Atrial Natriuretic Factor Production Research Articles

Differential effects of Pyk2 and FAK on the hypertrophic response of cardiac myocytes

The related cytoplasmic non-receptor tyrosine kinases Pyk2 (proline-rich tyrosine kinase 2) and FAK (focal adhesion kinase) have been implicated in phenylephrine-induced G-protein-coupled receptor-mediated signaling mechanisms leading to cardiomyocyte hypertrophy. We report that, in phenylephrine-stimulated neonatal rat ventricular myocytes (NRVM), Pyk2 augments expression of the hypertrophic marker atrial natriuretic factor (ANF) but reduces cytoskeletal organization and cell spreading. In contrast, FAK attenuates ANF production but does not alter cytoskeletal organization and cell spreading. Pyk2 and FAK exhibit differential localization in both unstimulated and phenylephrine-stimulated myocytes. Pyk2 catalytic activity is required for Pyk2 to augment ANF secretion but is not necessary to reduce cell spreading. Pyk2 autophosphorylation is required but not sufficient for Pyk2 to augment ANF secretion. Expression of the Pyk2 FERM domain as an autonomous fragment inhibits phenylephrine-mediated ANF secretion and reduces cell spreading. In addition, expression of the Pyk2 FERM domain inhibits the ability of Pyk2 to augment ANF secretion; this is correlated with reduced Pyk2 autophosphorylation. These data indicate that Pyk2 and FAK have different roles and occupy different positions in signaling pathways leading to the development of cardiomyocyte hypertrophy.

Angiotensin II receptor antagonism reverts the selective cardiac BNP upregulation and secretion observed in myocarditis

The cardiac natriuretic peptides atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are discoordinately regulated in myocardial inflammation associated with acute allograft rejection in humans and during in vitro exposure of cardiocyte cultures to some proinflammatory cytokines. We used experimental autoimmune myocarditis (EAM) to determine whether the discoordinate regulation of ANF and BNP was specific to the situations above or was generally associated with other types of myocardial inflammation. The dependency of this process to angiotensin signaling was also determined, given that previous work demonstrated beneficial effects of the angiotensin receptor blocker olmesartan in myocarditis. Histopathological changes, plasma and cardiac ANF, BNP, and selected cytokines gene expression as well as plasma cytokine levels using a cytokine array were determined in EAM, angiotensin receptor blocker-treated, and control rats. It was found that EAM specifically increases BNP but not ANF circulating levels, thus mimicking the findings in acute cardiac allograft rejection and the effect of some proinflammatory cytokines on cardiocyte cultures in vitro. Plasma cytokine array and real-time PCR revealed that lipopolysaccharide-induced CXC chemokine, monocyte chemotactic protein-1, and tissue inhibitor of metalloproteinase-1 were increased in plasma and in the myocardium of EAM rats. Olmesartan treatment reversed virtually all neuroendocrine and histopathological cardiac changes induced by EAM, thus providing a mechanistic insight into this phenomenon. It is concluded that the inflammatory process contributes specific cytokines, leading to the disregulation of cardiac ANF and BNP production observed during myocardial inflammation, and that this process is angiotensin receptor 1 dependent.

Ca 2+/calmodulin-dependent protein kinase II activates apoptosis signal-regulating kinase 1 and nuclear factor-kappaB to induce cardiomyocyte hypertrophy

