Effects of SCH 34826, an orally active inhibitor of atrial natriuretic peptide degradation, in healthy volunteers.

Atrial natriuretic peptide is cleared from plasma by clearance receptors and by enzymatic degradation by way of a neutral metalloendopeptidase. Inhibition of neutral metalloendopeptidase activity appears to provide an interesting approach to interfere with metabolism of atrial natriuretic peptide to enhance the renal and haemodynamic effects of endogenous atrial natriuretic peptide. In this study, the effects of SCH 34826, a new orally active neutral metalloendopeptidase inhibitor, have been evaluated in a single-blind, placebo-controlled study involving eight healthy volunteers who had maintained a high sodium intake for 5 days. SCH 34826 had no effect on blood pressure or heart rate in these normotensive subjects. SCH 34826 promoted significant increases in excretion of urinary sodium, phosphate, and calcium. The cumulative 5-hour urinary sodium excretion was 15.7 +/- 7.3 mmol for the placebo and 22.9 +/- 5, 26.7 +/- 6 (p less than 0.05), and 30.9 +/- 6.8 mmol (p less than 0.01) for the 400, 800, and 1600 mg SCH 34826 doses, respectively. During the same time interval, the cumulative urinary phosphate excretion increased by 0.3 +/- 0.4 mmol after placebo and by 1.5 +/- 0.3 (p less than 0.01), 1.95 +/- 0.3 (p less than 0.01), and 2.4 +/- 0.4 mmol (p less than 0.001) after 400, 800, and 1600 mg SCH 34826, respectively. There was no change in diuresis or excretion of urinary potassium and uric acid. The natriuretic response to SCH 34826 occurred in the absence of any change in plasma atrial natriuretic peptide levels but was associated with a dose-dependent elevation of urinary atrial natriuretic peptide and cyclic guanosine monophosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Midregional pro-atrial natriuretic peptide and procalcitonin improve survival prediction in VAP.

Ventilator-associated pneumonia (VAP) affects mortality, morbidity and cost of critical care. Reliable risk estimation might improve end-of-life decisions, resource allocation and outcome. Several scoring systems for survival prediction have been established and optimised over the last decades. Recently, new biomarkers have gained interest in the prognostic field. We assessed whether midregional pro-atrial natriuretic peptide (MR-proANP) and procalcitonin (PCT) improve the predictive value of the Simplified Acute Physiologic Score (SAPS) II and Sequential Related Organ Failure Assessment (SOFA) in VAP. Specified end-points of a prospective multinational trial including 101 patients with VAP were analysed. Death <28 days after VAP onset was the primary end-point. MR-proANP and PCT were elevated at the onset of VAP in nonsurvivors compared with survivors (p = 0.003 and p = 0.017, respectively) and their slope of decline differed significantly (p = 0.018 and p = 0.039, respectively). Patients with the highest MR-proANP quartile at VAP onset were at increased risk for death (log rank p = 0.013). In a logistic regression model, MR-proANP was identified as the best predictor of survival. Adding MR-proANP and PCT to SAPS II and SOFA improved their predictive properties (area under the curve 0.895 and 0.880). We conclude that the combination of two biomarkers, MR-proANP and PCT, improve survival prediction of clinical severity scores in VAP.

Four-hour infusions of synthetic atrial natriuretic peptide in normal volunteers.

Two doses of synthetic atrial natriuretic peptide (0.5 and 5.0 micrograms/min) and its vehicle were infused intravenously for 4 hours in eight salt-loaded normal volunteers, and the effect on blood pressure, heart rate, renal hemodynamics, solute excretion, and secretion of vasoactive hormones was studied. The 0.5 micrograms/min infusion did not alter blood pressure or heart rate, whereas the 5.0 micrograms/min infusion significantly reduced the mean pressure by 20/9 mm Hg after 2.5 to 3 hours and increased the heart rate slightly. Inulin clearance was not significantly changed, but the mean p-aminohippurate clearance fell by 13 and 32% with the lower and higher doses, respectively. Urinary excretion of sodium and chloride increased slightly with the lower dose. With the higher dose, a marked increase in urinary excretion of sodium, chloride, and calcium was observed, reaching a peak during the second hour of the infusion. Potassium and phosphate excretion did not change significantly. A brisk increase in urine flow rate and fractional water excretion was seen only during the first hour of the high-dose infusion. Signs and symptoms of hypotension were observed in two subjects. No change in plasma renin activity, angiotensin II, or aldosterone was observed during either infusion, but a marked increase occurred after discontinuation of the high-dose infusion. In conclusion, the 5 micrograms/min infusion induced a transient diuretic effect, delayed maximal natriuretic activity, and a late fall in blood pressure, with no change in inulin clearance but a dose-related decrease in p-aminohippurate clearance. Despite large amounts of sodium excreted and blood pressure reduction, no counterregulatory changes were observed in the renin-angiotensin-aldosterone system or plasma vasopressin levels during the infusion.

