Cardiac fibroblasts are major production and target cells of adrenomedullin in the heart in vitro

Cardiac and intestinal tissue conduct developmental and reparative processes in response to lymphangiocrine signaling

Lymphatic vessels conduct a diverse range of activities to sustain the integrity of surrounding tissue. Besides facilitating the movement of lymph and its associated factors, lymphatic vessels are capable of producing tissue-specific responses to changes within their microenvironment. Lymphatic endothelial cells (LECs) secrete paracrine signals that bind to neighboring cell-receptors, commencing an intracellular signaling cascade that preludes modifications to the organ tissue's structure and function. While the lymphangiocrine factors and the molecular and cellular mechanisms themselves are specific to the organ tissue, the crosstalk action between LECs and adjacent cells has been highlighted as a commonality in augmenting tissue regeneration within animal models of cardiac and intestinal disease. Lymphangiocrine secretions have been owed for subsequent improvements in organ function by optimizing the clearance of excess tissue fluid and immune cells and stimulating favorable tissue growth, whereas perturbations in lymphatic performance bring about the opposite. Newly published landmark studies have filled gaps in our understanding of cardiac and intestinal maintenance by revealing key players for lymphangiocrine processes. Here, we will expand upon those findings and review the nature of lymphangiocrine factors in the heart and intestine, emphasizing its involvement within an interconnected network that supports daily homeostasis and self-renewal following injury.

Alpha-Calcitonin Gene Related Peptide: New Therapeutic Strategies for the Treatment and Prevention of Cardiovascular Disease and Migraine

Alpha-calcitonin gene-related peptide (α-CGRP) is a vasodilator neuropeptide of the calcitonin gene family. Pharmacological and gene knock-out studies have established a significant role of α-CGRP in normal and pathophysiological states, particularly in cardiovascular disease and migraines. α-CGRP knock-out mice with transverse aortic constriction (TAC)-induced pressure-overload heart failure have higher mortality rates and exhibit higher levels of cardiac fibrosis, inflammation, oxidative stress, and cell death compared to the wild-type TAC-mice. However, administration of α-CGRP, either in its native- or modified-form, improves cardiac function at the pathophysiological level, and significantly protects the heart from the adverse effects of heart failure and hypertension. Similar cardioprotective effects of the peptide were demonstrated in pressure-overload heart failure mice when α-CGRP was delivered using an alginate microcapsules-based drug delivery system. In contrast to cardiovascular disease, an elevated level of α-CGRP causes migraine-related headaches, thus the use of α-CGRP antagonists that block the interaction of the peptide to its receptor are beneficial in reducing chronic and episodic migraine headaches. Currently, several α-CGRP antagonists are being used as migraine treatments or in clinical trials for migraine pain management. Overall, agonists and antagonists of α-CGRP are clinically relevant to treat and prevent cardiovascular disease and migraine pain, respectively. This review focuses on the pharmacological and therapeutic significance of α-CGRP-agonists and -antagonists in various diseases, particularly in cardiac diseases and migraine pain.

Phenotypic Variation Between Stromal Cells Differentially Impacts Engineered Cardiac Tissue Function

IMPACT STATEMENT

Understanding the relationship between parenchymal and supporting cell populations is paramount to recapitulate the multicellular complexity of native tissues. Incorporation of stromal cells is widely recognized to be necessary for the stable formation of stem cell-derived cardiac tissues; yet, the types of stromal cells used have varied widely. This study systematically characterized several stromal populations and found that stromal phenotype and morphology was highly variable depending on cell source and exerted differential impacts on cardiac tissue function and induced pluripotent stem cell-cardiomyocyte phenotype. Therefore, the choice of supporting stromal population can differentially impact the phenotypic or functional performance of engineered cardiac tissues.

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.

Natural and synthetic peptides in the cardiovascular diseases: An update on diagnostic and therapeutic potentials

Several peptides play an important role in physiological and pathological conditions into the cardiovascular system. In addition to well-known vasoactive agents such as angiotensin II, endothelin, serotonin or natriuretic peptides, the vasoconstrictor Urotensin-II (Uro-II) and the vasodilators Urocortins (UCNs) and Adrenomedullin (AM) have been implicated in the control of vascular tone and blood pressure as well as in cardiovascular disease states including congestive heart failure, atherosclerosis, coronary artery disease, and pulmonary and systemic hypertension. Therefore these peptides, together with their receptors, become important therapeutic targets in cardiovascular diseases (CVDs). Circulating levels of these agents in the blood are markedly modified in patients with specific CVDs compared with those in healthy patients, becoming also potential biomarkers for these pathologies. This review will provide an overview of current knowledge about the physiological roles of Uro-II, UCN and AM in the cardiovascular system and their implications in cardiovascular diseases. It will further focus on the structural modifications carried out on original peptide sequences in the search of analogues with improved physiochemical properties as well as in the delivery methods. Finally, we have overviewed the possible application of these peptides and/or their precursors as biomarkers of CVDs.

MiRNA Deregulation in Cardiac Aging and Associated Disorders

The prevalence of age-related diseases is increasing dramatically, among which cardiac disease represents the leading cause of death. Aging of the heart is characterized by various molecular and cellular hallmarks impairing both cardiomyocytes and noncardiomyocytes, and resulting in functional deteriorations of the cardiac system. The aging process includes desensitization of β-adrenergic receptor (βAR)-signaling and decreased calcium handling, altered growth signaling and cardiac hypertrophy, mitochondrial dysfunction and impaired autophagy, increased programmed cell death, low-grade inflammation of noncanonical inflammatory cells, and increased ECM deposition. MiRNAs play a fundamental role in regulating the processes underlying these detrimental changes in the cardiac system, indicating that MiRNAs are crucially involved in aging. Among others, MiR-34, MiR-146a, and members of the MiR-17-92 cluster, are deregulated during senescence and drive cardiac aging processes. It is therefore suggested that MiRNAs form possible therapeutic targets to stabilize the aged failing myocardium.

