Deficiency of Cardiac Natriuretic Peptide Signaling Promotes Peripartum Cardiomyopathy-Like Remodeling in the Mouse Heart.

BACKGROUND: The maternal circulatory system and hormone balance both change dynamically during pregnancy, delivery, and the postpartum period. Although atrial natriuretic peptides and brain natriuretic peptides produced in the heart control circulatory homeostasis through their common receptor, NPR1, the physiologic and pathophysiologic roles of endogenous atrial natriuretic peptide/brain natriuretic peptide in the perinatal period are not fully understood. METHODS: To clarify the physiologic and pathophysiologic roles of the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system during the perinatal period, the phenotype of female wild-type and conventional or tissue-specific Npr1-knockout mice during the perinatal period was examined, especially focusing on maternal heart weight, blood pressure, and cardiac function. RESULTS: In wild-type mice, lactation but not pregnancy induced reversible cardiac hypertrophy accompanied by increases in fetal cardiac gene mRNAs and ERK1/2 (extracellular signaling-regulated kinase) phosphorylation. Npr1-knockout mice exhibited significantly higher plasma aldosterone level than did wild-type mice, severe cardiac hypertrophy accompanied by fibrosis, and left ventricular dysfunction in the lactation period. Npr1-knockout mice showed a high mortality rate over consecutive pregnancy-lactation cycles. In the hearts of Npr1-knockout mice during or after the lactation period, an increase in interleukin-6 mRNA expression, phosphorylation of signal transducer and activator of transcription 3, and activation of the calcineurin-nuclear factor of the activated T cells pathway were observed. Pharmacologic inhibition of the mineralocorticoid receptor or neuron-specific deletion of the mineralocorticoid receptor gene significantly ameliorated cardiac hypertrophy in lactating Npr1-knockout mice. Anti-interleukin-6 receptor antibody administration tended to reduce cardiac hypertrophy in lactating Npr1-knockout mice. CONCLUSIONS: These results suggest that the characteristics of lactation-induced cardiac hypertrophy in wild-type mice are different from exercise-induced cardiac hypertrophy, and that the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system plays an important role in protecting the maternal heart from interleukin-6-induced inflammation and remodeling in the lactation period, a condition mimicking peripartum cardiomyopathy.

Differential Regulation of ANP and BNP in Acute Decompensated Heart Failure: Deficiency of ANP.

OBJECTIVES: This study investigated the differential regulation of circulating atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in patients with acute decompensated heart failure (ADHF) and tested the hypothesis that a relative deficiency of ANP exists in a subgroup of patients with ADHF. BACKGROUND: The endocrine heart releases the cardiac hormones ANP and BNP, which play a key role in cardiovascular (CV), renal, and metabolic homeostasis. In heart failure (HF), both plasma ANP and BNP are increased as a compensatory homeostatic response to myocardial overload. METHODS: ANP and BNP concentrations were measured in a small group of patients with ADHF (n = 112). To support this study's goal, a total of 129 healthy subjects were prospectively recruited to establish contemporary normal values for ANP and BNP. Plasma 3',5'cyclic guanosine monophosphate (cGMP), ejection fraction (EF), and body mass index (BMI) were measured in these subjects. RESULTS: In cases of ADHF, 74% of patients showed elevated ANP and BNP. Importantly, 26% of patients were characterized as having normal ANP (21% of this subgroup had normal ANP and elevated BNP). Cyclic GMP was lowest in the ADHF group with normal levels of ANP (p < 0.001), whereas BMI and EF were inversely related to ANP levels (p = 0.003). CONCLUSIONS: Among a subgroup of patients hospitalized with ADHF, the presence of an ANP deficiency is consistent with a differential regulation of ANP and BNP and suggests the existence of a potentially compromised compensatory cardiac endocrine response. These findings have implications for the pathophysiology, diagnostics, and therapeutics of human HF.

Developmental origins of pregnancy-induced cardiac changes: establishment of a novel model using the atrial natriuretic peptide gene-disrupted mice.