A liver metalloendopeptidase which degrades the circulating hypotensive peptide hormones bradykinin and atrial natriuretic peptide

A new metalloendopeptidase was purified to apparent homogeneity from a homogenate of normal human liver using successive steps of chromatography on DEAE-cellulose, hydroxyapatite and Sephacryl S-200. The purified enzyme hydrolyzed the Pro7-Phe8 bond of bradykinin and the Ser25-Tyr26 bond of atrial natriuretic peptide. No cleavage was produced in other peptide hormones such as vasopressin, oxytocin or Met- and Leu-enkephalin. This enzyme activity was inhibited by 1 mM divalent cation chelators such as EDTA, EGTA and o-phenanthroline and was insensitive to 1 µM phosphoramidon and captopril, specific inhibitors of neutral endopeptidase (EC 3.4.24.11) and angiotensin-converting enzyme (EC 3.4.15.1), respectively. With Mr 85 kDa, the enzyme exhibits optimal activity at pH 7.5. The high affinity of this endopeptidase for bradykinin (Km = 10 µM) and for atrial natriuretic peptide (Km = 5 µM) suggests that it may play a physiological role in the inactivation of these circulating hypotensive peptide hormones.

Imidazoline receptors in the heart: a novel target and a novel mechanism of action that involves atrial natriuretic peptides

Chronic stimulation of sympathetic nervous activity contributes to the development and maintenance of hypertension, leading to left ventricular hypertrophy (LVH), arrhythmias and cardiac death. Moxonidine, an imidazoline antihypertensive compound that preferentially activates imidazoline receptors in brainstem rostroventrolateral medulla, suppresses sympathetic activation and reverses LVH. We have identified imidazoline receptors in the heart atria and ventricles, and shown that atrial I1-receptors are up-regulated in spontaneously hypertensive rats (SHR), and ventricular I1-receptors are up-regulated in hamster and human heart failure. Furthermore, cardiac I1-receptor binding decreased after chronic in vivo exposure to moxonidine. These studies implied that cardiac I1-receptors are involved in cardiovascular regulation. The presence of I1-receptors in the heart, the primary site of production of natriuretic peptides, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), cardiac hormones implicated in blood pressure control and cardioprotection, led us to propose that ANP may be involved in the actions of moxonidine. In fact, acute iv administration of moxonidine (50 to 150 µg/rat) dose-dependently decreased blood pressure, stimulated diuresis and natriuresis and increased plasma ANP and its second messenger, cGMP. Chronic SHR treatment with moxonidine (0, 60 and 120 µg kg-1 h-1, sc for 4 weeks) dose-dependently decreased blood pressure, resulted in reversal of LVH and decreased ventricular interleukin 1ß concentration after 4 weeks of treatment. These effects were associated with a further increase in already elevated ANP and BNP synthesis and release (after 1 week), and normalization by 4 weeks. In conclusion, cardiac imidazoline receptors and natriuretic peptides may be involved in the acute and chronic effects of moxonidine.

