R. Stephen Krombach

Modulation of the Renin-Angiotensin Pathway Through Enzyme Inhibition and Specific Receptor Blockade in Pacing-Induced Heart Failure I. Effects on Left Ventricular Performance and Neurohormonal Systems

BACKGROUND The goal of this study was to determine the effects of ACE inhibition (ACEI) alone, AT1 angiotensin (Ang) II receptor blockade alone, and combined ACEI and AT1 Ang II receptor blockade on LV function, systemic hemodynamics, and neurohormonal system activity in a model of congestive heart failure (CHF). METHODS AND RESULTS Pigs were randomly assigned to each of 5 groups: (1) rapid atrial pacing (240 bpm) for 3 weeks (n=9), (2) ACEI (benazeprilat, 0.187 mg x kg(-1) x d(-1)) and rapid pacing (n=9), (3) AT1 Ang II receptor blockade (valsartan, 3 mg x kg(-1) x d(-1)) and rapid pacing (n=9), (4) ACEI and AT1 Ang II receptor blockade (benazeprilat/valsartan, 0.05/3 mg x kg(-1) d(-1)) and rapid pacing (n=9), and (5) sham controls (n=10). In the pacing group, LV fractional shortening (LVFS) fell (13.4+/-1.4% versus 39.1+/-1.0%) and end-diastolic dimension (LVEDD) increased (5.61+/-0.11 versus 3.45+/-0.07 cm) compared with control (P<.05). With AT1 Ang II blockade and rapid pacing, LVEDD and LVFS were unchanged from pacing-only values. ACEI reduced LVEDD (4.95+/-0.11 cm) and increased LVFS (20.9+/-1.9%) from pacing-only values (P<.05). ACEI and AT1 Ang II blockade reduced LVEDD (4.68+/-0.07 cm) and increased LVFS (25.2+/-0.9%) from pacing only (P<.05). Plasma norepinephrine and endothelin increased by more than fivefold with chronic pacing and remained elevated with AT1 Ang II blockade. Plasma norepinephrine was reduced from pacing-only values by more than twofold in the ACEI group and the combination group. ACEI and AT1 Ang II receptor blockade reduced plasma endothelin levels by >50% from rapid-pacing values. CONCLUSIONS These findings suggest that the effects of ACEI in the setting of CHF are not solely due to modulation of Ang II levels but rather to alternative enzymatic pathways and that combined ACEI and AT1 Ang II receptor blockade may provide unique benefits for LV pump function and neurohormonal systems in the setting of CHF.

Myocardial matrix metalloproteinase activity and abundance with congestive heart failure

