Cardiac Atrial Natriuretic Peptide mRNA Research Articles

Abstract 19679: Mitochondrial Aldehyde Dehydrogenase 2 (ALDH2) Ameliorates Angiotensin II-Induced Cardiac Remodeling and Myocardial Dysfunction through Inhibition of Mitochondrial Oxidative Stress and Induction of Autophagy

Angiotensin II-induced cardiac damage is associated with oxidative stress, mitochondrial injury, cardiac remodeling and contractile dysfunction. ALDH2, a mitochondrial enzyme governing mitochondrial and cardiac function, displays distinct polymorphism and predisposes increased prevalence of hypertension. This study was designed to evaluate the role of ALDH2 in angiotensin II-induced myocardial remodeling and contractile dysfunction. Echocardiographic, cardiomyocyte contractile and intracellular Ca 2+ properties were examined in WT and ALDH2 transgenic mice with or without angiotensin II perfusion. Cardiac histology and autophagy, a process governing hypertrophy and oxidative stress, were evaluated. Myocardial contractile function and intracellular Ca 2+ handling were compromised in angiotensin II-perfused WT mice, the effects of which were significantly attenuated by ALDH2. H&E and Masson trichrome staining revealed cardiomyocyte hypertrophy and interstitial fibrosis associated with greater echocardiographic LV mass and wall thickness. ALDH2 ameliorated angiotensin II-induced cardiomyocyte hypertrophy, cardiac interstitial fibrosis, cardiomyocyte apoptosis, and cardiac atrial natriuretic peptide mRNA levels. The beneficial effect of ALDH2 was independent of blood pressure regulation and was linked to decreased ER stress, autophagy, and 5' AMP-activated protein kinase phosphorylation. Myocardial ER stress and autophagy were facilitated by angiotensin II associated with higher phosphorylation of AMPK. Mitochondria from angiotensin II perfused WT hearts showed clustered mitochondrial patterns, decreased numbers, and volume fractions but increased trans-sectional areas. All of these effects were reduced in ALDH2 mice. The ALDH2 activator Alda-1 ameliorated angiotensin II-induced mitochondrial injury and autophagy induction. Human study also revealed a positive correlation between high blood pressure prevalence and ALDH2 gene mutation. In summary, ALDH2 may provide a blood pressure-independent protection against angiotensin II-induced mitochondrial remodeling and cardiac contractile dysfunction, possibly through modulation of mitochondrial oxidative stress and autophagy induction.

Caloric Restriction Ameliorates Angiotensin II–Induced Mitochondrial Remodeling and Cardiac Hypertrophy

Angiotensin II-induced cardiac damage is associated with oxidative stress-dependent mitochondrial dysfunction. Caloric restriction (CR), a dietary regimen that increases mitochondrial activity and cellular stress resistance, could provide protection. We tested that hypothesis in double transgenic rats harboring human renin and angiotensinogen genes (dTGRs). CR (60% of energy intake for 4 weeks) decreased mortality in dTGRs. CR ameliorated angiotensin II-induced cardiomyocyte hypertrophy, vascular inflammation, cardiac damage and fibrosis, cardiomyocyte apoptosis, and cardiac atrial natriuretic peptide mRNA overexpression. The effects were blood pressure independent and were linked to increased endoplasmic reticulum stress, autophagy, serum adiponectin level, and 5' AMP-activated protein kinase phosphorylation. CR decreased cardiac p38 phosphorylation, nitrotyrosine expression, and serum insulin-like growth factor 1 levels. Mitochondria from dTGR hearts showed clustered mitochondrial patterns, decreased numbers, and volume fractions but increased trans-sectional areas. All of these effects were reduced in CR dTGRs. Mitochondrial proteomic profiling identified 43 dTGR proteins and 42 Sprague-Dawley proteins, of which 29 proteins were in common in response to CR. We identified 7 proteins in CR dTGRs that were not found in control dTGRs. In contrast, 6 mitochondrial proteins were identified from dTGRs that were not detected in any other group. Gene ontology annotations with the Panther protein classification system revealed downregulation of cytoskeletal proteins and enzyme modulators and upregulation of oxidoreductase activity in dTGRs. CR provides powerful, blood pressure-independent, protection against angiotensin II-induced mitochondrial remodeling and cardiac hypertrophy. The findings support the notion of modulating cardiac bioenergetics to ameliorate angiotensin II-induced cardiovascular complications.

