Elevation of circulating and ventricular adrenomedullin in human congestive heart failure

Increased plasma levels of adrenomedullin, a vasoactive peptide, in patients with end-stage pulmonary disease

AIM

To study adrenomedullin (AM) plasma levels in patients with severe lung disease and to analyze the relationship between AM and heart changes, hemodynamics and blood gases.

METHODS

Case control study of 56 patients (36 men, 20 women) with severe lung disease and 9 control subjects (7 men, 2 women). Patients with end-stage pulmonary disease, including chronic obstructive pulmonary disease (COPD, n=11), cystic fibrosis (CF, 26), idiopatic pulmonary fibrosis (ILD, n=9), and idiopatic pulmonary arterial hypertension (PAH, n=10), who were evaluated for lung trasplantation between January 1997 and September 2000, and nine patients who underwent lung surgery for a solitary benign nodule. AM plasma levels in pulmonary artery (mixed venous blood, vein) and aorta or femoral artery (arterial, art), art and vein blood gases, pulmonary hemodynamics, systemic hemodynamics, two-dimensional transthoracic echocardiography and echo-Doppler study.

RESULTS

Plasma AM (art and ven) levels were higher among patients' group compared to the controls (AMart p<0.02 and AMven p<0.04) for CF, ILD, PAH (AMart, pg ml(-1) Controls 13.7+/-3.6, COPD 22.8+/-6.2, CF 28.1+/-11.4, ILD 34.1+/-14.3, PAH 35.1+/-18.9; AMven, pg ml(-1) Controls 14.2+/-4.8, COPD 28.1+/-12.6, CF 31.7+/-14.1, ILD 38.7+/-16.5, PAH 40.1+/-4.4). We found with a trend towards higher concentration in ILD and PAH patients compared to COPD and CF but no statistical significant differences. Mixed-venous AM was higher than arterial AM in all groups resulting in AM uptake (AMPulmUp pg min(-1) Controls 4.8+/-22.6, COPD 21.1+/-44.9, CF 20.6+/-45.1, ILD 23.7+/-38.5, PAH 29.9+/-49.7). The univariate analysis showed a weak but significant correlation between AMart and mean systemic arterial pressure, heart rate, mean pulmonary arterial pressure and systemic vascular resistance. In the multivariate analysis, four variables emerged as independent factors of AMart including mean pulmonary arterial pressure, heart rate, mean systemic arterial pressure and left ventricular diastolic diameter (F=8.6, p<0.00001, r=0.60, r2=0.32). A similar weak correlation was apparent between AMven, systemic vascular resistance, and mean pulmonary arterial pressure. The results of multivariate analysis identify right atrial enlargement, mean right atrial pressure, heart rate and left ventricular dimensions as the only independent variables related to AMven (F=4.3, p<0.0004 r=0.56, r2=0.26). AM pulmonary uptake was significantly correlated with AMven (r=0.65), but not with hemodynamic, blood gas and echocardiographic variables.

CONCLUSIONS

AM plasma levels are elevated in patients with severe lung disease in face of a preserved pulmonary uptake. These results suggest that the high AM plasma levels in patients with severe lung disease are not caused by a reduced pulmonary clearance, instead suggesting a systemic production.

Adrenomedullin messenger RNA expression is increased in myocardial tissue of patients with idiopathic dilated cardiomyopathy

Increased plasma levels of adrenomedullin (ADM) have been reported in patients with congestive heart failure Immunohistochemical ADM has been identified in failing human ventricle, but the gene expression pattern of ADM messenger RNA (mRNA) in myocardial tissue of patients with heart failure has not been elucidated. In this study, gene expression of ADM mRNA (analyzed by northern blot) and tissue concentration of ADM (measured by radioimmunoassay) were assessed in the explanted hearts of 17 patients with idiopathic dilated cardiomyopathy (IDC) and in 7 organ donors with no cardiopathy (controls). Myocardial tissue samples of patients with IDC showed increased ADM mRNA gene expression (p < 0.05) and decreased immunoreactive ADM protein content (p < 0.02) compared with controls.

Neuroendocrine evaluation of cardiac disease

Current evidence favors the view that regardless of etiology, there is a predictable sequence of neuroendocrine activation that operates in most dogs and cats with progressive heart disease and that it is largely, but not entirely, independent of etiology. The natriuretic peptides and sympathetic nervous system seem to be early responders to developing cardiac and hemodynamic perturbations in both species. BNP plays a particularly prominent role in cats, possibly as a reflection of disease etiology. Shortly thereafter, plasma endothelin concentrations rise, reflecting the impact of the hemodynamic alterations on the vasculature. Endothelin and the natriuretic peptides directly suppress plasma renin release but have divergent effects on aldosterone. Activation of the tissue RAAS may operate early on to further the progression of heart failure, but evidence of plasma RAAS activation occurs comparatively late and near the time of development of overt CHF. Finally, in animals with severe CHF that are prone to hypotension,vasopressin levels may also rise, contributing to the retention of free water and congestion that is refractory to diuretics. Although oversimplified, this scenario seems to be consistent with data obtained in human, canine, and feline patients. These observations provide some impetus for evaluating ACE inhibitors in cats and beta-receptor-blocking drugs in dogs and cats. Perhaps we are also a little closer to identifying useful biochemical markers that can aid in the diagnosis of heart disease, guide therapy, and improve our understanding of the biologic processes occurring in our patients.

Increased adrenomedullin immunoreactivity and mRNA expression in coronary plaques obtained from patients with unstable angina

OBJECTIVE

To examine the expression and localisation of adrenomedullin in human coronary atherosclerotic lesions from patients with unstable angina (UAP) and stable angina (SAP), and to study the relation between adrenomedullin expression and plaque instability.

DESIGN

A retrospective observational study.

PATIENTS

Directional coronary atherectomy samples were obtained from 15 patients with UAP and 12 with SAP.

METHODS

The localisation of adrenomedullin was examined by immunohistochemistry, and adreno-medullin mRNA expression was measured by quantitative polymerase chain reaction.

RESULTS

Adrenomedullin immunoreactivity was preferentially localised in macrophages, intimal smooth muscle cells, and proliferated microvessels. The mean number of adrenomedullin positive cells in five high power fields (x 400) per specimen was higher in patients with UAP than in those with SAP (mean (SEM), 110 (13) v 76 (7); p < 0.05); and the ratio of adrenomedullin positive to total cells was higher in patients with UAP (43.0 (2.2)% v 34.2 (2.0)%; p < 0.01). More adrenomedullin mRNA was expressed in the plaque of patients with UAP than in those with SAP (60.4 (16.9)% v 9.7 (3.3)%; p < 0.01).

CONCLUSIONS

The findings suggest that adrenomedullin is involved in the development of atherosclerosis and plaque instability in human coronary arteries, in an autocrine or paracrine manner.

Novel fish-derived adrenomedullin in mammals: structure and possible function

Adrenomedullin (AM) has been recognized as a member of the calcitonin (CT)/CT gene-related peptide (CGRP) family. However, an independent AM family consisting of five paralogous peptides exists in teleost fish. Among them, the peptide named AM1 is an ortholog of mammalian AM as determined by the linkage analysis of orthologous genes and the presence of proAM N-terminal 20 peptide (PAMP)-like sequence in the prosegment. Since the peptides named AM2 and 3 are distinct from other members with respect to the precursor sequence, tissue distribution of the transcripts, and exon-intron organization, we searched for their mammalian orthologs from genome databases, which resulted in an identification of AM2 in human, rat, and mouse. AM2 was expressed abundantly in the submaxillary gland, kidney, and some vascular and digestive tissues of mice. AM2 injected in vivo induced potent cardiovascular and renal effects in mice. In the heart and kidney of mice, AM2 was localized in endothelial cells of the coronary vessels and in glomeruli and vasa recta, respectively. AM2 increased cAMP accumulation in cells expressing human CT receptor-like receptor (CRLR) and one of receptor activity-modifying proteins (RAMPs), but it was no more potent than CGRP and AM. AM2 was also less potent than CT in cells expressing CT receptor and RAMP. There remains a possibility that a new AM2-specific receptor or an additional RAMP that enables CRLR to be an AM2-specific receptor, exists in mammals.