Ca 2+/calmodulin-dependent protein kinase (CaMK) is an important molecule in cardiomyocyte hypertrophy. We previously showed that the activation of apoptosis signal-regulating kinase 1 (ASK1) or its transcription factor NF-kappaB is sufficient for cardiomyocyte hypertrophy. Recently, it was reported that in C. elegans, UNC-43, a homologue to CaMKII, activates NSY-1, which is a homologue of mammalian ASK1. We hypothesized that ASK1-NF-kappaB signaling pathway was a downstream target of CaMKII. In vitro kinase assay indicates that infection of isolated neonatal cardiomyocytes with adenoviral vector expressing CaMKIIdelta3 (AdCaMKIIdelta3) induced the activation of ASK1, while KN93, an inhibitor of CaMKII, inhibited phenylephrine-induced ASK1 activation. Overexpression of CaMKIIdelta3 induced hypertrophic responses, including increases in protein synthesis, atrial natriuretic factor production and the enhancement of sarcomeric organization. KN93 inhibited these hypertrophic responses induced by phenylephrine. Infection of cardiomyocytes with an adenoviral vector expressing a dominant negative mutant of ASK1 (AdASK(KM)) inhibited the CaMKIIdelta3-induced hypertrophic responses. To evaluate NF-kappaB activation, we measured the activity of kappaB-dependent reporter gene assay and IkappaBalfa degradation by Western blotting. Overexpression of CaMKIIdelta3 increased the luciferase activity and induced IkappaBalfa degradation. Coinfection of AdCaMKIIdelta3 with AdASK (KM) and preincubation with KN93 attenuated CaMKIIdelta3- and phenylephrine-induced NF-kappaB activation, respectively. Expression of a degradation resistant mutant of IkappaBalfa inhibited CaMKIIdelta3-induced hypertrophic responses. These results indicate that CaMKIIdelta3 induces cardiomyocyte hypertrophy mediated through ASK1-NF-kappaB signal transduction pathway.

The Small GTP-binding Protein Rac1 Induces Cardiac Myocyte Hypertrophy through the Activation of Apoptosis Signal-regulating Kinase 1 and Nuclear Factor-κB

The small guanine nucleotide-binding protein Rac1 has emerged as an important molecule involved in cardiac myocyte hypertrophy. Recently, we reported on apoptosis signal-regulating kinase (ASK) 1 and a transcriptional factor, nuclear factor-kappaB (NF-kappaB), as novel signaling intermediates in cardiac myocyte hypertrophy. The aim of the study presented here was to clarify the role of Rac1 in the ASK1-NF-kappaB signaling pathway. Infection of isolated neonatal cardiac myocytes with an adenovirus expressing a constitutively active form of Rac1 (RacV12) enhanced the expression of a kappaB-dependent reporter gene construct and induced the degradation of IkappaBalpha. Expression of a degradation-resistant mutant of IkappaBalpha inhibited the RacV12-induced hypertrophic responses, including increases in protein synthesis and atrial natriuretic factor production and the enhancement of sarcomeric organization. An immune complex kinase assay indicated that the expression of RacV12 activated ASK1. Expression of a dominant negative mutant of ASK1 eliminated the RacV12-induced NF-kappaB activation and the biochemical and morphological hypertrophic responses, whereas expression of a dominant negative form of Rac1 attenuated phenylephrine-induced activation of ASK1 and NF-kappaB and cardiac myocyte hypertrophy. These findings suggest that Rac1 induces cardiac myocyte hypertrophy mediated through ASK1 and NF-kappaB.

Involvement of Reactive Oxygen Species-mediated NF- κ B Activation in TNF- α -induced Cardiomyocyte Hypertrophy

We examined the intracellular signaling mechanism for tumor necrosis factor- α (TNF-α )-induced cardiac hypertrophy in isolated rat neonatal cardiomyocytes. TNF- α enhanced the expression of a κ B-dependent reporter gene construct in a dose-dependent manner, which was transiently transfected in cardiomyocytes. Electrophoretic mobility shift assay demonstrated that TNF- α induced nuclear factor- κ B (NF- κ B)-specific DNA binding. Cultured cardiomyocytes were infected with a recombinant adenoviral vector expressing a degradation-resistant mutant of I κ B α (AdI κ B α 32/36A). The Iκ B α mutant suppressed NF- κ B activation induced by TNF- α. In cardiomyocytes infected with AdI κ B α 32/36A, TNF- α -induced hypertrophic responses, including increases in cell size, protein synthesis and atrial natriuretic factor production and enhancement of sarcomeric organization, were remarkably attenuated compared to the cells infected with an adenovirus expressing bacterial β -galactosidase. Using a reactive oxygen species (ROS)-sensitive fluorescent dye, 2′, 7′-dichlorofluorescin, we observed an increase in fluorescent signal in cardiomyocytes over time, upon addition of TNF- α. Preincubation of n-acetyl cysteine (NAC), an antioxidant, prior to TNF- α treatment, abolished TNF- α -induced ROS generation. NAC abolished TNF-α -induced NF- κ B activation and hypertrophic responses. These findings indicated that TNF-α -induced cardiomyocyte hypertrophy is mediated through NF- κ B activation via the generation of ROS.

