Comparison between angiotensin receptor antagonism and converting enzyme inhibition in heart failure

This study was designed to assess the influence of the activation status of the renin angiotensin system (RAS) on the hemodynamic effects of EXP 3174 (an angiotensin AT1 receptor antagonist) and enalaprilat (an angiotensin converting enzyme inhibitor) in tachycardia-induced heart failure. Thirteen dogs were chronically instrumented to measure left ventricular (LV) pressure, its first time derivative (LV dP/dt), atrial and aortic pressures, and cardiac output. EXP 3174 (0.1 mg/kg, iv) or enalaprilat (1 mg/kg, iv) were administered in conscious dogs with heart failure induced by right ventricular pacing (250 beats/min, 3 weeks). EXP 3174 and enalaprilat produced significant vasodilation but the effects of EXP 3174 on mean aortic pressure (MAP), cardiac output, and total peripheral resistance (TPR) were only 50% of those produced by enalaprilat. When dogs were grouped according to their baseline plasma renin activity (PRA) values, in dogs with normal PRA (0.5 ± 0.1 ng/ml/h) EXP 3174 did not produce significant change in MAP and TPR, while enalaprilat decreased significantly MAP and TPR. In contrast, in dogs with high PRA (6.7 ± 3.2 ng/ml/h), EXP 3174 produced significant reductions in MAP and TPR, which were similar to those produced by enalaprilat. Thus, in conscious dogs with heart failure, enalaprilat is effective whether the RAS is activated or not. In contrast, EXP 3174 is effective only when the RAS is activated. These results may help in the choice of inhibitors of the RAS in heart failure. Received: 22 September 1998, Returned for revision: 14 October 1998, Revision received: 23 November 1998, Accepted: 8 December 1998     

Endothelium-dependent vasodilatation in Sprague-Dawley rats with postinfarction hypertrophy: Lack of endothelial dysfunction in vitro

The hypothesis was tested whether postinfarction hypertrophy/congestive heart failure in rats is associated with endothelial dysfunction and increased vascular generation of reduced oxygen species. Myocardial infarction was induced in Sprague-Dawley rats by ligation of the left coronary artery. After 16 weeks, endothelium-dependent (with acetylcholine) and -independent (with sodium nitroprusside) relaxation were studied in isolated aortic rings, and isolated rings from the femoral and mesenteric arteries. The generation of superoxide, hydrogenperoxide, and peroxynitrite was measured in arteries using lucigenin- and luminol-enhanced chemiluminescence techniques. Systolic blood pressure decreased over the 16 week study period as compared to shamoperated control rats; organ weights (lungs, right and left ventricles) significantly increased in coronary artery ligated rats indicating development of congestive heart failure. Surprisingly, concentration response curves with acetylcholine and sodium nitroprusside were almost identical in myocardial infarction rats as compared to control animals, irrespective of which type of vessel was studied (aorta, femoral or mesenteric arteries). In addition, no differences in the production of reduced radical species were found in aortic tissue from heart failure rats as compared to control rats. Received: 3 March 1998, Returned for 1. revision: 20 April 1998, 1. Revision received: 14 May 1998, Returned for 2. revision: 25 June 1998, 2. Revision received: 8 July 1998, Accepted: 9 July 1998     

Uncoupling between left ventricular contractility and relaxation after direct-current counter shocks

