The lung as a possible target organ for atrial natriuretic polypeptide secreted from the heart

Expression patterns of natriuretic peptides in pre-hibernating and hibernating anatolian ground squirrel (Spermophilus xanthoprymnus) lung

Anatolian ground squirrel (Spermophilus xanthoprymnus) is a true hibernator. This animal transiently reduces pulmonary function during hibernation. Continuance of pulmonary function is very important to survive ground squirrels during the hibernation. Natriuretic peptides may be key players in the modulation of pulmonary hemostasis. However, NPs' role in pulmonary function during hibernation remains unclear. We aimed to investigate the localization and distribution of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) in squirrel lungs during pre-hibernation and hibernation periods using immunohistochemistry. Our immunohistochemical data indicate that ANP, BNP, and CNP were produced by the mucosal epithelium of terminal and respiratory bronchioles, smooth muscle cells in the lamina propria of terminal bronchioles and vascular smooth muscle cells, alveolar type II cells, and macrophages. ANP immunoreactivity was weaker than BNP and CNP immunoreactivities in these cells. The results also demonstrate that the number of ANP, BNP and CNP positive alveolar type II cells tended to increase, although statistically non-significant, during the hibernation period, but the expression of NPs in other pulmonary cells is unaffected by hibernation. This study firstly investigates ANP, BNP and CNP distribution in the Anatolian ground squirrel lung. However, further studies are required to dissect their functional roles during the hibernation.

Intrinsic defence capacity and therapeutic potential of natriuretic peptides in pulmonary hypertension associated with lung fibrosis

BACKGROUND AND PURPOSE

Idiopathic pulmonary fibrosis (IPF) is a progressive fibro-proliferative disorder refractory to current therapy commonly complicated by the development of pulmonary hypertension (PH); the associated morbidity and mortality are substantial. Natriuretic peptides possess vasodilator and anti-fibrotic actions, and pharmacological augmentation of their bioactivity ameliorates renal and myocardial fibrosis. Here, we investigated whether natriuretic peptides possess an intrinsic cytoprotective function preventing the development of pulmonary fibrosis and associated PH, and whether therapeutics targeting natriuretic peptide signalling demonstrate efficacy in this life-threatening disorder.

EXPERIMENTAL APPROACH

Pulmonary haemodynamics, right ventricular function and markers of lung fibrosis were determined in wild-type (WT) and natriuretic peptide receptor (NPR)-A knockout (KO) mice exposed to bleomycin (1 mg·kg⁻¹). Human myofibroblast differentiation was studied in vitro.

KEY RESULTS

Exacerbated cardiac, vascular and fibrotic pathology was observed in NPR-A KO animals, compared with WT mice, exposed to bleomycin. Treatment with a drug combination that raised circulating natriuretic peptide levels (ecadotril) and potentiated natriuretic peptide-dependent signalling (sildenafil) reduced indices of disease progression, whether administered prophylactically or to animals with established lung disease. This positive pharmacodynamic effect was diminished in NPR-A KO mice. Atrial natriuretic peptide and sildenafil synergistically reduced TGFβ-induced human myofibroblast differentiation, a key driver of remodelling in IPF patients.

CONCLUSIONS AND IMPLICATIONS

These data highlight an endogenous host-defence capacity of natriuretic peptides in lung fibrosis and PH. A combination of ecadotril and sildenafil reversed the pulmonary haemodynamic aberrations and remodelling that characterize the disease, advocating therapeutic manipulation of natriuretic peptide bioactivity in patients with IPF.

Atrial natriuretic peptide/natriuretic peptide receptor A (ANP/NPRA) signaling pathway: a potential therapeutic target for allergic asthma

Allergic asthma is a chronic inflammatory disease of airway and immune disorder is an acknowledged mechanism. Numerous data demonstrate Th1/Th2 cells play an important role in the development of allergic asthma. Atrial natriuretic peptide (ANP) is a multifunctional hormone secreted by cardiac atria, lung, and so forth, which has been recognized for several decades due to its general effects on cardiovascular system, and natriuretic peptide receptor A (NPRA) is the major effecting receptor for ANP. In recent years, more and more studies suggest that ANP/NPRA signaling pathway is implicated in modulation of immnue and inflammatory reaction. Moreover, there are some reports about significant changes of ANP production in peripheral blood from asthmatics in acute exacerbation compared with patients during the remission and the healthy. Nevertheless, it is unknown that why ANP shows an observable change and what role ANP plays in asthma until now. We propose that ANP/NPRA signaling pathway is involved in immune dysfunction and airway inflammation of allergic asthma based on our experimental results, which suggests ANP/NPRA signaling pathway may be a potential therapeutic target for allergic asthma.

Bronchodilator effect of infused B-type natriuretic peptide in asthma

STUDY OBJECTIVE

To determine the bronchodilator effect of recombinant human B-type natriuretic peptide (BNP; nesiritide) on patients with asthma.

DESIGN

A prospective, open-label study.

SETTING

Outpatient setting.

PATIENTS

Eight adult patients with asthma confirmed by > 12% and > 200 mL increase in FEV1 after bronchodilator inhalation.

INTERVENTIONS

An IV nesiritide bolus, 2 microg/kg, followed by continuous infusion for a total of 3 h at escalating doses of 0.01, 0.02, and 0.03 microg/kg/min for 1 h each as tolerated.

MEASUREMENTS

Spirometry and forced oscillation technique (FOT) measurements were both obtained at baseline and every 30 min during the infusion. Two doses of albuterol, 90 microg, inhalation via metered-dose inhaler were then administered at the end of nesiritide infusion, followed by repeat spirometry and FOT measurements after 30 min. Primary end points were FEV1 and FVC changes after the nesiritide infusion for 3 h. Wilcoxon signed-ranks tests were used to compare the effects of nesiritide and albuterol.

