Expression of B-type natriuretic peptide in atrial natriuretic peptide gene disrupted mice

Plasma concentrations of peptide hormones: Unrealistic levels of vasopressin (AVP), oxytocin (OXT), and brain natriuretic peptide (BNP)

Hormones are specific molecules measured in biological fluids by elaborate analytical systems requiring meticulous attention. Variation between laboratories can be expected. However, recently published measurements of AVP, OXT, and BNP in human plasma under basal/control conditions include numbers which, between publications, vary by 100-10 000-fold. Generally, the methods descriptions are scant, at best, and provide no information about quality control measures. Clearly, two results describing the same basal hormone concentration by numbers three orders of magnitude apart are incongruent providing reason for concern. Basal concentrations of bioactive AVP, OXT, and BNP in human plasma are in the order of 1-10 pmol/L. Therefore, assay systems applied to plasma must be able to measure concentrations of less than 1 pmol/L with appropriate specificity and accuracy. Basal concentrations of AVP, OXT, and BNP above 100 pmol/L should be reconsidered, as such results do not reflect bioactive hormone levels in humans, rats, or mice. Any concentration above 1000 pmol/L is of concern because such levels of bioactive hormone may be seen only under extreme conditions, if at all.

Natriuretic peptides and neprilysin inhibition in hypertension and hypertensive organ damage

The family of natriuretic peptides (NPs) discovered in mammalian tissues including cardiac atrium and brain consists of three members, namely, atrial, B- and C-type natriuretic peptides (ANP, BNP, CNP). Since the discovery, basic and clinical studies have been vigorously performed to explore the biological functions and pathophysiological roles of NPs in a wide range of diseases including hypertension and heart failure. These studies revealed that ANP and BNP are hormones secreted from the heart into the blood stream in response to pre- or after-load, counteracting blood pressure (BP) elevation and fluid retention through specific receptors. Meanwhile, CNP was found to be produced by the vascular endothelium, acting as a local mediator potentially serving protective functions for the blood vessels. Because NPs not only exert blood pressure lowering actions but also alleviate hypertensive organ damage, attempts have been made to develop therapeutic agents for hypertension by utilizing this family of NPs. One strategy is to inhibit neprilysin, an enzyme degrading NPs, thereby enhancing the actions of endogenous peptides. Recently, a dual inhibitor of angiotensin receptor-neprilysin was approved for heart failure, and neprilysin inhibition has also been shown to be beneficial in treating patients with hypertension. This review summarizes the roles of NPs in regulating BP, with special references to hypertension and hypertensive organ damage, and discusses the therapeutic implications of neprilysin inhibition.

Transmission of pruriceptive signals

In this chapter we discuss the many recent discoveries of the mechanisms by which itch is transmitted: the neurotransmitters and the responses they trigger, the mechanisms by which specific neuronal targets are activated, and the specificity of the pathways. Current data reveal that DRG neurons and spinal cord cells use a remarkably selective set of transmitters to convey pruritic information from the periphery to the brain: glutamate and Nppb are released from primary itch-sensory cells; these molecules activate secondary spinal cord pruriceptive-specific neurons, which in turn utilize Grp to activate tertiary pruriceptive-selective neurons. Intersecting this basic linear excitatory pathway, inhibitory input from dynorphin and neurons that express the somatostatin receptor modify itch sensation. Cumulatively, these studies paint an elegantly simple picture of how itch signals are transformed and integrated in the spinal cord and open new avenues for research efforts aimed at understanding and better treating itch.

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.

