Haemodynamic responses to rat adrenomedullin in anaesthetized spontaneously hypertensive rats

Plasma Clearance of Intravenously Infused Adrenomedullin in Rats with Acute Renal Failure

Plasma adrenomedullin concentrations are reportedly elevated in patients with renal failure; however, the underlying mechanism is unclear. In this study, we investigated the plasma clearance of synthetic human adrenomedullin (AM) in two models of rats with renal dysfunction; one was induced by subcutaneous injection of mercury chloride (RD-Ag) and the other by completely blocking bilateral renal blood flow (RD-Bl). Sixty minutes after starting intravenous AM infusion, AM levels in RD-Ag, RD-Bl, and rats with normal renal function (NF) were still increased slightly; however, plasma AM levels in RD-Ag rats were approximately three times as high as in RD-Bl and NF rats. Plasma AM disappearance after the end of treatment was similar among the three groups. Pharmacokinetic analysis revealed that elevated plasma AM in RD-Ag rats may be caused by a reduced volume of distribution. The adrenomedullin functional receptor is composed of heterodimers, including GPCR, CLR (calcitonin receptor-like receptor, CALCRL), and the single transmembrane proteins, RAMP2 or RAMP3 (receptor activity modifying protein). Calcrl expression was downregulated in the lungs and kidneys of RD-Ag rats. Furthermore, the plasma concentration of exogenous AM was elevated in mice deficient in vascular endothelium-specific Ramp2. These results suggest that decreased plasma AM clearance in RD-Ag is not due to impaired renal excretion but to a decreased volume of distribution caused by a reduction in adrenomedullin receptors.

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.

Bench-to-bedside pharmacology of adrenomedullin

The bioactive peptide adrenomedullin (AM) exerts pleiotropic actions in various organs and tissues. In the heart, AM has an inhibitory effect on ventricular remodeling, suppressing cardiomyocyte hypertrophy and the proliferation of cardiac fibroblasts. This pharmacological property was shown not only in rat models of acute myocardial infarction, but also clinically in patients with this cardiac disease. An originally characterized feature of AM was a potent vasodilatory effect, but this peptide was found to be important for vascular integrity and angiogenesis. AM-induced angiogenesis is involved in tumor growth, while AM inhibits apoptosis of some types of tumor cell. A unique pharmacological property is anti-inflammatory activity, which has been characterized in sepsis and inflammatory bowel diseases; thus, there is an ongoing clinical trial to test the efficacy of AM for patients with intractable ulcerative colitis. These activities are assumed to be mediated via the specific receptor formed by calcitonin receptor-like receptor and receptor activity-modifying protein 2 or 3, while some questions remain to be answered about the molecular mechanisms of this signal transduction system. Taking these findings together, AM is a bioactive peptide with pleiotropic effects, with potential as a therapeutic tool for a wide range of human diseases from myocardial infarction to malignant tumors or inflammatory bowel diseases.

Biological properties of adrenomedullin conjugated with polyethylene glycol

Adrenomedullin (AM) is a vasodilator peptide with pleiotropic effects, including cardiovascular protection and anti-inflammation. Because of these beneficial effects, AM appears to be a promising therapeutic tool for human diseases, while intravenous injection of AM stimulates sympathetic nerve activity due to short-acting potent vasodilation, resulting in increased heart rate and renin secretion. To lessen these acute reactions, we conjugated the N-terminal of human AM peptide with polyethylene glycol (PEG), and examined the biological properties of PEGylated AM in the present study. PEGylated AM stimulated cAMP production, an intracellular second messenger of AM, in cultured human embryonic kidney cells expressing a specific AM receptor in a dose-dependent manner, as did native human AM. The pEC50 value of PEGylated AM was lower than human AM, but no difference was noted in maximum response (Emax) between the PEGylated and native peptides. Intravenous bolus injection of 10nmol/kg PEGylated AM lowered blood pressure in anesthetized rats, but the acute reduction became significantly smaller by PEGylation as compared with native AM. Plasma half-life of PEGylated AM was significantly longer than native AM both in the first and second phases in rats. In summary, N-terminal PEGylated AM stimulated cAMP production in vitro, showing lessened acute hypotensive action and a prolonged plasma half-life in comparison with native AM peptide in vivo.

