The interaction between atrial natriuretic peptide and cardiac parasympathetic function

Natriuretic Peptide Receptors (NPRs) as a Potential Target for the Treatment of Heart Failure

PURPOSE OF REVIEW

Heart failure is defined as a complex clinical syndrome that results from any structural or functional impairment of ventricular filling or ejection of blood. The natriuretic peptide is known to exert its biological action on the kidney, heart, blood vessels, renin-angiotensin system, autonomous nervous system, and central nervous system. The natriuretic peptide-natriuretic receptor system plays an important role in the regulation of blood pressure and body fluid volume through its pleiotropic effects.

RECENT FINDINGS

The clinical and animal studies suggest that natriuretic peptide-natriuretic receptors are important targets for the treatment of heart failure and other cardiovascular diseases. Even though attempts targeting natriuretic peptide receptors are underway for heart failure treatment, they seem insufficient despite the receptor systems' potential. This review summarizes natriuretic peptide-natriuretic receptor system's physiological actions and potential target for the treatment of heart failure. Natriuretic peptides play multiple roles in different parts of the body, almost all of the activities related to this receptor system appear to have the potential to be harnessed to treat heart failure or symptoms associated with heart failure.

Cyclic nucleotide regulation of cardiac sympatho-vagal responsiveness

Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are now recognized as important intracellular signalling molecules that modulate cardiac sympatho-vagal balance in the progression of heart disease. Recent studies have identified that a significant component of autonomic dysfunction associated with several cardiovascular pathologies resides at the end organ, and is coupled to impairment of cyclic nucleotide targeted pathways linked to abnormal intracellular calcium handling and cardiac neurotransmission. Emerging evidence also suggests that cyclic nucleotide coupled phosphodiesterases (PDEs) play a key role limiting the hydrolysis of cAMP and cGMP in disease, and as a consequence this influences the action of the nucleotide on its downstream biological target. In this review, we illustrate the action of nitric oxide-CAPON signalling and brain natriuretic peptide on cGMP and cAMP regulation of cardiac sympatho-vagal transmission in hypertension and ischaemic heart disease. Moreover, we address how PDE2A is now emerging as a major target that affects the efficacy of soluble/particulate guanylate cyclase coupling to cGMP in cardiac dysautonomia.

Efficacy and safety of nesiritide in patients with decompensated heart failure: a meta-analysis of randomised trials

OBJECTIVES

Current evidence suggests that nesiritide may have effects on renal function and decrease the incidence of mortality. However, a clear superiority using nesiritide in terms of renal toxicity and mortality in patients with heart failure was not consistently proven by previous studies. We performed a meta-analysis of all randomised trials to obtain the best estimates of efficacy and safety of nesiritide for the initial treatment of decompensated heart failure.

METHOD

We performed a meta-analysis of randomised trials of nesiritide in patients with decompensated heart failure (n=38,064 patients, in 22 trials). Two reviewers independently extracted data. Data on efficacy and safety outcomes were collected. We calculated pooled relatives risk (RRs), weighted mean difference and associated 95% CIs.

RESULTS

Compared with placebo, dobutamine and nitroglycerin, nesiritide indicated no increasing risk of total mortality. Compared with the combined control therapy, nesiritide was associated with non-significant differences in short-term mortality (RR 1.24; 95% CI 0.85 to 1.80; p=0.27), mid-term mortality (RR 0.86; 95% CI 0.60 to 1.24; p=0.42) and long-term mortality (RR 0.94; 95% CI 0.75 to 1.18; p=0.61). Nesiritide therapy increased the risk of hypotension (p<0.00 001) and bradycardia (p=0.02) when compared with control therapy. Compared with dobutamine or placebo therapy, no differences in serum creatinine, blood urea nitrogen and creatinine clearance, and no risk of the need for dialysis was observed in nesiritide therapy.