RESULTS

Baseline measurements (mean +/- SD) were as follows: FEV1, 1.89 +/- 0.87 L; FVC, 3.02 +/- 0.99 L; respiratory resistance at 5 Hz (Rrs5), 10.3 +/- 3.85 cm H2O . s/L; and mean respiratory resistance at 5 to 20 Hz, 7.56 +/- 1.92 cm H2O/L/s. Mean baseline serum BNP level was 27 +/- 27 pg/mL. After 180 min of nesiritide infusion, the following measurements showed significant changes: FEV1 increased to 2.41 +/- 0.78 L (mean increase, 520 mL), p = 0.012; FVC increased to 3.65 +/- 1.05 L (mean increase, 630 mL), p = 0.017; and Rrs5 decreased to 8.24 +/- 4.02 cm H2O/L/s, p = 0.017. After albuterol, there were no further significant changes in these measurements.

CONCLUSION

IV nesiritide is an effective bronchodilator in patients with asthma.

Atrial natriuretic peptide in hypoxia

A growing number of mammalian genes whose expression is inducible by hypoxia have been identified. Among them, atrial natriuretic peptide (ANP) synthesis and secretion is increased during hypoxic exposure and plays an important role in the normal adaptation to hypoxia and in the pathogenesis of cardiopulmonary diseases, including chronic hypoxia-induced pulmonary hypertension and vascular remodeling, and right ventricular hypertrophy and right heart failure. This review discusses the roles of ANP and its receptors in hypoxia-induced pulmonary hypertension. We and other investigators have demonstrated that ANP gene expression is enhanced by exposure to hypoxia and that the ANP so generated protects against the development of hypoxic pulmonary hypertension. Results also show that hypoxia directly stimulates ANP gene expression and ANP release in cardiac myocytes in vitro. Several cis-responsive elements of the ANP promoter are involved in the response to changes in oxygen tension. Further, the ANP clearance receptor NPR-C, but not the biological active NPR-A and NPR-B receptors, is downregulated in hypoxia adapted lung. Hypoxia-sensitive tyrosine kinase receptor-associated growth factors, including fibroblast growth factor (FGF) and platelet derived growth factor (PDGF)-BB, but not hypoxia per se, inhibit NPR-C gene expression in pulmonary arterial smooth muscle cells in vitro. The reductions in NPR-C in the hypoxic lung retard the clearance of ANP and allow more ANP to bind to biological active NPR-A and NPR-B in the pulmonary circulation, relaxing preconstricted pulmonary vessels, reducing pulmonary arterial pressure, and attenuating the development of hypoxia-induced pulmonary hypertension and vascular remodeling.

Guanylyl cyclases, nitric oxide, natriuretic peptides, and airway smooth muscle function

Airway smooth muscle (ASM) plays an important role in asthma pathophysiology through its contractile and proliferative functions. The cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) are second messengers capable of mediating the effects of a variety of drugs and hormones. There is a large body of evidence to support the hypothesis that cAMP is a mediator of the ASM's relaxant effects of drugs, such as beta2-adrenoceptor agonists, in human airways. Although most attention has been paid to this second messenger and the signal transduction pathways it activates, recent evidence suggests that cGMP is also an important second messenger in ASM with important relaxant and antiproliferative effects. Here, we review the regulation and function of cGMP in ASM and discuss the implications for asthma pathophysiology and therapeutics. Recent studies suggest that activators of soluble and particulate guanylyl cyclases, such as nitric oxide donors and natriuretic peptides, have both relaxant and antiproliferative effects that are mediated through cGMP-dependent and cGMP-independent pathways. Abnormalities in these pathways may contribute to asthma pathophysiology, and therapeutic manipulation may complement the effects of beta2-adrenoceptor agonists.

Plasma levels of atrial natriuretic peptide in severe burn injury

Atrial natriuretic peptide (ANP) plays a part in the regulation of volume homeostasis and possibly, in the pathophysiology of water and electrolyte disorder. Patients with serious burn injuries risk huge body fluids losses, which are compensated for by perfusion. Blood volume and the renin and aldosterone system are also disturbed. This study measured plasma ANP and vasoactive intestinal polypeptide (VIP) in patients with >20% total burned surface area (TBSA), at admission and 24 h post-admission.Eleven patients (mean age 46.5 years, 8 males) with a mean TBSA of 34.5% were sampled. Standard treatment was given. Eleven closely age-matched volunteers were used as controls. A specific ELISA method suitable for the measurement of ANP and VIP was used.ANP was higher (p<0.0001), while VIP was lower (p=NS) in patients' samples compared to controls. While the level of VIP was higher at 24 h post-admission, mean ANP level remained about the same. The increased levels of plasma ANP may result from volaemic disturbances during resuscitation, low VIP levels, the increase in pulmonary resistance or post-burn stress.

Atrial natriuretic peptide is not degraded by the lungs in humans

In an attempt to identify and quantify the sites of atrial natriuretic peptide (ANP) degradation, particularly the lungs, a new tracer method to study ANP metabolism in vivo in humans was developed and applied to patients with left ventricular dysfunction. Thirteen male, normotensive, cardiac patients with different degrees of left ventricular myocardial involvement were enrolled in the study. The study protocol required constant infusion (3 patients) or bolus injection (10 patients) of 125I-labeled ANP just upstream of the right atrium and blood sampling from different sites (pulmonary artery, aorta, inferior vena cava, and femoral vein) during the hemodynamic study. Data analysis was based on a kinetic model consisting of three blocks in series (right heart, lungs and left heart, and periphery) supplied by the same plasma flow (plasma cardiac output). Plasma levels of native ANP were measured with a sensitive and specific immunoradiometric assay method. ANP values measured in the aorta (163.9 +/- 144.8 pg/mL, n = 80) were superimposable on those measured in the pulmonary artery (161.8 +/- 136.5 pg/mL, n = 80). Negligible extraction of 125I-labeled ANP was found in the lungs and left heart block (on average 0.08 +/- 3.92%), whereas the peripheral block extraction (46.2 +/- 7.8%) accounted for almost total hormone removal from the blood (whole body extraction was 46.4 +/- 6.6%). ANP metabolic clearance rate (3.11 +/- 1.48, range 1.4-6.8 L/min) declined with the progression of left ventricular dysfunction (plasma cardiac output 3.46 +/- 1.08, range 1.2-5.7 L/min), and a close correlation between metabolic clearance rate and cardiac output was evident. Our data suggest that lungs do not extract, or extract only very small amounts, of labeled ANP administered iv to patients with different degrees of left ventricular myocardial involvement, and whole body extraction of labeled ANP remains relatively stable with the progression of disease, and the large reductions in clearance values observed in our patients can be ascribed mainly to the reductions in cardiac output.