Pregnancy evokes many challenges on the maternal cardiovascular system that may unmask predispositions for future disease. This is particularly evident for women who develop pregnancy-related disorders, for example, pre-eclampsia and gestational diabetes or hypertension. Such pregnancy-related syndromes increase the risk for cardiovascular disease (CVD) postpartum. As a result, pregnancy has been termed as a cardiovascular stress test and an indicator or marker to predict the development of CVD later in life. In addition, pregnancy-related disorders impact the development of offspring also placing them at a higher risk for disease. Utilizing pregnancy as a physiological stressor, the current investigation sought to determine whether the cardiovascular system of offspring exposed to gestational hypertension in utero would respond adversely to the stress of pregnancy. Heterozygous atrial natriuretic peptide gene-disrupted (ANP+/-) offspring were generated by either crossing male wildtype ANP+/+ with female knockout ANP-/- to produce ANP+/-KO mice or crossing female wildtype ANP+/+ with male knockout ANP-/- to produce ANP+/-WT mice. To study the cardiovascular stress induced by pregnancy, female ANP+/-WT and ANP+/-KO mice were mated with male wildtype ANP+/+ mice to initiate pregnancy. Cardiac size and molecular expression of the renin-angiotensin (RAS) and natriuretic peptide systems (NPS) were compared between offspring groups. Our data demonstrate that gestational hypertension and lack of maternal ANP did not significantly impact the progression and regression of pregnancy-induced cardiac hypertrophy over gestation and postpartum in ANP+/- offspring. Additionally, the molecular cardiac expression of the RAS and NPS did not differ between offspring groups. Future investigation should assess potential differences in cardiac function and the impact of fetal-programming on offspring cardiovascular adaptations during pregnancy in more severe models of pregnancy-related hypertensive syndrome such as angiotensin II or isoproterenol infusion.

Targeting cardiac natriuretic peptides in the therapy of diabetes and obesity.

INTRODUCTION: Atrial and B-type Natriuretic Peptides (NP) are cardiac hormones with potent cardiovascular and metabolic effects. They signal through the NPRA/cGMP system and are inactivated by a clearance receptor NPRC and neutral endopeptidases (NEP). Recombinant ANP and BNP are currently used as drug treatment for acute decompensated congestive heart failure. Recent literature indicate that a defective NP system is linked to obesity and predict the risk of type 2 diabetes (T2D). Areas covered: This article reviews recent epidemiological, clinical and preclinical evidences that NP system deficiency may be causal of obesity and T2D. The molecular mechanisms of the NP pathway in several metabolic target tissues are presented. The therapeutic potential of NP in obesity and T2D is discussed. Expert opinion: Targeting the NP pathway may offer a novel therapeutic avenue for the management of obesity and T2D. The benefit/risk of drugs increasing circulating NP levels by blocking NPRC and NEP, and/or enhancing NPRA signaling should be assessed in obese and type 2 diabetic individuals.

Natriuretic peptides buffer renin-dependent hypertension.

The renin-angiotensin-aldosterone system and cardiac natriuretic peptides [atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP)] are opposing control mechanisms for arterial blood pressure. Accordingly, an inverse relationship between plasma renin concentration (PRC) and ANP exists in most circumstances. However, PRC and ANP levels are both elevated in renovascular hypertension. Because ANP can directly suppress renin release, we used ANP knockout (ANP(-/-)) mice to investigate whether high ANP levels attenuate the increase in PRC in response to renal hypoperfusion, thus buffering renovascular hypertension. ANP(-/-) mice were hypertensive and had reduced PRC compared with that in wild-type ANP(+/+) mice under control conditions. Unilateral renal artery stenosis (2-kidney, 1-clip) for 1 wk induced similar increases in blood pressure and PRC in both genotypes. Unexpectedly, plasma BNP concentrations in ANP(-/-) mice significantly increased in response to two-kidney, one-clip treatment, potentially compensating for the lack of ANP. In fact, in mice lacking guanylyl cyclase A (GC-A(-/-) mice), which is the common receptor for both ANP and BNP, renovascular hypertension was markedly augmented compared with that in wild-type GC-A(+/+) mice. However, the higher blood pressure in GC-A(-/-) mice was not caused by disinhibition of the renin system because PRC and renal renin synthesis were significantly lower in GC-A(-/-) mice than in GC-A(+/+) mice. Thus, natriuretic peptides buffer renal vascular hypertension via renin-independent effects, such as vasorelaxation. The latter possibility is supported by experiments in isolated perfused mouse kidneys, in which physiological concentrations of ANP and BNP elicited renal vasodilatation and attenuated renal vasoconstriction in response to angiotensin II.