The left ventricular (LV) myocardial collagen matrix has been proposed to participate in the maintenance of LV geometry. Thus alterations in the composition of the LV myocardial collagen matrix may influence LV function. The matrix metalloproteinases (MMPs) are a family of enzymes that contribute to extracellular remodeling in several disease states. However, the types of MMPs expressed in the normal and congestive heart failure (CHF) state and the relation to MMP activity remained unclear. Accordingly, after 3 wk of pacing (240 beats/min), changes in LV function, substrate-specific MMP activity, and MMP subclass abundance were measured in comparison with control pigs (n = 6). Changes in LV function and geometry were measured by echocardiography; LV end-diastolic dimension increased (3.6 +/- 0.1 vs. 6.0 +/- 0.1 cm, P < 0.05) and LV fractional shortening decreased (47 +/- 1 vs. 15 +/- 1%, P < 0.05) compared with controls. Degradation of fibrillar collagen is achieved through the combined action of interstitial collagenase (MMP-1), gelatinase A (MMP-2), and stromelysin (MMP-3) (He, C., S. Wilheilm, A. Pentland, B. Marmer, G. Grant, A. Eisen, and G. Goldberg. Proc. Natl. Acad. Sci. USA 86:2632-2636, 1989; Woessner, J. FASEB J. 5: 2145-2154, 1991). Accordingly, the relative abundance of specific MMPs (MMP-1, MMP-2, and MMP-3) was examined by immunoblotting. With pacing CHF, the relative abundance for MMP-1 increased to 319 +/- 94%, MMP-2 increased to 194 +/- 31%, and MMP-3 increased to 493 +/- 159% (all P < 0.05). With pacing CHF, LV myocardial zymographic activity for the substrate gelatin increased by 119% (P < 0.05) and for the substrate collagen III by 153% (P < 0.05) over controls. Caseinolytic activity also increased with pacing CHF by 139% (P < 0.05) over controls. In conclusion, LV myocardial MMP activity and abundance increased with pacing-induced CHF. These findings demonstrate that pacing-induced CHF leads to changes in myocardial MMP activity and expression that may be responsible for LV remodeling in CHF.The left ventricular (LV) myocardial collagen matrix has been proposed to participate in the maintenance of LV geometry. Thus alterations in the composition of the LV myocardial collagen matrix may influence LV function. The matrix metalloproteinases (MMPs) are a family of enzymes that contribute to extracellular remodeling in several disease states. However, the types of MMPs expressed in the normal and congestive heart failure (CHF) state and the relation to MMP activity remained unclear. Accordingly, after 3 wk of pacing (240 beats/min), changes in LV function, substrate-specific MMP activity, and MMP subclass abundance were measured in comparison with control pigs ( n = 6). Changes in LV function and geometry were measured by echocardiography; LV end-diastolic dimension increased (3.6 ± 0.1 vs. 6.0 ± 0.1 cm, P < 0.05) and LV fractional shortening decreased (47 ± 1 vs. 15 ± 1%, P < 0.05) compared with controls. Degradation of fibrillar collagen is achieved through the combined action of interstitial collagenase (MMP-1), gelatinase A (MMP-2), and stromelysin (MMP-3) (He, C., S. Wilheilm, A. Pentland, B. Marmer, G. Grant, A. Eisen, and G. Goldberg. Proc. Natl. Acad. Sci. USA 86: 2632-2636, 1989; Woessner, J. FASEB J. 5: 2145-2154, 1991). Accordingly, the relative abundance of specific MMPs (MMP-1, MMP-2, and MMP-3) was examined by immunoblotting. With pacing CHF, the relative abundance for MMP-1 increased to 319 ± 94%, MMP-2 increased to 194 ± 31%, and MMP-3 increased to 493 ± 159% (all P < 0.05). With pacing CHF, LV myocardial zymographic activity for the substrate gelatin increased by 119% ( P < 0.05) and for the substrate collagen III by 153% ( P < 0.05) over controls. Caseinolytic activity also increased with pacing CHF by 139% ( P < 0.05) over controls. In conclusion, LV myocardial MMP activity and abundance increased with pacing-induced CHF. These findings demonstrate that pacing-induced CHF leads to changes in myocardial MMP activity and expression that may be responsible for LV remodeling in CHF.

Effects of Growth Hormone Supplementation on Left Ventricular Morphology and Myocyte Function With the Development of Congestive Heart Failure

BACKGROUND Release of growth hormone (GH), putatively through alterations in insulin growth factor-1 (IGF-1) levels, has been implicated to influence left ventricular (LV) myocardial structure and function. The objective of this study was to determine contributory mechanisms by which GH supplementation may influence LV function with the development of congestive heart failure (CHF). METHODS AND RESULTS Pigs were assigned to the following groups: (1) chronic pacing at 240 bpm for 3 weeks (n = 10), (2) chronic pacing and GH supplementation (200 microg x kg(-1) x d(-1), n = 10), and (3) controls (n = 8). GH treatment increased IGF-1 plasma levels by nearly 2.5-fold throughout the pacing protocol. In the untreated pacing CHF group, LV fractional shortening was reduced and peak wall stress increased. In the pacing CHF and GH groups, LV fractional shortening was higher and LV wall stress lower than untreated CHF values. Steady-state myocyte velocity of shortening was reduced with pacing CHF and was unchanged from CHF values with GH treatment. In the presence of 25 nmol/L isoproterenol, the change in myocyte shortening velocity was reduced in the untreated CHF group and increased in the GH-treated group. LV sarcoplasmic reticulum Ca(2+)-ATPase abundance was reduced with pacing CHF but was normalized with GH treatment. CONCLUSIONS Short-term GH supplementation improved LV pump function in pacing CHF as a result of favorable effects on LV remodeling and contractile processes. Thus, GH supplementation may serve as a novel therapeutic modality in developing CHF.

