Haemodynamic effects of atrial natriuretic peptide in hypoxic chronic obstructive pulmonary disease

Pulmonary Hemodynamic Responses to Brain Natriuretic Peptide and Sildenafil in Patients With Pulmonary Arterial Hypertension

STUDY OBJECTIVES

Brain natriuretic peptide (BNP) blunts hypoxic pulmonary hypertension in animal models, but its acute hemodynamic effects in patients with pulmonary arterial hypertension (PAH) are not known. The aim of this study was to determine if human B-type natriuretic peptide is a safe and efficacious pulmonary vasodilator in patients with PAH and if the pulmonary hemodynamic effects are potentiated by phosphodiesterase inhibition.

DESIGN

Open-label study.

SETTING

Medical ICUs of three tertiary care hospitals in New England.

PATIENTS

Thirteen consecutive adult patients undergoing right-heart catheterization and a pulmonary vasodilator trial for the initial evaluation of PAH.

INTERVENTIONS

Patients were administered inhaled nitric oxide (iNO), i.v. epoprostenol, and a 3-h infusion of BNP alone and 1 h after an oral dose of the phosphodiesterase-5 inhibitor sildenafil.

RESULTS

iNO and sildenafil alone decreased mean pulmonary artery pressure (mPAP) without a significant fall in pulmonary vascular resistance (PVR). Epoprostenol decreased both mPAP and PVR. BNP alone had no significant effect on pulmonary hemodynamics, but the combination of sildenafil plus BNP decreased mPAP and PVR for up to 6 h after stopping BNP. The decrease in mPAP with sildenafil plus BNP (+/- SE) was greater than after 1 h of sildenafil alone (44.6 +/- 3.8 to 40.6 +/- 3.9 mm Hg, p = 0.027). An acute vasodilator response, defined as a decrease in mPAP > 10 mm Hg and end mPAP < 40 mm Hg, was seen in 0 of 8 patients with iNO, 1 of 13 patients with epoprostenol, 0 of 13 patients with BNP, and 4 of 12 patients with sildenafil plus BNP. BNP decreased mean systemic arterial pressure (5.6 +/- 2.8 mm Hg) but had no effect on cardiac output or systemic vascular resistance.

CONCLUSIONS

A 3-h BNP infusion does not significantly improve pulmonary hemodynamics in most patients with PAH but is well tolerated and augments the acute pulmonary vasodilator effect of sildenafil.

Atrial natriuretic peptide stimulates cat carotid body chemoreceptors in vivo

It is known that atrial natriuretic peptide (ANP) is released from cardiac myocyte and other stores during hypoxia and is involved in pulmonary-cardiovascular reflexes and in natriuresis and diuresis. Since the carotid body initiates hypoxic chemoreflexes, we hypothesized that ANP could potentiate the hypoxic stimulation of the carotid body chemoreceptor in vivo. We studied the effect of close intra-arterial injection of ANP on carotid chemoreceptor activity in anesthetized male cats which were paralyzed and artificially ventilated. Graded doses of ANP (0-10 nmoles) were administered by intra-arterial injections and they produced an excitatory response. Single dose of ANP (6.5 nmoles) at four steady-state levels of arterial PO(2), at constant PCO(2), produced increases of chemoreceptor activity. This increase of chemoreceptor activity with ANP in the presence of CO(2)-HCO(3)(-) in vitro could make a difference from those without CO(2)-HCO(3)(-) in vivo.

Atrial natriuretic peptide infusion and nitric oxide inhalation in patients with acute respiratory distress syndrome

Aim:

To study the effects of infusion of atrial natriuretic peptide (ANP) versus the inhalation of nitric oxide (NO) in patients with an early acute respiratory distress syndrome (ARDS).

Methods:

Ten patients with severe ARDS were studied in a crossover study design, within 72 hours after starting mechanical ventilation. We studied the effects of ANP infusion (10 ng/kg/min for 1 hour) and of inhalation of NO (20 ppm for 1 hour) on hemodynamic and respiratory patient parameters, as well as the effects on plasma levels of ANP, guanosine 3',5'-cyclic monophosphate, nitrate and endothelin-1.