Left ventricular (LV) contractility and relaxation are physiologically coupled on the basis of intracellular calcium cycling. The relation has been reported to be unique. However, this may not be always true if relaxation is predominantly impaired. Direct current counter (DC) shocks develop myocardial interstitial edema, inducing diastolic heart failure. Thus, we hypothesized that LV contractility-relaxation coupling would be altered in an experimental model of diastolic dysfunction by DC shocks. The relation between Emax (LV contractility index) and the time constant of LV pressure decay (tau) was evaluated in isovolumic contraction of seven isolated, blood perfused dog hearts. There existed a hyperbolic relation between Emax and tau in control (= pre-DC) hearts. After the application of five consecutive 80 J DC shocks, Emax was unchanged (from 4.6 ± 1.0 to 5.2 ± 0.8 mmHg · ml⁻¹· 100 g) but tau was markedly prolonged (from 36 ± 12 to 74 ± 38 ms, P < 0.01). Thus, DC shocks induced a strikingly upward displacement of the hyperbolic curve compared with the control. The slope of the linear relation between Emax and the reciprocal of tau (= a relaxation velocity index normalized for contractility) significantly decreased after DC shocks. We conclude that the coupling between LV contractility and relaxation is not unique, but can be altered acutely by DC shocks. A dissociation of contractility-relaxation coupling may be of help for distinguishing diastolic heart failure and exploring its pathogenesis. Received: 2 November 1998, Returned for 1. revision: 2 December 1998, 1. Revision received: 15 February 1999, Returned for 2. revision: 2 March 1999, 2. Revision received: 14 April 1999, Accepted: 24 April 1999     

Phase angle convergence of multiple monophasic action potential reordings precedes spontaneous termination of ventricular fibrillation

Aims To elucidate the mechanism of spontaneous termination of ventricular fibrillation (VF) and to define an indicator of its occurrence, the phase angle, a novel measure to assess synchrony of activation, was evaluated. Methods and results In 7 isolated rabbit hearts, 7 monophasic action potentials were recorded simultaneously. Ventricular fibrillation was induced by T wave shocks. Cycle lengths (CL) and phase angles between all 7 recordings were analyzed until spontaneous termination or shock-induced defibrillation. Average phase angle was calculated as activation time difference to a reference channel and expressed as a fraction of the reference channel's CL with 1 equaling a complete CL. Initial CLs and phase angles were similar in sustained and terminating episodes (CL: 141±16 ms vs 142±24 ms, phase angle: 0.244±0.11 vs 0.263±0.1, p=NS). During spontaneous termination, CL increased slightly by 7%. Average phase angle converged gradually over the last three activations before termination of ventricular fibrillation by 22–48% (p<0.0005), eventually resulting in phase angles similar to paced rhythms directly prior to spontaneous termination of ventricular fibrillation. Conclusions Gradual synchronization of activation is part of the electrophysiological mechanism resulting in spontaneous ventricular fibrillation termination and can be detected three activations before termination. Phase angle convergence may be useful to detect spontaneous termination of ventricular fibrillation. Received: 24 October 1997, Returned for 1. revision: 24 November 1997, 1. Revision received: 21 January 1998, Returned for 2. revision: 4 March 1998, 2. Revision received: 29 April 1998, Returned for 3. revision: 25 May 1998, 3. Revision received: 15 June 1998, Accepted: 17 June 1998     

ATP-sensitive potassium channels do not have a main role in mediating late preconditioning protection against arrhythmias and stunning in conscious sheep

Objective Although late preconditioning protects against stunning following several short periods of ischemia-reperfusion, it is not clear if it confers protection against stunning and malignant arrhythmias after a sustained reversible ischemia, and whether KATP channels are involved as triggers and/or end effectors of the protective mechanism. The purpose of this work was thus to test these issues in conscious sheep. Methods Five groups were considered: CONT (control): the animals were submitted to 12 min ischemia followed by 2 h reperfusion; SWOP (late preconditioning): on the first day, the animals were preconditioned with 6 periods of 5 min ischemia 5 min reperfusion and 24 h later they were submitted to 12 min ischemia followed by 2 h reperfusion; GLIB: same as CONT with the KATP channel inhibitor glibenclamide (0.4 mg/kg) infused 30 min prior to the 12 min ischemia; SWOPG2: same as SWOP with glibenclamide before the 12 min ischemia; SWOPG1: same as SWOP with glibenclamide prior to the preconditioning stimulus. Results Percent reperfusion recovery of wall thickening fraction (% WTh) showed late preconditioning protection against stunning throughout reperfusion (SWOP vs CONT, p < 0.01). Arrhythmia severity index (ASI) also demonstrated that late preconditioning protects against malignant arrhythmias at the onset of reperfusion (CONT: 4.87 ± 1.62 vs SWOP: 1.39 ± 0.93, p < 0.01). Glibenclamide was unable to prevent preconditioning, both against stunning and arrhythmia incidence, when administered either before the preconditioning stimulus (SWOPG1 vs CONT, p < 0.01) or before the sustained ischemia (SWOPG2 vs GLI, p < 0.01). Conclusions Results indicate that late preconditioning protects against stunning and arrhythmias following a reversible, sustained ischemia in conscious sheep and that KATP channel participation is negligible as triggers and end effectors of both types of protection. Received: 19 March 2001, Returned for revision: 9 April 2001, Revision received: 14 May 2001, Accepted: 16 May 2001     

