Cardiac Peptide Research Articles

Hypoxic activation of the atrial natriuretic peptide gene promoter through direct and indirect actions of hypoxia-inducible factor-1.

Atrial natriuretic peptide (ANP) is a cardiac peptide, the transcription of which is up-regulated in the ischaemic ventricle. However, the molecular mechanism of ANP induction is unclear. This study demonstrated that ANP mRNA expression in rat ventricular myocardium is induced in an early phase of ischaemia, preceded by hypoxia-inducible factor-1 (HIF-1) alpha expression. The ANP gene was also induced by hypoxia or HIF-1 inducers such as CoCl2 and desferrioxamine in H9c2 and neonatal cardiomyocytes. The 2307 bp 5'-flanking region of the rat ANP gene was cloned and fused to the luciferase gene. Evidence of the promoter activity was only apparent in the myocytes and was induced by hypoxia and HIF-1 inducers. The overexpression of HIF-1alpha markedly enhanced ANP promoter activity, and a dominant-negative isoform completely suppressed it. We demonstrated that the promoter regions are essential for hypoxic ANP induction. One promoter region, containing the HIF-1-binding sequence, is regulated directly by HIF-1. The other region is also activated by HIF-1 despite having no HIF-1-binding sequence. These results suggest that HIF-1 enhances the transactivation of the ANP gene in hypoxic myocytes, implying that stimulation of the ANP promoter by HIF-1 may in fact be responsible for the induction of the ANP gene in ischaemic ventricular myocardium.

Gq-coupled receptor agonists mediate cardiac hypertrophy via the vasculature.

The Gq-coupled receptor-signaling pathway has been implicated in the cardiac hypertrophic response to stress, but little is actually known about the contributions of Gq signaling in either the heart or the vasculature. Therefore, we developed a line of transgenic mice that express a peptide inhibitor of Gq (GqI) in vascular smooth muscle to determine if vascular Gq signaling was important in the cardiac hypertrophic response. After chronic administration of the Gq agonists phenylephrine, serotonin, and angiotensin II, we observed an attenuation of mean arterial blood pressure and an inhibition of cardiac hypertrophy in the transgenic mice with vascular-specific GqI expression. In contrast, cardiac GqI peptide expression did not attenuate the hypertension or the cardiac hypertrophy. Importantly, all mice were capable of cardiac hypertrophy, because direct beta-adrenergic receptor stimulation induced a similar level of hypertrophy in both lines of transgenic mice. This clearly suggests that after chronic Gq-coupled receptor agonist administration, it is the hypertensive state induced by vascular Gq activation that mediates remodeling of the heart, rather than direct stimulation of cardiac Gq-coupled receptors. Thus, the contribution of vascular Gq-coupled signaling to the development of cardiac hypertrophy is significant and suggests that expression of the GqI peptide is a novel therapeutic strategy to lower Gq-mediated hypertension and cardiac hypertrophy.

Salmon cardiac natriuretic peptide is a volume-regulating hormone.

The present study tested the hypothesis that salmon cardiac peptide (sCP), a new member of the family of natriuretic peptides, has an important role in the regulation of fluid balance and cardiovascular function. Intra-arterial administration of sCP increased urine output in salmon. It had a diuretic effect in rat as well, but the potency was lower. sCP increased the sodium excretion in proportion to the increased urine flow. Blood pressure was not affected by sCP in either species. Acute volume expansion elevated the plasma level of sCP in salmon, and an acute transfer of salmon from fresh to sea water decreased the circulating sCP level. Cardiac immunoreactive sCP or sCP mRNA levels were not affected by transfer to sea water. These results indicate that sCP has an important physiological role in defending salmon against volume overload but that it does not appear to contribute to the short-term regulation of blood pressure. sCP provides an excellent model of the general mechanisms of regulation of the A-type (atrial) natriuretic peptide system.

Cytokines that regulate autoimmune myocarditis.

