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

Cellular cross talk between epicardial fat and cardiovascular risk

A variety of fat compartments have several local and systemic effect and play a crucial role in the maintenance of health and development of disease. For the past few years, special attention has been paid to epicardial fat. It is the visceral fat compartment of the heart and has several local and systemic effects. It can perform a role in the development of cardiometabolic risk. The epicardial adipose tissue (EAT) is a unique and multifunctional fat compartment of the heart. It is located between the myocardium and the visceral pericardium. During normal physiological conditions, the EAT has metabolic, thermogenic, and mechanical (cardioprotective) characteristics. The EAT can produce several adipocytokines and chemokines depending on microenvironments. It can influence through paracrine and vasocrine mechanism and participate in the development and progression of cardiovascular (CVS) diseases. In addition, metabolic disease leads to changes in both thickness and volume of the EAT, and it can modify the structure and the function of heart. It has been associated with various CVS diseases such as, cardiomyopathy, atrial fibrillation, and coronary artery disease. Therefore, EAT is a potential therapeutic target for CVS risk.

Donor Human Milk: Effects of Storage and Heat Treatment on Oxidative Stress Markers

Mother's own milk is the first choice for the feeding and nutrition of preterm and term newborns. When mother's own milk is unavailable or in short supply donor human milk (DM) could represent a solution. Heat treatment and cold storage are common practices in Human Milk Banks (HMBs). Currently, Holder pasteurization process is the recommended heat treatment in all international guidelines. This method is thought to lead to a good compromise between the microbiological safety and nutritional/biological quality of DM. Moreover, storage of refrigerated milk is a common practice in HMBs and in NICUs. Depending on the length and on the type of storage, human milk may lose some important nutritional and functional properties. The available data on oxidative stress markers confirm that pasteurization and refrigeration affected this important elements to variable degrees, even though it is rather difficult to quantify the level of deterioration. Nonetheless, clinical practice demonstrates that many beneficial properties of human milk are preserved, even after cold storage and heat treatment. Future studies should be focused on the evaluation of new pasteurization techniques, in order to achieve a better compromise between biological quality and safety of DM.

Adrenomedullin, a Novel Target for Neurodegenerative Diseases

Neurodegenerative diseases represent a heterogeneous group of disorders whose common characteristic is the progressive degeneration of neuronal structure and function. Although much knowledge has been accumulated on the pathophysiology of neurodegenerative diseases over the years, more efforts are needed to understand the processes that underlie these diseases and hence to propose new treatments. Adrenomedullin (AM) is a multifunctional peptide involved in vasodilation, hormone secretion, antimicrobial defense, cellular growth, and angiogenesis. In neurons, AM and related peptides are associated with some structural and functional cytoskeletal proteins that interfere with microtubule dynamics. Furthermore, AM may intervene in neuronal dysfunction through other mechanisms such as immune and inflammatory response, apoptosis, or calcium dyshomeostasis. Alterations in AM expression have been described in neurodegenerative processes such as Alzheimer's disease or vascular dementia. This review addresses the current state of knowledge on AM and its possible implication in neurodegenerative diseases.

Human Milk Adrenomedullin Is Unstable During Cold Storage at 4°C

INTRODUCTION

Under some circumstances human milk (HM) extraction and refrigerated storage may be necessary. Depending on the length and on the type of cold storage, milk may lose some important properties, but current advices on safe HM storage are discordant. Moreover until now no data in literature were present on the effect of prolonged cold storage on biologically active components of the HM such as adrenomedullin (AM). This important peptide is involved in response to hypoxia and inflammation, associated with neovascularization, in several tissues. The aim is to evaluate: (a) the presence of AM in preterm and term HM and (b) the concentration of AM in refrigerated milk at 4°C at 24-hour intervals, up to 96 hours of storage.

MATERIALS AND METHODS

The experiment was repeated four times. Immediately after collection, each HM sample deriving from each mother was divided into two parts as follows: "Pool" line and "Single Mother" line. One part (Pool line) was pooled and then divided into five aliquots. The other part (Single Mother line) was divided into five aliquots. From each line, one aliquot was analyzed within 3 hours, while the others were stored in the refrigerator for 24, 48, 72, and 96 hours, respectively, and then analyzed. AM levels were determined using a specific ELISA test.

RESULTS

AM was detectable in all samples. Its concentration was significantly higher in preterm milk with respect to term milk (p < 0.05). Significant differences were observed during the cold storage: the AM levels decreased steadily during the storage and the remaining concentration at 96 hours is ∼2%.

DISCUSSION

This study provides evidences regarding the presence of AM in HM, regardless of the gestational age. In particular, the refrigeration of fresh HM in controlled conditions significantly affected its bioactivity and nutritional quality related with AM, already at 24 hours.

Protective Effect of Daikenchuto on Dextran Sulfate Sodium-Induced Colitis in Mice

Aim. To investigate the effect of daikenchuto (TJ-100; DKT) for ulcerative colitis (UC) model mouse and assess its anti-inflammatory mechanisms. Methods. We evaluated the effects of DKT on dextran sulfate sodium- (DSS-) induced experimental colitis. First, we assessed the short-term effects of DKT using two groups: 5% DSS group and 5% DSS with DKT group. Colon length; histological scores; and interleukin- (IL-) 10, IL-1β, and tumor necrosis factor-α mRNA expression profiles were analyzed using real-time PCR. Second, we assessed the long-term effects of DKT, by comparing survival time between 2% DSS and 2% DSS with DKT groups. Results. After 7 days, the colon lengths of DSS + DKT group were longer than those of the DSS group (mean values: 6.11 versus 5.69 cm, p < 0.05). Furthermore, compared to DSS group, the DSS + DKT group maintained significantly higher levels of serum hemoglobin (13.1 versus 10.7 g/dL, p < 0.05) and exhibited significantly higher expression levels of IL-10 (p < 0.05). The 2% DSS + DKT group exhibited significantly longer survival time than the 2% DSS group (70 versus 44 days, p < 0.01). Conclusion. Our results indicate that DKT prevented inflammation in the colon, indicating its potential as a new therapeutic agent for UC.

