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Plasma levels of adrenomedullin in patients with mitral stenosis
Valvular and Congenital Heart Disease
Plasma levels of adrenomedullin in patients with mitral stenosis Keiji Yamamoto, MD, Uichi Ikeda, MD, Hiromichi Sekiguchi, MD, and Kazuyuki Shimada, MD Tochigi, Japan
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. (Am Heart J 1998;135:542-9.)
Adrenomedullin, a potent hypotensive peptide, was originally isolated from a human adrenal pheochromocytoma with a detection system that is based on the ability of the peptide to elevate platelet cyclic adenosine monophosphate (AMP) levels.1 Adrenomedullin is composed of 52 amino acids and has limited structural homology with calcitonin gene-related peptide and amylin.1 The principal physiologic action of adrenomedullin appears to be that of a potent vasodilator. Systemic administration causes a rapid and marked drop in blood pressure and an increase in pulmonary blood flow.1-3 We have found that adrenomedullin also acts on the heart and elevates its levels of cyclic AMP.4 Because adrenomedullin has been reported to be present in the heart5 and kidney6 and to be secreted from vascular smooth muscle cells7 and endothelial cells,8 adrenomedullin may play an important role as a From the Department of Cardiology, Jichi Medical School. Supported by grants from the Ministry of Education, Culture and Science of Japan (#8670821) and Uehara Memorial Foundation. Submitted Jan. 30, 1997; accepted Sept. 5, 1997. Reprint requests: Keiji Yamamoto, MD, Department of Cardiology, Jichi Medical School, Minamikawachi, Tochigi 329-04, Japan. Copyright © 1998 by Mosby, Inc. 0002-8703/98/$5.00 + 0 4/1/86275
paracrine or autocrine hormone in the circulation. Immunoreactive adrenomedullin has been detected in human plasma.9 Plasma adrenomedullin levels have been reported to be increased in patients with hypertension,10 acute myocardial infarction,11 chronic renal failure12 and congestive heart failure.13-15 Plasma adrenomedullin concentration increases in proportion to the severity of heart failure along with increases in levels of hormones such as norepinephrine, atrial natriuretic peptide, brain natriuretic peptide, renin, and aldosterone, which are known to modulate the development of congestive heart failure.14,15 Over the past several years, percutaneous mitral balloon valvuloplasty has become an accepted alternative to open surgical procedures in the treatment of patients with mitral stenosis.16 Many previous studies have confirmed that this procedure is highly successful. It has a low complication rate and is associated with marked short- and long-term improvement in both hemodynamic values and symptoms among patients with mitral stenosis.17,18 In previous studies, we measured plasma concentrations of endothelin-1 in blood samples obtained from the right and left atria of patients with mitral stenosis who were undergoing percutaneous mitral valvuloplasty
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Figure 1
Figure 2
Plasma concentrations of adrenomedullin in blood from peripheral veins of healthy subjects and patients with mitral stenosis. Bars show mean ± SE of 15 samples.
Table I. Clinical characteristics of 15 patients who underwent percutaneous mitral valvuloplasty Characteristic Sex (n) Male Female Age (yr) History of rheumatic fever (n) Previous surgical commissurotomy (n) NYHA functional class (n) I II III Cardiac rhythm (n) Sinus Atrial fibrillation Mean left atrial diameter (mm) Echocardiographic score >8 (n) Mitral regurgitation (n) None One-fourth NYHA, New York Heart Association.
Value
3 12 54 ± 2 8 0 10 4 1 3 12 53 ± 2 8 12 3
Plasma concentrations of adrenomedullin in blood from the peripheral vein, right atrium, and left atrium of patients with mitral stenosis. Bars show mean value ± SE of 13 samples.
and found that endothelin-1 production was increased in the pulmonary circulation.19 It is unknown, however, whether adrenomedullin levels are increased in the pulmonary circulation of these patients. In this study, we first determined circulating concentrations of adrenomedullin in patients with mitral stenosis and correlated circulating adrenomedullin levels with cardiovascular hemodynamic measurements. Second, we sought to determine whether, like production of endothelin-1, adrenomedullin production increases in the pulmonary circulation. Third, we investigated whether hemodynamic resolution with percutaneous mitral valvuloplasty affects plasma adrenomedullin levels of these patients.
Methods Patients Between June 1995 and July 1996, 15 patients (three men, 12 women; mean ± SE age 54 ± 2 years, range 38 to 73 years) with severe rheumatic mitral stenosis underwent percutaneous mitral valvuloplasty through the antegrade transseptal approach with an Inoue balloon.16 The clinical
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Figure 3
Figure 4
Plasma concentrations of adrenomedullin in peripheral veins of patients with mitral stenosis 1 week before and 1 week after valvuloplasty. Bars show mean value ± SE of 15 samples.
Relations between plasma concentrations of adrenomedullin in the peripheral vein and mean pulmonary artery pressure (A) or mean pulmonary arterial wedge pressure (B) among patients with mitral stenosis before valvuloplasty. Regression analysis revealed highly significant correlations between plasma concentrations of adrenomedullin and mean pulmonary artery pressure (y = 0.64x + 37.46, r = 0.60, p = 0.02) or mean pulmonary arterial wedge pressure (y = l.29x + 28.22, r = 0.77, p = 0.0008).