Sex-specific differences in natriuretic peptide and nitric oxide synthase expression in ANP gene-disrupted mice

Sex-specific differences in hormone-mediated gene regulation may influence susceptibility to cardiac hypertrophy, a primary risk factor for cardiovascular disease. Under hormonal influence, natriuretic peptide (NP) and nitric oxide synthase (NOS) systems modulate cardio-protective gene programs through common downstream production of cyclic guanosine 3'-5' monophosphate (cGMP). Ablation of either system can adversely affect cardiac adaptation to stresses and insults. This study elucidates sex-specific differences in cardiac NP and NOS system gene expression and assesses the impact of the estrous cycle on these systems using the atrial natriuretic peptide gene-disrupted (ANP(-/-)) mouse model. Left ventricular expression of the NP and NOS systems was analyzed using real-time quantitative polymerase chain reaction in 13- to 16-week-old male, proestrous and estrous female ANP(+/+) and ANP(-/-) mice. Left ventricular and plasma cGMP levels were measured to assess the convergent downstream effects of the NP and NOS systems. Regardless of genotype, males had higher expression of the NP system while females had higher expression of the NOS system. In females, transition from proestrus to estrus lowered NOS system expression in ANP(+/+) mice while the opposite was observed in ANP(-/-) mice. No significant changes in left ventricular cGMP levels across gender and genotype were observed. Significantly lower plasma cGMP levels were observed in ANP(-/-) mice compared to ANP(+/+) mice. Regardless of genotype, sex-specific differences in cardiac NP and NOS system expression exist, each sex enlisting a predominant system to conserve downstream cGMP. Estrous cycle-mediated alterations in NOS system expression suggests additional hormone-mediated gene regulation in females.

B-type natriuretic peptide: from posttranslational processing to clinical measurement

BACKGROUND

Plasma cardiac natriuretic peptides and peptide fragments from their molecular precursors are markers of heart disease. Clinical studies have defined the current diagnostic utility of these markers, whereas biochemical elucidation of peptide structure and posttranslational processing has revealed new plasma peptide forms of potential clinical use.

CONTENT

Natriuretic propeptide structures undergo variable degrees of endo- and exoproteolytic cleavages as well as amino acid modifications, which leave the plasma phase of the peptides highly heterogeneous and dependent on cardiac pathophysiology and capacity. An ongoing characterization of the molecular heterogeneity may not only help us to appreciate the biosynthetic capacity of the endocrine heart but may also lead to the discovery of new and more disease-specific targets for future molecular diagnosis.

SUMMARY

Peptides derived from pro-atrial natriuretic peptide and pro-B-type natriuretic peptide are useful plasma markers in heart failure. New data have defined cardiac myocytes as competent endocrine cells in posttranslational processing and cellular secretion.

Impact of acute and chronic stressor experiences on heart atrial and brain natriuretic peptides in response to a subsequent stressor

The impact of stressful events on processes related to cardiovascular functioning might vary with previous stressor experiences, just as such sensitization effects have been detected with respect to several neurochemical and hormonal processes. The present investigation assessed the impact of a psychosocial stressor on factors directly or indirectly related to cardiovascular functioning among CD-1 mice that had previously experienced an acute or chronic stressor regimen. These factors included plasma variations of atrial and brain natriuretic peptides (ANP and BNP, respectively), inflammatory cytokines in plasma, mRNA expression of natriuretic peptides and inflammatory cytokines in the ventricles, and norepinephrine (NA) levels and utilization within the locus coeruleus, a brain region implicated in cardiac functioning. A social stressor (exposure to a dominant mouse) increased NE levels and utilization within the locus coeruleus, plasma corticosterone, cytokine and ANP levels. Among mice initially exposed to an acute stressor (restraint), NE utilization, ventricular ANP mRNA expression, and plasma interleukin-6 (IL-6) concentrations were markedly increased by the subsequent social stressor. In chronically stressed mice some of the effects of the social stressor were dampened, including changes of plasma corticosterone, locus coeruleus NE utilization, as well as plasma and ventricular IL-6 mRNA expression. Conversely, plasma ANP was markedly enhanced by the combined stressor events as was ventricular BNP and IL-1β mRNA expression. It seems that stressors may profoundly influence (sensitize or desensitize) on factors that could influence cardiovascular functioning. It remains to be determined whether these actions would be translated as pathophysiological outcomes.