Extracellular Signal-regulated Kinase Plays an Essential Role in Hypertrophic Agonists, Endothelin-1 and Phenylephrine-induced Cardiomyocyte Hypertrophy

The extracellular signal-regulated kinase (ERK) pathway is activated by hypertrophic stimuli in cardiomyocytes. However, whether ERK plays an essential role or is implicated in all major components of cardiac hypertrophy remains controversial. Using a selective MEK inhibitor, U0126, and a selective Raf inhibitor, SB-386023, to block the ERK signaling pathway at two different levels and adenovirus-mediated transfection of dominant-negative Raf, we studied the role of ERK signaling in response of cultured rat cardiomyocytes to hypertrophic agonists, endothelin-1 (ET-1), and phenylephrine (PE). U0126 and SB-386023 blocked ET-1 and PE-induced ERK but not p38 and JNK activation in cardiomyocytes. Both compounds inhibited ET-1 and PE-induced protein synthesis and increased cell size, sarcomeric reorganization, and expression of beta-myosin heavy chain in myocytes with IC(50) values of 1-2 microm. Furthermore, both inhibitors significantly reduced ET-1- and PE-induced expression of atrial natriuretic factor. In cardiomyocytes transfected with a dominant-negative Raf, ET-1- and PE-induced increase in cell size, sarcomeric reorganization, and atrial natriuretic factor production were remarkably attenuated compared with the cells infected with an adenovirus-expressing green fluorescence protein. Taken together, our data strongly support the notion that the ERK signal pathway plays an essential role in ET-1- and PE-induced cardiomyocyte hypertrophy.

Twin-to-Twin Transfusion Syndrome: Role of the Fetal Renin-Angiotensin System

An unbalanced blood supply to monochorionic twins, based on placental anastomotic shunting, is the cause of twin-to-twin transfusion syndrome (TTS), which may lead to restricted growth and renal tubular dysgenesis in the donor twin and visceromegaly in the recipient. About 5 percent of these pregnancies are affected. Survival has improved in recent years, but perinatal mortality rates as high as 50 percent are still reported, and some survivors have neurological morbidity. The facts that the donor twin typically is oliguric and the recipient polyuric, possibly because of hypervolemia secondary to increased production of atrial natriuretic factor, suggest that activation of the renin-angiotensin system in the donor twin might be an adverse adaptive change in TTS. This idea was tested in a retrospective autopsy study of 21 monochorionic twin pairs dying of TTS and 39 control subjects. Renal morphology was compared in the two groups, and renin expression was examined immunohistochemically and by in situ hybridization using a renin cDNA clone. Ten of the 21 donor twins, studied at a gestational age of 18 to 30 weeks, exhibited renal tubular dysgenesis affecting the deep cortex; distal tubules and collecting ducts were comparatively spared. Renin protein was overexpressed, and there frequently was evidence of renin production by mesangial cells. The kidneys of recipient twins were enlarged and congested and almost always exhibited hemorrhagic infarction. The glomeruli were very enlarged and focal mesangiolysis was sometimes observed. Preglomerular and interlobular arteries were thickened in about half of the recipient twins. No renin-positive cells were detected in 19 of these 21 infants. Renin expression was lacking or at most very limited in six of the seven recipient fetuses tested. The renal lesions seen in these TTS fetuses are ascribed in part to hemodynamic changes: hypovolemia in the donor and both hypervolemia and polycythemia in the recipient. Hypovolemia activates renin synthesis in the donor, possibly harming both fetuses by promoting hypoperfusion in the donor infant and raising blood pressure in the recipient. Am J Pathol 2000;156:629–636