A growing body of evidence suggests that autoimmune responses are involved in the pathogenesis of myocarditis and postinfectious cardiomyopathy. Autoimmunity may also arise after ischaemic or traumatic damage to heart tissue. Myocarditis leading to heart failure can be mimicked in rodents by immunisation with cardiac alpha myosin and peptides derived from it. Cytokines and chemokines, produced mainly by T-cells and antigen-presenting cells, control immune responses by acting as either potentiating or inhibitory agents. Gene targeting and experiments with antibodies and/or antagonists blocking cytokines and their receptors have uncovered mechanisms whereby such regulatory molecules are involved in the pathogenesis of myocarditis. Identification of regulatory key cytokines and the associated pro- or anti-inflammatory pathways involved in the pathogenesis of cardiac inflammation may have important implications for therapeutic strategies and vaccine design in the future.

Cytokines that regulate autoimmune myocarditis.

A growing body of evidence suggests that autoimmune responses are involved in the pathogenesis of myocarditis and postinfectious cardiomyopathy. Autoimmunity may also arise after ischaemic or traumatic damage to heart tissue. Myocarditis leading to heart failure can be mimicked in rodents by immunisation with cardiac alpha myosin and peptides derived from it. Cytokines and chemokines, produced mainly by T-cells and antigen-presenting cells, control immune responses by acting as either potentiating or inhibitory agents. Gene targeting and experiments with antibodies and/or antagonists blocking cytokines and their receptors have uncovered mechanisms whereby such regulatory molecules are involved in the pathogenesis of myocarditis. Identification of regulatory key cytokines and the associated pro- or anti-inflammatory pathways involved in the pathogenesis of cardiac inflammation may have important implications for therapeutic strategies and vaccine design in the future.

The neuro‐cardio‐endocrine response to acute subarachnoid haemorrhage

Whereas cardiac hormones increase after subarachnoid haemorrhage (SAH), and may contribute to sodium wastage and hyponatraemia, there is controversy concerning the relative roles of atrial natriuretic peptide (ANP) vs. brain natriuretic peptide (BNP) and the factors initiating their secretion. Noting previous work linking stress hormone responses with cardiac injury after SAH, we have studied responses in stress hormones, markers of cardiac injury and the temporal changes in ANP and BNP and related them to changes in sodium status post ictus and during recovery from acute SAH. Eighteen patients with verified SAH of variable severity were studied in a single unit for a 14-day period post ictus under controlled conditions of sodium and fluid intake. All received a standardized protocol of daily dexamethasone and nimodipine throughout the study. Severity was graded using criteria of Hess and Hunt at admission. Stress hormones (AVP, catecholamines and admission plasma cortisol), markers of cardiac injury (ECG and daily plasma troponin T) and cardiac hormones (ANP and BNP) were measured daily and related to severity, plasma sodium and renin-aldosterone activity. Hormone levels (ANP, BNP and endothelin) in cerebrospinal fluid (CSF) were also measured in nine patients. Intense neurohormonal activation (AVP, cortisol and catecholamines) at admission was associated with increased levels of both plasma ANP and BNP whereas levels in CSF were unaffected. In individual patients plasma levels of ANP and BNP were strongly correlated (P < 0.001). Cardiac events (abnormal ECG and/or elevated troponin) occurred in six of seven patients graded severe but neither stress hormones nor cardiac peptides differed significantly in patients with mild (n = 11) vs. severe (n = 7) SAH. During the course of a progressive fall in plasma sodium concentration (P = 0.001), there was a delayed activation of renin-aldosterone which was inversely correlated with declining levels of plasma ANP/BNP (P < 0.002). Excessive secretion of both ANP and BNP occurs in all patients after acute subarachnoid haemorrhage and is unrelated to severity, stress hormone activation or markers of cardiac injury. Inhibition of renin-aldosterone by cardiac hormones may impair renal sodium conservation and contribute to developing hyponatraemia. In the absence of evidence for activation of natriuretic peptides within the brain, the prompt and consistent increase in both ANP and BNP strongly supports the view that the heart is the source of increased natriuretic peptide secretion after acute subarachnoid haemorrhage.

Pronatriuretic peptide is a sensitive marker of the endocrine function of teleost heart.