The role of adrenomedullin and receptors in glomerular hyperfiltration in streptozotocin-induced diabetic rats

BACKGROUND

Since adrenomedullin (AM) elicits vasodilatation by binding to specific AM receptors consisted of calcitonin-receptor-like receptor (CRLR)/receptor-activity-modifying protein 2 (RAMP2) or CRLR/receptor-activity-modifying protein 3 (RAMP3) on endothelial cells and stimulating nitric oxide production, AM possibly involves in glomerular capillary dilatation in early phase of diabetic nephropathy.

METHODS

Streptozotocin (STZ)-induced diabetic Sprague-Dawley rats at 4 weeks after the injection were employed for expression studies of AM, RAPM2, and RAMP3. The measurement of AM peptide levels in kidney tissue, plasma, and urine was performed. Human aortic endothelial cells (HAEC) were used to investigate functional link between glucose-induced AM production and nitric oxide release.

RESULTS

STZ rats showed glomerular hypertrophy and increased urinary NO2- and NO3- excretion. By Northern blot analyses, AM and RAPM2 mRNAs significantly increased in the kidneys of STZ rats, while RAMP3 mRNA was not altered. In STZ rats, AM peptide was actively secreted into urine (1280 +/- 360 fmol/day vs. control 110 +/- 36 fmol/day). AM peptide was mainly detected on cortical and medullary collecting duct cells in control rat kidneys and AM peptide and mRNA were up-regulated on afferent arterioles and glomeruli of STZ rats. RAMP2 expression was detected on afferent arterioles and not in glomeruli in control rats and it was up-regulated on glomerular endothelial cells in STZ rats. In HAEC culture, d-glucose stimulated AM and nitric oxide production and they were suppressed by addition of AM antisense oligodeoxynucleotides.

CONCLUSION

Up-regulated expression of AM and RAMP2 in afferent arterioles and glomeruli may be related to selective dilatation of glomerular capillary in acute phase of type 1 diabetes.

Adrenomedullin as a sensitive marker for coronary and peripheral arterial complications in patients with atherosclerotic risks

Plasma adrenomedullin (AM) levels are elevated in various pathological states including cardiovascular and inflammatory diseases. The present study investigated whether an increased AM level is a marker of vascular complications in patients with atherosclerotic risks. In 114 patients with cardiovascular risks and/or diseases including ischemic heart disease (IHD) and peripheral arterial disease (PAD), plasma AM concentration and other inflammatory markers such as high sensitive C-reactive protein (CRP) and interleukin (IL)-6 were examined. The plasma AM level was not altered by the absence or presence of each of four major risk factors, i.e., hypertension, diabetes mellitus, hyperlipidemia, and smoking and its level was not significantly correlated with blood pressure, plasma glucose, or serum lipid levels. The patients with IHD had a significantly higher concentration of plasma AM than those without IHD. The AM level in subjects with PAD was also increased significantly compared with those without PAD. The plasma AM was strongly correlated with inflammatory parameters such as CRP and IL-6. Among AM, CRP, and IL-6, however, only AM was an independent predictor for both IHD and PAD by multiple logistic regression analysis. Our findings suggest the possibility that plasma AM is a novel sensitive marker for the presence of vascular lesions in patients with atherosclerotic risks.

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS blocks CGRP and adrenomedullin vasoactive responses in the microvasculature

Calcitonin gene-related peptide (CGRP) is a potent microvascular dilator neuropeptide that is considered to play an essential role in neurogenic vasodilatation and in maintaining functional integrity in peripheral tissues. We have examined the effect of the nonpeptide CGRP antagonist BIBN4096BS on responses to CGRP and the structurally related peptide adrenomedullin, AM, in murine isolated aorta and mesentery preparations, and in the cutaneous microvasculature in vivo. We show for the first time that BIBN4096BS is an effective antagonist of CGRP and AM responses in the murine mesenteric and cutaneous microvasculature, and of CGRP in the murine aorta. After local administration, BIBN4096BS selectively inhibits the potentiation of microvascular permeability in the cutaneous microvasculature by CGRP and AM, with no effect on responses induced by other microvascular vasodilators. BIBN4096BS reversed both newly developed and established vasoactive responses induced by CGRP. The ability of CGRP to potentiate plasma extravasation was lost when coinjected with compound 48/80 (where mast cells would be activated to release proteases), but regained when soybean trypsin inhibitor was coinjected with compound 48/80. These results demonstrate that BIBN4096BS is a selective antagonist of responses induced by CGRP and AM in the mouse microvasculature, and CGRP in the mouse aorta. The ability of BIBN4096BS to block an established CGRP microvascular vasodilatation indicates that the sustained vasodilator activity of CGRP is due to the retention of the active intact peptide and the continued involvement of the CGRP receptor.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Adrenomedullin modulates hemodynamic and cardiac effects of angiotensin II in conscious rats

We examined whether adrenomedullin, a vasoactive peptide expressed in the heart, modulates the increase in blood pressure, changes in systolic and diastolic function, and left ventricular hypertrophy produced by long-term administration of ANG II or norepinephrine in rats. Subcutaneous administration of adrenomedullin (1.5 μg·kg−1·h−1) for 1 wk inhibited the ANG II-induced (33.3 μg·kg−1·h−1 sc) increase in mean arterial pressure by 67% ( P < 0.001) but had no effect of norepinephrine-induced (300 μg·kg−1·h−1 sc) hypertension. Adrenomedullin enhanced the ANG II-induced improvement in systolic function, resulting in a further 9% increase ( P < 0.01) in the left ventricular ejection fraction and 19% increase ( P < 0.05) in the left ventricular fractional shortening measured by echocardiography, meanwhile norepinephrine-induced changes in systolic function were remained unaffected. Adrenomedullin had no effect on ANG II- or norepinephrine-induced left ventricular hypertrophy or expression of hypertrophy-associated genes, including contractile protein and natriuretic peptide genes. The present study shows that adrenomedullin selectively suppressed the increase in blood pressure and augmented the improvement of systolic function induced by ANG II. Because adrenomedullin had no effects on ANG II- and norepinephrine-induced left ventricular hypertrophy, circulating adrenomedullin appears to act mainly as a regulator of vascular tone and cardiac function.

Expression of adrenomedullin and proadrenomedullin N-terminal 20 peptide in PC12 cells after exposure to nerve growth factor

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are multi-functional peptides derived from the same precursor, proadrenomedullin. We have studied the regulatory mechanism of expression of these peptides during neuronal differentiation of rat pheochromocytoma PC12 cells by nerve growth factor (NGF). The cellular levels of the peptides increased slightly, and then progressively decreased below the control by NGF. Immunoreactive (ir)-AM in the medium was transiently increased by NGF. Cytochemical staining showed that ir-AM and ir-PAMP were abundantly present in cytoplasm in the undifferentiated cells, and were decreased during culture with NGF. There was no preferential localization of ir-AM or ir-PAMP in neurites in comparison with in cytoplasm in the differentiated cells. Northern blot analysis showed that mRNA encoding these peptides, as detected as a band of 1.6 kb, increased more than three-fold at 1 h after the addition of NGF and then progressively decreased to one fifth of the control during 72 h. Degradation rate of the mRNA was slowed by NGF even when mRNA level is decreased after 72 h of NGF treatment. The transcription rate of their gene increased transiently and then decreased by the long-term treatment with NGF. These results demonstrate that expression of AM and PAMP is regulated by NGF along with time-dependent differentiation: AM gene transcription is transiently activated by NGF, whereas it was suppressed during neuronal differentiation of the cells.