Endothelium-derived intermedin/adrenomedullin-2 protects human ventricular cardiomyocytes from ischaemia-reoxygenation injury predominantly via the AM₁ receptor

Application of intermedin/adrenomedullin-2 (IMD/AM-2) protects cultured human cardiac vascular cells and fibroblasts from oxidative stress and simulated ischaemia-reoxygenation injury (I-R), predominantly via adrenomedullin AM1 receptor involvement; similar protection had not been investigated previously in human cardiomyocytes (HCM). Expression of IMD, AM and their receptor components was studied in HCM. Receptor subtype involvement in protection by exogenous IMD against injury by simulated I-R was investigated using receptor component-specific siRNAs. Direct protection by endogenous IMD against HCM injury, both as an autocrine factor produced in HCM themselves and as a paracrine factor released from HCMEC co-cultured with HCM, was investigated using peptide-specific siRNA for IMD. IMD, AM and their receptor components (CLR, RAMPs1-3) were expressed in HCM. IMD 1nmol L(-1), applied either throughout ischaemia (3h) and re-oxygenation (1h) or during re-oxygenation (1h) alone, attenuated HCM injury (P<0.05); cell viabilities were 59% and 61% respectively vs. 39% in absence of IMD. Cytoskeletal disruption, protein carbonyl formation and caspase activity followed similar patterns. Pre-treatment (4 days) of HCM with CLR and RAMP2 siRNAs attenuated (P<0.05) protection by exogenous IMD. Pre-treatment of HCMEC with IMD (and AM) siRNA augmented (P<0.05) I-R injury: cell viabilities were 22% (and 32%) vs. 39% untreated HCMEC. Pre-treatment of HCM with IMD (and AM) siRNA did not augment HCM injury: cell viabilities were 37% (and 39%) vs. 39% untreated HCM. Co-culture with HCMEC conferred protection from injury on HCM; such protection was attenuated when HCMEC were pre-treated with IMD (but not AM) siRNA before co-culture. Although IMD is present in HCM, IMD derived from HCMEC and acting in a paracrine manner, predominantly via AM1 receptors, makes a marked contribution to cardiomyocyte protection by the endogenous peptide against acute I-R injury.

Epicardial-derived adrenomedullin drives cardiac hyperplasia during embryogenesis

BACKGROUND

Growth promoting signals from the epicardium are essential for driving myocardial proliferation during embryogenesis. In adults, these signals become reactivated following injury and promote angiogenesis and myocardial repair. Therefore, identification of such paracrine factors could lead to novel therapeutic strategies. The multi-functional peptide adrenomedullin (Adm 5 gene, AM 5 protein) is required for normal heart development. Moreover, elevated plasma AM following myocardial infarction offers beneficial cardioprotection and serves as a powerful diagnostic and prognostic indication of disease severity.

RESULTS

Here, we developed a new model of Adm overexpression by stabilizing the Adm mRNA through gene-targeted replacement of the endogenous 30 untranslated region. As expected, Admhi/hi mice express three-times more AM than controls in multiple tissues, including the heart. Despite normal blood pressures, Admhi/hi mice unexpectedly showed significantly enlarged hearts due to increased cardiac hyperplasia during development. The targeting vector was designed to allow for reversion to wild-type levels by means of Cre-mediated modification. Using this approach, we demonstrate that AM derived from the epicardium, but not the myocardium or cardiac fibroblast, is responsible for driving cardiomyocyte hyperplasia.

CONCLUSIONS

AM is produced by the epicardium and drives myocyte proliferation during development, thus representing a novel and clinically relevant factor potentially related to mechanisms of cardiac repair after injury.

Shared and separate functions of the RAMP-based adrenomedullin receptors

Adrenomedullin (AM) is a novel hypotensive peptide that exerts a variety of strongly protective effects against multiorgan damage. AM-specific receptors were first identified as heterodimers composed of calcitonin-receptor-like receptor (CLR), a G protein coupled receptor, and one of two receptor activity-modifying proteins (RAMP2 or RAMP3), which are accessory proteins containing a single transmembrane domain. RAMPs are required for the surface delivery of CLR and the determination of its phenotype. CLR/RAMP2 (AM₁ receptor) is more highly AM-specific than CLR/RAMP3 (AM₂ receptor). Although there have been no reports showing differences in intracellular signaling via the two AM receptors, in vitro studies have shed light on their distinct trafficking and functionality. In addition, the tissue distributions of RAMP2 and RAMP3 differ, and their gene expression is differentially altered under pathophysiological conditions, which is suggestive of the separate roles played by AM₁ and AM₂ receptors in vivo. Both AM and the AM₁ receptor, but not the AM₂ receptor, are crucial for the development of the fetal cardiovascular system and are able to effectively protect against various vascular diseases. However, AM₂ receptors reportedly play an important role in maintaining a normal body weight in old age and may be involved in immune function. In this review article, we focus on the shared and separate functions of the AM receptor subtypes and also discuss the potential for related drug discovery. In addition, we mention their possible function as receptors for AM2 (or intermedin), an AM-related peptide whose biological functions are similar to those of AM.