We recently characterized a novel heart-specific hormone from salmon (salmon cardiac peptide, sCP). We have now prepared a recombinant plasmid expressing the NH(2)-terminal fragment of pro-sCP (NT-pro-sCP) and used it to set up a specific RIA for the peptide. Because of the sensitivity of the assay and the high circulating levels, NT-pro-sCP can be measured from as little as 2 microl of serum. This enables repeated sampling from the same animal in different experimental setups. Mechanical load increased the release of NT-pro-sCP from isolated perfused salmon ventricle, in parallel with sCP. Bolus injection of human endothelin-1 (ET-1; 1 microg) in the dorsal aorta of salmon resulted in an extensive increase of serum NT-pro-sCP (from 0.99 +/- 0.11 to 4.6 +/-1.5 nmol/l). The response was abolished by pretreatment with a specific type A ET (ET(A)) receptor antagonist (BQ-123) but not with a type B ET receptor antagonist (BQ-788). The NT-pro-sCP levels had a good correlation with those of sCP (r(2) = 0.75). Our results demonstrate the practical usefulness of circulating NT-pro-sCP as a marker of the endocrine function of salmon heart. They also suggest that ET-1 has an important role in regulating sCP release from teleost heart by an ET(A) receptor-mediated mechanism.

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.

Clinical relevance of cardiac natriuretic peptides measured by means of competitive and non-competitive immunoassay methods in patients with renal failure on chronic hemodialysis.

Increased levels of cardiac natriuretic peptides in patients undergoing hemodialysis may be a marker of cardiomyopathy and in consequence may be suitable prognostic indicators for the risk of development of cardiac disease. We measured plasma levels of ANP, BNP, proANP(1-98) and proBNP(1-76)-related peptides with some competitive and non-competitive immunoassay methods in patients with renal failure on chronic hemodialysis in order to compare the analytical performances of these methods and to evaluate the clinical usefulness of each assay for patients with chronic renal failure. ANP and BNP values significantly decreased after hemodialysis (on average, ANP by 36% and BNP by 16%); while all proANP and proBNP values tended to increase, but only proANP(1-30) (by 14.4%) and Nt-proBNP (by 9.5%) significantly. Although significant correlations were found among all the circulating levels of cardiac peptides studied, N-terminal pro-peptides correlated better among themselves than with ANP and BNP; ANP was only slightly correlated with all the other peptides, the only exception being BNP. Only BNP levels significantly increased according to the degree of ventricular hypertrophy and/or ventricular function in patients with chronic renal failure. The ANP assay is preferable in physiological and clinical studies for the rapid changes in atrial pre-load. BNP would be more useful in the follow-up of cardiac complications in patients with end-stage renal disease on regular hemodialysis. The assays of N-terminal proANP(1-98)-and proBNP(1-76)-related peptides proved to be of limited use, because they were not able to detect acute changes in pre-load during hemodialysis and were less useful than BNP levels as markers of ventricular hypertrophy and/or functional cardiac impairment.

Localization of Salmon Cardiac Peptide (sCP) in the Heart of Salmon (Salmo salar L.)

We have previously cloned and characterized a novel cardiac hormone from the salmon (Salmo salar) which has a uniquely heart-specific distribution and a low structural similarity with any other known natriuretic peptides. Specific antibodies were raised in goat against the salmon cardiac peptide. For localization and quantification, four different methods were applied: immunohistochemistry (avidin–biotin peroxidase), transmission electron microscopy, cryoimmunoelectron microscopy (protein A-gold), and a specific radioimmunoassay. Both atrial and ventricular myocytes stained immunohistochemically. The staining was similar in all myocytes and no specific myoendocrine cells were found. Within a single myocyte, both atrial and ventricular, the staining was stronger near the nucleus. Transmission electron microscopy revealed that both the atrium and the ventricle contained small sarcoplasmic granules of similar type with a diameter of 100 to 200 nm and an electron-dense core with a clear halo. The granules were typical vesicles which can be found in secretory cells utilizing the regulatory pathway. The highest number of granules was found near the nucleus, but granules were located also near the Golgi apparatus, between myofilament bundles, and in subsarcolemmal positions. Gold particles, conjugated to antibodies raised against the salmon cardiac peptide, were deposited on similar sarcoplasmic granules found in transmission electron microscopy. Among the sarcoplasmic granules with gold particles there were granules which did not show any cardiac peptide immunoreactivity. A significantly (Student's t test, P < 0.05) higher concentration of cardiac peptide was found in the heart atrium than in the ventricle, 16.2 ± 3.5 pmol/mg tissue (n = 8) and 4.5 ± 1.7 pmol/mg tissue (n = 8), respectively. The findings show that the salmon cardiac peptide is localized in secretory granules in both compartments of the heart. The morphology of the granules suggests that both the atrium and the ventricle utilize the regulatory pathway to release salmon cardiac peptide.

