Atrial Natriuretic Peptide mRNA Research Articles

Ventricular expression of natriuretic peptides in Npr1(-/-) mice with cardiac hypertrophy and fibrosis.

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones that regulate blood pressure and volume, and exert their biological actions via the natriuretic peptide receptor-A gene (Npr1). Mice lacking Npr1 (Npr(-/-)) have marked cardiac hypertrophy and fibrosis disproportionate to their increased blood pressure. This study examined the relationships between ANP and BNP gene expression, immunoreactivity and fibrosis in cardiac tissue, circulating ANP levels, and ANP and BNP mRNA during embryogenesis in Npr1(-/-) mice. Disruption of the Npr1 signaling pathway resulted in augmented ANP and BNP gene and ANP protein expression in the cardiac ventricles, most pronounced for ANP mRNA in females [414 +/- 57 in Npr1(-/-) ng/mg and 124 +/- 25 ng/mg in wild-type (WT) by Taqman assay, P < 0.001]. This increased expression was highly correlated to the degree of cardiac hypertrophy and was localized to the left ventricle (LV) inner free wall and to areas of ventricular fibrosis. In contrast, plasma ANP was significantly greater than WT in male but not female Npr1(-/-) mice. Increased ANP and BNP gene expression was observed in Npr1(-/-) embryos from 16 days of gestation. Our study suggests that cardiac ventricular expression of ANP and BNP is more closely associated with local hypertrophy and fibrosis than either systemic blood pressure or circulating ANP levels.

Differential regulation of atrial and brain natriuretic peptides and its implications for the management of left ventricular volume overload.

In this study, we investigated the possibility that the atrial and brain natriuretic peptide expression in left ventricular volume overload (VOL) is transcriptionally regulated. We further evaluated the diagnostic and/or prognostic potential of this expression for the management of patients with this disorder. We compared the myocardial mRNA expression and plasma levels of the two peptides in VOL patients using donor hearts and in healthy blood donors as controls. The atrial natriuretic peptide (ANP) mRNA was elevated by 38% (P < 0.03) in the right atrium and by 53% (P < 0.003) in the left atrium, but was unchanged in the ventricular chambers of the patient group (n = 19) compared with controls (n = 8). Plasma ANP concentration was elevated by 62% (P < 0.001) compared with blood donor controls (n = 79). It increased slightly (by 36%) 2 h following surgery, and remained at 64% higher (P < 0.03 vs. presurgery) for the 5 days following surgery. The brain natriuretic peptide (BNP) mRNA was elevated by approximately one-fold in both the left ventricle (P < 0.02) and right atrium (P < 0.05), by 94% (P < 0.02) in the right ventricle and by 89% (P < 0.05) in the left atrium. Its plasma level in the patients was 3.4-fold (P < 0.00003) higher than in control subjects. It increased significantly by 1.2-fold (P < 0.01) 2 h following surgery, but dropped significantly (P < 0.05 vs. 2 h post surgery) to presurgical levels 5 days following surgery. The results show chamber-specific elevation in both atrial and brain natriuretic peptide expression and differences in their circulating levels in VOL, suggesting that BNP is a potential prognostic indicator in the postsurgical management of these patients.

Oxytocin induces differentiation of P19 embryonic stem cells to cardiomyocytes.

We recently discovered the existence of the oxytocin/oxytocin receptor (OT/OTR) system in the heart. Activation of cardiac OTR stimulates the release of atrial natriuretic peptide (ANP), which is involved in regulation of blood pressure and cell growth. Having observed elevated OT levels in the fetal and newborn heart at a stage of intense cardiomyocyte hyperplasia, we hypothesized a role for OT in cardiomyocyte differentiation. We used mouse P19 embryonic stem cells to substantiate this potential role. P19 cells give rise to the formation of cell derivatives of all germ layers. Treatment of P19 cell aggregates with dimethyl sulfoxide (DMSO) induces differentiation to cardiomyocytes. In this work, P19 cells were allowed to aggregate from day 0 to day 4 in the presence of 0.5% DMSO, 10(-7) M OT and/or 10(-7) M OT antagonist (OTA), and then cultured in the absence of these factors until day 14. OT alone stimulated the production of beating cell colonies in all 24 independently growing cultures by day 8 of the differentiation protocol, whereas the same result was obtained in cells induced by DMSO only after 12 days. Cells induced with OT exhibited increased ANP mRNA, had abundant mitochondria (i.e., they strongly absorbed rhodamine 123), and expressed sarcomeric myosin heavy chain and dihydropyridine receptor-alpha 1, confirming a cardiomyocyte phenotype. In addition, OT as well as DMSO increased OTR protein and OTR mRNA, and OTA completely inhibited the formation of cardiomyocytes in OT- and DMSO-supplemented cultures. These results suggest that the OT/OTR system plays an important role in cardiogenesis by promoting cardiomyocyte differentiation.

