Cardiac secretion of adrenomedullin in human heart failure

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.

Plasma N-terminal pro-brain natriuretic peptide and adrenomedullin: new neurohormonal predictors of left ventricular function and prognosis after myocardial infarction

BACKGROUND

Newly discovered circulating peptides, N-terminal pro-brain natriuretic peptide (N-BNP) and adrenomedullin (ADM), were examined for prediction of cardiac function and prognosis and compared with previously reported markers in 121 patients with myocardial infarction.

METHODS AND RESULTS

The association between radionuclide left ventricular ejection fraction (LVEF) and N-BNP at 2 to 4 days (r=-.63, P<.0001) and 3 to 5 months (r=-.58, P<.0001) after infarction was comparable to that for C-terminal BNP and far stronger than for ADM (r=-.26, P<.01), N-terminal atrial natriuretic peptide (N-ANP), C-terminal ANP, cGMP, or plasma catecholamine concentrations. For prediction of death over 24 months of follow-up, an early postinfarction N-BNP level > or = 160 pmol/L had sensitivity, specificity, positive predictive value, and negative predictive values of 91%, 72%, 39%, and 97%, respectively, and was superior to any other neurohormone measured and to LVEF. Only 1 of 21 deaths occurred in a patient with an N-BNP level below the group median (Kaplan-Meier survival analysis, P<.00001). For prediction of heart failure (left ventricular failure), plasma N-BNP > or = 145 pmol/L had sensitivity (85%) and negative predictive value (91%) comparable to the other cardiac peptides and was superior to ADM, plasma catecholamines, and LVEF. By multivariate analysis, N-BNP but not ADM provided predictive information for death and left ventricular failure independent of patient age, sex, LVEF, levels of other hormones, and previous history of heart failure, myocardial infarction, hypertension, or diabetes.

CONCLUSIONS

Plasma N-BNP measured 2 to 4 days after myocardial infarction independently predicted left ventricular function and 2-year survival. Stratification of patients into low- and high-risk groups can be facilitated by plasma N-BNP or BNP measurements, and one of these could reasonably be included in the routine clinical workup of patients after myocardial infarction.

Evidence for cAMP-independent mechanisms mediating the effects of adrenomedullin, a new inotropic peptide

BACKGROUND

Adrenomedullin (ADM), a new vasorelaxing and natriuretic peptide, may function as an endogenous regulator of cardiac function, because ADM and its binding sites have been found in the heart. We characterize herein the cardiac effects of ADM as well as the underlying signaling pathways in vitro.

METHODS AND RESULTS

In isolated perfused, paced rat heart preparation, infusion of ADM at concentrations of 0.1 to 1 nmol/L for 30 minutes induced a dose-dependent, gradual increase in developed tension, whereas proadrenomedullin N-20 (PAMP; 10 to 100 nmol/L), a peptide derived from the same gene as ADM, had no effect. The ADM-induced positive inotropic effect was not altered by a calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP8-37, or H-89, a cAMP-dependent protein kinase inhibitor. ADM also failed to stimulate ventricular cAMP content of the perfused hearts. Ryanodine (3 nmol/L), a sarcoplasmic reticulum Ca2+ release channel opener, suppressed the overall ADM-induced positive inotropic effect. Pretreatment with thapsigargin (30 nmol/L), which inhibits sarcoplasmic reticulum Ca2+ ATPase and depletes intracellular Ca2+ stores, attenuated the early increase in developed tension produced by ADM. In addition, inhibition of protein kinase C by staurosporine (10 nmol/L) and blockade of L-type Ca2+ channels by diltiazem (1 micromol/L) significantly decreased the sustained phase of ADM-induced increase in developed tension. Superfusion of atrial myocytes with ADM (1 nmol/L) in isolated left atrial preparations resulted in a marked prolongation of action potential duration between 10 and -50 mV transmembrane voltage, consistent with an increase in L-type Ca2+ channel current during the plateau.

CONCLUSIONS

Our results show that ADM enhances cardiac contractility via cAMP-independent mechanisms including Ca2+ release from intracellular ryanodine- and thapsigargin-sensitive Ca2+ stores, activation of protein kinase C, and Ca2+ influx through L-type Ca2+ channels.