Endothelial Restoration of Receptor Activity-Modifying Protein 2 Is Sufficient to Rescue Lethality, but Survivors Develop Dilated Cardiomyopathy

RAMPs (receptor activity-modifying proteins) serve as oligomeric modulators for numerous G-protein-coupled receptors, yet elucidating the physiological relevance of these interactions remains complex. Ramp2 null mice are embryonic lethal, with cardiovascular developmental defects similar to those observed in mice null for canonical adrenomedullin/calcitonin receptor-like receptor signaling. We aimed to genetically rescue the Ramp2(-/-) lethality in order to further delineate the spatiotemporal requirements for RAMP2 function during development and thereby enable the elucidation of an expanded repertoire of RAMP2 functions with family B G-protein-coupled receptors in adult homeostasis. Endothelial-specific expression of Ramp2 under the VE-cadherin promoter resulted in the partial rescue of Ramp2(-/-) mice, demonstrating that endothelial expression of Ramp2 is necessary and sufficient for survival. The surviving Ramp2(-/-) Tg animals lived to adulthood and developed spontaneous hypotension and dilated cardiomyopathy, which was not observed in adult mice lacking calcitonin receptor-like receptor. Yet, the hearts of Ramp2(-/-) Tg animals displayed dysregulation of family B G-protein-coupled receptors, including parathyroid hormone and glucagon receptors, as well as their downstream signaling pathways. These data suggest a functional requirement for RAMP2 in the modulation of additional G-protein-coupled receptor pathways in vivo, which is critical for sustained cardiovascular homeostasis. The cardiovascular importance of RAMP2 extends beyond the endothelium and canonical adrenomedullin/calcitonin receptor-like receptor signaling, in which future studies could elucidate novel and pharmacologically tractable pathways for treating cardiovascular diseases.

Epicardial Fat: Physiological, Pathological, and Therapeutic Implications

Epicardial fat is closely related to blood supply vessels, both anatomically and functionally, which is why any change in this adipose tissue's behavior is considered a potential risk factor for cardiovascular disease development. When proinflammatory adipokines are released from the epicardial fat, this can lead to a decrease in insulin sensitivity, low adiponectin production, and an increased proliferation of vascular smooth muscle cells. These adipokines move from one compartment to another by either transcellular passing or diffusion, thus having the ability to regulate cardiac muscle activity, a phenomenon called vasocrine regulation. The participation of these adipokines generates a state of persistent vasoconstriction, increased stiffness, and weakening of the coronary wall, consequently contributing to the formation of atherosclerotic plaques. Therefore, epicardial adipose tissue thickening should be considered a risk factor in the development of cardiovascular disease, a potential therapeutic target for cardiovascular pathology and a molecular point of contact for "endocrine-cardiology."

The heart as an endocrine organ

The concept of the heart as an endocrine organ arises from the observation that the atrial cardiomyocytes in the mammalian heart display a phenotype that is partly that of endocrine cells. Investigations carried out between 1971 and 1983 characterised, by virtue of its natriuretic properties, a polypeptide referred to atrial natriuretic factor (ANF). Another polypeptide isolated from brain in 1988, brain natriuretic peptide (BNP), was subsequently characterised as a second hormone produced by the mammalian heart atria. These peptides were associated with the maintenance of extracellular fluid volume and blood pressure. Later work demonstrated a plethora of other properties for ANF and BNP, now designated cardiac natriuretic peptides (cNPs). In addition to the cNPs, other polypeptide hormones are expressed in the heart that likely act upon the myocardium in a paracrine or autocrine fashion. These include the C-type natriuretic peptide, adrenomedullin, proadrenomedullin N-terminal peptide and endothelin-1. Expression and secretion of ANF and BNP are increased in various cardiovascular pathologies and their levels in blood are used in the diagnosis and prognosis of cardiovascular disease. In addition, therapeutic uses for these peptides or related substances have been found. In all, the discovery of the endocrine heart provided a shift from the classical functional paradigm of the heart that regarded this organ solely as a blood pump to one that regards this organ as self-regulating its workload humorally and that also influences the function of several other organs that control cardiovascular function.

Adrenomedullin attenuates vascular calcification in fructose-induced insulin resistance rats

AIM

To determine the therapeutic effects of adrenomedullin (ADM) on vascular calcification and related molecular mechanism in fructose-induced insulin resistance rats.

METHODS

Rats received ordinary drinking water or 10% fructose in drinking water for 12 weeks and subcutaneous injection of normal saline or ADM (3.6 μg kg(-1) ) twice a day for the last 4 weeks. Levels of ADM, calcitonin receptor-like receptors (CRLR), receptor activity-modifying proteins (RAMP) as well as calcium content, alkaline phosphatase (ALP) activity, osteoblastic and contractile smooth muscle markers in aortic media were measured.

RESULTS

The levels of ADM, CRLR, RAMP2 and RAMP3 in aortic media were increased in fructose-fed rats. ADM treatment attenuated the fructose-induced insulin resistance, increased blood pressure, fasting glucose, insulin, triglycerides and cholesterol levels. It improved VSMCs proliferation and disordered arrangement and hyperplasia of elastic fibres in fructose-fed rats. Calcium deposits, calcium content and ALP activity in the aortic media were increased in fructose-fed rats, which were attenuated by ADM treatment. The osteoblastic markers such as osteopontin (OPN), bone morphogenetic protein 2 (BMP2) proteins and core binding factor alpha-1 (Cbfα-1) protein and mRNA expressions were increased in fructose-fed rats. ADM treatment increased the OPN protein expression, but reduced the BMP2 protein, Cbfα-1 protein and mRNA expression. Contractile smooth muscle markers such as α-actin and smooth muscle 22α (SM-22α) were downregulated in fructose-fed rats, which were recovered by ADM treatment.

CONCLUSION

Administration of ADM attenuates insulin resistance, calcium deposition and osteogenic transdifferentiation in aortic media in fructose-fed rats.

Adrenomedullin Function in Vascular Endothelial Cells: Insights from Genetic Mouse Models

Adrenomedullin is a highly conserved peptide implicated in a variety of physiological processes ranging from pregnancy and embryonic development to tumor progression. This review highlights past and present studies that have contributed to our current appreciation of the important roles adrenomedullin plays in both normal and disease conditions. We provide a particular emphasis on the functions of adrenomedullin in vascular endothelial cells and how experimental approaches in genetic mouse models have helped to drive the field forward.

Anti-colitis and -adhesion effects of daikenchuto via endogenous adrenomedullin enhancement in Crohn's disease mouse model

BACKGROUND AND AIMS

Adrenomedullin (ADM) is a member of the calcitonin family of regulatory peptides, and is reported to have anti-inflammatory effects in animal models of Crohn's disease (CD). We investigated the therapeutic effects of daikenchuto (DKT), an extracted Japanese herbal medicine, on the regulation of endogenous ADM in the gastrointestinal tract in a CD mouse model.