CONCLUSIONS

Our findings indicated that, in patients with heart failure, nesiritide was not associated with the risk of mortality. However, it increased the risk of cardiovascular adverse events. The change of serum creatinine and creatinine clearance had no significant difference, and no risk of the need for dialysis was observed after low-dose nesiritide treatment.

Patent ductus arteriosus in preterm infants is associated with cardiac autonomic alteration and predominant parasympathetic stimulation

BACKGROUND

Hemodynamic disorders in patent ductus arteriosus (PDA) may alter the stimulation of the autonomic nervous system.

AIM

The objective of this study was to analyze the orthosympathetic-parasympathetic balance in preterm infants with PDA.

STUDY DESIGN AND SUBJECTS

Patients were included from consecutive admissions to Amiens University Hospital from 2009 to 2011. We defined a PDA group and a Control group (echographic criteria). For each patient, three 4-minutes segments of ECG were recorded during quiet sleep and the RR chronologic series were extracted, and spectral (Fourier Transform) and time-domain analyses were performed. For each parameter of heart rate variability (HRV), average of three measures was determined and analysed.

RESULTS

Forty-four patients were included for analysis. The total HRV power, LF/HF ratio and SDNN were lower in the PDA group (n = 22, gestational age 28.2 w ± 1.9) than in the Control group (n = 22, gestational age 28.8 w ± 2). The decrease in LF power destabilized the autonomic balance in favour of parasympathetic stimulation. After adjustment for postconceptional age, PDA was still associated with parameters of autonomic neural stimulation.

CONCLUSION

These results suggest association of PDA with predominance of parasympathetic stimulation in preterm infants. The mechanisms of homeostasis in patients with PDA are very complex and involve both circulatory adaptations and control by autonomic pathway. If confirmed, our results could be interesting for future researches aiming to verify the interest of new targeted therapies for the management of PDA.

Relationship between status of plasma atrial natriuretic peptide and heart rate variability in human subjects

A relationship may exist between plasma atrial natriuretic peptide (P-ANP) and heart rate variability (HRV), which reflects the activity of the autonomic nervous system. We performed a survey in human subjects to examine the relationship between P-ANP and HRV parameters. Three ethnic groups (Han, Uygur, and Kazakh) provided blood and urine samples and underwent 24-h ambulatory blood pressure monitoring and 24-h ECG recording (24-h Holter ECG). There was a positive correlation between P-ANP and HF, as well as a negative correlation between P-ANP and the LF/HF ratio, in all subjects from the 3 ethnic groups. There was no association of BP with any of the blood, urinary, and HRV parameters. Our results suggested the possibility of a relationship between P-ANP and HRV, which reflects autonomic activity. These findings are consistent with the previous report of a close relationship between ANP and cardiac parasympathetic and/or sympathetic activity.

The role of atrial natriuretic peptide in modulating cardiac electrophysiology

Since the discovery of atrial natriuretic peptide (ANP) in 1981, significant progress has been made in understanding the mechanism of its release and its role in salt and water balance in the body. It has also become clear that ANP plays a key role in cardiac electrophysiology, modulating the autonomic nervous system and regulating the function of cardiac ion channels. The clinical importance of this role was established when mutations in NPPA, the gene encoding ANP, were identified as a cause of familial atrial fibrillation. This review examines our current understanding of the electrophysiological effects of ANP, and their physiological relationship to clinical studies linking ANP and atrial fibrillation.

Neuromodulators of peripheral cardiac sympatho-vagal balance

The traditional model of efferent cardiac noradrenaline and acetylcholine release being driven solely via brainstem integration of circulatory reflex afferent input needs to be modified in the light of the discovery of numerous local cardiac factors that impact on peripheral neuronal neurotransmitter release. These neuromodulators can be intrinsic to sympathetic ganglia or vagal neurons (such as neuronal nitric oxide synthase), act as cotransmitters between these neuronal populations (such as neuropeptide Y) or are released from the myocardium itself to act on neurons in a paracrine manner (such as natriuretic peptides). Both myocardial infarction and congestive heart failure are characterized by enhanced regulation of these neuromodulators. This review will focus on recent evidence that nitric oxide, natriuretic peptides and neuropeptide Y act by converging on neuronal cyclic nucleotide-dependent pathways to alter the autonomic phenotype in both health and disease.

