ANP, BNP, and CNP enhance bradycardic responses to cardiopulmonary chemoreceptor activation in conscious sheep

Serotoninergic Modulation of Basal Cardiovascular Responses and Responses Induced by Isotonic Extracellular Volume Expansion in Rats

BACKGROUND:

Isotonic blood volume expansion (BVE) induced alterations of sympathetic and parasympathetic activity in the heart and blood vessels, which can be modulated by serotonergic pathways.

OBJECTIVE:

To evaluate the effect of saline or serotonergic agonist (DOI) administration in the hypothalamic paraventricular nucleus (PVN) on cardiovascular responses after BVE.

METHODS:

We recorded pulsatile blood pressure through the femoral artery to obtain the mean arterial pressure (MAP), systolic (SBP) and diastolic blood pressure (DBP), heart rate (HR) and the sympathetic-vagal ratio (LF/HF) of Wistar rats before and after they received bilateral microinjections of saline or DOI into the PVN, followed by BVE.

RESULTS:

No significant differences were observed in the values of the studied variables in the different treatments from the control group. However, when animals are treated with DOI followed by BVE there is a significant increase in relation to the BE control group in all the studied variables: MBP (114.42±7.85 vs 101.34±9.17); SBP (147.23±14.31 vs 129.39±10.70); DBP (98.01 ±4.91 vs 87.31±8.61); HR (421.02±43.32 vs 356.35±41.99); and LF/HF ratio (2.32±0.80 vs 0.27±0.32).

DISCUSSION:

The present study showed that the induction of isotonic BVE did not promote alterations in MAP, HR and LF/HF ratio. On the other hand, the injection of DOI into PVN of the hypothalamus followed by isotonic BVE resulted in a significant increase of all variables.

CONCLUSION:

These results suggest that serotonin induced a neuromodulation in the PVN level, which promotes an inhibition of the baroreflex response to BVE. Therefore, the present study suggests the involvement of the serotonergic system in the modulation of vagal reflex response at PVN in the normotensive rats.

FUNDAMENTO:

Expansão de volume extracelular (EVEC) promove alterações da atividade simpática e parassimpática no coração e vasos sanguíneos, os quais podem ser moduladas por vias serotoninérgicas.

OBJETIVO:

Avaliar o efeito da administração de salina ou agonista serotoninérgico (DOI) nos núcleos paraventriculares hipotalâmico (NPV) sobre respostas cardiovasculares após EVEC.

MÉTODOS:

Foram obtidos registros da pressão arterial pulsátil, por meio da artéria femoral, para obtenção dos valores da pressão arterial média (PAM), sistólica (PAS), diastólica (PAD), frequência cardíaca (FC) e razão simpático-vagal (LF/HF) de ratos Wistar antes e após receberem microinjeções bilaterais no NPV de salina ou DOI seguida de EVEC.

RESULTADOS:

Não foram observadas diferenças significativas dos valores das variáveis estudadas nos diferentes tratamentos do grupo controle. Entretanto, quando os animais são tratados com DOI seguida de EVEC ocorre aumento significativo em relação ao grupo controle com EVEC em todas as variáveis estudadas: PAM (114,42±7,85 vs 101,34±9,17), PAS (147,23±14,31 vs 129,39±10,70), PAD (98,01 ±4,91 vs 87,31±8,61), FC (421,02±43,32 vs 356,35±41,99) e LF/HF (2,32±0,80 vs 0,27±0,32).

DISCUSSÃO:

O presente estudo mostrou que a indução de EVEC isotônica não promoveu alterações na PAM, PAD, PAS, FC e LF/HF. Por outro lado, os animais que receberam microinjeção de DOI no NPV seguida de EVEC apresentaram aumento significativo de todas as variáveis.

CONCLUSÃO:

Esses resultados sugerem que a serotonina exerce uma neuromodulação em nivel do NPV, e essa promove uma inibição da resposta barorreflexa frente à EVEC. Assim, o presente trabalho sugere o envolvimento serotoninérgico na neuromodulação no nivel do NPV na resposta reflexa vagal em ratos normotensos.