Adrenomedullin and adrenotensin increase the transcription of regulator of G‑protein signaling 2 in vascular smooth muscle cells via the cAMP‑dependent and PKC pathways

The regulator of G‑protein signaling 2 (RGS2) has been shown to be crucial in the regulation of vascular tone and blood pressure. The vascular activities of adrenomedullin (ADM) and adrenotension (ADT), two natural peptides, are dependent upon the modulation of RGS2 expression. However, the effects and pathways involved in their modulation remain unknown. This study aimed to observe the changes of RGS2 expression in response to ADM and ADT in cultured vascular smooth muscle cells and to clarify the potential signaling pathways in vitro. In the present study, vascular smooth muscle cells (VSMCs) were cultured with ADM and ADT of various concentrations for different time periods, and the gene expression of RGS2 was analyzed by PCR. ADM significantly increased the gene expression at 0.5 h to ~35‑fold of that at baseline, whereas ADT marginally increased the expression after 1‑2 h. SQ22,536 and chelerythrine were used to block the protein kinase A (PKA) and PKC pathways activated by incubation with ADM. The gene expression of RGS2 was reduced by SQ22,536 only. Furthermore, when SQ22,536 and chelerythrine were added to the cells incubated with ADT, the gene expression was markedly reduced by both SQ22,536 and chelerythrine. In conclusion, ADM immediately showed a marked increase in the gene expression of RGS2 in cultured VSMCs via a cAMP‑dependent pathway and ADT gradually showed a marginal increase in the gene expression via a cAMP‑dependent pathway and a PKC pathway.

Human adrenomedullin and its binding protein ameliorate sepsis-induced organ injury and mortality in jaundiced rats

Sepsis is a serious complication for patients with obstructive jaundice. Although administration of adrenomedullin (AM) in combination with its binding protein (AMBP-1) is protective after injury, it remains unknown whether AM/AMBP-1 ameliorates sepsis-induced organ injury and mortality in the setting of biliary obstruction. The aim of this study is, therefore, to test the efficacy of human AM/AMBP-1 in a rat model of obstructive jaundice and polymicrobial sepsis. To study this, obstructive jaundice was induced in male adult rats (275-325g) by common bile duct ligation (BDL). One week after BDL, the rats were subjected to sepsis by cecal ligation and puncture (CLP). Plasma levels of AM and AMBP-1 were measured at 20h after CLP. In additional groups of BDL+CLP rats, human AM/AMBP-1 (24/80microg/kg body weight (BW)) or vehicle (i.e., human albumin) was administered intravenously at 5h after CLP. Blood and tissue samples were collected at 20h after CLP for various measurements. To determine the long-term effect of human AM/AMBP-1 after BDL+CLP, the gangrenous cecum was removed at 20h after CLP and 7-day survival was recorded. Our results showed that plasma levels of AM were significantly increased while AMBP-1 levels were markedly decreased after BDL+CLP (n=8, P<0.05). Administration of human AM/AMBP-1 attenuated tissue injury and inflammatory responses after BDL+CLP. Moreover, human AM/AMBP-1 significantly increased the survival rate from 21% (n=14) to 53% (n=15). Thus, human AM/AMBP-1 ameliorates sepsis-induced organ injury and mortality in jaundiced rats. Human AM/AMBP-1 can be further developed as a novel treatment for sepsis in jaundiced patients.

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.

Human adrenomedullin and its binding protein attenuate organ injury and reduce mortality after hepatic ischemia-reperfusion

OBJECTIVE

To determine whether administration of a vasoactive peptide, human adrenomedullin (AM), in combination with its binding protein (ie, AMBP-1), prevents or minimizes hepatic ischemia-reperfusion (I/R) injury.

SUMMARY BACKGROUND DATA

Hepatic I/R injury results from tissue hypoxia and subsequent inflammatory responses. Even though numerous pharmacological modalities and substances have been studied to reduce I/R-induced mortality, none have been entirely successful. We have shown that administration of AM/AMBP-1 produces significant beneficial effects under various pathophysiological conditions. However, it remains unknown if human AM/AMBP-1 has any protective effects on hepatic I/R-induced tissue damage and mortality.