The expression and secretion of atrial natriuretic factor and brain natriuretic peptide by rat proximal tubular cells

We examined the expression of both the natriuretic peptides and natriuretic peptide receptors (NPR) in primary cultures of rat proximal tubular (RPT) cells using Northern blot assay for peptides and receptors and radioimmunoassay and immunohistochemical analysis for atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and C-type natriuretic peptide. Freshly isolated cells expressed mRNA coding for ANF, BNP, and the NPR-C. The presence of ANF and BNP in freshly isolated cells was confirmed by immunocytochemical staining. As cells approached confluence, there was a marked increase in mRNA expression for ANF and BNP. Immunocytochemical analysis and radioimmunoassay confirmed that both these peptides were co-localised in RPT cells and present in the cell supernatant. These changes in peptide expression were associated with a concurrent decrease in the expression of the NPR-C and the appearance of the NPR-A and -B. These results confirm that freshly isolated RPT cells possess the components of an autocrine natriuretic peptide system and that growth in primary culture is associated with changes in both peptide system and that growth in primary culture is associated with changes in both peptide and receptor subtype expression, raising the possibility that the endogenous production of ANF and BNP may be involved in the control of control cell growth.

Relative Abundance of Placental Pro-Atrial Natriuretic Factor mRNA in Normal Pregnancy and Pre-Eclampsia

Atrial natriuretic factor (ANF), produced by cytotrophoblast cells of the human placenta, may be involved in the regulation of uteroplacental blood flow. Pre-eclampsia is associated with maternal hypertension and reduced uteroplacental perfusion. The relationship between pre-eclampsia and placental production of ANF is not known. This study measured pro-ANF mRNA levels by Northern blot analysis in placentae delivered by caesarean section at preterm and term gestations from women with normotensive and pre-eclamptic pregnancies and found no significant difference between pre-eclampsia and normal pregnancy at either gestation. This result suggests that placental production of ANF is not altered at the pretranslational level during pre-eclampsia.

Atrial natriuretic factor and brain natriuretic peptide gene expression in the spontaneous hypertensive rat during postnatal development

The increase in natriuretic peptides (NP), atrial natriuretic factor (ANF), and brain natriuretic peptide (BNP) production and release by cardiocytes that occurs in hypertension has been considered to be a compensatory mechanism against ventricular overload. Studies on NP production in the spontaneously hypertensive rat (SHR), an experimental model of human hypertension, have produced controversial results and were carried out when hypertension was already established (> 17 weeks). At this time, age-related physiologic and molecular changes in cardiac muscle are difficult to separate from those related to hypertension, ie, increased ANF production and plasma levels. In addition, most of the studies used male rats because the rate of increase in arterial blood pressure—as well as the level to which it rises—is greater in males than in females. Studies of a similar nature using female SHR are not available. The aim of this work was to determine 1) whether ANF and BNP production and secretion increase with the development of hypertension in genetically hypertensive rats; 2) whether a sexual dimorphism in ANF and BNP production and secretion is present in the genetically hypertensive rat during the development of hypertension; and 3) whether the demand for ANF and BNP is the same from each chamber of the heart under these experimental conditions. Age-matched male and female SHR, Wistar-Kyoto (WKY), and Sprague Dawley (SD) rats at 2, 4, and 8 weeks of age were used. The normotensive SD were included to provide a wider basis for baseline findings, as WKY rats are not always a suitable control for SHR due to genetic variations. Natriuretic peptide plasma levels and tissue content were measured by radioimmunoassay. ANF, BNP, as well as α- and β-myosin heavy chain (MHC) mRNA were estimated by Northern blot analysis. Blood pressure (BP) of more than 150 mm Hg was found only in 8-week-old male SHR. Plasma immunoreactive (ir)ANF and irBNP increased significantly at puberty (8 weeks) in both male and female SHR. The earliest molecular change encountered during the development of hypertension was a significant increase in BNP mRNA in the right and left atria from both male and female 8-week-old SHR. In the ventricles from both male and female SHR, there was no increase in the ratio of left ventricular wet weight/body weight, no increase in ventricular ANF mRNA transcripts, and no myosin heavy chain isoform switch (a protein marker of hypertrophy). irBNP ventricular concentration, however, increased significantly in both male and female SHR, but only in female SHR was there a concomitant increase in BNP mRNA. These results suggest that 1) ANF and BNP production are not coordinated in all cardiac compartments during the development of hypertension; 2) upregulation of BNP in the atria from male and female SHR is the earliest event detected at 8 weeks; 3) the prehypertensive stage, in the genetically hypertensive female rats, is associated with an increase in ventricular irBNP concentration and BNP mRNA; 4) there is a dissociation between BP and plasma levels of NP; and 5) as well, there is a dissociation between NP gene expression and MHC isoform switch. The regulation of NP is not coordinated in either gender during the development of hypertension. The activation of the BNP gene in female SHR suggests that BNP might play an important role at the onset of hypertension.

