect serum osmolality and electrolyte metabolism. These findings suggest that BNP may be involved in the central regulation of water consumption.

Changes in plasma level of alpha-atrial natriuretic polypeptide (alpha-ANP) and responsiveness of the aorta to exogenous alpha-ANP subsequent to myocardial infarction in rats.

The changes in plasma level of alpha-atrial natriuretic polypeptide (alpha-ANP) and the relaxing responses to exogenous alpha-ANP of strips of rat aorta pretreated with methoxamine were examined at one, four and eight weeks after myocardial infarction induced by left coronary ligation. Responses to a beta-adrenergic stimulant, isoprenaline, and sodium nitroprusside of the vessel pretreated with high potassium were also evaluated up to twelve weeks. Plasma concentrations of immunoreactive alpha-ANP, which were measured at one, four and twelve weeks, were significantly elevated in rats with myocardial infarction (MI-rats) as compared with sham-operated rats (sham-rats). The relaxation responses of the aorta to exogenenous alpha-ANP in MI-rats were significantly reduced at one and four weeks as compared with sham-rats. The difference was, however, less obvious at eight weeks. The responses to isoprenaline tended to be reduced from the 1st week to the 12th week, and the difference was significant at eight weeks, whereas those to methoxamine and sodium nitroprusside were unchanged. It is concluded that the MI-rats are partially resistant to the vasodilating effects of alpha-ANP and isoprenaline without any change in responses to the alpha-stimulant and sodium nitroprusside, although these changes are transient.

Changes in Plasma Level of Alpha-Atrial Natriuretic Polypeptide (Alpha-ANP) and Responsiveness of the Aorta to Exogenous Alpha-ANP Subsequent to Myocardial Infarction in Rats

The changes in plasma level of alpha-atrial natriuretic polypeptide (alpha-ANP) and the relaxing responses to exogenous alpha-ANP of strips of rat aorta pretreated with methoxamine were examined at one, four and eight weeks after myocardial infarction induced by left coronary ligation. Responses to a beta-adrenergic stimulant, isoprenaline, and sodium nitroprusside of the vessel pretreated with high potassium were also evaluated up to twelve weeks. Plasma concentrations of immunoreactive alpha-ANP, which were measured at one, four and twelve weeks, were significantly elevated in rats with myocardial infarction (Ml-rats) as compared with sham-operated rats (sham-rats). The relaxation responses of the aorta to exogenenous alpha-ANP in Ml-rats were significantly reduced at one and four weeks as compared with sham-rats. The difference was, however, less obvious at eight weeks. The responses to isoprenaline tended to be reduced from the 1st week to the 12th week, and the difference was significant at eight weeks, whereas those to methoxamine and sodium nitroprusside were unchanged. It is concluded that the Ml-rats are partially resistant to the vasodilating effects of alpha-ANP and isoprenaline without any change in responses to the alpha-stimulant and sodium nitroprusside, although these changes are transient.

Peptides derived from atrial natriuretic polypeptide precursor in human and monkey brains.

Using radio-immunoassays for the C-terminal sequence of alpha-atrial natriuretic polypeptide [atrial natriuretic factor (ANF)-(99-126)], alpha-ANP (17-28) [ANF-(115-126)], which corresponds to gamma-human ANP [115-126; gamma-hANP-(115-126)] and for the N-terminal sequence of gamma-hANP [human ANF-(1-126)], gamma-hANP-(1-25) [human ANF-(1-25)], we detected the parallel distribution of alpha-hANP-like immunoreactivity and gamma-hANP-(1-25)-like immunoreactivity in the human and monkey brains, with the highest concentrations in the midbrain and the pons. High performance gel permeation chromatography coupled with the two radio-immunoassays and also with another radio-immunoassay using a monoclonal antibody against the N-terminal sequence of alpha-ANP revealed that gamma-ANP is synthesized in the brain and cleaved into N-terminally deleted form(s) of alpha-ANP and 10-K N-terminal fragment(s) of gamma-ANP, which coexist within the neuron. These results suggest that the post-translational processing of gamma-ANP in the brain is different from that in the heart.

Gamma-atrial natriuretic polypeptide (gamma ANP)-derived peptides in human plasma: cosecretion of N-terminal gamma ANP fragment and alpha ANP.