characteristics are summarized in Table I. Twelve patients had chronic atrial fibrillation, and three had sinus rhythm before valvuloplasty. Ten patients were in New York Heart Association functional class I, four in class II, and one in class III. None of the patients had undergone commissurotomy. Criteria for exclusion from valvuloplasty were severe mitral regurgitation, aortic stenosis, aortic regurgitation, history of systemic embolism, left atrial clot (as detected with two-dimensional transesophageal echocardiography with a biplanar probe), diabetes mellitus, and renal or hepatic insufficiency. Hemodynamic studies were performed the morning after an overnight fast. Vasodilators were withheld for at least 24 hours before evaluation. Chronic, stable doses of digoxin and diuretics were continued but were administered on an evening schedule. The age-matched control group consisted of 15 healthy volunteers (three men and 12 women; mean value ± SE age 52 ± 2 years) who were receiving no medication. All control subjects were nonsmokers with no evidence of metabolic, neoplastic, or inflammatory disease. This study was approved by our institutional human investigations committee. Written informed consent was obtained from all patients and volunteers before participation in the study. All patients underwent M-mode, two-dimensional, and Doppler echocardiography the day before valvuloplasty. Mean value ± SE left atrial diameter determined at M-mode echocardiography20 was 53 ± 2 mm (Table I). Transesophageal echocardiography performed on all patients showed no intra-
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cardiac thrombus. Morphologic characteristics of the mitral valve and subvalvular structures were classified with an echocardiographic scoring system.21
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Figure 5
Cardiac catheterization and valvuloplasty Right- and left-sided heart studies including measurements of cardiac output, biplanar left ventriculography and right arteriography, and coronary angiography were performed with percutaneous technique through the right groin immediately before percutaneous mitral valvuloplasty. Percutaneous mitral valvuloplasty was performed with an Inoue single-balloon catheter.16 In brief, the balloon catheter was inserted into the left ventricle through the septum according to the Brockenbrough technique. After the distal half was inflated at the ventricle, the balloon was pulled back to the mitral orifice position. The balloon was then fully inflated until the indentation disappeared. It was then deflated and pulled back to the left atrium. The diameter of the inflated balloon was 24 mm in 11 patients and 25 mm in four patients. Right- and left-sided heart studies, including measurements of cardiac output and biplanar left ventriculography, were performed with the same procedure after valvuloplasty. These manipulations were performed with fluoroscopic guidance with the same predetermined projections as those used for left ventriculography. Effective areas of balloon dilation were determined by geometric analysis and normalized for body surface area, as described previously.22 The severity of mitral regurgitation was assessed according to the method of Sellers et al.23 Hemodynamic variables, including pressure in the right atrium, right ventricle, pulmonary artery, pulmonary arterial wedge position, left atrium and ascending aorta, as well as the cardiac index, were measured before and after valve dilation. Pressures in the left atrium and left ventricle were simultaneously recorded to determine the mean transmitral gradient. Cardiac output was determined with the thermodilution method for 13 patients with mild or no tricuspid regurgitation. For two patients with moderate tricuspid regurgitation, cardiac output was determined with the direct Fick method. The following variables were determined: systemic vascular resistance, total pulmonary resistance, and pulmonary vascular resistance.24 Mitral valve area was calculated with the Gorlin formula.25
Blood sampling and plasma assays Blood samples were obtained from the antecubital veins of all 15 patients 1 week before and 1 week after valvuloplasty. For 13 of the 15 patients, immediately before inflation of the balloon during valvuloplasty, blood samples were obtained from the right and left atria through a thermodilution catheter (7F) and an Inoue balloon catheter (12F), respectively. A 5 ml sample of whole blood was drawn into a polypropylene tube containing 5 mg EDTA
Relations between percentage decreases in plasma concentrations of adrenomedullin in peripheral vein and mean pulmonary artery pressure (A) or mean pulmonary arterial wedge pressure (B) after valvuloplasty. Regression analysis revealed weak but significant correlations between percentage decreases in plasma concentrations of adrenomedullin and mean pulmonary artery pressure (y = 0.67x + 0.13, r = 0.55, p = 0.03) or mean pulmonary arterial wedge pressure (y = 0.61x – 1.28, r = 0.52, p = 0.04).
and 2500 KIU (kallidinogenase inactivator units) aprotinin for use in assays. All samples were placed on ice. Plasma was promptly separated by means of centrifugation at 1600g at 4° C for 30 minutes, immediately frozen and stored at –80° C until the molecular markers were assayed.
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Table II. Hemodynamic characteristics of patients with mitral stenosis before and after valvuloplasty Characteristic Heart rate (beats/min) Mean arterial pressure (mm Hg) Mean pulmonary artery pressure (mm Hg) Mean pulmonary arterial wedge pressure (mm Hg) Mean right atrial pressure (mm Hg) Mean left atrial pressure (mm Hg) Cardiac index (L/min/m2) Systemic vascular resistance (dyne · sec/cm5 · m2) Total pulmonary resistance (dyne · sec/cm5 · m2) Pulmonary vascular resistance (dyne · sec/cm5 · m2) Mean transmitral gradient (mm Hg) Mitral valve area (cm2)
Value before 65 ± 3 80.8 ± 2.0 35.2 ± 2.5 24.4 ± 1.6 6.1 ± 0.4 18.1 ± 1.4 2.79 ± 0.14 2843 ± 93 996 ± 63 280 ± 14 14.5 ± 0.8 0.80 ± 0.05
Value after 67 ± 3 79.6 ± 1.8 27.2 ± 2.4* 17.5 ± 1.5* 4.6 ± 0.3† 13.3 ± 1.2† 2.86 ± 0.13 2798 ± 89 891 ± 38 247 ± 11‡ 7.3 ± 0.9* 1.29 ± 0.06*
*p < 0.001. †p < 0.002. ‡p < 0.02 versus before.
Plasma concentration of adrenomedullin was measured with specific radioimmunoassay for human adrenomedullin [1-52] as previously described.15 In brief, plasma (1 ml) was extracted on C-18 Bond Elute Cartridges and eluted with 75% methanol containing 1% trifluoroactetic acid. Concentrated eluates were then assayed with a specific and sensitive radioimmunoassay for adrenomedullin (Phoenix, Mountain View, Calif.). Samples and standards were incubated with 100:1 antibody raised against human adrenomedullin [1-52] at 4° C for 24 hours. Iodine 125 labeled adrenomedullin (100 µl) was added, and incubation was continued for another 24 hours at 4° C. Free and bound fractions were separated through addition of a second antibody and centrifuged. Radioactivity in the pellet was measured with a gamma counter. Minimal detectable concentration for the assay was 0.5 pg per tube, and the half-maximal inhibition dose of radioiodinated ligand binding by adrenomedullin was 10 pg per tube. Recovery rate was 72% ± 2%, and intra-assay and interassay variations were 10% and 12%, respectively.