Attenuation of ischemic myocardial injury and dysfunction by cardiac fibroblast-derived factor(s)

Fibroblasts, the majority of non-cardiomyocytes in the heart, are known to release several kinds of substances such as cytokines and hormones that affect cell and tissue functions. We hypothesized that undefined substance (s) derived from cardiac fibroblasts may have the potential to protect against ischemic myocardium. To assess our hypothesis, using rats, we investigated: (1) the effect of cardiac fibroblast-conditioned medium (CM) on the viability of hypoxic cardiomyocytes in vitro, (2) the effect of CM on left ventricular (LV) function in global ischemia-reperfusion in an ex vive model, (3) the mechanism underlying cardioprotection by CM. Seventy-two hours after starting a hypoxic culture, the viability of cardiomyocytes was higher (P < 0.05) in the CM treated group (41.4%) compared to the control (20.5%). In Langendorff's preparation, 30 min after ischemia-reperfusion, LV end-diastolic pressure was lower, and LV developed pressure and -LVdP/dt were higher (P < 0.01 or P < 0.05) in the CM group than in the control, although coronary flow did not differ between the two groups. Pretreatment with a protein kinase C inhibitor or a mitochondrial ATP-sensitive K+ channel blocker attenuated these changes of LV function in the CM group. Such cardioprotection was achieved by a fraction of the CM having a molecular weight (MW) > 50,000, but not by that of the CM with a lower MW. In addition, a specific antibody against hepatocyte growth factor (HGF, MW is 84,000) did not reduce the cardioprotection afforded by CM. There may be an unknown cardioprotective substance other than HGF in rats, which mimics ischemic preconditioning and has MW > 50,000.

Adrenomedullin and adrenomedullin binding protein-1 prevent metabolic acidosis after uncontrolled hemorrhage in rats

OBJECTIVE

Management of trauma victims with uncontrolled hemorrhage remains a major problem in combat casualty care at the far-forward battlefield setting. The neuroendocrine response to hemorrhage is to maintain perfusion to the heart and brain, often at the expense of other organ systems. Decreased organ perfusion after hemorrhagic shock is associated with metabolic acidosis, in which the up-regulated endothelin-1 plays an important role. We have recently shown that vascular responsiveness to adrenomedullin (AM), a newly discovered vasodilator peptide, is depressed after hemorrhage and resuscitation. Down-regulation of AM binding protein (AMBP-1) appears to be responsible for this hyporesponsiveness. We therefore hypothesized that administration of AM/AMBP-1 would prevent metabolic acidosis after uncontrolled hemorrhage via down-regulation of endothelin-1.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

A research institute laboratory.

SUBJECTS

Male Sprague-Dawley rats (275-325 g).

INTERVENTIONS

A rat model of uncontrolled hemorrhage with an extremely low volume of fluid resuscitation was used to mimic the combat situation.

MEASUREMENTS AND MAIN RESULTS

Both lumbar veins of male adult rats were isolated and severed at the junction to the vena cava. The abdomen was kept open but covered with a saline wet gauze for 45 mins and then closed in layers. The animals received 1 mL of normal saline (vehicle) with or without AM (12 microg/kg of body weight) and AMBP-1 (40 microg/kg of body weight) over 45 mins. Various variables were measured at 4 hrs after resuscitation. The bleed-out volumes in the vehicle group and the AM/ AMBP-1 treatment group were 6.78 +/- 0.19 and 6.81 +/- 0.25 mL/rat, respectively. The results indicate that AM/AMBP-1 administration prevented metabolic acidosis, mitigated organ injury, down-regulated preproendothelin-1 gene expression, and decreased plasma levels of endothelin-1 after hemorrhage.

CONCLUSIONS

AM/AMBP-1 may provide a novel approach for the treatment of uncontrolled hemorrhage. The beneficial effect of AM/AMBP-1 is associated with down-regulation of endothelin-1.

Participation of adrenomedullin and its relation with vascular endothelial growth factor in androgen regulation of prostatic blood flow in vivo

OBJECTIVES

We had previously reported that androgen-regulated prostatic blood flow and vascular endothelial growth factor (VEGF) were involved in the signal transduction pathway. Adrenomedullin (ADM) is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities that are regulated by androgen. ADM is abundantly expressed in the prostate. We focused on ADM and evaluated its participation and relation with VEGF in androgen prostatic blood flow regulation using a castrated rat model.

METHODS

We examined the effect of locally injected dihydrotestosterone (DHT) and ADM, and the co-administration of DHT with an ADM receptor antagonist (ADM 22-52) on prostatic blood flow. Furthermore, prostatic blood flow was evaluated after ADM and VEGF administration with each other's antagonist, VEGF neutralizing antibody and ADM 22-52, respectively. Changes in the mRNA expression levels of ADM in the prostate after castration and successive androgen stimulation were also evaluated.

RESULTS

The administration of ADM promptly increased prostatic blood flow in a dose-dependent manner within 30 minutes. The DHT-induced increase in prostatic blood flow was completely abolished by co-administration with anti-ADM. Anti-ADM inhibited the VEGF-induced prostatic blood flow elevation, but a VEGF neutralizing antibody did not affect the ADM-mediated blood flow elevation. Furthermore, upregulation of the ADM gene induced by DHT was inhibited by co-administration with a VEGF-neutralizing antibody.

CONCLUSIONS

These results have clearly demonstrated the direct regulation of prostatic blood flow by ADM and its involvement in androgenic prostatic blood flow regulation. Furthermore, ADM was estimated to be a downstream mediator of VEGF action in the signal transduction pathway.

Plasma adrenomedullin relation with Doppler-derived dP/dt in patients with congestive heart failure

BACKGROUND

Increased circulating adrenomedullin (AM) concentration has been reported in congestive heart failure (HF) and considered as a possible marker of cardiac dysfunction.

HYPOTHESIS

The study was undertaken to assess the relationship between circulating AM concentration and left ventricular (LV) functional state, estimated by echo-Doppler techniques in patients with mild to moderate HF and different degrees of LV dysfunction.

METHODS

Plasma AM, B-type natriuretic peptide (BNP), and N-terminal (NT) proBNP levels were measured in 55 patients with HF (New York Heart Association [NYHA] I n = 8, II n = 26, III n = 21) and in 20 controls; dP/dt was calculated by the Doppler tracing of the mitral regurgitation jet.

