Immunohistochemical localization of adrenomedullin in canine heart and aorta

Adrenomedullin: Continuing to explore cardioprotection

Adrenomedullin (AM), a peptide isolated from an extract of human pheochromocytoma, comprises 52 amino acids with an intramolecular disulfide bond and amidation at the carboxy-terminus. AM is present in various tissues and organs in rodents and humans, including the heart. The peptide concentration increases with cardiac hypertrophy, acute myocardial infarction, and overt heart failure in the plasma and the myocardium. The principal function of AM in the cardiovascular system is the regulation of the vascular tone by vasodilation and natriuresis via cyclic adenosine monophosphate-dependent or -independent mechanism. In addition, AM may possess unique properties that inhibit aldosterone secretion, oxidative stress, apoptosis, and stimulation of angiogenesis, resulting in the protection of the structure and function of the heart. The AM receptor comprises a complex between calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein (RAMP) 2 or 3, and the AM-CLR/RAMP2 system is essential for heart development during embryogenesis. Small-scale clinical trials have proven the efficacy and safety of recombinant AM peptide therapy for heart failure. Gene delivery and a modified AM peptide that prolongs the half-life of the native peptide could be an innovative method to improve the efficacy and benefit of AM in clinical settings. In this review, we focus on the pathophysiological roles of AM and its receptor system in the heart and describe the advances in AM and proAM-derived peptides as diagnostic biomarkers as well as the therapeutic application of AM and modified AM for cardioprotection.

The Role of Adrenomedullin in Cardiovascular Response to Exercise - A Review

Adrenomedullin (ADM), the product of the vascular endothelial and smooth muscle cells, and cardiomyocytes, is considered to be a local factor controlling vascular tone, cardiac contractility and renal sodium excretion. The aim of this article was to review the existing data on the effect of different types of exercise on plasma ADM concentration in healthy men. The results of studies on the effect of dynamic exercise on the plasma ADM are contradictory. Some authors reported an increase in plasma ADM, while others showed a slight decrease or did not observe any changes. The inverse relationship between plasma ADM and mean blood pressure observed during maximal exercise support the concept that ADM might blunt the exercise-induced systemic blood pressure increase. Positive relationships between increases in plasma ADM and those in noradrenaline, atrial natriuretic peptide (ANP) or interleukin-6 observed during prolonged exercise suggest that the sympathetic nervous system and cytokine induction may be involved in ADM release. Increased secretion of ADM and ANP during this type of exercise may be a compensatory mechanism attenuating elevation of blood pressure and preventing deterioration of cardiac function. Studies performed during static exercise have showed an increase in plasma ADM only in older healthy men. Positive correlations between increases in plasma ADM and those in noradrenaline and endothelin-1 may indicate the interaction of these hormones in shaping the cardiovascular response to static exercise. Inverse relationships between exercise-induced changes in plasma ADM and those in cardiovascular indices may be at least partly associated with inotropic action of ADM on the heart. Interactions of ADM with vasoactive peptides, catecholamines and hemodynamic factors demonstrate the potential involvement of this peptide in the regulation of blood pressure and myocardial contractility during exercise.

Adrenomedullin is expressed during rodent dental tissue development and promotes cell growth and mineralization

BACKGROUND INFORMATION

ADM (adrenomedullin) has pleiotropic effects, including regulation of inflammation, infection, angiogenesis, mineralized-tissue formation and development. Recently, we demonstrated up-regulation of the ADM transcript in diseased pulpal tissue while the protein is sequestered within the dentine extracellular matrix during dentinogenesis. The present study aimed to characterize ADM localization during rodent dental tissue development and determine its potential effects on dental cells. Finally, we sought to profile ADM transcript levels in adult organs and tissues to compare its expression in teeth relative to other tissues.

RESULTS

Immunohistochemical analysis of developmental rat oral tissues indicated that, at E16 (embryonic day 16), ADM was present in dental epithelium and, by E18, ADM localized to the dental papilla and inner and outer dental epithelia. By E20, ADM was detected in secretory odontoblasts and ameloblasts and exhibited a similar expression profile to that of the key dentinogenesis signalling molecule, TGF-beta1 (transforming growth factor-beta1). Cell growth analysis in the dental MDPC-23, OD-21 and control 3T3 cell lines exposed to ADM (range 10(-15)-10(-7) M) together with EDTA-extracted DMPs (dentine matrix proteins) (range 0.00001-1000 mg/ml) containing comparable concentrations of ADM demonstrated that ADM stimulated a biphasic response in dental cell growth, comparable with that of DMPs, with peak stimulation observed at approximately 10(-11) M. For mineralization analysis, cell lines were exposed to combinations of 50 microg/ml ascorbic acid, 10 mM beta-G (beta-glycerophosphate), 10(-8) M DEX (dexamethasone) and ADM (range 10(-15)-10(-7) M). The results demonstrated that ADM could substitute for DEX to stimulate mineralization. Postnatally, multiple tissue expression profiling indicated abundant ADM levels in tongue and pulpal tissues.

CONCLUSIONS

During oral and dental tissue development ADM initially localizes to epithelial tissue, whereas during later stages it is present in mineralized secreting cells, including odontoblasts. ADM may regulate proliferation and mineralization processes during development, whereas, in adulthood, it may be important for maintaining dental tissue homoeostasis.