METHODS

Colitis was induced in mice by intrarectal instillation of 2,4,6-trinitrobenzenesulfonic acid (TNBS); afterwards, DKT was given orally. Colonic damage was assessed on day 3 by macroscopic and microscopic observation, enzyme immunoassays of proinflammatory cytokines in the colonic mucosa, and serum amyloid A (SAA), a hepatic acute-phase protein. To determine the involvement of ADM, an ADM antagonist was instilled intrarectally before DKT administration. The effect of DKT on ADM production by intestinal epithelial cells was evaluated by enzyme immunoassay and real-time PCR.

RESULTS

DKT significantly attenuated mucosal damage and colonic inflammatory adhesions, and inhibited elevations of SAA in plasma and the proinflammatory cytokines TNFα and IFNγ in the colon. Small and large intestinal epithelial cells produced higher levels of ADM after DKT stimulation. A DKT-treated IEC-6 cell line also showed enhanced ADM production at protein and mRNA levels. Abolition of this effect by pretreatment with an ADM antagonist shows that DKT appears to exert its anti-colitis effect via up-regulation of endogenous ADM in the intestinal tract.

CONCLUSION

DKT exerts beneficial effects in a CD mouse model through endogenous release and production of ADM. Endogenous ADM may be a therapeutic target for CD.

Increased plasma levels of the mature and intermediate forms of adrenomedullin in obesity

Adrenomedullin (AM) is a cardiovascular protective peptide produced in various organs and tissues including adipose tissue. In the present study, we measured the plasma AM levels of subjects with or without obesity by two assay methods to separately evaluate the biologically active AM-NH(2) and the intermediate form of AM-glycine (AM-Gly). We measured the total AM and AM-NH(2) levels of plasma in 52 obese and 172 non-obese residents of a Japanese community, who received regular health check-ups and had no overt cardiovascular disease. AM-Gly values were obtained by subtracting AM-NH(2) levels from those of total AM. Both the AM-NH(2) and AM-Gly levels of the subjects with obesity were higher than those without obesity, and significant relationships were noted between body mass index (BMI) and the plasma levels of the two molecular forms of AM in a simple regression analysis. Moreover, the significant factors identified by multivariate analyses were BMI and serum triglyceride for AM-NH(2) and diastolic blood pressure, insulin, high-density lipoprotein-cholesterol, and plasma renin activity for AM-Gly. These results suggest active roles for the two molecular forms of AM in metabolic disorders associated with obesity in subjects without overt cardiovascular disease.

Midregional proadrenomedullin as a prognostic tool in community-acquired pneumonia

BACKGROUND

Midregional proadrenomedullin (MR-proADM) is a potential prognostic biomarker in patients with community-acquired pneumonia (CAP). Previous work has been hampered by sample size and illness spectrum limits. We sought to describe the pattern of MR-proADM in a broad CAP cohort, confirm its prognostic role, and compare its performance to procalcitonin, a novel biomarker of infection.

METHODS

We conducted a multicenter prospective cohort study in 28 community and teaching EDs. Patients with a clinical and radiographic diagnosis of CAP were enrolled. We stratified MR-proADM levels a priori into quartiles and quantified severity of illness using the pneumonia severity index (PSI); and confusion (abbreviated mental test score of <or= 8), urea >or= 7 mmol/L, respiratory rate >or= 30 breaths/min, BP < 90 mm Hg systolic or < 60 mm Hg diastolic, age >or= 65 years (CURB-65). The primary outcome was 30-day mortality.

RESULTS

A total of 1,653 patients formed the study cohort. MR-proADM levels consistently rose with PSI class and 30-day mortality (p < 0.001). MR-proADM had a higher area under the curve for 30-day mortality than procalcitonin (0.76 vs 0.65, respectively; p < 0.001), but adding MR-proADM to the PSI in all subjects minimally improved performance. Among low-risk subjects (PSI classes I to III), mortality was low and did not differ by MR-proADM quartile. However, among high-risk subjects (PSI class IV/V; n = 546), subjects in the highest MR-proADM quartile (n = 232; 42%) had higher 30-day mortality than those in MR-proADM quartiles 1 to 3 (23% vs 9%, respectively; p < 0.0001). Similar results were seen with CURB-65. MR-proADM and procalcitonin levels were generally concordant; only 6% of PSI class IV/V subjects in the highest MR-proADM quartile had very low procalcitonin levels (< 0.1 ng/mL).

CONCLUSIONS

In our multicenter CAP cohort, MR-proADM levels correlate with increasing severity of illness and death. High MR-proADM levels offer additional risk stratification in high-risk CAP patients, but otherwise MR-proADM levels do not alter PSI-based risk assessment in most CAP patients.

The relationship between adrenomedullin, metabolic factors, and vascular function in individuals with type 2 diabetes

OBJECTIVE

Subjects with type 2 diabetes are at risk for vascular injury. Several vasoactive factors (e.g., angiotensin) have been implicated. We hypothesize that adrenomedullin, a novel vascoactive factor, is deranged in subjects with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Using a new immunoluminometric method, plasma midregional proadrenomedullin (MR-proADM) was measured in four groups of Chinese subjects: healthy (n = 100, fasting plasma glucose [FPG] <5.6 mmol/l), impaired fasting glucose (IFG) (n = 60, FPG 5.6-6.9 mmol/l), and diabetic subjects with (n = 100) and without (n = 100) nephropathy. Resting forearm cutaneous microcirculatory perfusion (RCMP) was quantified in vivo using 2-dimensional laser Doppler flowmetry. We investigated the relationship between plasma MR-proADM concentrations, multiple metabolic factors, and vascular function.

RESULTS

We observed a stepwise increase in MR-proADM among the groups: healthy group mean +/- SD 0.27 +/- 0.09, IFG group 0.29 +/- 0.13, diabetic group 0.42 +/- 0.13, and diabetic nephropathy group 0.81 +/- 0.54 nmol/l (diabetic vs. healthy and IFG groups, P = 0.04; and diabetic nephropathy group vs. all, P < 0.01). Statistical adjustment for sex, age, BMI, and blood pressure did not affect the conclusions. Multiple linear regression analysis revealed that highly sensitive C-reactive protein (beta = 0.11; P = 0.01), insulin resistance index (beta = 0.20; P = 0.001), LDL cholesterol (beta = 0.31; P < 0.001), and adiponectin (beta = 0.33; P < 0.001) were significant predictors of plasma MR-proADM concentrations among nondiabetic individuals. Among subjects with diabetes, plasma MR-proADM concentrations correlated significantly with RCMP (r = 0.43, P = 0.002).

CONCLUSIONS

Plasma MR-proADM concentration was elevated in subjects with type 2 diabetes. This was further accentuated when nephropathy set in. MR-proADM was related to multiple metabolic factors and basal microcirculatory perfusion. Adrenomedullin might play a role in the pathogenesis of diabetic vasculopathy.