Statistical analysis Data were expressed as mean value ± SEM. Statistical analyses were performed with a Macintosh Quadra 650 computer with the Stat View 4.0 software package. Differences were analyzed with the Wilcoxon signed-rank test for paired observations and the Mann-Whitney U test for unpaired observations. Simple linear regression analysis was used to compare measurements obtained by means of catheterization and the levels of molecular markers. Values of p < 0.05 were considered statistically significant.
Results Changes in hemodynamic variables Table II represents the hemodynamic characteristics of 15 patients with mitral stenosis before and after
valvuloplasty. After valvuloplasty, mean pulmonary artery pressure, mean pulmonary arterial wedge pressure, mean left atrial pressure, and mean transmitral gradient measured from simultaneous left atrial and left ventricular pressure tracings decreased significantly. The mitral valve area increased significantly from 0.80 ± 0.05 to 1.29 ± 0.06 cm2 (p < 0.001).
Plasma adrenomedullin levels Plasma adrenomedullin level in the peripheral vein was 27.3 ± 3.2 pg/ml among healthy subjects (n = 15) (Fig. 1). This level increased to 59.8 ± 2.7 pg/ml among patients with mitral stenosis before valvuloplasty (n = 15, p < 0.0001). We also measured the levels of adrenomedullin in the right and left atria of 13 of 15 patients immediately before valvuloplasty. As shown in Fig. 2, plasma levels of adrenomedullin in the peripheral vein and right atrium were significantly higher than those in the left atrium.
Correlation between hemodynamic variables and adrenomedullin levels Plasma adrenomedullin level in the peripheral veins of patients with mitral stenosis before valvuloplasty correlated significantly with mean pulmonary artery pressure (Fig. 3, A), mean pulmonary arterial wedge pressure (Fig. 3, B), mean left atrial pressure (r = 0.65, p = 0.01), mean right atrial pressure (r = 0.58, p = 0.03), mean transmitral gradient (r = 0.57, p = 0.03) and pulmonary vascular resistance (r = 0.75, p = 0.001). However, no correlation was detected with mitral valve area, cardiac index, or total pulmonary
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resistance. Plasma adrenomedullin levels in the right atrium also correlated significantly with mean pulmonary artery pressure (r = 0.64, p = 0.02), mean pulmonary arterial wedge pressure (r = 0.72, p = 0.006), mean left atrial pressure (r = 0.59, p = 0.03), mean right atrial pressure (r = 0.55, p = 0.04), mean transmitral gradient (r = 0.55, p = 0.04) and pulmonary vascular resistance (r = 0.70, p = 0.007). Adrenomedullin levels in the left atrium did not correlate with these variables.
Effects of percutaneous mitral valvuloplasty on adrenomedullin levels After percutaneous mitral valvuloplasty, cardiovascular hemodynamic measurements improved significantly (Table II). Valvuloplasty also caused significant decreases in peripheral plasma adrenomedullin levels from 59.8 ± 2.7 to 49.9 ± 3.1 pg/ml (p < 0.02) (Fig. 4). Furthermore, percentage decrease in plasma adrenomedullin levels in the peripheral vein correlated significantly with percentage decreases in mean pulmonary artery pressure (Fig. 5, A) and mean pulmonary arterial wedge pressure (Fig. 5, B).
Discussion In this study, plasma levels of adrenomedullin in the peripheral vein of patients with mitral stenosis were significantly higher than those of healthy subjects. Levels in the peripheral veins and the right atria of the patients were significantly higher than those in the left atrium. Plasma adrenomedullin levels in the peripheral vein and right atrium correlated significantly with mean pulmonary artery pressure. In addition, percutaneous mitral valvuloplasty significantly decreased plasma adrenomedullin levels. Percentage decrease in plasma adrenomedullin levels in the peripheral vein correlated significantly with percentage decrease in mean pulmonary artery pressure. These findings suggest that adrenomedullin may play an important role in the pulmonary circulation of these patients. Adrenomedullin is a newly discovered amino acid peptide that has potent vasodilating1 and natriuretic effects.6 Studies with excised human tissue and an antibody to adrenomedullin have shown that the lung contains the largest amount of adrenomedullin; smaller quantities are present in the kidney, adrenal gland, and plasma.1 Ribonucleic acid (RNA) blot analyses indicate that rat adrenomedullin messenger RNA is expressed in adrenal glands, lung, kidney, heart, spleen, duodenum, and submandibular glands.26,27 Previous studies demonstrated that
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adrenomedullin level is increased in the plasma of patients with congestive heart failure,13-15 and thus this peptide has been speculated to have an important role in the pathophysiologic process of congestive heart failure. Which organs produce and secrete adrenomedullin into the circulating plasma remains unknown. Vascular tissues are considered to be the main sources of circulating adrenomedullin.7,28 Sugo et al.7 found that cultured vascular endothelial cells actively synthesize adrenomedullin in vitro at levels comparable to the synthesis of endothelin-1. Sugo et al.28 also reported that vascular smooth muscle cells produce and secrete adrenomedullin in vitro. Kobayashi et al.14 reported that plasma adrenomedullin level correlated significantly with mean pulmonary artery pressure and mean pulmonary capillary wedge pressure of patients with congestive heart failure and that the elevation in pulmonary arterial pressure may play a role in increased secretion of adrenomedullin in heart failure. Jougasaki et al.15 reported that plasma adrenomedullin levels in the anterior interventricular vein and coronary sinus of patients with congestive heart failure were significantly higher than those in aorta; they concluded that the failing human heart secretes adrenomedullin. In our study, the levels were significantly higher in the right atrium than in the left atrium. This finding suggests that the pulmonary vascular beds are