METHODS

Seventy percent hepatic ischemia was induced in male adult rats by placing a microvascular clip across the hilum of the left and median lobes for 90 minutes. After removing the clip, human AM alone, human AMBP-1 alone, human AM in combination with human AMBP-1 or vehicle was administered intravenously over a period of 30 minutes. Blood and tissue samples were collected 4 hours after reperfusion for various measurements. In additional groups of animals, the nonischemic liver lobes were resected at the end of 90-minute ischemia. The animals were monitored for 7 days and survival was recorded.

RESULTS

After hepatic I/R, plasma levels of AM were significantly increased, whereas AMBP-1 levels were markedly decreased. Likewise, gene expression of AM in the liver was increased significantly, whereas AMBP-1 expression was markedly decreased. Administration of AM in combination with AMBP-1 immediately after the onset of reperfusion down-regulated inflammatory cytokines, decreased hepatic neutrophil infiltration, inhibited liver cell apoptosis and necrosis, and reduced liver injury and mortality in a rat model of hepatic I/R. On the other hand, administration of human AM alone or human AMBP-1 alone after hepatic I/R failed to produce significant protection.

CONCLUSIONS

Human AM/AMBP-1 may be a novel treatment to attenuate tissue injury after an episode of hepatic ischemia.

Differential hormonal profiles of adrenomedullin and proadrenomedullin N-terminal 20 peptide in patients with heart failure and effect of treatment on their plasma levels

BACKGROUND

Adrenomedullin (AM) is a potent vasodilatory peptide discovered in human pheochromocytoma tissue. Proadrenomedullin N-terminal 20 peptide (PAMP) processed from an AM precursor is also a novel hypotensive peptide which inhibits catecholamine secretion from sympathetic nerve endings.

HYPOTHESIS

The present study sought to examine the relationships between the two peptides and other clinical parameters by measuring the plasma AM and PAMP concentrations in 98 patients with heart failure.

METHODS

In all, 98 patients [65 men and 33 women, aged 58.2 +/- 11.0 years, mean +/- standard deviation (SD)] with heart failure and 26 healthy volunteers (12 men and 14 women, aged 54.1 +/- 8.6 years) were examined in this study. Heart failure was secondary to previous myocardial infarction in 58 patients, valvular disease in 28, cardiomyopathy in 9, and congenital heart disease in 3. All patients were classified into two groups of class I or II (Group 1) and class III or IV (Group 2) according to the New York Heart Association (NYHA) functional classification.

RESULTS

Both plasma AM and PAMP concentrations in the patients were significantly higher than those in healthy volunteers. In addition, plasma AM and PAMP concentrations in patients in class III or IV of New York Heart Association (NYHA) classification were significantly higher than those in NYHA class I or II. The elevated plasma concentrations of these peptides in patients in NYHA class III or IV significantly decreased in response to the treatment for 7 days. There was a significant correlation between plasma AM and PAMP, though the plasma concentration of PAMP was one-fifth to one-seventh of that of AM in patients and controls. The plasma AM concentration correlated significantly with the plasma concentrations of atrial and brain natriuretic peptides, epinephrine, and right atrial pressure, whereas such a relationship was not noted for the plasma PAMP concentration.

CONCLUSIONS

Judging from the difference in not only the biological actions but also the hormonal profiles between AM and PAMP, they may differentially modulate the cardiovascular system in patients with heart failure, although they are processed from the same precursor.

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.

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.

Effects of adrenomedullin inhalation on hemodynamics and exercise capacity in patients with idiopathic pulmonary arterial hypertension

BACKGROUND

Adrenomedullin (AM) is a potent pulmonary vasodilator peptide. However, whether intratracheal delivery of aerosolized AM has beneficial effects in patients with idiopathic pulmonary arterial hypertension remains unknown. Accordingly, we investigated the effects of AM inhalation on pulmonary hemodynamics and exercise capacity in patients with idiopathic pulmonary arterial hypertension.