Beta1 integrins participate in the hypertrophic response of rat ventricular myocytes.

Multiple signaling pathways have been implicated in the hypertrophic response of ventricular myocytes, yet the importance of cell-matrix interactions has not been extensively examined. Integrins are cell-surface molecules that link the extracellular matrix to the cellular cytoskeleton. They can function as cell signaling molecules and transducers of mechanical information in noncardiac cells. Given these properties and their abundance in cardiac cells, we evaluated the hypothesis that beta1 integrin function is involved in the alpha1-adrenergic mediated hypertrophic response of neonatal rat ventricular myocytes. The hypertrophic response of this model required interaction with extracellular matrix proteins. Specificity of these results was confirmed by demonstrating that ventricular myocytes plated onto an anti-beta1 integrin antibody supported the hypertrophic gene response. Adenovirus-mediated overexpression of beta1 integrin augmented the myocyte hypertrophic response when assessed by protein synthesis and atrial natriuretic factor production, a marker gene of hypertrophic induction. DNA synthesis was not altered by integrin overexpression. Transfection of cultured cardiac myocytes with either the ubiquitously expressed beta1A integrin or the cardiac/skeletal muscle-specific beta1 isoform (beta1D) activated reporter expression from both the atrial natriuretic factor and myosin light chain-2 ventricular promoters, genetic markers of ventricular cell hypertrophy. Finally, suppression of integrin signaling by overexpression of free beta1 integrin cytoplasmic domains inhibited the adrenergically mediated atrial natriuretic factor response. These findings show that integrin ligation and signaling are involved in the cardiac hypertrophic response pathway.

IGF-I and bFGF Differentially Influence Atrial Natriuretic Factor andα-smooth Muscle Actin Expression in Cultured Atrial Compared to Ventricular Adult Rat Cardiomyocytes

In the present study, we compare expression, storage and secretion of the atrial natriuretic factor (ANF) in atrial and ventricular adult rat cardiomyocytes (aARC and vARC) in long-term culture. The influence of insulin-like growth factor-I (IGF-I) and of basic fibroblast growth factor (bFGF) on ANF production and secretion, as well as on the expression of a structural component,α-smooth muscle actin (α-sm actin), was studied in the two cell types. Antibodies againstα-ANF were used for immunocytochemical localization of ANF. aARC contained more ANF-granules than vARC, and they were distributed throughout the cell bodies. Quantitative determination of ANF storage and secretion was done by radioimmunoassay (RIA;125I), and it was demonstrated that aARC stored and secreted ANF 18- and 16-times more, respectively, when compared to vARC. Immuno-electron microscopy confirmed that ANF storing secretory granules were present in both types of cardiomyocytes. Expression of ANF andα-sm actin in aARC and vARC responded differently to treatment with either IGF-I or bFGF. In aARC, neither IGF-I nor bFGF had an influence on expression of ANF. In vARC, expression of ANF was downregulated by IGF-I and upregulated by bFGF with regard to both immunoreactivity and message. In contrast to vARC, expression ofα-sm actin was not affected by IGF-I in aARC, whereas bFGF produced a strong upregulation similar to that found in vARC. Mitogen-activated protein kinases (MAPK) 42 and 44, though, were equally activated by bFGF and IGF-I in both aARC and vARC.