Altered expression of the natriuretic peptide system in genetically modified heme oxygenase-1 mice treated with high dietary salt

Heme oxygenase-1 (HO-1) has been well established as a cytoprotective molecule, and has been shown to exert cardioprotective effects in both hypertension and cardiac hypertrophy. However, the precise mechanism of the cardioprotective effect of HO-1 has yet to be fully elucidated. With the natriuretic peptide system (NPS) as a key player in cardiovascular homeostasis and tissue dynamics, we sought to examine the effect of high dietary salt treatment in genetic models of HO-1 expression, and assessed the expression of the NPS in the left ventricle (LV), to determine if the effects of altered HO-1 expression may be due to modified levels of the NPS. Age-matched 12-week old male HO-1 knockout (HO-1(-/-)) and HO-1 cardiomyocyte-specific transgenic overexpressing (HO-1(Tg)) mice were treated with either normal salt (NS; 0.8%) or high salt (HS; 8.0%) chow for 5 weeks. LV mRNA expression was determined using quantitative real-time PCR. ANP peptide level was measured in the LV and plasma using radioimmunoassay, and LV cyclic 3'-5' guanosine monophosphate level was measured using an enzyme immunoassay kit. HO-1(-/-) fed HS diet had significantly higher left ventricle-to-body weight ratio (LV/BW) compared to HO-1(+/+) mice fed NS diet. HO-1(-/-) mice had significantly reduced expression of the NPS compared to controls, and these mice did not exhibit a salt-induced increase in ANP expression. HS treatment had no noticeable effect on LV/BW in HO-1(Tg) mice compared to controls. HO-1(Tg) mice had significantly higher ANP and BNP expression compared to controls. There were no differences in LV cGMP levels among all genotypes and dietary treatments. HO-1 ablation resulted in significantly lower mRNA expression of the NPS, whereas HO-1 overexpression resulted in higher mRNA expression of the NPS. Both were substantiated by peptide levels as measured by RIA. These data indicate that the detrimental effect of reduced HO-1 expression and the cardioprotective effect of increased HO-1 expression may be due, in part, to altered expression of the NPS.

Biosynthesis of cardiac natriuretic peptides

Cardiac-derived peptide hormones were identified more than 25 years ago. An astonishing amount of clinical studies have established cardiac natriuretic peptides and their molecular precursors as useful markers of heart disease. In contrast to the clinical applications, the biogenesis of cardiac peptides has only been elucidated during the last decade. The cellular synthesis including amino acid modifications and proteolytic cleavages has proven considerably more complex than initially perceived. Consequently, the elimination phase of the peptide products in circulation is not yet well characterized. An ongoing characterization of the molecular heterogeneity will help appreciate the biosynthetic capacity of the endocrine heart and could introduce new diagnostic possibilities. Notably, different biosynthetic products may not be equal markers of the same pathophysiological processes. An inefficient post-translational prohormone maturation will also affect the biology of the cardiac natriuretic peptide system. This review aims at summarizing the myocardial synthesis of natriuretic peptides focusing on B-type natriuretic peptide, where new data has disclosed cardiac myocytes as highly competent endocrine cells. The structurally related atrial natriuretic peptide will be mentioned where appropriate, whereas C-type natriuretic peptide will not be considered as a cardiac peptide of relevance in mammalian physiology.

Anhedonia and altered cardiac atrial natriuretic peptide following chronic stressor and endotoxin treatment in mice

