ANP in regulation of arterial pressure and fluid-electrolyte balance: lessons from genetic mouse models

Downregulation of the kidney glucagon receptor, essential for renal function and systemic homeostasis, contributes to chronic kidney disease

The glucagon receptor (GCGR) in the kidney is expressed in nephron tubules. In humans and animal models with chronic kidney disease, renal GCGR expression is reduced. However, the role of kidney GCGR in normal renal function and in disease development has not been addressed. Here, we examined its role by analyzing mice with constitutive or conditional kidney-specific loss of the Gcgr. Adult renal Gcgr knockout mice exhibit metabolic dysregulation and a functional impairment of the kidneys. These mice exhibit hyperaminoacidemia associated with reduced kidney glucose output, oxidative stress, enhanced inflammasome activity, and excess lipid accumulation in the kidney. Upon a lipid challenge, they display maladaptive responses with acute hypertriglyceridemia and chronic proinflammatory and profibrotic activation. In aged mice, kidney Gcgr ablation elicits widespread renal deposition of collagen and fibronectin, indicative of fibrosis. Taken together, our findings demonstrate an essential role of the renal GCGR in normal kidney metabolic and homeostatic functions. Importantly, mice deficient for kidney Gcgr recapitulate some of the key pathophysiological features of chronic kidney disease.

Atrial natriuretic peptide T2238C gene polymorphism and the risk of cardiovascular diseases: A meta‑analysis

The present study aimed to investigate the association between atrial natriuretic peptide (ANP) T2238C (rs5065) gene polymorphism and the risk of cardiovascular disease. Relevant literature was obtained by searching databases. The odds ratios (ORs) of the ANP T2238C locus genotype distribution in the case group of cardiovascular diseases and the control group of a non-cardiovascular population were pooled using R software. Sensitivity analysis was used to verify the stability of the results. Egger's linear regression test was used to assess the publication bias of the included literature. Studies were classified according to quality assessment score of the Newcastle-Ottawa scale, year, region, sample size and underlying disease for subgroup analysis, and meta-regression analysis was performed. A total of 12 studies comprising 45,619 patients were included. ANP rs5065 mutant gene C allele was a significant risk factor for myocardial infarction relative to T allele (OR=2.55, 95% CI=1.47-4.43, P=0.0008), CC+CT genotype was a significant risk factor for cerebrovascular events relative to TT (OR=1.14, 95% CI=1.04-1.26, P=0.0048) and the mutant CC genotype was a potential risk factor for the composite cardio-cerebral vascular events (CVE) relative to CT+TT (OR=1.40, 95% CI=0.96-2.04, P=0.081). In studies fulfilling the Hardy-Weinberg equilibrium, the CC genotype was a significant risk factor for the composite CVE relative to TT (OR=2.39, 95% CI=1.40-4.10, P=0.0018) and the CC genotype was a significant risk factor for composite CVE relative to CT+TT (OR=2.41, 95% CI=1.41-4.13, P=0.0015). The P-value of the Egger's test for publication bias was 0.436, which was not statistically significant. The results of the sensitivity analysis were relatively stable. Subgroup analysis indicated that the publication year was a potential source of heterogeneity. Regression analysis was performed for the recessive model in the composite CVE and the results showed that the study region (Europe) was one of the sources of heterogeneity (P=0.016). In conclusion, ANP 2238T/C mutation may increase the risk of myocardial infarction, cerebrovascular events and composite CVE.

Cardiac Localized Polycystin-2 plays a Functional Role in Natriuretic Peptide Production and its Absence Contributes to Hypertension

Cardiovascular complications are the most common cause of mortality in patients with autosomal dominant polycystic kidney disease (ADPKD). Hypertension is seen in 70% of patients by the age of 30 prior to decline in kidney function. The natriuretic peptides (NPs), atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), are released by cardiomyocytes in response to membrane stretch, increasing urinary excretion of sodium and water. Mice heterozygous for Pkd2 have attenuated NP responses and we hypothesized that cardiomyocyte-localized polycystin proteins contribute to production of NPs. Cardiomyocyte-specific knock-out models of polycystin-2 (PC2), one of the causative genes of ADPKD, demonstrate diurnal hypertension. These mice have decreased ANP and BNP expression in the left ventricle. Analysis of the pathways involved in production, maturation, and activity of NPs identified decreased transcription of CgB, PCSK6, and NFAT genes in cPC2-KOs. Engineered heart tissue with human iPSCs driven into cardiomyocytes with CRISPR/Cas9 KO of PKD2 failed to produce ANP. These results suggest that PC2 in cardiomyocytes are involved in NP production and lack of cardiac PC2 predisposes to a hypertensive volume expanded phenotype, which may contribute to the development of hypertension in ADPKD.

Molecular Signaling Mechanisms and Function of Natriuretic Peptide Receptor-A in the Pathophysiology of Cardiovascular Homeostasis

The discovery of atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP) and their cognate receptors has greatly increased our knowledge of the control of hypertension and cardiovascular homeostasis. ANP and BNP are potent endogenous hypotensive hormones that elicit natriuretic, diuretic, vasorelaxant, antihypertrophic, antiproliferative, and antiinflammatory effects, largely directed toward the reduction of blood pressure (BP) and cardiovascular diseases (CVDs). The principal receptor involved in the regulatory actions of ANP and BNP is guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which produces the intracellular second messenger cGMP. Cellular, biochemical, molecular, genetic, and clinical studies have facilitated understanding of the functional roles of natriuretic peptides (NPs), as well as the functions of their receptors, and signaling mechanisms in CVDs. Transgenic and gene-targeting (gene-knockout and gene-duplication) strategies have produced genetically altered novel mouse models and have advanced our knowledge of the importance of NPs and their receptors at physiological and pathophysiological levels in both normal and disease states. The current review describes the past and recent research on the cellular, molecular, genetic mechanisms and functional roles of the ANP-BNP/NPRA system in the physiology and pathophysiology of cardiovascular homeostasis as well as clinical and diagnostic markers of cardiac disorders and heart failure. However, the therapeutic potentials of NPs and their receptors for the diagnosis and treatment of cardiovascular diseases, including hypertension, heart failure, and stroke have just begun to be expanded. More in-depth investigations are needed in this field to extend the therapeutic use of NPs and their receptors to treat and prevent CVDs.

Chronobiology of Natriuretic Peptides and Blood Pressure in Lean and Obese Individuals

BACKGROUND

Diurnal variation of natriuretic peptide (NP) levels and its relationship with 24-h blood pressure (BP) rhythm has not been established. Obese individuals have a relative NP deficiency and disturbed BP rhythmicity.

OBJECTIVES

This clinical trial evaluated the diurnal rhythmicity of NPs (B-type natriuretic peptide [BNP], mid-regional pro-atrial natriuretic peptide [MR-proANP], N-terminal pro-B-type natriuretic peptide [NT-proBNP]) and the relationship of NP rhythm with 24-h BP rhythm in healthy lean and obese individuals.

METHODS

On the background of a standardized diet, healthy, normotensive, lean (body mass index 18.5 to 25 kg/m²) and obese (body mass index 30 to 45 kg/m²) individuals, age 18 to 40 years, underwent 24-h inpatient protocol involving ambulatory BP monitoring starting 24 h prior to the visit, controlled light intensity, and repeated blood draws for assessment of analytes. Cosinor analysis of normalized NP levels (normalized to 24-h mean value) was conducted to assess the diurnal NP rhythm and its relationship with systolic BP.

RESULTS

Among 52 participants screened, 40 participants (18 lean, 22 obese; 50% women; 65% Black) completed the study. The median range spread (percentage difference between the minimum and maximum values) over 24 h for MR-proANP, BNP, and NT-proBNP levels was 72.0% (interquartile range [IQR]: 50.9% to 119.6%), 75.5% (IQR: 50.7% to 106.8%), and 135.0% (IQR: 66.3% to 270.4%), respectively. A cosine wave-shaped 24-h oscillation of normalized NP levels (BNP, MR-proANP, and NT-proBNP) was noted both in lean and obese individuals (p_rhythmicity <0.05 for all). A larger phase difference between MR-proANP BP rhythm (-4.9 h vs. -0.7 h) and BNP BP rhythm (-3.3 h vs. -0.9 h) was seen in obese compared with lean individuals.

CONCLUSIONS

This human physiological trial elucidates evidence of diurnal NP rhythmicity and the presence of an NP-BP rhythm axis. There exists a misalignment of the NP-BP diurnal rhythm in the obese, which may contribute to the disturbed diurnal BP pattern observed among obese individuals. (The Diurnal Rhythm in Natriuretic Peptide Levels; NCT03834168).

