Ca(2+)-dependent cosecretion of adrenomedullin and catecholamines mediated by nicotinic receptors in bovine cultured adrenal medullary cells

High Plasma Levels of Human Chromogranin a and Adrenomedullin in Patients with Pheochromocytoma

Aims and background

The aim of our study was to investigate the plasma chromogranin A (CgA) and adrenomedullin (AM) levels in patients with pheochromocytomas.

Methods and study design

We collected blood samples for measurement of plasma CgA and AM in 21 patients with pheochromocytomas, 43 healthy subjects and 26 patients with solid non-functioning adrenocortical adenomas. In 11 patients with pheochromocytomas plasma CgA and AM were measured again four weeks after tumor removal. CgA and AM were measured by means of a novel solid-phase two-site immunoradiometric assay based on monoclonal antibodies (CgA-RIA CT, CIS bio international) and by a specific radioimmunoassay (RIA, Phoenix Pharm. Inc.), respectively.

Results

The mean plasma CgA level (±SD) in patients with pheochromocytomas (204 ± 147.9 ng/mL) was significantly higher (P <0.001) than that in healthy subjects (41.6 ± 10.7 ng/mL) and in patients with non-functioning adrenocortical adenomas (47.3 ± 17.6 ng/mL). The mean plasma AM concentration (±SD) in patients with pheochromocytomas (27.5 ± 10.4 pg/mL) was significantly higher (P <0.001) than that in HS (13.8 ± 4.5 pg/mL) and in patients with non-functioning adrenocortical adenomas (16.6 ± 7.3 pg/mL). Plasma CgA levels correlated with plasma AM levels (r = 0.501; P <0.02) and with plasma metanephrine levels (r = 0.738; P <0.0001) in patients with pheochromocytomas. In 11 patients with pheochromocytomas plasma CgA and AM concentrations significantly decreased after tumor removal (P <0.001 for both). Circulating CgA and AM had a sensitivity of 76.2% and 81%, a specificity of 97.7% and 90.7%, and an accuracy of 91% and 88%, respectively.

Conclusion

This study demonstrates that circulating CgA and AM levels are increased in pheochromocytoma patients compared with healthy subjects and patients with non-functioning adrenocortical adenomas. Moreover, at the time of diagnosis plasma CgA levels correlated with plasma AM levels and with plasma metanephrine levels in all patients with pheochromocytomas. In conclusion, plasma CgA and AM concentrations may represent additional biochemical parameters for clinical monitoring of patients with pheochromocytomas.

Shear stress-induced endothelial adrenomedullin signaling regulates vascular tone and blood pressure

Hypertension is a primary risk factor for cardiovascular diseases including myocardial infarction and stroke. Major determinants of blood pressure are vasodilatory factors such as nitric oxide (NO) released from the endothelium under the influence of fluid shear stress exerted by the flowing blood. Several endothelial signaling processes mediating fluid shear stress-induced formation and release of vasodilatory factors have been described. It is, however, still poorly understood how fluid shear stress induces these endothelial responses. Here we show that the endothelial mechanosensitive cation channel PIEZO1 mediated fluid shear stress-induced release of adrenomedullin, which in turn activated its Gs-coupled receptor. The subsequent increase in cAMP levels promoted the phosphorylation of endothelial NO synthase (eNOS) at serine 633 through protein kinase A (PKA), leading to the activation of the enzyme. This Gs/PKA-mediated pathway synergized with the AKT-mediated pathways leading to eNOS phosphorylation at serine 1177. Mice with endothelium-specific deficiency of adrenomedullin, the adrenomedullin receptor, or Gαs showed reduced flow-induced eNOS activation and vasodilation and developed hypertension. Our data identify fluid shear stress-induced PIEZO1 activation as a central regulator of endothelial adrenomedullin release and establish the adrenomedullin receptor and subsequent Gs-mediated formation of cAMP as a critical endothelial mechanosignaling pathway regulating basal endothelial NO formation, vascular tone, and blood pressure.

Adrenomedullin-epinephrine cotreatment enhances cardiac output and left ventricular function by energetically neutral mechanisms

Adrenomedullin (AM) used therapeutically reduces mortality in the acute phase of experimental myocardial infarction. However, AM is potentially deleterious in acute heart failure as it is vasodilative and inotropically neutral. AM and epinephrine (EPI) are cosecreted from chromaffin cells, indicating a physiological interaction. We assessed the hemodynamic and energetic profile of AM-EPI cotreatment, exploring whether drug interaction improves cardiac function. Left ventricular (LV) mechanoenergetics were evaluated in 14 open-chest pigs using pressure-volume analysis and the pressure-volume area-myocardial O(2) consumption (PVA-MVo(2)) framework. AM (15 ng·kg(-1)·min(-1), n = 8) or saline (controls, n = 6) was infused for 120 min. Subsequently, a concurrent infusion of EPI (50 ng·kg(-1)·min(-1)) was added in both groups (AM-EPI vs. EPI). AM increased cardiac output (CO) and coronary blood flow by 20 ± 10% and 39 ± 14% (means ± SD, P < 0.05 vs. baseline), whereas controls were unaffected. AM-EPI increased CO and coronary blood flow by 55 ± 17% and 75 ± 16% (P < 0.05, AM-EPI interaction) compared with 13 ± 12% (P < 0.05 vs. baseline) and 18 ± 31% (P = not significant) with EPI. LV systolic capacitance decreased by -37 ± 22% and peak positive derivative of LV pressure (dP/dt(max)) increased by 32 ± 7% with AM-EPI (P < 0.05, AM-EPI interaction), whereas no significant effects were observed with EPI. Mean arterial pressure was maintained by AM-EPI and tended to decrease with EPI (+2 ± 13% vs. -11 ± 10%, P = not significant). PVA-MVo(2) relationships were unaffected by all treatments. In conclusion, AM-EPI cotreatment has an inodilator profile with CO and LV function augmented beyond individual drug effects and is not associated with relative increases in energetic cost. This can possibly take the inodilator treatment strategy beyond hemodynamic goals and exploit the cardioprotective effects of AM in acute heart failure.