Chronic stressors and inflammatory immune activation may contribute to pathophysiological alterations associated with both major depression and cardiovascular disease. The present study, conducted in mice, assessed whether a chronic stressor of moderate severity that induced an anhedonic effect, when coupled with a bacterial endotoxin, lipopolysaccharide (LPS), additively or interactively provoked circulating and heart atrial natriuretic peptide (ANP), a potentially useful diagnostic and prognostic tool in cardiac diseases. As well, given the potential role of inflammatory processes in both depression and cardiovascular disease, we assessed pro-inflammatory mRNA expression in heart in response to the stressor and the LPS treatments. Male CD-1 mice that had been exposed to a chronic, variable stressor over 4 weeks displayed reduced sucrose consumption, possibly reflecting the anhedonic effects of the stressor. Treatment with LPS (10mug) provoked increased circulating corticosterone levels in both chronically stressed and non-stressed mice. Moreover, ANP concentrations in plasma and in the left ventricle were increased by both the stressor and the LPS treatments, as were left atrial and ventricular cytokine (interleukin-1beta; tumor necrosis factor-alpha) mRNA expression. Further, these treatments synergistically influenced the rise of plasma ANP. A link may exist between stressor-provoked depressive features (anhedonia) and immune activation, with elevated levels of ANP, a potential marker of cardiovascular disturbance. These findings are consistent with the view that chronic stressors and inflammatory immune activation may represent a common denominator subserving the frequent comorbidity between these illnesses.

Elevated renal norepinephrine in proANP gene-disrupted mice is associated with increased tyrosine hydroxylase expression in sympathetic ganglia

The sympatholytic properties of atrial natriuretic peptide (ANP) contribute to its vasodilatory and natriuretic effects. High circulating catecholamine levels, along with renal dysfunction, present in proANP gene-disrupted (-/-) mice are thought to contribute to the hypertension characteristic of this model. To further understand the mechanism by which the absence of ANP leads to stimulation of sympathetic activity we measured tyrosine hydroxylase expression in mice with and without ANP. The adrenal and prevertebral ganglionic expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine production, was significantly increased in ANP -/- mice. ANP's sympatholytic properties include the depression of ganglionic and adrenal TH expression and catecholamine production. Thus, these results suggest that the absence of ANP's sympatholytic effects is not completely compensated for in ANP -/- mice. In addition, mice devoid of ANP display an increase in renal sympathetic nerve activity from birth through to adulthood which may lead to structural and/or functional changes in the early postnatal kidney that contribute to the hypertensive phenotype of ANP -/- mice. The over-activation of the sympathetic nervous system in mice lacking ANP confirms the important role of this peptide in the modulation of sympathetic nerve activity and its contribution to blood pressure homeostasis.

Estrogen delays the progression of salt-induced cardiac hypertrophy by influencing the renin-angiotensin system in heterozygous proANP gene-disrupted mice

Left ventricular hypertrophy is considered an independent risk factor for cardiac morbidity and mortality, and many studies have shown that women have a lower incidence of left ventricular hypertrophy even after correcting for numerous risk factors. This cardio-protective effect seen in women has been attributed to estrogen, which likely modulates specific growth-promoting systems such as the renin-angiotensin system, and in turn may lead to the prevention of left ventricular hypertrophy. Furthermore, the underlying mechanisms responsible are poorly understood. The aim of the present study was to examine the effect of estrogen in relation to its impact on the development of left ventricular hypertrophy through its interaction with the renin-angiotensin system by using the proANP heterozygous (ANP +/-) mouse as a model of salt-sensitive cardiac hypertrophy. Male, female ANP +/- mice and also ovariectomized female ANP +/- mice treated with oil or estrogen, were fed either a normal or high-salt diet. All four groups exhibited a general suppression of the renin-angiotensin system under the high salt challenge. However, after the 5-week treatment period, marked left ventricular hypertrophy was noted only in the male and oil-injected ovariectomized female ANP +/- mice treated with high salt. Collectively, we provide direct evidence that the differences in cardiac hypertrophy between genders in ANP +/- mice is attributed to estrogen. Furthermore, estrogen may play a key role in slowing down the progression of salt-induced left ventricular hypertrophy in ANP +/- mice, in part, independent of the classical systemic renin-angiotensin system and possibly through other pathways.