Gestational hypertension in atrial natriuretic peptide knockout mice and the developmental origins of salt-sensitivity and cardiac hypertrophy.

OBJECTIVE: To determine the effect of gestational hypertension on the developmental origins of blood pressure (BP), altered kidney gene expression, salt-sensitivity and cardiac hypertrophy (CH) in adult offspring. METHODS: Female mice lacking atrial natriuretic peptide (ANP-/-) were used as a model of gestational hypertension. Heterozygous ANP+/- offspring was bred from crossing either ANP+/+ females with ANP-/- males yielding ANP+/-(WT) offspring, or from ANP-/- females with ANP+/+ males yielding ANP+/-(KO) offspring. Maternal BP during pregnancy was measured using radiotelemetry. At 14weeks of age, offspring BP, gene and protein expression were measured in the kidney with real-time quantitative PCR, receptor binding assay and ELISA. RESULTS: ANP+/-(KO) offspring exhibited normal BP at 14weeks of age, but displayed significant CH (P<0.001) as compared to ANP+/-(WT) offspring. ANP+/-(KO) offspring exhibited significantly increased gene expression of natriuretic peptide receptor A (NPR-A) (P<0.001) and radioligand binding studies demonstrated significantly reduced NPR-C binding (P=0.01) in the kidney. Treatment with high salt diet increased BP (P<0.01) and caused LV hypertrophy (P<0.001) and interstitial myocardial fibrosis only in ANP+/-(WT) and not ANP+/-(KO) offspring, suggesting gestational hypertension programs the offspring to show resistance to salt-induced hypertension and LV remodeling. Our data demonstrate that altered maternal environments can determine the salt-sensitive phenotype of offspring.

Relative atrial natriuretic peptide deficiency and inadequate renin and angiotensin II suppression in obese hypertensive men.

Obesity is a strong risk factor for hypertension, but the mechanisms by which obesity leads to hypertension are incompletely understood. On this background, we assessed dietary sodium intake, serum levels of natriuretic peptides (NPs), and the activity of the renin-angiotensin system in 63 obese hypertensive men (obeseHT: body mass index, ≥30.0 kg/m(2); 24-hour ambulatory blood pressure, ≥130/80 mm Hg), in 40 obese normotensive men (obeseNT: body mass index, ≥30.0 kg/m(2); 24-hour ambulatory blood pressure, <130/80 mm Hg), and in 27 lean normotensive men (leanNT: body mass index, 20.0-24.9 kg/m(2); 24-hour ambulatory blood pressure, <130/80 mm Hg). All study subjects were medication free. As a surrogate estimate for dietary sodium intake, we measured sodium excretion in a 24-hour urine collection and we measured serum levels of midregional proatrial NP and plasma levels of renin and angiotensin II. The obese men had higher mean (±SD) urinary sodium excretion (obeseHT, 213.6±85.2 mmol; obeseNT, 233.0±70.0 mmol) than the lean normotensive men (leanNT, 155.5±51.7 mmol; P=0.003). ObeseHT had lower (median [interquartile range]) serum midregional proatrial NP levels (49.2 [37.3-64.7] pmol/L) than leanNT (69.3 [54.3-82.9] pmol/L; P=0.003), whereas obeseNT had midregional proatrial NP levels in between (54.1 [43.2-64.7] pmol/L); obeseNT had lower (median [interquartile range]) plasma levels of renin (5.0 [3.0-8.0] mIU/L versus 9.0 [4.0-18.0]) and angiotensin II (2.4 [1.5-3.5] pmol/L versus 4.2 [2.2-7.9]) than obeseHT (P≤0.049), whereas obeseHT had similar plasma levels of renin and angiotensin II as leanNT (P≥0.19). Thus, despite a high sodium intake and a high blood pressure, obese hypertensive men have a relative NP deficiency and an inadequate renin-angiotensin system suppression.

Role of corin and atrial natriuretic peptide in preeclampsia.