RESULTS

The study was completed in 51 patients. Adrenomedullin levels were higher than in controls (19.2 +/- 1.4 vs. 13.3 +/- 0.7, p < 0.005) and elevated in proportion to NYHA functional class. B-type natriuretic peptide and NT-proBNP were 344 +/- 67 vs. 12 +/- 2 pg/ml and 2196 +/- 623 vs. 52 +/- 4 pg/ml, respectively (p < 0.0001); dP/dt was better related to AM (r = 0.582, p < 0.001) than to the other peptides. Adrenomedullin was significantly (p < 0.001) different between patients grouped according to the dP/dt cut-off predictive of event-free survival.

CONCLUSIONS

The combination of depressed contractility and increased AM may provide a clue for further characterization of the severity of LV dysfunction in HF, independent of baseline LV ejection fraction.

Adrenomedullin: regulator of systemic and cardiac homeostasis in acute myocardial infarction

During and following acute myocardial infarction, a variety of endogenous mediators are elevated, one of which is adrenomedullin (AM). AM is a multifunctional peptide that has been identified as having a putative beneficial role following an ischemic insult at both systemic and local levels. Classically described as a potent vasodilator, natriuretic, and diuretic agent, experimental infarct models also demonstrate AM to exhibit antiproliferative and antiapoptotic functions in the myocardium, counterregulating the effects of mediators such as angiotensin-II and endothelin-1. Less well documented are the angiogenic and inflammatory modulating potentials of AM, which may also contribute toward reducing adverse ventricular remodeling. The review examines clinical and experimental studies, looking at the effects of AM and cellular mechanisms that could be involved in mediating cardioprotective effects and ultimately optimizing left ventricular remodeling. Finally, the possibility of enhancing endogenous actions of AM by pharmacological intervention is considered.

Adrenomedullin gene expression and levels in the cardiovascular system after treatment with lipopolysaccharide

To study the effect of septicaemia, the temporal changes in tissue adrenomedullin (AM) and preproAM mRNA levels were studied in the heart and blood vessels after lipopolysaccharide (LPS) injection. Radioimmunoassay and solution hybridization-RNase protection assays were used to follow the changes in AM and its mRNA levels respectively after intraperitoneal injection of 10 mg/kg LPS in rats. The preproAM mRNA levels increased at 1 h in the right atrium after LPS injection, while the AM contents decreased at 1 h in the left atrium. The preproAM mRNA levels increased at 3 and 6 h in the left ventricle, whereas it increased at 6 h in the right ventricles after LPS injection. There was an increase in preproAM mRNA levels at 1 and 3 h in the mesenteric artery, while AM levels were increased at 1, 3 and 6 h. However, there were no such changes in the thoracic aorta. There were also increases in tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta and IL-6 in the heart, and in the mesenteric artery (TNF-alpha and IL-1beta) and in thoracic aorta (IL-1beta and IL-6). The present results suggest that the biosynthesis and secretion of AM may be increased in cardiovascular tissues of rats injected with LPS, and that AM may play multiple roles in inflammation.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by lysophosphatidic acid

Lysophosphatidic acid (LPA) is a bioactive phospholipid having growth factor-like activity on fibroblasts and is involved in cardiovascular diseases such as hypertension and heart failure by inducing vascular remodeling, characterized by fibroblast proliferation and migration in adventitia. Among various bioactive factors that LPA works with, adrenomedullin (ADM) is a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We studied rat aortic adventitia to explore the possible paracrine/autocrine interaction between endogenous ADM and LPA. LPA stimulation of the adventitia to secrete ADM and express its mRNA was concentration dependent. ADM inhibited LPA-induced proliferation in adventitial cells and attenuated the activity of mitogen-activated protein kinase (MAPK) stimulated by LPA. In contrast, treatment with specific antagonists of the ADM receptor potentiated the LPA-induced proliferation in adventitial cells. We concluded that LPA stimulates the adventitia to produce and secrete ADM, which in turn regulates the vascular biological effects of LPA.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Production and autocrine/paracrine effects of endogenous insulin-like growth factor-1 in rat cardiac fibroblasts

Insulin-like growth factor (IGF)-1 appears to play an important role in cardiac hypertrophy or remodeling. However, the role of endogenous IGF-1 in the growth of cardiac myocytes and fibroblasts remains unclear. This study investigated the major site of the production of cardiac IGF-1 and the local effects of endogenous IGF-1 secreted from cardiac cells. A significant expression of IGF-1 mRNA was found in cultured neonatal and adult rat cardiac fibroblasts, but not in myocytes. In addition, an in vivo examination by in situ hybridization histochemical analyses demonstrated the IGF-1 transcripts in the interstitial fibrotic tissue of the ventricle. Time-dependent secretion of IGF-1 protein was also observed in cultured cardiac fibroblasts. An antibody against IGF-1 decreased collagen synthesis in cardiac fibroblasts under basal conditions. Fibroblast-conditioned medium, as well as exogenous IGF-1, increased protein synthesis in cardiac myocytes, and this increase was inhibited by antibodies against IGF-1 and IGF-1 receptor, IGF binding protein-3, and IGF-1 receptor antagonist. These observations suggest that IGF-1 is produced and released mainly from cardiac fibroblasts and that endogenous IGF-1 promotes collagen synthesis by cardiac fibroblasts and hypertrophy of myocytes as an autocrine and a paracrine factor. Cardiac IGF-1 may function as an endogenous modulator of cardiac hypertrophy or remodeling.

