Hemodynamic, Renal, and Hormonal Effects of Adrenomedullin Infusion in Patients With Congestive Heart Failure
Background—Experimental studies have shown that adrenomedullin (AM) causes vasodilatation, diuresis, and a positive inotropic effect. In humans, however, whether infusion of AM has beneficial effects in congestive heart failure (CHF) remains unknown.
Methods and Results—Hemodynamic, renal, and hormonal responses to intravenous infusion of human AM (0.05 μg · kg−1 · min−1) were examined in 7 patients with CHF and 7 normal healthy subjects (NL). In NL group, AM significantly decreased mean arterial pressure (−16 mm Hg, P<0.05) and increased heart rate (+12 bpm, P<0.05). In CHF group, AM also decreased mean arterial pressure (−8 mm Hg, P<0.05) and increased heart rate (+5 bpm, P<0.05), but to a much lesser degree (P<0.05 versus NL). AM markedly increased cardiac index (CHF, +49%; NL, +39%, P<0.05) while decreasing pulmonary capillary wedge pressure (CHF, −4 mm Hg; NL, −2 mm Hg, P<0.05). AM significantly decreased mean pulmonary arterial pressure only in CHF (−4 mm Hg, P<0.05). AM increased urine volume (CHF, +48%; NL, +62%, P<0.05) and urinary sodium excretion (CHF, +42%; NL, +75%, P<0.05). Only in CHF, plasma aldosterone significantly decreased during (−28%, P<0.05) and after (−36%, P<0.05) AM infusion. These parameters remained unchanged in 7 patients with CHF and 6 healthy subjects who received placebo.
Conclusions—Intravenous infusion of AM has beneficial hemodynamic and renal effects in patients with CHF.
Adrenomedullin (AM) is a novel hypotensive peptide, originally isolated from human pheochromocytoma.1 Infusion of AM causes vasodilatation, diuresis, and natriuresis in normal animals.2 3 AM also increases cardiac output and left ventricular contractility in vivo4 and exerts a direct inotropic effect in vitro.5 We and others have shown that plasma AM levels are increased in patients with congestive heart failure (CHF).6 7 Tissue levels of AM peptide and mRNA have also been shown to be increased in heart, kidney, and lungs in rats with CHF.8 These findings suggest that AM may play a role in the regulation of volume and pressure homeostasis in CHF as a paracrine and/or autocrine factor and as a circulating hormone.
Recently, Rademaker et al have demonstrated beneficial hemodynamic and renal effects of AM infusion in sheep with CHF induced by rapid pacing.9 In humans, systemically administered AM has been shown to significantly decrease mean arterial pressure in healthy subjects without any adverse effects.10 11 These findings raise the possibility that intravenous infusion of AM may also be beneficial in human subjects with CHF. However, there has been no clinical study to address the effects of AM in patients with CHF. Thus, the purposes of this study were (1) to investigate the hemodynamic, renal, and hormonal effects of short-term intravenous infusion of human AM in patients with CHF, and (2) to compare the effects of AM in CHF patients with those in normal healthy subjects (NL).
Seven patients with CHF (CHF-AM group) and 7 normal healthy volunteers (NL-AM group) received AM. Additionally, 7 patients with CHF (CHF-placebo group) and 6 healthy volunteers (NL-placebo group) received placebo. Although nonrandomized, CHF-placebo group and NL-placebo group were studied after CHF-AM group and NL-AM group to exclude the effects of hemodynamic alterations. Patients with one or both of the following conditions were excluded: (1) chronic renal impairment (serum creatinine level ≥2.0 mg/dL) and (2) systolic blood pressure <100 mm Hg. There was no significant difference in baseline characteristics between CHF-AM group and CHF-placebo group (Table 1⇓). The study was approved by the ethics committee of the National Cardiovascular Center, and all patients gave written informed consent.
Preparation of Human AM
Human AM was obtained from the Peptide Institute Inc, Osaka, Japan. The homogeneity of human AM was confirmed by reverse-phase, high-performance liquid chromatography and amino acid analysis. AM was dissolved in saline with 4% D-mannitol and was sterilized by passage through a 0.22-μm filter (Millipore Co). Then, randomly selected vials were submitted for sterility and pyrogen testing. The chemical nature and content of the human AM in vials were verified by high-performance liquid chromatography and radioimmunoassay.