Chronic Myocarditis Induced by T Cells Reactive to a Single Cardiac Myosin Peptide: Persistent Inflammation, Cardiac Dilatation, Myocardial Scarring and Continuous Myocyte Apoptosis

Recent recognition that an autoimmune myocarditis may precede, and result in, dilated cardiomyopathy has focused attention on immune mechanisms of myocardial injury. In this paper, we describe a model of chronic autoimmune myocarditis in the Lewis rat. The production of myocarditis has been previously described by this group and in brief is accomplished by a single tail vein infusion of activated T cells specific for a 17-amino acid peptide from rat cardiac myosin. In this report, animals were followed for approximately 6 months post-T-cell infusion. Hearts from animals which received cardiac myosin specific T cells all showed extensive fibrosis associated with ongoing inflammation. Apoptosis, identified by TdT-mediated dUTP nick end labelling (TUNEL), was identified as a mode of myocyte death in hearts with acute and chronic myocarditis but not in age- and sex-matched controls. Immunohistochemistry was used to characterize the immune infiltrate and adhesion molecules in hearts with chronic myocarditis and these findings were compared to hearts with acute myocarditis. We propose that this rat model of chronic myocarditis mimics human disease, since inflammation results in ventricular dilatation and myocyte hypertrophy reminiscent of dilated cardiomyopathy. This model offers potential for further investigation of immune, functional and possible therapeutic aspects of autoimmune related cardiomyopathies.

Effects of dihydropyridine receptor II-III loop peptides on Ca2+ release in skinned skeletal muscle fibers

In skeletal muscle fibers, the intracellular loop between domains II and III of the alpha(1)-subunit of the dihydropyridine receptor (DHPR) may directly activate the adjacent Ca(2+) release channel in the sarcoplasmic reticulum. We examined the effects of synthetic peptide segments of this loop on Ca(2+) release in mechanically skinned skeletal muscle fibers with functional excitation-contraction coupling. In rat fibers at physiological Mg(2+) concentration ([Mg(2+)]; 1 mM), a 20-residue skeletal muscle DHPR peptide [A(S(20)); Thr(671)-Leu(690); 30 microM], shown previously to induce Ca(2+) release in a triad preparation, caused only small spontaneous force responses in approximately 40% of fibers, although it potentiated responses to depolarization and caffeine in all fibers. The COOH-terminal half of A(S(20)) [A(S(10))] induced much larger spontaneous responses but also caused substantial inhibition of Ca(2+) release to both depolarization and caffeine. Both peptides induced or potentiated Ca(2+) release even when the voltage sensors were inactivated, indicating direct action on the Ca(2+) release channels. The corresponding 20-residue cardiac DHPR peptide [A(C(20)); Thr(793)-Ala(812)] was ineffective, but its COOH-terminal half [A(C(10))] had effects similar to A(S(20)). In the presence of lower [Mg(2+)] (0.2 mM), exposure to either A(S(20)) or A(C(10)) (30 microM) induced substantial Ca(2+) release. Peptide C(S) (100 microM), a loop segment reported to inhibit Ca(2+) release in triads, caused partial inhibition of depolarization-induced Ca(2+) release. In toad fibers, each of the A peptides had effects similar to or greater than those in rat fibers. These findings suggest that the A and C regions of the skeletal DHPR II-III loop may have important roles in vivo.

Novel cardiac peptide hormone in several teleosts.