Relationship between male hormonal status, Bezold–Jarisch reflex function, and ACE activity (cardiac and plasmatic)

The negative relationship between androgens and the Bezold–Jarisch reflex (BJR) has been demonstrated, but no studies evaluated the physiological influence of testosterone on this reflex. We evaluated the influence of male rat castration on the BJR, cardiac morphometric parameters, and the plasmatic and the cardiac angiotensin converting enzyme (ACE) activity. After castration (CAS), the rats were divided into 24 and 72 h (CAS24H, CAS72H), and 7 and 21 days (CAS7D, CAS21D) groups. The BJR was studied by administering increasing doses of phenylbiguanide (PBG; 1.5–24 μg/kg) at different times after castration. Castration results in the following: (i) reduction in testosterone levels (SHAM: 238.7 ± 15.1; CAS24H: 9.0 ± 0.5; CAS72H: 6.7 ± 0.4; CAS7D: 5.2 ± 0.2; and CAS21D: 2.2 ± 0.3 ng/dL; p < 0.05); (ii) no changes in 17β-estradiol; (iii) a reduced BJR sensitivity (PBG 6 μg/kg; SHAM: 77 ± 7; CAS24H: 63 ± 10; CAS72H: 55 ± 6; CAS7D: 54 ± 4; and CAS21D: 35 ± 2%; p < 0.01); (iv) a decrease in cardiac (SHAM: 107 ± 6; CAS24H: 92 ± 2; CAS72H: 82 ± 3; CAS7D: 54 ± 3; and CAS21D: 43 ± 4%; p < 0.05) and plasmatic (SHAM: 135 ± 8; CAS24H: 102 ± 5; CAS72H: 99 ± 3; CAS7D: 89 ± 4; and CAS21D: 56 ± 6%; p < 0.05) ACE activity. No changes were observed in cardiac morphometry and hemodynamic parameters. Therefore, castration leads to decrease in testosterone levels as early as 24 h, reduction in ACE activity and loss of BJR sensitivity 7 days after castration. The loss of BJR sensitivity was not related to cardiac morphometric changes and cardiovascular hemodynamics.

Differences in autonomic balance in patients with cardioinhibitory and vasodepressor type of reflex syncope during head-up tilt test and active standing

OBJECTIVE

To improve the pathophysiological understanding of cardioinhibitory and vasodepressor reflex syncope, by evaluating orthostatic effects on electrical and hemodynamic variables. To unravel the pathogeneses further, we studied these effects during both the passive head-up tilt test and the active standing test.

BACKGROUND

The current knowledge of the compromised autonomic balance in patients with reflex syncope is limited. The orthostatic responses to head-up tilt test in cardioinhibitory and vasodepressor patients differ, suggesting different pathogeneses; however, the more physiological active standing test represents daily life situations better.

METHODS

We included 74 patients; 36 cardioinhibitory and 38 vasodepressor. Patients were compared with respect to vascular hemodynamics and heart rate variability during the change from supine to upright position. Resting electrolytes, brain natriuretic peptide (BNP), pro-atrial natriuretic peptide (pro-ANP), and the C-terminal of pro-vasopressin, copeptin were measured.

RESULTS

Resting systolic blood pressure was higher in cardioinhibitory (117.8 ± 15.7 mmHg) than in vasodepressor patients (109.1 ± 15.3 mmHg, p < 0.001). Changes in heart rate tended to be smaller in cardioinhibitory patients (6.7 ± 9.8 vs. 10.7 ± 8.9 bpm, p = 0.056). Heart rate variability was lower and changed less in cardioinhibitory patients (p < 0.05). Cardioinhibitory patients had higher pro-ANP levels (63.5 ± 18.8 pM) compared to vasodepressor patients (54.2 ± 31.4 pM, p = 0.018). Responses during active standing were attenuated compared to head-up tilt in both groups.