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 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.

The effect of adrenomedullin (ADM) on tyrosine hydroxylase (TH) enzyme activity and blood pressure in cold exposed rats

It is known that, under stress conditions the hypothalamo-pituitary-adrenal (HPA) axis is stimulated and catecholamine production is increased. Adrenomedullin (ADM) is a novel peptide that elicits a long-vasorelaxation, and participates in blood pressure regulation via different mechanisms. In the present study, we investigated the administration of ADM on tyrosine hydroxylase (TH) enzyme activity in cold exposed rats. Four groups of Sprague-Dawley rats were studied for their TH enzyme activity in the adrenal medulla and hypothalamus. In addition to measuring blood pressure in these rats, TH enzyme activity in both the adrenal medulla and hypothalamus were examined in four groups of Sprague-Dawley rats: animals exposed to room temperature and cold stress (8 masculine C, 48 h), and rats injected with ADM (1.0 nmol/kg, i.v.) alone and/or together with cold stress. TH activity was shown to be increased in cold treated groups and decreased in ADM and ADM + cold stress group. Our findings appear to suggest that external ADM application caused an opposite effect on the same system in rats, decreasing the activity of tyrosine hydroxylase (TH) enzyme activity. Furthermore, externally applied ADM was shown to produce its expected hypotensive effect in cold-stressed rats. Our results suggest that a possible explanation for the effects of ADM is that, the uptake of ADM under cold stress may effect TH activity in studied tissues.

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.

Pathophysiological function of adrenomedullin and proadrenomedullin N-terminal peptides in adrenal chromaffin cells

Adrenomedullin (AM) and peptides of the proadrenomedullin N-terminal 20 peptide (PAMP20) family are multifunctional peptides abundantly expressed in the adrenal medulla. These peptides are released by regulated exocytosis along with catecholamines upon stimulation of adrenal chromaffin cells. They are also released gradually during culture, and this release is stimulated by a 3',5'-cyclic adenosine monophosphate (cAMP)-dependent pathway. The expression and release of AM increase under hypoxia in chromaffin cells. The expression of AM in pheochromocytoma PC12 cells is reduced during neuronal differentiation with nerve growth factor. On the other hand, PAMP20 and PAMP12 suppress catecholamine release and synthesis by interfering with nicotinic cholinergic receptors. AM increases blood flow in the adrenal gland, and causes a gradual release of catecholamine, but does not modify regulated exocytosis upon the stimulation of cells. Current data indicate that the expression of these peptides is regulated by intracellular signaling pathways, and changes under various physiological and pathological conditions. AM and PAMP20 family peptides have distinct physiological functions. PAMP20 and PAMP12 are endogenous peptides that modulate chromaffin cell function in an autocrine manner, whereas AM may mainly regulate vascular cell function in a paracrine manner.

Contribution of adrenomedullin to homeostatic response to cold stress in rat model

Acute stress known to stimulate sympathetic activity as well as the hypothalamo-pituitary-adrenal (HPA) axis, produces a significant increase in adrenomedullin (ADM) levels in the pituitary gland, plasma and adrenal glands, all of which are key components of HPA axis, suggesting a regulatory or protective role for ADM in countering HPA activation following a variety of physiological and psychological stressors. This study was conducted to assess a rat model for in depth investigation of biochemical mechanisms and consequences of cold stress. Four groups of Sprague-Dawley rats were observed for their serum total protein, glucose, trigliceride and cholesterol levels as well as their blood pressures after housing at room temperature, administration of ADM (1.0 nm/kg), exposing to cold stress (8 degrees C for 48 h) and exposing to ADM injection in addition to cold stress. The results suggest that application of ADM in addition to cold stress may act via receptors on different end-organs and causes altered metabolic regulation taking partial or total occupation of ADM receptors, stimulated in response to cold application induced physiologic ADM release before pharmacological ADM administration.

Aldosterone augments adrenomedullin production without stimulating pro-adrenomedullin N-terminal 20 peptide secretion in vascular smooth muscle cells

OBJECTIVE

Both adrenomedullin (AM) and pro-adrenomedullin N-terminal 20 peptide (PAMP), processed from the same precursor of prepro-adrenomedullin (preproAM), have differential biological properties; AM dilates blood vessels and presumably affects the vascular remodeling, while PAMP inhibits catecholamine secretion. Since aldosterone has been shown to be involved in vascular remodeling, we examined the effects of aldosterone on AM and PAMP secretion and preproAM gene expression in human aortic vascular smooth muscle cells (VSMC).

METHODS

AM and PAMP secreted from human VSMC incubated with aldosterone were measured by radioimmunoassay, and preproAM gene expression was evaluated by quantitative polymerase chain reaction.