In pregnancy, uterine spiral artery remodeling is an adaptive morphological change at the maternal and fetal interface, which is critical for dilating the artery and promoting blood flow to the fetus. Incompletely remodeled spiral arteries have been recognized as a common pathological feature in preeclamptic patients. To date, the molecular mechanism that controls spiral artery remodeling is not well defined. Corin is a transmembrane serine protease discovered in the heart, where it converts pro-atrial natriuretic peptide (pro-ANP) to active ANP, a cardiac hormone that regulates salt-water balance and blood pressure. Recent studies show that corin is up-regulated in the decidua of the pregnant uterus, suggesting a potential role of corin in pregnancy. In mice lacking corin or ANP, high blood pressure and proteinuria were found at late gestational stages. Histological analysis indicated delayed trophoblast invasion and impaired spiral artery remodeling in the uterus. In humans, CORIN gene mutations were identified in patients with preeclampsia. In this review, we discuss the function of corin and ANP in regulating blood pressure and their potential role in preeclampsia.

Role of corin in trophoblast invasion and uterine spiral artery remodelling in pregnancy.

In pregnancy, trophoblast invasion and uterine spiral artery remodelling are important for lowering maternal vascular resistance and increasing uteroplacental blood flow. Impaired spiral artery remodelling has been implicated in pre-eclampsia, a major complication of pregnancy, for a long time but the underlying mechanisms remain unclear. Corin (also known as atrial natriuretic peptide-converting enzyme) is a cardiac protease that activates atrial natriuretic peptide (ANP), a cardiac hormone that is important in regulating blood pressure. Unexpectedly, corin expression was detected in the pregnant uterus. Here we identify a new function of corin and ANP in promoting trophoblast invasion and spiral artery remodelling. We show that pregnant corin- or ANP-deficient mice developed high blood pressure and proteinuria, characteristics of pre-eclampsia. In these mice, trophoblast invasion and uterine spiral artery remodelling were markedly impaired. Consistent with this, the ANP potently stimulated human trophoblasts in invading Matrigels. In patients with pre-eclampsia, uterine Corin messenger RNA and protein levels were significantly lower than that in normal pregnancies. Moreover, we have identified Corin gene mutations in pre-eclamptic patients, which decreased corin activity in processing pro-ANP. These results indicate that corin and ANP are essential for physiological changes at the maternal-fetal interface, suggesting that defects in corin and ANP function may contribute to pre-eclampsia.

Atrial natriuretic peptide increases inflammation, infarct size, and mortality after experimental coronary occlusion.

Acute coronary artery occlusion triggers the release of atrial natriuretic peptide (ANP) from the heart. ANP affects vasodilation, natriuresis, and inflammation, but the integrated biological effects of ANP on myocardial infarction are unknown. To elucidate these effects, the left anterior coronary artery was ligated in anesthetized, ANP-deficient (ANP(-/-)) and congenic wild-type (ANP(+/+)) mice. The survival of ANP(-/-) mice was markedly better (56%) at 30 days postinfarction than the survival of ANP(+/+) mice (20%, P < 0.01). Surviving mice were comparable initially, but ANP(-/-) mice developed more cardiac hypertrophy (P < 0.001) and had lower contractility indexes 30 days after infarction (P < 0.05). An analysis 24 h after coronary occlusion showed that ANP(-/-) mice had smaller infarcts than ANP(+/+) mice (62.6 +/- 12.1 vs. 100.8 +/- 3.8%, P < 0.001) adjusted for comparable areas at risk for ischemia. The administration of ANP to ANP(-/-) mice via osmotic minipumps significantly enlarged infarct size to levels comparable with those observed in ANP(+/+) mice (P < 0.05). There was no difference in neutrophil migration into the noninfarcted myocardium of ANP(-/-) mice undergoing actual versus sham-operated coronary occlusion. By comparison, after coronary occlusion, the neutrophil infiltration into the myocardium was enhanced in ANP(+/+) (P < 0.0005) and ANP(-/-) mice administered ANP (P < 0.0005). The expression of P-selectin, a molecule that mediates neutrophil adhesion, was significantly greater after coronary occlusion in the vasculature of ANP(+/+) or ANP(-/-) mice treated with ANP than in ANP(-/-) mice (P < 0.002). Taken together, these results indicate that ANP increases P-selectin, neutrophil infiltration, infarct size, and mortality following experimental coronary occlusion.

Assessment of embryonic myocardial cell differentiation using a dual fluorescent reporter system.