not the main source of adrenomedullin among patients with mitral stenosis. The mechanism of metabolism of adrenomedullin remains undefined. Nishikimi et al.29 investigated the sites of clearance of circulating adrenomedullin in human subjects. They found that the plasma concentration of adrenomedullin in the aorta was slightly but significantly lower than that in the pulmonary artery and that the pulmonary circulation might be one of the sites of adrenomedullin clearance. Our study also demonstrated that the plasma level of adrenomedullin in the left atrium was significantly lower than that in the right atrium, suggesting that circulating adrenomedullin was partially cleared in the pulmonary circulation. The observation that the lung contains the largest amount of adrenomedullin also supports this hypothesis.1 However, the mechanism by which plasma adrenomedullin is removed in the pulmonary circulation has not been fully investigated. Successful percutaneous mitral valvuloplasty improved clinical symptoms and hemodynamic values for patients with mitral stenosis. Tsai et al.30 reported that plasma atrial natriuretic peptide levels decreased significantly with concomitant decreases in mean pressure in the left atrium, pulmonary artery, and right atrium after valvuloplas-
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ty. Our study demonstrated that plasma adrenomedullin levels in patients with mitral stenosis decreased significantly with concomitant decreases in mean pulmonary artery pressure, mean pulmonary arterial wedge pressure, mean left atrial pressure, and pulmonary vascular resistance. These findings further support our premise that the elevation in pulmonary artery pressure plays a role in increased secretion of adrenomedullin in these patients. However, plasma adrenomedullin levels after valvuloplasty were still significantly higher than those of healthy subjects and did not return to a baseline normal, probably because percutaneous mitral valvuloplasty did not completely resolve mitral stenosis and the final mitral valve area of 1.29 cm2 was rather small. In this study, despite a significant decrease in adrenomedullin levels after mitral valvuloplasty, there were no concomitant measured changes in blood pressure. Adrenomedullin was found to be a potent hypotensive peptide. Ishiyama et al.2 reported that intravenous administration of human adrenomedullin to rats caused a rapid and marked reduction in mean blood pressure associated with a decrease in total peripheral resistance. However, Kohno et al.10 demonstrated that plasma adrenomedullin levels did not correlate with blood pressure levels of patients with essential hypertension. Jougasaki et al.15 reported that plasma adrenomedullin levels increased in proportion to the severity of heart failure but that mean arterial pressure of patients with chronic heart failure except for New York Heart Association functional class IV did not differ from that of controls. In our study, no patient was in New York Heart Association functional class IV. If there had been more patients with severe chronic heart failure in this study, there might have been concomitant measured changes in blood pressure. In addition, there were no systemic differences between patients who did and did not decrease their adrenomedullin levels after mitral valvuloplasty.
Study limitations All patients with mitral stenosis received the same doses of therapeutic agents, such as diuretics and digoxin, before and after valvuloplasty, but the comparison might be somewhat tenuous because intake of water and physical activity were different. In addition, the comparisons made between the peripheral and atrial adrenomedullin measurements were somewhat ambiguous, because the peripheral venous samples were collected 1 week before and 1 week after the procedure. There was a discrepancy between pulmonary arterial wedge pressure and left atrial pressure.
Inappropriate pulmonary arterial wedge measurements for some patients might have caused this discrepancy. This study involved a relatively small population of patients who were examined very carefully. A larger trial may further elucidate the usefulness of quantifying levels of adrenomedullin for patient care.
Conclusions This study demonstrated that plasma adrenomedullin levels among patients with mitral stenosis correlate positively with mean pulmonary artery pressure and pulmonary arterial wedge pressure, suggesting that adrenomedullin may play an important role in the pulmonary circulation of these patients.
References 1. Kitamura K, Kangawa K, Kawamoto M, Ichiki Y, Nakamura S, Matsuo H, et al. Adrenomedullin: a novel hypotensive peptide isolated from human pheochromocytoma. Biochem Biophys Res Commun 1993;192:553-60. 2. Ishiyama Y, Kitamura K, Ichiki Y, Nakamura S, Kida O, Kangawa K, et al. Hemodynamic effects of a novel hypotensive peptide, human adrenomedullin, in rats. Eur J Pharmacol 1993;241:271-3. 3. Lippton H, Chang JK, Hao Q, Summer W, Hyman AL. Adrenomedullin dilates the pulmonary vascular bed in vivo. J Appl Physiol 1994; 76:2154-6. 4. Ikeda U, Kanbe T, Kawahara Y, Yokoyama M, Shimada K. Adrenomedullin augments inducible nitric oxide synthase expression in cytokine-stimulated cardiac myocytes. Circulation 1996;94:2560-5. 5. Jougasaki M, Wei C-M, Heublein DM, Sandberg SM, Burnett JC Jr. Immunohistochemical localization of adrenomedullin in canine heart and aorta. Peptides 1995;16:773-5. 6. Jougasaki M, Wei C-M, Aarhus LL, Heublein DM, Sandberg SM, Burnett JC Jr. Renal localization and actions of adrenomedullin: a natriuretic peptide. Am J Physiol 1995;268 (Renal Fluid Electrolyte Physiol) 37:F657-63. 7. Sugo S, Minamino N, Shoji H, Kangawa K, Kitamura K, Eto T, et al. Interleukin-1, tumor necrosis factor and lipopolysaccharide additively stimulate production of adrenomedullin in vascular smooth muscle cells. Biochem Biophys Res Commun 1995;207:25-32. 8. Sugo S, Minamino N, Shoji H, Kangawa K, Miyamoto K, Kitamura K, et al. Endothelial cells actively synthesize and secrete adrenomedullin. Biochem Biophys Res Commun 1994;201:1160-6. 9. Kitamura K, Ichiki Y, Tanaka M, Kawamoto M, Emura J, Sakakibara S, et al. Immunoreactive adrenomedullin in human plasma. FEBS Lett 1994;341:288-90. 10. Kohno M, Hanehira T, Kano H, Horio T, Yokokawa K, Ikeda M, et al. Plasma adrenomedullin concentrations in essential hypertension. Hypertension 1996;27:102-7. 11. Kobayashi K, Kitamura K, Hirayama N, Date H, Kashiwagi T, Ikushima I, et al. Increased plasma adrenomedullin in acute myocardial infarction. Am Heart J 1996; 131:676-80. 12. Ishimitsu T, Nishikimi T, Saito Y, Kitamura K, Eto T, Kangawa K, et al. Plasma levels of adrenomedullin, a newly identified hypotensive peptide, in patients with hypertension and renal failure. J Clin Invest 1994; 94:2158-61. 13. Jougasaki M, Wei C-M, McKinley LJ, Burnett JC Jr. Elevation of circu-