RESULTS

Cultured human VSMC secreted both AM and PAMP into the media, while the secretion rate of AM was much higher than that of PAMP. Aldosterone increased preproAM gene expression in the cultured VSMC in a dose-dependent fashion following incubation for 48 h, with a concomitant increase in AM secretion from the cells, but PAMP secretion remained unchanged. Aldosterone-stimulated AM secretion was significantly reduced by spironolactone. Reverse-phase high-performance liquid chromatography analyses showed that immunoreactive AM secreted from the VSMC untreated or treated with aldosterone emerged at the point of human AM(1-52)-NH2.

CONCLUSIONS

AM production was stimulated by aldosterone in cultured human VSMC without an increase in PAMP secretion, suggesting a possible role of AM in modulating vascular remodeling by aldosterone.

Adrenomedullin in the adrenal

Adrenomedullin (AM) was originally characterized in extracts of an adrenal medullary tumor. Since this original finding the peptide and its mRNA have also been found in the adrenal cortex, specifically, in the cells of the aldosterone-secreting zona glomerulosa. It is clear that the synthesis of AM is actively regulated in both cortex and medulla. Much research effort has been focused on identifying a role for AM in the adrenal gland. To date, no consistent effect on medullary catecholamine biosynthesis has been demonstrated. In the cortex the actions of AM are controversial and appear to depend on both the tissue preparation used and on the specific receptor population expressed in the individual gland. The results of further studies on the long-term actions of AM on adrenal growth and differentiation are awaited with interest.

Regulation of adrenomedullin expression and release

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

Proadrenomedullin-derived peptides in the paracrine control of the hypothalamo-pituitary-adrenal axis

Adrenomedullin (ADM) and proadrenomedullin N-terminal 20 peptide (PAMP) are widely distributed in various body tissues and organs, including the hypothalamo-pituitary-adrenal (HPA) axis. ADM and PAMP inhibit in vitro release of ACTH from pituitary corticotropes, and findings suggest that this effect may become relevant when an exceedingly high ACTH secretion must be counteracted. ADM directly supresses angiotensin-II- and K+-stimulated aldosterone secretion from ZG cells, acting through calcitonin gene-related peptide (CGRP) type 1 ADM(22-52)-sensitive receptors, the activation of which is likely to impair Ca2+ influx. In contrast, ADM stimulates medullary chromaffin cells to release catecholamines, which in turn enhance aldosterone secretion acting in a paracrine manner. Also this effect of ADM occurs via CGRP1 receptors, which are coupled with the adenylate cyclase-dependent cascade. There is indication that in vivo these two opposite effects of ADM on ZG may interact with each other when normal aldosterone secretion has to be restored. ADM exerts a mitogenic effect on rat ZG, acting via CGRP1 receptors that activate the tyrosine kinase-dependent mitogen-activated protein kinase cascade. These findings, along with the demonstration of a high level of ADM gene expression in adrenocortical adenomas and carcinomas, may suggest a role for ADM as adrenocortical growth stimulator and tumor promoter. PAMP, like ADM, suppresses aldosterone response of ZG cells to Ca2+-dependent agonists, but, in contrast with ADM, it inhibits catecholamine release by adrenal medulla. Both effects of PAMP are mediated by PAMP(12-20)-sensitive receptors, whose signaling mechanism is likely to involve the blockade of voltage-gated Ca2+ channels. The concentrations attained by ADM and PAMP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their content in the hypothalamo-pituitary complex and adrenal gland is consistent with a paracrine mechanism of action, which may play an important role in pathophysiological conditions where the function of the HPA axis has to be reset.

Regulation of adrenomedullin secretion from cultured cells

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

Adrenomedullin and proadrenomedullin N-terminal 20 peptide (PAMP) in adrenal chromaffin cells

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are peptides having multiple physiological functions and are most abundantly expressed in the adrenal medulla. In addition to PAMP, PAMP12, a 12 amino acid peptide with sequence identity to PAMP between amino acids 9-20, has also been shown to be expressed in the adrenal medulla. AM, PAMP and PAMP12 are released along with catecholamines by regulated exocytosis upon stimulation of adrenal chromaffin cells. PAMP and PAMP12 regulate catecholamine release and synthesis by interfering with nicotinic cholinergic receptors in these chromaffin cells. AM may also cause gradual release of catecholamine from these cells. AM, PAMP and PAMP12 are endogenous peptides that modulate chromaffin cell function via different mechanisms.

Biosynthesis and secretion of adrenomedullin and proadrenomedullin N-terminal 20 peptide in a rat model of endotoxin shock

To study the biosyntheses and pathophysiological roles of adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) in septic shock, we compared the time course of plasma concentrations of these peptides and blood pressure in rats injected with either 0.9% saline (control group) or lipopolysaccharide (LPS group). The plasma AM concentration in the LPS group did not increase 30 and 60 min after LPS injection, at which time points the blood pressure remained low. Thereafter, AM rapidly increased, and it amounted to 35 times the basal value 4 h after injection, when the blood pressure returned to the basal level. The increment of plasma PAMP in the LPS group was lower than that of AM. We also examined the tissue concentration of AM and PAMP--as well as the tissue expression of proadrenomedullin (proAM) mRNA--in the LPS and control groups. LPS significantly increased the tissue concentrations of AM and PAMP in the lung, but decreased them in the adrenal gland and cardiac atrium. The LPS injection augmented proAM gene transcription in the lung, adrenal gland and aorta. In an immunohistochemical examination, AM staining was intense in alveolar endothelial cells of the lung in the LPS group. Thus, this septic shock model had high plasma levels of PAMP as well as AM, while the biosynthesis and secretion of the two peptides may have been differentially regulated in various tissues of rats injected with LPS. The present results suggest that these two bioactive peptides may play different roles in the pathophysiology of septic shock.