Characterisation of the function of adult guinea-pig ventricular myocytes following co-culture with neonatal rat myocytes

Adult guinea-pig myocytes were co-cultured with a layer of spontaneously contracting neonatal rat myocytes based on a method described by Weisensee D. (In Vitro Cell Dev Biol 31: 190–195, 1995). Contractile studies were performed on freshly isolated, 24 and 48 h co-cultured adult guinea-pig myocytes to investigate whether alterations in contractile function had occurred. No difference was found between freshly isolated and 24 h co-cultured adult guinea-pig myocytes in terms of sensitivity to calcium, isoprenaline, frequency response and beat duration. After 48 h, the frequency response was depressed (P<0.02) and the beat was prolonged (P<0.05) when compared to that of freshly isolated myocytes. In the presence of the SR Ca²⁺ ATPase inhibitor, thapsigargin, the beat was significantly prolonged (P=0.003) in 24 h co-cultured myocytes but not in freshly isolated myocytes. These findings show that adult guinea-pig myocytes can be maintained in co-culture with neonatal rat myocytes with little change in contractile function for 24 h but after this time contractile function begins to deteriorate. Received: 3 March 1998, Returned for 1. revision: 25 March 1998, 1. Revision received: 26 May 1998, Returned for 2. revision: 18 June 1998, 2. Revision received: 23 July 1998, Accepted: 23 July 1998     

Post-ejection thickening as a marker of viable myocardium. An echocardiographic study in patients with chronic coronary artery disease

Summary The study aim was to assess whether post-ejection thickening (PT) is an useful marker of viable myocardium in patients with chronic coronary artery disease. Twenty-three patients with critical coronary stenoses were submitted to dobutamine and dipyridamole stress-echocardiographies and dipyridamole-early-redistribution ²⁰¹TI SPECT within 15 days from coronary arteriography. They were selected for the presence of PT in segments that could be optimally studied by M-mode echocardiography and were hypo-akinetic in basal conditons. PT (occurring between end-ejection and mitral valve opening) was found in 58% of dysfunctional critically perfused regions. Ninety-eight percent of the regions with PT and 6% of those without PT improved during low-dose dobutamine stress-echocardiography. Segments with PT had, respectively, higher and lower SPECT early-redistribution thallium activity than dysfunctional segments without PT and normokinetic regions. Therefore, regions with PT were viable and had a moderate decrease in coronary perfusion. Akinetic segments without PT did not show any inotropic reserve. After revascularization almost all the segments with PT improved. In conclusion, PT is a pattern of myocardial contraction easily detected by M-mode echocardiography in the clinical setting. If the results of this study are further confirmed, PT may become a sign for the recognition of myocardial viability. Received: 18 November 1996, Returned for 1. revision: 20 December 1996, 1. Revision received: 30 March 1997, Returned for 2. revison: 21 May 1997, 2. Revision received: 11 August 1997, Returned for 3. revision: 9 September 1997, 3. Revision received: 26 February 1998, Accepted: 25 March 1998     