Caffeine decreases the expression of Na+/K+-ATPase and the type 3 Na+/H+ exchanger in rat kidney.

1. The aim of the present study was to explore the mechanisms underlying the renal effects of caffeine. 2. Male Sprague-Dawley rats were treated with caffeine, consisting of a single oral bolus (0.2%, 20 mL/kg) followed by supplementation in drinking water (0.2%) for 1 day. Rats treated the same but given water without caffeine served as controls. 3. The expression of alpha1- and beta1-subunits of Na+/K+-ATPase, the type 3 Na+/H+ exchanger (NHE3) and aquaporin-1 was determined in the kidney by western blot analysis. 4. To explore possible involvement of local humoral mediators, the tissue expression of nitric oxide synthase (NOS) proteins was determined by western blot analysis and the expression of atrial natriuretic peptide (ANP) mRNA was determined by semiquantitative reverse transcription-polymerase chain reaction. 5. Following treatment with caffeine, the expression of alpha1- and beta1-subunits of Na+/K+-ATPase, as well as that of NHE3, was decreased. Accordingly, the catalytic activity of Na+/K+-ATPase was decreased. In contrast, the expression of aquaporin-1 was not altered significantly. 6. The expression of the endothelial isoform of NOS was increased, along with tissue nitrite/nitrate levels. The expression of ANP mRNA was increased. 7. It is suggested that caffeine decreases Na+/K+-ATPase and NHE3 activities and increases nitric oxide and ANP activities in the kidney.

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.

Calcineurin inhibition attenuates mineralocorticoid-induced cardiac hypertrophy.

It remains unclear how mineralocorticoids induce cardiac hypertrophy and fibrosis. Recently, activation of the calcium-dependent phosphatase, calcineurin, has been shown to induce cardiac hypertrophy. In the present study, we examine the role of calcineurin in mineralocorticoid-induced cardiac hypertrophy and fibrosis. Uninephrectomized Wistar-Kyoto rats were placed on a 1.0% NaCl diet and treated with aldosterone (0.75 microg x h(-1)) for 6 weeks with or without the calcineurin inhibitors, FK506 (0.5 mg x kg(-1) x d(-1)) or cyclosporine A (10 mg x kg(-1) x d(-1)). The effect of the angiotensin II type 1 receptor antagonist, losartan (10 mg x kg(-1) x d(-1))on aldosterone-induced cardiac hypertrophy was also studied. Treatment with aldosterone increased the heart weight/body weight ratio, cardiomyocyte size, and collagen amount. The expression of mRNA of both type-III collagen and atrial natriuretic peptide in the heart were increased by aldosterone administration. Both calcineurin activity and its mRNA expression were also increased in aldosterone-induced hypertrophic heart. Treatment with losartan, FK506, or cyclosporine partially prevented aldosterone-induced cardiac hypertrophy and fibrosis. These results suggest that calcineurin is involved in the development of cardiac hypertrophy and fibrosis induced by mineralocorticoid excess. Inhibition of calcineurin may therefore prevent cardiac hypertrophy and fibrosis in mineralocorticoid hypertension.

Genomic sequence and cardiac expression of atrial natriuretic peptide in cats.

To determine the nucleotide and amino acid sequence of atrial natriuretic peptide (ANP) in cats and its typical regions of cardiac expression. 5 healthy adult mixed-breed cats. 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. 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. 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.