Intrauterine exposure to cocaine increased plasma ANP (atrial natriuretic peptide) but did not alter hypoxanthine concentrations in the sheep fetus

To assess the effects of cocaine, administered to the ewe, on the secretion of atrial natriuretic peptide (ANP), Plasma Renin Activity (PRA) and hypoxanthine in the fetus we studied 6 chronically cannulated sheep fetuses late in gestation. The ewe was given an intravenous injection of cocaine (2 mg/kg). Maternal and fetal arterial blood samples were withdrawn prior to the injection and at 2, 5, 10, 15, 45 and 60 min after the injection for the measurement of ANP, PRA and hypoxanthine. Fetal arterial blood pressure (MAP), plasma ANP and protein levels increased and pH and pO2 decreased after cocaine was administered to the ewe. Fetal plasma hypoxanthine and PRA did not change. These results suggest that cocaine administration to the ewe is associated with fetal hypertension, hypoxemia and acidemia all of which may serve as stimuli for the secretion of ANP.

Haemodynamic effects of atrial natriuretic peptide in hypoxic chronic obstructive pulmonary disease

BACKGROUND

Pulmonary artery pressure is elevated in patients with advanced chronic obstructive pulmonary disease (COPD). Release of atrial natriuretic peptide (ANP) is increased in pulmonary hypertension and this hormone may both selectively vasodilate pulmonary vessels and inhibit pulmonary vascular remodelling. The hypothesis that ANP has a physiological role in protection of the pulmonary circulation from pressure overload, and that it may be beneficial in patients with COPD, has been examined.

METHODS

Ten patients with hypoxic COPD were infused for 30 minute periods with saline followed by ANP at 0.4, 2, and 10 pmol/kg/min respectively via a pulmonary artery catheter whilst monitoring haemodynamics and oxygenation.

RESULTS

Levels of immunoreactive ANP (irANP) increased from a mean (SD) of 23 (15) pmol/l to a maximum of 94 (41) pmol/l. Neither systemic blood pressure, cardiac output nor total systemic vascular resistance showed any correlation with irANP levels. There were negative correlations between levels of ANP and mean pulmonary artery pressure which fell from 28.7 to 25.9 mm Hg, pulmonary artery wedge pressure which fell from 6.5 to 4.6 mmHg, and total pulmonary vascular resistance which fell from 489 to 428 dynes s cm-5. There was a small fall in PaCO2 from 6.2 to 5.9 kPa, whilst venous admixture and oxygen delivery both increased non-significantly.

CONCLUSIONS

At these pathophysiological concentrations there was evidence that ANP selectively reduced right ventricular afterload. These data support the hypotheses that increased plasma levels of ANP may be beneficial in hypoxic COPD, and that endogenous ANP may ameliorate pulmonary hypertension in humans.

Effect of intravenous atrial natriuretic peptide on gas exchange in humans

The aim of this work was to establish whether a physiological increase in atrial natriuretic peptide (ANP) plasma levels affects pulmonary gas exchange in humans. Ten volunteers received an infusion of either ANP (4 pmol.kg-1.min-1) or physiological saline, for 60 min. Baseline measures of the alveolar-arterial PO2 difference and of the physiological dead space were within normal limits and remained stable during and after the infusion of ANP or saline, although plasma ANP and cGMP rose significantly (p < 0.01) (mean +/- SEM: ANP: 13.4 +/- 3.9 to 56.0 +/- 10.4 pmol/l; cyclic GMP: 3.8 +/- 0.3 to 17.0 +/- 3.8 nmol/l). We conclude that a physiological increase in plasma ANP does not affect pulmonary gas exchange significantly in humans.

Effect of atrial natriuretic peptide on bronchial tone in anesthetized rabbits

The effect of atrial natriuretic peptide (ANP) on histamine-induced bronchoconstriction was studied in vivo (in normoxic and in hypoxic rabbits) and in vitro. Thirty-two anesthetized rabbits, spontaneously breathing room air or 10% O2, received infusions of ANP (20, 40, or 80 ng/min/kg normoxia; 20 ng/min/kg hypoxia) or the vehicle for 100 min. After 75 min of ANP infusion, bronchoconstriction was induced inhaling histamine; respiratory resistance (Rrs) was measured prior to and until 20 min posthistamine. The results show that the histamine-induced increase in Rrs was significantly reduced by ANP 80 ng/kg/min in normoxia, and by ANP 20 ng/kg/min in hypoxia. In vitro, ANP had no effect on tracheal and bronchial smooth muscle precontracted with histamine or acetylcholine. These results show that ANP can decrease a histamine-induced bronchoconstriction in vivo but not in vitro, suggesting an indirect mechanism of action.