Plasma levels of adrenomedullin in patients with mitral stenosis

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

Induction of adrenomedullin by hypoxia and cobalt chloride in human colorectal carcinoma cells

Adrenomedullin (ADM) is a vasodilator peptide, first isolated from human pheochromocytoma. To explore the pathophysiological role of ADM in ischemic conditions, we investigated the effects of hypoxia on ADM production and ADM mRNA expression in a cultured human colorectal carcinoma cell line, DLD-1. Northern blot analysis and radioimmunoassay showed that hypoxia stimulated the accumulation of ADM mRNA in the DLD-1 cells and immunoreactive ADM (ir-ADM) in the cultured media. Exposure to hypoxia for 12 hours increased ADM mRNA levels about 6-fold and ir-ADM levels about 4-fold. Moreover, treatment of DLD-1 cells with cobalt chloride, which mimics hypoxic states, significantly increased ADM mRNA levels about 18-fold and ir-ADM levels about 4-fold. These results suggest that ADM plays an important role in the pathophysiology of ischemic states.

Cardiac production and secretion of adrenomedullin are increased in heart failure

Plasma adrenomedullin (AM) levels are reportedly increased in heart failure, but whether the cardiac production and secretion of AM is increased in heart failure remains unknown. To investigate the sites of production and secretion of AM in heart failure, we measured plasma AM levels and peptide and mRNA levels of AM in various tissues in rats with heart failure. We also examined whether the heart actually secretes AM into the circulation in patients with heart failure. We measured plasma and tissue AM levels by specific radioimmunoassay and AM mRNA by Northern blot analysis in rats with heart failure produced by aortocaval fistula. We also measured plasma AM levels in the coronary sinus and aorta in patients with left ventricular dysfunction before and after rapid right ventricular pacing. The increase in plasma AM levels in heart failure rats correlated with ventricular weight. Tissue AM levels were increased in the heart and lungs but not in the kidneys or adrenals of rats with heart failure. Similarly, tissue AM mRNA levels were also increased in the heart and lungs of heart failure rats. Plasma AM levels were higher in the coronary sinus than in the aorta in patients with left ventricular dysfunction. Rapid right ventricular pacing increased plasma atrial natriuretic peptide but not AM. These results suggest that plasma AM levels are increased in heart failure in proportion to the severity of heart failure and that cardiac production and secretion of AM is increased in heart failure rats. The lung may be another site for increased production of AM in heart failure rats. Human failing heart actually secretes AM into the circulation, and the regulation of AM secretion appears to differ from that of atrial natriuretic peptide.

Analysis of responses to human synthetic adrenomedullin and calcitonin gene-related peptides in the hindlimb vascular bed of the cat

Vasodilator responses to human adrenomedullin (hADM), a newly discovered hypotensive peptide, human calcitonin gene-related peptide-alpha (hCGRP-alpha) and hCGRP-beta, which share structural homology with hADM, were compared in the hindlimb vascular bed of the cat under constant flow conditions. Injections of hADM (0.003-1 nmol), hCGRP-alpha, and hCGRP-beta (0.003-0.3 nmol) into the perfusion circuit caused dose-related decreases in hindlimb perfusion pressure. Vasodilator responses to hCGRP-alpha and hCGRP-beta were similar in potency and duration, and the doses of hCGRP-alpha and hCGRP-beta required to reduce hindlimb perfusion pressure 40 mm Hg (ED40 mm Hg) were significantly lower than the ED40 mm Hg for hADM. The duration of the hindlimb vasodilator responses to hCGRP-alpha and hCGRP-beta were significantly longer than the duration of the response to hADM. Amylin, a peptide that shares structural homology with ADM and with CGRP, had no significant effect on hindlimb perfusion pressure when injected in doses up to 1 nmol. Decreases in hindlimb perfusion pressure in response to hADM, hCGRP-alpha, and hCGRP-beta were not altered by L-N5-(1-iminoethyl)-ornithine (L-NIO) in a dose of the nitric oxide synthase inhibitor that decreased the vasodilator response to acetylcholine or by the cyclooxygenase inhibitor, meclofenamate, in a dose that decreased the vasodilator response to archidonic acid. The present data demonstrate that hADM, hCGRP-alpha, and hCGRP-beta have potent, but relatively short-lasting, vasodilator activity, and that vasodilator responses are not dependent on the release of nitric oxide or vasodilator prostaglandins in the hindlimb vascular bed of the cat.