Effects of brain mineralocorticoid receptor blockade on blood pressure and renal functions in DOCA–salt hypertension

In normotensive rats, we have previously demonstrated a role of brain mineralocorticoid receptors in blood pressure and renal function control. In the present study, the coordinate cardiovascular and renal effects of brain mineralocorticoid receptor blockade were examined by intracerebroventricular (i.c.v.) administration of a selective mineralocorticoid receptor antagonist (RU28318; 3,3-oxo-7 propyl-17-hydroxy-androstan-4-en-17yl-propionic acid lactone) in rats with hypertension induced by deoxycorticosterone acetate (DOCA) and salt. DOCA pellets were implanted s.c. in male Wistar rats given 0.9% NaCl as drinking solution 3 or 5 weeks before assessment of the effects of i.c.v. injection of RU28318 on cardiovascular and renal functions. Changes in expression of brain angiotensinogen, atrial natriuretic peptide (ANP) and mineralocorticoid receptor mRNA in specific brain areas in 3-week DOCA–salt rats were evaluated by in situ hybridization. The rise in systolic blood pressure induced by DOCA–salt treatment was most marked during the first 3 weeks. At 3 and 5 weeks after implantation of the DOCA-pellets a single i.c.v. injection of 10 ng of RU28318 significantly decreased systolic blood pressure during 24 h as assessed at 2, 8 and 24 h, while heart rate was not altered. Increased urinary excretion of water and electrolytes was observed in 3- and 5-week DOCA–salt rats during the period 0–8 h after i.c.v. injection of RU28318 while the suppressed plasma renin activity was not affected. The expression of brain angiotensinogen, ANP and mineralocorticoid receptor mRNA was not altered by 3-week DOCA–salt treatment, but 3 h after i.c.v. injection of RU28318, mineralocorticoid receptor mRNA expression in hippocampal cell fields responded with an increase of about 40%. In conclusion, these results demonstrate that in rats with hypertension induced by DOCA–salt, brain mineralocorticoid receptor blockade affects renal function and blood pressure regulation.

Radiation-induced changes in gene expression and distribution of atrial natriuretic peptide (ANP) in different anatomical regions of the rat heart

Purpose : To examine the effects of whole-heart irradiation on gene expression and distribution of atrial natriuretic peptide (ANP) in atrial appendages and left ventricles of the rat heart. Material and methods : Female Sprague-Dawley rats were irradiated with a single dose of 0, 15 or 20 Gy locally to the heart. At intervals up to 16 months post-irradiation, the localization of ANP was examined using immunohistochemical techniques. Absolute mRNA concentrations were determined using the competitive PCR assay. Results : Histological and immunohistochemical studies demonstrated that whole-heart irradiation caused a reduction of atrial ANP, which is due to a substantial loss of ANP-producing atrial myocytes and accumulation of collagen (replacement fibrosis). On the other hand, ANP became detectable in the subendocardium of the irradiated left ventricles. Positive staining of ANP was mainly found in the proximity of injured areas consisting of degeneration of myocytes and fibrosis. At the transcriptional level, reduction of atrial ANP expression at 1 month post-irradiation was followed by recovery at 3 months. Thereafter, ANP mRNA concentrations followed the mRNA pattern of controls and even appeared to increase at 16 months. In the left ventricle, dose-dependent and progressive elevation of ANP gene expression could be observed during the observation period and reached a 20-fold increase as compared with sham-irradiated age-matched controls. Conclusions : The distribution of ANP after local irradiation of the rat heart depends on the severity of the pathological/structural changes (i.e. myocyte degeneration and fibrosis). In radiation-induced heart disease, elevated ANP expression in the left ventricle is most probably involved in the observed chronic elevation of plasma ANP levels.

Overexpression of endothelial nitric oxide synthase attenuates cardiac hypertrophy induced by chronic isoproterenol infusion.