Effects of adrenomedullin on aldosterone-induced cell proliferation in rat cardiac fibroblasts

Aldosterone induces cardiac remodeling in cardiovascular diseases by stimulating the proliferation, production and secretion of collagen in fibroblasts. It also stimulates vascular smooth muscle cells to produce and secrete adrenomedullin (ADM), which has a cytoprotective effect against cardiovascular damage. We examined the effect of aldosterone on ADM production and secretion in rat cardiac fibroblasts, and the effect of ADM on aldosterone-stimulated fibroblast proliferation to observe the interaction between endogenous ADM and aldosterone. We detected ADM produced and secreted from cultured cardiac fibroblasts and the intracellular cAMP level by radioimmunoassay; evaluated cell proliferation by the level of [3H]-thymine incorporation; measured preproADM gene expression by reverse transcriptase polymerase chain reaction (RT-PCR); and monitored extracellular signal related kinase (ERK) activity by the phosphorylation of myelin basic protein in the presence of [gamma-32P] ATP. Our results showed that aldosterone-stimulated secretion of ADM and its mRNA expression were concentration-dependent, which could be inhibited by the specific antagonist of mineralocorticoid receptor, spironolactone. In contrast, ADM inhibited aldosterone-induced fibroblast proliferation and ERK activity. Treatment with ADM24-50 (a new antagonist of specific ADM receptors) and calcitonin gene-related peptide (CGRP)8-37 (the antagonist of CGRP receptor type 1), to attenuate the action of endogenous ADM, reinforced the aldosterone-induced proliferation and inhibited the intracellular cAMP production stimulated by aldosterone. Thiorphan, an inhibitor of ADM degradation, inhibited the [3H]-thymine incorporation and reinforced the intracellular cAMP level induced by aldosterone. We reach the conclusion that aldosterone stimulates rat cardiac fibroblasts to produce and secrete ADM, which in turn regulates the proliferation-induced effects of aldosterone in these cells.

Adrenomedullin receptors: pharmacological features and possible pathophysiological roles

Three receptor activity modifying proteins (RAMPs) chaperone calcitonin-like receptor (CLR) to the cell surface. RAMP2 enables CLR to form an adrenomedullin (AM)-specific receptor that is sensitive to AM-(22-52) (AM(1) receptor). RAMP3 enables CLR to form an AM receptor sensitive to both calcitonin gene-related peptide (CGRP)-(8-37) and AM-(22-52) (AM(2) receptor), though rat and mouse AM(2) receptors show a clear preference for CGRP alpha-(8-37) over AM-(22-52). RAMP1 enables CRL to form the CGRP-(8-37)-sensitive CGRP(1) receptor, which can also be activated by higher concentrations of AM. Here we review the available information on the pharmacological features and possible pathophysiological roles of the aforementioned AM receptors.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by aldosterone

OBJECTIVE

Aldosterone is involved in cardiovascular diseases such as hypertension and heart failure by inducing sodium retention and vascular remodeling, which is characterized by fibroblast proliferation and migration in adventitia. It is well known that aldosterone stimulates vascular smooth muscle cells and fibroblasts to produce and secrete adrenomedullin (ADM), a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We examined the effect of aldosterone on ADM production and secretion and its mRNA expression in rat aortic adventitia to study the paracrine/autocrine interaction between endogenous ADM and aldosterone.

METHODS

ADM produced and secreted from adventitia stimulated by aldosterone in the absence or presence of spironolactone, RU486 or spironolactone together with RU486 were detected by radioimmunoassay, proliferation in adventitia cells was evaluated by the level of [H]-thymine incorporation, and preproADM gene expression was measured by semi-quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Adventitial ADM secretion and mRNA expression stimulated by aldosterone were concentration-dependent as was the inhibitive effect of ADM on aldosterone-induced proliferation. The induction of aldosterone in ADM secretion was mediated by mineralocorticoid receptor. Antagonists of specific receptors of calcitonin gene-related peptide (CGRP) receptor type 1 and ADM both potentiated the proliferation effect induced by aldosterone; and thiorphan, an inhibitor of the enzyme for ADM degradation, inhibited the adventitial [H]-thymine incorporation induced by aldosterone. ADM inhibited the activity of extracellular signal related kinase (ERK) stimulated by aldosterone.

CONCLUSION

Aldosterone stimulates adventitia to produce and secrete ADM, which in turn, antagonizes the aldosterone-induced proliferation in adventitia.

Thyroid hormone and blood pressure regulation

Thyroid hormone has well-recognized effects on the cardiovascular system and blood pressure regulation. Blood pressure is altered across the entire spectrum of thyroid disease. The effects of hyperthyroidism include increased cardiac output, contractility, tachycardia, widened pulse pressure, decreased systemic vascular resistance, and increased basal metabolic rate. The manifestations of hypothyroidism are in marked contrast to those of hyperthyroidism and include decreased cardiac output, narrow pulse pressure, increased systemic vascular resistance, and decreased metabolic rate. Although thyroid hormone affects almost all tissues of the body and mediates changes in homeostasis, adaptations of the cardiovascular system can result in changes in blood pressure to accommodate the new demands on the system. In this paper, we review the direct and indirect thyroid hormone-mediated effects on blood pressure.

Tumor necrosis factor-alpha downregulates adrenomedullin receptors in human coronary artery smooth muscle cells

We examined the effects of tumor necrosis factor (TNF)-alpha on the expression and functionality of adrenomedullin (AM) receptors in cultured human coronary artery smooth muscle cells. Analysis of real-time quantitative polymerase chain reactions showed that these cells abundantly express two AM receptors comprised of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1) or RAMP2. TNF-alpha induced time- and dose-dependent decreases in the expression of CRLR and RAMP1/2 mRNAs, thereby diminishing AM-evoked cAMP production. The suppression of these three mRNAs was unaffected by inhibiting NOS, protein kinase G, protein kinase A, superoxide formation or NF-kappaB activation.