Obesity and Serial NT-proBNP Levels in Guided Medical Therapy for Heart Failure With Reduced Ejection Fraction: Insights From the GUIDE-IT Trial

Background

Obese patients have lower NT‐proBNP (N‐terminal pro‐B‐type natriuretic peptide) levels. The prognostic implications of achieving NT‐proBNP levels ≤1000 pg/mL in obese patients with heart failure (HF) receiving biomarker‐guided therapy are not completely known. We evaluated the prognostic implications of obesity and having NT‐proBNP levels (≤1000 pg/mL) in the GUIDE‐IT (Guiding Evidence‐Based Therapy Using Biomarker‐Intensified Treatment in HF) trial participants.

Methods and Results

The risk of adverse cardiovascular events (HF hospitalization or cardiovascular mortality) was assessed using multivariable‐adjusted Cox proportional hazard models based on having NT‐proBNP ≤1000 pg/mL (taken as a time‐varying covariate), stratified by obesity status. The study outcome was also assessed on the basis of the body mass index at baseline. The predictive ability of NT‐proBNP for adverse cardiovascular events was assessed using the likelihood ratio test. Compared with nonobese patients, obese patients were mostly younger, Black race, and more likely to be women. NT‐proBNP levels were 59.0% (95% CI, 39.5%–83.5%) lower among obese individuals. The risk of adverse cardiovascular events was lower in obese (hazard ratio [HR], 0.48; 95% CI, 0.29–0.59) and nonobese (HR, 0.32; 95% CI, 0.19–0.57) patients with HF who had NT‐proBNP levels ≤1000 pg/mL, compared with those who did not. There was no interaction between obesity and having NT‐proBNP ≤1000 pg/mL on the study outcome (P>0.10). Obese patients had a greater risk of developing adverse cardiovascular events (HR, 1.39; 95% CI, 1.01–1.90) compared with nonobese patients. NT‐proBNP was the strongest predictor of adverse cardiovascular event risk in both obese and nonobese patients.

Conclusions

On‐treatment NT‐proBNP level ≤1000 pg/mL has favorable prognostic implications, irrespective of obesity status. NT‐proBNP levels were the strongest predictor of cardiovascular events in both obese and nonobese individuals in this trial.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT01685840.

Identifying roles for peptidergic signaling in mice

Despite accumulating evidence demonstrating the essential roles played by neuropeptides, it has proven challenging to use this information to develop therapeutic strategies. Peptidergic signaling can involve juxtacrine, paracrine, endocrine, and neuronal signaling, making it difficult to define physiologically important pathways. One of the final steps in the biosynthesis of many neuropeptides requires a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), and lack of amidation renders most of these peptides biologically inert. PAM, an ancient integral membrane enzyme that traverses the biosynthetic and endocytic pathways, also affects cytoskeletal organization and gene expression. While mice, zebrafish, and flies lacking Pam (Pam^KO/KO ) are not viable, we reasoned that cell type-specific elimination of Pam expression would generate mice that could be screened for physiologically important and tissue-specific deficits. Conditional Pam^cKO/cKO mice, with loxP sites flanking the 2 exons deleted in the global Pam^KO/KO mouse, were indistinguishable from wild-type mice. Eliminating Pam expression in excitatory forebrain neurons reduced anxiety-like behavior, increased locomotor responsiveness to cocaine, and improved thermoregulation in the cold. A number of amidated peptides play essential roles in each of these behaviors. Although atrial natriuretic peptide (ANP) is not amidated, Pam expression in the atrium exceeds levels in any other tissue. Eliminating Pam expression in cardiomyocytes increased anxiety-like behavior and improved thermoregulation. Atrial and serum levels of ANP fell sharply in PAM myosin heavy chain 6 conditional knockout mice, and RNA sequencing analysis identified changes in gene expression in pathways related to cardiac function. Use of this screening platform should facilitate the development of therapeutic approaches targeted to peptidergic pathways.

Emerging pathways of communication between the heart and non-cardiac organs

The breakthrough discovery of cardiac natriuretic peptides provided the first direct demonstration of the connection between the heart and the kidneys for the maintenance of sodium and volume homeostasis in health and disease. Yet, little is still known about how the heart and other organs cross-talk. Here, we review three physiological mechanisms of communication linking the heart to other organs through: i) cardiac natriuretic peptides, ii) the microRNA-208a/mediator complex subunit-13 axis and iii) the matrix metalloproteinase-2 (MMP-2)/C-C motif chemokine ligand-7/cardiac secreted phospholipase A2 (sPLA2) axis – a pathway which likely applies to the many cytokines, which are cleaved and regulated by MMP-2. We also suggest experimental strategies to answer still open questions on the latter pathway. In short, we review evidence showing how the cardiac secretome influences the metabolic and inflammatory status of non-cardiac organs as well as the heart.

ARNi: A Novel Approach to Counteract Cardiovascular Diseases

Cardiovascular diseases (CVDs) still represent the greatest burden on healthcare systems worldwide. Despite the enormous efforts over the last twenty years to limit the spread of cardiovascular risk factors, their prevalence is growing and control is still suboptimal. Therefore, the availability of new therapeutic tools that may interfere with different pathophysiological pathways to slow the establishment of clinical CVDs is important. Previously, the inhibition of neurohormonal systems, namely the renin–angiotensin–aldosterone system (RAAS) and the sympathetic nervous system, has proven to be useful in the treatment of many CVDs. Attempts have recently been made to target an additional hormonal system, that of the natriuretic peptides (NPs), which, when dysregulated, can also play a role in the development CVDs. Indeed, a new class of drug, the angiotensin receptor–neprilysin inhibitors (ARNi), has the ability to counteract the effects of angiotensin II as well as to increase the activity of NPs. ARNi have already been proven to be effective in the treatment of heart failure with reduced ejection fraction. New evidence has suggested that, in the next years, the field of ARNi application will widen to include other CVDs, such as heart failure, with preserved ejection fraction and hypertension.

Natriuretic peptides in heart failure: Current achievements and future perspectives

The last two centuries have witnessed countless discoveries in the field of medicine that found their roots in the up growing development of technology as well as in the visionary ideas of brilliant scientists and research groups. One of the most important discoveries in the field of cardiovascular medicine allowed to break the paradigm identifying the heart with mere mechanical pump and to characterize its intriguing endocrine properties. Indeed, the discovery of hormones produced by the cardiac chambers, the natriuretic peptides, represents one of the milestones of the current conception of complexity of integrated human physiology. In the last four decades, the role of these hormones in the regulation of the cardiovascular system, in physiology and diseases, has been defined piece after piece. From diagnostic and prognostic markers, natriuretic peptides have become one of the most relevant clinical biomarker and a reliable target for establishing the efficacy of therapies. Recently and successfully, natriuretic peptide-based strategies are proposed as therapeutic weapons to improve outcome in heart failure. The future will witness potential further therapeutic application of natriuretic peptides that are currently being actively investigated.

Molecular and genetic aspects of guanylyl cyclase natriuretic peptide receptor-A in regulation of blood pressure and renal function

Natriuretic peptides (NPs) exert diverse effects on several biological and physiological systems, such as kidney function, neural and endocrine signaling, energy metabolism, and cardiovascular function, playing pivotal roles in the regulation of blood pressure (BP) and cardiac and vascular homeostasis. NPs are collectively known as anti-hypertensive hormones and their main functions are directed toward eliciting natriuretic/diuretic, vasorelaxant, anti-proliferative, anti-inflammatory, and anti-hypertrophic effects, thereby, regulating the fluid volume, BP, and renal and cardiovascular conditions. Interactions of NPs with their cognate receptors display a central role in all aspects of cellular, biochemical, and molecular mechanisms that govern physiology and pathophysiology of BP and cardiovascular events. Among the NPs atrial and brain natriuretic peptides (ANP and BNP) activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and initiate intracellular signaling. The genetic disruption of Npr1 (encoding GC-A/NPRA) in mice exhibits high BP and hypertensive heart disease that is seen in untreated hypertensive subjects, including high BP and heart failure. There has been a surge of interest in the NPs and their receptors and a wealth of information have emerged in the last four decades, including molecular structure, signaling mechanisms, altered phenotypic characterization of transgenic and gene-targeted animal models, and genetic analyses in humans. The major goal of the present review is to emphasize and summarize the critical findings and recent discoveries regarding the molecular and genetic regulation of NPs, physiological metabolic functions, and the signaling of receptor GC-A/NPRA with emphasis on the BP regulation and renal and cardiovascular disorders.