Atrial natriuretic factor and pulmonary status in premature infants with respiratory distress syndrome: preliminary investigation

We studied the correlation of atrial natriuretic factor (ANF) with lung compliance in a series of 16 premature infants with respiratory distress syndrome (RDS). The infants were followed during the first week of life by sequential Doppler echocardiography, lung compliance, and ANF measurements. Plasma ANF concentration varied between 38 and 2220 pg/mL; mean concentrations of 393 and 123 pg/mL with the ductus open and with it closed, respectively (P < 0.01). The arteriolar/alveolar oxygen-tension ratio showed an inverse correlation with the logarithm (In) of the ANF concentration (r = -0.55, P = 0.0002). Both mean airway pressure and In ANF showed an inverse correlation with the arteriolar/alveolar oxygen tension ratio (R = -0.77, F = 20.5 and 13.8, respectively). Plasma ANF was inversely correlated to lung compliance (r = -0.64, P < 0.0001). In infants with RDS, plasma ANF concentrations increase with the severity of respiratory distress. Because ANF increases endothelial permeability, in this preliminary investigation lead to the hypothesis that it may contribute to respiratory distress by causing extravasation of fluid from the pulmonary circulation in these patients.

Distribution of atrial natriuretic peptides in the sand rat (Psammomys obesus) in comparison to that in the rat

Atrial natriuretic peptides (ANP) are a family of humoral compounds involved in water and salt homeostasis. Immunoreactive ANP (IR-ANP) was determined in the plasma and tissues of the rat and the sand rat (Psammomys obesus) using sensitive and specific radioimmunoassay. IR-ANP from the rat and the sand rat elute at identical retention times from reverse phase HPLC indicating that the same chemical entity is present in both species. IR-ANP highest levels were found, in both species, in the heart but it was also present in the adrenal gland, lung, kidney, liver, plasma and several loci in the central nervous system. The IR-ANP levels in the heart, adrenal gland, kidney, liver, cerebellum and cerebral cortex were lower in the sand rat compared to the rat. The plasma IR-ANP level of the diabetes-resistant sand rat was further decreased to about 10% of the level in the diabetes-resistant sand rat.

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.

Direct secretion from left atrium and pulmonary extraction of human atrial natriuretic peptide

To evaluate direct secretion from the left atrium and pulmonary extraction of human atrial natriuretic peptide (hANP), we measured plasma hANP levels in the pulmonary artery, pulmonary vein, and left atrium in patients with either mitral stenosis or atrial septal defect. Left atrial pressure in patients with mitral stenosis was significantly higher than that in patients with atrial septal defect (7.5 +/- 1.0 mm Hg vs 3.1 +/- 0.5 mm Hg, p less than 0.01). The significant increase in the hANP level in the left atrium was recognized only in patients with mitral stenosis (149 +/- 33 pg/ml in the left atrium vs 130 +/- 28 pg/ml in the pulmonary vein, p less than 0.05). The plasma hANP level in the pulmonary vein was significantly lower than that in the pulmonary artery in both patients with mitral stenosis and those with atrial septal defect, which suggests that hANP is extracted in the lung. We conclude that hANP is secreted not only through the coronary sinus but also directly from the left atrium, stimulated by high left atrial pressure, and that circulating hANP is partially extracted in the pulmonary circulation.

Atrial and brain natriuretic peptides share binding sites on cultured cells from the rat trachea

We examined the distribution of binding sites for alpha-atrial natriuretic peptide (125I-ANP1-28) and the recently discovered porcine brain natriuretic peptide (125I-pBNP) on immunocytochemically identified cells in dissociated culture preparations of the rat trachea. Specific binding sites for both 125I-ANP1-28 and 125I-pBNP were evenly distributed over distinct subpopulations of smooth muscle myosin-like immunoreactive muscle cells, fibronectin-like immunoreactive fibroblasts and S-100-like immunoreactive glial cells. Neither keratin-like immunoreactive epithelial cells nor protein gene product 9.5-like immunoreactive paratracheal neurones expressed natriuretic peptide binding sites, although autoradiographically labelled glial cells were seen in close association with both neuronal cell bodies and neurites. The binding of each radiolabelled peptide was abolished by the inclusion of either excess (1 microM) unlabelled rat ANP or excess unlabelled porcine BNP, suggesting that ANP and BNP share binding sites in the trachea. Furthermore, the ring-deleted analogue, Des-[Gln18, Ser19, Gly20, Leu21, Gly22]-ANF4-23-NH2, strongly competed for specific 125I-ANP1-28 and 125I-pBNP binding sites in the tracheal culture; this suggests that virtually all binding sites were of the "clearance" (ANP-C or ANF-R2) receptor subtype.

Cytochemical and biochemical observations on the alveolar guanylate cyclase of golden hamster lung

Particulate guanylate cyclase (GTP pyrophosphate-lyase (cyclizing] has been cytochemically evidentiated in the cells which make-up the lung air-blood barrier. The cytochemical procedure utilized demonstrates the presence of membrane-bound guanylate cyclase activity through precipitation of lead pyrophosphate in tissues incubated with GTP or with guanylyl imidodiphosphate. Electron microscopic examination reveals that guanylate cyclase (GC) is localized, as micropinocytic vesicles, within endothelial components of small blood vessels, in basal lamina and in the flat alveolar cells. The secretory alveolar cells also exhibit the positive GC reactivity in their peripheric cytoplasm and in their microvilli. The observations support that GC and cGMP are involved in cellular transport phenomena. The enzyme might play a role in the secretion process of surface active material. Positive staining has been found also in other types of cells, namely alveolar macrophages and fibroblasts. A biochemical evaluation of GC activity shows that about 30-40% of this activity is associated with the particulate fraction, which justifies its abundance in the cytochemical reports shown in the paper.

[Atrial natriuretic factor in men]

The atrial natriuretic peptide (ANP) is rapidly secreted in case of acute changes in atrial volume and heart rate. Its effects are mainly natriuretic and vasodilator. This hormone is of interest to the anaesthetist because induction of anaesthesia, epidural anaesthesia and administration of morphine all result in changes in ANP plasma concentration.

