Attenuated natriuretic response to adrenomedullin in experimental heart failure

Journal of Cardiac Failure Vol. 7 No. 1 2001

Experimental Studies

Attenuated Natriuretic Response to Adrenomedullin in Experimental Heart Failure MICHIHISA JOUGASAKI, MD, PhD, DENISE M. HEUBLEIN, CLT, SHARON M. SANDBERG, BS, JOHN C. BURNETT, Jr, MD Rochester, Minnesota

ABSTRACT Background: The recently discovered vasodilating and positive inotropic peptide, adrenomedullin (ADM), has strong natriuretic actions. ADM-induced natriuresis is caused by an increase in glomerular filtration rate and a decrease in distal tubular sodium reabsorption. Although ADM is activated in human and experimental heart failure, the role of ADM in the kidney in heart failure remains undefined. Methods and Results: The present study was performed to determine the renal hemodynamic and urinary excretory actions of exogenously administered ADM in a canine model of acute heart failure produced by rapid ventricular pacing. Experimental acute heart failure was characterized by a decrease in cardiac output and an increase in pulmonary capillary wedge pressure with an increase in plasma ADM concentration. Intrarenal infusion of ADM (1 and 25 ng/kg/min) induced an increase in urinary sodium excretion in the normal control dogs (change in urinary sodium excretion [⌬UNaV], ⫹94.5 ␮Eq/min during 1 ng/kg/min ADM infusion and ⫹128.1 ␮Eq/min during 25 ng/kg/min ADM infusion). In the acute heart failure dogs, intrarenal ADM infusion resulted in an attenuated increase in urinary sodium excretion (⌬UNaV, ⫹44.8 ␮Eq/min during 1 ng/kg/min ADM infusion and ⫹51.8 ␮Eq/min during 25 ng/kg/min ADM infusion). Both glomerular and tubular actions of ADM were attenuated in the acute heart failure group compared with responses in the normal control group. Conclusion: The present study shows that the renal natriuretic responses to ADM are markedly attenuated in experimental acute heart failure. This study provides insight into humoral mechanisms that may promote sodium retention in heart failure via a renal hyporesponsiveness to natriuretic actions of ADM. Key words: hormone, peptides, natriuresis, distal tubular function.

Adrenomedullin (ADM) is a recently described peptide hormone that participates in the homeostasis of

intravascular volume and vascular tone (1). ADM consists of 52 amino acids with an intramolecular disulfide bond; it shares a structural homology with other peptide hormones such as calcitonin gene-related peptide (CGRP) and amylin. Although ADM was originally isolated and cloned from the extracts of human pheochromocytoma (2), both vascular smooth muscle cells and endothelial cells have been reported to produce and secrete ADM (3,4). Furthermore, vascular smooth muscle cells possess specific ADM receptors functionally coupled to adenylate cyclase (5,6), indicating that ADM elicits its vasodilating action via an autocrine and/or paracrine fashion. Recently, we have reported that ADM is present in the kidney, and intrarenal infusion of ADM

From the Cardiorenal Research Laboratory, Division of Cardiovascular Diseases, Mayo Clinic and Foundation, Rochester, Minnesota. Supported by grants from the American Heart Association of the Minnesota Affiliate (MN-97-GB-06), the National Institutes of Health (HL 36634), the National Kidney Foundation of the Upper Midwest, the Miami Heart Research Institute, the Bruce and Ruth Rappaport Program in Vascular Biology, and the Mayo Foundation. Manuscript received October 28, 2000; revised manuscript received January 18, 2001; revised manuscript accepted January 22, 2001. Reprint requests: Michihisa Jougasaki, MD, PhD, Cardiorenal Research Laboratory, Mayo Clinic and Foundation, 915 Guggenheim, 200 First Street, SW, Rochester, MN 55905. Copyright © 2001 by Churchill Livingstone威 1071-9164/01/0701-0011$35.00/0 doi:10.1054/jcaf.2001.23233