Effect of adrenergic blockade on plasma adrenomedullin concentration during static handgrip in patients with heart failure

Our previous study showed that static handgrip caused increases in the plasma adrenomedullin (ADM) both in patients with heart failure (HF) and healthy subjects. The present study was designed to determine the role of the sympathetic nervous system in mediating plasma ADM changes during handgrip in patients with HF. Twelve male HF patients (II class NYHA) treated with carvedilol, a non-selective adrenergic blocker (TC) and 12 patients untreated with carvedilol (UC) performed two 3-min bouts of static handgrip at 30% of maximal voluntary contraction, alternately with each hand. At the end of both exercise bouts and in 5 min of the recovery period, plasma ADM and catecholamines were determined. In addition, heart rate, blood pressure and stroke volume (SV) were measured. The baseline plasma ADM, noradrenaline (NA) and adrenaline (A) levels were similar in the two groups of patients, while SV was higher (P<0.05) in TC than in UC. During exercise plasma ADM concentrations were lower (P<0.05) in TC than in UC, but the handgrip-induced increases in plasma ADM did not differ between the groups. Plasma ADM correlated with NA concentrations (r = 0.764) and with SV (r = -0.435) and increases in plasma ADM expressed as percentage of baseline values correlated with those of plasma NA (r = 0.499), diastolic BP (r = 0.550) and total peripheral resistance (r = 0.435). The study suggests that the sympathetic nervous system may be involved in the stimulation of ADM secretion during static exercise either directly or by changes in the haemodynamic response.

Reduced maternal expression of adrenomedullin disrupts fertility, placentation, and fetal growth in mice

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. Plasma AM expression dramatically increases during pregnancy, and alterations in its levels are associated with complications of pregnancy including fetal growth restriction (FGR) and preeclampsia. Using AM+/- female mice with genetically reduced AM expression, we demonstrate that fetal growth and placental development are seriously compromised by this modest decrease in expression. AM+/- female mice had reduced fertility characterized by FGR. The incidence of FGR was also influenced by the genotype of the embryo, since AM-/- embryos were more often affected than either AM+/- or AM+/+ embryos. We demonstrate that fetal trophoblast cells and the maternal uterine wall have coordinated and localized increases in AM gene expression at the time of implantation. Placentas from growth-restricted embryos showed defects in trophoblast cell invasion, similar to defects that underlie human preeclampsia and placenta accreta. Our data provide a genetic in vivo model to implicate both maternal and, to a lesser extent, embryonic levels of AM in the processes of implantation, placentation, and subsequent fetal growth. This study provides the first genetic evidence to our knowledge to suggest that a modest reduction in human AM expression during pregnancy may have an unfavorable impact on reproduction.

The gene expression of adrenomedullin, calcitonin-receptor-like receptor and receptor activity modifying proteins (RAMPs) in CCl4-induced rat liver cirrhosis

This study was undertaken to determine AM expression in carbon tetrachloride (CCl4)-induced liver cirrhosis developed with peritoneal ascites. Sprague-Dawley rats received subcutaneous injections of CCl4 twice weekly in olive oil (1:1, 0.3 ml per kg body weight) for 6 or 12 weeks until ascites developed, or saline in olive oil as control. At 6 weeks, fibrosis developed and at 12 weeks cirrhosis developed with ascites formation. At both 6 and 12 weeks, increases in plasma renin and AM were evident, as was the gene expression of AM. At 12 weeks after CCl4 injection, the gene expression of calcitonin-like-receptor (CRLR) and receptor activity modifying proteins (RAMP1, RAMP2 and RAMP3) were all elevated when compared to the control. The results suggest that liver cirrhosis increases mRNA expressions of AM, CRLR and RAMP1, RAMP2 and RAMP3 and that the increase in AM gene expression precedes the development of cirrhosis. The increase in AM synthesis as reflected by an increase in AM gene expression, together with a lack of increase in AM peptide at both 6 and 12 weeks may suggest an elevation of AM release. Given the potent vasodilatory action of AM, the increase in the synthesis and release of AM in the cirrhotic liver may also contribute to peripheral vasodilatation in liver cirrhosis.

Adrenomedullin inhibits insulin exocytosis via pertussis toxin-sensitive G protein-coupled mechanism

Direct effects of adrenomedullin on insulin secretion from pancreatic beta-cells were investigated using a differentiated insulin-secreting cell line INS-1. Adrenomedullin (1-100 pM) inhibited insulin secretion at both basal (3 mM) and high (15 mM) glucose concentrations, although this inhibitory effect was not observed at higher concentrations of adrenomedullin. The inhibition of glucose-induced insulin secretion by adrenomedullin was restored with 12-h pretreatment with 1 microg/ml pertussis toxin (PTX), suggesting that this effect could be mediated by PTX-sensitive G proteins. Cellular glucose metabolism evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide colorimetric assay was not affected by adrenomedullin at concentrations that inhibited insulin secretion. Moreover, electrophysiological studies revealed that 10 pM adrenomedullin had no effect on membrane potential, voltage-gated calcium currents, or cytosolic calcium concentration induced by 15 mM glucose. Finally, insulin release induced by cAMP-raising agents, such as forskolin plus 3-isobutyl-1-methylxanthine or the calcium ionophore ionomycin, was significantly inhibited by 10 and 100 pM adrenomedullin. In conclusion, adrenomedullin at picomolar concentrations directly inhibited insulin secretion from beta-cells. This effect is likely due to the inhibition of insulin exocytosis through the activation of PTX-sensitive G proteins.