Results:

Despite an approximate 50% increase in mixed venous ANP plasma concentration (from 86 ± 21 to 123 ± 33 ng/l, P < 0.05) during ANP infusion, there were no changes in mean pulmonary artery pressure, pulmonary vascular resistance index, extravascular lung water index, or in pulmonary gas exchange. NO inhalation, in contrast, lowered mean pulmonary artery pressure (from 26 ± 1.9 to 23.9 ± 1.7 mmHg, P < 0.01), pulmonary vascular resistance index (from 314 ± 37 to 273 ± 32 dynes/cm⁵/m², P < 0.05) and central venous pressure (from 8.2 ± 1.2 to 7.3 ± 1.1 mmHg, P < 0.02). Furthermore, NO inhalation improved pulmonary gas exchange, reflected by a decrease in alveolar-arterial oxygen gradient (from 41.9 ± 3.9 to 40.4 ± 3.6 kPa, P < 0.05), a small increase in oxygenation (PaO₂/FiO₂ from 17.7 ± 1.4 to 19.7 ± 1.1 kPa, P = 0.07) and a small decrease in venous admixture (Q_s/Q_t from 35.7 ± 2.0 to 32.8 ± 2.7%, P = 0.11).

Conclusion:

This study shows that, in contrast to NO inhalation, infusion of ANP neither improves oxygenation nor attenuates pulmonary hypertension or pulmonary edema in patients with severe ARDS.

Changes in ANP responsiveness of normal and hypertensive porcine intrapulmonary arteries during maturation

Pulmonary vascular resistance falls rapidly after birth, but endothelium-dependent relaxation is relatively poor during the perinatal period. Atrial natriuretic peptide (ANP) is a potent vasodilator; however, its role in the process of perinatal adaptation is uncertain. Porcine intrapulmonary conduit arteries (IPA) from fetal, newborn (< 5 min), 3-, 6-, and 17-d-old, and adult pigs, and from piglets made hypoxic from 0 to 3, 3 to 6, or 14 to 17 d, were isolated and mounted for isometric force recording. Rings were precontracted with prostaglandin-F2 alpha (PGF2 alpha, 10 microM) or KCl (40 mM). ANP was added cumulatively (10 pM to 100 nM). C-type natriuretic peptide (CNP) was added as a single concentration of 100 nM. Accumulation of cGMP under basal conditions and stimulated by ANP or CNP was measured by radioimmunoassay system. Frozen sections of lung tissue were incubated with 125I-labeled alpha-ANP, and binding site density was assessed on IPA with an image analysis system. ANP relaxed IPA in pigs at all ages, but the effect was significantly greater at 6 and 17 d of age. Hypoxia in animals from 14 to 17 d old impaired ANP-induced relaxation. CNP relaxed IPA poorly: < 12% at all ages. ANP increased cGMP accumulation in both normal and hypoxic animals. CNP did not increase cGMP generation in IPA from normal animals but did so in IPA from 3-d-old hypoxic animals. ANP-specific binding sites were demonstrated on the pulmonary artery smooth muscle cells, with greater binding in the young animals. The increased relaxant responses to ANP during adaptation may be important in maintaining low pulmonary vascular resistance. In contrast, CNP was largely ineffective in relaxing pulmonary arteries.

Correlation of Atrial Natriuretic Factor and Renin-Aldosterone System With Chronic Pulmonary Hypertension Among Residents in a High Altitude

The study was performed to evaluate right ventricular contractility, plasma renin activity, and atrial natriuretic peptide in high altitude pulmonary arterial hypertension (HAPH). Sixty-eight patients with signs of pulmonary artery hypertension (PPA,syst > 25 mmHg, PPA > 15 mmHg) (Group II) and 40 with normal coronary angiograms and normal pulmonary artery pressures (Group I) were included in the study. Right heart catheterization with estimation of right ventricular and pulmonary artery pressures were performed in all the patients. The blood samples were taken from the pulmonary artery for measurement of mean oxygen saturatioýn (SaO2), atrial natriuretic factor (ANF) level, plasma renin activity (PRA), aldosterone level, and sodium and potassium concentrations. Statistical analysis was performed using unpaired Student's t test and linear regression analysis. The patients with HAPH had higher pulmonary artery pressures (PPA,syst, PPA, PPA,diast), total pulmonary resistance (Rpulm,tot), and right ventricular systolic pressure (PRv,syst). The significant correlation was found between ANF and PRA with right ventricular contractility indices and pulmonary vascular resistance.