The heart as an endocrine organ

The concept of the heart as an endocrine organ arises from the observation that the atrial cardiomyocytes in the mammalian heart display a phenotype that is partly that of endocrine cells. Investigations carried out between 1971 and 1983 characterised, by virtue of its natriuretic properties, a polypeptide referred to atrial natriuretic factor (ANF). Another polypeptide isolated from brain in 1988, brain natriuretic peptide (BNP), was subsequently characterised as a second hormone produced by the mammalian heart atria. These peptides were associated with the maintenance of extracellular fluid volume and blood pressure. Later work demonstrated a plethora of other properties for ANF and BNP, now designated cardiac natriuretic peptides (cNPs). In addition to the cNPs, other polypeptide hormones are expressed in the heart that likely act upon the myocardium in a paracrine or autocrine fashion. These include the C-type natriuretic peptide, adrenomedullin, proadrenomedullin N-terminal peptide and endothelin-1. Expression and secretion of ANF and BNP are increased in various cardiovascular pathologies and their levels in blood are used in the diagnosis and prognosis of cardiovascular disease. In addition, therapeutic uses for these peptides or related substances have been found. In all, the discovery of the endocrine heart provided a shift from the classical functional paradigm of the heart that regarded this organ solely as a blood pump to one that regards this organ as self-regulating its workload humorally and that also influences the function of several other organs that control cardiovascular function.

Hypertension: physiology and pathophysiology

Despite major advances in understanding the pathophysiology of hypertension and availability of effective and safe antihypertensive drugs, suboptimal blood pressure (BP) control is still the most important risk factor for cardiovascular mortality and is globally responsible for more than 7 million deaths annually. Short-term and long-term BP regulation involve the integrated actions of multiple cardiovascular, renal, neural, endocrine, and local tissue control systems. Clinical and experimental observations strongly support a central role for the kidneys in the long-term regulation of BP, and abnormal renal-pressure natriuresis is present in all forms of chronic hypertension. Impaired renal-pressure natriuresis and chronic hypertension can be caused by intrarenal or extrarenal factors that reduce glomerular filtration rate or increase renal tubular reabsorption of salt and water; these factors include excessive activation of the renin-angiotensin-aldosterone and sympathetic nervous systems, increased formation of reactive oxygen species, endothelin, and inflammatory cytokines, or decreased synthesis of nitric oxide and various natriuretic factors. In human primary (essential) hypertension, the precise causes of impaired renal function are not completely understood, although excessive weight gain and dietary factors appear to play a major role since hypertension is rare in nonobese hunter-gathers living in nonindustrialized societies. Recent advances in genetics offer opportunities to discover gene-environment interactions that may also contribute to hypertension, although success thus far has been limited mainly to identification of rare monogenic forms of hypertension.

Interactive roles of NPR1 gene-dosage and salt diets on cardiac angiotensin II, aldosterone and pro-inflammatory cytokines levels in mutant mice

OBJECTIVE

The objective of the present study was to elucidate the interactive roles of guanylyl cyclase/natriuretic peptide receptor-A (NPRA) gene (Npr1) and salt diets on cardiac angiotensin II (ANG II), aldosterone and pro-inflammatory cytokines levels in Npr1 gene-targeted (1-copy, 2-copy, 3-copy, 4-copy) mice.

METHODS

Npr1 genotypes included 1-copy gene-disrupted heterozygous (+/-), 2-copy wild-type (+/+), 3-copy gene-duplicated heterozygous (++/+) and 4-copy gene-duplicated homozygous (++/++) mice. Animals were fed low, normal and high-salt diets. Plasma and cardiac levels of ANG II, aldosterone and pro-inflammatory cytokines were determined.

RESULTS

With a high-salt diet, cardiac ANG II levels were increased (+) in 1-copy mice (13.7 ± 2.8 fmol/mg protein, 111%) compared with 2-copy mice (6.5 ± 0.6), but decreased (-) in 4-copy (4.0 ± 0.5, 38%) mice. Cardiac aldosterone levels were increased (+) in 1-copy mice (80 ± 4 fmol/mg protein, 79%) compared with 2-copy mice (38 ± 3). Plasma tumour necrosis factor alpha was increased (+) in 1-copy mice (30.27 ± 2.32 pg/ml, 38%), compared with 2-copy mice (19.36 ± 2.49, 24%), but decreased (-) in 3-copy (11.59 ± 1.51, 12%) and 4-copy (7.13 ± 0.52, 22%) mice. Plasma interleukin (IL)-6 and IL-1α levels were also significantly increased (+) in 1-copy compared with 2-copy mice but decreased (-) in 3-copy and 4-copy mice.

CONCLUSION

These results demonstrate that a high-salt diet aggravates cardiac ANG II, aldosterone and pro-inflammatory cytokine levels in Npr1 gene-disrupted 1-copy mice, whereas, in Npr1 gene-duplicated (3-copy and 4-copy) mice, high salt did not render such elevation, suggesting the potential roles of Npr1 against salt loading.

A genetic variant of the atrial natriuretic peptide gene is associated with left ventricular hypertrophy in a non-diabetic population--the Malmö preventive project study

Background

Epidemiological studies have shown considerable heritability of blood pressure, thus suggesting a role for genetic factors. Previous studies have shown an association of a single nucleotide polymorphism rs5068 in the NPPA locus gene with higher levels of circulating atrial natriuretic peptide as well as with lower intra individual blood pressure, but up to date, no association between rs5068 and cardiac organ damage, i.e. left ventricular hypertrophy, has been accounted for in humans. We sought to explore if rs5068 is associated with left ventricular hypertrophy as measured by echocardiographic examination in a non-diabetic population.

Methods

968 non-diabetic individuals from the Malmö Preventive Project (mean age 67 years; 31% women) were genotyped and examined with echocardiography. Logistic regression was used to adjust for covariates.

Results

The minor allele of rs5068 was associated with decreased prevalence of left ventricular hypertrophy (p = 0.021) after adjustment for sex and age. In the multivariate logistic analysis including; age, sex, systolic blood pressure, antihypertensive and/or cardioprotective treatment, body mass index and fasting plasma glucose, the association of rs5068 with left ventricular hypertrophy was, as expected, attenuated (p = 0.061).

Conclusion

In a non-diabetic population, the minor allele of rs5068 was associated with lower left ventricular mass. These findings suggest that rs5068, or genetic variants in linkage disequilibrium, might affect susceptibility to left ventricular hypertrophy and support the possible protective role of natriuretic peptides.

Genetic dissection of sodium and potassium transport along the aldosterone-sensitive distal nephron: importance in the control of blood pressure and hypertension

In this review, we discuss genetic evidence supporting Guyton's hypothesis stating that blood pressure control is critically depending on fluid handling by the kidney. The review is focused on the genetic dissection of sodium and potassium transport in the distal nephron and the collecting duct that are the most important sites for the control of sodium and potassium balance by aldosterone and angiotensin II. Thanks to the study of Mendelian forms of hypertension and their corresponding transgenic mouse models, three main classes of diuretic receptors (furosemide, thiazide, amiloride) and the main components of the aldosterone- and angiotensin-dependent signaling pathways were molecularly identified over the past 20 years. This will allow to design rational strategies for the treatment of hypertension and for the development of the next generation of diuretics.

Emerging Roles of Natriuretic Peptides and their Receptors in Pathophysiology of Hypertension and Cardiovascular Regulation

Thus far, three related natriuretic peptides (NPs) and three distinct receptors have been identified, which have advanced our knowledge towards understanding the control of high blood pressure, hypertension, and cardiovascular disorders to a great extent. Biochemical and molecular studies have been advanced to examine receptor function and signaling mechanisms and the role of second messenger cGMP in pathophysiology of hypertension, renal hemodynamics, and cardiovascular functions. The development of gene-knockout and gene-duplication mouse models along with transgenic mice have provided a framework for understanding the importance of the antagonistic actions of natriuretic peptides receptor in cardiovascular events at the molecular level. Now, NPs are considered as circulating markers of congestive heart failure, however, their therapeutic potential for the treatment of cardiovascular diseases such as hypertension, renal insufficiency, cardiac hypertrophy, congestive heart failure, and stroke has just begun to unfold. Indeed, the alternative avenues of investigations in this important are need to be undertaken, as we are at the initial stage of the molecular therapeutic and pharmacogenomic implications.

