Atrial natriuretic peptide in man

Atrial Fibrillation in Chronic Kidney Disease: An Overview

Chronic kidney disease (CKD) is a condition that can be caused due to any etiology leading to structural damage to the kidney, which can be measured by a decrease in estimated glomerular filtration rate (eGFR) and the presence of damage biomarkers for more than three months. This article has discussed the causal relationship between atrial fibrillation (AF) and CKD, a few of them being inflammation, renin-angiotensin-aldosterone system (RAAS) activation, anemia, and uremia associated with CKD. This review mentioned the clinical impact of the presence of AF in CKD patients. The presence of AF in CKD patients aggravates the renal dysfunction, which in turn adds to the generation of AF. This article explores the various pharmacological and interventional treatment modalities, including antiarrhythmics, anticoagulants, and cardiac ablation, and their complications, leading to restricted usage in CKD patients.

Signal transducer and activator of transcription 3 in the heart transduces not only a hypertrophic signal but a protective signal against doxorubicin-induced cardiomyopathy

The signal transducer and activator of transcription (STAT) 3, a transcriptional factor downstream of several cytokines, is activated by Janus kinase families and plays a pivotal role in cardiac hypertrophy through gp130. To determine the physiological significance of STAT3 in vivo, transgenic mice with cardiac-specific overexpression of the Stat3 gene (STAT3-TG) were generated. STAT3-TG manifested myocardial hypertrophy at 12 wk of age with increased expression of the atrial natriuretic factor (ANF), beta-myosin heavy chain (MHC), and cardiotrophin (CT)-1 genes. The animals were injected i.p. with 15 mg/kg doxorubicin (Dox), an antineoplastic drug with restricted use because of its cardiotoxicity. The survival rates after 10 days were 25% (5/20) for control littermates (WT), but 80% (16/20) for STAT3-TG (P < 0.01). WT showed increased expression of beta-MHC and ANF mRNAs in the hearts 1 day after Dox treatment; this expression peaked at 3 days, suggesting that the WT suffered from congestive heart failure. Although the expression of these mRNAs was elevated in STAT3-TG hearts before Dox treatment, no additional increase was observed after the treatment. Dox administration significantly reduced the expression of the cardiac alpha-actin and Stat3 genes in WT hearts but not in STAT3-TG. These results provide direct evidence that STAT3 transduces not only a hypertrophic signal but also a protective signal against Dox-induced cardiomyopathy by inhibiting reduction of cardiac contractile genes and inducing cardiac protective factors.

Endotoxin-induced atrial natriuretic factor release: in vivo and in vitro studies

OBJECTIVE

We evaluated the effects of coliform endotoxin on the circulating levels of atrial natriuretic factor and renal function. To understand the direct effects of endotoxin in the release of atrial natriuretic factor by cardiac tissue, studies in isolated rat atria were performed.

STUDY DESIGN

In vivo studies were used. Anesthetized dogs were studied, with one group receiving isotonic saline solution (n = 6) and the other group receiving 50 microg/kg of coliform endotoxin (n = 7) as a continuous infusion over a 4-hour period. Cardiovascular parameters, renal function, and circulating levels of atrial natriuretic factor were measured at specified time intervals. In another set of experiments with in vitro studies left atria from Sprague-Dawley rats were isolated and perfused. In the control group (n = 9) the standard Krebs perfusate was used. In the endotoxin group (n = 9) coliform endotoxin was added at a concentration of 250 microg/mL to the standard perfusate. Atrial pressure was used as an index of stretch, and atrial natriuretic factor was measured from the perfusate.

RESULTS

Administration of endotoxin resulted in decreased blood pressure (P < .05) with a concomitant increase in heart rate. Renal artery flow, however, showed an increase (P < .05) initially followed by a return to its baseline value, with a sustained increase occurring in the saline solution control group. A significant (P < .05) and sustained increase in the circulating levels of atrial natriuretic factor after endotoxin infusion did not prevent the decrease in fractional sodium excretion (P < .05) and creatinine clearance despite an increase in the urinary output. Serum sodium, serum potassium, and osmolalities, however, remained relatively stable. The study pertaining to isolated atria showed that in the presence of low atrial pressures, addition of endotoxin had no significant effect on the release of atrial natriuretic factor. With the increase in atrial pressure atrial natriuretic factor release was significantly higher in the group directly exposed to endotoxin compared with the control group.