Natriuretic peptide expression in the heart of the TTR-ANP transgenic mouse-Comparison to the normal heart

The transgenic mice, TTR-ANP, carrying a fusion gene comprising the transthyretin promoter and the atrial natriuretic peptide (ANP) structural sequence, are known to have elevated ANP plasma levels as well as lowered blood pressure levels. On the other hand, it is not known whether these transgenic mice show changed natriuretic peptide (NP) expression patterns in the heart. Therefore, we examined the distribution of NPs in the myocardium and the conduction system of transgenic mice overexpressing ANP, as well as in wild-type littermates. The hearts were serially sectioned and processed for immunohistochemistry, with antisera against ANP and brain natriuretic peptide (BNP). Florescence microscopy was performed for qualitative analysis. Immunoreactivity for ANP and BNP was detected to a similar degree in the conduction system of both transgenic and wild-type mice. The nodal tissues never exhibited immunoreactions for ANP or BNP, whereas Purkinje fibers of the atrioventricular junctional tissue, bundle branches, and the peripheral Purkinje fiber network exhibited specific immunoreactivity. Atrial and ventricular myocytes of both transgenic and wild-type mice exhibited ANP and BNP to a similar extent. This is the first study examining the expression pattern of NPs in the cardiac conduction system of the mouse as well as the pattern of ANP and BNP expression in the conduction system of TTR-ANP transgenic mice and its wild-type siblings. The findings in this study suggest that ectopic ANP expression and release do not repress cardiac production of ANP.

Receptor binding occurrence and plasma levels of natriuretic peptides in response to sympathectomy

In the present investigation the relationship between the sympathetic nervous system and the endocardial levels of receptor binding sites for natriuretic peptides and the plasma content of atrial natriuretic peptide were analyzed in rats. In order to destruct the cardiac sympathetic nerve terminals, chemical sympathectomy with 6-hydroxydopamine was made in parallel with intravenous measurements of blood pressure and heart frequency. By use of immunohistochemical and enzyme-linked-immunosorbent techniques the expression of tyrosine hydroxylase-positive sympathetic nerve terminals and plasma levels of pro-atrial natriuretic peptide were determined, respectively. The occurrence of receptor binding sites for natriuretic peptides was examined by in vitro receptor autoradiography. In contrast to the marked occurrence of natriuretic peptide receptor binding sites seen in the ventricular endocardium of control rats, the sympathectomized rats exhibited a decreased number of binding sites for natriuretic peptides in the endocardium of both the right and left chambers. Interestingly, this was found in parallel with a significant decrease of systolic and diastolic blood pressure and increased plasma levels of pro-atrial natriuretic peptide in the treated group of rats. These findings, together with those in previous studies, give support to an idea that one part of the blood pressure-decreasing effects, seen in patients treated with beta-adrenergic blockade, might be through a reduction of the natriuretic clearance receptor C, then giving rise to increased levels of atrial natriuretic peptide.