Adrenomedullin expression in coronary circulation after stent implantation as a prognostic factor for restenosis

The authors determined the changes in adrenomedullin (AM) expression in the coronary circulation of patients with ischemic heart disease who underwent coronary stent implantation. Blood samples were drawn from the coronary sinus before, immediately after and four hours after coronary stent implantation, and plasma levels of AM were measured. AM levels in the coronary sinus blood were significantly increased four hours after stent implantation. On the other hand, in the femoral arterial blood, no significant changes in AM levels were observed. A significant positive correlation was found between AM level in the coronary sinus blood four hours after stent implantation and late loss index six months after the procedure. These results suggest that inflammation after coronary stent implantation induces AM expression, which might play an important role in restenosis after stenting.

Type 2 diabetes and cardiovascular disease: getting to the fat of the matterThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigators' Forum

The increasing national prevalence of obesity is a major public health concern and a substantial burden on the health care resources of Canada. In addition to the direct health impact of obesity, this condition is a well-established risk factor for the development of various prevalent comorbidities including type 2 diabetes, hypertension, and cardiovascular disease. Historically, adipose tissue has been regarded primarily as an organ for energy storage. However, the discovery of leptin in the mid 1990’s revolutionized our understanding of this tissue and has focused attention on the endocrine function of adipose tissue as a source of secreted bioactive peptides. These compounds, collectively termed adipokines, regulate a number of biological functions including appetite and energy balance, insulin sensitivity, lipid metabolism, blood pressure, and inflammation. The physiological importance of adipokines has led to the hypothesis that changes in the synthesis and secretion of these compounds in the obese are a causative factor contributing to the development of obesity and obesity-related diseases in these individuals. Following from this it has been proposed that pharmacologic manipulation of adipokine levels may provide novel effective therapeutic strategies to treat and prevent obesity, type 2 diabetes, and cardiovascular disease.

Murine atrial HL-1 cells express highly active peptidylglycine alpha-amidating enzyme

Peptidylglycine-alpha-hydroxylating monooxygenase (PHM; EC 1.14.17.3) catalyzes the rate limiting step in peptide alpha-amidation, a posttranslational modification that is essential for receptor recognition and signal transduction. Secretory granules of the cardiac atrium contain the highest natural concentration of PHM and clearly demonstrate regulation of PHM expression and activity. The HL-1 atrial myocyte cell line faithfully maintains the differentiated phenotype of native atrial cells and thus provides an in vitro model system for investigating the mechanisms that regulate PHM. We observed that the specific activity of PHM expressed in HL-1 cells is five times higher than that found in rat atrium. The increased activity of HL-1 cell PHM was not reflected by a difference in Km for peptide substrate, change in copper optimum, altered sensitivity to inactivation by suicide inhibitor or variance in response to limited proteolysis by trypsin. Additionally, mixing experiments indicated that the increased activity in HL-1 cells versus rat atrium was not due to a diffusible factor. Based upon these findings we propose that the increased Vmax of HL-1 cell PHM results from a structural or conformational difference that involves either differential posttranslational modification and/or a high affinity chaperone that serves to regulate enzymatic activity by protein-protein interaction. The mechanism involved may participate in physiologic regulation of PHM.

Adrenomedullin: a new target for the design of small molecule modulators with promising pharmacological activities

Adrenomedullin (AM) is a 52-amino acid peptide with a pluripotential activity. AM is expressed in many tissues throughout the body, and plays a critical role in several diseases such as cancer, diabetes, cardiovascular and renal disorders, among others. While AM is a protective agent against cardiovascular disorders, it behaves as a stimulating factor in other pathologies such as cancer and diabetes. Therefore, AM is a new and promising target for the development of molecules which, through their ability to regulate AM levels, could be used in the treatment of these pathologies.

Genomic expression patterns of cardiac tissues from dogs with dilated cardiomyopathy

OBJECTIVE

To evaluate global genome expression patterns of left ventricular tissues from dogs with dilated cardiomyopathy (DCM).

SAMPLE POPULATION

Tissues obtained from the left ventricle of 2 Doberman Pinschers with end-stage DCM and 5 healthy control dogs.

PROCEDURE

Transcriptional activities of 23,851 canine DNA sequences were determined by use of an oligonucleotide microarray. Genome expression patterns of DCM tissue were evaluated by measuring the relative amount of complementary RNA hybridization to the microarray probes and comparing it with gene expression for tissues from 5 healthy control dogs.

RESULTS

478 transcripts were differentially expressed (> or = 2.5-fold change). In DCM tissue, expression of 173 transcripts was upregulated and expression of 305 transcripts was downregulated, compared with expression for control tissues. Of the 478 transcripts, 167 genes could be specifically identified. These genes were grouped into 1 of 8 categories on the basis of their primary physiologic function. Grouping revealed that pathways involving cellular energy production, signaling and communication, and cell structure were generally downregulated, whereas pathways involving cellular defense and stress responses were upregulated. Many previously unreported genes that may contribute to the pathophysiologic aspects of heart disease were identified.

CONCLUSIONS AND CLINICAL RELEVANCE

Evaluation of global expression patterns provides a molecular portrait of heart failure, yields insights into the pathophysiologic aspects of DCM, and identifies intriguing genes and pathways for further study.

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.

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.

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.

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.

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.

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.