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results in renal vasodilatation and increased urinary sodium excretion in the dogs (7). ADM-mediated natriuresis was associated with an increase in glomerular filtration rate and a decrease in distal tubular sodium reabsorption. Interestingly, although ADM has been known as a vasodilating and hypotensive peptide hormone, intrarenal infusion of ADM increases arterial blood pressure (7), which is mediated by renal nerves (8). Therefore, ADM is considered to play an important role in the regulation of cardiovascular and renal function. In addition to the autocrine and paracrine role of ADM, ADM circulates in plasma, and the plasma concentration of ADM is reported to be increased in patients with hypertension (9 –11) and chronic renal failure (9,12). Recent studies from both our group and others have shown that circulating ADM is also elevated in patients with chronic congestive heart failure (13–16). Indeed, the heart secretes ADM in congestive heart failure (14), suggesting that the heart releases a member of natriuretic peptide in response to increases in cardiac filling pressure. It is of interest that ADM is also produced in the kidney and may function in an autocrine and paracrine fashion in the control of sodium excretion. Although the role of ADM in congestive heart failure remains unknown, previous investigators have reported the beneficial hemodynamic and renal responses to ADM in rat aortocaval shunt models (17) and ovine pacinginduced heart failure models (18). More recently, Nagaya et al have reported that intravenous ADM infusion has beneficial hemodynamic and renal effects in patients with congestive heart failure (19). However, the precise renal actions of ADM in congestive heart failure remain undefined. Therefore, the present study was performed to examine the renal response to intrarenal infusion of ADM in an experimental canine model of acute heart failure that is produced by rapid ventricular pacing.

Methods Experimental Protocol Experiments were performed in 2 groups of anesthetized male mongrel dogs (normal control, n ⫽ 6; acute heart failure, n ⫽ 5) weighing between 18 and 24 kg. Dogs were maintained on a normal sodium diet with standard dog chow (Lab Canine Diet 5006; Purina Mills, St Louis, MO) with free access to tap water. All studies conformed according to the guidelines of the American Physiologic Society. On the evening before the experiment, 300 mg (8.1 mEq) of lithium carbonate were administered orally, and the dogs were fasted overnight. All dogs were anesthetized with pentobarbital sodium (Ampro Pharmaceutical, Arcadia, CA) given intravenously (30 mg/kg). Supplemental nonhypotensive doses

of pentobarbital sodium were given as necessary to maintain anesthesia during the experiment. After tracheal intubation, the dogs were mechanically ventilated (Harvard respirator; Harvard Apparatus, Millis, MA) with supplemental oxygen at 4 L/min. The right external jugular vein was cannulated with a flow-directed, balloon-tipped, thermodilution catheter (model 93A-133-7F; American Edwards Laboratory, Anasco, Puerto Rico), which was advanced into the pulmonary artery for the measurement of cardiac filling pressure and determination of cardiac output. Cardiac outputs were measured by thermodilution method with a Cardiac Output Model 9520-A computer (Edwards Laboratories, Santa Ana, CA) in triplicate and averaged. Five dogs underwent rapid ventricular pacing to produce acute heart failure, which (as in humans) is characterized by a decrease in cardiac output and an increase in cardiac filling pressures. The heart was exposed through a left thoracotomy incision at the fifth intercostal space. After the pericardium was opened, a pacemaker lead was implanted into the right ventricular myocardium and then connected to the pacemaker generator. The pericardium and chest wall were then carefully closed. A flank incision was made, and the left kidney was exposed via a retroperitoneal approach. The ureter was cannulated with a polyethylene catheter (PE-200) for timed urine collection. A calibrated noncannulating electromagnetic flow probe was placed carefully around the left renal artery and connected to a flowmeter (model FM 5010; Carolina Medical Electronics, King, NC) for continuous monitoring of renal blood flow. In addition, one curved 23-gauge needle, attached to polyethylene tubing (PE-50), was inserted into the renal artery proximal to the flow probe. The patency of the needle was maintained by infusion of saline (1 mL/min). Finally, a right femoral vein was cannulated with a polyethylene catheter (PE-240) for intravenous infusion of inulin and supplemental anesthesia. A right femoral artery was also cannulated with a polyethylene catheter (PE-240) for measurement of arterial blood pressure and sampling of arterial blood. After completion of the surgical preparation, a priming dose of inulin (ICN Biomedicals, Cleveland, OH) dissolved in isotonic saline solution was injected, followed by a constant infusion of 1 mL/min to achieve a steady-state plasma inulin concentration between 40 and 60 mg/dL. The dogs were placed in dorsal suspension and allowed to stabilize for 60 minutes without intervention. Body temperature was maintained by an external warming system (infrared heating lamp and heating pad model K-1-3; GormanRupp Industries Division, Bellville, OH). Intrarenal Infusion of ADM After an equilibration period of 60 minutes, a 15minute baseline clearance was performed in the normal