Atrial natriuretic peptide in peripheral organs other than the heart

The heart atria represent the major site of synthesis of atrial natriuretic peptide (ANP) in mammals including man, and its function as a regulator of water and salt homeostasis has been repeatedly suggested. However, more recently ANP has been located in organs not intimately related to cardiovascular physiology, e.g. the adrenals, lungs, and gut, as well as tissues belonging to the lymphatic, reproductive or endocrine systems. Thus, ANP might serve many more physiological roles than originally thought, but the functional significance of ANP in these non-cardiac tissues is presently poorly understood.

Atrial natriuretic polypeptide is removed by the lungs and released into the left atrium as well as the right atrium in humans

To examine the sites of release and removal of plasma atrial natriuretic polypeptide plasma levels in the femoral vein, right atrium, pulmonary artery, pulmonary capillary bed, left atrium and aortic root were measured in 11 control subjects and 22 patients with mitral stenosis. Mean plasma natriuretic polypeptide levels in the femoral vein, right atrium, pulmonary artery, pulmonary capillary bed, left atrium and aortic root were, respectively, 64 +/- 29, 124 +/- 72, 103 +/- 44, 83 +/- 30, 106 +/- 46 and 101 +/- 35 pg/ml in the control subjects and 321 +/- 170, 500 +/- 234, 458 +/- 266, 356 +/- 209, 434 +/- 222 and 432 +/- 217 pg/ml in the patients with mitral stenosis. In both the control subjects and the patients with mitral stenosis, there was a significant increase between the femoral vein and the right atrium and between the pulmonary capillary bed and the left atrium and a significant decrease between the pulmonary artery and the pulmonary capillary bed. Blood samples were also taken simultaneously from the pulmonary vein and the pulmonary capillary bed, as well as from the pulmonary artery and the left atrium, in 25 patients (11 control subjects, 5 patients with mitral stenosis and 9 patients with atrial septal defect). There was no difference in plasma atrial natriuretic polypeptide levels between the pulmonary capillary bed and the pulmonary vein in these 25 patients. It is concluded that atrial natriuretic polypeptide 1) is released into the left as well as the right atrium, and 2) is removed by the lungs.

[Atrial natriuretic factor]

Although ANF research started 30 years ago, the atrial natriuretic factor (ANF) was only discovered recently (1981). The presence of such a factor has been suspected for many years because of histological and physiological arguments. In 1956, Kish found "dense granules" in the atrial walls of guinea pigs. Gauer and Henry could explain some of their experimental results on diuresis and natriuresis only by suggesting the presence of a third hormonal factor, but neither by the renin-angiotensin system, nor the anti-diuretic hormone. Hall et al. were the first to recognize a link between the granules and water and sodium metabolism. But it was De Bold who published the crucial experiment in 1981: injecting right atrial extracts to anaesthetized rats rapidly induced intense and transitory diuresis and natriuresis. ANF was born, and, at the same time, the concept of the heart as an endocrine gland. Indeed, ANF corresponds to the strict definition of a hormone. It has the following properties: natriuresis and diuresis via an increase in glomerular filtration fraction without any major changes in renal plasma flow; direct vasodilation of the large arteries with only few effects on small arterioles and veins. The stimuli for ANF secretion are mechanical and pharmacological, especially drugs currently used by anaesthetists. Atrial distension is the main mechanical stimulus. An increase in atrial transmural pressure is always followed by a release in ANF, but this effect is not constant for increases in intra-luminal pressure. It is the former pressure gradient alone that reflects the volume of the right atrium, the mechanical stimulus for ANF secretion. Tachycardia, or, more precisely, an increase in the atrial contraction rate, also leads to an important release of ANF. Cardiac nerves are not necessary for this, as demonstrated by studies in heart transplant patients. Only few pharmacological agents have been shown to really stimulate ANF secretion. In rats, morphine has a direct secretory effect, whereas ketamine hydrochloride, diethylether and chloral hydrate do so by increasing the release of catecholamines. The effects of alpha, beta adrenergic agonists and calcium agonists remain controversial. ANF, which has diuretic and vasodilator effects, plays a part, together with the renin-angiotensin system and the anti-diuretic hormone, in blood volume control in mammals. However, it has a special role to play, because it is a rapid release hormone: rapid vascular filling leads to an increase in ANF in less than 1 minute, with a parallel increase in diuresis.

Atrial natriuretic peptide attenuates the development of pulmonary hypertension in rats adapted to chronic hypoxia

To test the hypothesis that chronic infusion of atrial natriuretic peptide (ANP) instituted before hypoxic exposure attenuates the development of pulmonary hypertension in hypoxia adapted rats, ANP (0.2 and 1.0 microgram/h) or vehicle was administered intravenously via osmotic minipump for 4 wk beginning before exposure to 10% O2 or to room air. Low dose ANP increased plasma ANP levels by only 60% of vehicle controls after 4 wk and significantly decreased mean pulmonary arterial pressure (MPAP) (P less than 0.01), the ratio of right ventricular weight to body weight (RV/BW) (P less than 0.01), and the wall thickness of small (50-100 microns) pulmonary arteries (P = 0.01) in hypoxia-adapted rats. ANP did not alter any of these parameters in air-control rats. High dose ANP increased plasma ANP levels by 230% of control and produced greater reductions in MPAP (P less than 0.001) and RV/BW) (P less than 0.05), but not in pulmonary arterial wall thickness, than the low dose. Neither dose of ANP altered mean systemic arterial pressure in either hypoxic or normoxic rats. The data demonstrate that chronic infusion of exogenous ANP at a dose that does not affect MPAP or RV weight in air-control rats attenuates the development of pulmonary hypertension and RV enlargement in rats adapted to chronic hypoxia.