Recent studies have identified the existence of undifferentiated myocardial cells during early embryonic as well as post-natal stages of heart development. While primitive cells present in the precardiac mesoderm can differentiate into multiple cell types of the cardiovascular system, the developmental potential of undifferentiated cells identified in the ventricular myocardium after chamber formation is not well characterized. A deeper understanding of mechanisms regulating myocardial cell differentiation will provide further insights into the normal and pathological aspects of heart development. Here, we showed that Nkx2.5 positive and sarcomeric myosin negative cells were predominantly localized in the right ventricular myocardium of CD1 mice at E11.5 stage. We confirmed that myocardial regions negative for saromeric myosin were also devoid of atrial natriuretic factor (ANF). These observations are consistent with our previous study, which showed that ANF expression is restricted to moderately differentiated and mature myocardial cells in E11.5 myocardium of C3H/FeJ mice. Further, we found that the receptor c-Kit, a marker for early embryonic myocardial progenitor cells, is not expressed in the undifferentiated cells of the E11.5 myocardium. To monitor the differentiation potential of Nkx2.5(+)/ANF(-) cells in vitro, we developed a novel double fluorescent reporter system. Subsequently, we confirmed that the majority of Nkx2.5(+)/ANF(-) cells expressed mature myocyte markers such as sarcomeric myosin, MLC2V and alpha-cardiac actin after 48 hrs in culture, albeit at lower levels compared to Nkx2.5(+)/ANF(+) or Nkx2.5(-)/ANF(+) cell populations. Our results suggest that fluorescent reporters under the control of lineage-specific promoters can be used to study myocardial cell differentiation in response to various exogenous or pharmacological agents.

Atrial natriuretic peptide inhibits transforming growth factor beta-induced Smad signaling and myofibroblast transformation in mouse cardiac fibroblasts.

This study tested the hypothesis that activation of atrial natriuretic peptide (ANP)/cGMP/protein kinase G signaling inhibits transforming growth factor (TGF)-beta1-induced extracellular matrix expression in cardiac fibroblasts and defined the specific site(s) at which this molecular merging of signaling pathways occurs. Left ventricular hypertrophy and fibrosis, collagen deposition, and myofibroblast transformation of cardiac fibroblasts in response to pressure overload by transverse aortic constriction were exaggerated in ANP-null mice compared with wild-type controls. ANP and cGMP inhibited TGF-beta1-induced myofibroblast transformation, proliferation, collagen synthesis, and plasminogen activator inhibitor-1 expression in cardiac fibroblasts isolated from wild-type mice. Following pretreatment with cGMP, TGF-beta1 induced phosphorylation of Smad3, but the resultant pSmad3 could not be translocated to the nucleus. pSmad3 that had been phosphorylated with recombinant protein kinase G-1alpha was analyzed by use of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and ion trap tandem mass spectrometry. The analysis revealed phosphorylation of Ser309 and Thr388 residues, sites distinct from the C-terminal Ser423/425 residues that are phosphorylated by TGF-beta receptor kinase and are critical for the nuclear translocation and down-stream signaling of pSmad3. These results suggest that phosphorylation of Smad3 by protein kinase G is a potential molecular mechanism by which activation of ANP/cGMP/protein kinase G signaling disrupts TGF-beta1-induced nuclear translocation of pSmad3 and downstream events, including myofibroblast transformation, proliferation, and expression of extracellular matrix molecules in cardiac fibroblasts. We postulate that this process contributes to the antifibrogenic effects of the natriuretic peptide in heart.

Pathophysiology of water and sodium retention: edematous states with normal kidney function.

Body fluid volume regulation by the kidney relies upon the complex interaction of numerous factors. However, in edematous disorders, extrarenal factors can override the 'innate wisdom' of the kidney. For example, in patients with cardiac failure or liver disease and in pregnant women, the normal kidney continues to retain sodium and water despite expanded blood, plasma and extracellular fluid volumes. Such fluid retention can ultimately lead to pulmonary congestion, ascites or peripheral edema. Understanding the kidney's modulation of total body sodium and water in these patients has been perplexing. Cardiac output cannot provide the sole afferent signal for the kidney to regulate sodium and water balance, as the normal kidney can retain excessive amounts of sodium and water when cardiac output is low (e.g. in low output cardiac failure) or high (e.g. cirrhosis or pregnancy). Therefore the integrity of the arterial circulation, which can be impaired either by a low cardiac output or arterial vasodilation, is an important factor in body fluid composition and volume regulation in health and disease.

Interactions between atrial natriuretic peptide and the renin-angiotensin system during salt-sensitivity exhibited by the proANP gene-disrupted mouse.