不同剂量碘化钾对大鼠肝脏抗氧化能力的影响

目的观察Wistar大鼠补充不同剂量碘化钾（KI）对肝脏抗氧化能力的影响。方法将Wistar大鼠随机分为6组：低碘组（LI）,适碘组（NI）,5倍高碘组（5HI）,10倍高碘组（10HI）,50倍高碘组（50HI）,100倍高碘组（100HI）。喂养3、6和12个月后,检测肝组织匀浆中的谷胱甘肽过氧化酶（GPx）活性、超氧化物歧化酶（SOD）活性以及丙二醛（MDA）含量。结果LI组GPx活性0.05）。在3和6个月时,4个HI组GPx活性、SOD活性和MDA含量均与NI组无差异（P〉0.05）。但100HI组在实验12个月时GPx活性和SOD活性均较NI组降低（P〈0.05）,而MDA含量无统计学差异（P〉0.05）。结论（1）低碘导致大鼠肝脏抗氧化能力降低;（2）长期摄入高剂量碘未见对肝脏产生明显过氧化损伤,仅于100倍高碘组抗氧化酶活性降低。     

Vitamin C and vitamin E status in the spontaneously diabetic BB rat before the onset of diabetes

Ascorbic acid (AA), dehydroascorbic acid (DHAA), and vitamin E were measured in tissues and plasma of 30 control and 30 spontaneously diabetic BioBreeding rats (BBdp) during development and before the onset of diabetes. At weaning, rats were fed an AIN-76 semisynthetic diet for 30, 64, or 113 days, after which plasma and tissues from 10 rats of each group were collected and analysed for AA, DHAA, and vitamin E. AA and DHAA levels were significantly increased in plasma and spleen of the diabetes-prone rats compared with those of the control group at 30 and 64 days, but the difference disappeared by 113 days. No differences were observed in liver, adrenals, thymus, and pancreas at any of the time periods. However, lower levels of vitamin E were observed in adrenal gland, thymus, and pancreas of the diabetes-prone rats. It is concluded that BBdp rats have an altered metabolism of AA, DHAA, and vitamin E, before the onset of diabetes. These changes could be due to genetic and physiological factors operating during development of this rat strain.     

Inconsistency of the slope and the volume intercept of the end-systolic pressure-volume relationship as individual indexes of inotropic state in conscious dogs: presentation of an index combining both variables

We tested the ability of the slope (Emax) and the volume intercept (Vo) of the end-systolic pressure-volume relationship (ESPVR) to indicate contractility changes in conscious dogs instrumented with sonomicrometers measuring left ventricular diameter in three orthogonal axes and a left ventricular pressure microtransducer. ESPVRs were generated by inferior vena caval occlusion under control conditions (C1 and C2) and during enhanced (I+) and depressed (I-) inotropic states achieved by infusion of dobutamine and injection of propranolol, respectively. No significant difference between the first control (C1) and I+ or between the second control (C2) and I- were found for either Emax (C1, 5.31 +/- 1.68 mm Hg/ml, mean +/- SD; I+, 5.37 +/- 1.44; C2, 5.20 +/- 1.62; I-, 4.18 +/- 1.32) or Vo (C1, 10.3 +/- 9.6 ml; I+, 7.3 +/- 9.1; C2, 9.9 +/- 9.0; I-, 12.7 +/- 12.5), despite significant changes in other indexes of contractility. Comparison of changes in Emax in individual animals in response to I+ and I- revealed that 63% were nonsignificant, 28% were significant and expected, and 9% were significant and paradoxical. Within defined volume limits and irrespective of individual changes in Emax and Vo, in all animals I+ shifted the ESPVR above and to the left of C1 and I- shifted the ESPVR below and to the right of C2. We thus integrated the changes in Emax and Vo by measuring the area beneath each ESPVR between defined limits of end-systolic volume. The values for area were: C1, 612 +/- 150 mm Hg.ml; I+, 745 +/- 191 (p less than .001); C2, 520 +/- 198; I-, 420 +/- 139 (p less than .001). We conclude that (1) neither Emax nor Vo are individually reliable indexes of changed contractility, and (2) the area beneath the ESPVR between defined end-systolic volume limits is a consistent indicator of variations in inotropic state.     