CONCLUSIONS

These studies demonstrate that the slow infusion of coliform endotoxin results in increased circulating levels of atrial natriuretic factor. This increase is in part due to the direct effect of endotoxin on the heart as indicated by studies in isolated atria. Our data suggest that atrial natriuretic factor in endotoxemia acts in an integrative manner with other hormones on a variety of target organs to modulate cardiovascular function and fluid balance.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Circadian blood pressure rhythm and atrial natriuretic peptide in prednisolone-induced blood pressure elevation

The effect of prednisolone, given as a 4-day oral treatment, on 24-h ambulatory blood pressure rhythm, vasoactive hormones and correlation between blood pressure and vasoactive hormones were studied in 11 healthy men. Blood pressure was monitored at intervals of 15 min during the day and of 30 min during the night. Plasma concentrations of angiotensin II, aldosterone, atrial natriuretic peptide (ANP) and arginine vasopressin and serum concentration of insulin were measured in the morning during basal conditions. The 24-h systolic, diastolic and mean blood pressures were significantly higher after prednisolone treatment. Waking blood pressure was not significantly changed, but sleeping systolic and mean blood pressures were significantly elevated after treatment. The nocturnal systolic blood pressure fall was less pronounced after treatment (before 22%, and after 16%, p<0.01), whereas the nocturnal, mean and diastolic dips were preserved. ANP was significantly increased by prednisolone treatment, from 10.1 to 14.6 pmol l-1, p<0.005. The changes in concentration of ANP were significantly correlated to the changes in 24-h diastolic blood pressure (r = -0.63, p<0.05), 24-h mean blood pressure (r = -0.68, p<0.05), waking diastolic blood pressure (r = 0.83, p<0.01) and waking mean blood pressure (r = -0.67, p<0.01). We found that short-term prednisolone treatment elevated the overall 24-h blood pressure, reduced systolic blood pressure fall during sleep, and increased plasma concentration of ANP, and that the increase in ANP was inversely correlated to the increase in blood pressure. We suggest that the increase in ANP is a secondary and compensatory phenomenon which at least to some extent counteracts the hypertensive and sodium retaining effect of prednisolone.

Functional explanation for increased atrial natriuretic peptide in systemic sclerosis

We related atrial natriuretic peptide (ANP) among 30 consecutive patients with systemic sclerosis (SScl) and 48 gender- and age-matched controls to the measurements of left ventricular (LV) function as evaluated by echocardiography and external pulse curves to determine possible causative factors for an increased level of plasma ANP. The patients had a markedly elevated plasma ANP level (239.4 +/- 59 vs. 178.2 +/- 36 pmol/l, p < 0.0005), which was not related to LV systolic function, heart rate, or blood pressure. Patients had LV hypertrophy and plasma ANP correlated directly to interventricular septal thickness (r = 0.41, p < 0.005), LV posterior wall thickness (r = 0.32, p < 0.01), and wall thickness to cavity dimension (r = 0.44, p < 0.0005), LV mass index (r = 0.40, p < 0.005). LV early filling properties were impaired, with reduction of atrial emptying index (p < 0.0005) and increased contribution of atrial contraction to LV filling. Plasma ANP correlated to atrial emptying index (r = 0.41, p < 0.0005) and to apex-cardiographic a wave (r = 0.28, p < 0.05). Plasma ANP was also related to left atrial dimension index (r = 0.27, p < 0.05), and was still related to atrial emptying index, but not to left atrial dimension, when considering the degree of LV hypertrophy in multivariate analysis. We conclude that ANP is elevated in patients with SScl. Reduced LV compliance, probably due to increased fibrosis, may cause changes in atrial pressure sufficient to stimulate ANP production without systolic dysfunction as a prerequisite.

Isatin is a potent endogenous antagonist of guanylate cyclase-coupled atrial natriuretic peptide receptors

Isatin (indole-2,3-dione) is an endogenous compound with anxiogenic properties. In the brain, highest levels (0.1 microgram/g) have been found in the rat hippocampus. In the present study, we show that isatin has little effect on a wide range of neurotransmitter and hormonal receptors but that it acts as an inhibitor of atrial natriuretic peptide (ANP) binding, with an IC50 of 4x 10(-7) M. It also inhibits ANP-activated particulate guanylate cyclase from rat kidney, heart and brain membranes in dose-dependent fashion, varying also with ANP concentration. These findings suggest that isatin is a new endogenous regulator of mammalian ANP activity, with potential implications for the control of both anxiety and natriuresis.