Guanylyl cyclase receptors mediate cardiopulmonary vagal reflex actions of ANP

Atrial natriuretic peptide (ANP) potentiates vagal cardiopulmonary reflexes due to chemosensory (Bezold-Jarisch [B-J] reflex) or mechanosensory (ramp baroreflex) activation. The ANP receptor mediating these actions is unknown. We examined the role of particulate guanylyl-cyclase (pGC) receptors in ANP-induced enhancement of cardiopulmonary vagal reflexes. Cardiopulmonary baroreceptor reflex function was assessed by bradycardic responses to ramp blood pressure rises after rapid intravenous methoxamine (100 micro g/kg bolus dose). The B-J reflex was evoked by 3 intravenous doses of serotonin (1 to 10 micro g/kg). In conscious, chronically instrumented rats (n=9), these tests were performed on each animal during randomized infusions of rat ANP (150 ng/kg per minute IV), saline (270 micro L/h IV), the pGC receptor antagonist HS-142-1 (3 mg/kg IV), or combined HS-142-1+ANP treatment. HS-142-1 alone attenuated normal B-J reflex (by 33+/-8%, P<0.05) but not ramp baroreflex responses. As we showed previously, ANP enhanced baroreflex and B-J reflex bradycardia (by approximately 140% and approximately 30%, respectively, P<0.05), compared with saline infusion. These ANP effects were completely blocked by HS-142-1, demonstrating that the cardiopulmonary vagal reflex actions of ANP occurred through pGC natriuretic peptide receptors. Additionally, we have provided evidence for the first time that pGC natriuretic peptide receptors are essential for the full expression of the B-J reflex but not for that of cardiopulmonary vagal baroreflexes. This tonic interaction between pGC natriuretic peptide receptors and cardiopulmonary chemosensitive receptors may be important during pathophysiological activation of B-J reflex, such as with myocardial infarction.

Natriuretic peptides in relation to the cardiac innervation and conduction system

During the past two decades, the heart has been known to undergo endocrine action, harbouring peptides with hormonal activities. These, termed "atrial natriuretic peptide (ANP)," "brain natriuretic peptide (BNP)," and "C-type natriuretic peptide (CNP)," are polypeptides mainly produced in the cardiac myocardium, where they are released into the circulation, producing profound hypotensive effects due to their diuretic, natriuretic, and vascular dilatory properties. It is, furthermore, well established that cardiac disorders such as congestive heart failure and different forms of cardiomyopathy are combined with increased expression of ANP and BNP, leading to elevated levels of these peptides in the plasma. Besides the occurrence of natriuretic peptides (NPs) in the ordinary myocardium, the presence of ANP in the cardiac conduction system has been described. There is also evidence of ANP gene expression in nervous tissue such as the nodose ganglion and the superior cervical ganglion of the rat, ganglia known to be involved in the neuronal regulation of the heart. Furthermore, in the mammalian heart, ANP appears to affect the cardiac autonomic nervous system by sympathoinhibitory and vagoexcitatory actions. This article provides an overview of the relationship between the cardiac conduction system, the cardiac innervation and NPs in the mammalian heart and provides data for the concept that ANP is also involved in neuronal cardiac regulation.

Natriuretic peptides like NO facilitate cardiac vagal neurotransmission and bradycardia via a cGMP pathway

We tested the hypothesis that natriuretic peptide receptors (NPRs) that are coupled to cGMP production act in a similar way to nitric oxide (NO) by enhancing acetylcholine release and vagal-induced bradycardia. The effects of enzyme inhibitors and channel blockers on the action of atrial natriuretic peptide (ANP), brain-derived natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) were evaluated in isolated guinea pig atrial-right vagal nerve preparations. RT-PCR confirmed the presence NPR B and A receptor mRNA in guinea pig sinoatrial node tissue. BNP and CNP significantly (P < 0.05) enhanced the heart rate (HR) response to vagal nerve stimulation. CNP had no effect on the HR response to carbamylcholine and facilitated the release of [(3)H]acetylcholine during atrial field stimulation. The particulate guanylyl cyclase-coupled receptor antagonist HS-142-1, the phosphodiesterase 3 inhibitor milrinone, the protein kinase A inhibitor H89, and the N-type calcium channel blocker omega-conotoxin all blocked the effect of CNP on vagal-induced bradycardia. Like NO, BNP and CNP facilitate vagal neurotransmission and bradycardia. This may occur via a cGMP-PDE3-dependent pathway increasing cAMP-PKA-dependent phosphorylation of presynaptic N-type calcium channels.