Effects of chronic noradrenaline on the nitric oxide pathway in human endothelial cells

Altered endothelium-dependent vasodilation has been observed in congestive heart failure (CHF), a disease characterized by a sustained adrenergic activation. The purpose of our study was to test the hypothesis that chronically elevated catecholamines influence the nitric oxide (NO) pathway in the human endothelium. Human umbilical vein endothelial cells (HUVEC) were exposed for 7 days to a concentration of noradrenaline (NA, 1 ng/mL) similar to that found in the blood of patients with CHF. Kinetics of endothelial constitutive NO synthase (ecNOS) and inducible NO synthase (iNOS) activity, measured by [³H]L-arginine to [³H]L-citrulline conversion, and protein expression of ecNOS and iNOS, assessed by Western blot analysis, were unaffected by chronic NA treatment. Furthermore, no changes in subcellular fraction-associated ecNOS were found; this indirectly shows that chronic NA did not cause phosphorylation of the enzyme. Moreover, [³H]L-arginine transport through the plasma membrane was conserved in chronically NA-treated cells. The data demonstrate that prolonged in vitro exposure to pathologic CHF-like NA does not affect the L-arginine NO pathway in human endothelial cells. Received: 11 July 1997, Returned for revision: 13 August 1997, Revision received: 6 October 1997, Returned for 2. revision: 17 November 1997, 2. Revision received: 5 January 1998, Accepted: 26 January 1998     

Effect of non-selective endothelin blockade, TAK-044, on the ischemic cellular injury of rat heart

The aim of this study is to evaluate the role of non-selective endothelin blockade (TAK-044) in ischemic myocardial injury. Forty anesthetized rats were separated into four groups: 1) TAK-I group, after preinjection of TAK-044 (3 mg/kg), LAD was ligated for 60 min and reperfused for 60 min; 2) Saline (SAL)-I group, LAD ligation and reperfusion without TAK-044; 3) TAK-C group, sham operated TAK group; 4) SAL-C group, sham-operated SAL group. Myocardium from each group was separated and analyzed by biochemical and ultrastructural procedures. Reperfusion arrhythmia (VT) was observed in 88 % of the SAL-I Group, in contrast to only 36% of the TAK-I group. At the end of reperfusion, hemodynamics indicated no significant differences between these two groups. The Ca⁺⁺-ATPase activity of sarcoplasmic reticulum (SR) was 3.9μmoles Pi/mg protein/h (39 % of SAL-C group) in the SAL-I group, while that in the TAK-I group was significantly higher at 6.1 (54%). The ratio of infarct/risk area was 58% in the SAL-I group and 36% in the TAK-I group. In the ultrastructural observations, irreversibly injured cells of the ischemic portion were reduced significantly from 35% (SAL-I group) to 14% (TAK-I group). Thus, our results indicated that endothelin blockade reduced ischemic cellular injury. The mechanism of this reduction was speculated to be a restistance to ischemic injury in the subcellular levels of the myocardium conferred by a reduction of vascular constriction and improvement of imbalance in the energy supply and demand. Received: 28 July 1998, Returned for 1. revision: 27 August 1998, 1.Revision received: 14 September 1998, Returned for 2. Revision: 1 October 1998, 2. Revision received: 13 October 1998, Returned for 3. Revision: 3 November 1998, 3. Revision received: 1 December 1998, Accepted: 7 December 1998     

Ultrastructural study of calcium shift in ischemic/reperfused rat heart under treatment with dimethylthiourea, diltiazem and amiloride