METHODS AND RESULTS

Acute hemodynamic responses to inhalation of aerosolized AM (10 microg/kg body wt) were examined in 11 patients with idiopathic pulmonary arterial hypertension during cardiac catheterization. Cardiopulmonary exercise testing was performed immediately after inhalation of aerosolized AM or placebo. The work rate was increased by 15 W/min until the symptom-limited maximum, with breath-by-breath gas analysis. Inhalation of AM produced a 13% decrease in mean pulmonary arterial pressure (54+/-3 to 47+/-3 mm Hg, P<0.05) and a 22% decrease in pulmonary vascular resistance (12.6+/-1.5 to 9.8+/-1.3 Wood units, P<0.05). However, neither systemic arterial pressure nor heart rate was altered. Inhalation of AM significantly increased peak oxygen consumption during exercise (peak o(2), 14.6+/-0.6 to 15.7+/-0.6 mL. kg(-1). min(-1), P<0.05) and the ratio of change in oxygen uptake to that in work rate (Deltao(2)/DeltaW ratio, 6.3+/-0.4 to 7.0+/-0.5 mL. min(-1). W(-1), P<0.05). These parameters remained unchanged during placebo inhalation.

CONCLUSIONS

Inhalation of AM may have beneficial effects on pulmonary hemodynamics and exercise capacity in patients with idiopathic pulmonary arterial hypertension.

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.

Endothelial PAS domain protein 1 (EPAS1) induces adrenomedullin gene expression in cardiac myocytes: role of EPAS1 in an inflammatory response in cardiac myocytes

Endothelial PAS domain protein 1 (EPAS1) has been identified as a member of the basic helix-loop-helix (bHLH)-PAS protein family, and plays a critical role in the regulation of hypoxia inducible genes. It remains unknown whether physiological stimuli other than hypoxia modulate EPAS1 expression. This study examined the inducible expression of EPAS1 by various cytokines and growth factors, and determined the target gene for EPAS1 in cardiac myocytes. In cultured cardiac myocytes, interleukin-1beta (IL-1beta) but not tumor necrosis factor alpha markedly increased the EPAS1 mRNA and protein levels in a time- and dose-dependent manner, whereas hypoxia increases the expression of EPAS1 protein but not its mRNA. Such an induction of EPAS1 by IL-1beta was efficiently inhibited by the pretreatment of the cells with Src kinase inhibitors, such as herbimycin A and PP1. The expression of adrenomedullin (AM) mRNA, which is also upregulated by IL-1beta, was dramatically increased in cardiac myocytes transduced with adenovirus expressing EPAS1. Transient transfection assays using the site-specific mutation of the AM promoter showed that EPAS1 overexpression increases the transcriptional activity through a sequence similar to the consensus HRE (hypoxia responsive element). These results suggest that IL-1beta induces the EPAS1 at the transcriptional level, which in turn activates the AM gene. Since IL-1beta has been implicated in the pathogenesis of heart failure and AM can ameliorate the cardiac function, our results suggest that EPAS1 plays a role in the adaptation of the cardiac myocytes during heart failure as well as in the regulation of gene expression by hypoxia.

Regional hemodynamic effects of adrenomedullin in Wistar rats: a comparison with calcitonin gene-related peptide

Because both vasodilation induced by adrenomedullin (AM) and that induced by calcitonin gene-related peptide (CGRP) may occur via the same receptor, the two peptides might play similar roles in circulation. To examine this possibility, we used the colored microsphere technique and an ultrasonic flowmeter to investigate the systemic and regional effects of an equivalent dose (650 pmol/l) of AM and CGRP in conscious Wistar rats. AM significantly decreased mean arterial pressure and peripheral resistance but increased heart rate and cardiac index (CI). On the other hand, hypotension induced by CGRP was not accompanied by an increment in Cl. Both AM and CGRP increased the femoral arterial blood flow measured by the flowmeter, with the increase by AM being significantly larger. The regional hemodynamic effects were quite different between the two peptides. AM increased the blood flow in the heart, lungs, kidneys, adrenal glands, and spleen, whereas CGRP increased blood flow only in the heart. On the other hand, CGRP increased the cutaneous and gastric blood flows, which were not affected by AM. These differences in the regional vasodilatory effects of AM and CGRP suggest that the two peptides do not play similar roles in circulatory regulation.