Isolation and Characterization of a Natriuretic Peptide from Crotalus oreganus abyssus (Grand Canyon Rattlesnake) and its Effects on Systemic Blood Pressure and Nitrite Levels

Studies on the therapeutic potential of venom peptides have significantly advanced the development of new peptide drugs. A good example is captopril, a synthetic peptide drug, which acts as an anti-hypertensive and potentiating bradykinin, inhibiting the angiotensin-converting enzyme, whose precursor was isolated from the venom of Bothrops jararacussu. The natriuretic peptide (NPs) family comprises three members, ANP (atrial natriuretic peptide), BNP (B-type natriuretic peptide) and CNP (C-type natriuretic peptide), and has an important role in blood pressure regulation and electrolyte homeostasis. In this study, we describe, for the first time, the isolation and characterization of a novel natriuretic-like peptide (Coa_NP), isolated from Crotalus Oreganus abyssus venom. The peptide has 32 amino acids and its complete sequence is SKRLSNGCFGLKLDRIGAMSGLGCWRLINESK. The Coa_NP has an average molecular mass of 3510.98 Da and its amino acid sequence presents the loop region that is characteristic of natriuretic peptides (17 amino acids, NP domain consensus; CFGXXXDRIXXXSGLGC). Coa_NP is a natriuretic peptide of the ANP/BNP-like family, since the carboxy terminal region of CNP has its own NP domain. The functional experiments showed that Coa_NP produced biological effects similar to those of the other natriuretic peptides: (1) a dose-dependent decrease in mean arterial pressure; (2) significant increases in plasma nitrite levels, and (3) vasorelaxation in thoracic aortic rings that were pre-contracted with phenylephrine. The structural and biological aspects confirm Coa_NP as a natriuretic peptide isolated from snake venom, thus expanding the diversification of venom components.

Pharmacokinetics of synthetic atrial natriuretic peptides in normal men.

The kinetics of atrial natriuretic peptides (ANP) and the kinetic profile of their effect on blood pressure and renal hemodynamic and electrolyte excretion were investigated in 20 salt-loaded healthy volunteers during and after constant rate infusion. At steady state, mean plasma concentrations of ANP were measured at 210, 430, and 2990 pg/ml and mean systemic clearance was 2.6, 2.5, and 1.7 L/min for ANP infusion rates of 0.5, 1, and 5 micrograms/min, respectively, which corresponds to the clearance rate of other vasoactive peptide hormones. The apparent volume of distribution averaged 17 L and the mean half-life was 4.5 minutes. ANP induced dose-related effects on systemic and renal hemodynamic, as well as urinary electrolyte excretion, albeit with a time lag between onset and full effect.

Role of atrial natriuretic peptides and neuropeptide Y in blood pressure regulation.

Atrial natriuretic peptides (ANP) are released into the circulation in response to enhanced atrial stretching. These peptides not only have diuretic and natriuretic properties, but also exert a relaxing effect on the vasculature. Moreover, they antagonize the contractions induced by norepinephrine and angiotensin II. Neuropeptide Y (NPY) is also a vasoactive peptide. It is widely distributed throughout the central and peripheral nervous systems. NPY is coreleased with norepinephrine by perivascular nerve endings. At high concentrations, this peptide has a direct vasoconstrictor effect. In addition, it enhances the vascular effect of various agonists, including norepinephrine and angiotensin II. Both ANP and NPY have an inhibitory effect on renin secretion. This effect may have important implications for the role of these peptides in cardiovascular regulation.

Differential responses of newborn pulmonary arteries and veins to atrial and C-type natriuretic peptides.

Atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are important dilators of the pulmonary circulation during the perinatal period. We compared the responses of pulmonary arteries (PA) and veins (PV) of newborn lambs to these peptides. ANP caused a greater relaxation of PA than of PV, and CNP caused a greater relaxation of PV than of PA. RIA showed that ANP induced a greater increase in cGMP content of PA than CNP. In PV, ANP and CNP caused a similar moderate increase in cGMP content. Receptor binding study showed more specific binding sites for ANP than for CNP in PA and more for CNP than for ANP in PV. Relative quantitative RT-PCR for natriuretic peptide receptor A (NPR-A) and B (NPR-B) mRNAs show that, in PA, NPR-A mRNA is more prevalent than NPR-B mRNA, whereas, in PV, NPR-B mRNA is more prevalent than NPR-A mRNA. In conclusion, in the pulmonary circulation, arteries are the major site of action for ANP, and veins are the major site for CNP. Furthermore, the differences in receptor abundance and the involvement of a cGMP-independent mechanism may contribute to the heterogeneous effects of the natriuretic peptides in PA and PV of newborn lambs.