Increase in plasma adrenomedullin in patients with heart failure characterised by diastolic dysfunction

OBJECTIVE

To investigate the relation between plasma adrenomedullin and the severity of diastolic dysfunction in patients with heart failure.

DESIGN

Prospective study.

SETTING

University teaching hospital.

PATIENTS

77 patients (mean (SEM) age 66.3 (1.2) years; 75% male) who were being followed in the outpatient clinic after admission to hospital for acute heart failure.

INTERVENTIONS

Same day echocardiography with Doppler studies; determination of venous adrenomedullin concentration by radioimmunoassay.

MAIN OUTCOME MEASURES

Plasma adrenomedullin concentration and its correlation with systolic and diastolic function.

RESULTS

31 patients (40%) had isolated diastolic dysfunction (ejection fraction > 50%), and the remaining 46 had a depressed ejection fraction (< 50%). Of the patients with diastolic dysfunction, 17 had a restrictive filling pattern. In all but one of these there was coexisting systolic failure (chi(2) = 10.7, p = 0.001). Patients with systolic heart failure and a restrictive filling pattern (group 1, n = 16) had a higher plasma adrenomedullin than those with systolic failure and a non-restrictive filling pattern (group 2, n = 30) or with isolated diastolic heart failure and a non-restrictive filling pattern (group 3, n = 30) (mean (SEM): 91.7 (21.1) v 38.4 (8.8) v 34.0 (6.5) pmol/l, both p < 0.05). All heart failure values were higher (p < 0.01) than the control value (6.9 (1.2) pmol/l). Ejection fraction and left ventricular dimensions were similar in groups 1 and 2. Plasma adrenomedullin did not correlate with ejection fraction or New York Heart Association functional class. Stepwise multiple regression analysis showed that the presence of a restrictive filling pattern was the only independent variable associated with a high plasma adrenomedullin.

CONCLUSIONS

Plasma adrenomedullin concentrations in patients with heart failure are determined by the presence of diastolic dysfunction, and are especially raised in the presence of a restrictive filling pattern. There appears to be no correlation with systolic dysfunction.

Increase in plasma adrenomedullin in patients with heart failure characterised by diastolic dysfunction

OBJECTIVE

To investigate the relation between plasma adrenomedullin and the severity of diastolic dysfunction in patients with heart failure.

DESIGN

Prospective study.

SETTING

University teaching hospital.

PATIENTS

77 patients (mean (SEM) age 66.3 (1.2) years; 75% male) who were being followed in the outpatient clinic after admission to hospital for acute heart failure.

INTERVENTIONS

Same day echocardiography with Doppler studies; determination of venous adrenomedullin concentration by radioimmunoassay.

MAIN OUTCOME MEASURES

Plasma adrenomedullin concentration and its correlation with systolic and diastolic function.

RESULTS

31 patients (40%) had isolated diastolic dysfunction (ejection fraction > 50%), and the remaining 46 had a depressed ejection fraction (< 50%). Of the patients with diastolic dysfunction, 17 had a restrictive filling pattern. In all but one of these there was coexisting systolic failure (χ2 = 10.7, p = 0.001). Patients with systolic heart failure and a restrictive filling pattern (group 1, n = 16) had a higher plasma adrenomedullin than those with systolic failure and a non-restrictive filling pattern (group 2, n = 30) or with isolated diastolic heart failure and a non-restrictive filling pattern (group 3, n = 30) (mean (SEM): 91.7 (21.1) v 38.4 (8.8) v 34.0 (6.5) pmol/l, both p < 0.05). All heart failure values were higher (p < 0.01) than the control value (6.9 (1.2) pmol/l). Ejection fraction and left ventricular dimensions were similar in groups 1 and 2. Plasma adrenomedullin did not correlate with ejection fraction or New York Heart Association functional class. Stepwise multiple regression analysis showed that the presence of a restrictive filling pattern was the only independent variable associated with a high plasma adrenomedullin.

CONCLUSIONS

Plasma adrenomedullin concentrations in patients with heart failure are determined by the presence of diastolic dysfunction, and are especially raised in the presence of a restrictive filling pattern. There appears to be no correlation with systolic dysfunction.

Current topics in pheochromocytoma

Pheochromocytoma is the tumor that produces catecholamines and originates from chromaffin cells, which are differentiated from sympathoadrenal progenitor cells of neural crest under the influence of glucocorticoids. Genetic abnormalities of familial pheochromocytomas have elucidated oncogenic genetic bases of the tumor, including gene abnormalities of the RET proto-oncogene in multiple endocrine neoplasia type 2, VHL gene in von Hippel Lindau's disease or the NF1 gene in neurofibromatosis. Co-localization of various substances with catecholamines in the tumor, including neuropeptide Y, opioid peptides or adrenomedulOFF peptide elevating cAMP production, is recognized. The significance of these substances in modulating clinical features of pheochromocytomas is not fully understood.