Effects of different types of anti-aging dietary restrictions on age-related atrial natriuretic factor changes: an immunochemical and ultrastructural study

The effects of two types of anti-aging dietary restrictions restrictions-60% diet restriction (DR) and every-other-day feeding (intermittent feeding, IF)-on age-related changes in atrial natriuretic factor (ANF) metabolism were studied in male Sprague Dawley rats by standard radioimmunological procedures and transmission electron microscopy. Both diet restrictions decreased plasma ANP (atrial natriuretic peptide) levels significantly (12-month-old rats: ad libitum fed controls 96 +/- 17.3 pg/mL, IF 63 +/- 4.8 pg/mL, DR 74 +/- 14.4 pg/mL; 24-month-old rats: AL 109 +/- 6.3 pg/mL, IF 75 +/- 8.9 pg/mL, DR 65 +/- 9.1 pg/mL). Dietary restriction prevented the age-related increase in ANP concentration in both the right atrium (12-month-old rats: AL 0.25 +/- 0.033 microgram/mg, IF 0.22 +/- 0.023 microgram/mg, DR 0.30 +/- 0.044 microgram/mg; 24-month-old rats: AL 0.39 +/- 0.037 microgram/mg, IF 0.10 +/- 0.015 microgram/mg, DR 0.07 +/- 0.011 microgram/mg) and left atrium (12-month-old rats: AL 0.23 +/- 0.033 microgram/mg, IF 0.13 +/- 0.019 microgram/mg, DR 0.17 +/- 0.035 microgram/mg; 24-month-old rats: AL 0.44 +/- 0.037 microgram/mg; IF 0.07 +/- 0.009 microgram/mg, DR 0.07 +/- 0.011 microgram/mg). Endocrine cardiocytes of diet-restricted senescent rats could be readily distinguished ultrastructurally from cells of ad libitum fed controls due to a higher number of beta-atrial specific granules of lower electrondensity. In conclusion, anti-aging diet restriction regimens fully prevented the age-related increase in the hormone store in atrial tissue, and lowered plasma ANP levels.

Atrial natriuretic peptide: relation to left ventricular filling properties in patients with systemic sclerosis

To determine the relation between left ventricular filling properties and plasma atrial natriuretic peptide in systemic sclerosis, we evaluated 30 consecutive patients and 48 age- and sex-matched controls. The venous plasma atrial natriuretic peptide was measured by radio-immunoassay. Left ventricular involvement was evaluated by echocardiography and mitral regurgitation was evaluated by Doppler. The patient group had markedly elevated plasma atrial natriuretic peptide as compared to the matched controls, (239.4 +/- 59 vs. 178.2 +/- 36 pmol/l, P < 0.0005). We found signs of impaired left ventricular filling properties among the patients with an increase of the Doppler A-wave velocity and A/E ratio. A relative reduction of early filling was found in spite of some degree of mitral regurgitation in two-thirds of the patients. The plasma atrial natriuretic peptide concentration was related to the A-wave velocity (r = 0.44, P < 0.0005), the A/E ratio (r = 0.40, P < 0.005), and also to the degree of mitral regurgitation (r = 0.43, P < 0.005). The relationship to the A-wave velocity remained when considering possible confounding factors. We conclude that the previously observed fibrotic process in systemic sclerosis does not prevent production and liberation of plasma atrial natriuretic peptide in relation to factors distending the left atrium, such as altered left ventricular filling properties and the presence of mitral regurgitation. However, the moderate relationships between atrial natriuretic peptide and haemodynamic variables indicate that the peptide might also be an independent indicator of cardiac involvement in systemic sclerosis.

Protective effect of atrial natriuretic peptide on electrical-field-stimulated rat ventricular strips during hypoxia

We have previously shown that atrial natriuretic peptide reduces lactate accumulation in non-beating rat ventricular myocardium exposed to hypoxic conditions, and that hypoxia induces release of atrial natriuretic peptide from isolated rat atrial tissue. In these studies we suggested that atrial natriuretic peptide may be physiologically important for protection of the myocardium during periods of oxygen deficit. In the present study, we used isolated strips of rat right ventricle, contracted by electrical-field-stimulation, as a model of a beating myocardium. After contraction stabilization, hypoxic conditions were introduced through aeration with 20% O2, held for 20 or 30 min., and then interrupted by reoxygenation with 95% O2. The contractile force was recorded and the percentage regain of the contractions after reoxygenation was considered as an indication of the amount of cell damage induced during the period of hypoxia. The results show that after 30 min. of hypoxia and subsequent reoxygenation, ventricular strips treated with atrial natriuretic peptide (0.1 microM) recovered 67.9 +/- 2.8% of the prehypoxic force of contraction; control strips from the same ventricle regained 44.9 +/- 4.4% (P = 0.015) of their initial contractile activity. After 20 min. of hypoxia followed by reoxygenation, a ventricular strip incubated together with an atrium regained 78.6 +/- 2.4% of the prehypoxic force of contraction as compared to a 60.2 +/- 2.7% regain (P = 0.002) for the control strip. We conclude that atrial natriuretic peptide protects the working ventricular myocardium during hypoxia, which further supports our previously reported suggestion that the effect on myocardial metabolism is physiologically relevant during situations of oxygen deficit in heart muscle.

