Transcriptional cofactor dyxin mediates hypertrophic response in the heart during angiotensin II-induced hypertension.

Dyxin is a LIM-domain containing transcriptional regulator protein shown to play a role in a hypertrophic response in the heart. Here, the effect of adenoviral dyxin overexpression was studied on cardiac function and gene expression in the normal heart and in angiotensin II (Ang II)-induced hypertension in rats. The adenovirus-mediated intramyocardial gene transfer of dyxin (1.5x109 infectious units/animal) was performed into the left ventricle (LV) of Sprague-Dawley rats with and without the Ang II (33 µg/kg/h) infusion, administered via osmotic minipumps for 1 and 2 weeks. Echocardiography was used to assess the structural and functional changes. Dyxin expression and localization in the heart was analyzed with quantitative RT-PCR and immunohistochemistry, respectively. In the normal rat heart, the adenoviral overexpression of dyxin did not alter LV function in normal hearts as assessed by echocardiography. Dyxin was found to be localized in the cardiomyocytes as shown by the immunohistochemical staining. In Ang II-induced hypertrophy, echocardiographic data revealed a significant increase in the posterior wall diameter both in systole (21%, P<0.05) and diastole (21%, P<0.01) as well as in the diameter of the interventricular septum in systole (19%, P<0.05) in the dyxin-injected group compared with the LacZ-injected animals after two weeks of Ang II infusion. Interestingly, a significant decrease in the levels of both atrial natriuretic peptide (ANP) mRNA (55%, P<0.01) and B-type natriuretic peptide (BNP) mRNA (68%, P<0.05) was observed in the dyxin-injected group compared with the LacZ control group after one week of Ang II infusion. These results indicate that dyxin overexpression was deteriorative against pressure overload by inducing structural changes in the LV in rats. Interestingly, simultaneous adenoviral overexpression of dyxin suppressed the Ang II-induced changes of ANP and BNP genes suggesting that dyxin might have a role as a regulator of the cardiac hypertrophic gene program.

Plasma levels of the proprotein convertase furin and incidence of diabetes and mortality.

BACKGROUND: Diabetes mellitus is linked to premature mortality of virtually all causes. Furin is a proprotein convertase broadly involved in the maintenance of cellular homeostasis; however, little is known about its role in the development of diabetes mellitus and risk of premature mortality. OBJECTIVES: To test if fasting plasma concentration of furin is associated with the development of diabetes mellitus and mortality. METHODS: Overnight fasted plasma furin levels were measured at baseline examination in 4678 individuals from the population-based prospective Malmö Diet and Cancer Study. We studied the relation of plasma furin levels with metabolic and hemodynamic traits. We used multivariable Cox proportional hazards models to investigate the association between baseline plasma furin levels and incidence of diabetes mellitus and mortality during 21.3-21.7 years follow-up. RESULTS: An association was observed between quartiles of furin concentration at baseline and body mass index, blood pressure and plasma concentration of glucose, insulin, LDL and HDL cholesterol (|0.11| ≤ ß ≤ |0.31|, P < 0.001). Plasma furin (hazard ratio [HR] per one standard deviation increment of furin) was predictive of future diabetes mellitus (727 events; HR = 1.24, CI = 1.14-1.36, P < 0.001) after adjustment for age, sex, body mass index, systolic and diastolic blood pressure, use of antihypertensive treatment, alcohol intake and fasting plasma level of glucose, insulin and lipoproteins cholesterol. Furin was also independently related to the risk of all-cause mortality (1229 events; HR = 1.12, CI = 1.05-1.19, P = 0.001) after full multivariable adjustment. CONCLUSION: Individuals with high plasma furin concentration have a pronounced dysmetabolic phenotype and elevated risk of diabetes mellitus and premature mortality.

Prognostic value of N-terminal natriuretic peptides in systemic sclerosis: a single centre study.