The effect of adrenomedullin, amylin fragment 8-37 and calcitonin gene-related peptide on contractile force, heart rate and coronary perfusion pressure in isolated rat hearts

The effect of human adrenomedullin, human amylin fragment 8-37 (amylin 8-37) and rat calcitonin gene-related peptide (CGRP) on contractile force, heart rate and coronary perfusion pressure has been investigated in the isolated perfused rat hearts. Adrenomedullin (2x10(-10), 2x10(-9) and 2x10(-8) M) produced a significant decrease in contractile force and perfusion pressure, but only the peptide caused a decline in heart rate at the highest dose. Amylin (10(-9), 10(-8) and 10(-7) M) significantly increased and then decreased contractile force. Two doses of amylin (10(-8) and 10(-7) M) induced a significant increase in heart rate, however amylin did not change perfusion pressure in all the doses used. Rat alpha CGRP (10(-8), 10(-7) and 10(-6) M) evoked a slight decline in contractile force following a significant increase in contractile force induced by the peptide. CGRP in all the doses raised heart rate and lowered perfusion pressure. Our results suggest that adrenomedullin has negative inotropic, negative chronotropic and coronary vasodilator actions. Amylin produces a biphasic inotropic effect and evokes a positive chronotropy. CGRP causes positive inotropic, positive chronotropic and vasodilatory effects in isolated rat hearts.

Plasma adrenomedullin concentration is increased in patients with peripheral arterial occlusive disease associated with vascular inflammation

Adrenomedullin (AM), a potent vasodepressor, is known to have anti-atherosclerotic and anti-inflammatory effects. However, there is no information about its level in severe atherosclerotic diseases, such as peripheral arterial occlusive disease (PAOD). The present study investigated the plasma concentration of AM and several inflammatory parameters in 72 patients with and without PAOD. The plasma AM concentration in patients with PAOD was significantly higher than in those without PAOD. Its concentration had significant correlations with ankle-brachial index and Fontaine's stage. The plasma AM level also correlated with high sensitive C-reactive protein and interleukin-6. As an additional study, plasma levels of two forms of AM drawn from the femoral artery and saphenous vein were measured in 27 other subjects. Both mature and intermediate forms of plasma AM in the femoral artery and saphenous vein were higher in patients with PAOD than in those without PAOD. A significant step-up of the mature form of AM from the femoral artery to the saphenous vein was observed. Our findings indicate that the plasma AM concentration was elevated in patients with PAOD in proportion to the severity of the disease and associated with vascular inflammation. An increased production of AM in PAOD may play a protective role against advanced atherosclerosis with an inflammatory signature.

Role of cyclooxygenase in ventricular effects of adrenomedullin: is adrenomedullin a double-edged sword in sepsis?

Adrenomedullin (ADM) is upregulated in cardiac tissue under various pathophysiological conditions. However, the direct inotropic effect of ADM on normal and compromised cardiomyocytes is not clear. In rat ventricular myocytes, ADM produced an initial (<30 min) increase in cell shortening and Ca2+ transient and, on prolonged incubation (>1 h), a marked decrease in cell shortening and Ca2+ transient. Both effects were sensitive to inhibition by the ADM antagonist ADM-(22–52). The increase and decrease in cell shortening and Ca2+ transient were attenuated by pretreatment with indomethacin [a nonspecific cyclooxygenase (COX) inhibitor], nimesulide and SC-236 (specific COX-2 inhibitors), and tranylcypromine (a prostacyclin synthase inhibitor); SQ-29548 (a thromboxane receptor antagonist) was without effect. Cells isolated from LPS-treated rats that were in the late, hypodynamic phase of septic shock also showed a marked decrease in cell shortening and Ca2+ transient. Because ADM is overexpressed in sepsis, we repeated the above protocol in cells isolated from LPS-treated rats. At 4 h after LPS injection, ADM levels markedly increased in plasma, ventricles, and freshly isolated ventricular myocytes. Decreases in cell shortening and Ca2+ transient in LPS-treated cells were reversed by pretreatment with ADM-(22–52). Anti-ADM (rat) IgG also reversed the decrease in cell shortening and other parameters of cell kinetics. Indomethacin, SC-236, and tranylcypromine restored cell contractility and the decrease in Ca2+ transient, whereas SQ-29548 had no effect, implying that prostacyclin played a role in both effects. However, with regard to cell-shortening kinetics, indomethacin and SQ-29548 decreased the amount of time taken by the cells to return to baseline, whereas SC-236 and tranylcypromine did not, implying that not only prostacyclin, but also thromboxane, is involved. The results indicate that ADM interacts with COX to yield prostanoids, which mediate its negative inotropic effect in LPS-treated rat ventricular myocytes.

Adrenomedullin in vascular diseases

A novel vasodilator, adrenomedullin (AM), which acts as an autocrine/paracrine factor in cardiovascular system, has antiproliferative and antimigrative effects. AM gene transfer prevents the development of cuff-induced vascular injury. Moreover, AM knockout mice exhibited an increase in angiotensin (Ang) II/salt loading-induced coronary arterial lesion, hypoxia-induced pulmonary vascular damage, and cuff-induced vascular injury associated with enhancement in reactive oxygen species (ROS) generation. In addition, AM expression was stimulated by ROS, and AM directly inhibits oxidative stress so that AM might be a negative feedback substance against ROS-induced organ damages. In addition, AM increases nitric oxide and ameliorates insulin resistance, leading to oxidative stress. Consequently, endogenous AM might compensatively inhibit the development of vascular diseases at least partly through an antioxidative effect.

Production of adrenomedullin from synovial cells in rheumatoid arthritis patients

It was recently reported that plasma levels of adrenomedullin (AM), identified as a vasorelaxant peptide, are significantly higher in rheumatoid arthritis (RA) patients than in osteoarthritis (OA) patients. The objective of the present study was to elucidate AM production in synovial cells from patients with RA. Adrenomedullin mRNA was detected in cultured synovial cells from RA patients by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemical analysis demonstrated the presence of AM in synovial cells from RA patients. In addition, we investigated AM levels in knee joint fluids from RA and OA patients. Those from RA patients were elevated approximately threefold over those of OA patients. In this study, we demonstrated for the first time AM expression in synovial cells from RA patients and high levels of AM production in RA joint fluid.

Impact of nitric oxide on adrenomedullin- and proadrenomedullin N-terminal 20 peptide-induced cardiac responses: action by alone and combined administration

The cardiac effects of adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) as well as the possible signaling pathways were investigated. In the isolated perfused rat heart, infusion of AM (10(-11) to 10(-8) M) and PAMP(10(-11) to 10(-8) M) for 10 min, alone or in combination, induced concentration-dependent decreases in the left ventricular pressure (LVP), LVP +/- dp/dtmax of the hearts. The effects were attenuated by Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase. ADM and PAMP alone or in combinations increased the coronary fluid (CF), which could be antagonized by L-NAME. Pretreatment of H89, an inhibitor of protein kinase A (PKA), failed to alter the AM- or PAMP-induced decreases in LVP and LVP +/- dp/dtmax, but further promoted the AM or PAMP increased CF. The cAMP content in left cardiac ventricle was increased significantly by ADM infusions but not by PAMP. There was no statistical difference in cAMP contents with ADM administrated alone from those combined with ADM and PAMP. In conclusion, this study reveals that ADM and PAMP infused alone or in combinations inhibited the function of rat hearts in vitro, which may be partly involved with the NOS/NO pathway, rather than cAMP/PKA.