Atrial natriuretic peptide and brain natriuretic peptide in cor pulmonale. Hemodynamic and endocrine effects

We have studied the hemodynamic and hormonal effects of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in eight patients with cor pulmonale. Subjects were studied twice and were given a 20-min placebo infusion followed by either ANP or BNP (3 pmol/kg/min then 10 pmol/kg/ min for 20 min each). Responses were measured after placebo infusion and following low-dose then high-dose ANP or BNP. Placebo infusion had no significant effects on either study day. Low-dose ANP and BNP significantly reduced mean pulmonary artery pressure (MPAP) from baseline by 3.7 mm Hg (95% confidence interval [CI], 1.4 to 6.1) and 3.0 mm Hg (95% CI, 0.6 to 5.4), respectively. High-dose ANP and BNP further reduced MPAP from baseline by 7.1 mm Hg (95% CI, 4.8 to 9.4) and 7.1 mm Hg (95% CI, 4.7 to 9.6), respectively. Effects on total pulmonary vascular resistance were similar. ANP and BNP had no confounding systemic hemodynamic effects. Plasma aldosterone was significantly suppressed from baseline by ANP: 156 pmol/L (95% CI, 93 to 220) after low dose, 275 pmol/L (95% CI, 207 to 343) after high dose; and by BNP: 92 pmol/L (95% CI, 30 to 153) after low dose, 159 pmol/L (95% CI, 98 to 220) after high dose. ANP and BNP produced dose-related pulmonary vasodilatation in patients with cor pulmonale, without worsening oxygen saturation or affecting systemic hemodynamics. ANP and BNP also exerted favorable neurohormonal effects by suppressing aldosterone.

Neutral endopeptidase inhibitors and the pulmonary circulation

1. Neutral endopeptidase (NEP) EC 3.4.24.11 is a zinc-metallopeptidase which is partly responsible for the degradation of atrial natriuretic peptide (ANP) in vivo. 2. ANP inhibits vascular smooth muscle cell proliferation, and elicits vasorelaxation of the systemic and, more potently, the pulmonary vasculature. Plasma ANP levels are elevated in human disease states characterized by pulmonary hypertension, and in animal models of these diseases. 3. However, the short in vivo half-life of ANP suggests that it has limited therapeutic potential. Therefore, it has been hypothesized that inhibition of the metabolism of ANP may prove successful in the treatment of pulmonary hypertension. 4. Several inhibitors of NEP have been shown to reduce the development of pulmonary hypertension secondary to chronic hypoxia in rats. In addition, the inhibitor SCH 42495, partially reversed the established cardio-pulmonary remodelling associated with this disease model, without elevating plasma ANP levels. 5. The physiological actions of ANP are many of the properties desirable in a treatment for pulmonary hypertension. Thus, attenuating the metabolism of this peptide using NEP inhibitors, should potentially enhance the effects of ANP, either by maintaining plasma levels or at a local, tissue level.

Bronchodilating effects of natriuretic and vasorelaxant peptides compared to salbutamol in asthmatics

In animal studies, the bronchial effects of urodilatin (URO, CDD/ANP-95-126, INN: ularitide) were superior to those of cardiodilatin/atrial natriuretic peptide (CDD, CDD/ANP-99-126). We compared the bronchodilating properties of intravenous URO and CDD in 36 clinically stable asthmatics showing a beta 2-agonist-induced increase of the FEV1 by > or = 15%. Any aerosol medication was discontinued for at least 8 h prior to the study. After baseline measurements of lung function parameters (FEV1, VC, PEF, MEF75, MEF50, MEF25) an intravenous infusion of 5.7, 11.4 or 17.1 pmol/kg/min URO or CDD was administered for 40 min in the morning. All measurements were repeated every 10 min during the infusion, for 30 min thereafter, and after the inhalation of 1.25 mg salbutamol (SALB). Both peptides had significant effects. While 11.4 pmol/kg/min URO dilated the central airways (FEV1, PEF, MEF75) slightly more potently than the peripheral bronchioles (MEF50, MEF25), 17.1 pmol/kg/min URO was as effective as SALB at all levels of the tracheobronchial tree. CDD reached only 50% of the SALB effect without a predominant localization of its action. The cardiovascular parameters revealed a significantly stronger vasorelaxant activity of CDD. In conclusion, the dose-dependent bronchodilating properties of intravenous URO were significantly superior to those of CDD.