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Palacios IF. Percutaneous balloon mitral valvotomy for patients with mitral stenosis: analysis of factors influencing early results. J Thorac Cardiovasc Surg 1988;96:33-8. Sellers RD, Levy M J, Amplatz K,. Lillehei CW. Left retrograde cardioangiography in acquired cardiac disease: technic, indications and interpretations in 700 cases. Am J Cardiol 1964;14:437-47. Yoshibayashi M, Nishioka K, Nakao K, Saito Y, Matsumura M, Ueda T, et al. Plasma endothelin concentrations in patients with pulmonary hypertension associated with chronic congestive heart failure. Circulation 1991;84:2280-5. Cohen MV, Gorlin R. Modified orifice equation for the calculation of mitral valve area. Am Heart J 1972;84:839-40. Kitamura K, Sakata J, Kangawa K, Kojima M, Matsuo H, Eto T. Cloning and characterization of cDNA encoding a precursor for human adrenomedullin. Biochem Biophys Res Commun 1993;194:720-5. Perret M, Broussard H, LeGros T, Burns A, Chang JK, Summer W, et al. The effects of adrenomedullin on the isolated heart. Life Sci 1993;53:377-9. Sugo S, Minamino N, Shoji H, Kangawa K, Kitamura K, Eto T, et al. Production and secretion of adrenomedullin from vascular smooth muscle cells: augmented production by tumor necrosis factor-alfa. Biochem Biophys Res Commun 1994;203:719-26. Nishikimi T, Kitamura K, Saito Y, Shimada K, Ishimitsu T, Takamiya M, et al. Clinical studies on the sites of production and clearance of circulating adrenomedullin in human subjects. Hypertension 1994;24:600-4. Tsai RC, Yamaji T, Ishibashi M, Takaku F, Fu M, Cherng WJ, et al. Atrial natriuretic peptide and vasopressin during percutaneous transvenous mitral valvuloplasty and relation to renin-angiotensin-aldosterone system and renal function. Am J Cardiol 1990;65:882-6.
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Plasma levels of adrenomedullin in patients with mitral stenosis Keiji Yamamoto, MD, Uichi Ikeda, MD, Hiromichi Sekiguchi, MD, and Kazuyuki Shimada, MD Tochigi, Japan
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. (Am Heart J 1998;135:542-9.)
Adrenomedullin, a potent hypotensive peptide, was originally isolated from a human adrenal pheochromocytoma with a detection system that is based on the ability of the peptide to elevate platelet cyclic adenosine monophosphate (AMP) levels.1 Adrenomedullin is composed of 52 amino acids and has limited structural homology with calcitonin gene-related peptide and amylin.1 The principal physiologic action of adrenomedullin appears to be that of a potent vasodilator. Systemic administration causes a rapid and marked drop in blood pressure and an increase in pulmonary blood flow.1-3 We have found that adrenomedullin also acts on the heart and elevates its levels of cyclic AMP.4 Because adrenomedullin has been reported to be present in the heart5 and kidney6 and to be secreted from vascular smooth muscle cells7 and endothelial cells,8 adrenomedullin may play an important role as a From the Department of Cardiology, Jichi Medical School. Supported by grants from the Ministry of Education, Culture and Science of Japan (#8670821) and Uehara Memorial Foundation. Submitted Jan. 30, 1997; accepted Sept. 5, 1997. Reprint requests: Keiji Yamamoto, MD, Department of Cardiology, Jichi Medical School, Minamikawachi, Tochigi 329-04, Japan. Copyright © 1998 by Mosby, Inc. 0002-8703/98/$5.00 + 0 4/1/86275
paracrine or autocrine hormone in the circulation. Immunoreactive adrenomedullin has been detected in human plasma.9 Plasma adrenomedullin levels have been reported to be increased in patients with hypertension,10 acute myocardial infarction,11 chronic renal failure12 and congestive heart failure.13-15 Plasma adrenomedullin concentration increases in proportion to the severity of heart failure along with increases in levels of hormones such as norepinephrine, atrial natriuretic peptide, brain natriuretic peptide, renin, and aldosterone, which are known to modulate the development of congestive heart failure.14,15 Over the past several years, percutaneous mitral balloon valvuloplasty has become an accepted alternative to open surgical procedures in the treatment of patients with mitral stenosis.16 Many previous studies have confirmed that this procedure is highly successful. It has a low complication rate and is associated with marked short- and long-term improvement in both hemodynamic values and symptoms among patients with mitral stenosis.17,18 In previous studies, we measured plasma concentrations of endothelin-1 in blood samples obtained from the right and left atria of patients with mitral stenosis who were undergoing percutaneous mitral valvuloplasty
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Figure 1
Figure 2
Plasma concentrations of adrenomedullin in blood from peripheral veins of healthy subjects and patients with mitral stenosis. Bars show mean ± SE of 15 samples.
Table I. Clinical characteristics of 15 patients who underwent percutaneous mitral valvuloplasty Characteristic Sex (n) Male Female Age (yr) History of rheumatic fever (n) Previous surgical commissurotomy (n) NYHA functional class (n) I II III Cardiac rhythm (n) Sinus Atrial fibrillation Mean left atrial diameter (mm) Echocardiographic score >8 (n) Mitral regurgitation (n) None One-fourth NYHA, New York Heart Association.