Direct coronary vasodilator action of adrenomedullin is mediated by nitric oxide

Increased circulating levels of adrenomedullin (ADM) cause peripheral vasodilatation and hypotension, accompanied by cardiac actions including tachycardia and increases in cardiac contractility, cardiac output, coronary conductance (CC) and coronary blood flow (CBF). It is unclear to what extent these cardiac effects are direct actions of ADM or secondary to the hypotension and altered cardiac loading. The direct cardiac actions of ADM were examined in conscious sheep previously implanted with aortic and coronary flow probes, and an indwelling left coronary artery cannula. Responses to infusion of ADM (0.5 microg kg(-1) h(-1) for 1 h) into the left coronary artery or jugular vein were compared (n=6). The effect of blockade of nitric oxide (NO) synthase with intracoronary (i.c.) N(omega)-nitro-l-arginine (l-NNA; 1.5 mg kg(-1) h(-1), infused for 2 h before and during ADM infusion, was assessed to determine whether the responses to ADM were mediated by NO (n=5). I.c. ADM caused large and sustained increases in CC (0.35+/-0.07-0.55+/-0.13 ml min(-1) mmHg-1, P<0.05) and CBF (28+/-6-42+/-9 ml min(-1), P<0.05), but had no effect on arterial pressure or indices of cardiac contractility (first differential of the upstroke of systole and peak aortic flow rate). Intravenous infusion of ADM had no effects. I.c. l-NNA, at a dose that abolished the coronary vasodilator action of acetylcholine, blocked ADM-induced coronary vasodilatation. In conclusion, ADM had a direct coronary vasodilator action that was mediated by release of endogenous NO and resulted in increased CBF. There was no evidence for a direct inotropic action of ADM.

Circulating and cardiac levels of apelin, the novel ligand of the orphan receptor APJ, in patients with heart failure

The orphan receptor APJ and its recently identified endogenous ligand, apelin, are expressed in the heart. However, their importance in the human cardiovascular system is not known. This study shows that apelin-like immunoreactivity is abundantly present in healthy human heart and plasma. Gel filtration HPLC analysis revealed that atrial and plasma levels of high molecular weight apelin, possibly proapelin, were markedly higher than those of mature apelin-36 itself. As assessed by quantitative RT-PCR analysis, left ventricular apelin mRNA levels were increased 4.7-fold in chronic heart failure (CHF) due to coronary heart disease (p<0.01) and 3.3-fold due to idiopathic dilated cardiomyopathy (p<0.05), whereas atrial apelin mRNA levels were unchanged. Atrial and plasma apelin-like immunoreactivity as well as atrial and ventricular APJ receptor mRNA levels were significantly decreased in CHF. Our results suggest that a new cardiac regulatory peptide, apelin, and APJ receptor may contribute to the pathophysiology of human CHF.

Angiotensin II modulates gene expression of adrenomedullin receptor components in rat cardiomyocytes

Both adrenomedullin (AM) and angiotensin II (Ang II) are locally-acting hormones in the cardiac ventricles. Previously we reported that AM inhibits Ang II-induced hypertrophy of cultured rat neonatal cardiomyocytes. In this study, we examined whether Ang II affects the gene expression of the AM receptor components of calcitonin-receptor-like receptor (CRLR) and receptor-activity-modifying protein (RAMP) in rat cardiomyocytes. The mRNA levels of RAMP1 and RAMP3 were significantly elevated following 24-h treatment with Ang II without a change of those of RAMP2 and CRLR. AM increased the intracellular cAMP level and the cAMP accumulation by AM was significantly amplified by the 24-h preincubation with Ang II. The effects of Ang II on RAMP1 and RAMP3 expression were abolished by an Ang II type 1 (AT1) receptor antagonist, but not by an AT2 receptor antagonist. Thus, Ang II modulates gene expression of the AM receptor components via AT1 receptor, suggesting alteration of AM actions by Ang II in cultured rat cardiomyocytes.

Increase in adrenomedullin gene expression in the left atrium and ventricle in the two-kidney one-clip renovascular hypertensive rats

The 2-kidney 1-clip rat model was set up by clipping the left renal artery. At 5 weeks after clipping, there was an increase in preproadrenomedullin mRNA levels in both the left atria and the left ventricle. Adrenomedullin (AM) contents, however, increased in the left ventricle but decreased in the left atrium. These changes were not observed at 2 weeks after clipping. There were no changes in AM or preproadrenomedullin mRNA levels in the thoracic aorta and the mesenteric artery, and in plasma AM levels at 2 weeks or 5 weeks after clipping. We concluded that there was an increase in the secretion of AM in the left ventricle and the left atria in the 5 week renovascular hypertensive rat. The lack of change in plasma AM level suggests a paracrine function for the peptide in this setting.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Adrenomedullin inhibits angiotensin AT1A receptor expression and function in cardiac fibroblasts

Adrenomedullin (AM) is a multifunctional peptide hormone with wide-ranging actions related to cardiovascular homeostasis. AM receptors are highly expressed in the heart and AM has antihypertrophic and antiproliferative effects on cardiac myocytes and fibroblasts, respectively. We have investigated the interaction between AM and angiotensin II (Ang II) signalling in neonatal cardiac fibroblast cultures to determine whether the antagonistic effects of AM are mediated via the modulation of Ang II receptors. Cardiac fibroblasts exclusively expressed the Ang II type 1 receptor (AT(1)R) and binding to this site was downregulated by 35% following an 18-h incubation with 100 nM AM. Levels of AT(1A)R mRNA were dose-dependently lowered by AM, with a maximal 40-50% inhibition by 6 h. The decreases in both AT(1)R binding and AT(1A)R mRNA levels were mimicked by 8-Br-cAMP or forskolin, suggesting that the effects of AM were mediated via an elevation of cAMP. In cardiac fibroblasts pretreated with AM, the Ang II induction of collagen biosynthesis was attenuated, although basal collagen synthesis was unaffected. These data suggest that AM mediates the heterologous downregulation of AT(1)R expression via a relatively rapid decrease in AT(1A)R mRNA pools. This interaction may represent a relevant pathophysiological mechanism for modulating Ang II responsiveness in the diseased heart.

Lessons from the adrenomedullin knockout mouse

Because vasolidator peptide adrenomedullin (AM) exhibits complicated action, we developed AM knockout mice in order to elucidate the physiological and pathophysiological role of AM. The AM(-/-) mice were embryonic lethal, so we could not evaluate directly the role of AM in this mutant mice. Thus, we loaded angiotensin II (AngII) and salt in AM(+/-) mice, which were viable and fertile. As a result, AngII and salt loading caused coronary vascular damage and left ventricular hypertrophy in AM(+/-) mice more greatly than AM(+/+) mice. Moreover, cuff placement of femoral artery stimulated intimal thickening more severely. This treatment increased local AM levels in AM(+/+) mice but not in AM(+/-) mice. The accelerated organ damage in AM(+/-) mice was accompanied with enhanced production of oxidative stress. Thus, our data suggest that intrinsic AM play a vascular protective role.

Mechanisms regulating adrenomedullin gene expression in the left ventricle: role of mechanical load

Adrenomedullin (AM) may function as an autocrine and/or paracrine factor in the heart, but the exact mechanisms regulating cardiac AM gene expression are unknown. The aim of the present study was to characterize the role of mechanical load in regulating gene expression of AM by using two hypertensive rat strains as experimental models. Acute pressure overload was produced by arginine(8)-vasopressin (AVP, 0.05 microg/kg/min, i.v.) infusion in conscious spontaneously hypertensive rats (SHR) and double transgenic rats (dTGR) harboring both the human renin and angiotensinogen genes and in their respective normotensive strains. A significant increase in left ventricular AM mRNA levels was seen in the left ventricles of all rat strains, the increase being augmented in hypertensive strains. Direct left ventricular wall stretch in isolated, perfused rat heart preparation also activated AM gene expression. However, stretching of cultured neonatal ventricular myocytes resulted in inhibition of AM gene expression, and stretch also blocked hypoxia-induced increase in AM gene expression. The present study shows that cardiac AM gene expression is upregulated in response to pressure overload and that this upregulation may be mediated via cell types other than cardiac myocytes.