Renal actions of atrial natriuretic peptide in spontaneously hypertensive rats: the role of nitric oxide as a key mediator

Atrial natriuretic peptide (ANP) is an important regulator of blood pressure (BP). One of the mechanisms whereby ANP impacts BP is by stimulation of nitric oxide (NO) production in different tissues involved in BP control. We hypothesized that ANP-stimulated NO is impaired in the kidneys of spontaneously hypertensive rats (SHR) and this contributes to the development and/or maintenance of high levels of BP. We investigated the effects of ANP on the NO system in SHR, studying the changes in renal nitric oxide synthase (NOS) activity and expression in response to peptide infusion, the signaling pathways implicated in the signaling cascade that activates NOS, and identifying the natriuretic peptide receptors (NPR), guanylyl cyclase receptors (NPR-A and NPR-B) and/or NPR-C, and NOS isoforms involved. In vivo, SHR and Wistar-Kyoto rats (WKY) were infused with saline (0.05 ml/min) or ANP (0.2 μg·kg−1·min−1). NOS activity and endothelial (eNOS), neuronal (nNOS), and inducible (iNOS) NOS expression were measured in the renal cortex and medulla. In vitro, ANP-induced renal NOS activity was determined in the presence of iNOS and nNOS inhibitors, NPR-A/B blockers, guanine nucleotide-regulatory (Gi) protein, and calmodulin inhibitors. Renal NOS activity was higher in SHR than in WKY. ANP increased NOS activity, but activation was lower in SHR than in WKY. ANP had no effect on expression of NOS isoforms. ANP-induced NOS activity was not modified by iNOS and nNOS inhibitors. NPR-A/B blockade blunted NOS stimulation via ANP in kidney. The renal NOS response to ANP was reduced by Gi protein and calmodulin inhibitors. We conclude that ANP interacts with NPR-C, activating Ca-calmodulin eNOS through Gi protein. NOS activation also involves NPR-A/B. The NOS response to ANP was diminished in kidneys of SHR. The impaired NO system response to ANP in SHR participates in the maintenance of high blood pressure.

Expression of the vasoactive proteins AT1, AT2, and ANP by pregnancy-induced mouse uterine natural killer cells

Angiotensin II receptor type 1 (AT1) activation leads to vasoconstriction and type 2 receptor (AT2) leads to vasodilation. Atrial natriuretic peptide (ANP) antagonizes the effects of AT1. In human and murine pregnancies, uterine natural killer (uNK) cells closely associate with decidual blood vessels. Protein localization of AT1, AT2, and ANP to mouse uNK cells was examined between gestation days (gds) 6 and 12, the interval of uNK cell expansion. Percentages of uNK cells expressing AT1 or AT2 changed between gd6 and gd10. Atrial natriuretic peptide did not localize to uNK cells at gd6 or 8, but did colocalize to uNK cells at gd10 and 12, times immediately after spiral arterial modification. This is the first report of AT1, AT2, and ANP expression in uterine immune cells. Expression of these molecules suggests that uNK cells have the potential to contribute to the changes in blood pressure that occur between days 5 and 12 of pregnancy in mice.

Excess dietary salt intake alters the excitability of central sympathetic networks

The ingestion of excess dietary salt (defined as NaCl) is strongly correlated with cardiovascular disease, morbidity, mortality, and is regarded as a major contributing factor to the pathogenesis of hypertension. Although several mechanisms contribute to the adverse consequences of dietary salt intake, accumulating evidence suggests that dietary salt loading produces neurogenically-mediated increases in total peripheral resistance to raise arterial blood pressure (ABP). Evidence from clinical studies and experimental models clearly establishes a hypertensive effect of dietary salt loading in a subset of individuals who are deemed "salt-sensitive". However, we will discuss and present evidence to develop a novel hypothesis to suggest that while chronic increases in dietary salt intake do not elevate mean ABP in "non-salt-sensitive" animals, dietary salt intake does enhance several sympathetic reflexes thereby predisposing these animals and/or individuals to the development of salt-sensitive hypertension. Additional evidence raises an intriguing hypothesis that these enhanced sympathetic reflexes are largely attributed to the ability of excess dietary salt intake to selectively enhance the excitability of sympathetic-regulatory neurons in the rostral ventrolateral medulla. Insight into the cellular mechanisms by which dietary salt intake alters the responsiveness of RVLM circuits will likely provide a foundation for developing new therapeutic approaches to treat salt-sensitive hypertension. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

Natriuretic peptides and the genomics of left-ventricular hypertrophy

Left-ventricular hypertrophy (LVH) is one of the strongest independent predictors of cardiovascular morbidity and mortality in the general population. Although hypertension and obesity are well-established, independent risk factors for the development of LVH, they explain less than 25% to 50% of the variance of left ventricular mass (LVM) in humans. A substantial body of evidence suggests that there is a genetic basis to the observed inter-individual variability in the susceptibility to the development of LVH. Given the continuous relationship between LVM and cardiovascular morbidity and mortality, elucidating the genetic determinants of inter-individual differences in the susceptibility to LVH is of considerable public health importance. It promises the opportunity to identify high-risk individuals for targeted intervention and may identify novel therapeutic targets for improved prevention and treatment strategies.

Role of nitric oxide as a key mediator on cardiovascular actions of atrial natriuretic peptide in spontaneously hypertensive rats

The objective was to study atrial natriuretic peptide (ANP) effects on mean arterial pressure (MAP) and cardiovascular nitric oxide (NO) system in spontaneously hypertensive rats (SHRs), investigating the receptors and signaling pathways involved. In vivo, SHRs and Wistar-Kyoto (WKY) rats were infused with saline (0.05 ml/min) or ANP (0.2 μg·kg−1·min−1) for 1 h. MAP and nitrites and nitrates excretion (NOx) were determined. NO synthase (NOS) activity and endothelial (eNOS), neuronal (nNOS) and inducible (iNOS) NOS expression were measured in the heart and aorta. In vitro, heart and aortic NOS activity induced by ANP was determined in the presence of iNOS and nNOS inhibitors, natriuretic peptide receptor (NPR)-A/B blocker, Gi protein, and calmodulin inhibitors. As a result, ANP diminished MAP and increased NOx in both groups. Cardiovascular NOS activity was higher in SHRs than in WKY rats. ANP increased NOS activity, but the activation was lower in SHRs than in WKY rats. ANP had no effect on NOS isoform expression. NOS activity induced by ANP was not modified by iNOS and nNOS inhibitors. NPR-A/B blockade blunted NOS stimulation via ANP in ventricle and aorta but not in atria. Cardiovascular NOS response to ANP was reduced by Gi protein and calmodulin inhibitors in both groups. In conclusion, in atria, ventricle, and aorta, ANP interacts with NPR-C receptors, activating Ca2+-calmodulin eNOS through Gi protein. In ventricle and aorta, NOS activation also involves NPR-A/B. The NOS response to ANP was impaired in heart and aorta of SHRs. The impaired NO-system response to ANP in hypertensive animals, involving alterations in the signaling pathway, could participate in the maintenance of high blood pressure in this model of hypertension.

Measurement of N-terminal proatrial natriuretic peptide in plasma of cats with and without cardiomyopathy

OBJECTIVE

To determine whether plasma N-terminal proatrial natriuretic peptide (Nt-proANP) concentrations in cats with cardiomyopathy (CM) differ from values in healthy cats and evaluate whether plasma Nt-proANP concentrations can be used to discriminate cats with CM and congestive heart failure (CHF) from CM-affected cats without CHF.

ANIMALS

16 cats that had CM without CHF, 16 cats that had CM with CHF, and 11 healthy control cats.

PROCEDURES

All cats underwent a physical examination, assessment of clinicopathologic variables (including plasma thyroxine concentration), thoracic radiography, and echocardiography. On the basis of findings, cats were assigned to 1 of 3 groups (control cats, cats with CM and CHF, and cats with CM without CHF). Venous blood samples were obtained from all 43 cats, and plasma Nt-proANP concentrations were measured by use of a human proANP(1-98) ELISA.

RESULTS

Plasma Nt-proANP concentrations differed significantly among the 3 groups. Median Nt-proANP concentration was 381 fmol/mL (range, 52 to 450 fmol/mL), 763 fmol/mL (range, 167 to 2,386 fmol/mL), and 2,443 fmol/mL (range, 1,189 to 15,462 fmol/mL) in the control group, in cats with CM without CHF, and in cats with CM and CHF, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Measurement of plasma Nt-proANP concentration could be of benefit in the assessment of cats with naturally occurring CM and might have potential as a screening marker for the disease. Furthermore, measurement of plasma NtproANP concentration may be useful for distinguishing cats with CM and CHF from those with CM and no CHF.