Cardiac expression of urocortin (Ucn) in diseased heart; preliminary results on possible involvement of Ucn in pathophysiology of cardiac diseases

Recently, several studies reported that urocortin (Ucn) had beneficial effects on cardiovascular system and was expressed both in the normal heart and in the heart of dilated cardiomyopathy (DCM), yet the relationship between high expression of Ucn and pathophysiology of Ucn in diseased heart has been discussed. Thus, the present study was designed to elucidate the expression of Ucn in the diseased heart by immunohistochemical approach using endomyocardial biopsy specimens. The involvement of immunoreactive Ucn in pathophysiology of cardiac disease was evaluated using endomyocardial biopsy specimens obtained from the patients with some heart diseases, including DCM and hypertrophic cardiomyopathy (HCM). Ucn was detected in all endomyocardial biopsy specimens of ventricular tissue obtained from the patients with such cardiac diseases, a specimens of atrial tissue, and normal heart specimens obtained from autopsy cases. In DCM patients, left ventricular end-diastolic pressure significantly elevated in severely stained group. On the contrary, in HCM patients, left ventricular ejection fraction was higher in the severely stained group. Ucn was expressed more abundantly in the diseased heart, especially in HCM and DCM, than in the normal heart. In conclusion, such close relationship between Ucn expression in the heart and cardiac function indicated that clinical features of Ucn resembled those of norepinephrine and Ucn could play a certain pathophysiological roles in the cardiac diseases.

Upregulation of ligand, receptor system, and amidating activity of adrenomedullin in left ventricular hypertrophy of severely hypertensive rats: effects of angiotensin-converting enzyme inhibitors and diuretic

OBJECT

We investigated the pathophysiological role of the cardiac adrenomedullin (AM) system, including the ligand, receptor and amidating activity in the hypertrophied heart in severe hypertension.

METHOD

We studied the following four groups: control Wistar-Kyoto rats (WKY), spontaneously hypertensive stroke-prone rats (SHR-SP), 8 weeks captopril-treated SHR-SP, and 8 weeks trichlormethiazide-treated SHR-SP. AM precursor is converted to inactive glycine-extended AM (AM-Gly) and subsequently AM-Gly is converted to active mature AM (AM-m) by enzymatic amidation. We measured AM-m, AM-total (AM-T; AM-T = AM-m + AM-Gly), and atrial natriuretic peptide (ANP) in the plasma and left ventricle (LV) by immunoradiometric assay. We also measured gene expression of AM and ANP was and gene expression and protein levels of AM receptor system components such as calcitonin receptor-like receptor (CRLR), receptor-activity modifying protein (RAMP) 2 and RAMP3.

RESULTS

At 7 weeks old, SHR-SP had higher blood pressure and ANP mRNA levels and lower plasma AM-T compared with WKY, however, there were no differences in other indices between the two groups. At 17 weeks old, SHR-SP had increased blood pressure, LV weight, plasma and LV ANP levels and mRNA levels of ANP compared with WKY. AM-m and AM-T levels in plasma (AM-m: + 31%; AM-T: + 56%) and the LV (AM-m: + 84%; AM-T: + 31%) were significantly higher in SHR-SP than in WKY. The LV tissue AM-m/AM-T ratio was significantly higher in SHR-SP (93.2%) than in WKY. The mRNA levels of AM, CRLR, and RAMP2 in the LV were significantly higher in SHR-SP than in WKY. Captopril and trichlormethiazide similarly decreased blood pressure and LV hypertrophy with the reduction of the LV AM-m and AM-T levels and mRNA abundance of AM and its receptor component.

CONCLUSION

These results suggest that cardiac AM system is upregulated in the hypertrophied heart in this hypertension model. Considering that AM acts as an anti-remodeling autocrine and/or paracrine factor, upregulation of the AM system may modulate the pathophysiology in LV hypertrophy.

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.

Altered gene expression of adrenomedullin and its receptor system and molecular forms of tissue adrenomedullin in left ventricular hypertrophy induced by malignant hypertension

To investigate the pathophysiological role of adrenomedullin (AM) in left ventricular hypertrophy (LVH) in hypertension, we measured the plasma level, left ventricle (LV) tissue level, and mRNA abundance of AM and the mRNA abundance of the AM receptor system in the LV. We also analyzed the molecular forms of AM in the plasma and LV tissue and investigated the relationships between AM and the degree of LVH. We studied the following three groups: control Wistar Kyoto rats (WKY), control spontaneously hypertensive rats (SHR), and deoxycorticosterone acetate (DOCA)-salt SHR (D-SHR). We measured AM-mature, active form, and AM-total (active form+inactive form) in plasma and the LV by a newly developed immunoradiometric assay. Gene expression of AM was measured by Northern blot analysis and gene expression of AM receptor system components, such as calcitonin receptor-like receptor (CRLR), receptor activity modifying protein 2 (RAMP2), and RAMP3 was measured by the reverse transcription polymerase chain reaction method. After 3 weeks of DOCA treatment, D-SHR was characterized by higher blood pressure, LV weight, and plasma atrial natriuretic peptide levels compared with those in the other two groups. Plasma AM-mature and AM-total levels were significantly higher in D-SHR than in the other two groups, whereas there were no significant differences in the AM-mature/AM-total ratio among the three groups. On the other hand, LV tissue AM-mature and AM-total levels were also significantly higher in D-SHR than in the other two groups, and the AM-mature/AM-total ratio was significantly higher in LV tissues than in plasma. Furthermore, the LV tissue AM-mature/AM-total ratio was significantly higher in D-SHR compared with the other two groups. The LV tissue AM-mature/AM-total ratio was significantly correlated with LV weight/body weight (r=0.92, p<0.001). The gene expression levels of AM, CRLR, RAMP2, and RAMP3 in the LV were significantly higher in D-SHR than in the other two groups. These results suggest that the AM amidating enzyme activity, ligand, and receptor system are all upregulated in the LV hypertrophy in this malignant hypertensive rat model. Considering that AM serves as a local antihypertrophic autocrine and/or paracrine factor, the induction of AM system observed here may modulate the pathophysiology of LV hypertrophy in certain forms of malignant hypertension.