Value
3 12 54 ± 2 8 0 10 4 1 3 12 53 ± 2 8 12 3
Plasma concentrations of adrenomedullin in blood from the peripheral vein, right atrium, and left atrium of patients with mitral stenosis. Bars show mean value ± SE of 13 samples.
and found that endothelin-1 production was increased in the pulmonary circulation.19 It is unknown, however, whether adrenomedullin levels are increased in the pulmonary circulation of these patients. In this study, we first determined circulating concentrations of adrenomedullin in patients with mitral stenosis and correlated circulating adrenomedullin levels with cardiovascular hemodynamic measurements. Second, we sought to determine whether, like production of endothelin-1, adrenomedullin production increases in the pulmonary circulation. Third, we investigated whether hemodynamic resolution with percutaneous mitral valvuloplasty affects plasma adrenomedullin levels of these patients.
Methods Patients Between June 1995 and July 1996, 15 patients (three men, 12 women; mean ± SE age 54 ± 2 years, range 38 to 73 years) with severe rheumatic mitral stenosis underwent percutaneous mitral valvuloplasty through the antegrade transseptal approach with an Inoue balloon.16 The clinical
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Figure 3
Figure 4
Plasma concentrations of adrenomedullin in peripheral veins of patients with mitral stenosis 1 week before and 1 week after valvuloplasty. Bars show mean value ± SE of 15 samples.
Relations between plasma concentrations of adrenomedullin in the peripheral vein and mean pulmonary artery pressure (A) or mean pulmonary arterial wedge pressure (B) among patients with mitral stenosis before valvuloplasty. Regression analysis revealed highly significant correlations between plasma concentrations of adrenomedullin and mean pulmonary artery pressure (y = 0.64x + 37.46, r = 0.60, p = 0.02) or mean pulmonary arterial wedge pressure (y = l.29x + 28.22, r = 0.77, p = 0.0008).
characteristics are summarized in Table I. Twelve patients had chronic atrial fibrillation, and three had sinus rhythm before valvuloplasty. Ten patients were in New York Heart Association functional class I, four in class II, and one in class III. None of the patients had undergone commissurotomy. Criteria for exclusion from valvuloplasty were severe mitral regurgitation, aortic stenosis, aortic regurgitation, history of systemic embolism, left atrial clot (as detected with two-dimensional transesophageal echocardiography with a biplanar probe), diabetes mellitus, and renal or hepatic insufficiency. Hemodynamic studies were performed the morning after an overnight fast. Vasodilators were withheld for at least 24 hours before evaluation. Chronic, stable doses of digoxin and diuretics were continued but were administered on an evening schedule. The age-matched control group consisted of 15 healthy volunteers (three men and 12 women; mean value ± SE age 52 ± 2 years) who were receiving no medication. All control subjects were nonsmokers with no evidence of metabolic, neoplastic, or inflammatory disease. This study was approved by our institutional human investigations committee. Written informed consent was obtained from all patients and volunteers before participation in the study. All patients underwent M-mode, two-dimensional, and Doppler echocardiography the day before valvuloplasty. Mean value ± SE left atrial diameter determined at M-mode echocardiography20 was 53 ± 2 mm (Table I). Transesophageal echocardiography performed on all patients showed no intra-
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cardiac thrombus. Morphologic characteristics of the mitral valve and subvalvular structures were classified with an echocardiographic scoring system.21
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Figure 5
Cardiac catheterization and valvuloplasty Right- and left-sided heart studies including measurements of cardiac output, biplanar left ventriculography and right arteriography, and coronary angiography were performed with percutaneous technique through the right groin immediately before percutaneous mitral valvuloplasty. Percutaneous mitral valvuloplasty was performed with an Inoue single-balloon catheter.16 In brief, the balloon catheter was inserted into the left ventricle through the septum according to the Brockenbrough technique. After the distal half was inflated at the ventricle, the balloon was pulled back to the mitral orifice position. The balloon was then fully inflated until the indentation disappeared. It was then deflated and pulled back to the left atrium. The diameter of the inflated balloon was 24 mm in 11 patients and 25 mm in four patients. Right- and left-sided heart studies, including measurements of cardiac output and biplanar left ventriculography, were performed with the same procedure after valvuloplasty. These manipulations were performed with fluoroscopic guidance with the same predetermined projections as those used for left ventriculography. Effective areas of balloon dilation were determined by geometric analysis and normalized for body surface area, as described previously.22 The severity of mitral regurgitation was assessed according to the method of Sellers et al.23 Hemodynamic variables, including pressure in the right atrium, right ventricle, pulmonary artery, pulmonary arterial wedge position, left atrium and ascending aorta, as well as the cardiac index, were measured before and after valve dilation. Pressures in the left atrium and left ventricle were simultaneously recorded to determine the mean transmitral gradient. Cardiac output was determined with the thermodilution method for 13 patients with mild or no tricuspid regurgitation. For two patients with moderate tricuspid regurgitation, cardiac output was determined with the direct Fick method. The following variables were determined: systemic vascular resistance, total pulmonary resistance, and pulmonary vascular resistance.24 Mitral valve area was calculated with the Gorlin formula.25
Blood sampling and plasma assays Blood samples were obtained from the antecubital veins of all 15 patients 1 week before and 1 week after valvuloplasty. For 13 of the 15 patients, immediately before inflation of the balloon during valvuloplasty, blood samples were obtained from the right and left atria through a thermodilution catheter (7F) and an Inoue balloon catheter (12F), respectively. A 5 ml sample of whole blood was drawn into a polypropylene tube containing 5 mg EDTA
Relations between percentage decreases in plasma concentrations of adrenomedullin in peripheral vein and mean pulmonary artery pressure (A) or mean pulmonary arterial wedge pressure (B) after valvuloplasty. Regression analysis revealed weak but significant correlations between percentage decreases in plasma concentrations of adrenomedullin and mean pulmonary artery pressure (y = 0.67x + 0.13, r = 0.55, p = 0.03) or mean pulmonary arterial wedge pressure (y = 0.61x – 1.28, r = 0.52, p = 0.04).
and 2500 KIU (kallidinogenase inactivator units) aprotinin for use in assays. All samples were placed on ice. Plasma was promptly separated by means of centrifugation at 1600g at 4° C for 30 minutes, immediately frozen and stored at –80° C until the molecular markers were assayed.