Local modulation of the natriuretic peptide system in the rat remnant kidney

BACKGROUND

The natriuretic peptide (NP) system plays a central role in the renal adaptations to acute volume expansion. However, the modulation of the NP system in chronic renal insufficiency (CRI) remains to be elucidated. In the present study, we evaluated cardiac haemodynamics, plasma type-B natriuretic peptide (BNP) levels and the expression of natriuretic peptide receptor A (NPR-A) and NPR-C in the renal cortex (RC) and medulla (RM) of Sham and (3/4) nephrectomized ((3/4)nx) rats, up to 26 weeks after surgery.

METHODS

Male Wistar-Han rats (190-220 g; n = 49) were randomly assigned to (3/4)nx or Sham surgery. Two, 10 and 26 weeks after surgery, non-invasive blood pressure (BP) and left ventricular (LV) haemodynamics were performed, and urine and blood were collected for metabolic studies and plasma BNP determination. In addition, tissue samples from RC and RM were obtained for NPR-A and NPR-C quantification (RT-PCR and western blotting) as well as NPR-A immunodetection.

RESULTS

In (3/4)nx rats, the progressive interstitial fibrosis and tubular atrophy were accompanied by a time-dependent increase of BP and impaired natriuretic response to volume expansion (VE). This was accompanied in (3/4)nx rats by an early and time-dependent elevation of BNP circulating levels that was not associated with cardiac dysfunction or increased myocardial BNP gene expression. In (3/4)nx rats, NPR-A expression in the remnant RM was consistently reduced at 2, 10 and 26 weeks, and this was accompanied by an increase in NPR-C expression in the remnant RC from (3/4)nx rats.

CONCLUSIONS

BP elevation and compromised natriuretic response to VE in (3/4)nx rats is associated with increased circulating BNP levels in the absence of cardiac dysfunction. This is accompanied in (3/4)nx rats by both impaired NPR-A expression in the RM and upregulation of NPR-C in the RC suggesting a novel mechanism for NP resistance in CRI.

Regulation of renin release by local and systemic factors

The renin-angiotensin system (RAS) is critically involved in the regulation of the salt and volume status of the body and blood pressure. The activity of the RAS is controlled by the protease renin, which is released from the renal juxtaglomerular epithelioid cells into the circulation. Renin release is regulated in negative feedback-loops by blood pressure, salt intake, and angiotensin II. Moreover, sympathetic nerves and renal autacoids such as prostaglandins and nitric oxide stimulate renin secretion. Despite numerous studies there remained substantial gaps in the understanding of the control of renin release at the organ or cellular level. Some of these gaps have been closed in the last years by means of gene-targeted mice and advanced imaging and electrophysiological methods. In our review, we discuss these recent advances together with the relevant previous literature on the regulation of renin release.

Natriuretic peptide precursor a gene polymorphisms and risk of blood pressure progression and incident hypertension

We tested the hypothesis that natriuretic peptide precursor A gene polymorphisms are significantly associated with blood pressure progression and incident hypertension among healthy, middle-aged women. We performed a prospective cohort study among 18 437 white women participating in the Women's Health Study who were free of hypertension at baseline. Two previously characterized single nucleotide polymorphisms within the natriuretic peptide precursor A gene (rs5063 G>A and rs5065 T>C) were genotyped. Blood pressure progression at 48 months and incident hypertension during the entire follow-up according to the different genotypes and inferred haplotypes were assessed by logistic regression and Cox proportional hazards models, respectively. At 48 months, 47.4% of women had blood pressure progression. The odds ratio (95% CIs) for blood pressure progression associated with the rs5063 variant was 0.85 (0.76 to 0.94; P=0.002). For the rs5065 variant, the corresponding odds ratio was 0.94 (0.88 to 1.00; P=0.050). During 9.8 years of follow-up, 29.6% of women developed incident hypertension. Hazard ratios (95% CIs) for incident hypertension were 0.88 (0.80 to 0.96; P=0.005) for the rs5063 variant and 0.95 (0.90 to 1.00; P=0.068) for the rs5065 variant. The odds ratios (95% CIs) of blood pressure progression for the G-T, G-C, and A-T haplotypes were 1.0 (referent), 0.91 (0.85 to 0.98; P=0.007), and 0.80 (0.71 to 0.89; P<0.001), respectively. For incident hypertension, the corresponding hazard ratios were 1.0 (referent), 0.95 (0.90 to 1.01; P=0.095), and 0.90 (0.81 to 0.99; P=0.031), respectively. If corroborated by other large-scale, prospective studies, our findings indicate that the natriuretic peptide precursor A gene plays a significant role in blood pressure regulation and development of hypertension.

A 'reverse' phylogenetic approach for identification of novel osmoregulatory and cardiovascular hormones in vertebrates

Vertebrates expanded their habitats from aquatic to terrestrial environments during the course of evolution. In parallel, osmoregulatory and cardiovascular systems evolved to counter the problems of desiccation and gravity on land. In our physiological studies on body fluid and blood pressure regulation in various vertebrate species, we found that osmoregulatory and cardiovascular hormones have changed their structure and function during the transition from aquatic to terrestrial life. In fact, Na(+)-regulating and vasodepressor hormones play essential roles in fishes, while water-regulating and vasopressor hormones are dominant in tetrapods. Accordingly, Na(+)-regulating and vasodepressor hormones, such as natriuretic peptide (NP) and adrenomedullin (AM), are much diversified in teleost fishes compared with mammals. Based on this finding, new NPs and AMs were identified in mammals and other tetrapods. These hormones have only minor roles in the maintenance of normal blood volume and pressure in mammals, but their importance seems to increase when homeostasis is disrupted. Therefore, such hormones can be used for diagnosis and treatment of body fluid and cardiovascular disorders such as cardiac/renal failure and hypertension. In this review, we introduce a new approach for identification of novel Na(+)-regulating and vasodepressor hormones in mammals based on fish studies. Until recently, new hormones were first discovered in mammals, and then identified and applied in fishes. However, chances are increasing in recent years to identify new hormones first in fishes then in mammals, based on the difference in the regulatory systems between fishes and tetrapods. As the direction is opposite from the traditional phylogenetic approach, we added 'reverse' to its name. The 'reverse' phylogenetic approach offers a typical example of how comparative fish studies can contribute to the general and clinical endocrinology.

Genetic determinants of blood pressure regulation

Hypertension is a multifactorial disorder that probably results from the inheritance of a number of susceptibility genes and involves multiple environmental determinants. Existing evidence suggests that the genetic contribution to blood pressure variation is about 30-50%. Although a number of candidate genes have been studied in different ethnic populations, results from genetic analysis are still inconsistent and specific causes of hypertension remain unclear. Furthermore, the abundance of data in the literature makes it difficult to piece together the puzzle of hypertension and to define candidate genes involved in the dynamic of blood pressure regulation. In this review, we attempt to highlight the genetic basis of hypertension pathogenesis, focusing on the most important existing genetic variations of candidate genes and their potential role in the development of this disease. Our objective is to review current knowledge and discuss limitations to clinical applications of genotypic information in the diagnosis, evaluation and treatment of hypertension. Finally, some principles of pharmacogenomics are presented here along with future perspectives of hypertension.

Corin gene minor allele defined by 2 missense mutations is common in blacks and associated with high blood pressure and hypertension

BACKGROUND

The natriuretic peptide system contributes to blood pressure regulation. Atrial and brain natriuretic peptides are cleaved into smaller biologically active molecules by corin, a transmembrane serine protease expressed in cardiomyocytes.

METHOD AND RESULTS

This genotype-phenotype genetic association study included replication samples and genomic control to correct for population stratification. Sequencing of the human corin gene identified 2 nonsynonymous, nonconservative single nucleotide polymorphisms (Q568P and T555I) in near-complete linkage disequilibrium, thus describing a single minor I555 (P568) corin gene allele. This allele was present in the heterozygote state in &12% of blacks but was extremely rare in whites (<0.5% were homozygous for the minor allele). In our primary population sample, the Dallas Heart Study, after adjustment for potential confounders, including population stratification, the corin I555 (P568) allele remained independently associated with increased risk for prevalent hypertension (odds ratio, 1.63; 95% CI, 1.11 to 2.38; P=0.013). The corin I555 (P568) allele also was associated with higher systolic blood pressure in subjects not using antihypertensive medication in unadjusted (133.7+/-20.7 versus 129.4+/-17.4 mm Hg; P=0.029) and adjusted (132.5+/-1.6 versus 128.9+/-0.6 mm Hg; P=0.029) analyses. The independent association of the minor corin allele with increased risk for prevalent hypertension was confirmed in the Multi-Ethnic Study of Atherosclerosis (odds ratio, 1.50; 95% CI, 1.09 to 2.06; P=0.014). In addition, the association of the minor corin I555 (P568) allele with higher systolic blood pressure was confirmed in adjusted analysis in the Chicago Genetics of Hypertension Study (125.8+/-1.9 versus 121.4+/-0.7 mm Hg; P=0.03).