Regulation of production and secretion of adrenomedullin in the cardiovascular system

Adrenomedullin (AM) has multi-functional properties, of which the vasodilatory hypotensive effect is the most characteristic. AM and its gene are ubiquitous in a variety of tissues and organs, in the cardiovascular system, as well as the adrenal medulla. AM secretion, especially in cardiovascular tissues, is regulated mainly by mechanical stressors such as shear stress, inflammatory cytokines such as interleukin (IL)-1, tumor necrosis factor (TNF), and lipopolysaccharide (LPS), hormones such as angiotensin (Ang) II and endothelin (ET)-1, and metabolic factors such as hypoxia, ischemia, or hyperglycemia. Elevation of plasma AM due to overproduction in response to one or more of these stimuli in pathological conditions may explain the raised plasma AM levels present in cardiovascular and renal diseases such as congestive heart failure, myocardial infarction, hypertension, chronic renal failure, stroke, diabetes mellitus, and septic shock. In addition to shear stress, stretching of cardiomyocytes may be another mechanical stimulus for AM synthesis and secretion. Our recent studies have shown the importance of aldosterone and additional hormonal factor on AM secretion in vascular wall.

Specificity of porcine calcitonin receptor and calcitonin receptor-like receptor in the presence of receptor-activity-modifying proteins

Adrenomedullin (AM), calcitonin gene-related peptide (CGRP), amylin (AMY) and calcitonin (CT) are members of the CGRP/CT superfamily of peptides. Among them, AM and CGRP are reported to share a core receptor, the calcitonin receptor-like receptor (CRLR), and the specificity of the CRLR is determined by the expression levels of receptor-activity-modifying proteins (RAMPs). In the case of AMY, co-expression of the calcitonin receptor (CTR) and RAMPs was recently reported to form its specific receptor. However, detailed analysis of the receptor specificity of the CRLR and CTR in the presence of RAMPs has so far been performed mainly in the human system. Thus, we cloned cDNAs encoding porcine CRLR, RAMP1, RAMP2 and RAMP3 precursors from a porcine lung and hypothalamus cDNA library, and determined their sequences. Then, porcine RAMPs, CRLR and CTR were expressed in COS-7 or porcine vascular smooth muscle cells, and the resulting receptor complexes were analyzed by the cyclic adenosine 3,5-monophosphate (cAMP) production assay. The specificity of CRLR was clearly determined by the expression of RAMPs; RAMP1 converted CRLR to CGRP receptor, while RAMP2 and RAMP3 converted it to AM receptor, but the affinity of CTR for AMY was not increased by the expression of any known RAMPs. In contrast to previous findings, porcine CTR and RAMP did not appear to form an AMY receptor having sufficient affinity and specificity for the physiological interaction.

Variations of human adrenomedullin gene and its relation to cardiovascular diseases

The studies concerning the structure and variations of the human adrenomedullin (AM) gene are reviewed, and their relations to the gene function and genetic predisposition to cardiovascular diseases are discussed. The genomic human AM gene is composed of four exons, and the whole nucleotide sequence corresponding to mature AM resides in the fourth exon. In chromosomal sublocalization, the AM gene is located in the distal portion of the short arm of chromosome 11 (11p15.1-3). Analysis of the promoter region of the AM gene has revealed that two transcription factors, nuclear factor for interleukin-6 expression (NF-IL6) and activator protein 2 (AP-2), participate in the regulation of AM gene expression. It is surmised that NF-IL6 mediates inflammatory stimuli and AP-2 mediates signals of phospholipase C and protein kinase C activation. In addition to these factors, hypoxia induces AM gene expression via the hypoxia inducible factor-1 (HIF-1) binding site. The 3'-end of the AM gene is flanked by a microsatellite marker of cytosine adenine (CA) repeats. In Japanese, there are four types of alleles with different CA-repeat numbers: 11, 13, 14 and 19. It is suggested that existence of the 19-repeat allele is associated with genetic predispositions to develop essential hypertension and diabetic nephropathy.

Adrenomedullin selectivity of calcitonin-like receptor/receptor activity modifying proteins

Co-expression of an initially orphan calcitonin receptor-like (CL)1 receptor with individual receptor-activity-modifying proteins (RAMP)1, -2 and -3 results in CL receptor/RAMP1, -2 and -3 proteins at the cell surface. The RAMP define the selectivity of the CL receptor for the vasodilatory peptides adrenomedullin (AM) and calcitonin gene-related peptide (CGRP). The selectivity for AM and CGRP agonists and antagonists of human, rat, porcine and bovine CL receptors, co-expressed with RAMP2 and -3, has been studied in different cell types. This revealed CL receptor/RAMP2 and CL receptor/RAMP3 as AM1 and AM2 receptor subtypes, respectively. The AM1 receptor crossreacts with CGRP at high and the AM2 receptor at lower concentrations. Here the pharmacological properties of the cloned AM receptors are compared to those revealed in tissues and cell lines. According to nomenclature recommendation of the IUPHAR (International Union of Pharmacology) subcommittee XXXII, the former CRLR is now the CL receptor (1).