Using RIAs for the N- and C-terminal fragments of the human atrial natriuretic polypeptide (ANP) precursor gamma ANP, that is gamma ANP-(1-25), and alpha ANP [gamma ANP-(99-126)], we studied the secretion of gamma ANP-derived peptides from the heart in normal subjects and patients with heart disease, chronic renal failure, and cirrhosis. We detected gamma ANP-(1-25)-like immunoreactivity (-LI) in plasma from normal subjects (n = 17) in considerable amounts [mean, 510 +/- 62 (+/- SE) pg/mL (174 +/- 21 pmol/L)]; the mean plasma alpha ANP-LI level at the same time in these subjects was 32.8 +/- 4.4 pg/mL (10.7 +/- 1.4 pmol/L). Gel permeation chromatographic analysis of plasma samples from normal subjects and patients with heart disease and chronic renal failure revealed two major components; one was alpha ANP, and the other was the 10K N-terminal gamma ANP fragment (N-peptide) resulting from the removal of alpha ANP (3K) from gamma ANP (13K). In addition, gamma ANP (13K), which possessed both gamma ANP-(1-25)-LI and alpha ANP-LI, and beta ANP, an antiparallel dimer of alpha ANP, were detected in some patients as minor components. A significant positive correlation between plasma levels of the N-terminal gamma ANP fragment and alpha ANP (P less than 0.01) and almost equal step-ups in the coronary sinus plasma levels of the N-terminal gamma ANP fragment and alpha ANP suggest that they are cosecreted in equimolar amounts. The high molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI (17.4 +/- 1.4) in normal subjects and the significantly higher ratio in patients with chronic renal failure (36.9 +/- 7.1; P less than 0.01) suggest the slower clearance of the N-terminal gamma ANP fragment than alpha ANP and a role for the kidney in its degradation. Since the molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI in patients with cirrhosis (20.7 +/- 2.7) was similar to that in normal subjects, it is unlikely that the N-terminal gamma ANP fragment is metabolized by the liver. In patients with heart disease, plasma gamma ANP-(1-25)-LI and alpha ANP-LI levels were higher in those with cardiac decompensation and were positively correlated with right atrial pressure, pulmonary arterial pressure, and pulmonary capillary wedge pressure, indicating cosecretion of the N-terminal gamma ANP fragment and alpha ANP in response to atrial stretch.(ABSTRACT TRUNCATED AT 400 WORDS)

Human atrial natriuretic polypeptide during escape from mineralocorticoid excess in man.

1. Plasma concentrations of human alpha-atrial natriuretic polypeptide (h-alpha ANP) during escape from the effects of mineralocorticoid excess were determined in six healthy volunteers. 2. Escape, as indicated by an abrupt increase in sodium excretion on the third to sixth day of 9 alpha-fludrocortisone acetate administration (0.6 mg/day), was observed in all subjects. 3. The mean plasma h-alpha ANP level was 30.9 +/- SEM 8.8 pmol/l on the control day; it increased exponentially in response to 9 alpha-fludrocortisone acetate administration, reached a significant level (114.0 +/- 22.4 pmol/l, P less than 0.05) on the day before escape and remained elevated during escape. 4. The 24 h creatinine clearance and blood pressure did not change significantly before the escape. Plasma h-alpha ANP increased markedly when the cumulative sodium balance exceeded 220 mmol. 5. These results suggest that h-alpha ANP may play a contributory role in natriuresis and diuresis after mineralocorticoid excess.

Relationship between plasma atrial natriuretic polypeptide concentration and hemodynamic measurements in children with congenital heart diseases

The plasma alpha-atrial natriuretic polypeptide (alpha-ANP) concentration in the peripheral veins of children with congenital heart diseases was measured by radioimmunoassay and compared with cardiac catheterization data. Every patient with heart failure had a higher alpha-ANP concentration (132.1 to 858.7 pg/mL) than the upper limit of the normal range (11.7 to 98.7 pg/mL), whereas more than half of the patients without heart failure had a normal alpha-ANP concentration. Although none of the 13 children with atrial septal defect had heart failure, their mean (+/- SD) plasma alpha-ANP concentration (99.4 +/- 40.7 pg/mL) was significantly higher than that in control children (44.6 +/- 22.3 pg/mL). The plasma alpha-ANP concentration was significantly correlated with the pulmonary blood flow/systemic blood flow (Qp/Qs) ratio in the children with atrial septal defect. In the 34 children with ventricular septal defect the plasma alpha-ANP concentration increased in relation to increasing size of the defect. The plasma alpha-ANP concentration was significantly correlated with the Qp/Qs ratio, pulmonary artery pressure, and left atrial pressure, estimated from mean pulmonary artery wedge pressure, in the children with ventricular septal defect. In the children with tetralogy of Fallot, the mean plasma alpha-ANP concentration was normal, and mean right and left atrial pressures were not increased. The elevated alpha-ANP concentration in the three patients with heart failure decreased after their conditions improved with various treatments. Thus the measurement of alpha-ANP concentration may be valuable in evaluating the presence or absence of heart failure and the response to treatment in children with congenital heart diseases. Distention of the right and left atrial might induce the release of alpha-ANP in patients with atrial and ventricular septal defects, respectively.

Isolation and structural analysis of the circulating human cardiodilatin (alpha ANP).