CONCLUSIONS

This study demonstrated that cardioinhibitory patients had higher blood pressure, attenuated hemodynamic responses, and reduced autonomic regulation compared to vasodepressor patients. Furthermore, cardioinhibitory patients showed a sympathetic predominance in their modulation of autonomic responses. Orthostatic responses induced by active standing were modest and did not sufficiently explain potential pathophysiological differences between cardioinhibitory and vasodepressor patients.

Effect of systemic B-type natriuretic peptide on cardiac vagal motoneuron activity

Intravenous B-type natriuretic peptide (BNP) enhances the bradycardia of reflexes from the heart, including the von Bezold-Jarisch reflex, but its site of action is unknown. The peptide is unlikely to penetrate the blood-brain barrier but could act on afferent or efferent reflex pathways. To investigate the latter, two types of experiment were performed on urethane-anesthetized (1.4 g/kg iv) rats. First, the activity was recorded extracellularly from single cardiac vagal motoneurons (CVMs) in the nucleus ambiguus. CVMs were identified by antidromic activation from the cardiac vagal branch and by their barosensitivity. Phenyl biguanide (PBG), injected via the right atrium in bolus doses of 1-5 mug to evoke the von Bezold-Jarisch reflex, caused a dose-related increase in CVM activity and bradycardia. BNP infusion (25 pmol.kg(-1).min(-1) iv) significantly enhanced both the CVM response to PBG (n = 5 rats) and the reflex bradycardia, but the log-linear relation between those two responses over a range of PBG doses was unchanged by BNP. The reflex bradycardia was not enhanced in five matched time-control rats receiving only vehicle infusions. In five other rats the cervical vagi were cut and the peripheral right vagus was stimulated supramaximally at frequencies of 1-20 Hz. The bradycardic responses to these stimuli were unchanged before, during, and after BNP infusion. We conclude that systemic BNP in a moderate dose enhances the von Bezold-Jarisch reflex activation of CVM, in parallel with the enhanced reflex bradycardia. That enhancement is due entirely to an action before the vagal efferent arm of the reflex pathway.

Nonuniformity in the von Bezold-Jarisch reflex

The von Bezold-Jarisch reflex (BJR) is a vagally mediated chemoreflex from the heart and lungs, causing hypopnea, bradycardia, and inhibition of sympathetic vasomotor tone. However, cardiac sympathetic nerve activity (CSNA) has not been systematically compared with vasomotor activity during the BJR. In 11 urethane-anesthetized (1-1.5 g/kg iv), artificially ventilated rats, we measured CSNA simultaneously with lumbar sympathetic activity (LSNA) while the BJR was evoked by right atrial bolus injections of phenylbiguanide (0.5, 1.0, 1.5, and 2 microg). Nerve and heartbeat responses were analyzed by calculating normalized cumulative sums. LSNA and heartbeats were always reduced by the BJR. An excitatory "rebound" component often followed the inhibition of LSNA but never outweighed it. For CSNA, however, excitation usually (in 7 of 11 rats) outweighed any initial inhibition, such that the net response to phenylbiguanide was excitatory. The differences in net response between LSNA, CSNA, and heartbeats were all significant (P < 0.01). A second experimental series on seven rats showed that methyl atropine (1 mg/kg iv) abolished the bradycardia of the BJR, whereas subsequent bilateral vagotomy substantially reduced LSNA and CSNA responses, both excitatory and inhibitory. These findings show that, during the BJR, 1) CSNA is often excited, 2) there may be coactivation of sympathetic and parasympathetic drives to the heart, 3) divergent responses may be evoked simultaneously in cardiac vagal, cardiac sympathetic, and vasomotor nervous pathways, and 4) those divergent responses are mediated primarily by the vagi.