Reduced baroreceptor sensitivity during hypotension in ANP-knockout mice

We studied baroreflex gain in inactin-anesthetized mice that had been genetically modified to be depleted of atrial natriuretic peptide (ANP -/-). Wild-type mice (ANP +/+) served as controls. ANP -/- mice had a significantly higher basal arterial blood pressure (ABP) than ANP +/+ mice [112 ± 7 vs. 80 ± 5 mmHg (mean ± SEM)]. Their basal heart rates were not different (491 ± 13 vs. 446 ± 19 bpm). A third group, composed of ANP +/+ mice only, was rendered acutely hypertensive by an intravenous infusion of arginine vasopressin acetate (0.3 pg bolus followed by 0.3 pg/h) so as to serve as a control for the elevated ABP in the ANP -/- mice. Transient changes in ABP were caused by bolus injections of oxymetazoline hydrochloride (1.5-3 ng) or sodium nitroprusside (20-100 ng). Baroreflex gain was calculated as the ratio of the peak heart rate change that followed the peak change in mean ABP resulting from injection of oxymetazoline or nitroprusside. There were no significant differences among the groups in their responses to transient hypertension. On the other hand, the ANP -/- mice showed a significantly depressed tachycardic response to transient hypotension when compared with the other two groups. We conclude that the ANP -/- mice are unable to increase efferent sympathetic nervous activity adequately above the high basal activity that is a feature of this animal model.Key words: atrial natriuretic peptides, knockouts, arterial blood pressure.

Nesiritide (hBNP): a new class of therapeutic peptide for the treatment of decompensated congestive heart failure

Natriuretic peptides are a family of endogenous peptide hormones with vasodilating, natriuretic, diuretic, and lusitropic properties. Administration of pharmacologic doses of exogenous natriuretic peptides may provide therapeutic benefit in patients with chronic heart failure. In controlled clinical trials, short-term administration of nesiritide (human brain natriuretic peptide) to patients with heart failure is associated with improved resting hemodynamics, modest increases in sodium excretion, evidence of suppression of neurohormonal activation, and improvements in symptoms of heart failure. Additional trials to determine the clinical efficacy and safety of nesiritide are warranted. (c)2001 by CHF, Inc.

Modulation of chronotropic and inotropic heart vagus actions as a non-pressor effect of angiotensin II in the anaesthetized rat

(1) In vagotomized, anaesthetized rats, effects of stimulation of cardiac N. vagus (2-25 Hz) on cardiac and circulatory functions were studied: we recorded transient reductions in heart rate (HR), in left-ventricular systolic pressure (LV Ps), in maximal change in left-ventricular pressure development (dp/dt)max and in mean arterial pressure (MAP, A. femoralis). (2) Bolus injection of angiotensin II (AII, 2.5-100 microg/kg body weight) caused (a) transient increases in HR, LV Ps and MAP (pressor effects, maximal changes occurred within 3 min after injection), and (b) dose-dependently reduced effects of vagus stimulation (non-pressor effects, recorded 10 min after injection). Due to fast breakdown of All in the circulatory system, all observed vagus stimulation effects were completely recovered within 1 h after injection. (3) Plasma concentration of AII was recorded with a highly specific radioimmunoassay: 10 min after AII injection (non-pressor range), plasma concentration was clearly higher than physiological levels in all experiments with 10 microg AII/kg at least. (4) Treatment with propranolol (beta-adrenoceptor blocker, 1 mg/kg body weight) did not reduce the vagus effects alone, but decreased the modulatory AII effects. This result hints at the activation of sympathetic beta-adrenergic receptors by AII counteracting the parasympathetic cardiac control.