Mature adrenomedullin concentrations in plasma during pregnancy

OBJECTIVE

Adrenomedullin is a novel peptide that exerts a potent, dose-dependent and long-lasting hypotensive effect. In human plasma, adrenomedullin consists of two molecular forms: mature and immature. Immature adrenomedullin is much less bioactive than mature adrenomedullin. Although a gradual increase in plasma adrenomedullin has been reportedly observed as pregnancy progressed, mature adrenomedullin has not been examined. The aim of this study was to elucidate the plasma level of mature adrenomedullin in pregnant women.

METHODS

We measured the concentrations of mature adrenomedullin in ten pregnant women in the first trimester, ten pregnant women in the third trimester, and ten non-pregnant controls with the immunoradiometric assay.

RESULTS

The mean concentration of mature adrenomedullin was significantly increased in pregnant women in the first trimester compared to age-matched non-pregnant subjects (p < 0.05). The mean concentration of mature adrenomedullin was significantly increased in pregnant women in the third trimester compared with pregnant women in the first trimester (p < 0.005).

CONCLUSION

Our study demonstrated that concentrations of mature adrenomedullin were elevated in pregnant women compared with non-pregnant women and its concentration in the third trimester was significantly higher than that in the first trimester.

Adrenomedullin and myocardial contractility in the rat

The effects of adrenomedullin in the regulation of myocardial contractility were investigated in the rat. In papillary muscles (n=6), adrenomedullin (0.1 to 10 nM) failed to show contractile effects. NO (nitric oxide) synthase inhibition with N(G)-nitro-L-arginine (L-NOARG) did not unmask any inotropic effect of adrenomedullin. The positive inotropic effect of isoprenaline (0. 01 nM to 10 microM) was identical after adrenomedullin, after L-NOARG, and after L-NOARG plus adrenomedullin (n=6 each). In field-stimulated rat ventricular myocytes, adrenomedullin (1, 10, and 100 nM; n=4 each) had impact neither on cell shortening nor on Ca(2+) transients. In isolated constant-flow perfused hearts (7.3+/-0.3 ml/min), adrenomedullin (1 nM, n=9; 10 nM, n=7) induced significant coronary vasodilation (-28%, -50%). In conclusion, adrenomedullin is a potent coronary vasodilator, but has no significant effects on myocardial contractility in the rat.

Adrenomedullin: potential in physiology and pathophysiology

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

Plasma and urine levels of adrenomedullin and proadrenomedullin N-terminal 20 peptide in chronic glomerulonephritis

Proadrenomedullin N-terminal 20 peptide (PAMP) is a novel hypotensive peptide present in the precursor of adrenomedullin (AM), a vasodilative and natriuretic peptide. We examined the plasma and urinary levels of these peptides in patients with chronic glomerulonephritis (CGN). The mean plasma AM concentration of the patients with CGN did not differ from that of control subjects (4.17 +/- 0.17 v 3.87 +/- 0.21 fmol/mL, respectively), whereas urinary AM excretion was significantly less in the patients with CGN (5.96 +/- 0.95 v control, 8.93 +/- 1.02 fmol/mg of creatinine; P < 0.05). Plasma concentrations and urinary excretion of PAMP were significantly less for the patients with CGN compared with control subjects (0.91 +/- 0.08 v 1.23 +/- 0.20 fmol/mL; P < 0.05 and 25.0 +/- 3.0 v 35.0 +/- 3.6 fmol/mg of creatinine, respectively; P < 0. 05). The plasma AM concentration was negatively correlated with plasma renin activity (r = -0.58; P < 0.01) and aldosterone concentration (r = -0.40; P < 0.05). Urinary excretions of AM and PAMP showed significant correlations with urine excretion of sodium (r = 0.39; P < 0.05 and r = 0.49; P < 0.01, respectively). These findings suggest that AM and PAMP may have roles in the regulation of sodium in patients with CGN.