Among factors underlying reperfusion injury are oxygen free radicals and Ca²⁺ influx via gated calcium channel or via Na⁺/H⁺–Na⁺/Ca²⁺ exchange which lead to calcium overload. The aim of the study was to ultrastructurally visualize the distribution of Ca²⁺ and to compare binding of calcium by the sarcolemma and calcium accumulation in mitochondria under therapy with an ·OH scavenger, dimethylthiourea (DMTU), Na⁺/H⁺ exchange inhibitor, amiloride, and calcium channel blocker, diltiazem, given alone or in combination to ischemic/reperfused hearts. Isolated working hearts subjected to 30 min ischemia and 30 min reperfusion were perfused with drugs added to the perfusate 15 min before ischemia and administered for the rest of the perfusion period. The cytochemical phosphate pyroantimonate method for localization of Ca²⁺ was used, and calcium distribution was analyzed with a computer image analyzer. All drugs given alone improved sarcolemmal ability to bind calcium. The best results were obtained with amiloride. All of the combined therapies gave even better results, but calcium accumulation in mitochondria diminished only with diltiazem therapy given alone or in combination with DMTU. Since the presence of Ca²⁺ deposits on the sarcolemma is believed to represent its normal function, and calcium sequestration by mitochondria reflects an increase in cytosolic calcium load, the lack of correlation between sarcolemmal and mitochondrial Ca²⁺ distribution might suggest impaired mechanisms of lowering cytoplasmic calcium or the existence of some mechanism other than Na⁺/Ca²⁺ exchange, mediated by activated Na⁺/H⁺ exchange. Received: 3 March 1997, Returned for 1. revision: 21 September 1997, 1. Revision received: 31 October 1997, Returned for 2. revision: 29 November 1997, 2. Revision received: 9 February 1998, Returned for 3. revision: 16 February 1998, 3. Revision received: 2 March 1998, Accepted: 3 March 1998     

The effects of levosimendan on the left ventricular function and protein phosphorylation in post-isschemic guinea pig hearts

The widely accepted theories for the decreased function in the stunned myocardium relate to Ca²⁺ desensitization and free radical-mediated tissue damage of the myofilaments. The aim of the present study was to examine whether the depressed contractile function and Ca²⁺ responsiveness of the stunned myocardium may be restored by a new Ca²⁺ sensitizer (levosimendan), which has been shown to improve the Ca²⁺ response of the myofilaments. The effects of levosimendan on the left ventricular function and the in vivo protein phosphorylation were examined in both the non-ischemic and the stunned myocardium. Myocardial stunning was induced in Langendorff-perfused guinea pig hearts by suspending the circulation for 8 min, followed by a 20-min reperfusion period. Perfusion of post-ischemic guinea pig hearts with levosimendan (0.03–0.48 μM, 6 min) was associated with dose- and time-dependent increases in both dP/dt_max (contractility) and dP/dt_min (speed of relaxation). When the effectiveness of levosimendan was compared in non-ischemic and post-ischemic hearts, no significant differences were noted in the relative stimulatory effects on contractility and relaxation, at any given time point (time-response curve) or concentration (dose-response curve). Perfusion of the guinea pig hearts with a high (0.3 μM) levosimendan concentration did not reveal any qualitative or quantitative difference in the phosphodiesterase inhibitory potential of the compound (elevation of tissue cyclic AMP levels and characteristics of protein phosphorylation) between the non-ischemic and the post-ischemic myocardium. However, when isoproterenol was adminstered to induce maximal in vivo phosphorylation of cardiac phosphorproteins, an attenuation of the ³²P-incorporation into troponin I was noted in the post-ischemic hearts. The decrease in isoproterenol-induced ³²P-incorporation into troponin I was associated with similar alterations in the tissue level of this protein. We conclude that the Ca²⁺ sensitizer levosimendan exerts dose- and time-dependent positive inotropic and lusitropic effects on the postischemic myocardium, lending support to the hypothesis tha Ca²⁺ desensitization of the myofibrils is involved in myocardial stunning. Received: 20 July 1998, Returned for 1. revision: 27 August 1998, 1. Revision received: 6 January 1999, Returned for 2. revision: 5 February 1999, 2. Revision received: 25 February 1999, Accepted: 3 March 1999     