Regulation of cardiac adrenomedullin in heart failure

Adrenomedullin (ADM), a potent natriuretic and vasorelaxing peptide with inotropic properties, is elevated in plasma in human and experimental congestive heart failure (CHF). Recent studies suggest that angiotensin II stimulates ADM production and secretion from cardiac myocytes and fibroblasts. In the present study, we investigated cardiac ADM in experimental CHF, and tested the hypothesis that angiotensin converting enzyme (ACE) inhibition modulates cardiac ADM in CHF. Cardiac tissue ADM immunoreactivity and gene expression were assessed by radioimmunoassay, immunohistochemistry, in situ hybridization and Northern blot analysis in normal and CHF dogs in the presence and absence of ACE inhibition. Experimental CHF was produced by progressive rapid ventricular pacing and characterized by increased ventricular ADM concentrations as well as increased ventricular ADM gene expression. ACE inhibition abolished the increases in ventricular ADM concentrations and ventricular ADM gene expression in CHF. Ventricular ADM gene expression was localized to ventricular myocytes and correlated with left ventricular mass index, suggesting that ventricular ADM is a marker for ventricular hypertrophy. In contrast, atrial ADM concentrations and gene expression did not change in CHF with or without ACE inhibition. Increased plasma ADM concentrations in CHF were also abolished with ACE inhibition. The present study demonstrates that circulating and ventricular ADM are activated in pacing-induced experimental CHF and that ACE inhibition reverses ventricular ADM activation in CHF. This study also indicates that cardiac ADM gene expression is differently regulated between atrium and ventricle in CHF.

Attenuated natriuretic response to adrenomedullin in experimental heart failure

BACKGROUND

The recently discovered vasodilating and positive inotropic peptide, adrenomedullin (ADM), has strong natriuretic actions. ADM-induced natriuresis is caused by an increase in glomerular filtration rate and a decrease in distal tubular sodium reabsorption. Although ADM is activated in human and experimental heart failure, the role of ADM in the kidney in heart failure remains undefined.

METHODS AND RESULTS

The present study was performed to determine the renal hemodynamic and urinary excretory actions of exogenously administered ADM in a canine model of acute heart failure produced by rapid ventricular pacing. Experimental acute heart failure was characterized by a decrease in cardiac output and an increase in pulmonary capillary wedge pressure with an increase in plasma ADM concentration. Intrarenal infusion of ADM (1 and 25 ng/kg/min) induced an increase in urinary sodium excretion in the normal control dogs (change in urinary sodium excretion [Delta UNaV], +94.5 microEq/min during 1 ng/kg/min ADM infusion and +128.1 microEq/min during 25 ng/kg/min ADM infusion). In the acute heart failure dogs, intrarenal ADM infusion resulted in an attenuated increase in urinary sodium excretion (Delta UNaV, +44.8 microEq/min during 1 ng/kg/min ADM infusion and +51.8 microEq/min during 25 ng/kg/min ADM infusion). Both glomerular and tubular actions of ADM were attenuated in the acute heart failure group compared with responses in the normal control group.

CONCLUSION

The present study shows that the renal natriuretic responses to ADM are markedly attenuated in experimental acute heart failure. This study provides insight into humoral mechanisms that may promote sodium retention in heart failure via a renal hyporesponsiveness to natriuretic actions of ADM.

Immunohistochemical detection of calcitonin gene-related peptide receptor (CGRPR)-1 in the endothelium of human coronary artery and bronchial blood vessels

The potent vasodilatory peptide, calcitonin gene-related peptide (CGRP) is present in the innervation of vascular tissue. The actions of CGRP occur via a receptor, CGRP receptor(R)-1, which is also a target for the cardioprotective peptide adrenomedullin. The human version of the pharmacologically-defined CGRPR-1 has been cloned but its distribution and cellular location is unknown. A rabbit antibody was generated to a synthetic peptide that corresponds to the C-terminus of human CGRPR-1 Immunochemical analysis of the human cell-line, SK-N-MC, which exhibits functional expression of the CGRPR-1 confirmed the antibody's specificity. The antiserum revealed specific staining in the endothelium of human coronary arteries. The vascular smooth muscle and ventricular myocardium were not immunoreactive. In bronchial blood vessels CGRPR-1-immunoreactivity was detected in the endothelium of the venules and not in the arterioles, which is particularly relevant for elucidating the putative role of CGRP in inflammation in this tissue.

Endothelin-1-Independent and Angiotensin II-Independent Induction of Adrenomedullin Gene Expression

-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 precise time course of induction of atrial and ventricular AM gene expression during pressure overload and to study whether endothelin-1 or angiotensin II plays a causal role in the activation of cardiac AM gene expression. The pressure overload was produced by arginine-vasopressin (AVP, 0.05 µg/kg per minute IV) infusion for 15 minutes, 30 minutes, 1 hour, 2 hours, or 4 hours in conscious rats. A significant increase in left ventricular AM mRNA levels was seen after 2 hours of pressure overload in the left ventricle and after 30 minutes in the left atrium. The left atrial immunoreactive AM (ir-AM) levels decreased significantly after 2 hours of pressure overload. Plasma ir-AM levels increased slightly in response to 4 hours of AVP infusion. Bolus injections of bosentan (mixed ET(A)/ET(B) receptor antagonist, 10 mg/kg IV), losartan (AT(1) receptor antagonist, 10 mg/kg IV), and their combination had no effect on the increase of cardiac AM mRNA and ir-AM levels produced by 2 hours of pressure overload. In addition, losartan, bosentan, and their combination did not affect plasma ir-AM levels in the vehicle-infused and AVP-infused animals. The present study indicates that cardiac AM gene expression is rapidly upregulated in response to pressure. The induction of ventricular and atrial AM gene expression by pressure overload is angiotensin II-independent and endothelin-1-independent.