To find out the significance of the newest member of the natriuretic peptide family, salmon cardiac peptide (sCP), we have determined the distribution of the peptide and its mRNA as well as the tissue and plasma molecular forms in several teleosts. Using probes based on the salmon sCP cDNA in Northern blot analysis we found mRNA homologous to that of sCP to be present in the heart of 15 fish species representing nine different genera. We developed a specific RIA for the salmon 29 amino acid peptide to be able to study the distribution of the peptide in the heart and plasma of different fish species. Despite the probable interspecies differences in the peptide sequence, large quantities of immunoreactive sCP were found in the atrium, ventricle and plasma of most of the fish species studied, suggesting that a cardiac hormone homologous to sCP has an endocrine function in a large variety of teleost species. The molecular form of the hormone secreted and stored in the tissue was determined by gel filtration high pressure liquid chromatography. In salmon, as in most of the other fish species studied, the predominant immunoreactive sCP in plasma corresponded to the low molecular weight form, with a size similar to that of the biologically active 29 amino acid sCP (sCP-29), whereas the form stored in the heart corresponded to the high molecular weight pro-sCP-sized material. The form secreted by isolated perfused salmon ventricle, in the basal state as well as when mechanically loaded, was the sCP-29-sized peptide, thus ruling out the possibility that the conversion from high to low molecular weight material is caused by plasma proteases. In conclusion, sCP-like peptides are produced and secreted from the heart of a large number of different fish species. Their post-translational processing appears to be remarkably similar to that of mammalian atrial natriuretic peptide.

Neuropeptide variability in man.

Previous studies have established short-term variability in the circulating plasma levels of cardiac peptides such as atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). Our aim was to investigate whether such variable patterns could be observed in other vasoactive peptides. We measured the immunoreactivity of vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), endothelin-1 (ET-1) and calcitonin gene-related peptide (CGRP) in peripheral venous plasma collected at 2-min intervals over a 20-min period from patients with chronic cardiac failure (CCF) and from control subjects. In a second study, blood samples were obtained at 2-min intervals from the pulmonary artery, femoral artery and antecubital vein from patients with normal cardiac function while right atrial pressure and heart rate were constant. Peripheral blood VIP, NPY and ET-1 had peaks and troughs (levels > 2SD from the mean) in both patients and controls, with approximate intervals of 10 min. Levels of CGRP showed little variation. The overall levels [median (range); pmol L-1] of VIP [patients 27 (2.1-85.5); controls 9.8 (0-34)] and NPY [patients 20 (0-110); controls 12 (5-19)] were higher in patients (P < 0.05). Circulating plasma levels of ET-1 and CGRP were about the same in both groups [ET-1: patients 18 (2-84); controls 18 (0-48); CGRP: patients 4 (1-18.5), controls 5.5 (1-15); P = NS]. Levels of CGRP, VIP and ET-1 were similar in the pulmonary and femoral arteries, whereas systemic arterial levels of NPY were higher than in the pulmonary artery. The data demonstrate marked variability in circulating levels of the neuropeptides studied. In addition, peaks and troughs were observed every 10-15 min from all three vascular beds. If these peptides are secreted in a pulsatile pattern, then interpretations of single measurements should be guarded. Furthermore, this study raises interesting questions about the physiology of hormone secretion in man.

Regulation of encephalitogenic T cells with recombinant TCR ligands.

We have previously described recombinant MHC class II beta1 and alpha1 domains loaded with free antigenic peptides with potent inhibitory activity on encephalitogenic T cells. We have now produced single-chain constructs in which the peptide Ag is genetically encoded within the same exon as the linked beta1 and alpha1 domains, overcoming the problem of displacement of peptide Ag from the peptide binding cleft. We here describe clinical effects of recombinant TCR ligands (RTLs) comprised of the rat RT1.B beta1alpha1 domains covalently linked to the 72-89 peptide of guinea pig myelin basic protein (RTL-201), to the corresponding 72-89 peptide from rat myelin basic protein (RTL-200), or to cardiac myosin peptide CM-2 (RTL-203). Only RTL-201 possessed the ability to prevent and treat active or passive experimental autoimmune encephalomyelitis. Amelioration of experimental autoimmune encephalomyelitis was associated with a selective inhibition of proliferation response and cytokine production by Ag-stimulated lymph node T cells and a drastic reduction in the number of encephalitogenic and recruited inflammatory cells infiltrating the CNS. The exquisitely selective inhibition could be observed between molecules that differ by a single methyl group (the single amino acid residue difference between RTL-200 (threonine) and RTL-201 (serine) at position 80 of the myelin basic protein peptide). These novel RTLs provide a platform for developing potent and selective human diagnostic and therapeutic agents for treatment of autoimmune disease.