Effect of AT2 blockade on cardiac hypertrophy as induced by high dietary salt in the proatrial natriuretic peptide (ANP) gene-disrupted mouse

The role of the angiotensin II type 2 receptor (AT2) during alterations in cardiac size remains largely unclear. Through employment of an AT2 antagonist, the present study explored a possible involvement of the AT2 receptor during salt-induced cardiac hypertrophy in the proatrial natriuretic peptide gene-disrupted mouse (ANP-/-). ANP-/- mice received either saline solution or the AT2 antagonist, PD123319, and were then placed on a high salt diet (8.0% NaCl) for 3 weeks. Cardiac and pulmonary size, expression of the renin-angiotensin system (RAS), and the behaviour of various hypertrophy marker genes were assessed. PD123319 caused enhanced expression of the systemic RAS, yet the cardiac RAS was largely unaffected. Although AT2 blockade did not alter whole cardiac mass, right ventricle mass, as well as pulmonary mass-to-body mass ratios were significantly decreased. Collagen type I was decreased in the latter tissues, likely contributing to the regression in mass. Several players essential in the maintenance of myocardial extracellular matrix homeostasis including B-type natriuretic peptide, matrix metalloproteinase-2, tumour necrosis factor, and transforming growth factor were also significantly altered by PD123319. These data suggest that AT2 blockade is involved in significant changes in myocardial extracellular matrix components translating into decreases in tissue mass in the salt-sensitive ANP-/- animal.

Noncompensation in peptide/receptor gene expression and distinct behavioral phenotypes in VIP- and PACAP-deficient mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are closely related neurotrophic peptides of the secretin/glucagon family. The two peptides are derived from a common ancestral gene and share many functional attributes in neuronal development/regeneration which occur not only from overlapping receptor subtype signaling but also through common mechanisms regulating their expression. Although PACAP or VIP null mice have been generated for study, it is unclear whether the expression of the complementary peptide or their receptor systems are altered in a compensatory manner during nervous system development. By radioimmunoassay and quantitative PCR measurements, we first show that PACAP and VIP have very different temporal patterns of expression in developing postnatal mouse brain. In wild-type animals, PACAP transcript and peptide levels increased rapidly 2- and 5-fold, respectively, within 1 week of age. These levels at 1 week of age were maintained through adulthood. VIP transcript and peptide levels, by contrast, increased 25- and 50-fold, respectively, over a later time course. In parallel studies of development, there were no apparent compensatory increases in brain VIP expression in the PACAP knockout animals, PACAP expression in the VIP-deficient animals, or receptor mRNA levels in either genotype. To the contrary, there was evidence for developmental delays in the expression of peptide and receptor transcripts in the knockout animals. A series of behavioral and neurological tests demonstrated differences between the knockout genotypes, revealing some functional distinctions between the two genes. These results suggest that the PACAP and VIP have evolved to possess distinct biological activities and intimate that the respective knockout phenotypes represent deficits unmitigated by the actions of the complementary related peptide.

A potential role for the endothelin ETA receptor in salt-sensitive hypertension of the proANP gene-disrupted mouse

We have previously shown that the partial disruption of the gene for atrial natriuretic peptide (ANP) results in a salt-sensitive phenotype. The present study examined the possibility that alterations in either the ANP natriuretic pathway or endothelin (ET) system in the kidney of the salt-challenged ANP +/- mouse was responsible for its salt-sensitive phenotype. Plasma ANP levels and renal cGMP activity were increased in response to a salt load in both ANP +/+ and +/- mice. However, the mRNA expression of proANP was found to be increased only in the ANP +/- kidney along with its guanylyl cyclase-linked receptor, NPRA; the upregulation of NPRA mRNA was limited to the renal medulla. This suggests that the renal ANP pathway remains capable of responding to a salt load in the ANP +/- animal, but may be compensating for other dysfunctional pathways. We also report a significant increase in renal ET-1 mRNA and ETA receptor protein expression in medulla and cortex of the salt-treated, ANP +/- mouse, but not its wild-type counterpart. In fact, ETA expression decreased in the renal cortex of the ANP +/+ salt-treated animal. The ETB receptor expression was not affected by diet in either genotype. We hypothesize that the salt-sensitive hypertension in the ANP +/- mouse is exacerbated, and possibly driven by the vasoconstrictive effects resulting from an upregulated ET-1/ETA pathway.