Adrenomedullin acts via nitric oxide and peroxynitrite to protect against myocardial ischaemia-induced arrhythmias in anaesthetized rats

1. The overall aim of this study was to determine if adrenomedullin (AM) protects against myocardial ischaemia (MI)-induced arrhythmias via nitric oxide (NO) and peroxynitrite. 2. In sham-operated rats, the effects of in vivo administration of a bolus dose of AM (1 nmol kg-1) was assessed on arterial blood pressure (BP), ex vivo leukocyte reactive oxygen species generation and nitrotyrosine deposition (a marker for peroxynitrite formation) in the coronary endothelium. 3. In pentobarbitone-anaesthetized rats subjected to ligation of the left main coronary artery for 30 min, the effects of a bolus dose of AM (1 nmol kg-1, i.v.; n=19) or saline (n=18) given 5 min pre-occlusion were assessed on the number and incidence of cardiac arrhythmias. In a further series of experiments, some animals received infusions of the NO synthase inhibitor N(G)-nitro-L-arginine (LNNA) (0.5 mg kg-1 min-1) or the peroxynitrite scavenger N-mercaptopropionyl-glycine (MPG) (20 mg kg-1 h-1) before AM. 4. AM treatment significantly reduced mean arterial blood pressure (MABP) and increased ex vivo chemiluminescence (CL) generation from leukocytes in sham-operated animals. AM also enhanced the staining for nitrotyrosine in the endothelium of coronary arteries. 5. AM significantly reduced the number of total ventricular ectopic beats that occurred during ischaemia (from 1185+/-101 to 520+/-74; P<0.05) and the incidences of ventricular fibrillation (from 61 to 26%; P<0.05). AM also induced a significant fall in MABP prior to occlusion. AM-induced cardioprotection was abrogated in animals treated with the NO synthase inhibitor LNNA and the peroxynitrite scavenger MPG. 6. This study has shown that AM exhibits an antiarrhythmic effect through a mechanism that may involve generation of NO and peroxynitrite.

Adrenomedullin: a new and promising target for drug discovery

Adrenomedullin (AM) is a 52 amino acid peptide that plays a critical role in several diseases such as hypertension, cancer, diabetes, cardiovascular and renal disorders, among others. Interestingly, AM behaves as a protective agent against some pathologies, yet is a stimulating factor for other disorders. Thus, AM can be considered as a new and promising target for the design of non-peptidic modulators that could be useful for the treatment of those pathologies, by regulating AM levels or the activity of AM. A full decade on from its discovery, much more is known about AM molecular biology and pharmacology, but this knowledge still needs to be applied to the development of clinically useful drugs.

Adrenomedullin: a protective factor for blood vessels

Adrenomedullin (AM) is a vasodilator peptide having a wide range of biological actions such as reduction of oxidative stress and inhibition of endothelial cell apoptosis. The AM gene is expressed in vascular walls, and AM was found to be secreted from cultured vascular endothelial cells, smooth muscle cells, and adventitial fibroblasts. Plasma AM levels in patients with arteriosclerotic vascular diseases are elevated in possible association with the severity of the disease. When administered over a relatively short period, AM dilates blood vessels via an endothelium-dependent or independent mechanism. Experiments in vitro have shown that AM exerts multiple actions on cultured vascular cells, which are mostly protective or inhibitory against vascular damage and progression of arteriosclerosis. Either prolonged infusion or overexpression of AM suppressed intimal thickening, fatty streak formation, and perivascular hyperplasia in rodent models for vascular remodeling or atherosclerosis. Intimal thickening induced by periarterial cuff was more severe in AM gene-knockout mice than their littermates, suggesting a protective role for endogenous AM. Moreover, AM has recently been suggested to possess angiogenetic properties. Collectively, a body of evidence suggests that AM participates in the mechanism against progression of vascular damage and remodeling, thereby alleviating the ischemia of tissues and organs.

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.

Levels of plasma total adrenomedullin are related with two acute phase inflammatory reactants (fibrinogen and sialic acid) but not with markers of endothelial dysfunction in Type 1 diabetes Adrenomedullin and vascular risk factors in Type 1 DM

Adrenomedullin (AM), an ubiquitous regulatory peptide with different actions, is known to be elevated in different clinical situations, including diabetes mellitus (DM), but its potential role in the pathogenesis of diabetic vascular complications is not clear. In the present study, we examined plasma total AM levels, and their association with different markers of endothelial dysfunction and with other established risk factors for cardiovascular diseases, in patients with Type 1 DM. We studied a total of 155 patients, 117 patients without any kind of vascular complications, 24 patients with retinopathy only, and 14 patients with retinopathy and microalbuminuria but normal renal function. None of them had clinical evidence of atherosclerotic disease. Compared with the control group (64 healthy participants), patients had raised fibrinogen, soluble E-selectin ((s)E-selectin), vascular cellular adhesion molecule (VCAM), angiotensin converting enzyme (ACE), and von Willebrand factor (vWf) (P<.001 in all cases), but plasma total AM, endothelin (ET), sialic acid, and homocysteine were not raised. In the diabetic group, AM levels correlated significantly with sialic acid (r=.16; P<.05), but a more significant correlation was found with fibrinogen (r=.30; P<.001). No correlation was found with the other parameters studied. In summary, plasma total AM levels seem to correlate with inflammatory markers but not with endothelial dysfunction markers in Type 1 diabetic patients without atherosclerotic disease.

Decreased synthesis of glomerular adrenomedullin in patients with IgA nephropathy

Adrenomedullin (AM) immunostaining and gene expression have seldom been measured in human kidneys. Because previous studies have shown that AM exerts antiproliferative effects on rat mesangial cells in vitro and that urine AM levels are decreased in patients with chronic glomerulonephritis, we measured glomerular AM and its gene expression in patients with primary IgA nephropathy (IgAN). Glomerular AM was measured by immunohistochemical staining, and glomerular AM mRNA was measured by in situ hybridization. Plasma and urine AM were measured by radioimmunoassay. The results showed that both the intensity of immunostaining for glomerular AM and the glomerular expression of AM mRNA were significantly decreased in IgAN patients compared with normal controls (both P < .05). Similar results were not observed in patients with non-IgA MsPGN. Glomerular AM immunostaining and glomerular AM mRNA expression were significantly correlated ( P < .001), and both were negatively correlated with the number of glomerular cells ( P < .05 and < .01, respectively). Both glomerular AM immunostaining and glomerular AM mRNA expression were correlated with urine AM levels (both P < .001), but not with plasma AM levels. The urine AM level was significantly lower in IgAN patients than in normal controls ( P < .01), whereas the plasma level was not different between the 2 groups. Our findings indicate that glomerular production of AM was decreased in patients with IgA nephropathy and that this lack of glomerular AM may be related to the pathogenesis of this mesangial disease.

Comparative study of the inhibitory effects of adrenomedullin on angiotensin II contraction in rat conductance and resistance arteries

Adrenomedullin (ADM), a ubiquitous vasoactive peptide, has been the target of a multitude of studies concerning its effect on the vascular tone. The present work aims at clarifying a series of its interactions with the renin-angiotensin system. The study uses the rat aorta ring as a model of conductance vessels, with or without vascular endothelium, and the second order branch of rat mesenteric arteries as a model of resistance arteries. Interactions between various concentrations of ADM and angiotensin II (Ang II) were studied, in the presence of L-NAME (a nitric oxide [NO] synthase inhibitor) and methylene blue (MB; a soluble guanylate cyclase inhibitor). Results point out differences in the mechanism of the inhibitory action of ADM upon Ang II effects in the two vessel types studied. Inhibition of Ang II contraction by ADM involves guanylate cyclase in both cases. However, NO is involved in ADM-induced inhibition of angiotensinergic vasoconstriction only in the conductance arteries, not in the resistance ones.

