Effects of combined angiotensin II and endothelin receptor blockade with developing heart failure: effects on left ventricular performance.

BACKGROUND: The goal of this study was to determine the comparative effects of angiotensin II type 1 (AT(1)) receptor inhibition alone, endothelin-1 (ET) receptor blockade alone, and combined receptor blockade on left ventricular (LV) function, contractility, 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) concomitant AT(1) receptor blockade (valsartan, 3 mg/kg per day) and rapid pacing (n=8), (3) concomitant ET receptor blockade (bosentan, 50 mg/kg BID) and rapid pacing (n=8), (4) concomitant combined AT(1) and ET receptor inhibition and rapid pacing (n=8), and (5) sham-operated control (n=9). LV stroke volume was reduced from the control value after rapid pacing, was unchanged with either AT(1) or ET receptor blockade alone, but was improved with combination treatment. LV peak wall stress was reduced in both groups with ET receptor blockade compared with the rapid pacing group. Plasma norepinephrine levels were increased by >3-fold after rapid pacing, remained increased in the monotherapy groups, but were reduced after combination treatment. LV myocyte velocity of shortening was reduced after rapid pacing-induced CHF, remained reduced after AT(1) receptor blockade, increased after ET receptor blockade (compared with rapid pacing-induced CHF values), and returned to within control values after combined blockade. CONCLUSIONS: Combined AT(1) and the ET receptor blockade in this model of CHF improved LV pump function, and contributory factors included the effects of LV loading conditions, neurohormonal system activity, and myocardial contractile performance. Thus, combined receptor blockade may provide a useful combinatorial therapeutic approach in CHF.

Myocyte endothelin exposure during cardioplegic arrest exacerbates contractile dysfunction after reperfusion.

Transient left ventricular (LV) dysfunction can occur after cardioplegic arrest. The contributory mechanisms for this phenomenon are not completely understood. We tested the hypothesis that exposure of LV myocytes to endothelin (ET) during simulated cardioplegic arrest would have direct effects on contractile processes with subsequent reperfusion. LV porcine myocytes were randomly assigned to three groups: 1) CONTROL: normothermic (37 degrees C) cell media (n = 204); 2) Cardioplegia: simulated cardioplegic arrest (K(+) 24 mEq/L, 4 degrees C x 2 h) followed by reperfusion and rewarming with cell media (n = 164); and 3) Cardioplegia/ ET: simulated cardioplegic arrest in the presence of ET (200 pM) followed by reperfusion with cell media containing ET (n = 171). Myocyte contractility was measured by computer-assisted video microscopy. In a subset of experiments, myocyte intracellular calcium was determined after Fluo-3 (Molecular Probes, Eugene, OR) loading by digital fluorescence image analysis. Myocyte shortening velocity was reduced after cardioplegic arrest compared with controls (52 +/- 2 vs 84 +/- 3 microm/s, respectively; P < 0.05) and was further reduced with cardioplegic arrest and ET exposure (43 +/- 2 microm/s, P < 0.05). Intracellular calcium was significantly increased in myocytes exposed to cardioplegia compared with normothermic control myocytes and was further augmented by cardioplegia with ET supplementation (P < 0.05). Exposure of the LV myocyte to ET during cardioplegic arrest directly contributed to contractile dysfunction after reperfusion. Moreover, alterations in intracellular calcium may play a role in potentiating the myocyte contractile dysfunction associated with ET exposure during cardioplegic arrest.

Endothelin receptor pathway in human left ventricular myocytes: relation to contractility.

BACKGROUND: Increased synthesis and release of the potent bioactive peptide endothelin-1 (ET-1) occurs during and after cardiac surgery. However, the cellular and molecular basis for the effects of ET-1 on human left ventricular (LV) myocyte contractility remains unknown. METHODS: LV myocyte contractility was examined from myocardial biopsies taken from patients (n = 30) undergoing elective coronary artery bypass. LV myocytes (n = 997, > 30/patient) were isolated using microtrituration and contractility examined by videomicroscopy at baseline and after ET-1 exposure (200 pmol/L). In additional studies, myocytes were pretreated to inhibit either protein kinase C (PKC) (chelerythrine, 1 micromol/L), the sodium/hydrogen (Na/H) exchanger (EIPA, 1 micromol/L), both PKC and the Na/H exchanger, or the ET(A) receptor (BQ-123, 1 micromol/L), followed with ET-1 exposure. RESULTS: Basal myocyte shortening increased 37.8 +/- 6.3% with ET-1 (p < 0.05). Na/H exchanger, PKC, and dual inhibition all eliminated the effects of ET-1. Furthermore, ET(A) inhibition demonstrated that ET-1 effects on myocyte contractility were mediated through the ET(A) receptor subtype. CONCLUSIONS: ET-1 directly influences human LV myocyte contractility, which is mediated through the ET(A) receptor and requires intracellular activation of PKC and stimulation of the Na/H exchanger.