To understand the involvement of the systemic and cardiac components of the renin-angiotensin system (RAS) in the development of cardiac hypertrophy induced by salt intake, the present study analyzed the effect of high dietary salt (8.0% NaCl) in mice possessing a full complement (+/+) or ablation (-/-) of atrial natriuretic peptide (ANP). A 3 week treatment of 8.0% NaCl was able to induce cardiac hypertrophy in both genotypes, though exaggerated hypertrophy was noted in the ANP -/- mouse. Although a marked decrease in angiotensin II (Ang II) plasma levels in both genotypes fed a high salt diet was observed, systemic RAS mRNA components were altered only in the ANP-/- animals and remained unchanged in ANP+/+ mice. Decreased Ang II plasma levels were better correlated with decreases in angiotensinogen protein expression observed in both genotypes. High salt had no effect on cardiac RAS mRNA components in the ANP-/- animals, but did cause a significant decrease in some cardiac RAS mRNA components in ANP+/+ mice. As expected, high salt was able to increase plasma ANP levels and ventricular mRNA expression of ANP (ANP+/+ mice only) and B-type NP in both genotypes. The latter peptides are key cardiac markers of hypertrophy whose increased expression correlate well with the physical salt-induced cardiac alterations observed in this study. These findings suggest that although the RAS does not play a key role in salt-induced cardiac hypertrophy, ANP is an important determinant of the degree of salt-sensitivity observed in the proANP gene-disrupted animal.

Left atrial diameter is a simple indicator of a deficiency in atrial natriuretic peptide secretion in patients with mitral stenosis: efficacy of postoperative supplementation with synthetic human alpha-atrial natriuretic peptide.

OBJECTIVE: With regard to a deficiency in atrial natriuretic peptide (ANP) secretion, the relationship between plasma ANP and left atrial diameter measured by echocardiography was examined and the efficacy of postoperative supplementation was evaluated. METHODS: (1) Ninety-six patients with mitral valve disease from 1997 to 2002 (M:F = 65:31, mean-age 65.3 +/- 8.9 years) were studied for relationship analyses. (2) Twenty-six patients with mitral stenosis and left atrial diameter > or = 60 mm undergoing mitral valve replacement (M:F = 17:9, mean-age 67.4 +/- 7.5 years) were randomly allocated to one of two groups; ANP-treated group (n = 13, 0.05 microg/kg/min of synthetic human alpha-ANP was postoperatively administered) and Control group (n = 13). RESULTS: (1) There were significant positive correlations between left atrial diameter and plasma renin-activity (r = 0.690, P < 0.01) and between left atrial diameter and plasma aldosterone (r = 0.757, P < 0.01). The maximum value of plasma ANP was 249.5 pg/mL accompanied with 56.2 mm of left atrial diameter in 29 patients suffering from mitral stenosis. There was a significant negative correlation between left atrial diameter and ANP in patients with left atrial diameter > 56.2 mm (r = - 0.725, P < 0.0001), whereas there was a significant positive correlation in patients with left atrial diameter < or = 56.2 mm (r = 0.529, P = 0.0066). (2) At 24 hours after operation, the ANP-treated group showed significantly lower plasma renin-activity (9.2 +/- 3.3 versus 36.2 +/- 7.4 ng/mL/h) and aldosterone (113.6 +/- 36.9 versus 473.8 +/- 95.8 pg/mL) than the Control group. CONCLUSIONS: Left atrial diameter can be a simple and useful indicator of a deficiency in endogenous ANP secretion in patients with mitral stenosis, and postoperative ANP supplementation contributes to suppressing further activation of renin-angiotensin system during the immediate postoperative period.

Pressure-independent enhancement of cardiac hypertrophy in atrial natriuretic peptide-deficient mice.