All cardiovascular drugs were withdrawn at least 24 hours before beginning the study procedure. A 7.5F Swan-Ganz catheter (TOO21H-7.5F, Baxter Co) was positioned in the pulmonary artery through a jugular vein. One 22-gauge cannula was inserted into a radial artery for hemodynamic measurements and blood sampling. Another 22-gauge cannula was inserted into a forearm vein for infusion of 0.9% saline, with or without AM. A bladder catheter was inserted for urine sampling. After an equilibration period of 60 minutes, saline was infused at a rate of 0.5 mL/min for 30 minutes. Baseline measurements were obtained during this period. Then, AM (0.05 μg · kg−1 · min−1) was intravenously administered at a rate of 0.5 mL/min for 30 minutes, followed by 30-minute saline infusion in CHF-AM group and NL-AM group (Figure 1⇓). Additionally, saline alone was intravenously administered for 90 minutes in CHF-placebo group and NL-placebo group. The patients were blinded as to which infusion was being given. Hemodynamic parameters including heart rate, mean arterial pressure, mean pulmonary arterial pressure, and pulmonary capillary wedge pressure were measured at 5-minute intervals during the protocol. At 15-minute intervals, cardiac output was determined by thermodilution method in triplicate. Blood samples were taken at 30-minute intervals before, during, and after infusion of AM or placebo; collection of urine samples followed the same regimen. Urine volume, urinary sodium excretion, urinary potassium excretion, and creatinine clearance were calculated with standard formulas.
Plasma total AM, mature AM, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured by immunoradiometric assay using a specific kit for each (Shionogi Co, Ltd).12 13 Plasma cyclic adenosine 3′, 5′-monophosphate (cAMP), cyclic guanosine 3′, 5′-monophosphate (cGMP), renin, aldosterone, norepinephrine, and epinephrine were measured with commercially available kits.14 15 Serum sodium and potassium were measured by flame photometry.
All data were expressed as mean±SEM unless otherwise indicated. Comparisons of parameters between the 2 groups were made by Fisher’s exact test or unpaired Student’s t test. Comparisons of clinical parameters between 4 groups were made by 1-way ANOVA, followed by Newman-Keuls test. Comparisons of the time course of parameters between 4 groups were made by 2-way ANOVA for repeated measures, followed by Newman-Keuls test. P<0.05 was considered statistically significant.
Hemodynamic Responses to AM
All subjects tolerated this study protocol, although one normal subject developed headache at the beginning of infusion of AM. The hemodynamic parameters remained unchanged in CHF-placebo group and NL-placebo group (Figure 2⇓). In contrast, infusion of AM significantly decreased mean arterial pressure (−16 mm Hg, P<0.05) and increased heart rate (+12 bpm, P<0.05) in NL-AM group. In CHF-AM group, AM also decreased mean arterial pressure (−8 mm Hg, P<0.05) and increased heart rate (+5 bpm, P<0.05), but to a much lesser degree (P<0.05 versus NL-AM). In both groups, AM significantly decreased pulmonary capillary wedge pressure (CHF-AM, −4 mm Hg; NL-AM, −2 mm Hg, P<0.05). Mean pulmonary arterial pressure significantly decreased with AM only in CHF-AM group (-4 mm Hg, P<0.05).
At the end of AM infusion, cardiac index markedly rose in both groups compared with baseline values (CHF-AM, +49%; NL-AM, +39%, P<0.05, Figure 3⇓). Stroke volume index also rose in both groups (CHF-AM, +40%; NL-AM, +17%, P<0.05). AM significantly decreased systemic vascular resistance in both groups (CHF-AM, −38%; NL-AM, −40%, P<0.05). Infusion of AM resulted in a significant decrease in pulmonary vascular resistance only in the CHF-AM group (−34%, P<0.05), which had significantly higher pulmonary vascular resistance than NL-AM group at baseline.
Renal Responses to AM
Infusion of AM significantly increased urine volume (CHF-AM, +48%; NL-AM, +62%, P<0.05, Figure 4⇓) and urinary sodium excretion (CHF-AM, +42%; NL-AM, +75%, P<0.05). AM also increased urinary excretion of potassium in both groups (CHF-AM, +29%; NL-AM, +44%, P<0.05). Creatinine clearance increased significantly only in NL-AM group (+29%, P<0.05). The renal parameters remained unchanged in CHF-placebo group and NL-placebo group.