Prostaglandin F2 alpha induces cardiac myocyte hypertrophy in vitro and cardiac growth in vivo.

Several prostaglandins [prostaglandin (PG) A2, -B2, -D2, -E2, -F2 alpha, and -I2 and carbaprostacyclin] and the thromboxane analogue U-46619 were analyzed for the ability to induce hypertrophy of rat neonatal cardiac ventricular myocytes. Myocyte hypertrophy was induced specifically by PGF2 alpha. Myocytes exposed to this prostanoid in culture increased in size and protein content. The contractile fibrils within the cells became organized into parallel arrays, and the cells tended to cluster and beat spontaneously. PGF2 alpha also induced the expression of c-fos, atrial natriuretic factor (ANF), and alpha-skeletal actin in these cells. The effects of PGF2 alpha were compared with several known cardiac myocyte hypertrophy factors (phenylephrine, endothelin-1, leukemia inhibitory factor, cardiotrophin-1, and angiotensin II). PGF2 alpha was found to be intermediate in potency among the factors but induced a level of ANF production that was approximately 10-fold higher than any of the other effectors. Responsiveness to PGF2 alpha was not limited to neonatal cardiocytes. Ventricular myocytes isolated from adult rats also responded specifically to PGF2 alpha with a morphological change similar to that observed with phenylephrine and by producing ANF. In rats, chronic administration of fluprostenol, a potent agonist analogue of PGF2 alpha, resulted in a dose-dependent increase in heart weight- and ventricular weight-to-body weight ratios. The amount of PGF2 alpha extractable from the hearts of rats with cardiac hypertrophy induced by myocardial infarction was also found to be greater than that in sham-operated control rats. These results indicate that PGF2 alpha may play an important role in inducing cardiac hypertrophy.

Intracoronary and systemic release of the atrial natriuretic factor and cyclic-guanosine monophosphate during coronary angioplasty

This study was undertaken to investigate intracoronary production and systemic release of the atrial natriuretic factor (ANF) and cyclic-guanosine monophosphate (c-GMP) during coronary angioplasty (PTCA). three coronary blood samples were collected, through a balloon catheter, from the area distal to the lesion: before balloon inflation, at maximum inflation and 5 min later. Four additional venous samples were collected: before PTCA, and 5 min, 2 h and 24 h after the procedure. Local intracoronary c-GMP production increased from the baseline level of 7.5±0.9 pmol/ml to 11.1±1.3 pmol/ml at maximum balloon inflation (p<0.01) and decreased 5 min later to 9.5 ±1.0 pmol/ml (p=NS). In contrast, intracoronary ANF production failed to show any significant change at any time during the procedure. Peripheral venous ANF levels increased from 79.1±11.1 pmol/ml to 99.9±16.6 pmol/ml 5 min after balloon inflation (p<0.05) and gradually decreased 2 h (91.9±13.6 pmol/ml) and 24 h (85.6±10.4 pmol/ml) after the procedure. Similarly, peripheral venous c-GMP levels increased from 11.3±1.7 pmol/ml before PTCA to 14.9±1.9 pmol/ml 5 min after balloon inflation (p<0.05), and then gradually decreased 2 h (10.8±1.4 pmol/ml) and 24 h (8.2±1.4 pmol/ml) after the procedure (p<0.01 and <0.0001 compared to the peak value, respectively). In conclusion, acute vessel occlusion and distension during balloon inflation stimulates intracoronary c-GMP production without affecting ANF release.

Evidence for load-dependent and load-independent determinants of cardiac natriuretic peptide production.