1. Homozygous deletion of the pro-atrial natriuretic peptide (Nppa) gene (ANP-/-) has been associated with both cardiac hypertrophy and salt-sensitive hypertension in mice, suggesting that cardiac hypertrophy in ANP-/- mice may be related, at least in part, to increased afterload. 2. To test the hypothesis that cardiac hypertrophy in ANP-/- mice is independent of blood pressure, male ANP-/- and wild-type ANP+/+ mice were fed a low (0.05%) or basal (0.55%) NaCl diet. Five weeks later, mean arterial pressure (MAP) was measured in conscious mice; the whole heart, atria, left and right ventricles (LV and RV, respectively), brain, lung, kidney, liver and spleen were weighed and fixed for histological analysis. Separate groups of mice were subjected to echocardiographic examination under tribromoethanol anaesthesia. 3. Mean arterial pressure and atrial, LV and RV mass were greater in ANP-/- mice than in ANP+/+ mice fed the basal salt diet. Salt depletion equalized MAP in the two genotypes, but did not alter the relative cardiac hypertrophy in ANP-/- mice. The ANP-/- mice had significant LV cardiomyocyte hypertrophy when fed either basal or low-salt diets. 4. Left ventricle chamber dimensions did not differ between genotypes, but were significantly reduced in mice fed the low-salt diet; LV posterior wall and septal thickness were greater in ANP-/- than ANP+/+ mice and were not altered by diet, indicating a concentric pattern of LV hypertrophy in ANP-/- mice. Left ventricle function (cardiac output, stroke volume, ejection fraction, circumferential wall stress and velocity of circumferential wall shortening) did not differ between strains on either diet; circumferential wall stress was reduced in the low-salt groups; other functional parameters were not altered by diet. 5. These findings indicate that ANP deletion results in cardiomyocyte hypertrophy and biventricular hypertrophy independent of blood pressure, supporting the concept that ANP has direct antihypertrophic effects in the heart.

Hypoxia reduces atrial natriuretic peptide clearance receptor gene expression in ANP knockout mice.

We tested the hypotheses that hypoxic exposure is associated with exacerbated pulmonary hypertension and right ventricular (RV) enlargement, reduced atrial natriuretic peptide (ANP) clearance receptor (NPR-C) expression, and enhanced B-type natriuretic peptide (BNP) expression in the absence of ANP. Male wild-type [ANP(+/+)], heterozygous [ANP(+/-)], and homozygous [ANP(-/-)] mice were studied after a 5-wk hypoxic exposure (10% O(2)). Hypoxia increased RV ANP mRNA and plasma ANP levels only in ANP(+/+) and ANP(+/-) mice. Hypoxia-induced increases in RV pressure were significantly greater in ANP(-/-) than in ANP(+/+) or ANP(+/-) mice (104 +/- 17 vs. 45 +/- 10 and 63 +/- 7%, respectively) as were increases in RV mass (38 +/- 4 vs. 26 +/- 5 and 29 +/- 4%, respectively). NPR-C mRNA levels were greatly reduced in the kidney, lung, and brain by hypoxia in all three genotypes. RV BNP mRNA and lung and kidney cGMP levels were increased in hypoxic mice. These findings indicate that disrupted ANP expression worsens hypoxic pulmonary hypertension and RV enlargement but does not alter hypoxia-induced decreases in NPR-C and suggest that compensatory increases in BNP expression occur in the absence of ANP.

[Inadequate secretion of atrial natriuretic peptide in children with acute brain injury]. / Secreción inadecuada de péptido natriurético auricular en niños con daño cerebral agudo.

OBJECTIVE: Fluid and electrolyte disturbances are frequent after acute brain damage. Atrial natriuretic peptide (ANP), which can also be found in brain tissue, could be a hormone implicated in such disorders (cerebral salt wasting syndrome). PATIENTS AND METHODS: Plasma ANP levels were analyzed in 50 children with acute neurological deterioration (secondary to traumatic, infectious, convulsive tumor or vascular disorders) evaluated according to the modified Glasgow Coma Scale (GCS). Hemodynamic stability was determined by standard monitoring. ANP, renin and aldosterone levels were determined by RIA and the results compared with a control group of healthy children. RESULTS: There was an increase in ANP levels in children with brain injury in comparison to the control group (p < 0.001), but not in children under one year of age. Renin and aldosterone were also significantly increased in this group of patients, with no difference in ANP, renin or aldosterone level found in function of their GCS score. All patients were hemodynamically stable and no correlation between hemodynamic and hormone variables was seen. Mechanical ventilation did not influence the hormone levels. CONCLUSIONS: There is an important increase in ANP levels in patients with acute neurological pathologies, but it was not related to the hemodynamic condition and its importance has yet to be established. One of its possible consequences is a secondary hypotonic/hypovolemic condition, a potentially dangerous event for the patient with intracranial hypertension that needs immediate treatment. Differentiation of this syndrome from inappropriate vasopressin secretion could be very important in children with acute brain injury.