Renal Response to ADM in Heart Failure ●

control group. This was followed by a 15-minute lead-in period during which ADM (1-52 human; Phoenix Inc, Mountain View, CA) infusion (1 ng/kg/min) was begun intrarenally. Then a 30-minute clearance period was performed. Intrarenal infusion rate of ADM was increased to 25 ng/kg/min with a 15-minute lead-in period and followed by a 30-minute clearance. These doses of 1 and 25 ng/kg/min were chosen based on the previous report (7). At the end of this clearance, the ADM infusion was stopped, and a 30-minute washing-out was followed by a 15-minute recovery clearance. In the acute heart failure group, a 15-minute baseline clearance before pacing was performed. The dogs then underwent rapid ventricular pacing at 184 ⫾ 4 beats per minute (bpm) for 1 hour to induce acute heart failure. This experimental acute heart failure model has been well established and used in the previous reports (20,21); it mimics human acute heart failure, with regard to acute left ventricular dysfunction with an increase in pulmonary capillary wedge pressure and a decrease in cardiac output. One hour after this maneuver, a second 15minute baseline clearance was performed. This was followed by a 15-minute lead-in period during which ADM infusion 1 ng/kg/min was begun intrarenally; then a 30-minute clearance period was performed. Intrarenal infusion rate of ADM was increased to 25 ng/kg/min with a 15-minute lead-in period and followed by a 30minute clearance. At the end of this clearance, the ADM infusion was stopped, and a 30-minute washing-out was followed by a 15-minute recovery clearance. During each experimental clearance, mean arterial blood pressure and renal blood flow were measured. At the midpoint of each clearance period, arterial blood was sampled for measurement of sodium, inulin, lithium, and ADM concentrations. At the end of each clearance, urine was measured for volume and concentrations of inulin, sodium, and lithium.

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rate]) ⫻ 100. Distal fractional reabsorption of sodium was calculated by the formula ([lithium clearance ⫺ sodium clearance]/lithium clearance) ⫻ 100. Blood for the measurement of ADM concentration was collected into prechilled ethylenediaminetetraacetic acid (EDTA) tubes, immediately placed on ice, and centrifuged at 2,500 revolutions/min at 4°C for 10 minutes. The plasma was separated and stored at ⫺20°C until the assay. Plasma concentration of ADM was measured with a specific radioimmunoassay for ADM (1-52) as previously described (13,14). In brief, plasma (1 mL) was extracted on C-18 Bond Elute Cartridges (Varian, Harbor City, CA) and eluted with 75% methanol containing 1% trifluoroacetic acid (TFA). Concentrated elutes were then assayed by using a specific and sensitive radioimmunoassay for ADM (Phoenix Inc). Minimal detectable concentration for the assay was 1 pg per tube, and the half-maximal inhibition dose of radioiodinated ligand binding by ADM was 20 pg per tube. Recovery was 72% ⫾ 2%, and intra-assay and interassay variations were 10% and 12%, respectively. Statistical Analysis Results of quantitative studies are expressed as means ⫾ SE. Statistical comparisons were performed by using the analysis of variance (ANOVA) for repeated measures followed by Fisher’s least significant difference test of repeated measures when appropriate. For statistical comparisons between before and after pacing in the acute heart failure group, Student paired t test was used. For analyses of data between the normal control group and acute heart failure group, absolute changes of the data from baseline were compared by using Student unpaired t test. Statistical significance was accepted for P value less than .05.