A new method was applied to isolate a polypeptide hormone from human blood. The polypeptides from 1,000 1 of hemofiltrate with a molecular weight lower than 20 kDaltons were adsorbed to 2.5 kg alginic acid, then eluted, precipitated, and desalted on a G-25 Sephadex column, thus obtaining a crude lyophilised plasma polypeptide extract. These polypeptides were further submitted to ion-exchange chromatography. Thereafter, two steps of HPLC were carried out to purify a distinct polypeptide which was the circulating form of cardiodilatin (CDD) in this case. The amino acid analysis, C-terminal enzymatic cleavage by carboxypeptidase A, and sequence analysis showed that the only form of circulating cardiodilatin is the 28 amino acid residue containing molecule, cardiodilatin-99-126 cleaved from the C-terminus of cardiodilatin-126 and identical with alpha-ANP (alpha atrial natriuretic polypeptide). Other bioactive molecular forms of the polypeptide hormones of the cardiodilatin family were not detected in the hemofiltrate. The isolation procedure was followed up by a bioassay using in vitro vascular smooth muscle relaxation.

Immunocytochemical evidence for CDD/ANP-like peptides in strands of myoendocrine cells associated with the ventricular conduction system of the rat heart.

Immunohistochemical investigations with different antisera against cardiodilatin 99-126 or alpha atrial natriuretic polypeptide revealed the presence of cardiac hormones not only in the atria of rats but also in strands of myoendocrine cells located in subendocardial regions of the ventricular septum. The localization of CDD-IR (cardiodilatin immunoreactivity) in the ventricle is associated with the location of the conduction system in the rat. The significance of the morphological relationship between cardiodilatin and the conduction system of the rat heart is discussed.

Atrial natriuretic factor in human blood.

To determine whether atrial natriuretic factor (ANF) is a circulating hormone in men, a radioimmunoassay suitable for the estimation of ANF in human plasma was developed and the nature of plasma ANF was characterized. Plasma ANF was extracted before radioimmunoassay by affinity chromatography on a column of ANF antibody-coupled agarose. When plasma ANF extract was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with the radioimmunoassay of the eluted gel slices for ANF, almost all of the ANF activities ran in the 3,000-mol-wt area, while three peaks of ANF were observed in human atrial tissue extract, molecular weights of which corresponded to 14,000, 6,000, and 3,000, respectively. Reversed-phase high performance liquid chromatography of atrial tissue extract resolved multiple forms of ANF. In contrast, one major peak was observed in human plasma extract, and its retention time coincided with that of synthetic human alpha-atrial natriuretic polypeptide. When 500 ml of 0.9% saline was infused into six healthy subjects over 45 min, plasma levels of ANF were unequivocally elevated. The mean plasma ANF concentrations rose from the baseline (23.0 +/- 2.5 pg/ml, mean +/- SEM, n = 6) to the peak (41.8 +/- 4.9 pg/ml, mean +/- SEM) at 75 min postinfusion. No significant change in plasma ANF, on the other hand, was found in the control group. These results suggest that ANF is a circulating hormone in men and is secreted in response to isotonic volume expansion.

Occurrence of atrial natriuretic polypeptide in brain

In order to determine whether or not atrial natriuretic polypeptides (ANPs) exist in the brain, we have studied extracts from the rat brain using a specific radioimmunoassay (RIA) for alpha-atrial natriuretic polypeptide. The presence and widespread distribution of alpha-rat ANP-like immunoreactivity (alpha-rANP-LI) have been demonstrated in the rat brain. The highest concentration of alpha-rANP-LI (20-22 ng/g) is in the hypothalamus and the septum. Moderate concentrations of alpha-rANP-LI (2-8 ng/g) are also found in the midbrain, cerebral cortex, olfactory bulb, thalamus, pons-medulla and hippocampus. High performance gel permeation chromatography coupled with the RIA revealed that alpha-rANP-LI found in the rat brain consists of three components eluting at the positions of gamma-rat ANP (gamma-rANP), beta-rat ANP (beta-rANP) and alpha-rANP, respectively. Among these a low molecular weight form of alpha-rANP-LI emerging at the elution position corresponding to alpha-rANP is predominant in the rat brain. This is in contrast to the finding that gamma-rANP, a high molecular weight form of 13k daltons is the dominant form of alpha-rANP-LI in the rat atrium. These results clearly show that there exists a widespread neural system containing ANPs in the brain.

Immuohistochemical demonstration of alpha-atrial natriretic plypeptide-containing neurons in the rat brain.

Using the immunoperoxidase technique in conjunction with specific antisera to alpha-atrial natriuretic polypeptide (alpha-ANP), it was shown that immunoreactive cell bodies and varicose fibers are widely distributed throughout the rat brain. The highest concentrations of alpha-ANP-containing neuronal cell bodies and fibers were found in the hypothalamus and septum. This result confirms the radioimmunological determination of alpha-ANP immunoreactivity in the rat brain.