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

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

Acute hemodynamic and renal effects of adrenomedullin in rats with aortocaval shunt

Heart failure is characterized by increased vascular resistance and water retention. Adrenomedullin is a peptide hormone with vasodilating and diuretic properties whose efficacy in heart failure has not been well established. We used an aortocaval shunt model of moderate heart failure in rats and infused increasing doses of adrenomedullin, both as bolus injections and 20-min infusions. In controls, a clear dose-dependent 4.8+/-1.0 to 13.6+/-2.3 mm Hg decrease in arterial blood pressure was observed after injection of 1 microg to 30 microg of adrenomedullin. In rats with aortocaval shunt, the hypotensive responses were significantly diminished. The urine flow rate, which was diminished at baseline in rats with aortocaval shunt, was increased and normalized by adrenomedullin administration. The glomerular filtration rate increased after infusion of adrenomedullin (0.5 microg/kg min(-1)) from 2.37+/-0.25 to 3.47+/-0.43 ml/min (P<0.01) in controls and from 1.79+/-0.33 to 2.58+/-0.49 (P<0.05) in rats with aortocaval shunt. Similarly, renal blood flow was significantly increased by adrenomedullin in both groups. Our results indicate a beneficial effect of adrenomedullin on renal function in rats with aortocaval shunt. These data suggest that adrenomedullin might be of potential therapeutic value in heart failure, without inordinately decreasing blood pressure.

Novel neuropeptides in the pathophysiology of heart failure: adrenomedullin and endothelin-1

The clinical success of neurohumoral manipulation by ACE inhibitors and beta blockers in heart failure has led to new therapeutic approaches. New neurohumoral factors are now viewed as offering the potential for treatment interventions. Not only do we consider blocking the production of deleterious hormones, but also, more recently, consideration has been given to augmenting the actions of factors with potentially beneficial actions. Hopefully such manipulation of ADM and ET-1 can result in further improvement in the well-being of heart failure patients.

Adrenomedullin gene expression is developmentally regulated and induced by hypoxia in rat ventricular cardiac myocytes

Adrenomedullin is a recently discovered hypotensive peptide that is expressed in a variety of cell and tissue types. Using the technique of differential display, the adrenomedullin gene was observed to be differentially expressed in developing rat heart. Reverse transcription-polymerase chain reaction analysis revealed that the level of adrenomedullin mRNA was significantly higher in adult ventricular cardiac muscle as compared with embryonic day 17 ventricular cardiac muscle. Adrenomedullin receptor mRNA was constitutively expressed throughout development of the ventricular heart. Two potential hypoxia-inducible factor-1 (HIF-1) consensus binding sites were identified in the mouse adrenomedullin promoter at -1095 and -770 nucleotides from the transcription start site. Exposure of cultured adult rat ventricular cardiac myocytes to hypoxia (1% O2) resulted in a significant, time-dependent increase in adrenomedullin mRNA levels. Transfection studies revealed that the 5'-flanking sequence of adrenomedullin was capable of mediating a hypoxia-inducible increase in transcription. Mutation of the putative HIF-1 consensus binding sites revealed that the major regulatory sequence that mediates the hypoxia-inducible transcriptional response is located at -1095. These data demonstrate that the adrenomedullin gene is developmentally regulated in ventricular cardiomyocytes, that adrenomedullin transcription can be induced by hypoxia, and that this response is primarily mediated by HIF-1 consensus sites in the adrenomedullin promoter.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Pressure natriuresis after adrenomedullin in anesthetized spontaneously hypertensive rats