Adrenomedullin, a multifunctional regulatory peptide

Since the discovery of adrenomedullin in 1993 several hundred papers have been published regarding the regulation of its secretion and the multiplicity of its actions. It has been shown to be an almost ubiquitous peptide, with the number of tissues and cell types synthesizing adrenomedullin far exceeding those that do not. In Section II of this paper we give a comprehensive review both of tissues and cell lines secreting adrenomedullin and of the mechanisms regulating gene expression. The data on circulating adrenomedullin, obtained with the various assays available, are also reviewed, and the disease states in which plasma adrenomedullin is elevated are listed. In Section III the pharmacology and biochemistry of adrenomedullin binding sites, both specific sites and calcitonin gene-related peptide (CGRP) receptors, are discussed. In particular, the putative adrenomedullin receptor clones and signal transduction pathways are described. In Section IV the various actions of adrenomedullin are discussed: its actions on cellular growth, the cardiovascular system, the central nervous system, and the endocrine system are all considered. Finally, in Section V, we consider some unresolved issues and propose future areas for research.

Effects of PAMP on mRNAs coding for catecholamine-synthesizing enzymes in PC12 cells

Proadrenomedullin N-terminal 20 peptide (PAMP) is a novel hypotensive peptide found in the N-terminal portion of the precursor of adrenomedullin (AM). Although PAMP and AM originate from the same precursor and exert both a potent hypotensive action, they seem to control blood pressure through different mechanisms. To gain new insight into the anticholinergic actions of PAMP, we determined the effects of PAMP on the tyrosine hydroxylase (TH)- and dopamine beta-hydroxylase (DBH) mRNA expression in the rat pheochromocytoma cell line PC12 stimulated by nicotine. PAMP (> or =1 microM) significantly inhibited the nicotine-induced increases of TH- and DBH mRNA expression in a concentration-dependent manner. Also, PAMP at the concentrations (> or =1 microM) significantly inhibited nicotine-induced cyclic adenosine monophosphate (cAMP) production. These results indicate that the anticholinergic hypotensive actions of PAMP can be explained, at least in part, by its inhibition of the expression of mRNAs coding for catecholamine-synthesizing enzymes, and that the inhibitory effect is mediated by the cAMP/protein kinase A pathway.

Cyclic AMP-dependent synthesis and release of adrenomedullin and proadrenomedullin N-terminal 20 peptide in cultured bovine adrenal chromaffin cells

Adrenomedullin and proadrenomedullin N-terminal 20 peptide are peptides with multiple physiological functions and are most abundant in adrenal medulla. We studied whether the cAMP-dependent pathway is involved in the regulation of synthesis and release of adrenomedullin and proadrenomedullin N-terminal 20 peptide in cultured bovine adrenal chromaffin cells. Exposure of the cells to dibutyryl cAMP (dbcAMP) increased a progressive accumulation of immunoreactive-adrenomedullin and immunoreactive-proadrenomedullin N-terminal 20 peptide in the extracellular medium, while reciprocally decreasing their cellular content in a time-dependent manner. The decrease of levels of both peptides in the cells was much greater in extent than the increase of the peptides in the medium. H89, an inhibitor of cAMP-dependent protein kinase attenuated these changes, induced by dbcAMP. The resulting changes by dbcAMP and H89 were similar to those of chromogranin B, a marker peptide of chromaffin granule. Northern blot analysis showed that the mRNA encoding these peptides, detected as a band of 1.6 kb, was decreased by the treatment with dbcAMP. The effect of dbcAMP on mRNA was attenuated by H89, and was reversible as the decreased mRNA level caused by dbcAMP could be returned to control levels by culturing cells after removal of dbcAMP. These results suggest that the cAMP-dependent protein kinase pathway stimulates the release of adrenomedullin and proadrenomedullin N-terminal 20 peptide, whereas it lowers synthesis of these peptides via the reduction of their transcript level.

Effects of adrenomedullin and PAMP on adrenal catecholamine release in dogs

We examined the effects of proadrenomedullin-derived peptides on the release of adrenal catecholamines in response to cholinergic stimuli in pentobarbital sodium-anesthetized dogs. Drugs were administered into the adrenal gland through the phrenicoabdominal artery. Splanchnic nerve stimulation (1, 2, and 3 Hz) and ACh injection (0.75, 1.5, and 3 microgram) produced frequency- or dose-dependent increases in adrenal catecholamine output. These responses were unaffected by infusion of adrenomedullin (1, 3, and 10 ng. kg-1. min-1) or its selective antagonist adrenomedullin-(22-52) (5, 15, and 50 ng. kg-1. min-1). Proadrenomedullin NH2-terminal 20 peptide (PAMP; 5, 15, and 50 ng. kg-1. min-1) suppressed both the splanchnic nerve stimulation- and ACh-induced increases in catecholamine output in a dose-dependent manner. PAMP also suppressed the catecholamine release responses to the nicotinic agonist 1, 1-dimethyl-4-phenylpiperazinium (0.5, 1, and 2 microgram) and to muscarine (0.5, 1, and 2 microgram), although the muscarine-induced response was relatively resistant to PAMP. These results suggest that PAMP, but not adrenomedullin, can act as an inhibitory regulator of adrenal catecholamine release in vivo.