Changes in endocrine atrial rat cardiocytes during growth and aging: an ultrastructural, morphometric and endocrinological study

The effects of age on atrial natriuretic factor (ANF) metabolism were studied in male Sprague Dawley rats by standard radioimmunological procedures, transmission electron microscopy, and ultrastructural morphometry. Plasma atrial natriuretic peptide (ANP) levels increased during growth (1-month-old rats: 64 +/- 8.7 pg/mL; 2-month-old rats: 105 +/- 8.1 pg/mL) and did not change thereafter. Immunoreactive (ir)-ANP concentration increased significantly in senescent rats, both in the right (12-month-old rats: 254 +/- 33 ng/mg; 24 month-old: 415 +/- 77 ng/mg) and left atrium (226 +/- 30 and 498 +/- 60 respectively). The ultrastructural morphological features of the endocrine cardiocytes of senescent rats were the presence of a few lysosomal structures and atrial specific granules of higher electron-density. Ultrastructural morphometry studies did not reveal any significant increase in the number or in the mean individual volume of atrial specific granules, compared with young adult rats. In conclusion, unlike younger rats, morphometric data in older and senescent rats show that atrial granularity may not necessarily change together with atrial ir-ANP contents; ir-hormone assay findings show that senescent rats have ANP plasma levels within the norm, and a much larger hormone store in atrial tissue.

Inhibition and down-regulation of protein kinase C in cultured atrial myocytes: effects on distribution of specific granules and secretion of atrial natriuretic peptide

Primary cultures of neonatal rat atrial myocytes were subjected to down-regulation of protein kinase C (PKC) and to inhibition of PKC activity. The effects on secretion of atrial natriuretic peptide (ANP), and the intracellular distribution of ANP-containing specific granules and their association to microtubules, were investigated. Treating the cultures with inhibitors of PKC, staurosporine or H7, a translocation of ANP-containing specific granules from the perinuclear sarcoplasm to the periphery of the myocytes was observed, and furthermore, secretion of ANP was significantly decreased. The microtubule network were not structurally affected by the PKC inhibitors. Down-regulation of PKC by 12-O-tetradecanoylphorbol 13-acetate (TPA) for 12 h was not followed by any alteration of localization of specific granules, and the amount of secreted ANP was still considerable. Treating the down-regulated cultures with staurosporine, secretion of ANP was still significantly reduced. The present results suggest that the decreased ANP secretion and the translocation of ANP-containing specific granules in the atrial myocytes following treatment with staurosporine or H7, is mediated through mechanisms not, or only partly, requiring PKC.

Subpressor calcium infusion increases isovolumic left ventricular relaxation time and atrial natriuretic peptide in humans

1. Subpressor calcium infusion for 1 h, which raised calcium levels to the upper limit of normal in normal subjects, increased plasma and urinary levels of atrial natriuretic peptide (ANP). 2. Heart rate fell, presumably due to carotid baroreflex stimulation (supported by the fall in noradrenaline) and the resultant fall in cardiac output prevented the expected rise in blood pressure due to the rise in total peripheral resistance (TPR). Thus the increase in ANP was not explained by an increase in blood pressure or noradrenaline. 3. There was no evidence for increased atrial stretch (no increase in atrial area or early velocity of left ventricular filling) as a mechanism for increased ANP. 4. Isovolumic left ventricular relaxation time increased, early velocity of ventricular filling decreased and TPR increased, consistent with increased tone in left ventricular and arteriolar muscle. 5. This suggests a direct effect of calcium on the atrial myocyte, stimulating ANP either through contractile or secretory mechanisms.