Results Analytical Methods Plasma for electrolyte and inulin measurement was obtained from blood collected in heparinized tubes. Plasma sodium and urine sodium were measured with ion-selective electrodes (Beckman Synchron Elise; Beckman, Brea, LA). Urinary sodium excretion was calculated by the formula (urinary sodium ⫻ urine flow). Plasma and urine inulin concentrations were measured by the anthrone method (22), and glomerular filtration rate was measured by the clearance of inulin. Plasma lithium and urine lithium were determined by flameemission spectrophotometry (model 357; Instrumentation Laboratory, Wilmington, MA). The lithium clearance technique was used to estimate proximal and distal fractional reabsorption of sodium (23). Proximal fractional reabsorption of sodium was calculated by the formula (1 ⫺ [lithium clearance/glomerular filtration

Cardiovascular Hemodynamic and Renal Functions and Plasma ADM Concentration in the Acute Heart Failure Group Table 1 reports the cardiovascular hemodynamic and renal functions and plasma ADM concentration before and during rapid ventricular pacing in the acute heart failure group. Acute heart failure induced by rapid ventricular pacing resulted in a decrease in cardiac output and an increase in pulmonary capillary wedge pressure. Mean arterial blood pressure tended to decrease and systemic vascular resistance tended to increase, although these changes did not reach significance. Renal function remained unchanged during rapid ventricular pacing. Plasma ADM concentration was significantly increased during acute heart failure (12.3 ⫾ 0.7 pg/mL) as com-

78 Journal of Cardiac Failure Vol. 7 No. 1 March 2001 Table 1. Cardiovascular Hemodynamic and Renal Functions and Plasma ADM Concentration Before Pacing and During Acute Heart Failure

MAP (mm Hg) HR (bpm) CO (L/min) SVR (RU) PCWP (mm Hg) RBF (mL/min) RVR (RU) GFR (mL/min) UV (mL/min) UNaV (␮Eq/min) FE Na (%) DFR Na (%) U osmol (m osmol/L) ADM (pg/mL)

Before Pacing

Acute Heart Failure

107 ⫾ 8 132 ⫾ 4 3.2 ⫾ 0.2 34.9 ⫾ 4.6 2.7 ⫾ 0.6 248 ⫾ 44 0.48 ⫾ 0.08 42.4 ⫾ 2.6 0.71 ⫾ 0.22 123.8 ⫾ 43.2 2.1 ⫾ 0.7 94.2 ⫾ 1.7 788 ⫾ 143 7.1 ⫾ 1.7

100 ⫾ 6 183 ⫾ 4* 2.0 ⫾ 0.2* 53.2 ⫾ 7.9 8.4 ⫾ 0.7* 159 ⫾ 7 0.62 ⫾ 0.03 37.1 ⫾ 3.6 0.66 ⫾ 0.43 44.0 ⫾ 9.3 0.8 ⫾ 0.1 97.1 ⫾ 0.7 917 ⫾ 261 12.3 ⫾ 0.7*

Values are means ⫾ SE. ADM, adrenomedullin; MAP, mean arterial pressure; HR, heart rate; CO, cardiac output; SVR, systemic vascular resistance; PCWP, pulmonary capillary wedge pressure; RBF, renal blood flow; RVR, renal vascular resistance; GFR, glomerular filtration rate; UV, urine flow; UNaV, urinary sodium excretion; FE Na, fractional sodium excretion; DFR Na, distal fractional reabsorption of sodium; U osmol, urine osmolality. * P ⬍ .05 versus before pacing.

pared with baseline before pacing (7.1 ⫾ 1.7 pg/mL, P ⬍ .05). Responses to Intrarenal ADM Infusion in the Normal Control Group and Acute Heart Failure Group Cardiovascular Hemodynamic Responses Table 2 summarizes the cardiovascular hemodynamic changes