Natriuretic peptide system: A link between fat mass and cardiac hypertrophy and hypertension in fat-fed female rats

The present study was designed to develop an animal model of hypertension and cardiac hypertrophy associated with obesity in female rats. Furthermore, we studied the involvement of the natriuretic peptide system in the mechanisms of these conditions. Obesity was induced in Wistar rats by a high fat diet and ovariectomy. The rats were divided into four groups: ovariectomized or sham-operated with high-fat diet and ovariectomized or sham-operated with control diet. After 24weeks of diet, rats were killed, and their tissues were removed. Cardiac atrial natriuretic peptide (ANP), clearance receptor (NPr-C) gene expression was determined by PCR. ANP concentrations were measured in plasma. Ovariectomized fat-fed rats (OF) showed increased body weight, visceral fat depot and blood pressure and decreased sodium excretion compared to other groups. Also, these rats showed higher heart-to-body weight and cell diameters of ventricular cardiomyocytes and lower cardiac ANP mRNA and plasma ANP than the control group. The adipocyte and renal NPr-C mRNA of OF rats were higher than the control group. These data showed that combined ovariectomy and high fat diet elicited obesity, hypertension and cardiac hypertrophy. These results suggest that the impairment of the natriuretic peptide system may be one of the mechanisms involved not only in development of hypertension but also in cardiac hypertrophy associated with obesity in ovariectomized rats.

Levosimendan improves cardiac function and survival in rats with angiotensin II-induced hypertensive heart failure

Calcium-sensitizing agents improve cardiac function in acute heart failure; however, their long-term effects on cardiovascular mortality are unknown. We tested the hypothesis that levosimendan, an inodilator that acts through calcium sensitization, opening of ATP-dependent potassium channels and phosphodiesterase III inhibition, improves cardiac function and survival in double transgenic rats harboring human renin and angiotensinogen genes (dTGRs), a model of angiotensin II (Ang II)-induced hypertensive heart failure. Levosimendan (1 mg kg(-1)) was administered orally to 4-week-old dTGRs and normotensive Sprague-Dawley rats for 4 weeks. Untreated dTGRs developed severe hypertension, cardiac hypertrophy, heart failure with impaired diastolic relaxation, and exhibited a high mortality rate at the age of 8 weeks. Levosimendan did not decrease blood pressure and did not prevent cardiac hypertrophy. However, levosimendan improved systolic function, decreased cardiac atrial natriuretic peptide mRNA expression, ameliorated Ang II-induced cardiac damage and decreased mortality. Levosimendan did not correct Ang II-induced diastolic dysfunction and did not influence heart rate. In a separate survival study, levosimendan increased dTGR survival by 58% and median survival time by 27% (P=0.004). Our findings suggest that levosimendan ameliorates Ang II-induced hypertensive heart failure and reduces mortality. The results also support the notion that the effects of levosimendan in dTGRs are mediated by blood pressure-independent mechanisms and include improved systolic function and amelioration of Ang II-induced coronary and cardiomyocyte damage.

The effect of water deprivation on the expression of atrial natriuretic peptide and its receptors in the spinifex hopping mouse, Notomys alexis

This study investigated the mRNA expression of the atrial natriuretic peptide (ANP) system (peptide and receptors) during water deprivation in the spinifex hopping mouse, Notomys alexis, a native of central and western Australia that is well adapted to survive in arid environments. Initially, ANP, NPR-A and NPR-C cDNAs (partial for receptors) were cloned and sequenced, and were shown to have high homology with those of rat and mouse. Using a semi-quantitative multiplex PCR technique, the expression of cardiac ANP mRNA and renal ANP, NPR-A, and NPR-C mRNA was determined in 7- and 14-day water-deprived hopping mice, in parallel with control mice (access to water). The levels of ANP mRNA expression in the heart remained unchanged, but in the kidney ANP mRNA levels were increased in the 7-day water-deprived mice, and were significantly decreased in the 14-day water-deprived mice. NPR-A mRNA levels were significantly higher in 7-day water-deprived mice while no change for NPR-A mRNA expression was observed in 14-day water-deprived mice. No variation in NPR-C mRNA levels was observed. This study shows that water deprivation differentially affects the expression of the ANP system, and that renal ANP expression is more important than cardiac ANP in the physiological adjustment to water deprivation.

Increase in G(i alpha) protein accompanies progression of post-infarction remodeling in hypertensive cardiomyopathy.