Hormonal Responses to AM
Baseline plasma total AM and mature AM were significantly higher in CHF-AM group than in NL-AM group (Table 2⇓). At the end of AM infusion, plasma total AM increased ≈3-fold in both groups compared with baseline values, whereas plasma-mature AM markedly increased (CHF-AM, 12-fold; NL-AM, 14-fold). During AM infusion, plasma cAMP was significantly increased (CHF-AM, +16%; NL-AM, +20%, P<0.05), whereas plasma cGMP was not changed in either group.
Baseline plasma renin and aldosterone were significantly higher in CHF-AM group than in NL-AM group. AM did not significantly change plasma renin in either group. In CHF-AM group, plasma aldosterone was significantly decreased at the end of AM infusion (−28%, P<0.05) and remained reduced even 30 minutes after discontinuation of the infusion (−36%, P<0.05). In contrast, no significant change in plasma aldosterone was observed in NL-AM group.
In NL-AM group, AM significantly increased plasma norepinephrine (+38%, P<0.05). In contrast, there was no significant change in plasma norepinephrine in CHF-AM group (−8%, P=NS). Plasma epinephrine was not changed in either group. Plasma ANP and BNP tended to decrease in CHF-AM group during AM infusion, although these changes did not reach statistical significance. The neurohumoral parameters remained unchanged in CHF-placebo group and NL-placebo group.
This is the first placebo-controlled clinical study to examine hemodynamic, renal and hormonal effects of intravenous infusion of AM in patients with CHF. In this study, we demonstrated that (1) infusion of AM significantly decreased mean arterial pressure and increased heart rate in both NL-AM group and CHF-AM group, but to a much lesser degree in CHF-AM group; (2) AM markedly increased cardiac index while significantly decreasing pulmonary capillary wedge pressure in both groups; and (3) AM significantly decreased mean pulmonary arterial pressure only in CHF-AM group. We also demonstrated that (4) AM caused significant increases in urine volume and urinary sodium excretion in both groups, and (5) in CHF-AM group, plasma aldosterone was significantly reduced during and after AM infusion.
Earlier studies have shown that AM dose-dependently increases cAMP levels in platelets and in cultured vascular smooth muscle cells.1 2 In the present study, intravenous infusion of AM significantly increased plasma cAMP in association with decreases in mean arterial pressure. It is therefore possible that AM may relax vascular smooth muscle through a cAMP-dependent mechanism. Lainchbury et al have shown that a markedly low dose of AM (0.008 μg · kg−1 · min−1) decreases mean arterial pressure by 7.7 mm Hg in healthy human subjects without a significant increase in plasma cAMP.10 The discrepancy may be explained in part by the difference in the dose of AM. AM is also known to regulate vascular tone through an endothelium-derived NO-dependent mechanism.16 Recently it has been reported that the vasorelaxant effect of AM is attenuated in patients with CHF, partly because of impaired production of NO in endothelial cells.17 These findings may support our results that AM decreased mean arterial pressure to a much lesser degree in CHF-AM group than in NL-AM group. The fall in mean arterial pressure was associated with a significant increase in heart rate in both groups, which is consistent with a previous study.11
Interestingly, AM significantly decreased mean pulmonary arterial pressure and pulmonary vascular resistance only in CHF-AM group, which had higher baseline values for both parameters than NL-AM group. It has been reported that there are many binding sites for AM in the lung18 and that AM preferentially dilates pulmonary arterial resistance vessels.19 20 Circulating AM has been shown to be increased and to be partially metabolized in the lungs of patients with pulmonary hypertension.21 These findings raise the possibility that AM plays a role in regulation of pulmonary vascular tone. Although further studies are necessary to demonstrate a specific pulmonary vasodilator effect of AM in patients with CHF, it is interesting to speculate that AM may be more effective in patients with increased pulmonary vascular resistance secondary to severe left heart failure.