Natriuretic peptide receptor B signaling in the cardiovascular system: protection from cardiac hypertrophy

Natriuretic peptides (NP) represent a family of structurally homologous but genetically distinct peptide hormones involved in regulation of fluid and electrolyte balance, blood pressure, fat metabolism, cell proliferation, and long bone growth. Recent work suggests a role for natriuretic peptide receptor B (NPR-B) signaling in regulation of cardiac growth by either a direct effect on cardiomyocytes or by modulation of other signaling pathways including the autonomic nervous system. The research links NPR-B for the first time to a cardiac phenotype in vivo and underlines the importance of the NP in the cardiovascular system. This manuscript will focus on the role of NPR-B and its ligand C-type natriuretic peptide in cardiovascular physiology and disease and will evaluate these new findings in the context of the known function of this receptor, with a perspective on how future research might further elucidate NPR-B function.

Influence of atrial fibrillation on cardiac brain natriuretic peptide release during haemodynamic stress in heart failure

BACKGROUND

The determinants of release of brain natriuretic peptide (BNP) in heart failure (HF) are incompletely understood, particularly, the effect of heart rhythm and haemodynamic stress.

AIMS

To investigate the effect of haemodynamic stress on cardiac BNP release in HF and differentiate this response for atrial fibrillation (AF) and sinus rhythm (SR).

METHODS

In 18 HF patients (ejection fraction<40%, 9 in AF and 9 in SR) haemodynamics and BNP levels were measured from arterial and coronary sinus samples at baseline, after 10 min of 20 degrees passive head up tilt (HUT) and after 10 min of isometric handgrip (IHG) exercise. From these data, we calculated a transcardiac BNP gradient and compared results between the AF and SR cohort.

RESULTS

During haemodynamic stress in both groups, there were no significance differences in left sided filling pressures. At baseline, there were no differences in BNP measurements between the SR and AF group. The transcardiac BNP gradient increased significantly in the SR (p=0.02) but not the AF cohort, after HUT. During IHG exercise, there was a significant decrease in cardiac BNP release in the AF cohort (p=0.03) but not the SR cohort.

CONCLUSION

These data imply in HF, cardiac rhythm influences cardiac BNP release in response to haemodynamic stress.

Cardioprotective functions of atrial natriuretic peptide and B-type natriuretic peptide: a brief review

1. If one was to design a hormone to protect the heart, it would have a number of features shown by the cardiac natriuretic peptides atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP). These hormones are made in cardiomyocytes and are released into the circulation in response to atrial and ventricular stretch, respectively. Atrial natriuretic peptide and BNP can reduce the preload and after-load in normal and failing hearts. They reduce blood volume over the short term by sequestering plasma and over the longer term by promoting renal salt and water excretion and by antagonizing the renin-angiotensin-aldosterone system at many levels. Each of these actions affords indirect benefit to a volume- or pressure-threatened heart. 2. Recent studies have identified additional modes of action of the natriuretic peptides that may also confer cardioprotective benefits, especially in heart disease. The emerging findings are: (i) that ANP and BNP antagonize the cardiac hypertrophic action of angiotensin II and continue working under conditions where endothelial nitric oxide (NO) function is compromised, such as in the presence of high glucose in diabetes; (ii) they potentiate the bradycardia caused by inhibitory ('autoprotective') cardio-cardiac reflexes; and, furthermore, (iii) BNP can suppress cardiac sympathetic nerve activity in humans, including those with heart failure. Thus, it appears that natriuretic peptides can shift sympathovagal balance in a beneficial direction (away from the sympathetic). The vagal reflex and antihypertrophic actions of the peptides are mediated by particulate guanylyl cyclase (pGC) natriuretic peptide receptors. 3. The multiple synergistic actions of the natriuretic peptides make them and their pGC receptors attractive targets for therapy in heart disease. Encouragingly, exogenous natriuretic peptides remain effective even when endogenous peptide levels are raised, as is the case in heart failure. They also remain effective in disease states where other protective mechanisms, such as the NO system, have become ineffective, offering yet further encouragement for the therapeutic use of the natriuretic peptides.