Angiotensin converting enzyme inhibition, AT1 receptor inhibition, and combination therapy with pacing induced heart failure : effects on left ventricular performance and regional blood flow patterns

BACKGROUND AT1 receptor activation has been demonstrated to cause increased vascular resistance properties which may be of particular importance in the setting of congestive heart failure (CHF). The overall goal of this study was to examine the effects of ACE inhibition (ACEI) alone, AT1 receptor blockade alone and combined ACEI and AT1 receptor blockade on LV pump function, systemic hemodynamics and regional blood flow patterns in the normal state and with the development of pacing induced CHF, both at rest and with treadmill induced exercise. METHODS AND RESULTS Pigs (25 kg) were instrumented in order to measure cardiac output (CO), systemic (SVR) and pulmonary vascular (PVR) resistance, neurohormonal system activity, and myocardial blood flow distribution in the conscious state and assigned to one of 4 groups: (1) rapid atrial pacing (240 bpm) for 3 weeks (n = 7); (2) ACEI (benazeprilat, 3.75 mg/day) and pacing (n = 7); (3) AT1 receptor blockade (valsartan, 60 mg/day) and rapid pacing (n = 7); and (4) ACEI and AT1 receptor blockade (benazeprilat/valsartan, 1/60 mg/day, respectively) and pacing (n = 7). Measurements were obtained at rest and with treadmill exercise (15 degrees, 3 miles/h; 10 min) in the normal control state and after the completion of the treatment protocols. With rapid pacing, CO was reduced at rest and with exercise compared to controls. ACEI or AT1 blockade normalized CO at rest, but remained lower than control values with exercise. Combination therapy normalized CO both at rest and with exercise. Resting SVR in the CHF group was higher than controls and SVR fell to a similar degree with exercise; all treatment groups reduced resting SVR. With exercise, SVR was reduced from rapid pacing values in the ACEI and combination therapy groups. PVR increased by over 4-fold in the rapid pacing group both at rest and with exercise, and was reduced in all treatment groups. In the combination therapy group, PVR was similar to control values with exercise. Plasma catecholamines and endothelin levels were increased by over 3-fold with chronic rapid pacing, and were reduced in all treatment groups. In the combination therapy group, the relative increase in catecholamines and endothelin with exercise were significantly blunted when compared to rapid pacing only values. LV myocardial blood flow at rest was reduced in the rapid pacing only and monotherapy groups, but was normalized with combination therapy. CONCLUSION These findings suggest that with developing CHF, combined ACE inhibition and AT1 receptor blockade improved vascular resistive properties and regional blood flow distribution to a greater degree than that of either treatment alone. Thus, combined ACEI and AT1 receptor blockade may provide unique benefits in the setting of CHF.

Chronic Amlodipine Treatment During the Development of Heart Failure

BACKGROUND This study examined the effects of chronic amlodipine treatment on left ventricular (LV) pump function, systemic hemodynamics, neurohormonal status, and regional blood flow distribution in an animal model of congestive heart failure (CHF) both at rest and with treadmill exercise. In an additional series of in vitro studies, LV myocyte contractile function was examined. METHODS AND RESULTS Sixteen pigs were studied under normal control conditions and after the development of chronic pacing-induced CHF (240 bpm, 3 weeks, n=8) or chronic pacing and amlodipine (1.5 mg . kg-1 . d-1, n=8). Under ambient resting conditions, LV stroke volume (mL) was reduced with CHF compared with the normal control state (16+/-2 versus 31+/-2, P<0.05) and increased with concomitant amlodipine treatment (29+/-2, P<0.05). At rest, systemic and pulmonary vascular resistance (dyne . s-1 . cm-5) increased with CHF compared with the normal control state (3102+/-251 versus 2156+/-66 and 1066+/-140 versus 253+/-24, respectively, both P<0.05) and were reduced with amlodipine treatment (2108+/-199 and 480+/-74, respectively, P<0.05). With CHF, LV stroke volume remained reduced and was associated with a 40% reduction in myocardial blood flow during treadmill exercise, whereas chronic amlodipine treatment normalized LV stroke volume and improved myocardial blood flow. Resting and exercise-induced plasma norepinephrine levels were increased by >5-fold in the CHF group and were reduced by 50% from CHF values with chronic amlodipine treatment. Resting plasma endothelin (fmol/mL) increased with CHF compared with the normal state (10.4+/-0.9 versus 3.1+/-0.3, P<0.05) and was reduced with amlodipine treatment (6.6+/-1.1, P<0.5). With CHF, LV myocyte velocity of shortening ( microm/s) was reduced compared with normal controls (39+/-1 versus 64+/-1, P<0.05) and was increased with chronic amlodipine treatment (52+/-1, P<0.05). CONCLUSIONS Chronic amlodipine treatment in this model of developing CHF produced favorable hemodynamic, neurohormonal, and contractile effects in the setting of developing CHF.