Adrenomedullin and heart failure

Evidence suggests that adrenomedullin (AM) plays a role in the pathophysiology of heart failure. Circulating concentrations of AM are elevated in cardiovascular disease in proportion to the severity of cardiac and hemodynamic impairment. Raised plasma AM levels following acute cardiac injury and in heart failure provide prognostic information on adverse outcomes. In heart failure, elevated circulating AM also identifies patients likely to receive long-term benefit from inclusion of additional anti-failure therapy (carvedilol). Administration of AM in experimental and human heart failure induces reductions in arterial pressure and cardiac filling pressures, and improves cardiac output, in association with inhibition of plasma aldosterone (despite increased renin release) and sustained (or augmented) renal glomerular filtration and sodium excretion. Furthermore, AM in combination with other therapies (angiotensin-converting enzyme inhibition and augmentation of the natriuretic peptides) results in hemodynamic and renal benefits greater than those achieved by the agents separately. Manipulation of the AM system holds promise as a therapeutic strategy in cardiac disease.

Ventricular adrenomedullin is associated with myocyte hypertrophy in human transplanted heart

Adrenomedullin (ADM) is a vasoactive and natriuretic peptide. While it is known that ADM is increased in failing human ventricles, the expression of ADM in human ventricular allografts remains unknown. The present study was designed to investigate tissue localization and intensity of ADM expression in ventricular biopsy specimens and to characterize ventricular ADM in human cardiac allografts. Thirty-three post-transplant endomyocardial biopsy specimens were examined immunohistochemically. The average score (range: 0-4) of ADM immunoreactivity (IR) was 2.4+/-0.9 (mean+/-standard deviation). Right ventricular (RV) systolic pressure was significantly increased with high ADM-IR (p=0.048) and the ADM-IR positively associated with myocyte size (r(2)=0.23, p=0.010). In contrast, ADM-IR was not associated with systemic blood pressure, serum creatinine, cyclosporine concentration, cardiac fibrosis, or allograft rejection. The present study shows that ADM-IR is present in human ventricular endomyocardium after transplantation, and ADM-IR is associated with the magnitude of RV pressure and myocyte size, suggesting an important role for ventricular ADM in the counteraction against overload as well as in the progress of myocyte hypertrophy after heart transplantation.

Roles of different peptide fragments derived from proadrenomedullin in the regulation of vascular tone in isolated rat aorta

The effects of proadrenomedullin N-terminal 20 peptide (PAMP) and adrenotensin (ADT) on adrenomedullin (ADM)-induced vasodilation were investigated in aortic rings from rat. ADM (10(-9) to 10(-7)M) relaxed the aorta preconstricted with phenylephrine in a concentration-dependent manner. Denudation of endothelium or pretreatment with nitric oxide synthase (NOS) inhibitor, L-NAME, attenuated the vasodilatory action of ADM. ADM-induced vasorelaxation in the aortic rings with endothelium was converted to contraction by PAMP, but not by ADT. The ADM-induced vasodilation was not affected by PAMP in aorta rings without endothelium or in intact aortic rings pretreated with L-NAME. ADM-stimulated nitrite production and NOS activity of the aortas, which was inhibited by PAMP, ADT or PAMP plus ADT. ADM, PAMP, and ADT increased the cyclic adenosine monophosphate (cAMP) contents in vascular tissue. The combination of ADM with PAMP or ADT caused a smaller increase in cAMP level as compared with that of PAMP or ADT alone. These results show that ADM-induced endothelium-dependent vasodilation could be converted to vasoconstriction in the presence of PAMP, probably through a NO-dependent pathway. There was no indication that cAMP was involved in the converting effect of PAMP on ADM vasodilator action.

Leukemia inhibitory factor is augmented in the heart in experimental heart failure

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that induces cardiac myocyte hypertrophy through the signal transducing molecule, glycoprotein 130. To date, localization of LIF in the heart and regulation of cardiac LIF expression in congestive heart failure (CHF) remain undefined. The present study investigates the potential activation of LIF expression in the failing canine heart that was produced by progressive rapid ventricular pacing. Immunohistochemistry for LIF revealed that LIF immunoreactivity was present in the atrial and ventricular myocytes of the normal heart and was markedly increased in the failing heart as compared to the normal heart. Northern blot analysis demonstrated that cardiac LIF mRNA was increased in both atrium and ventricle in CHF as compared to the normal heart (P<0.01). Linear regression analysis revealed a positive correlation between atrial LIF mRNA and atrial pressure (r=0.87, P<0.001 in right atrium and r=0.86, P<0.001 in left atrium). Positive correlations between left ventricular LIF mRNA and left ventricular dimensions (r=0.91, P<0.0001 in end-systolic diameter; r=0.86, P<0.001 in end-diastolic diameter), and an inverse correlation between left ventricular LIF mRNA and left ventricular ejection fraction (EF) were observed (r=-0.93, P<0.0001). There was a positive correlation between left ventricular LIF mRNA and left ventricular mass index (LVMI) (r=0.85, P<0.001). The present study demonstrates that cardiac LIF immunoreactivity and its gene expression are increased in a canine model of experimental CHF and suggests a potential role for LIF in the pathophysiology of CHF.

Immunohistological localization and possible functions of adrenomedullin

In this short review, we describe the distribution of adrenomedullin (AM)-immunoreactive cells in human tissues and their related biological properties, focusing on the blood coagulation and mucosal defense systems. AM is widely distributed in human tissues, especially in cardiovascular and endocrine tissues. Within vessels, AM has been immunohistochemically detected in vascular smooth muscle cells (SMCs) and endothelial cells (ECs). In atherosclerotic lesions, the peptide is present not only in these cells, but also in macrophages, and the most intense AM immunoreactivity is detected in macrophages located in shoulder lesions of atheromatous plaque, which are considered to be rupture-prone regions. AM inhibits tissue factor production, and augments the production and release of tissue factor pathway inhibitor from aortic ECs. AM also induces the release of antithrombin and urokinase-type plasminogen activator from ECs. Taken together, these antithrombotic properties of the peptide are expected to play an important role in the maintenance of blood circulation. Furthermore, AM immunoreactivity is observed in mucosal and glandular epithelia of the gastrointestinal, respiratory and reproductive systems. AM and the proadrenomedullin N-terminal 20 peptide (PAMP) show strong antibacterial activity against Escherichia coli. In addition, AM is also present in the auditory system. These lines of evidence suggest that AM and its related peptides not only play a role in vasodilatation, but also exhibit multiple biological activities in mammals.

Direct measurement of glycine-extended adrenomedullin in plasma and tissue using an ultrasensitive immune complex transfer enzyme immunoassay in rats

The mature form of the vasodilator peptide adrenomedullin (AM-m) is synthesized from a glycine-extended precursor (AM-Gly) by enzymatic amidation. We have developed a highly sensitive enzyme immunoassay (Immune Complex Transfer Enzyme Immunoassay; ICTEIA) that enables us to measure levels of AM-Gly in plasma and tissue directly. The detection limit of this assay is 1 amol/assay, and the intra- and inter-assay precision are 4.5-14.1% and 9.9-20.5%, respectively. Dilution curves for plasma samples showed good linearity, and the analytical recovery was 107-116.6%. Using ICTEIA, we determined that the plasma concentration of immunoreactive AM-Gly is substantially higher than that of AM-m (5.22 +/- 2.56 vs. 1.21 +/- 0.79 fmol/ml). In contrast, levels of AM-Gly were much lower than those of AM-m in the lung, heart, kidney, adrenal gland and liver. We also evaluated AM-Gly and AM-m levels in rats in a morbid state induced by intraperitoneal administration of lipopolysaccharide (LPS). In most tissues, levels of AM-m and AM-Gly were both increased by LPS; however, AM-Gly/AM-m ratios were not significantly affected, which suggests that AM-Gly is rapidly converted to AM-m in tissue.