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Table II. Hemodynamic characteristics of patients with mitral stenosis before and after valvuloplasty Characteristic Heart rate (beats/min) Mean arterial pressure (mm Hg) Mean pulmonary artery pressure (mm Hg) Mean pulmonary arterial wedge pressure (mm Hg) Mean right atrial pressure (mm Hg) Mean left atrial pressure (mm Hg) Cardiac index (L/min/m2) Systemic vascular resistance (dyne · sec/cm5 · m2) Total pulmonary resistance (dyne · sec/cm5 · m2) Pulmonary vascular resistance (dyne · sec/cm5 · m2) Mean transmitral gradient (mm Hg) Mitral valve area (cm2)
Value before 65 ± 3 80.8 ± 2.0 35.2 ± 2.5 24.4 ± 1.6 6.1 ± 0.4 18.1 ± 1.4 2.79 ± 0.14 2843 ± 93 996 ± 63 280 ± 14 14.5 ± 0.8 0.80 ± 0.05
Value after 67 ± 3 79.6 ± 1.8 27.2 ± 2.4* 17.5 ± 1.5* 4.6 ± 0.3† 13.3 ± 1.2† 2.86 ± 0.13 2798 ± 89 891 ± 38 247 ± 11‡ 7.3 ± 0.9* 1.29 ± 0.06*
*p < 0.001. †p < 0.002. ‡p < 0.02 versus before.
Plasma concentration of adrenomedullin was measured with specific radioimmunoassay for human adrenomedullin [1-52] as previously described.15 In brief, plasma (1 ml) was extracted on C-18 Bond Elute Cartridges and eluted with 75% methanol containing 1% trifluoroactetic acid. Concentrated eluates were then assayed with a specific and sensitive radioimmunoassay for adrenomedullin (Phoenix, Mountain View, Calif.). Samples and standards were incubated with 100:1 antibody raised against human adrenomedullin [1-52] at 4° C for 24 hours. Iodine 125 labeled adrenomedullin (100 µl) was added, and incubation was continued for another 24 hours at 4° C. Free and bound fractions were separated through addition of a second antibody and centrifuged. Radioactivity in the pellet was measured with a gamma counter. Minimal detectable concentration for the assay was 0.5 pg per tube, and the half-maximal inhibition dose of radioiodinated ligand binding by adrenomedullin was 10 pg per tube. Recovery rate was 72% ± 2%, and intra-assay and interassay variations were 10% and 12%, respectively.
Statistical analysis Data were expressed as mean value ± SEM. Statistical analyses were performed with a Macintosh Quadra 650 computer with the Stat View 4.0 software package. Differences were analyzed with the Wilcoxon signed-rank test for paired observations and the Mann-Whitney U test for unpaired observations. Simple linear regression analysis was used to compare measurements obtained by means of catheterization and the levels of molecular markers. Values of p < 0.05 were considered statistically significant.
Results Changes in hemodynamic variables Table II represents the hemodynamic characteristics of 15 patients with mitral stenosis before and after
valvuloplasty. After valvuloplasty, mean pulmonary artery pressure, mean pulmonary arterial wedge pressure, mean left atrial pressure, and mean transmitral gradient measured from simultaneous left atrial and left ventricular pressure tracings decreased significantly. The mitral valve area increased significantly from 0.80 ± 0.05 to 1.29 ± 0.06 cm2 (p < 0.001).
Plasma adrenomedullin levels Plasma adrenomedullin level in the peripheral vein was 27.3 ± 3.2 pg/ml among healthy subjects (n = 15) (Fig. 1). This level increased to 59.8 ± 2.7 pg/ml among patients with mitral stenosis before valvuloplasty (n = 15, p < 0.0001). We also measured the levels of adrenomedullin in the right and left atria of 13 of 15 patients immediately before valvuloplasty. As shown in Fig. 2, plasma levels of adrenomedullin in the peripheral vein and right atrium were significantly higher than those in the left atrium.
Correlation between hemodynamic variables and adrenomedullin levels Plasma adrenomedullin level in the peripheral veins of patients with mitral stenosis before valvuloplasty correlated significantly with mean pulmonary artery pressure (Fig. 3, A), mean pulmonary arterial wedge pressure (Fig. 3, B), mean left atrial pressure (r = 0.65, p = 0.01), mean right atrial pressure (r = 0.58, p = 0.03), mean transmitral gradient (r = 0.57, p = 0.03) and pulmonary vascular resistance (r = 0.75, p = 0.001). However, no correlation was detected with mitral valve area, cardiac index, or total pulmonary
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resistance. Plasma adrenomedullin levels in the right atrium also correlated significantly with mean pulmonary artery pressure (r = 0.64, p = 0.02), mean pulmonary arterial wedge pressure (r = 0.72, p = 0.006), mean left atrial pressure (r = 0.59, p = 0.03), mean right atrial pressure (r = 0.55, p = 0.04), mean transmitral gradient (r = 0.55, p = 0.04) and pulmonary vascular resistance (r = 0.70, p = 0.007). Adrenomedullin levels in the left atrium did not correlate with these variables.
Effects of percutaneous mitral valvuloplasty on adrenomedullin levels After percutaneous mitral valvuloplasty, cardiovascular hemodynamic measurements improved significantly (Table II). Valvuloplasty also caused significant decreases in peripheral plasma adrenomedullin levels from 59.8 ± 2.7 to 49.9 ± 3.1 pg/ml (p < 0.02) (Fig. 4). Furthermore, percentage decrease in plasma adrenomedullin levels in the peripheral vein correlated significantly with percentage decreases in mean pulmonary artery pressure (Fig. 5, A) and mean pulmonary arterial wedge pressure (Fig. 5, B).