CONCLUSIONS

The corin I555 (P568) allele is common in blacks and is associated with higher blood pressure and an increased risk for prevalent hypertension.

Regulatable atrial natriuretic peptide gene therapy for hypertension

Hypertension (HTN) is a disease that begins with dysfunctional renal-sodium excretion and progresses to a syndrome of highly elevated systolic, diastolic, and mean arterial pressures. Inadequacies in the therapy of HTN have led to the investigation of the gene therapy of this disease by using systemic overproduction of vasodilatory peptides, such as atrial natriuretic peptide (ANP). However, gene-therapy approaches to HTN using ANP are limited by the need for long-term ANP gene expression and, most important, control of ANP gene expression. Here, we introduce a helper-dependent adenoviral vector carrying the mifepristone (Mfp)-inducible gene-regulatory system to control in vivo ANP expression. In the BPH/2 mouse model of HTN, Mfp-inducible ANP expression was seen for a period of >120 days after administration of vector. Physiological effects of ANP, including decreased systolic blood pressure, increased urinary cGMP output, and decreases in heart weight as a percentage of body weight were also under the control of Mfp. Given these capabilities, this vector represents a paradigm for the gene therapy of HTN.

Urinary responses to acute moxonidine are inhibited by natriuretic peptide receptor antagonist

We have previously shown that acute intravenous injections of moxonidine and clonidine increase plasma atrial natriuretic peptide (ANP), a vasodilator, diuretic and natriuretic hormone. We hypothesized that moxonidine stimulates the release of ANP, which would act on its renal receptors to cause diuresis and natriuresis, and these effects may be altered in hypertension. Moxonidine (0, 10, 50, 100 or 150 microg in 300 microl saline) and clonidine (0, 1, 5 or 10 microg in 300 microl saline) injected intravenously in conscious normally hydrated normotensive Sprague-Dawley rats (SD, approximately 200 g) and 12-14-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) dose-dependently stimulated diuresis, natriuresis, kaliuresis and cGMP excretion, with these effects being more pronounced during the first hour post-injection. The actions of 5 microg clonidine and 50 microg moxonidine were inhibited by yohimbine, an alpha2-adrenoceptor antagonist, and efaroxan, an imidazoline I1-receptor antagonist. Moxonidine (100 microg) stimulated (P<0.01) diuresis in SHR (0.21+/-0.04 vs 1.16+/-0.06 ml h(-1) 100 g(-1)), SD (0.42+/-0.06 vs 1.56+/-0.19 ml h(-1) 100 g(-1)) and WKY (0.12+/-0.04 vs 1.44+/-0.21 ml h(-1) 100 g(-1)). Moxonidine-stimulated urine output was lower in SHR than in SD and WKY. Moxonidine-stimulated sodium and potassium excretions were lower in SHR than in SD, but not WKY, demonstrating an influence of strain but not of pressure. Pretreatment with the natriuretic peptide antagonist anantin (5 or 10 microg) resulted in dose-dependent inhibition of moxonidine-stimulated urinary actions. Anantin (10 microg) inhibited (P<0.01) urine output to 0.38+/-0.06, 0.12+/-0.01, and 0.16+/-0.04 ml h(-1) 100 g(-1) in SD, WKY, and SHR, respectively. Moxonidine increased (P<0.01) plasma ANP in SD (417+/-58 vs 1021+/-112 pg ml(-1)) and WKY (309+/-59 vs 1433+/-187 pg ml(-1)), and in SHR (853+/-96 vs 1879+/-229 pg ml(-1)). These results demonstrate that natriuretic peptides mediate the urinary actions of moxonidine through natriuretic peptide receptors.

Biology of natriuretic peptides and their receptors

Increasing evidence suggests that natriuretic peptides (NPs) play diverse roles in mammals, including renal hemodynamics, neuroendocrine, and cardiovascular functions. Collectively, NPs are classified as hypotensive hormones; the main actions of NPs are implicated in eliciting natriuretic, diuretic, steroidogenic, antiproliferative, and vasorelaxant effects, important factors in the control of body fluid volume and blood pressure homeostasis. One of the principal loci involved in the regulatory actions of NPs is their cognate plasma membrane receptor molecules, which are activated by binding with specific NPs. Interaction of NPs with their receptors plays a central role in physiology and pathophysiology of hypertension and cardiovascular disorders. Gaining insight into the intricacies of NPs-specific receptor signaling pathways is of pivotal importance for understanding both hormone-receptor biology and the disease states arising from abnormal hormone receptor interplay. During the last decade there has been a surge in interest in NP receptors; consequently, a wealth of information has emerged concerning molecular structure and function, signaling mechanisms, and use of transgenics and gene-targeted mouse models. The objective of this present review is to summarize and document the previous findings and recent discoveries in the field of the natriuretic peptide hormone family and receptor systems with emphasis on the structure-function relationship, signaling mechanisms, and the physiological and pathophysiological significance in health and disease.

Neurochemical brain groups activated after an isotonic blood volume expansion in rats

In order to establish the involvement of particular neurochemical brain groups in the response to blood volume expansion, we analyzed Fos-labeling in combination with immunolabeling for serotonin, tyrosine hydroxylase, vasopressin and oxytocin, 90 min after a sham or i.v. isotonic blood volume expansion (BVE) in unanesthetized, unrestrained rats. We also examined the changes in concentration of oxytocin, atrial natriuretic peptide and vasopressin plasma, induced by blood volume load, to confirm our previous studies. The results demonstrate the participation of specific paraventricular and supraoptic nucleus groups of cells (oxytocinergic-vasopressinergic), serotoninergic dorsal raphe nucleus cells and catecholaminergic A1/A2/A6 groups (in the caudal ventrolateral medulla, nucleus of the solitary tract and locus coeruleus respectively), in the regulatory response to BVE. They provide detailed neuroanatomical evidence to support previous observations showing the contribution of these neurochemical systems in the neural, behavioral and endocrine response to isotonic BVE.

Cell-specific activation of the atrial natriuretic factor promoter by PITX2 and MEF2A

The PITX2 homeodomain protein is mutated in patients with Axenfeld-Rieger syndrome and is involved in the development of multiple organ systems, including the heart. We have examined the interaction of PITX2 isoforms with myocyte-enhancing factor 2A (MEF2A), which is a known regulator of cardiac development. A direct interaction between PITX2a and MEF2A was demonstrated using yeast two-hybrid and GST pull-down assays. To study the functional significance of this interaction, we used the atrial natriuretic factor (ANF) promoter. Coexpression of MEF2A and PITX2a or Pitx2c resulted in a strong synergistic activation of the ANF promoter in LS8 oral epithelial cells but not in other cell lines (NIH/3T3, Chinese hamster ovary, or C2C12). The synergism was dependent on promoter context, because it required MEF2 binding sites and was not seen with two other PITX2 target promoters. DNA binding by MEF2A was required but not sufficient for synergism. Upstream activators of p38 MAP kinases, MKK3 and MKK6, increased PITX2a and Pitx2c activity to yield up to 90-fold activation of the ANF promoter in LS8 cells. Because Axenfeld-Rieger syndrome is autosomal dominant and affects development of the oral epithelium, we tested one of the known PITX2 mutants. The PITX2a-K88E mutant protein suppressed wild type PITX2a synergism with MEF2A. These results demonstrate a promoter- and cell-specific functional interaction between PITX2 and MEF2A and suggest the possibility of coordinate control by these factors in the oral epithelium.