Endogenous nitric oxide (NO) inhibits the contractile response to beta-adrenergic stimulation, but its effect on cardiac hypertrophy mediated by beta-adrenoceptors remains unclear. The present study was designed to determine whether overproduction of endothelial NO synthase (eNOS) could inhibit cardiac hypertrophy induced by chronic isoproterenol (ISO) infusion (30mg/kg per day) using eNOS overexpressing (eNOS-Tg) mice and wild-type (WT) mice. In a separate group, WT mice were treated with ISO and hydralazine to decrease blood pressure to the same levels in eNOS-Tg mice. The eNOS expression, NOS activity, and cGMP levels in the heart were remarkably higher in eNOS-Tg mice than in WT mice. ISO increased both heart weight and the heart/body weight ratio, which were significantly attenuated in eNOS-Tg mice compared with WT or hydralazine-treated WT mice. Histological examination revealed that the extent of fibrosis was not significantly different among the 3 groups, and that the increase in myocyte size was more than 10% lower in eNOS-Tg than in the other groups. In addition, up-regulated expression of atrial natriuretic peptide mRNA associated with cardiac hypertrophy was significantly inhibited in eNOS-Tg mice during ISO infusion. These results indicate that endogenous NO might act as a negative modulator for the hypertrophic response to beta-adrenergic stimulation.

Cardiac gene expression and synthesis of atrial natriuretic peptide in the nitrofen model of congenital diaphragmatic hernia in rats: Effect of prenatal dexamethazone treatment

Background/Purpose: The aim of this study was to determine the gene and protein levels of atrial natriuretic peptide (ANP) in the heart of nitrofen-induced congenital diaphragmatic hernia (CDH) in rats and to evaluate the effect of antenatal dexamethazone (Dex) treatment. Methods: CDH model was induced in pregnant rats after administration of 100 mg of nitrofen on day 9.5 of gestation (term, day 22). Dexamethazone (Dex, 0.25 mg/kg) was given by intaperitoneal injection on days 18.5 and 19.5 of gestation. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 3 groups: group I, control (n = 10); group II, nitrofen-induced CDH (n = 10); group III, nitrofen-induced CDH with antenatal Dex treatment (n = 10). ANP protein was measured using enzyme-linked immunosorbent assay (ELISA) technique. Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of atrial natriuretic peptide (ANP) mRNA expression. Results: There was a significant reduction in ANP mRNA (P < .05) and protein (P < .01) levels in heart of group II (CDH) compared with group I. Antenatal Dex treatment significantly increased both ANP mRNA and protein levels in the heart of CDH animals (P < .05). Conclusions: The reduced cardiac ANP gene expression and ANP synthesis indicates that the heart in CDH is functionally immature and may be unable to respond to hemodynamic load accompanying persistent pulmonary hypertension (PPH). ANP or drugs such as steroids, which raise endogenous ANP levels, may have a therapeutic application in CDH complicated by PPH. J Pediatr Surg 36:1497-1501. Copyright © 2001 by W.B. Saunders Company.

Ventricular production of natriuretic peptides and ventricular structural remodeling in hypertensive heart failure.

Brain natriuretic peptide (BNP) is a strong predictor of left ventricular (LV) hypertrophy (LVH) and dysfunction. However, our recent studies suggested that LVH is not necessarily associated with enhanced production of BNP in hypertension. This study aimed to clarify the relation of the characteristics of hypertrophy with the degree of gene expression of BNP in the developmental process of hypertensive heart failure. Serial changes in LV geometry, histology and atrial natriuretic peptide (ANP) and BNP mRNA levels, were assessed in a hypertensive heart failure model using Dahl salt-sensitive rats (n = 24). We further studied effects of alpha1-receptor antagonist (doxazosin: 1 mg/kg per day, n = 5) and angiotensin II type 1 receptor (AT1R) antagonist (candesartan cilexetil: 1 mg/kg per day, n = 5). The BNP mRNA level was not elevated at the compensatory hypertrophic stage when ANP mRNA level was elevated. BNP mRNA level was increased with further progression of hypertrophy and development of fibrosis. AT1R blockade prevented such fibrosis and further progression of hypertrophy with normalization of BNP mRNA levels. Compensatory hypertrophy was not suppressed; therefore, ANP mRNA level, although decreased, was still beyond the normal level. The alpha1-receptor blockade slightly attenuated LV hypertrophy with a slight decrease in ANP mRNA levels. LV fibrosis was not prevented, and the BNP mRNA level was not decreased. BNP gene expression is not enhanced by initial compensatory hypertrophy, but is enhanced by LV fibrosis and late stage progression of hypertrophy dependent on AT1R-mediated signaling pathway.

Reduced oxygen tension increases atrial natriuretic peptide release from atrial cardiocytes.