Effects of angiotensin type-I receptor blockade on pericardial fibrosis.

BACKGROUND: Reoperative cardiac surgical procedures are associated with a significantly greater complication rate than that of the initial procedure. Enhanced collagen synthesis can occur due to increased production of angiotensin II (Ang-II) and subsequent activation of Ang AT(1) receptor. Accordingly, the goal of the current study is to test the hypothesis that increased Ang AT(1) receptor activity following pericardiotomy contributes to pericardial thickening and fibrosis. MATERIALS AND METHODS: Adult pigs were randomly assigned to three protocols: (1) pericardiotomy with 28-day recovery period (n = 5); (2) pericardiotomy with Ang AT(1) receptor blockade instituted throughout the 28-day recovery period using 60 mg/day valsartan (n = 5); and (3) sham controls (n = 6). Pericardium samples were collected and analyzed by biochemical and histomorphometrical methods. Pericardial fibrosis occurred postpericardiotomy as indicated by increased hydroxyproline content from normal value of 50 +/- 3 microg/mg to 75 +/- 4 microg/mg (P < 0. 05). RESULTS: Pericardial thickness was increased postpericardiotomy to 2.7 +/- 0.4 mm compared to normal values of 0.4 +/- 0.05 mm (P < 0.05). Ang AT(1) receptor blockade reduced pericardial thickness by 50% and the relative degree of fibrosis was comparable to that of the normal group. CONCLUSIONS: The results from this pericardial fibrosis animal model suggest that Ang AT(1) receptor activation contributes to the development of pericardial thickening and collagen accumulation in the postoperative period. Thus, Ang AT(1) receptor inhibition may provide a novel therapeutic strategy to prevent pericardial fibrosis that follows cardiac surgical procedures.

Angiotensin-converting enzyme and matrix metalloproteinase inhibition with developing heart failure: comparative effects on left ventricular function and geometry.

The progression of congestive heart failure (CHF) is left ventricular (LV) myocardial remodeling. The matrix metalloproteinases (MMPs) contribute to tissue remodeling and therefore MMP inhibition may serve as a useful therapeutic target in CHF. Angiotensin converting enzyme (ACE) inhibition favorably affects LV myocardial remodeling in CHF. This study examined the effects of specific MMP inhibition, ACE inhibition, and combined treatment on LV systolic and diastolic function in a model of CHF. Pigs were randomly assigned to five groups: 1) rapid atrial pacing (240 beats/min) for 3 weeks (n = 8); 2) ACE inhibition (fosinopril, 2.5 mg/kg b.i.d. orally) and rapid pacing (n = 8); 3) MMP inhibition (PD166793 2 mg/kg/day p.o.) and rapid pacing (n = 8); 4) combined ACE and MMP inhibition (2.5 mg/kg b.i.d. and 2 mg/kg/day, respectively) and rapid pacing (n = 8); and 5) controls (n = 9). LV peak wall stress increased by 2-fold with rapid pacing and was reduced in all treatment groups. LV fractional shortening fell by nearly 2-fold with rapid pacing and increased in all treatment groups. The circumferential fiber shortening-systolic stress relation was reduced with rapid pacing and increased in the ACE inhibition and combination groups. LV myocardial stiffness constant was unchanged in the rapid pacing group, increased nearly 2-fold in the MMP inhibition group, and was normalized in the ACE inhibition and combination treatment groups. Increased MMP activation contributes to the LV dilation and increased wall stress with pacing CHF and a contributory downstream mechanism of ACE inhibition is an effect on MMP activity.

ATP-sensitive potassium channel activation before cardioplegia. Effects on ventricular and myocyte function.