Expression of proadrenomedullin derived peptides in the mammalian pituitary: co-localization of follicle stimulating hormone and proadrenomedullin N-20 terminal peptide-like peptide in the same secretory granules of the gonadotropes

Expression of proadrenomedullin-derived peptides in the rat, cow and human pituitary was studied by a variety of techniques. Immunocytochemical detection showed a widespread expression of adrenomedullin peptide in the adenohypophysis and the neural lobe, with low expression in the intermediate pituitary. Proadrenomedullin N-20 terminal peptide (PAMP)-immunoreactivity was also present in the anterior pituitary but showed a more marked heterogeneous distribution, with cells going from very strong to negative immunostaining. Lower levels of PAMP were found in the neural lobe. Interestingly, the distribution of adrenomedullin and PAMP immunoreactivity in the anterior pituitary did not completely overlap. In the present study, we concentrated our efforts to determine which cell type of the adenohypophysis expresses PAMP. Paraffin and semithin serial sections immunostained for PAMP and the classical pituitary hormones revealed that a subpopulation of the gonadotropes expresses high levels of PAMP-immunoreactive material. Ultrastructural analysis clearly showed PAMP-immunoreactivity in the follicle stimulating hormone (FSH)-containing large secretory granules of the gonadotropes, suggesting simultaneous secretion of PAMP and FSH by this cell type. Three mouse adenohypophysis-derived cell lines (AtT20, GH3, and alphaT3-1 derived from corticotropes, lacto/somatotropes and gonadotropes, respectively) were also analysed and showed expression of both proadrenomedullin-derived peptides and their mRNA. Functional studies in these three cell lines showed that neither adrenomedullin nor PAMP was able to stimulate cAMP production in our experimental conditions. Taken together, our results support that proadrenomedullin derived peptides are expressed in the pituitary in cell-specific and not overlapping patterns, that could be explained by differences in postranslational processing. Our data showing costorage of PAMP and FSH in the same secretory granules open a way by which PAMP could be involved in the control of reproductive physiology in a coordinated manner with FSH.

Positive inotropy mediated via CGRP receptors in isolated human myocardial trabeculae

Isometric contractile force were studied on isolated human myocardial trabeculae that were paced at 1.0 Hz in tissue baths. Alpha calcitonin gene-related peptide (alpha-CGRP) had a potent positive inotropic effect in most trabeculae from both the right atrium and left ventricle, and this effect was partially antagonized by the CGRP(1) receptor antagonist alpha-CGRP-(8-37) (10(-6) M). Amylin and the CGRP(2) receptor agonist [Cys(acetylmethoxy)(2, 7)]CGRP had a positive inotropic effect in some trabeculae, whereas adrenomedullin had no inotropic effect. Using reverse transcriptase-polymerase chain reaction (PCR) mRNAs encoding the human calcitonin receptor-like receptor and the receptor associated modifying proteins (RAMPs) RAMP1, RAMP2, and RAMP3 were detected in human myocardial trabeculae from both the right atrium and left ventricle. In conclusion, functional CGRP(1) and CGRP(2) receptors may mediate a positive inotropic effect at both the atrial and ventricular level of the human heart. mRNAs for calcitonin receptor-like receptor and specific RAMPs further support the presence of CGRP receptors.

Adrenomedullin: potential in physiology and pathophysiology

Adrenomedullin (ADM), a 52-amino acid ringed-structure peptide with C-terminal amidation, was originally isolated from human pheochromocytoma. ADM mediates vasodilatory and natriuretic properties through the second messenger cyclic adenosine 3',5'-monophosphate (cAMP), nitric oxide and the renal prostaglandin system. ADM immunoreactivity and its gene are widely distributed in cardiovascular, pulmonary, renal, gastrointestinal, cerebral and endocrine tissues. ADM is also synthesized and secreted from vascular endothelial and smooth muscle cells. When injected intravenously, ADM increases flow rates predominantly in organs in which the ADM gene is highly expressed, suggesting that ADM acts as a local autocrine and/or paracrine vasoactive hormone. In addition, ADM is a circulating hormone and its plasma concentration is increased in various cardiorenal diseases such as hypertension, chronic renal failure and congestive heart failure. Current evidence suggests that ADM plays an important role in fluid and electrolyte homeostasis and cardiorenal regulation, however further investigations are required to address the importance of ADM under various physiological and pathophysiological conditions.

Positive inotropy of calcitonin gene-related peptide and amylin on porcine isolated myocardium

Isolated porcine myocardial trabeculae from right atria and left ventricles were paced at 1.5 Hz in tissue baths, and changes in isometric contractile force upon exposure to agonist were studied. Alpha calcitonin gene-related peptide (alpha-CGRP) increased contractile force in nearly half of the trabeculae, whereas the selective CGRP(2) receptor agonist [Cys(acetylmethoxy)(2,7)]-CGRP had effect in only a few. Preincubation with the CGRP(1) receptor antagonist alpha-CGRP-(8-37) (10(-6) M) almost completely blocked positive inotropic responses to alpha-CGRP. Amylin had weak positive inotropic effects in some atrial, but not in ventricular trabeculae. Adrenomedullin did not affect contractility in either atrial or ventricular trabeculae. In conclusion, these results suggest that alpha-CGRP has a positive inotropic effect that can be mediated by both CGRP(1) and CGRP(2) receptors. Amylin seems to have a potential positive inotropic effect on atrial tissue, whereas no direct effect of adrenomedullin could be measured.

Regulation of cardiac adrenomedullin-mRNA in different stages of experimental heart failure

Adrenomedullin (AM) is a peptide hormone with vasodilating and natriuretic properties. AM plasma concentrations are elevated in heart failure. Whether cardiac AM-mRNA synthesis is increased in heart failure is not known. We measured AM-mRNA/GAPDH-mRNA in all four heart chambers in compensated and overt heart failure in rats with two different sizes of aortocaval shunt. Left and right atrial AM-mRNA expressions were unchanged in both heart failure models. Similarly, left and right ventricular AM-mRNA expressions were unchanged in compensated heart failure. In overt heart failure, however, the AM-mRNA expression was significantly increased in the left ventricle (145+/-20 vs. 100+/-3% of control, p<0.05). The right ventricular AM-mRNA expression was significantly increased only in a subgroup of animals with pulmonary congestion (lung weight >2.0 g, 141+/-16 vs. 100+/-11% of control, p<0.05). Ventricular AM concentrations were elevated in both ventricles in overt heart failure. AM plasma concentrations were significantly higher in the subgroup with pulmonary congestion than in rats with compensated heart failure (496+/-95 vs. 143+/-7 pmol/l, p<0.01). These data indicate that ventricular AM-mRNA expression and AM concentrations were upregulated only in advanced stages of heart failure. However, the exact contribution of cardiac AM synthesis to the increased AM plasma levels remains to be established.