during the baseline, intrarenal infusion of ADM (1 and 25 ng/kg/min), and recovery period in the normal control group and acute heart failure group. Mean arterial blood pressure increased during the infusion rate of 25 ng/kg/ min and remained elevated during the recovery period in the normal control group. In the acute heart failure group, mean arterial blood pressure increased with the lower ADM infusion rate of 1 ng/kg/min and remained increased during the infusion rate of 25 ng/kg/min. The increment in mean arterial blood pressure was significantly greater in the acute heart failure group than in the normal control group (P ⬍ .05 between groups). Fig. 1 shows the changes in mean arterial blood pressure during the intrarenal infusion of ADM (1 and 25 ng/kg/min) and the recovery period in both the normal control group and the acute heart failure group. Heart rate was significantly reduced at the lower ADM infusion rate of 1 ng/kg/min and remained decreased during the higher infusion rate of 25 ng/kg/min and during the recovery period in the normal control group. Plasma ADM Concentration Table 2 also reports circulating ADM concentration at baseline, during ADM infusion, and during the recovery period in the normal control group and acute heart failure group. In both the normal control group and the acute heart failure group, plasma ADM concentration did not increase with infusion of ADM 1 ng/kg/min but significantly increased with the higher dose of ADM (25 ng/kg/min). Plasma ADM concentration in the acute heart failure group tended to be higher than the normal control group during the infusion of ADM (1 and 25 ng/kg/min) and after the infusion of ADM; however, these changes did not reach significance.

Table 2. Hemodynamic Responses to Intrarenal Infusion of ADM and Plasma ADM Concentration in the Normal Control Group and Acute Heart Failure Group

Normal control group MAP (mm Hg) HR (bpm) CO (L/min) SVR (RU) PCWP (mm Hg) ADM (pg/mL) Acute heart failure group MAP (mm Hg) HR (bpm) CO (L/min) SVR (RU) PCWP (mm Hg) ADM (pg/mL)

Baseline

1 ng/kg/min

25 ng/kg/min

Recovery

122 ⫾ 5 135 ⫾ 10 3.1 ⫾ 0.4 41.2 ⫾ 4.0 2.7 ⫾ 0.6 6.4 ⫾ 1.1

126 ⫾ 5 124 ⫾ 8* 2.8 ⫾ 0.4 48.4 ⫾ 4.4 2.5 ⫾ 0.6 23.1 ⫾ 4.8

132 ⫾ 3*† 113 ⫾ 8*† 2.3 ⫾ 0.3*† 63.9 ⫾ 7.1*† 3.0 ⫾ 0.6 122.9 ⫾ 25.5*†

132 ⫾ 4*† 111 ⫾ 7*† 2.0 ⫾ 0.3*† 74.2 ⫾ 10.3*† 3.3 ⫾ 0.7 55.5 ⫾ 9.6*‡

100 ⫾ 6 183 ⫾ 4 2.0 ⫾ 0.2 53.2 ⫾ 7.9 8.4 ⫾ 0.7 12.3 ⫾ 0.7

112 ⫾ 6*¶ 185 ⫾ 4 1.8 ⫾ 0.2 63.7 ⫾ 7.6 8.9 ⫾ 1.1 38.1 ⫾ 5.0

125 ⫾ 8*†¶ 184 ⫾ 4 1.5 ⫾ 0.1 82.8 ⫾ 8.5 8.5 ⫾ 1.8 160.2 ⫾ 14.2*†

119 ⫾ 7* 187 ⫾ 4 1.5 ⫾ 0.1 83.7 ⫾ 7.3 8.6 ⫾ 2.3 66.4 ⫾ 4.1*†‡

Values are means ⫾ SE. ADM, adrenomedullin; MAP, mean arterial pressure; HR, heart rate; CO, cardiac output; SVR, systemic vascular resistance; PCWP, pulmonary capillary wedge pressure. * P ⬍ .05 versus baseline. † P ⬍ .05 versus 1 ng/kg/min ADM. ‡ P ⬍ .05 versus 25 ng/kg/min. ¶ P ⬍ .05 versus normal control group.

Renal Response to ADM in Heart Failure ●

Fig. 1. Changes in mean arterial pressure (MAP) during intrarenal ADM infusion (1 and 25 ng/kg/min) and during the recovery period in the normal control group and the acute heart failure (AHF) group. Open bars represent the normal control group, and solid bars represent the AHF group. * P ⬍ .05 versus baseline of each group. † P ⬍ .05 versus normal control group.