Nitric oxide and cardiac failure

Cardiac myocytes express two types of nitric oxide (NO) synthase, eNOS and iNOS. eNOS activity is regulated by the contractile state of the heart, while iNOS expression is induced by cytokines. Nitric oxide induced by cytokines causes negative inotropic and lethal effects on cardiac myocytes. Expression of iNOS in the myocardium is increased in patients with dilated cardiomyopathy with clinical evidence of heart failure. Several neurohumoral factors activated in chronic heart failure augment cardiac iNOS expression and could cause cardiac dysfunction and cell damage.

Adrenomedullin in experimental congestive heart failure: cardiorenal activation

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

Plasma concentrations of adrenomedullin correlate with the extent of pulmonary hypertension in patients with mitral stenosis

OBJECTIVE

To examine the pathophysiological significance of adrenomedullin in the pulmonary circulation by investigating the relation between plasma concentrations of adrenomedullin and central haemodynamics in patients with mitral stenosis.

METHODS

Plasma concentrations of adrenomedullin in blood samples obtained from the femoral vein, pulmonary artery, left atrium, and aorta were measured by a newly developed specific radio-immunoassay in 23 consecutive patients with mitral stenosis (16 females and seven males, aged 53 (10) years (mean (SD)) who were undergoing percutaneous mitral commissurotomy.

RESULTS

Patients with mitral stenosis had higher concentrations of adrenomedullin than age matched normal controls (3.9 (0.3) v 2.5 (0.3) pmol/l, p < 0.001). There was a reduction in adrenomedullin concentrations between the pulmonary artery and the left atrium (3.8 (0.2) v 3.2 (0.4) pmol/l, p < 0.001). The venous concentrations of adrenomedullin correlated with mean pulmonary artery pressure (r = 0.65, p < 0.001), total pulmonary vascular resistance (r = 0.83, p < 0.0001), and pulmonary vascular resistance (r = 0.65, p < 0.001). Plasma concentrations of adrenomedullin did not change immediately after percutaneous mitral commissurotomy; however, they decreased significantly one week later.

CONCLUSIONS

Plasma concentrations of adrenomedullin are increased in patients with mitral stenosis. This may help to attenuate the increased pulmonary arterial resistance in secondary pulmonary hypertension due to mitral stenosis.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Hormonal and humeral considerations in hypertensive disease

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

Plasma adrenomedullin concentrations and cardiac and arterial hypertrophy in hypertension

It has been reported that plasma concentrations of adrenomedullin (AM), a novel vasodilator peptide, are higher in patients with essential hypertension than those in normotensive subjects. To clarify the clinical significance of increased levels of AM in patients with essential hypertension, in this study we examined the relationship between plasma concentrations of AM and the structure of the left ventricle or carotid artery. Plasma AM concentrations; renin activity; and norepinephrine, epinephrine, and creatinine concentrations in 50 patients with untreated essential hypertension without renal dysfunction and heart failure were measured. We also measured the mean wall thickness of the left ventricle and left ventricular mass index by M-mode echocardiography and intimal-medial thickness and arterial distensibility of the carotid artery by ultrasonography. Hypertensive patients were divided into two groups: hypertensives with and those without left ventricular hypertrophy. Plasma AM concentrations in hypertensive patients with left ventricular hypertrophy were significantly higher than in hypertensive patients without left ventricular hypertrophy (7.87+/-2.70 vs 5.74+/-1.65 fmol/mL, P<.01). In all hypertensive patients, plasma AM concentrations were not correlated with blood pressure, plasma renin activity, plasma norepinephrine, plasma epinephrine, or plasma creatinine concentration. Plasma AM concentrations were positively correlated with left ventricular mass index or mean wall thickness (r=.37, P=.009; r=.40, P=.004, respectively) and inversely correlated with carotid artery distensibility (r=-.33, P=.02), whereas plasma AM concentrations were not correlated with intimal-medial thickness. These results suggest that the observed elevation of plasma AM in patients with essential hypertension with normal renal function may be partly related to cardiac hypertrophy and decreased carotid artery distensibility.

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.

Different secretion patterns of adrenomedullin, brain natriuretic peptide, and atrial natriuretic peptide during exercise in hypertensive and normotensive subjects

The purpose of this study was to investigate the effect of exercise on plasma concentrations of adrenomedullin, brain natriuretic peptide (BNP), and atrial natriuretic peptide (ANP) in patients with essential hypertension (n = 15) and in normotensive controls (n = 10). Exercise consisted of two fixed workloads, 40 and 80 watts of work load using a supine bicycle ergometer. Plasma levels of all three peptides at rest were significantly higher in hypertensives than in controls. Plasma concentrations of ANP increased with exercise in both groups and had greater increments in hypertensive patients than in normotensives. Plasma concentrations of BNP increased only in patients with hypertension and the levels of increase correlated with basal plasma BNP levels (r = 0.94, p < 0.001) and with left ventricular mass (r = 0.62, p < 0.01) determined by echocardiography. In contrast, plasma adrenomedullin did not change with exercise in either group. These results suggest that secretion patterns of these peptides are regulated by different mechanisms and that the amount and kind of peptides mobilized by exercise may depend on the underlying diseases or pathophysiologic condition.