Biological and clinical roles of adrenomedullin in circulation control and cardiovascular diseases

1. Adrenomedullin (AM) is found ubiquitously in tissues and organs, especially in cardiovascular tissues and in the kidney, lung and endocrine glands. It has multifunctional biological properties, of which, its effects on the control of circulation and body fluid volume regulation seem to be the most outstanding and characteristic. 2. Acute administration of a high dose of AM induces a vasodilator depressor response, cardiac inotropic effects, diuresis and suppression of aldosterone secretion in experimental animals. 3. Long-term continuous administration of a very low dose of AM causes vasodilation in sheep (0.5 microgram/kg per h) and hypotension in rats (0.8 microgram/kg per h). 4. The plasma concentration of AM increases under pathological conditions such as congestive heart failure, myocardial infarction and hypertensive and renal diseases. Under these disease conditions, AM may be produced in vascular endothelial and smooth muscle cells and in cardiac myocytes in response to volume expansion, hypertension and activated humoral factors, such as catecholamine and the renin-angiotensin system. 5. Increased AM in the circulating blood and cardiovascular tissues may counteract pathological deviation in the system that controls circulation and body fluid volume, acting against cardiovascular damage and disease. 6. Because of these beneficial properties in the cardiovascular system, AM and its pharmaceutical ligands should prove useful in the treatment of cardiovascular diseases.

Adrenomedullin is upregulated in the heart and aorta during the early and late stages of sepsis

Although circulating levels of adrenomedullin (ADM), a newly reported vasodilatory peptide with 52 amino acid residues in the human and 50 amino acid residues in the rat, are elevated during the early and late stages of sepsis, ADM levels in cardiovascular tissues and its precise localization remain to be determined. To study this, rats were subjected to sepsis by cecal ligation and puncture (CLP), followed by administration of 3 ml/100 g b.wt. normal saline to these and sham-operated animals. The heart and thoracic aorta were harvested at 5 h (i.e. the early stage of sepsis) and 20 h (late sepsis) after CLP. Tissue levels of ADM were determined by radioimmunoassay. The localization of ADM in the left ventricle and thoracic aorta was examined by using immunohistochemistry and electron microscopy techniques. The results indicated that ADM levels in the heart and thoracic aorta increased significantly at 5 h after CLP and remained elevated at 20 h after the onset of sepsis. Immunohistochemistry findings showed that ADM immunoreaction products were localized in the cytoplasm of the cardiac myocytes and aortic endothelial cells. Using electron microscopy, ADM immunoreaction products were found in the cytoplasmic matrixes. The immunostainings were also associated with the outer membranes of mitochondria and vesicles of the myocytes as well as vascular endothelial cells. It appears that the cardiovascular tissues, among other organ systems, contribute to the increased levels of plasma ADM under those conditions. Since ADM is localized in different cell populations in the heart and the large blood vessel (i.e. myocytes versus vascular endothelial cells), this peptide may play a differential role in regulating cardiac and vascular functions during sepsis as an autocrine and/or paracrine mediator.

Adrenomedullin promotes epithelial restitution of rat and human gastric mucosa in vitro

We have investigated the effect of adrenomedullin (AM) on restitution of mucosal integrity following damage in rat and human gastric mucosa, measuring the potential difference (PD) on a mucosal strip mounted on an Ussing chamber. Mucosal damage was induced by 0.5, 1.0, and 2.0 M NaCl solution, and it caused an immediate and significant decrease in PD. In the rat AM group, PD recovered significantly more than in control group at 120 min after exposure to 0.5 M (p < 0.01) and 1.0 M (p < 0.05) NaCl solution. In the human AM group, PD completely recovered at 120 min after exposure to 0.5 M (p < 0.05) NaCl solution. In rat mucosa damaged by 0.5 M NaCl solution, the effect was inhibited by human (h)-CGRP(8-37) and there was no significant difference between the h-CGRP(8-37) group and control group. On immunohistochemical examination of rat gastric mucosa, AM was detected within the chief cell. AM probably promotes epithelial restitution primarily through the CGRP receptor, but it does not ameliorate more severe damage of gastric mucosa in vitro.

Production and secretion of adrenomedullin in cultured rat cardiac myocytes and nonmyocytes: stimulation by interleukin-1beta and tumor necrosis factor-alpha

The present study investigated the secretion level and gene expression of adrenomedullin (AM), a novel vasorelaxant peptide, in cultured neonatal rat cardiac myocytes and nonmyocytes, and the effects of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF alpha) on its production and secretion in these cells. Under serum-free conditions, both myocytes and nonmyocytes secreted immunoreactive (ir-) AM into the culture medium in a time-dependent manner. The secretion rates of ir-AM from myocytes and nonmyocytes per 10(5) cells were almost equivalent. The expression of AM messenger RNA was also observed in cultured myocytes and nonmyocytes. The peptide secretion and messenger RNA level of AM in cardiac myocytes were increased after stimulation with IL-1beta. In nonmyocytes, IL-1beta and TNF alpha remarkably augmented both the release of ir-AM into the medium and AM gene expression after 24 and 48 h of incubation. These observations indicate that cardiac ventricular cells (i.e. myocytes and nonmyocytes) actively produce AM and also suggest that cytokines such as IL-1beta and TNF alpha regulate the gene expression and secretion of this peptide in the ventricles. On the basis of these results and the findings that IL-1beta and TNF alpha are involved in heart failure and cardiac hypertrophy, AM may play a role as an autocrine/paracrine modulator in some cardiac disorders.