Renal Responses to ADM Table 3 reports the renal hemodynamic and urinary excretory changes during baseline, intrarenal infusion of ADM (1 and 25 ng/kg/ min), and the recovery period in the normal control group and acute heart failure group. In the normal control group, intrarenal infusion of ADM resulted in a marked diuretic and natriuretic response. Glomerular filtration rate tended to increase dur-

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ing ADM infusion rate of 1 ng/kg/min, but not significantly. Glomerular filtration rate significantly increased during the ADM infusion rate of 25 ng/kg/min. Renal blood flow significantly increased during the intrarenal infusion of ADM (1 and 25 ng/kg/min). Renal vascular resistance tended to decrease, but not significantly. Urine flow, urinary sodium excretion, and fractional sodium excretion significantly increased at the infusion rate of 1 ng/kg/min and persisted during the intrarenal infusion of ADM. Distal fractional reabsorption of sodium significantly decreased at the lower infusion rate of 1 ng/kg/ min and lasted during the higher infusion rate of ADM (25 ng/kg/min) and during the recovery period. Urine osmolality significantly decreased during the infusion of ADM (1 and 25 ng/kg/min) and during the recovery period. In the acute heart failure group, glomerular filtration rate tended to increase during the intrarenal infusion of ADM, although this change did not reach significance. Renal vasodilatation induced by intrarenal ADM infusion was attenuated in the acute heart failure group as compared with the normal control group, but not significantly. Urine flow tended to increase during the intrarenal infusion of ADM, but it did not reach significance. Urinary sodium excretion tended to increase during the ADM infusion rate of 1 ng/kg/min, but not significantly. Urinary sodium excretion significantly increased during the higher infusion rate of ADM (25 ng/kg/min). Distal fractional reabsorption of sodium tended to decrease during the lower infusion rate of ADM (1 ng/kg/min), although not significantly. Distal fractional reabsorption

Table 3. Renal Responses to Intrarenal Infusion of ADM in the Normal Control Group and Acute Heart Failure Group

Normal control group GFR (mL/min) RBF (mL/min) RVR (RU) UV (mL/min) UNaV (␮Eq/min) FE Na (%) DFR Na (%) U osmol (m osmol/L) Acute heart failure group GFR (mL/min) RBF (mL/min) RVR RU UV (mL/min) U Na V (␮Eq/min) FE Na (%) DFR Na (%) U osmol (m osmol/L)

Baseline

1 ng/kg/min

25 ng/kg/min

Recovery

28.8 ⫾ 2.6 157 ⫾ 17 0.82 ⫾ 0.07 0.34 ⫾ 0.08 65.1 ⫾ 14.7 1.7 ⫾ 0.5 95.9 ⫾ 0.9 1196 ⫾ 315

35.8 ⫾ 3.4 187 ⫾ 17* 0.70 ⫾ 0.04 0.76 ⫾ 0.14* 159.6 ⫾ 25.5* 3.4 ⫾ 0.7* 91.9 ⫾ 1.4* 726 ⫾ 135*

49.0 ⫾ 3.1*† 183 ⫾ 20* 0.75 ⫾ 0.06 1.20 ⫾ 0.28*† 193.2 ⫾ 13.4* 2.9 ⫾ 0.4* 90.6 ⫾ 1.4* 628 ⫾ 162*

34.6 ⫾ 3.1‡ 90 ⫾ 22*†‡ 2.05 ⫾ 0.5*†‡ 0.60 ⫾ 0.13‡ 109.7 ⫾ 17.4*†‡ 2.4 ⫾ 0.6 92.8 ⫾ 1.3* 721 ⫾ 201*

37.1 ⫾ 3.6 159 ⫾ 7 0.62 ⫾ 0.03 0.66 ⫾ 0.43 44.0 ⫾ 9.3 0.8 ⫾ 0.1 97.1 ⫾ 0.7 917 ⫾ 261

43.7 ⫾ 6.9 176 ⫾ 13 0.65 ⫾ 0.08 0.89 ⫾ 0.33 88.8 ⫾ 21.8¶ 1.3 ⫾ 0.2¶ 95.6 ⫾ 0.7¶ 600 ⫾ 138*

38.1 ⫾ 4.0¶ 186 ⫾ 15* 0.69 ⫾ 0.08 0.88 ⫾ 0.33 95.8 ⫾ 29.6*¶ 1.9 ⫾ 0.6* 94.1 ⫾ 1.5*¶ 807 ⫾ 238