Hypertensive cardiac hypertrophy and myocardial infarction (MI) are clinically relevant risk factors for heart failure. There is no specific information addressing signaling alterations in the sequence of hypertrophy and post-MI remodeling. To investigate alterations in beta-adrenergic receptor G-protein signaling in ventricular remodeling with pre-existing hypertrophy, MI was induced by coronary artery ligation in Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Ten weeks after the induction of MI, the progression of left ventricular dysfunction and increases in plasma atrial natriuretic peptide (ANP) and cardiac ANP mRNA were more pronounced in SHR than WKY. In addition, the impaired contractile response to beta-adrenergic stimulation was observed in the noninfarcted papillary muscle isolated from SHR. Immunochemical G(s alpha) protein and beta-adrenoceptor density were not significantly altered by MI in both strains. However, immunochemical G(i alpha) was increased (1.5-fold) in the noninfarcted left ventricle of the SHR in which infarction had been induced when compared with that in SHR that underwent sham operation. This increase was observed especially in rats with a high plasma ANP level. Furthermore, there was a positive correlation between G(i alpha) and the extent of post-MI remodeling in WKY. A similar correlation between G(i alpha) and the extent of hypertensive hypertrophy was observed in SHR. In conclusion, the vulnerability of hypertrophied hearts to ischemic damage is greater than that of normotensive hearts. An increase in G(i alpha) could be one mechanism involved in the transition from cardiac hypertrophy to cardiac failure when chronic pressure overload and loss of contractile mass from ischemic heart disease coexist.

Influence of salt intake on atrial natriuretic peptide gene expression in rats.

Mammalian atrial cardiocytes produce and secrete a peptide hormone called atrial natriuretic peptide (ANP), which causes diuresis, natriuresis, a decrease of blood pressure and inhibition of smooth muscle contraction, renin and aldosterone release. Despite a variety of investigations, the influence of salt intake on the transcriptional regulation and the circulating levels of ANP is still not clear. This study sought to examine the influence of different levels of long-term dietary salt intake on the expression of the ANP gene in different regions of the rat heart. To this end male Sprague-Dawley rats were fed either a high-salt (4% saline chow) or a low-salt (0.02% saline chow) diet for 5, 10 or 20 days. Another group had access to normal chow and received 1% NaC1 as a drinking solution for 10 days. During the experiment sodium and chloride uptake via food or drinking solutions was monitored and sodium and chloride excreted in the urine was determined. ANP mRNA levels in the atria and the ventricles were assayed. We found that no form of the different salt diets had influence on cardiac ANP mRNA levels at any of the times examined though excretion rates of sodium and chloride differed by a factor of 200. Also plasma immunoreactive ANP remained unaltered. At the same time plasma renin activities were markedly increased in rats fed a low-salt diet and substantially suppressed in rats fed a high-salt diet, suggesting the efficacy of the salt diet. Our findings suggest that ANP gene expression and secretion of the active hormone are probably not involved in salt balance during chronic salt loading given by dietary food or by 1% NaCl in the drinking water.

Effect of Angiotensin II Blockade on the Fibroproliferative Response to Phenylephrine in the Rat Heart

In this study we infused phenylephrine into adult Wistar rats and used losartan to test for a possible role of angiotensin II in the phenylephrine-induced fibrosis. Phenylephrine, given by Alzet minipumps at a rate of 25 mg.kg-1.d-1, produced a rapid and striking fibrotic response that was obvious after 1 day and progressed throughout a 3-day infusion period. Northern and Western blot analyses showed large increases in cardiac fibronectin expression and atrial natriuretic peptide mRNA, corresponding to fibroblast proliferation and myocyte hypertrophy, respectively. Cardiac fibrosis, fibronectin mRNA, and atrial natriuretic peptide mRNA were blocked by prazosin (7 mg.kg-1.d-1). Administration of losartan (10 mg.kg-1.d-1) resulted in a threefold decrease in interstitial and perivascular fibroblast proliferation, as measured by proliferating cell nuclear antigen immunoreactivity (p < .05), a marked reduction of fibronectin mRNA in the heart, and a moderate reduction of cardiac atrial natriuretic peptide mRNA. The data suggest that effects mediated by a1-adrenergic and angiotensin type 1 receptors may promote cardiac fibrosis.

Atrial natriuretic peptide mRNA is regulated by glucocorticoids invivo

In these studies glucocorticoids were found to increase the plasma levels of atrial natriuretic peptide (ANP) as well as the expression of the ANP gene in the Sprague-Dawley rat. Plasma ANP rose two-fold after 48 hrs. of exposure to dexamethasone (1 mg/day) in both intact and adrenalectomized animals. This was accompanied by a 1.5-2.0 fold increase in the levels of atrial and ventricular ANP transcripts. Deoxycorticosterone acetate (5 mg/day), administered on the same schedule, failed to increase either plasma ANP levels or cardiac ANP mRNA accumulation. These effects suggest that ANP may have a potential role as a mediator of glucocorticoid activity in the cardiovascular system and support the hypothesis that ANP is a glucocorticoid-regulated gene.