Neurochemical brain groups activated after an isotonic blood volume expansion in rats

In order to establish the involvement of particular neurochemical brain groups in the response to blood volume expansion, we analyzed Fos-labeling in combination with immunolabeling for serotonin, tyrosine hydroxylase, vasopressin and oxytocin, 90 min after a sham or i.v. isotonic blood volume expansion (BVE) in unanesthetized, unrestrained rats. We also examined the changes in concentration of oxytocin, atrial natriuretic peptide and vasopressin plasma, induced by blood volume load, to confirm our previous studies. The results demonstrate the participation of specific paraventricular and supraoptic nucleus groups of cells (oxytocinergic-vasopressinergic), serotoninergic dorsal raphe nucleus cells and catecholaminergic A1/A2/A6 groups (in the caudal ventrolateral medulla, nucleus of the solitary tract and locus coeruleus respectively), in the regulatory response to BVE. They provide detailed neuroanatomical evidence to support previous observations showing the contribution of these neurochemical systems in the neural, behavioral and endocrine response to isotonic BVE.

Comparative study in the effect of C-type natriuretic peptide on gastric motility in various animals

AIM

To investigate the effect of natriuretic peptides on gastric motility in various animals, and the effect of C-type natriuretic peptide (CNP) on spontaneous contraction of gastric smooth muscle in rat, guinea-pig and human in vitro was compared.

METHODS

Spontaneous contraction of gastric smooth muscle was recorded by four channel physiograph.

RESULTS

In the guinea-pig and rat gastric antral circular smooth muscle, CNP markedly decreased the amplitude of spontaneous contraction but it didn't affect the frequency, however, the contractile activity was completely inhibited by CNP in gastric antral longitudinal smooth muscle. In the human gastric antral circular and longitudinal smooth musle, CNP completely inhibited spontaneous contraction. In the circular smooth muscle of guinea-pig and rat gastric fundus, CNP obviously decreased the amplitude of spontaneous contraction but it didn't affect the frequency, however, the contractile activity was completely inhibited by CNP in smooth muscle of fundus longitudinal. In the circular and longitudinal smooth muscle of guinea-pig gastric body, CNP at first induced a relaxation and then an increase in amplitude of spontaneous contraction (rebound contraction), but the frequency was not changed. After the circular smooth muscle of gastric body was pretreated with atropine, an M receptor blocker, the rebound contraction was abolished; In circular and longitudinal smooth muscle of rat gastric body, CNP induced a transient and slight relaxation and successively followed by the recovery in amplitude of spontaneous contraction but it also didn't affect the frequency. After the smooth muscle was pretreated with atropine, the transient and slight relaxation was replaced by long term and complete inhibition; The percentage of CNP-induced inhibition was 76.77+/-6.21 % (fundus), 67.21+/-5.32 % (body) and 58.23+/- 6.21 % (antral) in the gastric circular muscle, however, the inhibitory percentage was 100+/-0.00 % (fundus), 68.66+/- 3.55 % (body) and 100+/-0.00 % (antrum) in the gastric longitudinal smooth muscle of guinea-pigs; In the rat, the percentage of CNP-induced inhibition was 95.87+/-4.12 % (fundus), 94.91+/-5.08 % (body) and 66.32+/-7.32 % (antrum)in the gastric circular smooth muscle, but in the longitudinal smooth muscle, CNP completely inhibited the spontaneous contraction. Using LY83583, a guanylate cyclase inhibitor, and zaparinast as a phosphoesterase inhibitor to inhibit the generation of cGMP, the effect of CNP on the spontaneous contraction was markedly weakened by LY83583, however, the inhibitory effect was enhanced by zaparinast.

CONCLUSION

(1) CNP can obviously inhibit the spontaneous contraction of gastric antral circular and longitudinal smooth muscle in the rat, guinea-pig and human. The order of inhibitory potency is human >rat> guinea-pig. (2) In the same animals, the inhibitory effect of CNP on spontaneous contraction is the most powerful in fundus and the weakest in antrum, in the same position, the inhibitory effect on the circular smooth muscle is more powerful than that on longitudinal smooth muscle. (3) The inhibitory effect of CNP on spontaneous contraction in the gastric smooth muscle is mediated by a cGMP dependent pathway.

Coronary ischemia induced by radiofrequency ablation in the left atrium

INTRODUCTION

We report three cases of transient, reversible coronary ischemia occurring after radiofrequency ablation in the left atrium.