46.5 ⫾ 6.7 156 ⫾ 15 0.80 ⫾ 0.10*† 0.50 ⫾ 0.22‡ 54.9 ⫾ 12.9‡ 0.8 ⫾ 0.2‡ 95.9 ⫾ 0.9 1049 ⫾ 239†‡

Values are means ⫾ SE. ADM, adrenomedullin; GFR, glomerular filtration rate; RBF, renal blood flow; RVR, renal vascular resistance; UV, urine flow; UNaV, urinary sodium excretion; FE Na, fractional sodium excretion; DFR Na, distal fractional reabsorption of sodium; U osmol, urine osmolality. * P ⬍ .05 versus baseline. † P ⬍ .05 versus 1 ng/kg/min. ‡ P ⬍ .05 versus 25 ng/kg/min. ¶ P ⬍ .05 versus normal control group.

80 Journal of Cardiac Failure Vol. 7 No. 1 March 2001

Fig. 2. Changes in glomerular filtration rate (GFR) during intrarenal ADM infusion (1 and 25 ng/kg/min) and during the recovery period in the normal control group and the acute heart failure (AHF) group. Open bars represent the normal control group, and solid bars represent the AHF group. * P ⬍ .05 versus baseline of each group. † P ⬍ .05 versus normal control group.

Fig. 4. Changes in distal fractional reabsorption of sodium (DFRNa) during intrarenal ADM infusion (1 and 25 ng/kg/min) and during the recovery period in the normal control group and the acute heart failure (AHF) group. Open bars represent the normal control group and solid bars represent the AHF group. * P ⬍ .05 versus baseline of each group. † P ⬍ .05 versus normal control group.

of sodium decreased during the higher infusion rate of ADM (25 ng/kg/min). Urine osmolality significantly decreased during the lower infusion rate of ADM (1 ng/ kg/min). Figs. 2, 3, and 4 show the changes in glomerular filtration rate, urinary sodium excretion, and distal fractional reabsorption of sodium, respectively, during the intrarenal infusion of ADM (1 and 25 ng/kg/min) and during the recovery period in both the normal control group and the acute heart failure group. The high dose of intrarenal ADM infusion (25 ng/kg/min) increased glo-

merular filtration rate in the normal control group, and this effect was attenuated in the acute heart failure group. The low and then high dose of intrarenal ADM infusion increased urinary sodium excretion in both groups, and this was attenuated in the acute heart failure group. Intrarenal infusion of ADM also decreased distal fractional reabsorption in both groups; again, this was attenuated in the acute heart failure group.

Fig. 3. Changes in urinary sodium excretion (UNaV) during intrarenal ADM infusion (1 and 25 ng/kg/min) and during the recovery period in the normal control group and the acute heart failure (AHF) group. Open bars represent the normal control group and solid bars represent the AHF group. * P ⬍ .05 versus baseline of each group. † P ⬍ .05 versus normal control group.

Discussion ADM is a recently described 52-amino acid peptide that has potent biological actions (1,2). ADM is considered to play an important role through its vasodilatory and natriuretic properties to maintain physiological cardiovascular and renal homeostasis. ADM is also a circulating hormone, and its plasma concentration is increased in congestive heart failure (13–16). To date, however, the role of ADM in the pathophysiology of congestive heart failure remains undefined. The present study shows that acute heart failure produced by rapid ventricular pacing is characterized by an increase in circulating endogenous ADM and that the renal natriuretic response to ADM is attenuated in acute heart failure. In the previous report, we have already shown that ADM is present in the glomeruli, cortical distal tubules, and medullary collecting duct cells of the kidney and that intrarenal infusion of ADM increases urinary sodium excretion and renal blood flow (7). Thus, ADM is considered to play an important role in the regulation of sodium balance. Recent studies by other investigators confirmed our finding that ADM is a new member of the