OBJECTIVES: Cardiac involvement is an important determinant of prognosis in systemic sclerosis (SSc). The identification of patients with high risk is of great importance. Our aim was to investigate the diagnostic and prognostic value of circulating concentrations of N-terminal fragments of A- and B-type natriuretic peptides (NT-proANP and NT-proBNP) in patients with SSc. METHODS: We prospectively studied 144 patients with SSc and followed them up for five years. Blood was collected for natriuretic peptide measurement at the time of the yearly scheduled cardiological check-up. The occurrence of clinically significant cardiac disease was measured as the composite of pulmonary arterial hypertension, cardiac revascularisation, development of left ventricular dysfunction or death. RESULTS: Patients diagnosed with heart involvement during the study had significantly higher levels of NT-proANP and NT-proBNP (791.4 ± 379.9 pmol/l vs. 608.0 ± 375.8 pmol/l, p<0.05 and 183.1 ± 162.6 vs. 125.7 ± 117.5 pmol/l, p<0.05, respectively). Receiver-operator-characteristic analysis identified <822.5 pmol/l as the best NT-proANP and <154.5 pmol/l as the best NT-proBNP threshold (sensitivity 56.3%, specificity 79.5%, negative predictive value: 86.4% and sensitivity 50.0%, specificity 76.8%, negative predictive value: 83.7%, respectively). During the follow-up, lower NT-proANP levels were significantly associated with a longer event-free survival (p<0.05), similar but a non-significant trend regarding NT-proBNP levels was also shown (p=0.052). CONCLUSIONS: In our cohort, NT-proANP had a supplementary prognostic value for cardiac involvement in systemic sclerosis. In addition, the high negative predictive value of natriuretic peptides supports the more extensive use in identifying SSc patients with high risk of future cardiac involvement.

Pregnane X receptor agonists impair postprandial glucose tolerance.

We conducted a randomized, open, placebo-controlled crossover trial to investigate the effects of the pregnane X receptor (PXR) agonist rifampin on an oral glucose tolerance test (OGTT) in 12 healthy volunteers. The subjects were administered 600 mg rifampin or placebo once daily for 7 days, and OGTT was performed on the eighth day. The mean incremental glucose and insulin areas under the plasma concentration-time curves (AUC(incr)) increased by 192% (P = 0.008) and 45% (P = 0.031), respectively. The fasting glucose, insulin, and C-peptide, and the homeostasis model assessment for insulin resistance, were not affected. The glucose AUC(incr) during OGTT was significantly increased in rats after 4-day treatment with pregnenolone 16α-carbonitrile (PCN), an agonist of the rat PXR. The hepatic level of glucose transporter 2 (Glut2) mRNA was downregulated by PCN. In conclusion, both human and rat PXR agonists elicited postprandial hyperglycemia, suggesting a detrimental role of PXR activation on glucose tolerance.

Regulation of cardiac melusin gene expression by hypertrophic stimuli in the rat.

AIM: Melusin is an integrin ß1-interacting protein proposed to act as a biomechanical sensor in the heart. We characterized mechanisms and signalling pathways regulating cardiac melusin expression. METHODS: Infusion of arginine(8) -vasopressin (AVP) in Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHR) and double transgenic rats (dTGR) harbouring both human angiotensinogen and renin genes as well as infusion of angiotensin II (Ang II) in SD rats were used. The effect of direct left ventricular (LV) wall stretch was analysed by using isolated perfused rat heart preparation. For the cell culture studies, mouse atrial HL-1 cell line and neonatal rat ventricular myocytes (NRVMs) were used. RESULTS: Left atrial melusin mRNA levels increased already after 30 min of AVP infusion. Ang II caused significant upregulation of left atrial melusin mRNA (2.1-fold at 6 h, P < 0.05) and protein (1.9-fold at 72 h, P < 0.05) levels. In contrast, LV melusin mRNA levels remained unchanged in response to both infusions, as well as to aortic banding-induced pressure overload. Direct LV wall stress or late-stage hypertensive heart disease did not modify LV melusin gene expression either. Interestingly, in atrial HL-1 cells, cyclic stretching increased melusin mRNA levels. Stretching and treatments with hypertrophic agonists increased melusin mRNA and protein levels in NRVMs, endothelin-1 being the most potent. PD98059, an extracellular signal-regulated protein kinase 1/2 inhibitor, markedly attenuated the endothelin-1-induced upregulation of melusin gene expression in NRVMs. CONCLUSION: Multiple hypertrophic stimuli regulate melusin expression predominately in the atria, which may represent a necessary initial step in early adaptive remodelling processes.