To test the hypothesis that reduced oxygen tension stimulates cardiac atrial natriuretic peptide (ANP) secretion, we measured ANP release and expression in neonatal rat atrial and ventricular cardiac myocytes exposed to 45 min and 3, 6, and 24 hr of 3% or 21% oxygen. In atrial cardiocytes, the percentage of increase in culture media ANP concentration from baseline was greater in cells exposed to 3% than in cells exposed to 21% oxygen after 3 hr (814% +/- 52% vs. 567% +/- 33%, P < 0.05) and 6 hr of exposure (1639% +/- 91% vs. 1155% +/- 73%, P < 0.05). No differences in the percentage of increase in culture media ANP concentration was seen at 45 min (284% +/- 27% vs. 201% +/- 16%, P = NS) or 24 hr (2499% +/- 250% vs. 2426% +/- 195%). There was a significant increase in cellular ANP content between 3 and 24 hr in atrial cardiocytes exposed to 21% oxygen (105% +/- 40% vs. 296% +/- 60%, P < 0.05), but not in atrial cardiocytes exposed to 3% oxygen (118% +/- 20% vs. 180% +/- 26%, P = NS). Steady-state ANP mRNA levels in atrial cardiocytes were not affected by oxygen tension. In ventricular cardiocytes, oxygen tension did not affect ANP secretion, cellular ANP content, or steady-state ANP mRNA levels. We conclude that reduced oxygen tension increases release of ANP from atrial, but not ventricular cardiocytes and that this mechanism may contribute to the elevation in plasma ANP seen during acute hypoxia.

Factors derived from adrenals are required for activation of cardiac gene expression in angiotensin II-induced hypertension.

The mechanisms mediating the activation of cardiac gene expression during pressure overload are not fully understood. We examined whether angiotensin II-induced activation of ventricular gene expression is related to blood pressure and ventricular mass or requires other factors by infusing angiotensin II in sham-operated and adrenalectomized rats. In sham-operated rats, angiotensin II (33 microg/kg x h, sc) produced a significant increase in mean arterial pressure (measured by telemetry) within 3 h. Mean arterial pressure (up to 45 h) and the increase in left ventricular hypertrophy in adrenalectomized rats during angiotensin II infusion were similar to those in sham-operated rats. Angiotensin II produced 3.6-fold (P < 0.01) and 20.4-fold (P < 0.001) increases in ventricular atrial natriuretic peptide mRNA levels at 12 and 72 h, respectively. Angiotensin II infusion for 12 h also significantly increased the ventricular mRNA levels of B-type natriuretic peptide (5.2-fold) and adrenomedullin (1.4-fold). Adrenalectomy either abolished (atrial natriuretic peptide and adrenomedullin) or blunted (B-type natriuretic peptide) the early activation of ventricular gene expression by angiotensin II. The baseline synthesis of atrial natriuretic peptide, B-type natriuretic peptide, and adrenomedullin in the ventricle remained unchanged in adrenalectomized rats. In conclusion, our results indicate that factors derived from the adrenals are required for angiotensin II-induced early activation of cardiac gene expression.

Myocardial adrenergic dysfunction in rats with transgenic, human renin-dependent hypertension.

We investigated cardiac function in rats transgenic for the human renin and angiotensinogen genes (TGR) to test the hypothesis that elevated local angiotensin II precipitates adrenergic dysfunction and abnormal contractile function. Hearts from TGR and Sprague-Dawley control rats, aged 6 weeks, were studied using the Langendorff model and papillary muscle preparations (n = 6-10 per group). Incremental isoproterenol (1 - 1000 nmol/l) and external Ca2+-concentrations (0.75-6.0 mmol/l) were tested. Cardiac protein and mRNA expression levels were determined by Western blot and RNAase protection assay. TGR rats showed left ventricular hypertrophy (54%), higher blood pressures (76 mmHg), and elevated plasma renin activity (seven-fold) compared to controls (P < 0.01). The effect of isoproterenol on TGR rat systolic and diastolic left ventricular performance was decreased in both in-vitro models compared to controls (two- to threefold, P < 0.01). TGR rat papillary muscles showed impaired force generation with abnormal basal and Ca2+-dependent relaxation. Gialpha2 and Gialpha3 protein levels were increased (20-30%) and SERCA2a and adenylyl cyclase protein levels were decreased (23 and 37%, respectively) in TGR hearts compared to controls, while Gsalpha or beta1 and beta2-receptor levels were unchanged. Cardiac angiotensin converting enzyme and atrial natriuretic peptide mRNA levels were increased more than four-fold in TGR with no differences for the angiotensin type1 receptor, beta1-receptor, SERCA2a, phospholamban, adenylyl cyclase V and angiotensinogen genes. TGR rat hearts develop severe adrenergic dysfunction with decreased adenylyl cyclase and abnormal intracellular Ca2+-homeostasis. Our findings emphasize angiotensin II as a major risk factor promoting early functional decline in cardiac hypertrophy. The data may have implications for patients with activating polymorphisms of the renin-angiotensin system and support the need for an early therapeutic intervention.