Endogenous adenosine suppresses norepinephrine-induced ventricular arrhythmias in rat heart

Adenosine is an antiarrhythmic substance particularly effective in catecholamine-dependent tachycardias. Although endogenous adenosine substantially accumulates in catecholamine-stimulated hearts, little is known about the antiarrhythmic potency of endogenous adenosine in this condition. Therefore, we sought to demonstrate a potential antifibrillatory effect of endogenous adenosine either by blockade of adenosine receptors with 8-phenyltheophylline (8-PT) or by suppression of endogenous adenosine release with nitrobenzyl-6-thioinosine (NBTI). The study was performed in spontaneously beating Langendorff-perfused rat hearts. Adenosine release into the effluent was determined by HPLC methods. Catecholamine stimulation was induced by perfusing the hearts with norepinephrine (1 μmol/l) for 30 min, which caused ventricular tachycardia (VT) in 31% and ventricular fibrillation (VF) in 25% of control hearts (n=35). When 8-PT (10 μmol/l) was added to the perfusion buffer prior to norepinephrine, the incidence of VT and VF increased to 79 and 68%, respectively. The addition of 8-PT did not affect the catecholamine-dependent formation of adenosine. Perfusion of the hearts with NBTI (10 μmol/l) prior to norepinephrine reduced adenosine release and increased the occurrence of both VT (65%) and VF (40%). In summary, the results indicate that adenosine is an endogenous antiarrhythmic substance, which accumulates in catecholamine-stimulated myocardium to a level, which effectively suppresses the occurrence of ventricular arrhythmias. Received: 26 November 1997, Returned for 1. revision: 18 December 1997, 1. Revision received: 15 January 1998, Returned for 2. revision: 29 January 1998, 2. Revision received: 18 February 1998, Accepted: 18 February 1998     

Coronary endothelial dysfunction after ischemia and reperfusion in the dog: A functional and morphological investigation

Coronary endothelial dysfunction is characterized by a lower response to endothelium-dependent vasodilators such as acetylcholine (ACh) and serotonin (5-HT), but by an unaltered response to endothelium-independent vasodilators such as nitroglycerin (NTG). In the present study, we investigated the vasoreactivity of the coronary bed in vivo, in a dog model of ischemia and reperfusion (I/R). We also assessed the morphology of the subepicardial arterioles and capillary bed by means of scanning electron microscopy (SEM). Anesthetized, instrumented dogs were divided in two groups. One group (N=27) was submitted to ischemia (60 min) and reperfusion (180 min) of the left circumflex coronary artery, the second group (N=8) was sham-operated. Prior to and following I/R, ACh, 5-HT, and NTG were given intracoronarily. At the end of the experiment a 1 cm³ myocardial biopsy was processed for SEM. The sham-operated dogs showed a reduction of basal coronary flow of 11%, but the vasoreactivity to ACh and 5-HT remained constant. In the I/R group, basal coronary flow was reduced by 35% (p<0.05), and the vasoreactivity to ACh and 5-HT, but not to NTG, was significantly blunted. At SEM the arterioles of the dogs submitted to I/R showed a marked adhesion of leukocytes associated with holes an the endothelial surface, while the capillary bed was free of changes and patent. Thus, following I/R, coronary endothelial dysfunction could be demonstrated in vivo by the blunting of the vasoreactive responses to two different endothelium-dependent vasodilators. The responses to NTG were not affected, probably because the function of the smooth muscle cell was preserved, and the capillary bed was patent. Received: 3 December 1997, Returned for 1. revision: 2 February 1998, 1. Revision received: 13 February 1998, Returned for 2. revision: 4 March 1998, 2. Revision received: 11 March 1998, Accepted: 11 March 1998     

Differential G protein receptor kinase 2 expression in compensated hypertrophy and heart failure after myocardial infarction in the rat