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.

Risk assessment in patients with unstable angina/non-ST-elevation myocardial infarction and normal N-terminal pro-brain natriuretic peptide levels by N-terminal pro-atrial natriuretic peptide

AIMS

To compare the accuracy of the N-terminal fragment of its pro-hormone (Nt-proBNP) and N-terminal pro-atrial natriuretic peptide (Nt-proANP) in the prediction of the 2 year mortality and to investigate whether additional measurement of Nt-proANP to troponin I (TnI) could improve risk assessment in the subgroups of patients with unstable coronary artery disease (UCAD) and normal Nt-proBNP.

METHODS AND RESULTS

Plasma levels of the TnI, Nt-proANP, and Nt-proBNP were determined in 120 consecutive patients with UCAD without ST-segment elevations and normal left ventricular function. In multivariable logistic regression analysis, TnI and Nt-proBNP were independent predictors of mortality (P=0.01 and P=0.02, respectively). However, in the group of patients with normal Nt-proBNP levels, only Nt-proANP and TnI were independently associated with mortality (P=0.007 and P=0.03, respectively). Accordingly, patients with elevated Nt-proANP levels in this group of patients had significantly higher mortality rate than patients with normal Nt-proANP levels (P=0.003).

CONCLUSION

Our results suggest that determination of Nt-proANP might improve risk assessment in patients with UCAD, especially when Nt-proBNP is in the normal range.

Atrial Natriuretic Peptide Dose-Dependently Inhibits Pressure Overload-Induced Cardiac Remodeling

We hypothesized that a single copy of the proatrial natriuretic peptide gene ( Nppa +/− ) would not be adequate to protect heterozygous mice against exaggerated cardiac hypertrophy and remodeling after pressure-overload stress. Nppa +/+ , Nppa +/− , and Nppa −/− mice were subjected to sham surgery or transverse aortic constriction and fed a basal salt diet. Heart weight varied inversely with Nppa gene load by 1 week after either surgery. Fractional shortening did not differ among genotypes at baseline and fell in Nppa −/− mice only after transverse aortic constriction. There was a graded response in collagen deposition related to atrial natriuretic peptide (ANP) expression after either surgery. A robust interstitial and perivascular fibrosis was noted in Nppa −/− and Nppa +/− but not in Nppa +/+ mice after transverse aortic constriction. Our findings are consistent with a growing body of evidence that ANP is an important modulator of cardiac hypertrophy and remodeling in response to hemodynamic stress. The observation that partial ANP deficiency results in exaggerated hypertrophy and remodeling after pressure overload suggests that genetic or environmental variation in ANP levels may play a role in the development of cardiac hypertrophy, remodeling, and failure in humans.

Effects of pressure overload on extracellular matrix expression in the heart of the atrial natriuretic peptide-null mouse

This study tested the hypothesis that atrial natriuretic peptide has direct antihypertrophic actions on the heart by modulating expression of genes involved in cardiac hypertrophy and extracellular matrix production. Hearts of male, atrial natriuretic peptide-null and control wild-type mice that had been subjected to pressure overload after transverse aortic constriction and control unoperated hearts were weighed and subjected to microarray, Northern blot, and immunohistochemical analyses. Microarray and Northern blot analyses were used to identify genes that are regulated differentially in response to stress in the presence and absence of atrial natriuretic peptide. Immunohistochemical analysis was used to identify and localize expression of the protein products of these genes. Atrial natriuretic peptide-null mice demonstrated cardiac hypertrophy at baseline and an exaggerated hypertrophic response to transverse aortic constriction associated with increased expression of the extracellular matrix molecules periostin, osteopontin, collagen I and III, and thrombospondin, as well as the extracellular matrix regulatory proteins, matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-3, and the novel growth factor pleiotrophin compared with wild-type controls. These results support the hypothesis that atrial natriuretic peptide protects against pressure overload-induced cardiac hypertrophy and remodeling by negative modulation of genes involved in extracellular matrix deposition.

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.