Endothelial responses of the aorta from adrenomedullin transgenic mice and knockout mice

Adrenomedullin (AM) is a potent vascular wall-derived vasorelaxing peptide which induces the release of nitric oxide (NO). To explore the role of endogenous AM in vascular function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists [AM (22-52), and calcitonin gene-related peptide (CGRP) (8-37)] on the isometric tension of aortic rings isolated from AM transgenic (TG) and knockout (KO) mice and wild type littermates (WT). ACh and AM caused a dose-dependent reduction of the isometric tension of aortic rings, but the degree of vasodilatation was smaller in TG than in KO or WT (% delta tension [10(-6) mol/l ACh]: KO -69 +/- 10%, WT -39 +/- 8%, TG -29 +/- 1%, p < 0.01). On the other hand, N(G)-nitro-L-arginine methyl ester, an NO synthase inhibitor, induced greater vasoconstriction in TG (% delta tension 10(-5)mol/l: KO +78 +/- 16%, WT +99 +/- 27%, TG +184 +/- 20%, p < 0.01), whereas E-4021, a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase inhibitor, caused greater vasodilation in TG mice. Both AM antagonists increased tension in TG to a greater extent than in KO or WT mice (% delta tension [10(-6) mol/l CGRP (8-37)]: KO +24 +/- 5%, WT +51 +/- 6%, TG +75 +/- 7%, p < 0.01). Endothelial denudation of the aorta diminished the vasoconstriction caused by the AM antagonists. In conclusion, the amounts of AM expressed in the aortic endothelium influenced baseline NO release. AM antagonists increased vascular tone in WT as well as in TG, suggesting that endogenous AM plays a physiological role in the regulation of aortic tone.

Cardioprotective effect of adrenomedullin in heart failure

Many neurohumoral factors participate in the pathophysiology of heart failure, and adrenomedullin (AM) may be involved in their derangement. This work reviews the accumulating evidence in support of a compensatory role of AM in heart failure, and describes the possible mechanisms of this role. It has been established that plasma AM levels are increased in patients with heart failure in proportion to the severity of the disease. Furthermore, recent studies suggest that plasma AM level is an independent prognostic indicator of heart failure. Thus, AM may be not only a biochemical marker for evaluating the severity of heart failure, but also a prognostic indicator of this syndrome. In patients with heart failure, AM production is increased not only in the plasma, but also in the heart. AM secretion from the failing human heart is also increased, but this increase is small and responds slowly to the stimulus. This phenomenon may be explained by the fact that AM is secreted via a constitutive pathway and that AM is an autocrine and/or a paracrine factor in the heart. An experiment using cultured myocytes suggested that cytokines and mechanical stress are important stimuli for AM production in the heart. Regarding the action of AM in the heart, recent studies have suggested that AM exerts an inotropic action both in vitro and in vivo. AM also attenuates cardiac hypertrophy in myocytes and inhibits proliferation and collagen production in cardiac fibroblasts. These results suggest that AM may be an antifibrotic, antihypertrophic, and positive inotropic factor in the failing and hypertrophied heart. Because AM has many cardiorenal actions, AM administration may be useful for the treatment of heart failure. Indeed, acute administration of AM has been shown to improve the hemodynamics, renal function, and hormonal parameters in patients with heart failure. Moreover, recent studies have shown that AM gene therapy or long-term AM infusion significantly improved cardiac hypertrophy and fibrosis, and prolonged the survival time in an animal model of hypertension and heart failure. In conclusion, these findings suggest that AM plays a compensatory role in the pathophysiology of heart failure and that administration of AM may be a new and promising approach for the treatment of patients with this syndrome.

Adrenomedullin promotes proliferation and migration of cultured endothelial cells

Adrenomedullin (AM) is a vasoactive hormone which exerts its action through cyclic adenosine monophosphate(cAMP) /cAMP-dependent protein kinase (PKA) cascade and intracellular Ca2+ mobilization. Recently, evidence has accumulated that AM plays a critical role in the regulation of vascular tone, remodeling and morphogenesis. And although numerous reports have examined the action of AM on cultured vascular cells, the results have not been consistent and have depended on the experimental conditions used. Accordingly, the purpose of this study was to clarify the effect of AM on the proliferation and migration of cultured endothelial cells. Our results revealed that AM promoted the growth and migration of endothelial cells (ECs). AM significantly promoted the proliferation of human umbilical vein endothelial cells (HUVECs) (56.0 +/- 8.7% over the controls at 10(-9) mol/l) and this stimulative effect was inhibited by two AM antagonists, AM(22-52) and calcitonin gene-related peptide (CGRP) (8-37). The number of HUVECs migrated to the lower surface of the transwell apparatus was also increased dose-dependently in the AM group (30.4 +/- 4.2% over the controls at 10(-7) mol/l), and this increase was suppressed by the two AM antagonists and by two PKA antagonists, adenosine 3'5'-cyclic monophosphorothioate Rp-isomer and myristoylated protein kinase A inhibitor amide 14-22. The promoting action of AM on endothelial migration was also suppressed by LY294002, an inhibitor for phosphatidylinositol 3-kinase, but not by N(G)-nitro-L-arginine-methyl ester (L-NAME), an antagonist for nitric oxide synthase (NOS). These results indicate that AM promotes proliferation and migration of ECs via a cAMP/PKA dependent pathway and lend support to the idea that AM exerts beneficial effects on vascular regeneration and might be used as a novel therapeutic strategy for patients with vascular disease.

Adrenomedullin in heart failure

Patients with heart failure have frequently been reported to show elevated levels of plasma adrenomedullin. These levels generally correlate with severity of hemodynamic dysfunction and also with neurohormonal indices which are activated according to the severity of heart failure. Furthermore, adrenomedullin gene expression in the heart and kidney is increased in experimental and clinical heart failure. A small number of studies have examined the responses to infusion of adrenomedullin in experimental and clinical heart failure. These studies have generally shown that infusion of adrenomedullin has beneficial hemodynamic effects and promotes maintenance or improvement in renal function, although most of these trials were of short duration. The available data suggest that adrenomedullin in the heart, kidney and plasma is increased in heart failure, possibly to counter the activation or actions of vasoconstricting and sodium-retaining hormone systems. An improved understanding of the role of adrenomedullin in heart failure might lead to the development of therapeutic agents acting through adrenomedullin receptors.

Role of adrenomedullin in congenital heart disease associated with pulmonary hypertension

The changes of adrenomedullin (ADM), endothelin-1 (ET-1) and nitric oxide (NO) levels before and after operation in congenital heart disease (CHD) associated with pulmonary hypertension (PH) were observed in order to investigate their role in CHD with PH and their clinical significance. The CHD patients were divided into 3 groups according to pulmonary artery systolic pressure (PASP): Non-PH group: PASP < or = 30 mmHg (n = 11); mild-PH group: PASP 31-49 mmHg (n = 10); moderate or severe-PH group: PASP > or = 50 mmHg (n = 12). The control group consisted of 15 health children. Plasma ADM, ET-1 and NO levels were determined by radioimmunoassay and colorimetry methods. The correlation between ADM and ET-1, NO, PASP was analyzed. The changes in plasma ADM, ET-1 and plasma NO on the 7th day after operation among the groups were compared. The results showed that plasma ADM levels in non-PH group were significantly higher than that in control group (P < 0.05), but there was no significant difference in ET-1 and NO levels between the two groups (P > 0.05). ADM and ET-1 levels in mild-PH group were significantly elevated as compared with those in non-PH group (both P < 0.05), but NO levels were decreased (P < 0.05). ADM and ET-1 levels in moderate or severe-PH groups were increased as compared with those in mild-PH group (both P < 0.01), but NO level significantly declined (P < 0.05). On the 7th day after operation, plasma ADM and ET-1 levels in PH group were significantly decreased (P < 0.05, P < 0.01) as compared with those before operation, but there was no significant difference in NO levels (P > 0.05). But NO levels in non-PH group were significantly increased (P < 0.05). Plasma ADM levels in CHD were positively correlated with PASP and ET-1 (r = 0.77, P < 0.01; r = 0.82, P < 0.01), negatively correlated with NO (r = -0.56, P < 0.05). It was concluded that during the progression of PH in the cases of CHD, plasma ADM, ET-1 and NO might play an important role in the development of PH. The increased ADM may represent a compensatory mechanism. It can interact with NO and ET-1 to regulate pulmonary circulation in the pathophysiology of PH with CHD. ADM may be involved in the defence mechanism against further increase of pulmonary arterial pressure. ADM could be used as a reliable indicator of the severity of CHD associated PH.