Pulmonary vasorelaxant activity of atrial peptides

Pulmonary vascular relaxant effects of the 28-amino acid atrial natriuretic peptide and atriopeptins I, II and III (21, 23 and 24 amino acid peptides, respectively) were studied in isolated blood vessels and in perfused rat lungs. In isolated tissue studies, intrapulmonary arteries were more responsive to the relaxant effects of atrial peptides than the main pulmonary artery or aorta. In perfused lung preparations, each of the four atrial peptides produced dose-dependent pulmonary vasodilation of PGF2 alpha or hypoxia-induced pulmonary vasoconstriction. Atriopeptin I was the least potent pulmonary vasodilator peptide in all studies. Pretreatment of perfused lungs with various peptidase inhibitors, including the angiotensin converting enzyme inhibitors, captopril and MK-521, the carboxypeptidase inhibitor, 1,10-phenanthroline, and the aminopeptidase inhibitor, bestatin, variably potentiated the pulmonary vasodilator activities of the atrial peptides. The results demonstrate that atrial peptides released from the right heart into the pulmonary circulation can have potent vasorelaxant effects in the pulmonary vascular bed and further suggest that upon passage through the lung atrial peptides may undergo metabolic degradation that alters their pulmonary vasodilator activities.

Atrial natriuretic peptide lowers pulmonary arterial pressure in patients with high altitude disease

The authors' previous studies have demonstrated that IV administration of atrial natriuretic peptide (ANP) produces a dose dependent decrease in pulmonary arterial pressure in rats adapted to chronic hypoxia. To examine the effects of ANP on chronic hypoxic pulmonary hypertension in man, alpha-human ANP (200 micrograms) was infused (20 micrograms/min X 10 min) into the right atrium via a Swan-Ganz catheter in four patients with pulmonary hypertension of high altitude. Following the infusion, pulmonary arterial pressure fell gradually and remained depressed for 1 hour. Peak reductions in pulmonary arterial systolic pressure (PASP) and mean pulmonary arterial pressure (MPAP) were 23% and 30%, respectively. Systemic arterial pressure, cardiac output and cardiac index also tended to decrease, but these changes did not reach statistical significance. The data suggest that ANP is useful in the treatment of chronic hypoxic pulmonary hypertension in man.

Does the olfactory system mediate water- and mineral-regulating mechanisms? Evidence of immunoreactive atrial natriuretic factor within olfactory mucosa

The immunoreactivity of atrial natriuretic factor (ANF) was studied in the rat olfactory mucosa (OM). Endogenous immunoreactive ANF (IR-ANF) was purified from OM using Vycor glass beads for extraction and reverse-phase HPLC: two of three IR-ANF peaks, identified by retention time, were identical to both the circulating form of ANF (Ser99-Tyr126) and the ANF pro-hormone (Asn1-Tyr126). A radioreceptor assay, employing rat renal glomerular membranes, revealed that endogenous IR-ANF competed with radiolabelled ANF. IR-ANF was localized by immunocytochemistry in secretory cells of Bowman's gland and in some cells of the epithelial layer. The relatively low concentration of IR-ANF in the OM (2.5 ng/mg protein) suggests a local role of ANF in this tissue. This hypothesis is supported by the presence in OM of ANF-binding sites, characterized by a KD of 95 pM and a Bmax of 130 fmol/mg protein. We propose that ANF could be released from the OM and act throughout in a paracrine (if not autocrine) manner on some yet-unidentified targets containing ANF-binding sites.

Release of atrial natriuretic factor (ANF) induced by acute airway obstruction

The aim of this study was to measure the effects of an increase in negative intrathoracic pressure on the release of ANF. With the subjects seated comfortably, 3 control blood samples were obtained over 30 minutes. Eight subjects then breathed for 30 min. through an inspiratory resistance in such a way that maximal inspiratory pleural pressures were between -30 to -40 cmH2O. Three blood samples were withdrawn after 20, 25, and 30 min., with the subject still breathing against the artificial resistance. Plasma concentrations of ANF were analysed by RIA. They measured: control value 24.6 +/- 3.7 pg ANF/mL (X +/- SE); with resistance 37.1 +/- 8.1 pg/mL (p less than or equal to .05). These results suggest that ANF could be released during an asthma attack.

Carbachol-induced cosecretion of immunoreactive atrial natriuretic peptides with catecholamines from cultured bovine adrenal medullary cells

The distribution and secretion of atrial natriuretic peptides (ANPs) were investigated in bovine adrenal medulla. (1) Cultured bovine adrenal medullary cells (2 x 10(6)/dish) contained 100.4 +/- 6.0 fmol of immunoreactive ANP (IR-ANP) and 207.3 +/- 6.6 nmol of catecholamines as epinephrine plus norepinephrine. (2) Stimulation of nicotinic but not muscarinic acetylcholine receptors caused a cosecretion of IR-ANP and catecholamines corresponding to the ratio of IR-ANP to catecholamines in cultured bovine adrenal medullary cells. (3) Carbachol-stimulated secretion of IR-ANP was dependent on the presence of extracellular Ca2+. (4) Chromaffin granules isolated from bovine adrenal medulla contained large amounts of IR-ANP and catecholamines, in the same ratio as did cultured adrenal medullary cells. (5) Reverse-phase HPLC analysis showed that both stored and secreted IR-ANP consisted of two components, which eluted at the position of ANP(99-126) or ANP(1-126). These results indicate that ANPs are stored as ANP(99-126) and ANP(1-126) in chromaffin granules, and are cosecreted in parallel with catecholamines in a Ca2+-dependent manner by the stimulation of nicotinic acetylcholine receptors.