Physiological regulation of cardiac contractility by endogenous reactive oxygen species.

Increased production of reactive oxygen species (ROS) has been linked to the pathogenesis of congestive heart failure. However, emerging evidence suggests the involvement of ROS in the regulation of various physiological cellular processes in the myocardium. In this review, we summarize the latest findings regarding the role of ROS in the acute regulation of cardiac contractility. We discuss ROS-dependent modulation of the inotropic responses to G protein-coupled receptor agonists (e.g. ß-adrenergic receptor agonists and endothelin-1), the potential cellular sources of ROS (e.g. NAD(P)H oxidases and mitochondria) and the proposed end-targets and signalling pathways by which ROS affect contractility. Accumulating new data supports the fundamental role of endogenously generated ROS to regulate cardiac function under physiological conditions.

N-terminal pro-atrial natriuretic peptide reflects cardiac remodelling in stage 1 hypertension.

Early detection of left ventricular hypertrophy (LVH) is beneficial, since treatment-induced regression of LVH has been unequivocally associated with a better prognosis. Our aim was to study the relation of cardiac remodelling and natriuretic peptides (NPs) in stage 1 hypertension. We studied 175 (46±7 years, 87 women and 88 men) apparently healthy middle-aged that had never been treated for hypertension. Left ventricular and atrial parameters were determined by magnetic resonance imaging. Systolic blood pressure (BP) correlated with left ventricular mass index (LVMI) (r=0.23, P<0.01) and ventricular septum thickness index (IVSI) (r=0.29, P<0.001). N-terminal pro-B-type NP (NT-proBNP) or N-terminal pro-atrial NP (NT-proANP) did not correlate with BP, LVMI or IVSI. NT-proANP correlated with left atrial area index (LAAI) (r=0.38, P<0.001), and subjects with LVH had higher LAAI than subjects with normal left ventricular geometry and no LVH (11.2±0.3 vs 10.0±0.2 cm(2) m(-2), P<0.001). In conclusion, measurement of NT-proBNP or NT-proANP does not appear to discriminate LVH in middle-aged, never treated and apparently healthy hypertensives. NT-proANP, but not NT-proBNP, reflects early cardiac remodelling in hypertensive heart disease.

The mixed-lineage kinase 1-3 signalling pathway regulates stress response in cardiac myocytes via GATA-4 and AP-1 transcription factors.

BACKGROUND AND PURPOSE: The mixed-lineage kinases (MLKs) act upstream of mitogen-activated protein kinases, but their role in cardiac biology and pathology is largely unknown. EXPERIMENTAL APPROACH: We investigated the effect of a MLK1-3 inhibitor CEP-11004 on G protein-coupled receptor agonist-induced stress response in neonatal rat cardiac myocytes in culture. KEY RESULTS: CEP-11004 administration dose-dependently attenuated phenylephrine and endothelin-1 (ET-1)-induced c-Jun N-terminal kinase activation. MLK inhibition also reduced ET-1- and phenylephrine-induced phosphorylation of p38 mitogen-activated protein kinase. In contrast, phenylephrine-induced extracellular signal-regulated kinase phosphorylation was further up-regulated by CEP-11004. ET-1 increased activator protein-1 binding activity 3.5-fold and GATA-binding protein 4 (GATA-4) binding activity 1.8-fold, both of which were attenuated with CEP-11004 administration by 59% and 63% respectively. Phenylephrine induced activator protein-1 binding activity by 2.6-fold, which was decreased by 81% with CEP-11004 administration. Phenylephrine also induced a 3.7-fold increase in the transcriptional activity of B-type natriuretic peptide (BNP), which was attenuated by 41% with CEP-11004 administration. In agreement, MLK inhibition also reduced hypertrophic agonist-induced secretion of immunoreactive atrial natriuretic peptide and BNP. CONCLUSIONS AND IMPLICATIONS: These results showed that inhibition of the MLK1-3 signalling pathway was sufficient for suppressing the activity of key nuclear effectors (GATA-4 and activator protein-1 transcription factors) in cardiac hypertrophy, and attenuated the agonist-induced atrial natriuretic peptide secretion and activation of BNP gene transcription.

Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 during cardiac remodelling in rats.

AIM: Accumulating evidence supports the concept that proinflammatory cytokines play an essential role in the failing heart. We examined the concomitant tumour necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 expression in myocytes in vitro as well as in vivo in cardiac remodelling. METHODS: We assessed TWEAK and its receptor Fn14 expression in response to angiotensin (Ang) II, myocardial infarction (MI) as well as to local adenovirus-mediated p38 gene transfer in vivo. The effect of various hypertrophic factors and mechanical stretch was studied in neonatal rat ventricular myocyte cell culture. RESULTS: Ang II increased Fn14 levels from 6 h to 2 weeks, the greatest increase in mRNA levels being observed at 6 h (6.3-fold, P < 0.001) and protein levels at 12 h (4.9-fold, P < 0.01). TWEAK mRNA and protein levels remained almost unchanged during Ang II infusion. Likewise, a rapid and sustained elevation of Fn14 mRNA and protein levels in the left ventricle was observed after experimental MI. Moreover, local p38 gene transfer increased Fn14 mRNA and protein but not TWEAK levels. Fn14 immunoreactive cells were mainly proliferating non-myocytes in the inflammation area while TWEAK immunoreactivity localized to cardiomyocytes and endothelial cells of the coronary arteries. Hypertrophic agonists and lipopolysaccharide increased Fn14 but not TWEAK gene expression in neonatal rat myocytes, while mechanical stretch upregulated Fn14 and downregulated TWEAK gene expression. CONCLUSIONS: In conclusion, the cardiac TWEAK/Fn14 pathway is modified in response to myocardial injury, inflammation and pressure overload. Furthermore, our findings underscore the importance of Fn14 as a mediator of TWEAK/Fn14 signalling in the heart and a potential target for therapeutic interventions.

Strong relationship between NT-proXNP levels and cardiac output following cardiac surgery in neonates and infants.

BACKGROUND: NT-proXNP, a new natriuretic peptide analyte, incorporates information about the concentrations of both N-terminal pro-atrial and pro-brain natriuretic peptides (NT-proANP, NT-proBNP). We aimed to investigate whether NT-proXNP is a reliable indicator of the cardiac index (CI) and the hemodynamic state in neonates and infants undergoing an open heart surgery. METHODS: We enrolled 26 children under the age of 1 year into this prospective study. All patients underwent an elective cardiac operation with cardiopulmonary bypass (CPB) to achieve complete biventricular repair. Peri-operative hemodynamic parameters were assessed by transpulmonary thermodilution and natriuretic peptide levels were recorded. RESULTS: The NT-proXNP level correlated significantly with the simultaneously measured NT-proANP level (r=0.60, P<0.001), but more strongly with the NT-proBNP level (r=0.89, P<0.001) and the arithmetic sum of both (r=0.88, P<0.001). NT-proXNP had a strong correlation with CI (r=-0.85, P<0.001), the stroke volume index (r=-0.80, P<0.001) and the global ejection fraction (r=-0.67, P<0.009) throughout the post-operative period. Conventionally measured parameters such as heart rate, mean arterial pressure and pulse-pressure product exhibited weaker correlations with CI than NT-proXNP. Among laboratory values, creatinine levels correlated significantly with CI (r=-0.77, P<0.001) and NT-proXNP (r=0.76, P<0.001) during the post-operative period. A post-operative NT-proXNP level of 3079 pmol/l was diagnostic for CI <3 l/min/m(2) with 89% sensitivity and 90% specificity (area under the curve: 0.91 +/- 0.05). CONCLUSION: NT-proXNP is a good marker of cardiac output following pediatric cardiac surgery and might be a useful tool in the recognition of a low output state.