In hypertension with cardiac hypertrophy, the specific contributions to increased production of the cardiac natriuretic peptides (NP) atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) by load and the hypertrophic process are not known. In the present work we determine ANF and BNP synthesis and secretion in the aortic-banded rat treated with dosage schedules of the ACE inhibitor ramipril that result in the prevention or regression of both hypertension and hypertrophy (high dosage) or in the prevention or regression of hypertrophy alone with persistent hypertension (low dosage). Myosin heavy chain (MHC) isoform switch was studied as an indicator of ventricular cardiocyte hypertrophy as well as the levels of collagen III mRNA as a measure of changes in extracellular matrix. Ramipril was administered for 6 weeks just after suprarenal aortic banding, or rats were banded for 6 weeks, after which ramipril was administered during the following 6 weeks. Banding caused an increase in blood pressure, left ventricular weight-to-body weight ratio, plasma and ventricular NP, ventricular NP mRNA, collagen III, and beta-MHC mRNA. Ramipril at 1 mg/kg normalized all these parameters while ramipril at 10 micrograms/kg normalized left ventricular weight-to-body weight ratio but not blood pressure. Plasma and ventricular NP content and mRNA levels were partially normalized by ramipril (10 micrograms/kg). Ramipril (10 micrograms/kg) prevented increased collagen III mRNA levels but did not affect beta-MHC mRNA levels. (1) NP production and secretion in aortic-banded rats are independently related to increased blood pressure and hypertrophy. (2) A load-dependent component is more important than a load-independent component in regulating left ventricular NP production. (3) ANF production is more sensitive than BNP production to the load-independent component. (4) Low-dose ramipril treatment reverses hypertrophy and the increased collagen III expression but does not reverse the increased beta-MHC isoform expression, suggesting that these are independently regulated processes. (5) Aortic banding and ACE inhibition do not affect atrial NP production and content.

Mechanical and neuroendocrine regulation of the endocrine heart

The cardiac natriuretic peptides (NP) -- atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) -- are polypeptide hormones produced by cardiocytes in the atria of mammals. ANF and BNP are continuously released from the heart, but appropriate mechanical or neuroendocrine stimuli increase their rate of release with or without a concomitant increase in synthesis. The results of our investigations lead us to propose that the endocrine response of the heart to pressure or volume load varies in relation to whether the challenge is acute, subacute or chronic. The acute response to stretch is based on a phenomenon referred to as "stretch-secretion coupling" which results in enhanced secretion of NP stored in the atria. NP release following stretch is made at the expense of a depletable NP pool with no apparent effect on synthesis. The stimulation of NP production that is seen during mineralcorticoid escape is referred to as "subacute" and is characterized by stimulation of atrial ANF and BNP gene transcription secondary to volume overload in which plasma ANF, but not plasma BNP, is significantly elevated. With chronic stimulation, as seen in DOCA-salt treatment at the hypertensive stage, activation of the cardiac fetal program in ventricle is seen together with a stimulation of ANF and BNP production in both atria and ventricles. However, the activation of NP gene expression in the atria is not necessarily associated with fetal isogene expression even though the ventricular hypertrophic process is characterized by the expression of fetal isogenes, including ANF and BNP, that are normally expressed in the fetal ventricle. It seems likely that the acute stimulation of NP release is based on an electromechanical coupling. However, protracted stimulation of release is seen in situations in which profound neuroendocrine changes have taken place, thus suggesting that the primary stimulus for chronically enhanced NP gene expression and NP release is based on changes in the hormonal environment of the atrial cardiocyte. It is concluded that the endocrine heart responds to changes in hemodynamic load with specific changes in translational, post-translational and storage processes for ANF and BNP following acute or chronic stimulation. As a result, plasma levels of ANF and BNP may be used as indicators of the degree of atrial hemodynamic overload and ventricular hypertrophy, respectively. It may be advanced that the endocrine heart differentiates and responds to different hemodynamic challenges in either acute or chronic conditions with specific changes in transcription, translation, post-translational processing, storage, and release of ANF and BNP. We propose that this differentiation is part of the reason for the heart to produce two hormones with similar spectra of activity. This paradigm warrants further investigation.