Atrial natriuretic peptide and mechanisms of cardiovascular control. Role of serotonergic receptors

Atrial natriuretic peptide (ANP) inhibits renal sympathetic nerve activity (RSNA), provided the vagi are intact. Afferents from chemosensitive cardiopulmonary receptors are specifically required. Such receptors produce the Bezold-Jarisch reflex, are prominent on the ventricular epicardium, and are richly supplied with 5-hydroxytryptamine type 3 (5-HT3) receptors. We tested the hypothesis that epicardial 5-HT3-sensitive neurons mediate depressor effects of ANP. Through a special catheter, anesthetized, sinoaortically denervated rats received pericardial test injections of ANP (28-amino acid rat ANP; 100 and 1,000 ng) in the presence or absence of 5-HT3 antagonist (Ondansetron, 20 micrograms/kg; n = 9). In other groups we observed the effects of systemic ANP while blocking either epicardial or systemic 5-HT3 receptors. Arterial blood pressure (ABP), heart rate, and RSNA were recorded continuously. Intravenous ANP (100 or 200 ng) decreased ABP and RSNA significantly. In contrast, intrapericardial ANP (100 or 1,000 ng) caused no significant fall in ABP or RSNA. Both intravenous and pericardial Ondansetron reduced the effects of intravenous ANP significantly, but the intravenous antagonism was significantly greater. We conclude that epicardial chemosensitive afferents are not sensitive to ANP and that sympathoinhibitory effects of ANP arise from a 5-HT3 agonist that cannot be produced when ANP is confined to the pericardial space.

Clonidine and ST-91 may activate imidazoline binding sites in the heart to release atrial natriuretic peptide

It is well established that the antihypertensive drug clonidine acts through specific imidazoline receptors in the brain and kidney to increase diuresis, natriuresis, and kaliuresis. We have previously shown that the effects of clonidine are associated with elevated plasma atrial natriuretic peptide (ANP). Similar to clonidine, ST-91, a clonidine analogue that does not cross the blood-brain barrier, evokes renal responses that are also associated with elevated plasma ANP. The mechanisms of ANP increase elicited by these imidazoline drugs are unclear. Since ANP is primarily released from the cardiac atria, we investigated the direct effect of the imidazoline drugs on ANP release by incubating left and right atrial sections with 10(-6) mol/L ST-91 in the presence and absence of efaroxan, a selective imidazoline I1 receptor antagonist, for 30 minutes at 37 degrees C. ST-91 significantly stimulated ANP release, and the effect was inhibited by 10(-6) mol/L efaroxan. Further studies using heart perfusion with the imidazoline drugs with and without antagonists over 30 minutes revealed that both clonidine and ST-91 gradually stimulated ANP release. Also, perfusion with these compounds resulted in a gradual decrease in heart rate, but bradycardia was significant only with clonidine. The effects of ST-91 were inhibited by 10(-6) mol/L efaroxan and to a lesser extent by 10(-6) mol/L yohimbine, implying that the actions of ST-91 were mainly mediated by I1 receptors. On the other hand, the actions of clonidine were inhibited by 10(-5) mol/L efaroxan and by 10(-6) mol/L yohimbine, an alpha2-adrenoceptor antagonist, which may suggest that the actions of clonidine were preferentially mediated by alpha2-adrenoceptors in the heart. These results indicate that the peripheral actions of clonidine are probably mediated by alpha2 and imidazoline receptors and may involve direct stimulation of ANP release by the cardiac atria--an effect that may account for the increase in plasma ANP levels and diuresis and natriuresis observed in vivo after administration of clonidine and its analogues.

Natriuretic peptide immunoreactivity in nerve structures and Purkinje fibres of human, pig and sheep hearts

Atrial natriuretic peptide is a well-described peptide in cardiac Purkinje fibres and has been shown to interfere with the autonomic regulation in the heart of various species, including man. Recently, we detected immunoreactivity for the peptide in intracardial ganglionic cells and nerve fibre varicosities of bovine hearts, by the use of a modified immunostaining technique that induced an improved detection of natriuretic peptides. These findings raised the question as to whether natriuretic peptides are detectable in these tissues in man and other species. The conduction system from human, pig and sheep hearts was dissected processed with antisera against atrial natriuretic peptide and the closely related brain natriuretic peptide. Immunostaining for the brain natriuretic peptide was detected in some Purkinje fibres in all of these species. Interestingly, in pig, sheep and human hearts, some ganglionic cells and nerve fibres showed atrial natriuretic peptide immunoreactivity, particularly in the soma of human ganglionic cells. This is the first study showing immunoreactivity for the atrial natriuretic peptide in nerve structures and for the brain natriuretic peptide in Purkinje fibres of the human heart. The results give a morphological correlate for the documented effects of atrial natriuretic peptide on the heart autonomic nervous system and for the presumable effects of brain natriuretic peptide in the conduction system of man.