Increased expression of atrial natriuretic peptide in the kidney of rats with bilateral ureteral obstruction

Whether the postobstructive diuresis can be related to an altered regulation of local atrial natriuretic peptide (ANP) in the kidney was investigated. Three groups of rats had both of their ureters obstructed for 48 hours. The kidneys were taken without releasing the obstruction in one group [bilateral ureteral obstruction (BUO)]. The obstruction was released in the other two groups and the animals were kept for 4 and 24 hours thereafter to collect urinary data (BUR-4 and BUR-24, respectively). Plasma and urine ANP levels were measured by radioimmunoassay. The mRNA expression of ANP, natriuretic peptide receptor-A (NPR-A), and NPR-C was determined by reverse transcription-polymerase chain reaction. ANP receptors were also quantitated by in vitro autoradiography. The activity of guanylyl cyclase was determined by the amount of cGMP generated in response to ANP. Urinary volume and sodium excretion increased in BUR-4, along with the ANP mRNA expression in the kidney and the urinary ANP excretion. The ANP excretion positively correlated with the urinary volume and sodium excretion. The mRNA expression of both NPR-A and NPR-C was decreased by BUO, the latter being far more prominently affected. The maximal binding capacity of radiolabeled ANP was decreased in the glomerulus and papilla in BUO. Not only the urinary parameters but also the mRNA expression of ANP, NPR-A, and NPR-C were comparable between BUR-24 and control rats. ANP-stimulated cGMP generation was reduced in the glomerulus and papilla in BUO animals, which was rapidly resumed following the release of the obstruction. Postobstructive diuresis may be due partially to an increased ANP activity in the kidney.

A genetic model provides evidence that the receptor for atrial natriuretic peptide (guanylyl cyclase-A) inhibits cardiac ventricular myocyte hypertrophy.

Guanylyl cyclase-A (NPR-A; GC-A) is the major and possibly the only receptor for atrial natriuretic peptide (ANP) or B-type natriuretic peptide. Although mice deficient in GC-A display an elevated blood pressure, the resultant cardiac hypertrophy is much greater than in other mouse models of hypertension. Here we overproduce GC-A in the cardiac myocytes of wild-type or GC-A null animals. Introduction of the GC-A transgene did not alter blood pressure or heart rate as a function of genotype. Cardiac myocyte size was larger (approximately 20%) in GC-A null than in wild-type animals. However, introduction of the GC-A transgene reduced cardiac myocyte size in both wild-type and null mice. Coincident with the reduction in myocyte size, both ANP mRNA and ANP content were significantly reduced by overexpression of GC-A, and this reduction was independent of genotype. This genetic model, therefore, separates a regulation of cardiac myocyte size by blood pressure from local regulation by a GC-mediated pathway.

Effects of combination of ACE inhibitor and angiotensin receptor blocker on cardiac remodeling, cardiac function, and survival in rat heart failure.