Ovine fetal lung fluid response to intravenous saline solution infusion: fetal atrial natriuretic factor effect

The fetal lung, a significant source of in utero fluid production, has been postulated to serve a regulatory role in maintenance of fetal body fluid homeostasis. Whereas the fetus responds to intravascular saline solution infusions with increased urine output, the fetal lung fluid response to this stimulus is unclear. Tracheal fluid output was measured in four chronically catheterized ovine fetuses (mean gestation, 129 +/- 1 days) subjected to successive 40-minute intravenous 0.9% saline solution infusions at rates of 0.5 and 1 ml/min/per kilogram of body weight. Tracheal fluid output decreased significantly (1.7 +/- 0.1 to 1.1 +/- 0.1 ml/10 min, p less than 0.01) during the infusion and returned to basal levels during the recovery period. Lung fluid osmolality and electrolyte concentration did not change. Fetal plasma atrial natriuretic factor increased significantly in response to the saline solution infusion (364 +/- 90 to 790 +/- 286 pg/ml, p less than 0.05) and returned to basal levels during the recovery period. There was a significant inverse correlation between plasma atrial natriuretic factor levels and tracheal fluid output. These results suggest that increased fetal plasma atrial natriuretic factor decreases lung fluid production. Lung fluid does not appear to compensate for fetal body water excess. Rather, lung fluid production appears to promote intrauterine pulmonary growth and to facilitate the transition to the extrauterine environment.

Vasodilator responses to alpha-human-atrial natriuretic peptide in isolated omental and pulmonary arteries from rabbit and man

In isolated vessels from the pulmonary and mesenteric/omental arterial circulations of rabbit and man, the effects of synthetic alpha-human atrial natriuretic peptide (alpha-hANP) were investigated. The vessels had an outer diameter of 0.6-1.2 mm and were contracted by noradrenaline (NA) and prostaglandin (PG) F2 alpha (mesenteric/omental arteries) or by 5-hydroxytryptamine (5-HT) and PGF2 alpha (pulmonary arteries). It was found that in rabbits, mesenteric vessels contracted by NA and PGF2 alpha were not significantly relaxed by alpha-hANP. Rabbit pulmonary vessels contracted by PGF2 alpha or 5-HT were concentration-dependently relaxed by alpha-hANP (maximum 70%). Human omental vessels contracted by NA and PGF2 alpha showed a moderate (30%) relaxation after addition of the peptide. Human pulmonary arteries contracted by 5-HT were relaxed by alpha-hANP almost to baseline, while PGF2 alpha-contracted vessels showed a maximum relaxation of 65%. It is concluded that alpha-hANP has a relatively selective effect on pulmonary arterial vessels from rabbit as well as man. The results suggest that the peptide may be involved in the regulation of pulmonary vascular tone.

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)

Atrial natriuretic peptide plasma levels during cardiac surgery

In this investigation, the hypothesis was tested that patients with valvular heart disease have higher atrial natriuretic peptide (ANP) plasma levels than patients with coronary artery disease during cardiac surgery. Six patients scheduled for valve replacement (group V) and seven scheduled for coronary artery bypass grafting (CABG) (group C) were studied. ANP plasma levels and hemodynamic measurements were obtained at several times during surgery. ANP levels were elevated in both groups compared to those measured in healthy volunteers; and ANP levels in valvular patients were found to be higher than in the CABG patients. In addition, isotonic fluid loading, rewarming during cardiopulmonary bypass, and weaning from cardiopulmonary bypass increased ANP from baseline in group C. Mean arterial pressure and ANP levels correlated in group C. Ejection fraction, pulmonary artery diastolic pressure, and right atrial pressure did not correlate with ANP levels in either group. In conclusion, patients with valvular heart disease have higher ANP levels during surgery compared to patients with coronary artery disease. This difference probably relates to different pressure and volume loads on atrial tissue.

Atrial natriuretic polypeptide in bovine adrenal medulla

Two radioimmunoassays for alpha-human atrial natriuretic polypeptide (alpha-hANP) with different specificities were used to study the tissue level and the nature of alpha-hANP-like immunoreactivity in the bovine adrenal gland. A considerable amount of alpha-hANP-like immunoreactivity was detected in the adrenal medulla (90.8 +/- 21.1 and 90.0 +/- 23.1 ng/g with the two radioimmunoassays), while no detectable amount (less than 1.0 ng/g) was present in the cortex. Gel permeation chromatographic analysis showed that ANP in the medulla is composed of two components of alpha-hANP-like immunoreactivity with high and low molecular weights in the approximate ratio of 2:1, eluting at the elution positions of gamma-hANP and alpha-hANP, respectively. Reverse-phase high performance liquid chromatographic analysis revealed that alpha-hANP-like immunoreactivity with a low molecular weight in the medulla consists of two major components, which comigrate with synthetic alpha-hANP(5-28) and alpha-hANP. When cultured bovine adrenal chromaffin cells were incubated in the presence of nicotine (10(-5) M), alpha-hANP-like immunoreactivity was released into the medium concomitantly with catecholamines from chromaffin cells. These findings indicate that a discrete ANP system is present in the adrenal medulla and that ANP is cosecreted with catecholamines from chromaffin cells, suggesting the possible involvement of ANP in the adrenomedullary function.

Atrial natriuretic factor immunoreactivity in human fetal lung tissue and perfusates

Immunoreactive atrial natriuretic factor (ANF) was detected in human fetal homogenates and perfusates using a sensitive and specific radioimmunoassay for the 28 amino acid (C-terminal) fragment. Three peaks of ANF immunoreactive material were found in the lung homogenates. With high performance liquid chromatography, the elution characteristics of the first immunoreactive peak were the same as those of circulating human ANF. The other two peaks have not been characterized, although one had a position similar to the 126 amino acid rat prohormone (Asn 1-Ile 110-Tyr 126). The time course of release of immunoreactive ANF by perfused human fetal lungs was also studied. It is suggested that ANF may play a role in early pulmonary function.