Hemodynamic and renal excretory effects of human brain natriuretic peptide infusion in patients with congestive heart failure. A double-blind, placebo-controlled, randomized crossover trial

BACKGROUND

The pharmacological effects of infusion of human brain natriuretic peptide (hBNP) in patients with severe congestive heart failure have not been characterized previously.

METHODS AND RESULTS

Twenty patients with severe congestive heart failure were randomized in a double-blind, placebo-controlled, crossover trial to receive incremental 90-minute infusions of hBNP (0.003, 0.01, 0.03, and 0.1 microgram/kg per minute) or placebo on 2 consecutive days. At the highest completed dose of the hBNP, mean pulmonary artery pressure decreased from 38.3 +/- 1.6 to 25.9 +/- 1.7 mm Hg; mean pulmonary capillary wedge pressure decreased from 25.1 +/- 1.1 to 13.2 +/- 1.3 mm Hg; mean right atrial pressure decreased from 10.9 +/- 1 to 4.8 +/- 1.0 mm Hg; mean arterial pressure decreased from 85.2 +/- 2.0 to 74.9 +/- 1.7 mm Hg; and cardiac index increased from 2.0 +/- 0.1 to 2.5 +/- 0.1 L/min per square meter (all P < .01 versus placebo). Urine volume and urine sodium excretion increased significantly during hBNP infusion when compared with placebo infusion (90 +/- 38 versus 67 +/- 27 mL/h and 2.6 +/- 2.4 versus 1.4 +/- 1.2 mEq/h, respectively, both P < .05 versus placebo), whereas creatinine clearance and urinary potassium excretion did not change.

CONCLUSIONS

Infusion of incremental doses of hBNP is associated with favorable hemodynamic and natriuretic effects in patients with severe congestive heart failure.

Direct chronotropic effects of atrial and C-type natriuretic peptides in anaesthetized dogs

1. The chronotropic effects of atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) were investigated using injections (50 micrograms in 1 ml of Tyrode solution as bolus over 1 min) directly into the sinus node artery of 21 anaesthetized and vagotomized dogs which had been pretreated with a beta-adrenoceptor antagonist. The injections were also repeated following: (a) alpha-adrenoceptor antagonism (prazosin) and muscarinic receptor antagonism (atropine); (b) inhibition of prostaglandin synthesis (indomethacin); (c) angiotensin II AT1 receptor antagonism (losartan); (d) histamine H1 (mepyramine) and H2 (cimetidine) receptor antagonism. 2. The results obtained indicate that ANP had no significant effect on the basal sinus rate, whereas CNP produced a slight but significant increase of 12 +/- 2 beats min-1. The effect of CNP was long-lasting (return to pre-injection levels after maximum effect in 17 +/- 3 min) and was not influenced by the various antagonists mentioned above. 3. During in vitro experiments on spontaneously beating right atria isolated from 6 dogs, the injection of CNP (50 micrograms in 1 ml of Tyrode solution) into the sinus node artery produced an increase in atrial rate of 14 +/- 1 beats min-1. 4. The results of this work indicate that CNP exerts a significant and prolonged positive chronotropic effect both in vivo and in vitro. Other studies are required to elucidate the mechanism of action of CNP on the heart conduction system, to ascertain the presence of natriuretic peptide receptor B in the region of the sinoatrial node and to determine the role of CNP in the control of heart rate.