Effects of adrenomedullin on the human adrenal glands: an in vitro study

Numerous lines of evidence indicate that adrenal medulla exerts a paracrine control on the secretory activity of the cortex by releasing catecholamines and several regulatory peptides. Adrenomedullin (ADM) is contained in adrenal medulla of several mammalian species, including humans. Thus, we investigated whether human ADM1-52 exerts a modulatory action on steroid secretion of human adrenal cortex in vitro. Dispersed adrenocortical cells (obtained from the gland tail deprived of chromaffin cells) and adrenal slices (including both capsule and medulla) were employed. ADM specifically inhibited angiotensin II-stimulated aldosterone secretion of dispersed cells and enhanced basal aldosterone production by adrenal slices, minimal effective concentrations being 10(-7) and 10(-9) mol/L, respectively. These effects of ADM were suppressed by the CGRP1 receptor antagonist CGRP8-37 (10(-5) mol/L). Neither basal and ACTH-stimulated aldosterone secretion of dispersed cells nor agonist-enhanced aldosterone production by adrenal slices were affected by ADM, which also did not alter cortisol secretion of both types of adrenal preparations. ADM (10(-6) mol/L) blunted the aldosterone secretagogue action of the Ca2+ ionophore A23187 (10(-5) mol/L) on dispersed cells and adrenal slices. The beta-adrenoceptor antagonist l-alprenolol (10(-6) mol/L) suppressed aldosterone response of adrenal slices to 10(-7) mol/L isoprenaline and ADM. ADM concentration dependently raised epinephrine and norepinephrine release by adrenal slices, minimal effective concentration being 10(-9) mol/L. Collectively, these findings suggest that ADM, acting via the CGRP1 receptor subtype, exerts a direct inhibitory effect on angiotensin II-stimulated aldosterone secretion, which, when the integrity of adrenal tissue is preserved, is overcome and reversed by an indirect stimulatory action, conceivably involving the release of catecholamines by adrenal chromaffin cells.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Tone-dependent vasodilator responses to proadrenomedullin NH2-terminal 20 peptide in the hindquarters vascular bed of the rat

Responses to proadrenomedullin NH2-terminal 20 peptide (PAMP) were investigated in the systemic and hindquarters vascular bed of the rat. Intravenous injections of PAMP and adrenomedullin (ADM) produced dose-related decreases in systemic arterial and hindquarters perfusion pressure, which were not altered by alpha-receptor or adrenergic nerve terminal blocking agents. PAMP was 100-fold less potent than ADM, and hindquarters vasodilator responses to both peptides were similar in innervated and denervated preparations. When baseline tone was increased with phenylephrine and U46619 or decreased with sodium nitroprusside, vasodilator responses to PAMP and ADM were correlated with the basal level of tone, suggesting that responses to both peptides are dependent on the baseline level of vasoconstrictor tone in the hindquarters vascular bed of the rat.

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.

Proadrenomedullin NH2-terminal 20 peptide has cAMP-mediated vasodilator activity in the mesenteric vascular bed of the cat

Responses to proadrenomedullin NH2-terminal 20 peptide (hPAMP), a truncated analogue [hPAMP(12-20)], and adrenomedullin (hADM) were investigated in the mesenteric vascular bed of the cat. Under constant-flow conditions, injections of hPAMP, hPAMP(12-20), and hADM caused dose-related decreases in mesenteric perfusion pressure. hADM was 100-fold more potent than hPAMP, and 1000-fold more potent than hPAMP(12-20). Vasodilator responses to hPAMP and hADM were not altered by adrenergic-blocking agents, were similar in innervated and denervated preparations, and were similar when tone was increased by sympathetic nerve stimulation or phenylephrine infusion. Vasodilator responses to hPAMP and hADM were increased in duration by rolipram, a cAMP phosphodiesterase inhibitor. The present data suggest that vasodilator responses to the hPAMP and hADM are mediated by an increase in cAMP and that an interaction with the adrenergic nervous system is not involved.