Alterations of adrenomedullin and its receptor system components in calcified vascular smooth muscle cells

Vascular calcification is a common finding in many cardiovascular diseases. Paracrine/autocrine changes in calcified vessels, and the secreted factors participate in and play an important role in the progress of calcification. Adrenomedullin (ADM) is a potent vasodilator peptide secreted by vascular smooth muscle cells (VSMCs) and vascular endothelial cells. Recently, receptor activity-modifying proteins (RAMPs) have been shown to transport calcitonin receptor-like receptor (CRLR) to the cell surface to present either as CGRP receptor or ADM receptor. In this work, we explored the production of ADM, alterations and significance of ADM mRNA and its receptor system components--CRLR and RAMPs mRNA in calcified VSMCs. Our results showed that calcium content, 45Ca2+ uptake and alkaline phosphatases (ALPs) activity in calcified VSMCs were increased, respectively, compared with control VSMCs. Content of ADM in medium was increased by 99% (p < 0.01). Furthermore, it was found that the levels of ADM, CRLR, RAMP2 and RAMP3 mRNA in calcified cells were elevated, respectively, compared with that of control. The elevated levels of CRLR, RAMP2 and RAMP3 mRNA were significant correlation with ADM mRNA (r = 0.83, 0.92 and 0.93, respectively, all p's < 0.01) in calcified VSMCs. The results show that calcified VSMCs generate an increased amount of ADM, up-regulate gene expressions of ADM and its receptor system components--CRLR, RAMP2 and RAMP3, suggesting an important role of ADM and its receptor system in the regulation of vascular calcification.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

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

Musclin, a Novel Skeletal Muscle-derived Secretory Factor

Skeletal muscle is involved in the homeostasis of glucose and lipid metabolism. We hypothesized that the skeletal muscle produces and secretes bioactive factor(s), similar to adipocytokines secreted by fat tissue. Here, we report the identification of a novel secretory factor, musclin, by signal sequence trap of mouse skeletal muscle cDNAs. Musclin cDNA encoded 130 amino acids, including NH(2)-terminal 30-amino acid signal sequence. Musclin protein contained a region homologous to natriuretic peptide family, and KKKR, a putative serine protease cleavage site, similar to the natriuretic peptide family. Full-length musclin protein and KKKR-dependent cleaved form were secreted in media of musclin cDNA-transfected mammalian cell cultures. Musclin mRNA was expressed almost exclusively in the skeletal muscle of mice. Musclin mRNA levels in skeletal muscle were markedly low in fasted, increased upon re-feeding, and were low in streptozotocin-treated insulin-deficient mice. Musclin mRNA expression was induced at late stage in the differentiation of C2C12 myocytes. In myocytes, insulin increased, while epinephrine, isoproterenol, and forskolin reduced musclin mRNA, all of which are known to increase the cellular content of cyclic AMP, a counter-regulator to insulin. Pathologically, overexpression of musclin mRNA was noted in the muscles of obese insulin-resistant KKAy mice. Functionally, recombinant musclin significantly attenuated insulin-stimulated glucose uptake and glycogen synthesis in myocytes. In conclusion, we identified musclin, a novel skeletal muscle-derived secretory factor. Musclin expression level is tightly regulated by nutritional changes and its physiological role could be linked to glucose metabolism.

Disassociated increases of adrenomedullin in the rat cerebrospinal fluid and plasma after salt loading and systemic administration of lipopolysaccharide

To determine the role of adrenomedullin (AM) in the fluid electrolyte homeostasis and endotoxin shock, cerebral spinal fluid (CSF) and plasma were sampled from rats after respective challenges. The AM levels were measured by a highly sensitive immunoassay. The AM levels in the CSF of the rats anesthetized with ether (10.7 +/- 0.60 fmol/ml) were significantly higher than those with isoflurane 5.17 +/- 0.70 fmol/ml, P < 0.01), while the plasma level did not differ significantly. The CSF levels of the rats received 2% saline drinking increased to 3 and 4 folds at day 5 and day 7, respectively, while the plasma levels did not differ from controls at both time points. The AM levels in CSF or plasma increased to 1.5 and 3 folds at 1.5 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS, 5 mg/kg), reached 6.5 and 30 folds at 6 h, respectively, while no change was observed in the controls. The present findings suggest that AM in the CSF is regulated independently from that in the plasma, the centrally synthesized AM plays and important role in the regulation of the fluid electrolyte homeostasis. Furthermore, the circulatory AM plays an important role in the endotoxin shock.

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

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

Circulating adrenomedullin is increased in relation with increased creatinine and atrial natriuretic peptide in liver-transplant recipients

OBJECTIVES

Circulating adrenomedullin (ADM), a potent vasorelaxing and natriuretic peptide involved in cardiovascular homeostasis, is increased after cardiac and renal transplantation. ADM is also implicated in hemodynamic abnormalities during liver cirrhosis, but whether ADM is increased late after liver transplantation is unknown.

PATIENTS

A total of 18 subjects--10 liver-transplant patients (Ltx) and 8 healthy subjects--were enrolled in the study.

DESIGN AND MEASUREMENTS

After a 15-min rest period in supine position, heart rate and systemic blood pressure were determined in all subjects. Then, venous blood samples were obtained in order to simultaneously determine the cyclosporine through levels, the biological (cyclosporine, renal and hepatic functions) and hormonal (ADM and atrial natriuretic peptide (ANP)) characteristics of the Ltx.

RESULTS

ADM (27.2+/-4.1 vs. 53.8+/-6.9 pmol/l, P=0.02), and ANP (5.9+/-0.9 vs. 12.8+/-1.4 pmol/l, P=0.001) were significantly increased in late, stable Ltx (35.4+/-9.6 months after transplantation). Furthermore, increased ADM correlated positively with elevated creatinine (r=0.76, P=0.01) and ANP (r=0.64, P=0.04) after liver transplantation.

CONCLUSIONS

Liver-transplant patients exhibit a sustained increase in circulating ADM. Such an increase likely results from renal impairment associated with volume regulation abnormalities, suggesting a potential role for ADM in volume regulation after liver transplantation.

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.