Adrenomedullin and the control of fluid and electrolyte homeostasis

Two potent hypotensive peptides, adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP), are encoded by the adrenomedullin gene. AM stimulates nitric oxide production by endothelial cells, whereas PAMP acts presynaptically to inhibit adrenergic nerves that innervate blood vessels. Complementary, but mechanistically unique, actions also occur in the anterior pituitary gland where both peptides inhibit adrenocorticotropin release. In the adrenal gland both AM and PAMP inhibit potassium and angiotensin II-stimulated aldosterone secretion. Natriuretic and diuretic actions of AM reflect unique actions of the peptide on renal blood flow and tubular function. In the brain AM inhibits water intake and, in a physiologically relevant manner, salt appetite. Both AM and PAMP act in the brain to elevate sympathetic tone, effects that mirror the positive inotropic action of AM in the heart. Cardioprotective actions in the brain and heart may be important counter-regulatory actions that buffer the extreme hypotensive actions of the peptides when released in sepsis. Thus the biologic actions of the proadrenomedullin-derived peptides seem well coordinated to contribute to the physiologic regulation of volume and electrolyte homeostasis.

Effects of dietary salt on adrenomedullin and its receptor mRNAs in rat kidney

There is accumulating evidence that adrenomedullin (ADM) is involved in the control of salt and water homeostasis. ADM is considered to act primarily in a paracrine fashion, and since the kidneys are target organs for ADM, we investigated the localization and regulation of ADM and ADM receptor (ADM-R) mRNAs in the kidney. mRNAs for ADM and ADM-R were colocalized in renal vessels, glomeruli, and inner medullary collecting ducts. ADM mRNA was also detected in proximal tubules, whereas ADM-R mRNA was found in distal convoluted tubules. By ribonuclease protection assay, the abundance of ADM mRNA was fourfold higher in cortex than in outer medulla and papilla. In isolated glomeruli, ADM mRNA was threefold higher compared with cortex. Conversely, ADM-R mRNA was fourfold higher in papilla than in renal cortex. This distribution of mRNAs for ADM and ADM-R suggests a cortical source of ADM and a preferential action of ADM in the papilla. Ten days of feeding a low-salt (0.02%) or a high-salt diet (4%) did not change ADM mRNA or ADM-R mRNA in any kidney zone.

Adrenomedullin stimulates renin release and renin mRNA in mouse juxtaglomerular granular cells

The recently discovered peptide adrenomedullin (AM) alters blood pressure through effects on the resistance vessels. Moreover, AM modifies the secretion of corticotropin and aldosterone and could thereby indirectly influence blood pressure through the renin-angiotensin-aldosterone system. Although plasma AM and renin concentration have been found to directly correlate, a causal linkage between AM and renin has not been shown. The present study tested the influence of AM on renin secretion and renin gene expression by renal juxtaglomerular granular cells. Prominent expression and release of AM by vascular structures has been reported; therefore, we investigated the local expression of AM in juxtaglomerular structures. Renin release from isolated perfused rat kidneys was dose-dependently increased by AM (1 to 30 nmol/L), whereas renal perfusate flow rate increased up to 17% at a constant perfusion pressure of 100 mm Hg. In primary cultures of mouse granular cells, AM augmented renin release, renin mRNA accumulation, and cAMP production in a dose- and time-dependent manner (threshold values in the range 10 pmol/L to 1 nmol/L). By reverse transcription-polymerase chain reaction, significant expression of the AM gene was detected in microdissected rat glomeruli with afferent arterioles and in primary cultures of mesangial and granular cells. We conclude that AM is expressed in juxtaglomerular structures and that it has a direct stimulatory effect on renin secretion and renin mRNA abundance by receptors on juxtaglomerular cells, possibly through increases in cAMP. AM could act as an autocrine/paracrine stimulatory factor in the control of renin secretion and renin gene expression.

Effects of adrenomedullin and proadrenomedullin N-terminal 20 peptide on rat zona glomerulosa cells

Adrenomedullin (ADM) and proadrenomedullin N-terminal 20 peptide (PAMP) derive from a 185-amino acid prohormone, called preproadrenomedullin, which is highly expressed in rat adrenal medulla. ADM and PAMP did not affect either basal or ACTH-stimulated aldosterone secretion of dispersed rat zona glomerulosa cells In contrast, both peptides markedly suppressed angiotensin-II-stimulated aldosterone production, PAMP being much more effective than ADM (minimal effective concentration, 10(-10) M versus 10(-8) M. IC50, 2.0 +/- 0.17 x 10(-9) M versus 3.1 +/- 0.22 x 10(-8) M; P<0.01. Maximum inhibition, 80% versus 43%, respectively). The inhibitory effect of 10(-7) M ADM was completely reversed by the competitive antagonist of type 1 calcitonin gene-related peptide (CGRP) receptors CGRP(8-37) (10(-6) M), while that of 10(-7) M PAMP did not, thereby suggesting that this last peptide acts through specific receptors. Collectively, these findings may suggest that of the two main preproadrenomedullin derived peptides is PAMP which has probably to be considered a physiologic inhibitor of mineralocorticoid secretion in rats.