Characterization of promoter elements required for cardiac chamber-specific expression.

Salmon cardiac natriuretic peptide (sCP, an A-type natriuretic peptide) is an excellent model for the study of cardiac chamber-specific gene expression because it is uniquely specific to the heart and its promoter drives gene expression effectively in mammalian cardiac atrial but not in ventricular cells. We have now prepared hybrid luciferase constructs containing specific sequences from both sCP and BNP 5' promoters. According to our results the simple addition of a short rat BNP proximal promoter fragment to the inert 846 nucleotide sCP proximal promoter increases 100 times the basal activity of the sCP promoter in rat ventricular cardiomyocytes, and also conveys inducibility by mechanical load and endothelin-1. Thus, a small rBNP promoter fragment can transform the prototypical A-type natriuretic peptide regulation of sCP to B-type regulation, a result which argues against a major role of repressors causing the low expression level of A-type peptides in ventricular cardiomyocytes.

Plasma N-terminal fragments of natriuretic peptides predict the risk of stroke and atrial fibrillation in men.

BACKGROUND: Risk stratification for cardiovascular outcomes is gaining importance in general population. Prognostic value of natriuretic peptides has been established in patients with heart failure. However, the prognostic significance of natriuretic peptides with respect to stroke is not well known in general populations. METHODS: Plasma natriuretic peptides were measured in a representative population-based sample of 958 men (age 46-65 years) from Eastern Finland. There were 46 cases of stroke, 74 of atrial fibrillation and 31 cases of ischaemic strokes during a follow-up of 9.6 years. RESULTS: The multivariable adjusted risk was 1.35-fold (95% CI 1.01 to 1.84, p = 0.049) for any stroke and 1.30-fold (95% CI 0.90 to 1.91, p = 0.0150) for ischaemic stroke for each log-transformed SD (0.240 pmol/l) increment in N-terminal fragment of proA-type natriuretic peptide. The respective risks were 1.36-fold (95% CI 1.05 to 1.76, p = 0.010) and 1.50-fold (95% CI 1.12 to 2.02, p = 0.007) for each log-transformed SD (0.237 pmol/l) increment in N-terminal fragment of proB-type natriuretic peptide. The multivariate adjusted risks for future atrial fibrillation were 1.71 (95% CI 1.32 to 2.22, p<0.001) and 1.68-fold (95% CI 1.38 to 2.07, p<0.001) for each log-transformed SD increment in N-terminal fragments of proA- and proB-type natriuretic peptides, respectively. CONCLUSIONS: N-terminal fragments of pro-atrial natriuretic peptide and pro-brain natriuretic peptide are new additional predictors of any stroke and atrial fibrillation. Natriuretic peptides provide prognostic information for stroke and atrial fibrillation and may help in identifying subjects at risk for stroke and atrial fibrillation.

Paricalcitol aggravates perivascular fibrosis in rats with renal insufficiency and low calcitriol.

Cardiovascular complications are a major problem in chronic renal failure. We examined the effects of plasma calcium, phosphate, parathyroid hormone (PTH), and calcitriol on cardiac morphology in 5/6 nephrectomized rats. Fifteen weeks after nephrectomy rats were given a control diet, high-calcium or -phosphorus diet, or given paricalcitol treatment for 12 weeks. Sham-operated rats were on a control diet. Blood pressure, plasma phosphate, and PTH were increased, while the creatinine clearance was reduced in remnant kidney rats. Phosphate and PTH were further elevated by the high-phosphate diet but suppressed by the high-calcium diet, while paricalcitol reduced PTH without influencing phosphate or calcium. The high-calcium diet increased, while the high-phosphate diet reduced plasma calcium. Plasma calcitriol was significantly reduced in other remnant kidney groups, but further decreased after paricalcitol. Cardiac perivascular fibrosis and connective tissue growth factor were significantly increased in the remnant kidney groups, and further increased in paricalcitol-treated rats. Hence, regardless of the calcium, phosphate, or PTH levels, cardiac perivascular fibrosis and connective tissue growth factor increase in rats with renal insufficiency in association with low calcitriol. Possible explanations are that aggravated perivascular fibrosis after paricalcitol in renal insufficiency may be due to further suppression of calcitriol, or to a direct effect of the vitamin D analog.