Vascular effects and electrolyte homeostasis of the natriuretic peptide isolated from Crotalus oreganus abyssus (North American Grand Canyon rattlesnake) venom

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Atrial stretch increases the gastric tonus of anesthetized rats

Aims: We assessed the effects of right atrial stretch on gastric tone and neuro-humoral pathways involved in this phenomenon. Main methods: Anesthetized male rats were submitted for monitoring of the mean arterial pressure (MAP) and central venous pressure (CVP). A balloon catheter positioned into the stomach monitored by plethysmography the gastric volume (GV). All rats were monitored for 55-min. After the first 20-min of monitoring (basal period), rats were either submitted to a 5-min interval of atrial stretch (AS) or maintained as controls. An intra-atrial balloon catheter was distended with 30,50, or 70 mu L of saline. GV and hemodynamic data were also monitored for a further 30-min. Another set of rats, either previously submitted to subdiaphragmaic vagotomy or splanchnicectomy plus celiac ganglionectomy or maintained as controls (sham), were also submitted to AS. Each subset consisted of six rats. The plasma level of the atrial natriuretic peptide (ANP) was measured in another group of rats. Data were compared by ANOVA followed by Bonferroni`s test. Key findings: In control rats, the GV, MAP, and CVP remained at stable levels throughout the studies. In addition to increase the CVP, AS also decreased (P<0.05) the GV by 14%, 11.5%, and 16.5% in the 30, 50, and 70 mu L groups, respectively. Vagotomy prevented the GV decrease. In contrast, the AS decreased (P<0.05) the GV by 21.3% in splanchnicectomized rats. Significance: AS decreased the GV of rats in a volume-dependent manner, a phenomenon prevented by vagotomy but enhanced by celiac ganglionectomy. (C) 2010 Elsevier Inc. All rights reserved.

Clinical pharmacology of atrial natriuretic (3-28) eicosahexapeptide.

The clinical pharmacology of a synthetic rat atrial natriuretic peptide (rANP) was evaluated in normal volunteers. During a dose-ranging study at 1-40 micrograms/min we observed a dose-dependent decrease in mean intra-arterial blood pressure, an acceleration of the heart rate and a transient increase in blood flow to the skin. During a 4-h constant-dose infusion at 0.5 and 5.0 micrograms/min, inulin clearance remained unchanged but there was a dose-related fall in paraaminohippurate (PAH) clearance and an increase in the filtration fraction. Urinary excretion of sodium, chloride and calcium increased in a dose-related fashion, but with the high dose the excretion curve had a bell-shape. No change in plasma renin activity, angiotensin II and aldosterone was observed during the rANP infusion despite the excretion of large amounts of sodium and a blood pressure reduction with the high dose. Indocyanine green clearance, a measure of hepatic blood flow, was significantly decreased by a 2-h rANP infusion at 1.0 microgram/min. In normal volunteers, therefore, rANP induced vasodilation and blood pressure reduction, a decrease in renal and hepatic blood flow and a natriuretic and transient diuretic effect without activation of the renin-angiotensin-aldosterone system.

Does plasma ANP participate in natriuresis induced by a-MSH?

a-Melanocyte-stimulating hormone (a-MSH; 0.6 and 3 nmol) microinjected into the anteroventral region of the third ventricle (AV3V) induced a significant increase in diuresis without modifying natriuresis or kaliuresis. Intraperitoneal (ip) injection of a-MSH (3 and 9.6 nmol) induced a significant increase in urinary sodium, potassium and water excretion. Intraperitoneal (3 and 4.8 nmol) or iv (3 and 9.6 nmol) administration of a-MSH did not induce any significant changes in plasma atrial natriuretic peptide (ANP), suggesting that the natriuresis, kaliuresis and diuresis induced by the systemic action of a-MSH can be dissociated from the increase in plasma ANP. These preliminary results suggest that a-MSH may be involved in a g-MSH-independent mechanism of regulation of hydromineral metabolism