Effects of adrenomedullin on human myocyte contractile function and beta-adrenergic response

BACKGROUND

Adrenomedullin has been demonstrated to cause systemic vasodilation, and increased plasma adrenomedullin levels have been observed in cardiovascular disease states such as heart failure. While adrenomedullin receptors have been localized to the myocardium, the effects of adrenomedullin on human myocyte contractility remained unknown.

METHODS AND RESULTS

Left ventricular myocytes were isolated from myocardial biopsies of patients (n = 16) undergoing elective coronary artery bypass surgery with normal left ventricular ejection fractions (51 +/- 1%). A total of 233 left ventricular myocytes were studied by videomicroscopy. Myocyte shortening velocity (microm/s) was measured at baseline and following the addition of either 3 nM, 30 nM, or 60 nM of adrenomedullin. The change in myocyte shortening velocity with increasing concentrations of adrenomedullin was computed. At all concentrations, adrenomedullin reduced myocyte shortening velocity from baseline values (P < 0.05). Next, the potential interaction of adrenomedullin with the beta-adrenergic receptor system was examined using 25 nM isoproterenol. The beta-adrenergic receptor-mediated increase in the myocyte shortening velocity was blunted with adrenomedullin (29 +/- 7 vs 63 +/- 13 microm/s, P < 0.05).

CONCLUSIONS

These unique findings demonstrate that adrenomedullin reduced contractility in isolated human left ventricular myocytes and exhibited a negative interaction with the beta-adrenergic receptor system. Past studies have shown that adrenomedullin induces nitric oxide synthesis and that nitric oxide can uncouple myocyte metabolism. Thus, while adrenomedullin causes systemic vasodilation, this peptide can also exert a negative contractile effect in human left ventricular myocytes.

Mature form of adrenomedullin is a useful marker to evaluate blood volume in hemodialysis patients

We investigated the pathophysiological significance of the mature form of adrenomedullin (AM) in hemodialysis (HD) patients. Thirty-nine HD patients were enrolled and divided into two groups: those undergoing ultrafiltration (UF) during an HD session, group I; and those not undergoing UF, group II. We measured mature AM, atrial natriuretic peptide (ANP), endothelin-1, nitric oxide, cyclic guanosine 3',5'-monophosphate, and catecholamine levels at 1-hour intervals during HD sessions. On-line optical measurement of hematocrit was used to estimate change in blood volume during HD. In group II, blood volume did not change significantly during HD, nor did plasma mature AM concentrations estimated at the beginning and end of the HD treatment (3.0 +/- 0.3 and 2.8 +/- 0.2 fmol/mL, respectively). However, blood volume decreased significantly in group I patients (-7.3% +/- 0.6%), as did plasma mature AM concentrations (from 4.4 +/- 0.3 to 3.1 +/- 0.3 fmol/mL; P < 0.01). In contrast to mature AM, plasma ANP concentrations declined in both groups (from 193 +/- 32 to 87 +/- 14 pg/mL in group I and 67 +/- 12 to 46 +/- 8 pg/mL in group II). We conclude that mature AM is a useful marker to evaluate circulating blood volume in HD patients. Circulating blood volume may regulate the conversion of AM from the inactive to the mature form.

Increased myocardial expression of RAMP1 and RAMP3 in rats with chronic heart failure

Calcitonin gene-related peptide (CGRP) and adrenomedullin (ADM) are potent vasodilators in humans and improved myocardial ischemia is observed after CGRP administration. Receptors for CGRP and ADM were already identified in heart. Receptor activity-modifying proteins (RAMPs) determine the ligand specificity of the calcitonin receptor-like receptor (CRLR); co-expression of RAMP1 and CRLR results in a CGRP receptor, whereas the association of RAMP2 or RAMP3 with CRLR gives an ADM receptor. As CGRP and ADM may play a beneficial role in heart failure, we investigated whether the CGRP and ADM receptors are upregulated in chronic heart failure. We have used semi-quantitative RT-PCR and Western-blot analysis to detect and quantify the mRNA and the protein of RAMP1 and RAMP3 in both atria and ventricles of failing hearts 6 months after aortic banding in rats. Our results showed for the first time an up-regulation of RAMP1 and RAMP3 mRNAs and proteins in this model of cardiac failure. No change was observed in mRNAs coding for CRLR, RAMP2, RDC1 (canine orphan receptor), and ADM. The present results suggested after congestive heart failure in adult rats, an up-regulation of the CGRP receptor (by an increase in RAMP1 that is associated with CRLR) in atria and ventricles and of ADM receptor (by increased RAMP3 expression that is associated with CRLR) in atria. These findings support a functional role for CGRP and ADM receptors to compensate the chronic heart failure in rats.

The adrenomedullin receptor acts as clearance receptor in pulmonary circulation

Adrenomedullin (AM) is a powerful pulmonary vasodilator with antimitogenic properties. We investigated the role of the AM receptor (AMR) and the calcitonin gene-related peptide type-1 receptor (CGRP1R) in regulating pulmonary vascular AM levels. The AMR antagonist hAM(22-52) (120 nmol/L) significantly elevated AM release compared with controls to 250% after 2 h in isolated rat lungs and to 830% after 4 h in pulmonary artery endothelial cells (PAEC). CGRP1R blockade had no effect. AMR blockade did not influence prepro-AM mRNA levels nor did inhibition of protein synthesis by cycloheximide (0.01 mg/mL) abolish the effect of the AMR antagonist. Radioligand-binding studies with PAEC membranes revealed a decrease by 44% of the AMR density in response to AMR antagonism. Altogether, the pulmonary vascular AMR represents not only a functionally active, but also a clearance receptor; its expression is constitutively stimulated by basal AM. This identifies a novel mechanism for controlling pulmonary AM levels.

Intravenous adrenomedullin in myocardial function and energy metabolism in patients after myocardial infarction

This study investigated the effects of adrenomedullin on left ventricular myocardial contraction and relaxation, coronary blood flow, and myocardial oxygen consumption in comparison with those of atrial natriuretic peptide (ANP). Fourteen patients who had had myocardial infarctions were randomly assigned to receive IV infusion of adrenomedullin (0.05 microg/kg/min) or ANP (0.05 microg/kg/min). Both adrenomedullin and ANP significantly decreased left ventricular systolic pressure (-17 mm Hg, -13 mm Hg, respectively, both p < 0.05). The increase in cardiac index by adrenomedullin (+31%) was significantly greater than that by ANP (+16%). Adrenomedullin significantly increased an index of myocardial contractility, Emax (2.5 +/- 0.3 mm Hg-3.7 +/- 0.3 mm Hg/ml, p < 0.05) and shortened an index of myocardial relaxation, Tau (52 +/- 5 ms-48 +/- 4 ms, p < 0.05). In contrast, ANP did not significantly alter either parameter. In addition, adrenomedullin, but not ANP, significantly increased coronary sinus blood flow (73 +/- 10 ml/min-86 +/- 10 ml/min, p < 0.05). Adrenomedullin did not increase myocardial oxygen consumption. Unlike ANP, IV administration of adrenomedullin enhanced left ventricular myocardial contraction and improved left ventricular relaxation without increasing myocardial oxygen consumption in patients who had had a myocardial infarction.

Regulation of adrenomedullin expression and release

Adrenomedullin (AM) was originally identified in the extracts of human pheochromocytoma tissue, but this peptide is now known to be synthesized and secreted from many kinds of cells in the body, including vascular smooth muscle cells, endothelial cells, fibroblasts, cardiac myocytes, epithelial cells, and cancer cells. In this review, we summarize AM-secreting and AM gene-expressing cells in addition to the regulation of secretion and gene expression of AM. Although the data are still limited to deduce the general features of AM gene expression, synthesis, and secretion, AM is assumed to be classified into the new class of biologically active peptides, which is mainly expressed and secreted from non-endocrine type cells by the stimulation with inflammation-related substances. It is also interesting that serious physiological conditions such as inflammation or hypoxia potently stimulate AM expression and release, suggesting its unique physiological function distinct from other known biologically active peptides.