Plasma levels of adrenomedullin in patients with mitral stenosis

Although plasma levels of adrenomedullin are elevated in patients with heart failure, levels in patients with mitral stenosis are unknown. We determined plasma levels of adrenomedullin in specimens of blood obtained from the peripheral veins of 15 consecutively treated patients with mitral stenosis 1 week before and 1 week after percutaneous mitral valvuloplasty. We also measured adrenomedullin in blood obtained from the right and left atria of 13 of 15 patients immediately before valvuloplasty. Plasma adrenomedullin level in the peripheral vein was 27.3 +/- 3.2 pg/ml among healthy subjects (n = 15) and 59.8 +/- 2.7 pg/ml among patients with mitral stenosis (n = 15, p < 0.0001). Plasma adrenomedullin level in the peripheral veins of patients with mitral stenosis before valvuloplasty correlated significantly with mean pulmonary artery pressure, mean pulmonary arterial wedge pressure, and mean left atrial pressure. Plasma levels of adrenomedullin in the peripheral vein and the right atrium were significantly higher than those in the left atrium (59.5 +/- 3.0 and 55.8 +/- 2.4 versus 45.9 +/- 2.9 pg/ml, n = 13, p < 0.005). Percutaneous mitral valvuloplasty caused a significant decrease in plasma adrenomedullin levels in peripheral veins from 59.8 +/- 2.7 to 49.9 +/- 3.1 pg/ml (p < 0.02). Percentage decrease in plasma adrenomedullin levels in the peripheral vein correlated significantly with percentage decreases in mean pulmonary artery pressure and mean pulmonary arterial wedge pressure. This study demonstrated that plasma adrenomedullin levels of patients with mitral stenosis correlated positively with mean pulmonary artery pressure and pulmonary arterial wedge pressure. These findings suggested that adrenomedullin may play an important role in the pulmonary circulation of these patients.

Cytoprotective effects of adrenomedullin in glomerular cell injury: central role of cAMP signaling pathway

Activation of cAMP signaling pathway was shown to inhibit some pathobiologic processes in mesangial cells (MC). We investigated whether adrenomedullin (ADM), a potent agonist of adenylate cyclase, is synthesized in MC and whether it can, via cAMP, suppress the generation of reactive oxygen metabolites (ROM) and proliferation of cells in glomeruli. With the use of an immunohistologic technique ADM was detected in mesangial and microvascular areas of rat glomeruli. MC grown in primary culture synthesized ADM, and the synthesis was stimulated by TNF alpha and IL-1 beta but not by PDGF and EGF. ADM inhibited ROM generation in MC dose-dependently and caused in situ activation of protein kinase A (PKA). In macrophages (cell line J774) ROM generation was about four times higher than in MC and was inhibited by ADM in a similar way as in MC. The rate of MC proliferation, measured by [3H]-incorporation, and the activity of mitogen-activated protein kinase (MAPK) stimulated by PDGF and EGF were dose-dependently inhibited by ADM; the maximum inhibition (at 10 nM ADM) was about -80%. Mitogenesis of MC and MAPK activity when stimulated to a similar extent by endothelin (ET-1) was inhibited by ADM to a significantly (P < 0.01) lesser degree (-30%). Further, ADM inhibited PDF-stimulated mitogenesis and activation of MAPK in cultured vascular smooth muscle cells (VSMC). The inhibition of PDGF-activated MAPK by ADM in VSMC was reversed by the protein kinase A (PKA) inhibitor, H89. Taken together, results indicate the adrenomedullin (ADM) generated in mesangial cells (MC) can suppress, via activation of the cAMP-protein kinase A (PKA) signaling pathway, reactive oxygen metabolites (ROM) generation in MC and infiltrating macrophages as well as mitogen-activated protein kinase (MAPK)-mediated mitogenesis in MC and vascular smooth muscle cells (VSMC). We suggest that introglomerular ADM may serve as a cytoprotective autoacoid that suppresses pathobiologic processes evoked by immuno-inflammatory injury of glomeruli.

Adrenomedullin in experimental congestive heart failure: cardiorenal activation

Adrenomedullin (ADM) is a new member of a family of vasodilating and natriuretic peptides that plays an important role in cardiorenal regulation. This study was designed to establish the plasma, urinary, cardiac, and renal tissue concentrations and immunohistochemical localizations of ADM in normal dogs and dogs with experimental congestive heart failure (CHF) produced by rapid ventricular pacing. Plasma ADM concentration was 5.6 +/- 0.4 pg/ml in normal dogs and significantly increased to 14.5 +/- 2.5 pg/ml in CHF dogs (P < 0.05). Ventricular and renal tissue ADM were significantly increased in CHF dogs compared with normals. Immunohistochemical examination revealed positive ADM immunostaining within the myocytes, and ventricular ADM immunoreactivity was significantly more intense in CHF dogs than in normals. ADM immunoreactivity was also observed in the glomerulus, distal tubules, and medullary collecting duct cells in the kidney, and the intensities of ADM immunoreactivity in these sites were increased in CHF dogs compared with normals. In addition, ventricular ADM was a powerful marker for left ventricular mass, and circulating ADM correlated positively with left ventricular end-diastolic pressure and inversely with cardiac output and ejection fraction. Despite an increase in renal tissue ADM, urinary ADM did not increase in CHF dogs. The current study demonstrates that plasma concentration of ADM is increased in experimental CHF and that ventricular and renal ADM is activated in the progression of CHF. Tissue and circulating ADM also are markers for the alterations in myocardial structure and function. This study supports a potential role for ADM in the neurohumoral activation in experimental CHF.