Two cases of pheochromocytoma associated with tetralogy of Fallot

We report two cases of pheochromocytoma combined with tetralogy of Fallot who showed different clinical courses. Case 1 was a 45-year-old woman with a history of radical operation for tetralogy of Fallot at 20 years of age. She presented with sudden hypertensive attack, and was diagnosed with pheochromocytoma of the left adrenal gland. She was treated surgically, and her high plasma noradrenaline level normalized. Case 2 was a 41-year-old woman who had been suffering from severe cyanosis due to tetralogy of Fallot throughout her life. A palliative operation had been performed at 7 years of age, but a radical operation had not been performed. She has had resistant hypertension since 38 years of age. She was diagnosed as having pheochromocytoma of the left adrenal gland at 41 years of age, but surgery was not performed. She was pharmacologically treated with doxazosin, followed by bisoprolol. Her symptoms somewhat improved, although she continued to have high plasma levels of noradrenaline and adrenomedullin. The combination of pheochromocytoma with tetralogy of Fallot or cyanotic congenital heart disease is rare; however, pheochromocytoma and congenital heart disease might be related through chronic hypoxia and/or gene abnormalities. The presence of pheochromocytoma worsens the hemodynamic state in patients with congenital heart disease regardless of whether radical surgery for congenital heart disease had been performed. Differential diagnosis of pheochromocytoma could be paramount in congenital heart disease patients who show unexpected or unusual symptoms.

Adrenomedullin influences dissociated rat area postrema neurons

The area postrema (AP) is one of a specialized group of central nervous system (CNS) structures devoid of a significant blood-brain barrier (BBB), collectively known as the circumventricular organs (CVO). While peptides are normally excluded from access to most regions of the CNS, the AP contains neurons with a high density of receptors for many circulating peptides, very likely including those for adrenomedullin (AM). In this study, whole-cell patch-clamp recordings were obtained from 114 dissociated rat AP neurons. The mean resting membrane potential (RMP) of these neurons (n=79) was -54.3+/-0.8 mV, the mean input resistance (IR) was 3.1+/-0.2 GOmega and the spike amplitude of neurons included in this study was always greater than 90 mV. Current-clamp studies showed that bath application of AM depolarized 39.2% (31 of 79) and hyperpolarized 45.6% (36 of 79) of neurons tested. Both effects were found to be concentration dependent from 10(-12) to 10(-7) M. These data support the idea that specific populations of CNS neurons within the AP are directly influenced by AM and support the concept that AM may act at AP to influence central autonomic control. We also examined the roles of specific ion channels in regulating the AM-induced excitability of AP neurons through voltage-clamp studies. These experiments suggest potential actions of AM in modulating voltage gated calcium channels, effects which have the additional consequence of inhibiting calcium activated potassium conductances (I(K(Ca))). These data demonstrate direct effects of AM on dissociated AP neurons and identify ion channels, the modulation of which, may underlie these effects.

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.

Changes of adrenomedullin and receptor activity modifying protein 2 (RAMP2) in myocardium and aorta in rats with isoproterenol-induced myocardial ischemia

Adrenomedullin is a potent vasodilator peptide originally isolated from a pheochromocytoma. Recently, a novel adrenomedullin receptor has been identified as a complex of calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 2 (RAMP2). To explore the pathophysiological roles of adrenomedullin and its receptor component RAMP2 in ischemic cardiovascular diseases, we studied the changes of adrenomedullin and RAMP2 mRNA in myocardium and aorta in rats with isoproterenol (ISO)-induced myocardial impairment. In ISO-treated rats, heart became enlarged markedly, the ratio of heart to body weight was increased by 54% (P<0.01), and myocardial malondialdehyde content and plasma lactate dehydrogenase activity was elevated by 43% (P<0.01) and 138% (P<0.01), respectively. Immunoreactive adrenomedullin (ADM) in plasma, myocardium and aorta was augmented by 116.7% (P<0.01), 50.8% (P<0.01) and 12.5% (P>0.05), respectively. ADM mRNA in myocardium and aorta was increased by 96.8% (P<0.01) and 38.5% (P<0.01), respectively. RAMP2 mRNA in myocardium and aorta was increased by 19.6% (P<0.05) and 15.8% (P<0.01), respectively. These results suggest that the increase of ADM level and the up-regulation of ADM and RAMP2 gene in myocardium and aorta may be significant in the pathogenesis of ischemic myocardiopathy.

Changes in amount of ADM mRNA and RAMP2 mRNA in calcified vascular smooth muscle cells

This work was aimed to explore the changes and significance of adrenomedullin (ADM) mRNA and receptor activity modifying protein 2 (RAMP2) mRNA in calcified vascular smooth muscle cells (VSMCs). Calcification of cultured rat VSMCs was produced by incubation with beta-glycerophosphate. Content of ADM released by VSMCs was measured by radioimmunoassay (RIA). The amount of ADM mRNA and RAMP2 mRNA was determined by competitive quantitative RT-PCR. The intracellular calcium content, alkaline phosphatases activity and cellular (45)Ca(2+)-uptake were determined. The results showed that the content of calcium, (45)Ca(2+)-uptake and alkaline phosphatases activity in calcified VSMCs were increased by 118%, 174% and seven-fold (all P<0.01), respectively, compared with control VSMCs. Content of ADM in medium was increased by 99% (P<0.01). Furthermore, it was found that the amount of ADM mRNA and RAMP2 mRNA in calcified cells was elevated by 78 and 56% (all P<0.05), respectively, compared with control. The elevated levels of RAMP2 mRNA were in positive correlation with ADM mRNA (r=0.76, P<0.05) in calcified VSMCs. In conclusion, calcified VSMCs generated an increased amount of ADM, and up-regulated gene expressions of ADM and RAMP2.

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.

Plasma Adrenomedullin Is Closely Correlated with Pulse Wave Velocity in Middle-Aged and Elderly Patients

Arterial stiffness as measured by pulse wave velocity (PWV) is a major predictor of cardiovascular disease. Adrenomedullin (AM), a hypotensive peptide, works as a compensatory factor for arterial sclerosis. The aim of this study was to investigate the relationship between PWV and the plasma concentration of AM in risk-loading patients. One hundred and twenty-six inpatients aged 30 to 75 years with or without varying degrees of atherosclerosis were investigated. Patients with heart and/or renal failure were excluded. The PWV was measured using an automatic waveform analyzer, and the plasma AM level was measured using a newly developed, hypersensitive immunoenzymometric assay system. The PWV increased with the increasing number of cardiovascular risk factors and organ damage in the patients. A positive correlation between the PWV and AM level was observed (r=0.375, p<0.0001, n=126). Seventy-four patients were receiving antihypertensive medications; medication did not affect the correlation. Multivariate regression analysis revealed that the PWV was significantly and independently associated with age, systolic blood pressure, and AM level. These results indicate that the plasma AM concentration could serve as a marker of advanced arterial sclerosis as estimated by increased PWV.