Expression of the atrial natriuretic peptide gene in the cardiac muscle of rat extrapulmonary and intrapulmonary veins

Atrial natriuretic peptide is a peptide regulating salt and water balance, originally isolated from the cardiac atrium, where it is synthesised as part of a precursor molecule in specialised myocardial cells. The myocardium extends into the extrapulmonary part of the pulmonary veins in many species, including man. In some small mammals, however, such as the rat, mouse, and bat, it extends further to veins in the peripheral parts of the lung. Since this myocardial layer is continuous with that in the atrium, we have looked for the possible expression of the atrial natriuretic peptide gene in this tissue in rats. Strong immunoreactivity was seen for both the peptide and the N terminal sequence (cardiodilatin) of its precursor in extrapulmonary veins and in intrapulmonary veins extending into the lung as far as the second branching point, where it was localised in the dense cored granules by electron microscopy; in situ hybridisation showed atrial natriuretic peptide messenger RNA at identical sites. Chromatography and radioimmunoassay of extracts of extrapulmonary and intrapulmonary veins showed most of the atrial natriuretic peptide immunoreactivity to be in the uncleaved (precursor molecule) form. Thus the peptide is synthesised in veins both outside and inside the lung, and these extra-atrial sites may be an important additional source of circulating atrial natriuretic peptide.

Alpha-human atrial natriuretic peptide (alpha-hANP) prevents pulmonary edema induced by arachidonic acid treatment in isolated perfused lung from guinea pig

Protective effect of alpha-human atrial natriuretic peptide (alpha-hANP) on pulmonary edema was investigated using an isolated perfused lung model. Infusion of alpha-hANP (1.7 to 22 ng/ml or 0.56 to 7.3 nM) prevented the edema induced in isolated lung from guinea pig by repeated treatment of 50 micrograms of arachidonic acid at 30 min intervals via the pulmonary artery. The antiedematic action of alpha-hANP was considered to be receptor mediated because the effective concentration was close to the Kd value of the binding of the ANP receptors in the lung homogenate.

Atrial natriuretic factor and sodium nitroprusside increase cyclic GMP in cultured rat lung fibroblasts by activating different forms of guanylate cyclase

We used cultured rat lung fibroblasts to evaluate the role of particulate and soluble guanylate cyclase in the atrial natriuretic factor (ANF)-induced stimulation of cyclic GMP. ANF receptors were identified by binding of 125I-ANF to confluent cells at 37 degrees C. Specific ANF binding was rapid and saturable with increasing concentrations of ANF. The equilibrium dissociation constant (KD) was 0.66 +/- 0.077 nM and the Bmax. was 216 +/- 33 fmol bound/10(6) cells, which corresponds to 130,000 +/- 20,000 sites/cell. The molecular characteristics of ANF binding sites were examined by affinity cross-linking of 125I-ANF to intact cells with disuccinimidyl suberate. ANF specifically labelled two sites with molecular sizes of 66 and 130 kDa, which we have identified in other cultured cells. ANF and sodium nitroprusside produced a time- and concentration-dependent increase in intracellular cyclic GMP. An increase in cyclic GMP by ANF was detected at 1 nM, and at 100 nM an approx. 100-fold increase in cyclic GMP was observed. Nitroprusside stimulated cyclic GMP at 10 nM and at 1 mM a 500-600-fold increase in cyclic GMP occurred. The simultaneous addition of 100 nM-ANF and 10 microM-nitroprusside to cells resulted in cyclic GMP levels that were additive. ANF increased the activity of particulate guanylate cyclase by about 10-fold, but had no effect on soluble guanylate cyclase. In contrast, nitroprusside did not alter the activity of particulate guanylate cyclase, but increased the activity of soluble guanylate cyclase by 17-fold. These results demonstrate that rat lung fibroblasts contain ANF receptors and suggest that the ANF-induced stimulation of cyclic GMP is mediated entirely by particulate guanylate cyclase.

Release of immunoreactive atrial natriuretic factor from the isolated perfused rat lung

The secretion of ANF by the rat lung was demonstrated in the present study. Four forms of immunoreactive ANF were detected in rat lung homogenates, including the 126 amino acid prohormone but only a low molecular mass peptide was released during lung perfusion. The released ANF inhibited forskolin-stimulated aldosterone secretion from rat zona glomerulosa cell suspensions, and this biological effect was comparable to that of the synthetic C-terminal part of the prohormone (Arg-101-Tyr-126).

Synthesis and presence of atrial natriuretic factor in rat ventricle

Rat heart ventricles contained immunoreactive atrial natriuretic factor (irANF) and mRNA for ANF. The size of ANF mRNA in the ventricle was identical with that of the atria. High performance gel filtration chromatography showed that 84% of ventricular irANF elutes at a position corresponding to the low molecular weight form of ANF (99-126) and 16% of irANF elutes at a position corresponding to the precursor form of ANF. The irANF content of the ventricles of spontaneously hypertensive rats was 3 times as much as that of Wistar Kyoto rats. These results suggest that ventricle synthesizes ANF in response to hypertension and processes in a manner different from that in atria.

Removal of atrial natriuretic peptide by perfused rabbit lungs in situ

Removal of iodinated 28-amino acid atrial natriuretic peptide ([125I]ANP) by rabbit lungs was measured by indicator-dilution methods. After bolus injection of 6.5 pmoles of [125I]ANP, 66.9 +/- 2.9% was removed in a single pass through the lungs. Removal was unaltered by a kininase II inhibitor but was reversibly decreased by unlabelled ANP. Thus the lungs can remove ANP from the pulmonary circulation by a mechanism that does not involve hydrolysis by kininase II. Lungs therefore may be involved in regulating systemic concentrations and hence renal and other actions of ANP.

Hypoxia-induced release of atrial natriuretic factor (ANF) from the isolated rat and rabbit heart

The effect of hypoxia on the release of atrial natriuretic factor (ANF) was studied in isolated, constant-flow perfused hearts of rats and rabbits. Effluent samples were frozen pending extraction and radioimmunoassay of ANF. Hypoxia (10 min) caused a 3.9-fold (rats) and 4.6-fold (rabbits) increase of ANF release over control values. ANF release returned to control levels within 8-11 min of reoxygenation. Prolonged (20 min) hypoxia evoked further ANF release. The increase in ANF release and decrease in ventricular pressure, heart rate and coronary perfusion pressure were fully reversible, suggesting that tissues were not damaged. These results demonstrate that hypoxia induces a massive release of ANF by an as yet unexplained mechanism.