Atrial natriuretic factor: its (patho)physiological significance in humans

The first human studies using relatively high-doses of ANF revealed similar effects as observed in the preceding animal reports, including effects on systemic vasculature (blood pressure fall, decrease in intravascular volume), renal vasculature (rise in GFR, fall in renal blood flow), renal electrolyte excretion (rises in many electrolytes), and changes in release of a number of different hormones. Whether all these changes are the result of direct ANF effects or secondary to a (single) primary event of the hormone remains to be determined. Certainly, it has been proven that more physiological doses of ANF fail to induce short-term changes in many of these parameters leaving only a rise in hematocrit, natriuresis and an inhibition of the RAAS as important detectable ANF effects in humans. This leads us to hypothesize that ANF is a "natriuretic" hormone with physiological significance. The primary function in humans is to regulate sodium homeostasis in response to changes in intravascular volume (cardiac atrial stretch). Induction of excess renal sodium excretion and extracellular volume shift appear to be the effector mechanisms. The exact mechanism of the natriuresis in humans still needs to be resolved. It appears however, that possibly a small rise in GFR, a reduction in proximal and distal tubular sodium reabsorption, as well as an ensuing medullary washout, are of importance. The pathophysiological role of ANF in human disease is unclear. One may find elevated plasma irANF levels and/or decreased responses to exogenous ANF in some disease states. Whether these findings are secondary to the disease state rather than the cause of the disease remains to be resolved. Therapeutic applications for ANF, or drugs that intervene in its production or receptor-binding, seem to be multiple. Most important could be the antihypertensive effect, although areas such as congestive heart failure, renal failure, liver cirrhosis and the nephrotic syndrome cannot be excluded. Although the data that have been gathered to date allowed us to draw some careful conclusions as to the (patho)physiological role of ANF, the exact place of ANF in sodium homeostatic control must still be better defined. To achieve this, we will need more carefully designed low-dose ANF infusion, as well as ANF-breakdown inhibitor studies. Even more promising, however, is the potential area of studies open to us when ANF-receptor (ant)agonists become available for human use.

Effect on atrial natriuretic peptide by bracing in scoliosis. Boston brace removal studied in 10 cases

The immediate effect of Boston brace removal on plasma levels of atrial natriuretic peptide and arginine vasopressin was studied in 10 patients with idiopathic scoliosis ranging in age from 12 to 16 years. Blood samples were drawn via the antecubital vein in the supine position with the brace on and 10 min after brace removal. ANP and AVP plasma levels were measured by radioimmunoassay. Although no differences were found in the plasma concentrations of arginine vasopressin while on and after removal of the brace, atrial natriuretic peptide levels showed an approximately 80 percent increase 10 min after brace removal, presumably due to central volume redistribution. The changes of atrial natriuretic peptide plasma levels observed may be related to previously reported changes of the glomerular filtration rate and urinary sodium excretion following brace removal.

Desensitization of atriopeptin stimulated accumulation and extrusion of cyclic GMP from a kidney epithelial cell line (MDCK)

Atriopeptin caused dose- (EC50 ca. 2 x 10(-8) M) and time-dependent increases in the intracellular concentration of cyclic GMP in the MDCK kidney epithelial cell line; an effect potentiated by the phosphodiesterase inhibitor, IBMX. The atriopeptin-catalysed increase in cyclic GMP was transient and reached a maximum some 10-20 min after challenge of cells with atriopeptin. The basis for the transience of this increase was shown to be due to the desensitization of guanylate cyclase coupled with extrusion of cyclic GMP from the cells and the degradation of cyclic GMP by phosphodiesterase activity. Atriopeptin-catalysed extrusion of cyclic GMP was time- and dose-(EC50 ca. 1.5 x 10(-8) M) dependent and was inhibited by probenecid but not by high external cyclic GMP concentrations. The extrusion process underwent apparent desensitization as did guanylate cyclase with similar half lives (T1/2 of ca. 20 min). Desensitization was dose-dependent upon atriopeptin and did not appear to be mediated by elevated cyclic GMP concentrations as pre-incubation with 8-bromo cyclic GMP did not cause desensitization and the half-times for desensitization were similar whether or not IBMX was present. The majority of the cyclic nucleotide phosphodiesterase activity was found in the cytosol fraction of the cells and could be separated into two cyclic AMP specific forms and two cyclic GMP preferring forms.

Endogenous atrial natriuretic factor after endopeptidase 24.11 inhibition by Thiorphan

The neutral endopeptidase 24.11 (NEP) was shown to degrade atrial natriuretic factor (ANF) in kidney membranes. An infusion of Thiorphan (25 micrograms/min/kg x 90 min), a specific NEP inhibitor, induced an increase in plasma ANF (65 +/- 26 to 163 +/- 52 pg/ml), plasma renin activity and in norepinephrine concentrations at 50 minutes of infusion in conscious rabbits. The increase in plasma ANF was accompanied by a gradual decrease in renal blood flow, despite maintenance of a stable mean arterial pressure. In conclusion, Thiorphan infusion produced an increase in endogenous plasma ANF. However, it may also have affected other hormonal systems which may have contributed to the overall dynamic and hormonal profile documented.