Beneficial hemodynamic and renal effects of adrenomedullin in an ovine model of heart failure

BACKGROUND

Adrenomedullin is a recently discovered endogenous peptide with hypotensive and natriuretic actions in normal animals. Circulating and ventricular adrenomedullin are elevated in congestive heart failure, suggesting a possible role in the pathophysiology of this disease. No studies have previously examined the effects of adrenomedullin in heart failure.

METHODS AND RESULTS

Eight sheep with pacing-induced heart failure received human adrenomedullin(1-52) at 10 and 100 ng x kg(-1) x min(-1) I.V. for 90 minutes each. Compared with vehicle control data, adrenomedullin increased plasma cAMP (high dose, P<.05) in association with dose-dependent falls in calculated peripheral resistance (13 mm Hg x L(-1) x min(-1), P<.001), mean arterial pressure (9 mm Hg, P<.001), and left atrial pressure (5 mm Hg, P<.001) and increases in cardiac output (0.5 L/min, P<.001). Adrenomedullin increased urine sodium (threefold, P<.05), creatinine (P<.05) and cAMP excretion (P<.01), creatinine clearance (P<.05), and renal production of cAMP (P<.05), whereas urine output was maintained during infusion and raised after infusion (P<.05). Adrenomedullin reduced plasma aldosterone levels (P<.05), whereas plasma atrial and brain natriuretic peptide concentrations were unchanged during infusion and rose after infusion (P<.01 and P<.05, respectively). Plasma catecholamine, cortisol, renin, calcium, and glucose concentrations were not significantly altered.

CONCLUSIONS

Adrenomedullin reduced ventricular preload and afterload and improved cardiac output in sheep with congestive heart failure. Despite the clear fall in arterial pressure, adrenomedullin increased creatinine clearance and sodium excretion and maintained urine output. These results imply an important pathophysiological role for adrenomedullin in the regulation of pressure and volume in heart failure and raise the possibility of a new therapeutic approach to this disease.

Hormonal and humeral considerations in hypertensive disease

This article has discussed the classic hormonal causes of hypertension. Pheochromocytoma and hyperaldosteronism have been discussed, and a clinical approach to evaluation of patients for these problems has been presented. Other humeral factors that influence volume pressure homeostasis have been discussed. It is likely that pharmacologic agents affecting these other factors will become available to patients with hypertension in the future.

Potent and long-lasting vasodilatory effects of adrenomedullin in humans. Comparisons between normal subjects and patients with chronic heart failure

BACKGROUND

Adrenomedullin (ADM) is a recently discovered hypotensive peptide that has been isolated from human pheochromocytoma cells. Observations that ADM is produced from cardiovascular tissue and is found in plasma suggest that it may be important in the regulation of regional vascular resistance.

METHODS AND RESULTS

Limb vascular responses to ADM were examined in 10 healthy subjects and compared with those in 18 patients with chronic heart failure (CHF). The peptide increased forearm blood flow (FBF) from 2.7 +/- 0.3 to 11.8 +/- 0.9 mL.min-1.100 mL-1 in the control group and from 2.4 +/- 0.3 to 6.5 +/- 0.7 mL.min-1.100 mL-1 in the CHF group. The ADM-induced FBF increase was significantly impaired in the CHF group (P < .01). After cessation of the infusion, an increased FBF level was sustained for > 60 minutes in the control group, whereas in the CHF group the response returned to the baseline in < 30 minutes. The ADM infusion increased forearm skin blood flow in both groups (P < .05), whereas the skin blood flow response was impaired in the CHF group (P < .01). The role of nitric oxide in ADM-induced vasorelaxation was also studied in 11 healthy subjects and 6 patients with CHF. FBF and skin blood flow responses during ADM administration were significantly attenuated by NG-monomethyl-L-arginine administration in healthy control subjects (P < .05), whereas both flow responses remained the same in the CHF group.

CONCLUSIONS

These observations demonstrate that ADM exerts a potent and long-lasting vasodilatory effect on skeletal muscle arteries with involvement of nitric oxide-dependent mechanisms in normal human peripheral vasculature and that these vascular effects are significantly attenuated in patients with CHF, in part because of impaired production of nitric oxide in the forearm resistance vessels.

A rat skeletal muscle cell line (L6) expresses specific adrenomedullin binding sites but activates adenylate cyclase via calcitonin gene-related peptide receptors