Cosegregation analysis of natriuretic peptide genes and blood pressure in the spontaneously hypertensive rat

1. The natriuretic peptide precursor A (Nppa) and B (Nppb) genes are candidate genes for hypertension and cardiac hypertrophy in the spontaneously hypertensive rat (SHR). The purpose of the present study was to determine the role of the Nppa and Nppb genes in the development of hypertension in the SHR. 2. A cohort (n = 162) of F2 segregating intercross animals was established between strains of hypertensive SHR and normotensive Wistar-Kyoto rats. Blood pressure and heart weight were measured in each rat at 12-16 weeks of age. Rats were genotyped using 11 informative microsatellite markers, distributed in the vicinity of the Nppa marker on rat chromosome 5 including an Nppb marker. The phenotype values were compared with genotype using the computer package mapmaker 3.0 (Whitehead Institute, Boston, MA, USA) to determine whether there was a link between the genetic variants of the natriuretic peptide family and blood pressure or cardiac hypertrophy. 3. A strong correlation was observed between the Nppa marker and blood pressure. A quantitative trait locus (QTL) for blood pressure on chromosome 5 was identified between the Nppa locus and the D5Mgh15 marker, less than 2 cM from the Nppa locus. The linkage score for the blood pressure QTL on chromosome 5 was 3.8 and the QTL accounted for 43% of the total variance of systolic blood pressure, 54% of diastolic blood pressure and 59% of mean blood pressure. No association was found between the Nppb gene and blood pressure. This is the first report of linkage between the Nppa marker and blood pressure in the rat. There was no correlation between the Nppa or Nppb genes or other markers in this region and either heart weight or left ventricular weight in F2 rats. 4. These findings suggest the existence of a blood pressure-dependent Nppa marker variant or a gene close to Nppa predisposing to spontaneous hypertension in the rat. It provides a strong foundation for further detailed genetic studies in congenic strains, which may help to narrow down the location of this gene and lead to positional cloning.

Ouabain-insensitive Na+-ATPase of proximal tubules is an effector for urodilatin and atrial natriuretic peptide

In the present paper we studied the effect of urodilatin and atrial natriuretic peptide (ANP) on the proximal tubule Na+-ATPase and (Na+K+)ATPase activities. Urodilatin and ANP inhibit the Na+-ATPase activity but not the (Na+K+)ATPase activity. Maximal effect was observed at a concentration of 10(-11) M for both peptides. In this condition, the enzyme activity decreases from 10.8 +/- 1.6 (control) to 5.7 +/- 0.9 or 6.1 +/- 0.7 nmol Pi mg(-1) min(-1) in the presence of urodilatin or ANP, respectively. This effect was completely reversed by 10(-6) M LY83583, a guanylyl cyclase inhibitor, and mimicked by 10 nM cGMP. Furthermore, both ANP and urodilatin increase cGMP production by 33% and 49%, respectively. This is the first demonstration that it was shown that urodilatin and ANP directly modulate primary active sodium transport in the proximal tubule. The data obtained indicate that this effect is mediated by the activation of the NPR-A/guanylate cyclase/cGMP pathway.

Obesity and hypertension

This article has discussed some of the mechanisms involved in the causal relation between obesity and hypertension. Obesity causes a constellation of maladaptive disorders that individually and synergistically contribute to hypertension, among other cardiovascular morbidities. Well-designed population-based studies are needed to assess the individual contribution of each of these disorders to the development of hypertension. In addition, because the control of obesity may eliminate 48% of the hypertension in whites and 28% in blacks, this article has offered an up-to-date on the management of this problem. It is hoped that this article will help scientists formulate a thorough understanding of obesity hypertension and form the basis for more research in this field, which has a huge impact on human life.

Renal effects of omapatrilat and captopril in salt-loaded, nitric oxide-deficient rats

Inhibition of nitric oxide synthases causes systemic hypertension and renal injury in rats. Our objective was to examine whether omapatrilat, a vasopeptidase inhibitor that inhibits both angiotensin-converting enzyme (ACE) and neutral endopeptidase, could induce better regression of renal injury than ACE inhibitor alone. Ten groups of rats were studied. They were fed either a normal (0.8% NaCl) or a high (4% NaCl) sodium diet. Eight of these groups received NG-nitro-L-arginine methyl ester (L-NAME, 20 mg x kg(-1) x d(-1)) in their drinking water. After 4 weeks, 1 group on each diet was killed and considered the L-NAME group, whereas the others received L-NAME alone, captopril (200 mg x kg(-1) x d(-1)) plus L-NAME, or omapatrilat (80 mg x kg(-1) x d(-1)) plus L-NAME for 4 additional weeks. In rats receiving L-NAME alone for 8 weeks, the mortality rate was approximately 90%, irrespective of the diet. In contrast, all rats survived in the captopril and the omapatrilat groups. In rats fed a normal-sodium diet, captopril and omapatrilat normalized systolic blood pressure and induced a complete regression of renal injury. Creatinine clearance and proteinuria were also normalized. In the high-sodium-diet groups, both treatments were less efficient: blood pressure remained elevated, and the regression of renal fibrosis was only partial. Although proteinuria decreased significantly with captopril or omapatrilat, creatinine clearance remained lower than in the controls. These results demonstrate that, in nitric oxide-deficient rats fed a normal-sodium diet, ACE and vasopeptidase inhibitors exhibit a marked renoprotective effect, whereas these treatments are less efficient in rats fed a high-sodium diet.

Heritability and genetic linkage of plasma natriuretic peptide levels

BACKGROUND

Natriuretic peptides play a critical role in the maintenance of salt and water homeostasis and regulation of vascular tone. Thus, interindividual variation in plasma natriuretic peptide levels may contribute to variation in susceptibility to volume overload and hypertension. It is unknown to what extent genetic factors contribute to variation in plasma natriuretic peptide levels.

METHODS AND RESULTS

We studied 1914 Framingham Study participants (mean age 57 years, 53% women) who underwent routine echocardiography and testing for plasma N-terminal proatrial natriuretic peptide (N-ANP) and brain natriuretic peptide (BNP). We estimated sex-specific multivariable models and used variance-components methods, implemented in SOLAR (Sequential Oligogenic Linkage Analysis Routines), to estimate heritability. Multipoint linkage analyses were performed using data from a 10-cM-density genome scan. Age, clinical, and echocardiographic variables accounted for 42% and 40% of the variation in log N-ANP and log BNP levels, respectively, in men. Corresponding values in women were 27% and 21%. Multivariable-adjusted heritabilities were 0.44 for log N-ANP and 0.35 for log BNP (P<0.0001). Genome-wide linkage analyses, based on 1142 participants from the 314 largest families, revealed 2 regions of suggestive linkage for log N-ANP and log BNP on chromosomes 2p25 (log-of-odds score 2.40) and 12p13 (log-of-odds score 2.13), respectively.

CONCLUSIONS

In this community-based sample, a substantial proportion of the unexplained variation in plasma natriuretic peptide levels was attributable to additive genetic effects. Additional studies using candidate gene approaches may provide insight into the genetic loci that regulate plasma natriuretic peptide levels in humans.

Alpha2A-adrenergic receptors mediate sympathoinhibitory responses to atrial natriuretic peptide in the mouse anterior hypothalamic nucleus

In the rat, activation of alpha2-adrenergic receptors in the anterior hypothalamic nucleus inhibits sympathetic nervous system activity. Furthermore, local release of atrial natriuretic peptide inhibits norepinephrine release in this nucleus, blocking local activation of alpha2-adrenergic receptors, and thereby contributes to NaCl-sensitive hypertension in spontaneously hypertensive rats. To further test the specificity of this mechanism, either alpha2-adrenergic receptor agonists or atrial natriuretic peptide was microinjected into anterior hypothalamic nucleus of conscious C57BL/6 mice in which the alpha2-adrenergic receptor was functionally deleted by a single point mutation (n=10 per group). In control mice, microinjection of either clonidine or guanabenz (10-3 to 10-7 mol/L) caused a rapid fall in mean arterial pressure that lasted for several minutes. In the knockout mice there was no response to the injection of either dose of either agonist. Microinjection of atrial natriuretic peptide (10-6 to 10-7 mol/L) caused a rapid increase in mean arterial pressure (8.2+/-1.3 and 6.55+/-1.2 mm Hg, respectively) in the control mice that was similar to the responses previously observed in Wistar-Kyoto rats. In contrast, the microinjections did not significantly alter mean arterial pressure in the knockout mice. These experiments demonstrate that in the anterior hypothalamic nucleus of the mouse (and probably in the rat) alpha2A-adrenergic receptors mediate both sympathoinhibitory responses to alpha2-adrenergic receptor agonists and the action of atrial natriuretic peptide.