Atrial Natriuretic Peptide Is Involved in Renal Actions of Moxonidine

Moxonidine, an antihypertensive imidazoline compound, reduces blood pressure by selective activation of central imidazoline I(1)-receptors and inhibition of sympathetic nerve activity and by direct actions on the kidney, with both mechanisms resulting in diuresis and natriuresis. We hypothesized that the hypotensive and renal actions of moxonidine may be mediated by atrial natriuretic peptide (ANP), a cardiac peptide involved in pressure and volume homeostasis through its vasodilatory, diuretic, and natriuretic actions. Renal parameters were measured on an hourly basis over a period of 4 hours in conscious rats that received bolus intravenous injections of moxonidine (1 to 150 microg/300 microL saline). During the first hour, moxonidine dose-dependently stimulated diuresis, natriuresis, kaliuresis, and urinary cGMP, the index of ANP activity. Moxonidine (50 microg) significantly (P<0.001) stimulated urinary volume (0.35+/-0.04 versus 1.05+/-0.09 mL/h per 100 g), sodium (14. 3+/-2.5 versus 51.8+/-6.5 micromol/h per 100 g), potassium (10.5+/-2. 3 versus 32.3+/-3.2 micromol/h per 100 g), and cGMP (325+/-52 versus 744+/-120 pmol/h per 100 g). Pretreatment with a selective imidazoline receptor antagonist, efaroxan, dose-dependently inhibited moxonidine-stimulated renal parameters. Efaroxan (25 microg per rat) significantly inhibited moxonidine-stimulated diuretic and natriuretic effects and urinary cGMP excretion (744+/-120 versus 381+/-137 pmol/h per 100 g, P<0.02). The alpha(2)-adrenoceptor antagonist yohimbine (50 microg per rat) partially yet significantly inhibited moxonidine-stimulated diuresis and natriuresis but not cGMP excretion. Plasma ANP was dose-dependently increased by moxonidine and was inhibited by pretreatment with efaroxan (220.8+/-36.9 versus 100.3+/-31.7 pg/mL, P<0.03) but not by yohimbine. In conclusion, selective in vivo activation of imidazoline receptors by moxonidine is associated with dose-dependent diuresis, natriuresis, and kaliuresis as well as stimulated plasma ANP and urinary cGMP excretion, thus implicating ANP in the renal actions of moxonidine.

Amelioration with vessel dilator of acute tubular necrosis and renal failure established for 2 days.

Seventeen Sprague-Dawley rats had ischemic nonoliguric acute renal failure (ARF) induced by vascular clamping resulting in their preischemic blood urea nitrogen (BUN) and creatinine levels of 16 +/- 1 and 0.56 +/- 0.05 mg/dl to increase to 162 +/- 4 and 8.17 +/- 0.5 mg/dl, P < 0.001, respectively, at day 4 of postischemia. Vessel dilator, a 37-amino-acid cardiac peptide hormone (0.3 microg x kg(-1) x min(-1) ip), decreased the BUN and creatinine levels to 53 +/- 17 mg/dl and 0.98 +/- 0.12 mg/dl (P < 0.001) in another seven animals where ARF had been established for 2 days. Water excretion doubled with ARF and was further augmented by vessel dilator. Transthoracic echocardiography revealed left ventricular dilation as a probable cause of the increase in vessel dilator in the circulation with ARF, and vessel dilator infusion reversed this dilation. At day 6 of ARF, mortality decreased to 14% with vessel dilator from 88% without vessel dilator. Acute tubular necrosis was <5% in the vessel dilator-treated rats compared with 25% to >75% in the placebo-treated ARF animals. We conclude that vessel dilator improves acute tubular necrosis and renal function in established ARF.

Does the mechanism of action of biatrial pacing for atrial fibrillation involve changes in cardiac haemodynamics? Assessment by Doppler echocardiography and natriuretic peptide measurements.