Atrial natriuretic peptide and cardiac electrophysiology: autonomic and direct effects

Atrial natriuretic peptide (ANP) has varied effects on cardiac electrophysiologic parameters including heart rate, intraatrial conduction time, and refractory period. ANP's vagoexcitatory and sympathoinhibitory actions as well as its direct actions on cardiac ion currents may be responsible for some of these effects. This review discusses the role of ANP in cardiac electrophysiology, its interactions with the autonomic nervous system and baroreceptor reflex, and its effects on cardiac ion currents.

Hemoconcentration and stress: a review of physiological mechanisms and relevance for cardiovascular disease risk

Elevated levels of hematocrit and hemoglobin have been identified as an independent risk factor for the development of a number of diseases, including hypertension, coronary heart disease, and stroke. A growing body of evidence also indicates that elevations in hematocrit and hemoglobin are present in situations involving both physical and mental stressors. This paper reviews the evidence linking decreases in plasma volume causing hemoconcentration with hemodynamic adjustments associated with activation of the sympathetic nervous system, and the potential relevance of stress-induced hemoconcentration in triggering deleterious cardiovascular events. The importance of blood viscosity in understanding the effects of hemoconcentration is discussed, along with the need to evaluate the degree of hemoconcentration during stress for accurate interpretation of changes in certain blood constituents.

Influence of atrial natriuretic factor on spontaneous baroreflex sensitivity for heart rate in humans

Our objective in these experiments was to evaluate the effects of atrial natriuretic factor on the gain of the spontaneous baroreceptor-heart rate reflex in humans. On two separate study days, we gave either atrial natriuretic factor during supine rest (16 nmol over 3 minutes, then 16 pmol/kg per minute) or saline (as vehicle) to nine healthy men (age, 23 +/- 1 years; mean +/- SEM) according to a random, double-blind design. Beat-by-beat RR interval and systolic pressure were recorded noninvasively. Sequences during which systolic pressure and the RR interval of the following beat changed in parallel (either increasing [Up] or decreasing [Down]) over at least three consecutive beats were identified and classified as baroreceptor-heart rate reflex sequences. Regression lines relating RR interval to the preceding systolic pressure were derived for each individual sequence. The mean value of the slopes of these regression lines was calculated to obtain the mean spontaneous baroreflex sensitivity for heart rate for each subject. Saline infusion did not change RR interval, systolic pressure, or number of baroreflex sequences nor the slope of the mean spontaneous baroreflex sensitivity for heart rate or slopes of Up or Down sequences. Atrial natriuretic factor, at a dose that lowers central venous pressure, did not affect systolic pressure, respiratory rate, or the number of baroreflex sequences but reduced RR interval from 952 +/- 35 to 930 +/- 40 ms (P < .04) and the mean slope of spontaneous baroreflex sensitivity for heart rate from 32.7 +/- 4.8 to 23.1 +/- 2.8 ms.mm Hg-1 (P < .04).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide in the innervation of the bovine heart conduction system: relationship with substance P and autonomic innervation--immunohistochemical studies

Recently, we observed that atrial natriuretic peptide (ANP) immunoreactivity (IR) was present not only in the Purkinje fibres, but also in nerve fibre varicosities in the conduction system of the bovine heart. These findings and previous observations that ANP is able to influence autonomic neurotransmission in the heart, lead us to elucidate the possible occurrence of ANP in the sympathetic and/or parasympathetic nervous systems and/or in various types of peptidergic innervation in the conduction system. The different parts of the conduction system of bovine hearts were dissected out and processed for immunohistochemistry including double-staining, using antisera against ANP, tyrosine hydroxylase and different neuropeptides. We observed that some of the nerve fibre varicosities exhibiting ANP-IR showed substance P-IR and that ANP was present as scattered immunoreactive granules in intracardial, presumably parasympathetic, ganglionic cells. The study shows that ANP is likely to be present in parasympathetic innervation and in afferent nerve endings in the bovine heart conduction system.