Atrial natriuretic factor production by the human placenta

Atrial natriuretic factor production by the human placenta

Atrial natriuretic factor in gynecologic malignancy

To determine whether plasma atrial natriuretic factor (ANF) levels are different in patients with gynecologic malignancy compared with those in healthy, nonpregnant women, and if differences do exist, whether chemotherapy plays a role. We compared the plasma levels of ANF in nonpregnant women free of malignancy (group 1, n = 25) and in patients with malignancy receiving at least one course of platinum-based chemotherapy (group 2, n = 32). To differentiate the contributory role of chemotherapy, another group of patients (group 3, n = 18) was studied before the initiation of chemotherapy. The ANF values (mean +/- standard error [SE]) in groups 1, 2, and 3 were 7.3 +/- 0.3, 13.8 +/- 0.8, and 14.6 +/- 1.8 fmol/mL of plasma, respectively. Significant differences (P < or = .001) occurred between groups 1 and 2 and 1 and 3, but not between 2 and 3. In comparing groups 2 and 3 for a specific type of cancer, there were no significant differences. The respective values (mean +/- SE) for endometrial, ovarian, and cervical cancer before chemotherapy were 9.9 +/- 1.7, 15.05 +/- 2.6, and 18.5 +/- 4.3 fmol/mL. After chemotherapy, the values remained at 9.3 +/- 1.5, 15.03 +/- 1.06, and 14.6 +/- 2.2 fmol/mL, respectively. Plasma ANF levels in gynecologic cancer patients were significantly higher than those in healthy, nonpregnant women. Levels were higher before chemotherapy started, thus negating the idea that chemotherapy may initiate the production and release of ANF.

Dissociation of cardiac hypertrophy, myosin heavy chain isoform expression, and natriuretic peptide production in DOCA-salt rats

We examined the relationship between cardiac hypertrophy, myosin heavy chain (MHC) isoform expression, and production of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) before and after the development of DOCA-salt hypertension. DOCA-salt rats exhibited significant left ventricular hypertrophy at the prehypertensive stage (1 week of treatment), without MHC isoform switch or change in natriuretic peptide gene expression. In the hypertensive stage (5 weeks of treatment), pronounced left ventricular hypertrophy was observed, and this was characterized by an increase in beta-MHC protein, resulting in a switch from 90% alpha-MHC to 51% alpha-MHC and 49% beta-MHC. ANF and BNP mRNA levels and peptide content were significantly increased at this stage. Unexpectedly, the MHC isoform switch was evident in the non-hypertrophied right ventricle to the same degree as in the left ventricle. Natriuretic peptide production was also increased in the right ventricle at 5 weeks of treatment, but to a lesser degree than in the left ventricle. In contrast, in the hypertrophied left atrium there was no MHC isoform switch, while ANF and BNP mRNA levels were augmented. Plasma ANF was significantly increased in the prehypertensive stage; this was accompanied by a partial depletion of atrial ANF stores. Plasma BNP was increased only in the hypertensive stage, reflecting an increase in ventricular BNP synthesis and secretion. These results suggest that 1) cardiac hypertrophy, MHC isoform expression, and stimulation of natriuretic peptide production are processes that may be dissociated from each other; 2) increases in plasma ANF without a concomitant increase in plasma BNP reflect atrial hemodynamic overload, while increases in both ANF and BNP in plasma are associated with ventricular hypertrophy; and 3) there exist differences in the storage, secretion, and processing patterns of ANF and BNP in the atria.

Atrial natriuretic factor production, atrial natriuretic factor receptors, and their effect on small cell lung cancer cells : Johnson BE, Ohsaki Y, Yang HK, Le PT, Jensen RT. NCI-Navy Medical Oncology Branch and Digestive Diseases Branch, National Institutes of Health, Bethesda, MD 20892

Atrial natriuretic factor production, atrial natriuretic factor receptors, and their effect on small cell lung cancer cells : Johnson BE, Ohsaki Y, Yang HK, Le PT, Jensen RT. NCI-Navy Medical Oncology Branch and Digestive Diseases Branch, National Institutes of Health, Bethesda, MD 20892