METHODS AND RESULTS

A 56-year-old man with a left atrial tachycardia that was mapped to the septum and roof of the atrium using a noncontact mapping developed 5-mm ST elevation in the anterolateral leads. Coronary angiography showed an occluded diagonal that was opened using intracoronary nitrate, which led to resolution of the ST changes. A 57-year-old man undergoing right upper pulmonary vein ablation developed 6-mm ST elevation in leads V1-V4, II, III, and aVF. Coronary angiography showed normal coronaries with slow flow into the left anterior descending artery, which resolved with nitrates. A 50-year-old man undergoing left lower pulmonary vein ablation developed 3-mm reversible inferior ST elevation. All patients were adequately anticoagulated after transseptal access to the left atrium.

CONCLUSION

Ablation in the left atrium, at the roof, septum, and left inferior wall, can cause transient coronary ischemia, possibly due to spasm, which can be reversed with intracoronary nitrates. This phenomenon has not been previously described.

Nesiritide for Acute Decompensated Heart Failure

Objective:

To evaluate nesiritide for the treatment of acute decompensated heart failure (HF) with respect to its pharmacology, pharmacokinetics, clinical efficacy, adverse effect profile, and outcomes.

Data Source:

Primary and review articles were identified by MEDLINE search (1966–March 2001). Data from the PRECEDENT trial and additional dosing/administration and safety information were obtained from Scios, Inc.

Study Selection:

All of the articles identified from the data sources were evaluated and all information deemed relevant was included in this review.

Data Synthesis:

Research into the cardiac natriuretic peptides has revealed that brain natriuretic peptide (BNP) is elevated in patients with HF and may counterregulate the pathophysiologic mechanisms involved in progression of the disease. Nesiritide (Natrecor), recombinant human BNP, is the first natriuretic peptide to be approved by the FDA for treatment of acute decompensated HF. Nesiritide is a potent venous and arterial vasodilator that reduces pulmonary capillary wedge pressure and systemic vascular resistance in a dose-dependent manner with minimal effect on heart rate. It improves signs and symptoms of HF; however, its effect on patient outcomes is unclear because of limited data. The most commonly reported adverse effects in clinical trials were dose-related hypotension and nausea.

Conclusions:

Nesiritide is an intravenous arterial and venous vasodilator that may be particularly useful in patients who may not tolerate the arrhythmogenic effects of dobutamine and milrinone or who cannot tolerate nitroglycerin and nitroprusside. Further well-designed comparative studies are needed to define nesiritide's place in management of acute decompensated HF.

Examination of the in vivo cardiac electrophysiological effects of nesiritide (human brain natriuretic peptide) in conscious dogs

BACKGROUND

Human brain natriuretic peptide (hBNP) is a new therapeutic agent, nesiritide, indicated in patients with decompensated congestive heart failure, a group at significant risk of developing cardiac arrhythmias. Whether hBNP has cardiac electrophysiologic effects has not been reported.

METHODS AND RESULTS

In 9 healthy, chronically instrumented, conscious dogs, hemodynamic and electrophysiologic parameters were assessed at baseline and during recombinant hBNP (nesiritide) infusion at 0.03 and 0.09 microg/kg/min after 1 hour at each dose. Infusion of hBNP produced dose-related increases (P <.001) in hBNP and cyclic GMP plasma levels and reductions (P <.05) in mean arterial pressure. Mean central venous pressure and sinus cycle length did not change significantly. Infusion of hBNP produced no significant changes in any of the electrophysiologic parameters including no change in surface ECG variables (P wave duration, PR interval, QRS duration, and QTc interval), corrected sinus node recovery time, atrioventricular nodal Wenckebach cycle length, and atrial and ventricular effective refractory periods measured at a 400 ms cycle length. Spontaneous or induced arrhythmias were not observed during hBNP infusion.

CONCLUSIONS

In conscious, healthy dogs, short-term infusion of recombinant hBNP has no significant effects on atrial or ventricular electrophysiologic parameters.