Adrenomedullin: a possible autocrine or paracrine hormone in the cardiac ventricles

Adrenomedullin (AM), a potent vasodilator peptide originally isolated from pheochromocytoma, is expressed in cardiovascular tissues such as those of the cardiac atria and ventricles. Cell culture experiments have shown that AM peptide is synthesized and secreted from cardiac myocytes and fibroblasts of neonatal rats. Humoral factors, such as angiotensin II (Ang II) and endothelin-1 (ET-1), and mechanical stress due to pressure and volume overload to the heart have been shown to be involved in AM expression of the myocardium in both in vitro and in vivo studies. The effects of AM on cardiomyocytes and cardiac fibroblasts have been examined in in vitro studies, with the result that AM was shown to exert inhibitory actions on myocyte hypertrophy and on proliferation and collagen production of cardiac fibroblasts in an autocrine or paracrine manner. In rats, experimental therapeutic intervention consisting of transfer of the AM gene or of recombinant AM appears to partly inhibit the progression of cardiac hypertrophy and remodeling. It has been shown that the calcitonin receptor-like receptor (CRLR) and receptor-activity-modifying protein (RAMP) act together to function as AM receptors, although in this regard there are a number of issues, including the cellular mechanism of AM actions, that remain to be addressed. In addition, the role of proadrenomedullin N-terminal 20 peptide (PAMP), which is derived from preproAM, is another topic for future experiments. Collectively, the research data accumulating in this area suggest that AM plays a role as an autocrine or paracrine hormone in the cardiac ventricles, and that AM might be utilized as a therapeutic tool in the treatment of hypertensive or ischemic heart disease.

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.

The calcitonin receptor-like receptor/receptor activity-modifying protein 1 heterodimer can function as a calcitonin gene-related peptide-(8-37)-sensitive adrenomedullin receptor

The receptor activity-modifying protein (RAMP)/calcitonin receptor-like (CRL) receptor heterodimer is thought to function as a receptor for either a calcitonin gene-related peptide (CGRP) (CRL receptor/RAMP1) or adrenomedullin (CRL receptor/RAMP2 or -3), depending on the RAMP isoform present. We examined the receptor specificity of adrenomedullin-induced increases in cAMP in human embryonic kidney (HEK)293 cells coexpressing human CRL receptor and human RAMP1 or RAMP2. In cells expressing CRL receptor/RAMP1, adrenomedulin-induced increases in cAMP were comparable to those induced by alpha-CGRP, and the CGRP receptor antagonist alpha-CGRP-(8-37), but not the adrenomedullin receptor antagonist adrenomedullin-(22-52), blocked the adrenomedullin-evoked responses. Cells expressing CRL receptor/RAMP2 responded more selectively to adrenomedullin; in this case, the effect was blocked by adrenomedullin-(22-52) but not by alpha-CGRP-(8-37). Real-time quantitative polymerase chain reaction confirmed that cotransfection of CRL receptor and RAMP1 had no effect on the endogenous expression of RAMP2. Thus, CRL receptor/RAMP1 likely functions as an adrenomedullin receptor as well as a CGRP receptor, which may explain why many of the actions of adrenomedullin are potently antagonized by alpha-CGRP-(8-37).

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.

Regulation of adrenomedullin secretion from cultured cells

Characterization of immunoreactive adrenomedullin (AM) secreted from cultured human vascular smooth muscle cells and 7 other cells indicates that AM is synthesized and secreted from all cultured cells we surveyed. The secretion rate of AM measured ranges from 0.001-6.83 fmol/10(5) cells/h, and endothelial cells, vascular smooth muscle cells and fibroblasts generally secrete AM at high rates. Based on the results of regulation of AM secretion from vascular wall cells, fibroblasts, macrophages and other cells measured in this and previous studies, AM secretion is found to be generally stimulated by inflammatory cytokines, lipopolysaccharide (LPS) and hormones. Especially, vascular smooth muscle cells and fibroblasts elicited uniform and strong stimulatory responses of AM secretion to tumor necrosis factor (TNF), interleukin-1 (IL-1), LPS and glucocorticoid, but endothelial cells did not elicit such prominent responses. AM secretion of monocyte-macrophage was mainly regulated by the degree of differentiation into macrophage and activation by LPS and inflammatory cytokines including interferon-gamma. The other examined cells showed weaker responses to LPS and IL-1. Although cultured cells may have been transformed as compared with those in the tissue, these data indicate that AM is widely synthesized and secreted from most of the cells in the body and functions as a local factor regulating inflammation and related reactions in addition to as a potent vasodilator. The responses of AM secretion to LPS and inflammatory cytokines suggest that fibroblasts, vascular smooth muscle cells and macrophage are the major sources of AM in the septic shock.

Effects of endothelin on adrenomedullin secretion and expression of adrenomedullin receptors in rat cardiomyocytes

Both endothelin (ET) and adrenomedullin (AM), produced by cardiac myocytes, are thought to be locally-acting hormones in the heart. Recently, calcitonin receptor-like receptor (CRLR) and receptor activity modifying proteins (RAMPs) have been shown to function together to serve as AM receptors stimulating cAMP production. In the present study, we examined the effects of ET on AM secretion, intracellular cAMP response to AM, and gene expressions of CRLR and RAMPs in cultured cardiac myocytes. Synthetic ET-1 dose-dependently increased AM secretion from the cardiomyocytes. AM increased the intracellular cAMP level in a dose-dependent manner and the cAMP accumulation by AM was significantly amplified by 24 h preincubation with ET-1. 10 nmol/L ET-1 significantly increased the CRLR mRNA level without any effect on RAMP1 mRNA. 1 micromol/L ET-1 significantly reduced the RAMP2 mRNA level, but ET-1 dose-dependently increased the RAMP3 mRNA level in the cardiac myocytes. These findings suggest that ET-1 not only stimulates AM secretion, but also modulates intracellular cAMP responses to AM probably by altering the expressions of CRLR and RAMPs in rat cardiomyocytes.