The mechanism and treatment of diastolic heart failure are poorly understood. We compared the effects of an ACE inhibitor, an angiotensin receptor blocker (ARB), and their combination on diastolic heart failure in Dahl salt-sensitive (DS) rats. DS rats fed an 8% NaCl diet from 7 weeks of age were treated with benazepril 10 mg/kg alone, valsartan 30 mg/kg alone, or combined benazepril and valsartan at 5 and 15 mg/kg, respectively, or at 1 and 3 mg/kg, respectively. At 16 weeks of age, DS rats exhibited prominent concentric left ventricular (LV) hypertrophy and diastolic dysfunction with preserved systolic function, as estimated by echocardiography. Despite comparable hypotensive effects among all drug treatments, the combination of benazepril 5 mg/kg and valsartan 15 mg/kg improved diastolic dysfunction and survival in DS rats more effectively than ACE inhibitor or ARB alone. Furthermore, the increase in LV endothelin-1 levels and hydroxyproline contents in DS rats was significantly suppressed only by combined benazepril and valsartan, and LV atrial natriuretic peptide mRNA upregulation in DS rats was suppressed to a greater extent by the combination therapy than monotherapy. The combination of ACE inhibitor and ARB, independently of the hypotensive effect, improved LV phenotypic change and increased LV endothelin-1 production and collagen accumulation, diastolic dysfunction, and survival in a rat heart failure model more effectively than either agent alone, thereby providing solid experimental evidence that the combination of these 2 agents is more beneficial than monotherapy for treatment of heart failure.

Occurrence and distribution of atrial natriuretic peptide-containing cells in the left ventricle of hypertensive rats. Effect of antihypertensive treatment.

In the ventricles of adult mammalian hearts, production of atrial natriuretic peptide (ANP) is negligible, restricted to the impulse-conducting cells, the papillary muscles, and a minority of subendocardial myocytes. ANP expression is reinduced in the ventricles of pressure-overloaded and failing hearts and is frequently used as a marker for myocyte hypertrophy. Using an immunohistochemical approach, we have characterized the size distribution of ANP-containing myocytes in the left ventricle of the spontaneously hypertensive rat (SHR) before and after chronic antihypertensive therapy and compared the results to age-matched normotensive Wistar rats (WR). Our findings show that in SHR the frequency of cells presenting ANP granularity is positively correlated with myocyte size (r=0.746, P<0.02). The highest proportion of ANP-positive myocytes (55-57%) was measured among cells of diameters 30-34 microm. In any corresponding cell size, the proportion of ANP-presenting myocytes was five- to tenfold higher in SHR than in the normotensive WR. We studied the effects of the antihypertensive drugs captopril, hydralazine, and nifedipine and found that, regardless of their effect on blood pressure or hypertrophy, all three eliminated ANP immunoproducts from the majority of the left ventricular myocytes and reduced the level of ANP mRNA, captopril being the most effective. The positive correlation between myocyte size and ANP expression was not maintained in the hearts of drug-treated SHR. Myocytes on the border of fibrotic areas or in regions of ANP presentation within the normal heart resisted the suppressive effect of the antihypertensive therapy, indicating that blood pressure or hypertrophy are not the sole correlates for ANP expression.

Increased expression of atrial natriuretic peptide in ureteral obstructed kidneys in rats.

Whether the natriuresis in the previously ureteral obstructed kidney may be related to an altered regulation of local atrial natriuretic peptide (ANP) was investigated. Male Sprague-Dawley rats were unilaterally obstructed of the left ureters for 48 hours. The left and right ureters were separately cannulated to collect urine samples. In some rats, both kidneys were removed without releasing the obstruction. Control rats were treated the same except that no ureteral obstruction was made. The mRNA expression of ANP and natriuretic peptide receptor (NPR)-A was determined in the kidney by reverse transcription-polymerase chain reaction. The guanylyl cyclase activity was measured by the amount of cGMP generated in response to ANP. Plasma levels of ANP were measured by radioimmunoassay. The ureteral obstruction did not significantly affect the plasma ANP levels. In the obstructed kidney, the creatinine clearance was decreased, while the fractional excretion of sodium increased. The expression of ANP mRNA was increased in the obstructed kidney. The NPR-A mRNA expression was not altered in the glomerulus, but was decreased in the papilla of the obstructed kidney. Nor was the guanylyl cyclase activity in the glomerulus altered. Although the guanylyl cyclase activity in the papilla was significantly decreased in the obstructed kidney, it was rapidly resumed upon releasing the obstruction. An increased local expression of ANP may, at least in part, account for the natriuresis in the previously ureteral obstructed kidney.