Role of adrenomedullin and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Adrenomedullin (ADM) is a hypotensive peptide, originally isolated from human pheochromocytomas, and then found to be widely distributed in the various body systems. ADM derives from preproadrenomedullin, a 185-amino acid residue prohormone, containing at its N-terminal a 20-amino acid sequence, named proadrenomedullin N-terminal 20 peptide (PAMP). ADM and PAMP immunoreactivities have been detected in the hypothalamo-pituitary-adrenal (HPA) axis of humans, rats, and pigs. Adrenal glands possess binding sites for both ADM and PAMP, the former being mainly of the subtype 1 of calcitonin gene-related peptide (CGRP) receptors. ADM exerts a direct inhibitory action on angiotensin II- or potassium-stimulated aldosterone secretion of zona glomerulosa cells. This effect is mediated by the CGRP1 receptor and its mechanism probably involves the blockade of Ca2+ influx. In contrast, ADM enhances aldosterone production by in situ perfused rat adrenals and human adrenal slices (containing medullary chromaffin cells), again through the activation of CGRP1 receptors. This aldosterone secretagogue effect of ADM is blocked by the beta-adrenoceptor antagonist l-alprenolol, thereby suggesting that it is indirectly mediated by the release of catecholamines by chromaffin cells. The effects of ADM on adrenal glucocorticoid release are doubtful and probably mediated by the increase in adrenal blood flow rate and the inhibition of ACTH release by pituitary corticotropes. The concentrations reached by ADM and PAMP in the blood rule out the possibility that they act on the HPA axis as circulating hormones. Conversely, their content in both adrenal and hypothalamo-pituitary complex is consistent with a paracrine mechanism of action, which may play a potentially important role in the regulation of fluid and electrolyte homeostasis.

Adrenomedullin: a new modulator of vascular tone

We have discovered a novel hypotensive peptide, designated "adrenomedullin", in human pheochromocytoma extracts. It has potent and long-lasting vasodilatory effects in several vascular systems. In addition to adrenomedullin, another hypotensive peptide, termed PAMP, is also produced from the adrenomedullin precursor. Although initially isolated from human pheochromocytoma and porcine adrenal medullary tissue, adrenomedullin mRNA is highly expressed in several peripheral organs including cardiovascular tissues. Taken together with the presence of adrenomedullin-specific receptors on VSMCs and the significant increase in plasma immunoreactive adrenomedullin levels in patients with hypertension, renal failure and congestive heart failure, adrenomedullin may participate in the pathogenesis of these diseases as a factor regulating blood pressure and circulation.

An accelerated increase of plasma adrenomedullin in acute asthma

A novel vasorelaxant peptide, adrenomedullin (AM), has been isolated from the acid extract of human pheochromocytoma. We have recently shown that AM inhibits histamine- and acetylcholine-induced bronchoconstriction in anesthetized guinea pigs in vivo, and this bronchodilatory effect is long-lasting. Here, we measured plasma AM concentrations in nine patients with an acute attack of bronchial asthma. The results were compared with values in 30 age-matched normal control subjects and seven age-matched stable asthmatic patients. The mean AM concentrations of patients with an acute asthma attack (98 +/- 22 pg/mL) were clearly higher than those of normal control subjects (18 +/- 2 pg/mL) and stable asthmatic patients (21 +/- 3 pg/mL). Reverse-phase high-performance liquid chromatography (HPLC) showed that the major component of plasma immunoreactive AM in patients with an asthma attack and in normal subjects equally corresponded to authentic human AM(1-52). Our results suggest that plasma AM is markedly increased in many of the patients during an acute attack of bronchial asthma, but it is not observed in stable asthmatic patients. Although this report is preliminary, the observed increase of circulating AM during an acute asthma attack may represent a compensatory mechanism against the bronchoconstriction, probably through its bronchodilatory action.

Adrenomedullin: localization in the gastrointestinal tract and effects on insulin secretion

Adrenomedullin is a novel hypotensive adrenal polypeptide originally isolated from a human pheochromocytoma and is structurally related to calcitonin gene-related peptide and islet amyloid polypeptide. Using immunocytochemistry, the occurrence of adrenomedullin in the adrenal gland and gastro-entero-pancreatic region in the rat was examined and its effect on insulin secretion from isolated rat islets was determined. Adrenomedullin-like immunoreactivity occurred in noradrenaline- and adrenaline-producing cells in the adrenal gland. Gastrointestinal endocrine cells, with increased density distally, displayed adrenomedullin-like immunoreactivity; these cells constituted a subpopulation of the enterochromaffin (serotonin-containing) cells. Co-localization of adrenomedullin with somatostatin, glicentin, gastrin/cholecystokinin, peptide YY or islet amyloid polypeptide was not encountered. Adrenomedullin-immunoreactive cells were not observed in the pancreatic islets. At 1, 10 and 100 nmol/l, adrenomedullin stimulated insulin release from isolated rat islets in the presence of 3.3 mmol/l glucose (P < 0.05) and at 100 nmol/l, the peptide potentiated insulin secretion also in the presence of 8.3 mmol/l glucose (P < 0.05). These findings suggest that, besides being an adrenal hypotensive peptide, adrenomedullin may be a gut hormone with a potential insulinotropic function.