Discussion In this study, plasma levels of adrenomedullin in the peripheral vein of patients with mitral stenosis were significantly higher than those of healthy subjects. Levels in the peripheral veins and the right atria of the patients were significantly higher than those in the left atrium. Plasma adrenomedullin levels in the peripheral vein and right atrium correlated significantly with mean pulmonary artery pressure. In addition, percutaneous mitral valvuloplasty significantly decreased plasma adrenomedullin levels. Percentage decrease in plasma adrenomedullin levels in the peripheral vein correlated significantly with percentage decrease in mean pulmonary artery pressure. These findings suggest that adrenomedullin may play an important role in the pulmonary circulation of these patients. Adrenomedullin is a newly discovered amino acid peptide that has potent vasodilating1 and natriuretic effects.6 Studies with excised human tissue and an antibody to adrenomedullin have shown that the lung contains the largest amount of adrenomedullin; smaller quantities are present in the kidney, adrenal gland, and plasma.1 Ribonucleic acid (RNA) blot analyses indicate that rat adrenomedullin messenger RNA is expressed in adrenal glands, lung, kidney, heart, spleen, duodenum, and submandibular glands.26,27 Previous studies demonstrated that
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adrenomedullin level is increased in the plasma of patients with congestive heart failure,13-15 and thus this peptide has been speculated to have an important role in the pathophysiologic process of congestive heart failure. Which organs produce and secrete adrenomedullin into the circulating plasma remains unknown. Vascular tissues are considered to be the main sources of circulating adrenomedullin.7,28 Sugo et al.7 found that cultured vascular endothelial cells actively synthesize adrenomedullin in vitro at levels comparable to the synthesis of endothelin-1. Sugo et al.28 also reported that vascular smooth muscle cells produce and secrete adrenomedullin in vitro. Kobayashi et al.14 reported that plasma adrenomedullin level correlated significantly with mean pulmonary artery pressure and mean pulmonary capillary wedge pressure of patients with congestive heart failure and that the elevation in pulmonary arterial pressure may play a role in increased secretion of adrenomedullin in heart failure. Jougasaki et al.15 reported that plasma adrenomedullin levels in the anterior interventricular vein and coronary sinus of patients with congestive heart failure were significantly higher than those in aorta; they concluded that the failing human heart secretes adrenomedullin. In our study, the levels were significantly higher in the right atrium than in the left atrium. This finding suggests that the pulmonary vascular beds are not the main source of adrenomedullin among patients with mitral stenosis. The mechanism of metabolism of adrenomedullin remains undefined. Nishikimi et al.29 investigated the sites of clearance of circulating adrenomedullin in human subjects. They found that the plasma concentration of adrenomedullin in the aorta was slightly but significantly lower than that in the pulmonary artery and that the pulmonary circulation might be one of the sites of adrenomedullin clearance. Our study also demonstrated that the plasma level of adrenomedullin in the left atrium was significantly lower than that in the right atrium, suggesting that circulating adrenomedullin was partially cleared in the pulmonary circulation. The observation that the lung contains the largest amount of adrenomedullin also supports this hypothesis.1 However, the mechanism by which plasma adrenomedullin is removed in the pulmonary circulation has not been fully investigated. Successful percutaneous mitral valvuloplasty improved clinical symptoms and hemodynamic values for patients with mitral stenosis. Tsai et al.30 reported that plasma atrial natriuretic peptide levels decreased significantly with concomitant decreases in mean pressure in the left atrium, pulmonary artery, and right atrium after valvuloplas-
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ty. Our study demonstrated that plasma adrenomedullin levels in patients with mitral stenosis decreased significantly with concomitant decreases in mean pulmonary artery pressure, mean pulmonary arterial wedge pressure, mean left atrial pressure, and pulmonary vascular resistance. These findings further support our premise that the elevation in pulmonary artery pressure plays a role in increased secretion of adrenomedullin in these patients. However, plasma adrenomedullin levels after valvuloplasty were still significantly higher than those of healthy subjects and did not return to a baseline normal, probably because percutaneous mitral valvuloplasty did not completely resolve mitral stenosis and the final mitral valve area of 1.29 cm2 was rather small. In this study, despite a significant decrease in adrenomedullin levels after mitral valvuloplasty, there were no concomitant measured changes in blood pressure. Adrenomedullin was found to be a potent hypotensive peptide. Ishiyama et al.2 reported that intravenous administration of human adrenomedullin to rats caused a rapid and marked reduction in mean blood pressure associated with a decrease in total peripheral resistance. However, Kohno et al.10 demonstrated that plasma adrenomedullin levels did not correlate with blood pressure levels of patients with essential hypertension. Jougasaki et al.15 reported that plasma adrenomedullin levels increased in proportion to the severity of heart failure but that mean arterial pressure of patients with chronic heart failure except for New York Heart Association functional class IV did not differ from that of controls. In our study, no patient was in New York Heart Association functional class IV. If there had been more patients with severe chronic heart failure in this study, there might have been concomitant measured changes in blood pressure. In addition, there were no systemic differences between patients who did and did not decrease their adrenomedullin levels after mitral valvuloplasty.
Study limitations All patients with mitral stenosis received the same doses of therapeutic agents, such as diuretics and digoxin, before and after valvuloplasty, but the comparison might be somewhat tenuous because intake of water and physical activity were different. In addition, the comparisons made between the peripheral and atrial adrenomedullin measurements were somewhat ambiguous, because the peripheral venous samples were collected 1 week before and 1 week after the procedure. There was a discrepancy between pulmonary arterial wedge pressure and left atrial pressure.
Inappropriate pulmonary arterial wedge measurements for some patients might have caused this discrepancy. This study involved a relatively small population of patients who were examined very carefully. A larger trial may further elucidate the usefulness of quantifying levels of adrenomedullin for patient care.
Conclusions This study demonstrated that plasma adrenomedullin levels among patients with mitral stenosis correlate positively with mean pulmonary artery pressure and pulmonary arterial wedge pressure, suggesting that adrenomedullin may play an important role in the pulmonary circulation of these patients.
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