This study demonstrated that AM markedly increased cardiac index and stroke volume index in both groups. This is consistent with results obtained from a previous animal study using conscious sheep.4 Considering the strong vasodilator effect of AM,1 2 4 a significant decrease in mean arterial pressure may be responsible for increased cardiac index during infusion. On the other hand, a recent binding study has shown abundant binding sites for AM in the ventricular myocardium.18 In fact, AM has been shown to increase cardiac cAMP,22 which is known to mediate the positive inotropic action of β-adrenergic stimulants. Alternatively, Szokodi et al have shown that AM produces a positive inotropic action through cAMP-independent mechanisms.5 These findings suggest that the increases in cardiac index and stroke volume index may be attributable not only to the fall in cardiac afterload but also to the direct positive inotropic action of AM.
In the present study, AM slightly but significantly increased urine volume and urinary sodium excretion in both CHF-AM group and NL-AM group, consistent with the results obtained from earlier animal studies.3 9 However, AM did not significantly increase creatinine clearance in CHF-AM group. Edwards et al have reported that AM dose-dependently increases intracellular cAMP levels in the cortical thick ascending limb and distal convoluted tubule dissected from rat kidney.23 These findings suggest that AM can directly inhibit tubular sodium resorption. In a previous human study, however, intravenous infusion of AM at 0.008 μg · kg−1 · min−1 did not induce diuresis or natriuresis in healthy subjects.10 The dose of the peptide may have been insufficient to reach a threshold for renal bioactivity. Because renal effects of systemically administered AM are relatively weak in both studies, significance of AM in the treatment of renal dysfunction remains to be determined.
The renin-angiotensin-aldosterone system is known to be excessively activated in patients with CHF, leading to adverse effects. In this study, CHF-AM group had high plasma renin and aldosterone, indicating activation of the renin-angiotensin-aldosterone system. Surprisingly, AM significantly decreased plasma aldosterone only in CHF-AM group, although there was no significant change in plasma renin. In vitro, AM has been shown to inhibit Ang II-induced secretion of aldosterone from dispersed rat adrenal zona glomerulosa cells.24 Thus, it is interesting to speculate that AM may play a compensatory role in the pathophysiology of CHF by inhibiting the augmented production of aldosterone. It should be noted that AM significantly increased plasma norepinephrine in NL-AM group but not in CHF-AM group. This suggests baroreceptor-mediated sympathetic discharge in response to the significant fall in blood pressure during AM infusion in NL-AM group. The reflex increase in sympathetic outflow might indirectly increase cardiac index and stroke volume index in NL-AM group. Although AM tended to decrease plasma NE, ANP, and BNP in CHF-AM group, these changes did not reach statistical significance. Further studies are necessary to elucidate the beneficial hormonal effects of AM.
It remains unclear whether exogenous AM functions at pathophysiological or pharmacological levels. It is generally supposed that AM-gly, an intermediate form of AM, is converted to mature AM, a 52-amino acid peptide with a C-terminal amide structure that exerts biological actions. However, most of immunoreactive AM in human plasma is in fact not mature AM, but AM-gly.12 Therefore, in the present study, mature AM was measured by a newly developed immunoradiometric assay kit. Unlike total AM (consisting of mature AM and AM-gly), plasma mature AM markedly increased during AM infusion, suggesting that infusion of AM produces biological actions at pharmacological levels. Baseline plasma mature AM was significantly higher in CHF-AM group than in NL-AM group. Nevertheless, AM at pharmacological levels increased plasma cAMP in association with cardiovascular effects in CHF-AM group. Thus, the additional administration of AM may be effective in patients with CHF.
Intravenous infusion of AM has beneficial hemodynamic and renal effects in patients with CHF. Further clinical trials are needed to investigate the potential therapeutic benefit of AM in CHF.
We thank Yoko Saito for technical assistance and Nobuo Shirahashi for helpful advice regarding statistical analysis. We also thank Kazuyuki Ueno and Masahiko Shibakawa for preparing adrenomedullin injection. This work was supported in part by Special Coordination Funds for Promoting Science and Technology (Encouragement System of COE) from the Science and Technology Agency of Japan.
Reprint requests to Noritoshi Nagaya, MD, Department of Internal Medicine, National Cardiovascular Center, 5-7-1 Fujishirodai, Suita, Osaka 565-8565, Japan.
- Received April 9, 1999.
- Revision received September 9, 1999.
- Accepted September 15, 1999.
- Copyright © 2000 by American Heart Association
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