Amlodipine therapy in congestive heart failure: hemodynamic and neurohormonal effects at rest and after treadmill exercise

This study examined the acute effects of amlodipine treatment on left ventricular pump function, systemic hemodynamics, neurohormonal status, and regional blood flow distribution in an animal model of congestive heart failure (CHF), both at rest and with treadmill exercise. A total of 14 pigs were studied under control conditions and after the development of pacing-induced CHF (240 beats per minute, 3 weeks, n = 7) or with CHF and acute amlodipine treatment for the last 3 days of pacing (1.5 mg/kg per day, n = 7). Under resting conditions, left ventricular stroke volume (mL) was reduced with CHF compared with the normal state (15+/-2 vs. 31+/-1, p<0.05) and increased with amlodipine treatment (23+/-4, p<0.05). At rest, systemic vascular resistance increased with CHF compared with the normal state (3,078+/-295 vs. 2,131+/-120 dyne x s cm(-5), p<0.05) and was reduced after amlodipine treatment (2,472+/-355 dyne x s cm(-5), p<0.05). With exercise, left ventricular stroke volume remained lower and systemic vascular resistance higher in the CHF group, but was normalized with amlodipine treatment. With exercise, left ventricular myocardial blood flow increased from resting values, but was reduced from the normal state with CHF (normal: 1.69+/-0.12 to 7.62+/-0.74 mL/min per gram vs. CHF: 1.26+/-0.12 to 4.77+/-0.45 mL/min per gram, both p<0.05) and was normalized with acute amlodipine treatment (1.99+/-0.35 to 6.29+/-1.23 mL/min per gram). Resting plasma norepinephrine was increased by >5-fold in the CHF group at rest and was not affected by amlodipine treatment. However, with exercise, amlodipine treatment blunted the increase in plasma norepinephrine by >50% when compared with untreated CHF values. Resting plasma endothelin levels increased with CHF compared with the normal state (10.9+/-0.9 vs. 2.8+/-0.4 fmol/mL, p<0.05) and was reduced with amlodipine treatment (7.5+/-1.5 fmol/mL, p<0.5). In other vascular beds, acute amlodipine treatment with CHF improved pulmonary and renal blood flow both at rest and with exercise; however, there were no effects observed on skeletal muscle blood flow. With the development of CHF, acute amlodipine treatment does not negatively influence left ventricular pump function, but rather may provide favorable hemodynamic and neurohormonal effects.

Inducible lethal ventricular arrhythmias in swine with pacing-induced heart failure

AbstractIntroduction: Rapid pacing-induced heart failure provides an excellent animal model for the study of heart failure. We studied the development of ventricular tachyarrhythmias using programmed stimulation in a pacing-induced heart failure model. We also studied action potential characteristics and the relationship between action potential and heart rate. Methods and results: Ten pigs were instrumented and were studied before the onset and every week after rapid pacing was instituted. Weekly echocardiograms and programmed stimulation were done in a sedated state. In vitro electrophysiologic studies were done on left ventricular myocardium in 4 heart-failure animals and 4 controls. All animals developed progressive heart failure with left ventricular dilatation and reduced percentage fractional shortening. No arrhythmias were induced at baseline or the first and second weeks. Ventricular fibrillation was induced in one animal on the third week and 4 animals on week 4, while there was no appreciable worsening in echocardiographic indices of ventricular dysfunction between weeks 3 and 4. Ventricular effective refractory period was unchanged during the 4 weeks. In vitro studies showed action potential prolongation in heart failure myocardium. However, action potential duration at pacing rates > 100 bpm were similar to controls. No early or delayed afterdepolarizations were observed. Conclusion: This study demonstrated an increased susceptibility to ventricular fibrillation with the development of heart failure which was not related to the degree of ventricular disfunction. Also, the normalization of action potential duration at higher heart rates suggests that the increased incidence of inducible ventricular fibrillation in this model may not be solely due to prolonged action potential duration.