Renal Response to ADM in Heart Failure ●

family of natriuretic factors (24,25) but one which may function as a local renally derived natriuretic hormone functioning in an autocrine and paracrine fashion. The mechanism of ADM-mediated natriuresis was attributed to both renal hemodynamic and tubular actions with increases in glomerular filtration rate and decreases in distal tubular sodium reabsorption (7). To date, however, there have been no reports of precise renal actions of ADM during the acute phase of congestive heart failure. In the present study, we have shown that intrarenal ADM infusion results in an attenuated increase in urinary sodium excretion in acute heart failure. Both glomerular and tubular actions of ADM have been attenuated in the acute heart failure group as compared with responses in the normal control group. It has been reported that the natriuretic actions of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are attenuated in human and experimental congestive heart failure (26 –28). Although there are differences such as species and dosage of the peptides between the present study and these previous studies, the extent of the attenuated natriuretic responses to ADM is comparable with those responses to ANP and BNP. Therefore, congestive heart failure is characterized by a renal hyporesponsiveness not only to ANP and BNP, but also to the newly discovered natriuretic peptide ADM. The renal resistance to these endogenous natriuretic peptides may promote sodium retention in congestive heart failure. Pathophysiological importance of ADM in congestive heart failure has been suggested by the reports that plasma ADM concentrations are increased in human congestive heart failure (13–16). According to these previous studies, circulating ADM progressively increases with the severity of clinical heart failure. Furthermore, studies document that the failing human heart secretes ADM, suggesting cardiac contribution to the increase in plasma ADM in human congestive heart failure (14). Recently, a preliminary study has reported that ventricular ADM gene expression is increased in experimental congestive heart failure (29). To date, however, there has been no report of circulating endogenous ADM in the acute phase of congestive heart failure. In the present study, rapid ventricular pacing to produce acute heart failure decreased cardiac output and increased pulmonary capillary wedge pressure with an increase in plasma ADM concentration. This study, therefore, establishes that ADM is acutely increased in response to rapid ventricular pacing. The functional significance of an increase in plasma ADM in acute heart failure is unknown. Because ADM has renal vasodilating and natriuretic actions, ADM may play a compensatory role in the progression of congestive heart failure as has been reported for ANP and BNP. The mechanism by which ADM is increased in experimental acute heart failure is unclear. An increase in plasma ADM may be caused by enhanced synthesis

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and/or release or decreased degradation and/or clearance of ADM. Because ADM immunoreactivity and ADM messenger RNA (mRNA) is present in the heart (30,31), ADM, like ANP and BNP, may be released by the heart, which is associated with hemodynamic changes including augmented atrial stretch or ventricular wall stress. Although not significant, the greater increase in plasma ADM concentration in the acute heart failure group during and after the infusion of ADM suggests the decreased clearance of ADM in acute heart failure. Further studies are necessary to elucidate the mechanism of an increase in plasma ADM concentration in experimental acute heart failure. An interesting observation in the present study is an augmented increase in mean arterial blood pressure in the acute heart failure group as compared with the normal control group during intrarenal ADM infusion. Although ADM is known as a vasodilating and hypotensive peptide hormone, intrarenal infusion of ADM causes hypertension, not hypotension (7). We have already shown that renal nerves mediate this hypertensive action (8). Other investigators reported that intracerebroventricular and intracisternal injection of ADM cause longlasting elevation of arterial pressure (32). ADM may have a functional role in linking kidney with the central nervous system control of arterial blood pressure. In the present study, hypertensive action of intrarenal ADM infusion was augmented in the acute heart failure group as compared with the normal control group. It is known that sympathetic nervous activity is augmented in pacing-induced experimental congestive heart failure (33). Therefore, intrarenal infusion of ADM may potentiate renal nerve–mediated sympathetic activity to produce this greater hypertensive response in pacing-induced congestive heart failure. In summary, the present study shows that acute heart failure produced by rapid ventricular pacing is characterized by an increase in circulating ADM and that the renal natriuretic responses to ADM are markedly attenuated in experimental acute heart failure. Therefore, heart failure is defined as a cardiorenal disease state that is characterized by a renal resistance to the glomerular filtration rate–promoting and tubular-inhibiting actions of ADM. This study provides further insight into the understanding of acute heart failure by focusing on the humoral mechanisms that may promote sodium retention in congestive heart failure via a renal hyporesponsiveness to ADM.

Acknowledgment The authors wish to thank Lawrence L. Aarhus for his excellent technical assistance.

82 Journal of Cardiac Failure Vol. 7 No. 1 March 2001

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