Guanylyl cyclase receptors mediate cardiopulmonary vagal reflex actions of ANP

Atrial natriuretic peptide (ANP) potentiates vagal cardiopulmonary reflexes due to chemosensory (Bezold-Jarisch [B-J] reflex) or mechanosensory (ramp baroreflex) activation. The ANP receptor mediating these actions is unknown. We examined the role of particulate guanylyl-cyclase (pGC) receptors in ANP-induced enhancement of cardiopulmonary vagal reflexes. Cardiopulmonary baroreceptor reflex function was assessed by bradycardic responses to ramp blood pressure rises after rapid intravenous methoxamine (100 micro g/kg bolus dose). The B-J reflex was evoked by 3 intravenous doses of serotonin (1 to 10 micro g/kg). In conscious, chronically instrumented rats (n=9), these tests were performed on each animal during randomized infusions of rat ANP (150 ng/kg per minute IV), saline (270 micro L/h IV), the pGC receptor antagonist HS-142-1 (3 mg/kg IV), or combined HS-142-1+ANP treatment. HS-142-1 alone attenuated normal B-J reflex (by 33+/-8%, P<0.05) but not ramp baroreflex responses. As we showed previously, ANP enhanced baroreflex and B-J reflex bradycardia (by approximately 140% and approximately 30%, respectively, P<0.05), compared with saline infusion. These ANP effects were completely blocked by HS-142-1, demonstrating that the cardiopulmonary vagal reflex actions of ANP occurred through pGC natriuretic peptide receptors. Additionally, we have provided evidence for the first time that pGC natriuretic peptide receptors are essential for the full expression of the B-J reflex but not for that of cardiopulmonary vagal baroreflexes. This tonic interaction between pGC natriuretic peptide receptors and cardiopulmonary chemosensitive receptors may be important during pathophysiological activation of B-J reflex, such as with myocardial infarction.

Treatment of the diabetic patient: focus on cardiovascular and renal risk reduction

Diabetes mellitus increases the risk for hypertension and associated cardiovascular diseases, including coronary, cerebrovascular, renal and peripheral vascular disease. The risk for developing cardiovascular disease is increased when both diabetes and hypertension co-exist; in fact, over 11 million Americans have both diabetes and hypertension. These numbers will continue to climb, internationally, since the leading associated risk for diabetes development, obesity, has reached epidemic proportions, globally. Moreover, the frequent association of diabetes with dyslipidemia, as well as coagulation, endothelial, and metabolic abnormalities also aggravates the underlying vascular disease process in patients who possess these comorbid conditions. The renin-angiotensin-aldosterone system (RAS) and arginine vasopressin (AVP) are overactivated in both hypertension and diabetes. Drugs that inhibit this system, such as ACE inhibitors and more recently angiotensin receptor antagonists (ARBs), have proven beneficial effects on the micro- and macrovascular complications of diabetes, especially the kidney. The BRILLIANT study showed that lisinopril reduces microalbuminuria better than CCB therapy. Numerous other long-term studies confirm this association with ACE inhibitors including the HOPE trial. Furthermore, the European Controlled trial of Lisinopril in Insulin-dependent Diabetes (EUCLID) study, showed that lisinopril slowed the progression of renal disease, even in individuals with mild albuminuria. In fact, there are now five appropriately powered randomized placebo-controlled trials to show that both ACE inhibitors and ARBs slow progression of diabetic nephropathy in people with type 2 diabetes. These effects were shown to be better than conventional blood pressure lowering therapy, including dihydropyridine CCBs. In patients with microalbuminuria, ACE inhibitors and ARBs reduce the progression of microalbuminuria to proteinuria and provide a risk reduction of between 38 and 60% for progression to proteinuria. This is important since microalbuminuria is known to be associated with increased vascular permeability and decreased responsiveness to vasodilatory stimuli. Recently, increased AVP levels have been lined to microalbuminuria and hyperfiltration in diabetes. The microvascular and macrovascular benefits of ACE inhibition, ARBs and possible role of AVP antagonists in diabetic patients will be discussed, as will be recommendations for its clinical use.

The natriuretic peptide system in eels: a key endocrine system for euryhalinity?

The natriuretic peptide system of a euryhaline teleost, the Japanese eel (Anguilla japonica), consists of three types of hormones [atrial natriuretic peptide (ANP), ventricular natriuretic peptide (VNP), and C-type natriuretic peptide (CNP)] and four types of receptors [natriuretic peptide receptors (NPR)-A, -B, -C, and -D]. Although ANP is recognized as a volume-regulating hormone that extrudes both Na(+) and water in mammals, ANP more specifically extrudes Na(+) in eels. Accumulating evidence shows that ANP is secreted in response to hypernatremia and acts to inhibit the uptake and to stimulate the excretion of Na(+) but not water, thereby promoting seawater (SW) adaptation. In fact, ANP is secreted immediately after transfer of eels to SW and ameliorates sudden increases in plasma Na(+) concentration through inhibition of drinking and intestinal absorption of NaCl. ANP also stimulates the secretion of cortisol, a long-acting hormone for SW adaptation, whereas ANP itself disappears quickly from the circulation. Thus ANP is a primary hormone responsible for the initial phase of SW adaptation. By contrast, CNP appears to be a hormone involved in freshwater (FW) adaptation. Recent data show that the gene expression of CNP and its specific receptor, NPR-B, is much enhanced in FW eels. In fact, CNP infusion increases (22)Na uptake from the environment in FW eels. These results show that ANP and CNP, despite high sequence identity, have opposite effects on salinity adaptation in eels. This difference apparently originates from the difference in their specific receptors, ANP for NPR-A and CNP for NPR-B. VNP may compensate the effects of ANP and CNP for adaptation to respective media, because it has high affinity to both receptors. On the basis of these data, the authors suggest that the natriuretic peptide system is a key endocrine system that allows this euryhaline fish to adapt to diverse osmotic environments, particularly in the initial phase of adaptation.

Genomic sequence and cardiac expression of atrial natriuretic peptide in cats

OBJECTIVE

To determine the nucleotide and amino acid sequence of atrial natriuretic peptide (ANP) in cats and its typical regions of cardiac expression.

ANIMALS

5 healthy adult mixed-breed cats.

PROCEDURE

Total RNA was extracted from samples obtained from the left and right atrium, left and right ventricle, and interventricular septum of each cat. The RNA was used to produce cDNA for sequencing and northern blot analysis. Genomic DNA was extracted from feline blood samples. Polymerase chain reaction primers designed from consensus sequences of other species were used to clone and sequence the feline ANP gene.

RESULTS

The feline ANP gene consists of 1,072 nucleotides. It consists of 3 exons (123, 327, and 12 nucleotides) separated by 2 introns (101 and 509 nucleotides). It has several typical features of eukaryotic genes and a putative steroid-response element located within the second intron. Preprohormone ANP consists of 153 amino acids. The amino acid sequence of the active form of feline ANP (ANP-30) is identical to that of equine, bovine, and ovine ANP-30 and differs from that of human, canine, and porcine ANP-28 only by 2 carboxy-terminal arginine residues. The ANP mRNA was detected only in the left and right atria.

CONCLUSIONS AND CLINICAL RELEVANCE

The genetic and protein structure and principal regions of cardiac expression of feline ANP are similar to those of other species. Results of this study should be helpful in future studies on the natriuretic response in cats to diseases that affect cardiovascular function.

Targeted disruption of the gene for natriuretic peptide receptor-A worsens hypoxia-induced cardiac hypertrophy

Targeted disruption of the gene for natriuretic peptide receptor-A (NPR-A) worsens pulmonary hypertension and right ventricular hypertrophy during hypoxia, but its effect on left ventricular mass and systemic pressures is not known. We examined the effect of 3 wk of hypobaric hypoxia (0.5 atm) on right and left ventricular pressure and mass in mice with 2 (wild type), 1, or 0 copies of Npr1, the gene that encodes for NPR-A in mice. Under normoxic conditions, right ventricular peak pressure (RVPP) was greater in 0 than in 2 copy mice, but there were no genotype-related differences in carotid artery PP (CAPP). The left ventricular free wall weight-to-body weight (LV/body wt) ratio was greater in 0 than in 2 copy mice and there was a trend toward a greater right ventricular weight-to-body weight (RV/body wt) ratio. Three weeks of hypoxia increased RVPP and RV/body wt in all genotypes. The increase in RVPP was similar in all genotypes (11-14 mmHg), but the hypoxia-induced increase in RV/body wt was more than twice as great in 0 copy mice than in 2 copy mice (1.11 +/- 0.06 to 2.65 +/- 0.46 vs. 0.96 +/- 0.04 to 1.4 +/- 0.09, P < 0.05). Chronic hypoxia had no effect on CAPP in any genotype and did not effect LV/body wt in 1 or 2 copy mice, but increased LV/body wt 41% in 0 copy mice. We conclude that absent expression of NPR-A worsens right ventricular hypertrophy and causes left ventricular hypertrophy during exposure to chronic hypoxia without increasing pulmonary or systemic arterial pressure responses.