Adrenomedullin (ADM), a peptide with potent vasodilatory and natriuretic actions, is elevated in patients with essential hypertension. Because pharmacological doses of ADM result in renal vasodilation and natriuresis, it has been suggested that ADM may play a modulatory role in hypertension through potential actions on renal pressure natriuresis. However, it is unclear whether elevation of plasma ADM within the pathophysiological range has similar actions. To determine the effects of pathophysiological doses of ADM on blood pressure and on the relationship between renal perfusion pressure (RPP) and renal hemodynamics and sodium excretion, renal function was determined at RPPs of 80, 105, 130, and 155 mm Hg in spontaneously hypertensive rats (SHR) infused with ADM at 50 ng x kg(-1) x min(-1) (ADM-50, n=5) and at 100 ng x kg(-1) x min(-1) (ADM-100, n=5) and in control SHR (n=5). Decreasing RPP from 155 to 80 mm Hg in control SHR decreased (P<.05) absolute sodium excretion from 0.81+/-0.25 to 0.04+/-0.02 microEq/min, fractional sodium excretion from 0.32+/-0.11% to 0.06+/-0.04%, and urine flow rate from 11.5+/-2.8 to 1.03+/-0.31 microL/min. ADM infusion elevated (P<.05) plasma ADM levels in ADM-infused SHR (679+/-47 pg/mL in ADM-50, 858+/-79 in ADM-100) compared with control (79.5+/-27.8). However, although reduction of RPP from 155 to 80 mm Hg in ADM rats decreased absolute sodium excretion (ADM-50, 0.98+/-0.10 to 0.09+/-0.04 microEq/min; ADM-100, 0.95+/-0.09 to 0.07+/-0.02 microEq/min), fractional sodium excretion (ADM-50, 0.31+/-0.03% to 0.17+/-0.04%; ADM-100, 0.33+/-0.02% to 0.09+/-0.01%), and urine flow (ADM-50, 13.6+/-1.4 to 1.73+/-0.75 microL/min; ADM-100, 13.5+/-1.5 to 1.07+/-0.16 microL/min), these decreases were not different from values found in controls. Renal plasma flow and glomerular filtration rate were also similar in control and ADM-treated SHR at each level of RPP. Thus, acute increases in ADM to levels found in pathophysiological conditions have no effect on blood pressure, pressure natriuresis, or renal autoregulation in the SHR. These findings do not support the hypothesis that ADM serves as a modulating factor in hypertension, at least in the SHR.

Effect of chronically infused adrenomedullin in two-kidney, one-clip hypertensive rats

The hypotensive effect of chronically infused adrenomedullin, a potent vasodilator peptide, was examined in conscious two-kidney, one-clip (2K-1C) hypertensive and sham-operated rats. They were infused with 1.0 microgram/h of synthetic human adrenomedullin for 14 days by means of osmotic minipumps. Control groups were infused on the same schedule with 0.9% saline. Systolic blood pressure was measured before and during the infusion. Plasma renin activity, aldosterone and human adrenomedullin concentrations were determined at day 14 of the infusion. A significant reduction of systolic blood pressure was observed in the adrenomedullin-infused 2K-1C rats at day 4, and systolic blood pressure remained significantly lower throughout the experiment compared to that of the control 2K-1C. A similar hypotensive effect was seen in the adrenomedullin-infused sham-operated rats. Both the plasma renin activity and aldosterone concentrations of the adrenomedullin-infused 2K-1C and sham groups were significantly reduced compared to those of the respective control, whereas, the plasma human adrenomedullin concentration in the adrenomedullin-infused groups was found to be within the physiological range. These findings demonstrated that chronically infused adrenomedullin had a hypotensive effect accompanied by significant reductions of plasma renin activity and plasma aldosterone concentration in 2K-1C hypertensive and sham-operated rats.

Hypotensive effect of chronically infused adrenomedullin in conscious Wistar-Kyoto and spontaneously hypertensive rats

1. The hypotensive effect of chronically infused human adrenomedullin (hAM), a potent vasodilator peptide that has been reported to have a natriuretic action, was examined in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. Conscious WKY rats and SHR were infused with 200 ng/h synthetic hAM for 14 days by means of osmotic minipumps. Control groups were infused at the same schedule with 0.9% saline. Systolic blood pressure (SBP) and daily urinary excretion of Na+ and K+ were measured before and during the infusion period. In addition, plasma renin activity (PRA), aldosterone and hAM concentrations were measured on day 14 of infusion. 3. A significant reduction in SBP was observed in hAM-treated SHR at day 2 and SBP remained significantly lower throughout the experiment compared with control SHR. Similarly, SBP in the hAM-treated WKY rats was found to be significantly lower than in control WKY rats during infusion. However, the hypotensive effect was not accompanied by any significant increase in urinary volume or Na+ excretion in hAM-treated rats of either strain. Chronic infusion with hAM significantly suppressed PRA and lowered the concentration of plasma aldosterone in WKY rats but not in SHR. The plasma aldosterone in WKY rats and SHR were 0.9 +/- 0.4 and 0.6 +/- 0.2 fmol/mL, respectively. 4. These findings demonstrate that chronically infused hAM has a hypotensive effect in both WKY rats and SHR without an increase in urinary volume or Na+ excretion at a plasma AM concentration within the physiological limit.