BACKGROUND: Pretreatment with potassium channel openers (PCOs) has been shown to provide protective effects in the setting of myocardial ischemia. The goal of the present study was to examine whether PCO pretreatment would provide protective effects on left ventricular (LV) and myocyte function after cardioplegic arrest. METHODS AND RESULTS: The first study quantified the effects of PCO pretreatment on LV myocyte contractility after simulated cardioplegic arrest. LV porcine myocytes were randomly assigned to 3 groups: (1) normothermic control: 37 degrees C x 2 hours (n = 116); (2) cardioplegia: K+ 24 mEq/L, 4 degrees C x 2 hours followed by reperfusion and rewarming (n = 62); and (3) PCO/cardioplegia: 5 minutes of PCO treatment (50 mumol/L, SR47063, 37 degrees C; n = 94) followed by cardioplegic arrest and rewarming. Myocyte contractility was measured after rewarming by videomicroscopy. The second study determined whether the effects of PCO pretreatment could be translated to an in vivo model of cardioplegic arrest. Pigs (weight 30 to 35 kg) were assigned to the following: (1) cardioplegia: institution of cardiopulmonary bypass (CPB) and cardioplegic arrest (K+ 24 mEq/L, 4 degrees C x 2 hours) followed by reperfusion and rewarming (n = 8); and (2) PCO/cardioplegia: institution of CPB, antegrade myocardial PCO perfusion without recirculation (500 mL of 50 mumol/L, SR47063, 37 degrees C), followed by cardioplegic arrest (n = 6). LV function was examined at baseline (pre-CPB) and at 0 to 30 minutes after separation from CPB by use of the preload-recruitable stroke work relation (PRSWR; x 10(5) dyne.cm/mm Hg). LV myocyte velocity of shortening was reduced after cardioplegic arrest and rewarming compared with normothermic control (37 +/- 3 vs 69 +/- 3 microns/s, P < 0.05) and was improved with 5 minutes of PCO treatment (58 +/- 3 microns/s). In the intact experiments, the slope of the PRSWR was depressed in the cardioplegia group compared with baseline with separation from CPB (1.07 +/- 0.15 vs 2.57 +/- 0.11, P < 0.05) and remained reduced for up to 30 minutes after CPB. In the PCO-pretreated animals, the PRSWR was higher after cessation of CPB when compared with the untreated cardioplegia group (1.72 +/- 0.07, P < 0.05). However, in the PCO pretreatment group, 50% developed refractory ventricular fibrillation by 5 minutes after CPB, which prevented further study. CONCLUSIONS: PCO pretreatment improved LV myocyte contractile function in an in vitro system of cardioplegic arrest. The in vivo translation of this improvement in contractile performance with PCO pretreatment was confounded by refractory arrhythmogenesis. Thus the application of PCO pretreatment as a protective strategy in the setting of cardiac surgery may be problematic.

Isolated left ventricular myocyte contractility in patients undergoing cardiac operations.

BACKGROUND: Because of methods required for obtaining isolated left ventricular myocytes, evaluation of the contractile function of isolated left ventricular myocytes in normal human patients has been limited. Accordingly, the goal of the present study was to develop a means to isolate human left ventricular myocytes from small myocardial biopsy specimens collected from patients undergoing elective coronary artery bypass operations and to characterize indices of myocyte contractile performance. METHODS: Myocardial biopsy specimens were obtained from the anterior left ventricular free wall of 22 patients undergoing coronary artery bypass operations. Myocytes were isolated from these myocardial samples by means of a stepwise enzymatic digestion method and micro-trituration techniques. Isolated left ventricular myocyte contractile function was assessed by computer-assisted high-speed videomicroscopy under basal conditions and in response to beta-adrenergic receptor stimulation with isoproterenol. RESULTS: A total of 804 viable left ventricular myocytes were successfully examined from all of the myocardial biopsy specimens with an average of 37+/-4 myocytes per patient. All myocytes contracted homogeneously at a field stimulation of 1 Hz with an average percent shortening of 3.7%+/-0.1% and shortening velocity of 51.3+/-1.3 microm/s. After beta-adrenergic receptor stimulation with isoproterenol, percent shortening and shortening velocity increased 149% and 118% above baseline, respectively (P < .05). CONCLUSION: The unique results of the present study demonstrated that a high yield of myocytes could be obtained from human left ventricular biopsy specimens taken during cardiac operations. These myocytes exhibited stable contractile performance and maintained the capacity to respond to an inotropic stimulus. The methods described herein provide a basis by which future studies could investigate intrinsic and extrinsic influences on left ventricular myocyte contractility in human beings.