Pulmonary hemodynamics and endothelin levels in pacing-induced heart failure: During rest and exercise☆

Elevated plasma levels of endothelin (ET) have been reported to accompany the development of heart failure (HF), and therefore, this potent vasoconstrictive peptide has been postulated to contribute to the altered pulmonary hemodynamics that occur in this disease process. The overall goal of this study was to examine more carefully the relationship between ET levels in the pulmonary system and pulmonary hemodynamics in the normal and HF states, during both rest and exercise. This study used a porcine model of chronic rapid pacing that has been shown in previous studies to produce left ventricular dysfunction and neurohormonal system activation consistent with the syndrome of HF. Pigs (n = 10) were chronically instrumented to measure pulmonary and systemic hemodynamics, parenchymal flow, and ET content and to obtain blood samples from the pulmonary circuit in the conscious state. Measurements were performed in the normal control state and again following the development of pacing-induced HF (240 beats/min per 21 days), both at rest and during treadmill exercise (3 mph, 15 degrees incline, 12 minutes). With HF, under ambient resting conditions, a threefold increase in pulmonary plasma ET occurred and was accompanied by a fivefold increase in pulmonary vascular resistance. During treadmill exercise, pulmonary plasma ET and pulmonary vascular resistance remained elevated in the HF group when compared with the normal state and were associated with a sixfold decrease in pulmonary parenchymal flow. Pulmonary parenchymal ET content was increased with HF when compared with values for normal control subjects (8.5 +/- 0.6 vs 5.6 +/- 0.8 fmol ET/mg protein, P < .05). Thus, the findings of this study suggest that in this model of HF, increased ET within the pulmonary circuit contributed to abnormalities in resistive properties and parenchymal flow.

Myocardial Bradykinin Following Acute Angiotensin-Converting Enzyme Inhibition, AT1 Receptor Blockade, or Combined Inhibition in Congestive Heart Failure

Background: The present study examined the effects of acute angiotensin-converting enzyme inhibition (ACEI), AT, receptor blockade (AT, block), or combined treatment on in vitro and in vivo bradykinin (BK) levels. Methods: BK levels were measured in isolated porcine myocyte preparations (n = 13) in the presence of exogenous BK (10-8 M); with an ACEI (benezaprilat; 0.1 mM) and BK; an AT, block (valsartan; 10-5 M) and BK; and combined treatment and BK. In a second study, myocardial microdialysis was used to measure porcine interstitial BK levels in both normal (n = 14) and pacing-induced congestive heart failure (CHF) (240 beats/min, 3 weeks, n = 16) under the following conditions: baseline, following ACEI (benezaprilat, 0.0625 mg/kg) or AT, block (valsartan, 0. I mg/kg), and a combined treatment (benezaprilat, 0.0625 mg/kg; valsartan, 0.1 mg/kg). Results: In the left ventricular myocyte study, BK levels increased over 93% with all treatments compared to untreated values (P < 0.05). In the in vivo study, basal interstitial BK values were lower in the CHF group than in controls (2.64 ± 0.57 vs 5.91 + 1.4 nM, respectively, P < 0.05). Following acute infusion of the ACEI, BK levels in the CHF state increased from baseline (57% ± 22; P < 0.05). Following combined ACEIIAT, block, BK levels increased from baseline in both control (42% ± 11) and CHF groups (60% ± 22; P < 0.05 for both). Conclusion: These findings suggest that ACEI, or combined ACEI/AT, block increased BK at the level of the myocyte and potentiated BK levels in the CHF myocardial interstitium.

Bradykinin degradation and relation to myocyte contractility.

Background: Past studies have demonstrated that exogenous bradykinin (BK) causes vasodilation and increases coronary blood flow, effects that may be beneficial in the setting of cardiac disease states. An important pathway for BK degradation is through angiotensin-converting enzyme (ACE), which results in the formation of a degradative peptide, BK(1-7). The goal of this study was to examine the effects of BK, BK(1-7), and the potential modulation of BK by ACE inhibition on myocyte contractility. Methods and Results: Contractile function was examined in isolated adult porcine (n = 15) left ventricular (LV) myocyte preparations in the presence or absence of BK (10-8 mol/L), BK(1-7) (10-8 mol/L), and with pretreatment by ACE inhibition (benazaprilat). Myocyte velocity of shortening fell by over 15% in the presence of BK and by 8% with BK(1-7) ( P < .05 vs basal). ACE inhibition blunted the negative effect of BK on myocyte velocity of shortening by over 60% (P < .05). Furthermore, robust ACE activity coupled with significant BK degradation was demonstrated in LV-isolated myocyte preparations, and BK proteolysis was influenced by ACE inhibition. Conclusion: These results suggest that BK has a direct effect on LV myocyte contractility, and that this effect may be mediated by proteolysis of BK at the level of the LV myocyte sarcolemma.