The antifibrillatory mechanism of biatrial (BI) pacing has not been fully elucidated. We investigated the role of a haemodynamic mechanism in eight patients implanted with a BI pacemaker (Chorus RM) by comparing changes in mitral Doppler flow and atrial and B-type natriuretic peptide levels (ANP, BNP) with BI pacing compared with sinus rhythm and right atrial (RA) pacing. Measurements were taken after 60 min in the supine position in each of two pairs of randomized pacing modes: (a) AAI40 beats x min(-1), (allows sinus rhythm mean rate 56 beats x min(-1), SR) vs AAI 40 beats x min(-1) with synchronized left atrial pacing (SRSync); (b) overdrive AAI RA pacing (89 beats x min(-1) (n = 6) or 70 beats x min(-1) (n = 2)) vs overdrive AAI BI pacing. Within each pair there was significant earlier activation of the left atrial Doppler signal in relation to the surface ECG P wave with BI pacing (SR 163 +/- 10 ms vs SRSync 144 +/- 21 ms (P = 0.02), and RA 232 +/- 14 ms vs BI 196 +/- 16 ms (P = 0.001)), and significant shortening of the P-R interval (SR 163 +/- 29 ms vs SRSync 148 +/- 20 (P = 0.007) and RA 261 +/- 27 ms vs BI 232 +/- 23 (P = 0.001)). The net observed effect was of no change in the atrioventricular timing sequence (delay of peak E or A to QRS/ mitral valve closure) and no change in other Doppler echo parameters. Levels of the cardiac peptides ANP and BNP were raised compared with healthy controls, but did not significantly change during the study. Acute BI pacing shortens the P-R interval and causes earlier left atrial contraction in relation to the surface electrocardiogram P wave. It does not alter the atrioventricular timing cycle, any other Doppler measurements or change cardiac peptide levels. This suggests that BI pacing does not cause haemodynamic changes that could account for any antifibrillatory properties.

Cardiac adrenomedullin gene expression and peptide accumulation after acute myocardial infarction in rats.

Plasma adrenomedullin (AM) has been shown to increase in the early phase of acute myocardial infarction (MI). However, little information is available regarding cardiac AM synthesis after MI. Accordingly, we examined the time course of ventricular AM production and potential stimulation of AM in the infarcted and noninfarcted regions in MI rats produced by coronary artery ligation. Compared with sham-operated rats, the ventricular AM peptide level 6 h after MI increased 1.5-fold in the infarcted region and 1.7-fold in the noninfarcted region in association with increased left ventricular end-diastolic pressure (EDP). Northern blot analysis also showed marked induction of AM gene expression in the infarcted region (11-fold) and the noninfarcted region (6-fold) 6 h after MI. The AM peptide level in the infarcted region reached its peak (2. 6-fold) 1 wk postinfarction and thereafter decreased to normal. In the noninfarcted region, however, the AM level remained elevated for at least 4 wk. Immunohistochemical studies demonstrated that intense immunostaining for AM was limited to myocytes in both the infarcted and noninfarcted regions. Interestingly, the AM level in the noninfarcted region correlated positively with infarct size (r = 0. 40, P < 0.01) and EDP (r = 0.52, P < 0.001). An oral angiotensin-converting enzyme inhibitor suppressed the overproduction of AM 1 wk postinfarction in association with decreases in EDP and mean arterial pressure. In summary, cardiac AM synthesis was rapidly induced in both the infarcted and noninfarcted regions after MI. The subsequent ventricular AM in the two regions demonstrated different time-concentration curves during 4 wk after MI. AM may be synthesized predominantly by cardiac myocytes, but not by fibroblasts, at least in part, in association with increased ventricular load after MI.

Treatment of heart failure guided by plasma aminoterminal brain natriuretic peptide (N-BNP) concentrations

There is currently no objective practical guide to intensity of drug treatment for individuals with heart failure. We hypothesised that pharmacotherapy guided by plasma concentrations of the cardiac peptide aminoterminal brain natriuretic peptide (N-BNP) would produce a superior outcome to empirical trial-based therapy dictated by clinical acumen. 69 patients with impaired systolic function (left-ventricular ejection fraction <40%) and symptomatic heart failure (New York Heart Association class II-IV) were randomised to receive treatment guided by either plasma N-BNP concentration (BNP group) or standardised clinical assessment (clinical group). During follow-up (minimum 6-months, median 9.5 months), there were fewer total cardiovascular events (death, hospital admission, or heart failure decompensation) in the BNP group than in the clinical group (19 vs 54, p=0.02). At 6 months, 27% of patients in the BNP group and 53% in the clinical group had experienced a first cardiovascular event (p=0.034). Changes in left-ventricular function, quality of life, renal function, and adverse events were similar in both groups. N-BNP-guided treatment of heart failure reduced total cardiovascular events, and delayed time to first event compared with intensive clinically guided treatment.