Increased plasma adrenomedullin in acute myocardial infarction

Adrenomedullin has a potent vasodilating effect comparable to that of calcitonin gene-related peptide. To investigate the pathophysiologic role of endogenous adrenomedullin, we determined sequentially the plasma adrenomedullin level in 15 consecutive patients with acute myocardial infarction (AMI). Plasma adrenomedullin was higher immediately after the onset of AMI and decreased gradually; plasma levels during the 3-week period after the AMI were higher than plasma levels in 15 healthy control subjects (p < 0.001), with higher levels in patients with congestive heart failure than in patients without congestive heart failure throughout the period of the study (p < 0.05). Plasma adrenomedullin was positively correlated with pulmonary capillary wedge pressure, pulmonary arterial pressure, right atrial pressure, and heart rate in the early stage of AMI. These findings suggest that the elevation of plasma adrenomedullin is related to the retention of body fluid volume, the enhancement of sympathetic activity, and/or the elevation of pressure in pulmonary vascular beds. Adrenomedullin may act against excessive vasoconstrictors increased in AMI.

Adrenomedullin and calcitonin gene-related peptide inhibit aldosterone secretion in rats, acting via a common receptor

Adrenomedullin (ADM) and calcitonin gene-related peptide (CGRP) did not affect either basal or ACTH-stimulated secretion of a1dosterone and corticosterone by dispersed rat capsular and inner adrenocortical cells, respectively. However, both peptides strongly depressed angiotensin-II (ANG- II)-stimulated a1dosterone production by capsular cells, the minimal effective concentration was 10(-7) M. The inhibitory effect of both ADM and CGRP was reversed by CGRP8-37, a specific CGRP1 receptor antagonist; a complete reversal was obtained with a CGRP8-37 concentration of 10(-6) M. Our findings indicate that ADM and CGRP specifically interfere with the intracellular mechanisms transducing the secretagogue signal of ANG-II, and suggest that the ADM effect is mediated by CGRP receptors

Adrenomedullin: A newly discovered hormone controlling fluid and electrolyte homeostasis

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

Adrenomedullin stimulates steroid secretion by the isolated perfused rat adrenal gland in situ: comparison with calcitonin gene-related peptide effects

Adrenomedullin (ADM), a vasodilatatory peptide contained in adrenal medulla, was found to induce a dose-dependent increase in aldosterone (ALDO) and corticosterone (B) release by the in situ perfused rat adrenal gland, along with a rise in the flow rate of the perfusion medium. The minimal effective dose for ALDO response was three and two orders of magnitude less than those able to evoke B and medium flow rate responses. Calcitonin gene-related peptide (CGRP), another vasodilatatory peptide contained in adrenal medulla and showing a slight homology in its amino acid sequence with ADM, elicited similar effects. CGRP (8-37), a specific antagonist of CGRP1 receptors, annulled all the effects of both ADM and CGRP, whereas l-alprenolol, a beta-adrenoceptor antagonist, partially reversed only ALDO response to the peptides. In light of these findings the following conclusions are drawn: i) ADM and CGRP stimulate rat adrenals in vivo to release B by raising blood flow rate; ii) ADM and CGRP enhance ALDO secretion via an indirect mechanism probably requiring the release of catecholamines by medullary chromaffin cells; and iii) the effects of ADM and CGRP on the rat adrenal gland are mediated by a common receptor of the CGRP1 subtype.

Adrenomedullin stimulates calcium efflux from adrenal chromaffin cells in culture: possible involvement of an Na+/Ca2+ exchange mechanism

The effect of adrenomedullin, a hypotensive peptide, on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. Adrenomedullin stimulated the efflux of 45Ca2+ from the cells in a concentration-dependent manner (10(-7)M - 3x10(-6)M). Adrenomedullin did not increase the intracellular free Ca2+ ([Ca2+]i) level and catecholamine secretion. The adrenomedullin-stimulated 45Ca2+ efflux was not inhibited by incubation with Ca2+-free medium, but was inhibited by incubation with Na+-free medium. These results indicate that adrenomedullin stimulates extracellular Na+-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably through its stimulatory effect on membrane Na+/Ca2+ exchange.

Vasodilative effect of adrenomedullin in isolated arteries of the dog

Adrenomedullin is known to induce profound hypotension in vivo, but the direct effect of this peptide on isolated arteries has not been demonstrated. This study estimated the vasodilative effects of adrenomedullin in comparison with those of calcitonin gene-related peptide (CGRP) in basilar, mesenteric, coronary, renal and femoral arteries isolated from the dog. Adrenomedullin (3 to 100 nM) and CGRP (1 to 30 nM) induced concentration-dependent relaxation of these arteries with and without endothelium, and the relaxing effects were slightly greater in endothelium-intact arteries than in denuded ones. The vasodilative potency of adrenomedullin relative to CGRP was smaller in the femoral artery than in basilar, mesenteric, coronary and renal arteries.

Production of bioactive enkephalin from the nonendocrine cell lines COS-7, NIH3T3, Ltk-, and C2C12

Enkephalin is synthesized from proenkephalin in neuroendocrine cells. For the attempt to induce nonneuroendocrine origin cells to produce enkephalin, we used a mammalian expression vector for fusion peptides, pMEproCT beta, in which a fused peptide is designed to be cleaved by a yeast Kex2-like endoprotease furin. Met-Enkephalin was expressed in four nonneuroendocrine cell lines: COS-7, C2C12, Ltk-, and NIH3T3. The four cell lines produced a marked amount of Met-enkephalin, which appeared as a single peak on reverse-phase HPLC. Because transplantation of adrenal medullary cells to the subarachnoid space has been used to alleviate terminal cancer pain, and enkephalin appears to play a central role in relieving pain, this enkephalin expression vector may be useful for direct enkephalin expression in pericancerous tissues.