Protein remodeling of extracellular matrix in rat myocardium during four-day hypoxia: the effect of concurrent hypercapnia.

The combination of long-term hypercapnia and hypoxia decreases pulmonary vascular remodeling and attenuation of right ventricular (RV) hypertrophy. However, there is limited information in the literature regarding the first stages of acclimatization to hypercapnia/hypoxia. The purpose of this study was to investigate the effect of four-day hypoxia (10% O2) and hypoxia/hypercapnia (10% O2 + 4.4% CO2) on the protein composition of rat myocardium. Expression of the cardiac collagen types and activities of matrix metalloproteinases (MMPs) and of their tissue inhibitor TIMP-1 were followed. The four-day hypoxia changed protein composition of the right ventricle only in the hypercapnic condition; remodeling was observed in the extracellular matrix (ECM) compartments. While the concentrations of pepsin-soluble collagenous proteins in the RV were elevated, the concentrations of pepsin-insoluble proteins were decreased. Furthermore, the four-day hypoxia/hypercapnia increased the synthesis of cardiac collagen due to newly synthesized forms; the amount of cross-linked particles was not affected. This type of hypoxia increased cardiac collagen type III mRNA, while cardiac collagen type I mRNA was decreased. MMP-2 activity was detected on the zymographic gel through appearance of two bands; no differences were observed in either group. mRNA levels for MMP-2 in the RV were significantly lower in both the hypoxic and hypoxic/hypercapnic animals. mRNA levels for TIMP-1 were reduced in the RV of both the hypoxic and hypoxic/hypercapnic animals. Hypoxia with hypercapnia increased the level of mRNA (6.5 times) for the atrial natriuretic peptide (ANP) predominantly in the RV. The role of this peptide in remodeling of cardiac ECM is discussed.

Temperature has a major influence on cardiac natriuretic peptide in salmon.

1. Natriuretic peptides have a major role in fluid and electrolyte homeostasis in vertebrates. Ambient temperature has a major influence on physiological processes in ectothermic animals. Here we have studied the mechanisms of regulation of a natriuretic peptide, sCP (salmon cardiac peptide), in salmon (Salmo salar) acclimatised and acclimated to varying temperatures. 2. The circulating and cardiac levels of sCP were found to be markedly upregulated in warm-acclimatised and warm-acclimated salmon. The release of sCP from isolated in vitro perfused salmon ventricle was, however, not increased by acclimation to higher temperatures, either in basal conditions or when stimulated by mechanical load. 3. Concomitant measurements of circulating sCP and the biologically inert N-terminal fragment of pro-sCP showed that the upregulation of circulating sCP at warm ambient temperature results from decreased elimination rather than increased secretion of sCP. This is the first direct evidence that changes in the elimination of a natriuretic peptide are used for important physiological regulation. 4. We found a paradoxical increase in cardiac sCP mRNA levels at cold temperatures which coincided with hypertrophy of the heart. sCP gene expression may therefore serve as a marker of cardiac hypertrophy in salmon, in analogy to that of atrial and brain natriuretic peptide (ANP and BNP, respectively) in mammals. 5. These results show that temperature has a major influence on the regulation of natriuretic peptide production and clearance in salmon. Salmon CP offers a novel model for the study of the endocrine function of the heart.

GATA4 mediates activation of the B-type natriuretic peptide gene expression in response to hemodynamic stress.