The role of the renin-angiotensin and natriuretic peptide systems in the pulmonary vasculature

1. The role of vasoactive peptide systems in the pulmonary vasculature has been studied much less extensively than systemic vascular and endocrine effects. The current understanding of the role of the renin-angiotensin (RAS) and natriuretic peptide systems (NPS) in the pulmonary circulation is therefore reviewed. 2. Plasma concentrations of angiotensin II, the main vasoactive component of the RAS, are elevated in pulmonary hypertension and may interact with hypoxaemia to cause further pulmonary vasoconstriction. Pharmacological manipulation of angiotensin II can attenuate hypoxic pulmonary vasoconstriction but larger studies are needed to establish the efficacy of this therapeutic strategy in established pulmonary hypertension. 3. Although all the known natriuretic peptides, ANP, BNP and CNP are elevated in cor pulmonale, only ANP and BNP appear to have pulmonary vasorelaxant activity in humans. ANP and BNP can also attenuate hypoxic pulmonary vasoconstriction, suggesting a possible counter-regulatory role for these peptides. Inhibition of ANP/BNP metabolism by neutral endopeptidase has been shown to attenuate development of hypoxic pulmonary hypertension but this property has not been tested in humans. 4. It is also well established that there are potentially important endocrine and systemic circulatory interactions between the RAS and NPS. This also occurs in the pulmonary circulation and in humans, where at least BNP acts to attenuate angiotensin II induced pulmonary vasoconstriction. This interaction may be particularly relevant as a mechanism to counter-regulate overactivity of the RAS.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutral endopeptidase (NEP) inhibition in rats with established pulmonary hypertension secondary to chronic hypoxia

1. Atrial natriuretic peptide (ANP) causes vasorelaxation in the pulmonary vasculature. ANP levels are elevated in conditions characterized by pulmonary hypertension and it has been hypothesized that ANP may be autoregulatory in the pulmonary circulation. 2. One route of ANP metabolism in vivo is by the action of the enzyme neutral endopeptidase (NEP). We have studied the effects of the NEP inhibitor, SCH 42495, in rats with established pulmonary hypertension secondary to chronic hypoxia. 3. Rats (n = 32) were divided into 4 groups. Normoxic controls were kept in air for 10 days (NC10) and all other animals were placed in a normobaric hypoxic chamber (F1 O2 10%). Chronic hypoxic controls were studied at 10 days (CHC10). After 10 days hypoxia the two remaining groups received oral treatment for a further 10 days, consisting of either SCH 42495 (30 mg kg-1, twice daily CHT20) or methyl cellulose vehicle (0.4%, twice daily, CHV20). 4. Animals were anaesthetized and blood collected for measurement of plasma ANP. Hearts were dissected and ventricles weighed and the histology of the pulmonary vasculature examined. 5. CHC10 rats had significant right ventricular hypertrophy (0.53 +/- 0.08) and pulmonary vascular remodelling (29.0 +/- 0.01%) and had gained significantly less body weight (33.2 +/- 5.5 g) than NC10 rats (0.31 +/- 0.04, 10.9 +/- 0.01%, and 59.2 +/- 11.9 g respectively). CHC10 rats had significantly elevated plasma ANP levels (58.4 +/- 9.9 pM) compared with NC10 rats (23.9 +/- 32 pM). Treatment with SCH 42495 caused a significant reduction in pulmonary vascular remodelling (25.0 +/- 0.01%) and right ventricular hypertrophy (0.52 +/- 0.09) in CHT20 rats compared with CHV20 controls (33.0 +/- 0.02% and 0.61 +/- 0.09 respectively). Pulmonary vascular remodelling was also significantly lower in CHT20 rats than CHC1O animals.6. Thus, short term inhibition of NEP causes regression of established pulmonary vascular remodelling and may be a useful therapeutic strategy in pulmonary hypertension.