Plasma levels of adrenomedullin and atrial and brain natriuretic peptides in the general population: their relations to age and pulse pressure

Adrenomedullin (AM) and atrial and brain natriuretic peptides (ANP and BNP) exert vasodilator and natriuretic actions and are thought to share roles in counteracting the progression of hypertension or heart failure as circulating or locally-acting hormones. However, little data is available with regard to their roles in subjects who have no apparent cardiovascular diseases. The present study was carried out to identify the factors that affect plasma levels of AM, ANP and BNP in the general population. We measured the plasma levels of AM, ANP and BNP in 184 local residents who had a scheduled regular health checkup, and compared the findings with those for other clinical parameters. Univariate analyses showed that the plasma levels of AM, ANP and BNP were significantly correlated with age. The plasma levels of ANP and BNP were also significantly correlated with systolic blood pressure (SBP) and with pulse pressure (PP), an indicator of the stiffness of the great vessels. Multivariate analyses conducted using a stepwise method revealed that age was a significant, independent variable for the plasma levels of AM, ANP and BNP. In addition, PP was a significant factor for the plasma levels of ANP and BNP, while the plasma AM was significantly associated with body mass index (BMI). Thus, the plasma levels of AM, ANP and BNP all increased in association with aging, and those of ANP and BNP increased in association with PP, suggesting possible relationships between the plasma levels and age-related changes in the cardiovascular system.

Adrenomedullin in mammalian and human skin glands including the mammary gland

Adrenomedullin is a peptide that has been ascribed numerous functions. In the present paper, adrenomedullin has been localized immunhistochemically in a variety of skin glands of humans, elephants and impalas: apocrine scent glands, eccrine sweat glands, holocrine glands and mammary glands. In the apocrine glands expression of adrenomedullin varied with respect to staining intensity and intracellular localization. In general, glands which appeared to be actively secreting were more strongly stained than quiescent glands. However, within a single glandular tubule, individual cells differed considerably in the staining intensity of adrenomedullin. Adrenomedullin was present in both non-lactating and lactating mammary secretory epithelia, both ducts and alveoli reacted positively. In human mammary glands displaying apocrine metaplasia, the apical protrusions were strongly positive. Furthermore, positive immunostaining was found in endothelium and often in smooth muscle cells of small arteries and veins and in mast cells as well. Many of the adrenomedullin-positive epithelial cells were most strongly stained in the area of the Golgi apparatus, the cellular apex and particularly close to the basal side of the cell membrane. This pattern suggests packaging of adrenomedullin into secretory granules and secretion both at the apex of cells and at their basis. The first form of secretion suggests exocrine secretion, the latter form endocrine secretion of adrenomedullin. A possible hormonal function is in line with basally located electron dense small secretory granules, which have been found by electron microscopy in the glandular epithelia studied.

Endothelial dysfunction in chronic heart failure: clinical and therapeutic implications

Chronic heart failure is a complex clinical syndrome in which abnormal vascular endothelial function has been shown to occur at both the experimental and clinical levels. Alterations in endothelial function may contribute to the increased vasomotor tone and to the vascular remodeling process observed in patients with chronic heart failure. Reduced shear stress, increased activity of the various vasoconstricting neurohormonal systems, and increased levels of proinflammatory cytokines promote endothelial dysfunction in chronic heart failure. This article summarizes the major mechanisms implicated in the pathophysiology of abnormal endothelial function in chronic heart failure, as well as the novel therapeutic interventions aimed at reducing endothelial dysfunction in patients with the syndrome.

Adrenomedullin as a pancreatic hormone

Adrenomedullin (AM) is a multiregulatory peptide which is expressed in a wide range of tissues. In the pancreas, AM was first found in mammals, including man, and its colocalization with the pancreatic polypeptide (PP) was established in islet F cells. In addition, three different AM receptors have been characterized in B-cells. AM has been also located in the pancreatic cells of other vertebrate classes. The frequency and distribution of AM cells vary between different animals; they can be found scattered among the exocrine tissue, in the islets, or in ductal epithelia. The colocalization of AM with other hormones presents different patterns, although in birds, as in mammals, it seems to colocalize only with PP. The best-determined pancreatic AM function is the inhibition of insulin secretion in B-cells, which seems to be linked to a recently discovered binding protein, factor H. In relation to this physiological role, clinical data show that AM is raised in some groups of both types I and II diabetic patients and AM might have triggered the disease in a subset of them. On the other hand, AM pancreatic cells are also involved in the response to septic shock by increasing AM circulating levels. A third putative function is the inhibition of amylase secretion by the exocrine pancreatic cells. AM has been found in embryonic mammalian pancreas from the earliest stages of the development, colocalizing with all pancreatic hormones, although in adults only coexpression with PP is kept. AM may play a role in the growth and morphogenesis of the pancreas.

Human adrenomedullin gene delivery protects against cardiovascular remodeling and renal injury

We investigated the potential roles of adrenomedullin (AM) in cardiovascular and renal function by somatic gene delivery. We showed that a single intravenous injection of the human AM gene under the control of cytomegalovirus promoter/enhancer induces a prolonged delay in blood pressure rise for several weeks in spontaneously hypertensive rats, Dahl salt-sensitive, DOCA-salt, and two-kidney one-clip hypertensive rats as compared to their respective controls injected with a reporter gene. Expression of the human AM transcript was identified in the heart, kidney, lung, liver and aorta of the rat after adenovirus-mediated AM gene delivery by RT-PCR followed by Southern blot analysis. Immunoreactive human AM levels were measured in rat plasma and urine following AM gene delivery. AM gene delivery induced significant reduction of left ventricular mass in these hypertensive animal models. It also reduces urinary protein excretion and increases glomerular filtration rate, renal blood flow and urinary cAMP levels. AM gene transfer attenuated cardiomyocyte diameter and interstitial fibrosis in the heart, and reduced glomerular sclerosis, tubular disruption, protein cast accumulation and renal cell proliferation in the kidney. In the rat model with myocardial ischemia/reperfusion injury, AM gene delivery significantly reduced myocardial infarction, apoptosis, and superoxide production. Furthermore, local AM gene delivery significantly inhibited arterial thickening, promoted re-endothelialization and increased vascular cGMP levels in rat artery after balloon angioplasty. Collectively, these results indicate that human AM gene delivery attenuates hypertension, myocardial infarction, renal injury and cardiovascular remodeling in animal models via cAMP and cGMP signaling pathways. These findings provide new insights into the role of AM in cardiovascular and renal function.