To identify the mechanisms that couple hemodynamic stress to alterations in cardiac gene expression, DNA constructs containing the rat B-type natriuretic peptide (BNP) promoter were injected into the myocardium of rats, which underwent bilateral nephrectomy or were sham-operated. Ventricular BNP mRNA levels were induced about 4-fold; and the BNP reporter construct containing the proximal 2200 bp, 5-fold, in response to 1-d nephrectomy. Deletion of sequences between bp -2200 and -114 did not affect basal or inducible activity of the BNP promoter. An activator protein-1-like site and two tandem GATA elements are located within this 114-bp sequence. Both deletion and mutation of the AP-1-like motif decreased basal activity but did not abolish the response to nephrectomy. In contrast, mutation or deletion of -90 bp GATA-sites abrogated the response to hemodynamic stress. The importance of these GATA elements to BNP promoter activation was further confirmed by the corresponding 38-bp oligonucleotide conferring hemodynamic stress responsiveness to a minimal BNP promoter. In gel mobility shift assays, nephrectomy increased left ventricular BNP GATA4 binding activity significantly. In conclusion, GATA elements are necessary and sufficient to confer transcriptional activation of BNP gene in response to hemodynamic stress.

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.

Mechanical load-induced alterations in B-type natriuretic peptide gene expression.

Atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and C-type natriuretic peptide are the known members of the mammalian natriuretic peptide system. Like ANP, BNP is a natriuretic and diuretic hormone that also causes peripheral vasodilation and inhibition of the sympathetic and renin-angiotensin systems. Although originally isolated from porcine brain, the BNP gene is expressed in a specific manner in cardiac myocytes in both the atria and the ventricles, but it is mainly released from the ventricles. The major determinant of BNP secretion is wall stretch, and the levels of BNP mRNA increase substantially in response to cardiac overload. In the clinical setting, BNP appears to be the most powerful neurohumoral predictor of left-ventricular function and prognosis. An acute increase in BNP gene expression occurs within 1 h and mimics the rapid induction of proto-oncogenes in response to hemodynamic stress. BNP can be used as a myocyte-specific marker to identify mechanisms that couple acute mechanical overload to alterations in cardiac gene expression. This paper is focused on the mechanisms that regulate BNP gene expression in cardiac overload. Particularly, autocrine-paracrine factors as well as cytoplasmic signaling pathways and transcription factors involved in mechanical stretch-induced BNP gene expression are discussed.

AM reverses pressor response to ET-1 independently of NO in rat coronary circulation.

Endothelin-1 (ET-1) elicits a vasoconstrictor response via ET(A) receptors, whereas simultaneous activation of ET(B) receptors triggers the release of nitric oxide (NO), which may limit the constrictor effect of ET-1. Recently, stimulation of ET(B) receptors has been shown to increase the secretion of adrenomedullin (AM), a newly identified vasorelaxing peptide. The present study was designed to see whether AM can oppose the vasoconstrictor response to ET-1. In the isolated perfused paced rat heart preparation, infusion of ET-1 at concentrations of 1 nmol/l for 30 min induced a significant coronary vasoconstriction, whereas it had no effect on perfusion pressure at a dose of 0.08 nmol/l. N(omega)-nitro-L-arginine methyl ester (L-NAME; 300 micromol/l), a potent inhibitor of NO synthase (NOS), did not change the perfusion pressure when added alone to the perfusion fluid but it unmasked the constrictor effect of ET-1 at both concentrations. In the presence of L-NAME, AM (0.03 to 1 nmol/l) markedly reversed the pressor response to ET-1 at both concentrations. Administration of AM (0.03 and 1 nmol/l) alone resulted in a dose-dependent decrease in perfusion pressure, which was not modified in the presence of L-NAME. In conclusion, the coronary vasoconstrictor response to ET-1 is markedly augmented in the presence of a NOS inhibitor. This constrictor response is substantially reversed by AM. Our results indicate that AM may serve as a paracrine modulator of ET-1-induced vasoconstriction independently of the NO pathway.