We have previously demonstrated specific binding sites for adrenomedullin, a novel member of the calcitonin family of peptides, in rat muscles. It is unclear whether these receptors are vascular or muscular. Receptors for the structurally similar calcitonin gene-related peptide (CGRP) are present on myocytes and might be involved in the regulation of myocyte glucose metabolism and control by motor neurons. We investigated whether adrenomedullin binding sites were present on L6 myocytes. Specific [125I]adrenomedullin binding sites were demonstrated where adrenomedullin competed with an IC50 of 0.22 +/- 0.04 nM (mean +/- S.E.M.) and a concentration of binding sites (Bmax) of 0.95 +/- 0.19 pmol/mg of protein (mean +/- S.E.M.). CGRP and the specific CGRP receptor antagonist CGRP(8-37) competed weakly at this site (IC50 > 10 and 601 +/- 298 nM respectively). Binding studies with [125I]CGRP revealed a binding site for CGRP (IC50 = 0.13 +/- 0.01 nM; Bmax = 0.83 +/- 0.10 pmol/mg of protein) where both CGRP(8-37) and adrenomedullin competed with [125I]CGRP with IC50 values of 1.15 +/- 0.12 and 8.68 +/- 0.98 nM respectively. Chemical cross-linking showed the CGRP and adrenomedullin binding site-ligand complexes to have approximate molecular masses of 82 and 76 kDa respectively. Both CGRP and adrenomedullin increased adenylate cyclase activity with similar potencies. In both cases adenylate cyclase activation was blocked by CGRP(8-37). Stimulation with 10 nM adrenomedullin or CGRP caused an increase in the percentage of total activated cellular cAMP-dependent protein kinase from 38% in resting cells to 100% and 98% respectively. Therefore in L6 cells adrenomedullin can bind to CGRP receptors, activating adenylate cyclase and cAMP-dependent protein kinase.

Cardiac secretion of adrenomedullin in human heart failure

Adrenomedullin (ADM) is a newly discovered endogenous vasorelaxing and natriuretic peptide. Recently, we have reported that plasma ADM is increased in severe congestive heart failure (CHF) in humans and that increased immunohistochemical staining is observed in the failing human ventricular myocardium. The present study was designed to test the hypothesis that the failing human ventricle secretes ADM and that circulating ADM progressively increases with the severity of clinical CHF. Plasma ADM was significantly increased in human CHF (39.8 +/- 3.6 pg/ml, P < 0.001 vs. normal) as compared with normal subjects (14.4 +/- 2.7 pg/ml). Plasma ADM was increased in mild CHF (NYHA class II, 30.1 +/- 3.4 pg/ml, P < 0.01 vs. normal), moderate CHF (NYHA class III, 31.5 +/- 3.0 pg/ml, P < 0.01 vs. normal), and severe CHF (NYHA class IV, 66.1 +/- 9.4 pg/ml, P < 0.001 vs. normal). In 13 patients with CHF in whom plasma samples were obtained from aorta (AO), coronary sinus (CS) and anterior interventricular vein (AIV), there was a significant step-up in plasma ADM between AO and AIV (50.6 +/- 9.3 pg/ml and 62.1 +/- 11.1 pg/ml, respectively, P < 0.01) and between AO and CS (50.6 +/- 9.3 pg/ml and 58.6 +/- 11.4 pg/ml, respectively, P < 0.05). The current study demonstrates that the failing human heart secretes ADM in human CHF suggesting contribution to the increase in plasma ADM, and indicates for the first time an additional endocrine system of cardiac origin which is activated in human CHF and may function in cardiorenal regulation.

Adrenomedullin: A newly discovered hormone controlling fluid and electrolyte homeostasis

Neural and humoral mechanisms controlling fluid and electrolyte homeostasis employ a diverse array of physiologic mechanisms that often, when aberrant, are the underlying cause of disease. Behavioral, hormonal, renal, and vascular responses to volume and osmotic challenges must be coordinated to achieve the goal of homeostasis. In recent years, it has become apparent that there exist a number of hormonal factors produced throughout the body that can coordinate these multiple regulatory mechanisms by complementary effects in several tissues. Thus, in addition to their vasoactive properties, recently characterized hormones such as the natriuretic peptides and the endothelins, as well as the better established renin-angiotensin system, exert central nervous, renal, cardiac, and pituitary effects that regulate normal fluid and electrolyte balance. Now a new player, adrenomedullin, has been added to the cast, and the interplay of multiple hormonal factors involved in the physiology and pathophysiology of volume and osmotic status continues to be elucidated.

Elevation of circulating and ventricular adrenomedullin in human congestive heart failure

BACKGROUND

Adrenomedullin (ADM) is a newly discovered vasodilating and natriuretic peptide that may play an important role in cardiorenal regulation. Although ADM was originally isolated from human pheochromocytoma, ADM-like immunoreactivity has also been widely detected in various tissues, including the cardiovascular system.

METHODS AND RESULTS

In view of reports that ADM circulates in the body and that ADM gene and ADM-like immunoreactivity are present in the heart, the present study was designed to determine the plasma concentration of ADM in healthy subjects and in patients with congestive heart failure (CHF) and to investigate the immunohistochemical presence and localization of ADM in normal and failing human hearts. Plasma ADM concentration was 13.2 +/- 2.3 pg/mL in healthy subjects (n = 11) and increased to 47.3 +/- 6.7 pg/mL in patients with CHF (n = 11 P < .05 versus normal). Human cardiac tissues were obtained from five patients with end-stage CHF undergoing cardiac transplantation. Five normal donor hearts that were used for cardiac transplantation served as sources for normal atrial tissues. Normal ventricular myocardium was also obtained by endomyocardial biopsy from the right ventricles of these donor hearts immediately before cardiac transplantation. Positive immunostaining was detected within the myocardia in both atria and ventricles of healthy and severely failing human transplanted hearts and was more intense in the atria than in the ventricles. Although there were no significant differences in the intensity of immunoreactivity between normal and failing atria, ADM immunoreactivity was significantly more intense in the ventricular myocytes from failing hearts compared with normal hearts.

CONCLUSIONS

The present study demonstrates that plasma concentration of ADM is increased in patients with CHF and that ADM is present in the human heart. ADM immunoreactivity is markedly increased in the failing human ventricle, suggesting that ventricular ADM expression may be influenced by the circumstances associated with CHF. This supports a potential role for this newly identified vasoactive and natriuretic peptide, ADM, in the neurohumoral activation that characterizes human CHF.