Treatment of heart failure in patients with diabetes mellitus

Patients with diabetes mellitus have an increased morbidity and mortality from cardiovascular disease. Both coronary artery disease and congestive heart failure (CHF) are largely responsible for the increased cardiovascular adverse events in patients with diabetes. This review discusses the pathophysiology of CHF, the mechanisms of left ventricular (LV) dysfunction and the neurohormonal mechanisms involved in both LV dysfunction and CHF. Diabetes with and without hypertension is an important cause of LV dysfunction and CHF. Diabetes may be responsible for the metabolic and ultrastructural causes of LV dysfunction, while hypertension may be responsible for the marked fibrotic changes that are found. Experimental induction of diabetes in animals has shed light on the biochemical and ultrastructural changes seen. The role of insulin to reverse both metabolic and structural changes is reviewed both from experimental data and with the limited amount of clinical data available. The therapy of CHF in patients with diabetes is similar to that of patients without diabetes, with therapy directed toward the use of beta-blockers and angiotensin converting enzyme (ACE) inhibitors. As the morbidity and mortality are higher in patients with diabetes, several studies have pointed out the importance of this subgroup where the opportunity to make a significant clinical impact exists. A significant opportunity exists to reduce morbidity and mortality with beta-blockers and ACE inhibitors when ischaemia and CHF are both present. However, studies in patients diabetes have been limited to post hoc subgroup analyses and rarely as predefined subgroups. Clinical trials involving patients with diabetes with and without hypertension and LV dysfunction are clearly needed in the future to adequately address the needs of this high risk subgroup.

Gene expression of adrenomedullin in failing myocardium: comparison to atrial natriuretic peptide

The expression of adrenomedullin (AM) and atrial natriuretic factor (ANF) were investigated in the myocardium of a rat model of chronic ischemic heart failure (CHF) compared with sham-operated controls. In addition, human myocardium of patients with end-stage heart failure due to idiopathic dilated cardiomyopathy compared with myocardium of normal subjects (NF) was studied. In CHF, similar AM levels but increased ANF expression were observed in left ventricular myocardium, as assessed by semiquantitative PCR. Functional experiments with freshly excised papillary muscles showed no influence of AM on myocardial contractility. In NF human myocardium, the expression of AM mRNA was threefold higher in atrial compared with ventricular tissue. In analogy, ANF mRNA was increased by approximately 15-fold in atrial tissue. In dilated cardiomyopathy, the expression of AM was significantly increased in right and left ventricles compared with NF. In parallel, ventricular ANF expression was enhanced.

Increased pericardial fluid concentrations of the mature form of adrenomedullin in patients with cardiac remodelling

BACKGROUND

There is evidence that adrenomedullin has autocrine or paracrine activities that oppose cardiac remodelling. However, it remains unclear whether it exerts those local functions in heart failure patients.

OBJECTIVE

To investigate the relation between plasma and pericardial fluid concentrations of adrenomedullin and left ventricular haemodynamic variables.

DESIGN

Samples of plasma and pericardial fluid were obtained from 50 patients undergoing cardiac surgery. They were classified into two groups: group N (n = 27) with a left ventricular end diastolic volume index (LVEDVI) < or = 90 ml/m(2); and group R (n = 23) with LVEDVI > 90 ml/m(2). Plasma and pericardial fluid concentrations of total adrenomedullin (tAM) and mature adrenomedullin (mAM) were measured and related to the preoperative haemodynamic variables.

RESULTS

Pericardial fluid concentrations of mAM were much higher than the plasma concentration in both group N and group R (mean (SEM), 10.6 (1.7) v 3.3 (0.2) fmol/ml, p = 0.0001; and 21.2 (2.8) v 3.9 (0.3) fmol/ml, p < 0.0001, respectively). The ratio mAM/tAM in pericardial fluid was significantly higher than in plasma (0.56 (0.02) v 0.28 (0.02), p < 0.0001). Pericardial fluid concentrations of mAM, but not plasma concentrations, were significantly correlated with LVEDVI, left ventricular end systolic volume index, left ventricular ejection fraction, and left ventricular mass index (r = 0.60, 0.63, -0.54, and 0.47, respectively).

CONCLUSIONS

Raised pericardial fluid concentrations of mAM may reflect the actions of adrenomedullin as a local mediator against cardiac remodelling in patients with left ventricular dysfunction.

Alterations of endothelium-dependent and -independent regulation of coronary blood flow during heart failure

Conflicting data concerning the changes in basal coronary blood flow and nitric oxide (NO)-releasing capacity in chronic heart failure may be due to different phases or duration of heart failure. To investigate endothelium-dependent and -independent regulation of coronary blood flow in different phases of heart failure, coronary pressure-flow relationships during long diastole were obtained before and after rapid pacing of 3 and 5 wk at 240 beats/min in 12 or 6 dogs. Neither basal coronary blood flow nor the slope of coronary pressure-flow relationships changed; however, zero-flow pressure increased slightly after rapid pacing. Intracoronary injection of N(G)-nitro-L-arginine methyl ester decreased coronary blood flow at a perfusion pressure of 50 mmHg by approximately 20% at baseline, 55% after 3 wk of rapid pacing, and 20% after 5 wk of rapid pacing. Acetylcholine-induced increase in coronary blood flow was maintained for 3 wk but was finally attenuated after 5 wk of rapid pacing. In contrast, the coronary blood flow response to adenosine gradually decreased with time. These results suggest that basal coronary blood flow is maintained until the late stage of heart failure, presumably by an increases in NO production during the early stage and then by other vasodilatory substances during the late stage, and that endothelium-dependent vasodilation via exogenously administered acetylcholine in resistance vessels is not necessarily impaired in the early stage despite the gradual reduction of endothelium-independent vasodilation via adenosine in chronic heart failure.

Effects of omapatrilat on pharmacodynamic biomarkers of neutral endopeptidase and Angiotensin-converting enzyme activity in humans

Vasopeptidase inhibition is a new concept in blood pressure management. A single molecule simultaneously inhibits two enzymes that regulate cardiovascular function: neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE)[1]. Development of vasopeptidase inhibitors stemmed from the need for new and more efficacious antihypertensive agents that not only reduce blood pressure but also treat hypertension as part of a larger syndrome involving endothelial dysfunction [2]. By inhibiting NEP and ACE, vasopeptidase inhibitors enhance the natriuretic peptide and kallikrein-kinin systems and inhibit the renin-angiotensin-aldosterone system. This article outlines the pharmacodynamic effects of the vasopeptidase inhibitor omapatrilat on biomarkers of NEP and ACE activity in humans.

Flow-induced pressure differentially regulates endothelin-1, urotensin II, adrenomedullin, and relaxin in pulmonary vascular endothelium

We hypothesized that increased pulmonary vascular pressure--one of the characteristics of congestive heart failure--directly regulates pulmonary endothelial vasoconstrictors (endothelin-1, urotensin II) and vasodilators (adrenomedullin, relaxin). To this end, we subjected pulmonary artery endothelial cells in a novel flow-chamber model to different shear stresses (17, 29, and 46 dyn/cm(2)) at low and elevated levels of downstream pressure (10 and 30 mm Hg). Application of elevated pressure over 16 h increased gene expression and peptide secretion of endothelin-1 at all shear levels, whereas secretion of adrenomedullin rose via decreased expression of its clearance receptor. In contrast, preprourotensin II mRNA and urotensin II peptide decreased in response to elevated pressure, and relaxin remained unaffected. This is the first study to identify pressure as key regulator of mediator synthesis by pulmonary vascular endothelium. Pressure-induced mediator regulation may represent an early event in the development of secondary pulmonary hypertension.