The onset of heart failure is associated with characteristic changes in myocardial expression of G protein receptor kinase 2 (GRK2). Although, GRK2 significantly contributes to the regulation of myocardial function in the failing heart, the GRK2 expression during cardiac hypertrophy without heart failure remains to be explored. We here report a differential expression of GRK2 in cardiac hypertrophy with or without heart failure in response to a myocardial infarction in the rat. Postmyocardial infarction animals were divided into two groups depending on the absence or presence of pulmonary edema, which is a manifestation of heart failure. Remarkably, cardiac GRK2 expression and activity were inhibited in animals with cardiac hypertrophy without heart failure, whereas animals with heart failure had elevated GRK2. Thus, three weeks after the infarction cardiac GRK2 expression in animals with hypertrophy alone was decreased to 0.34 of control, whereas in the group of animals with heart failure GRK2 expression was 1.89-fold higher than in sham-operated animals. GRK2 activity was affected in a similar way, three and nine weeks after the infarction cardiac GRK2 activity was reduced to 0.58 and 0.62 in animals with hypertrophy without heart failure when compared to sham operated animals. By contrast, GRK2 activity was increased by 1.32- and 1.21-fold three and nine weeks postinfarction in animals with heart failure when compared to sham animals. These data suggest that GRK2 expression is differentially regulated in hypertrophic, non-failing and hypertrophic, failing hearts. Received: 26 August 2002, Returned for 1. revision: 9 September 2002, 1. Revision received: 25 September 2002, Returned for 2. revision: 24 October 2002, 2. Revision received: 3 November 2002, Accepted: 9 November 2002 Correspondence to: S. P. Sheikh     

Nonlinearity and load sensitivity of end-systolic pressure-volume relation of canine left ventricle in vivo.

The effects of mechanical changes in loading conditions on the left ventricular end-systolic pressure-volume relation (ESPVR) were studied in nine open-chest dogs, including three dogs studied before and after beta-adrenergic blockade. Left ventricular pressure was measured with a micromanometer, and left ventricular volume was measured with a conductance catheter. ESPVRs were obtained by increasing left atrial inflow over wide volume ranges (as much as threefold) under three different conditions: control or high or low aortic impedance. High impedance was obtained by occlusion of the descending aorta, and low impedance was obtained by a shunt between the subclavian artery and the left atrium. In the unblocked animals in 21 of 28 runs, a second-order polynomial equation gave a better fit for the ESPVR than a linear relation. To quantify the effects of the changes in aortic impedance on the ESPVR, we calculated from the quadratic equation its volume intercept (V18) and its local slope (E18) at an end-systolic pressure (Pes) of 18 kPa. In the unblocked animals, a statistically significant difference was found in V18 between low impedance (21.50 +/- 6.27 ml) and high impedance (14.10 +/- 8.98 ml; p less than 0.005) and between control (19.14 +/- 9.58 ml) and high impedance (p less than 0.05). In most dogs, E18 was increased at high and decreased at low impedance, but not significantly. In the additional experiments with beta-blockade, the nonlinearity diminished somewhat, but the load dependency of the ESPVR remained present after beta-blockade because the same leftward shift of the ESPVR with high aortic impedance was found. Two other relations, namely, of dP/dtmax and of stroke work versus end-diastolic volume, were also investigated, which on the whole showed the same behavior as the ESPVR. These results indicate that the ESPVR and dP/dtmax-Ved and stroke work-end-diastolic volume relations, when studied over a wide volume range, are nonlinear and that changes in loading conditions influence indexes of contractility derived from these relations, especially the volume intercepts, in such a way that an increase in aortic impedance may be interpreted as an increase in contractility. Blocking the beta-adrenergic receptors did not influence the load dependency of the ESPVR but, in some cases, tended to decrease the nonlinearity in concordance with the relation between contractility and nonlinearity in isolated hearts.     

Differential activation of mitogen-activated protein kinases in ischemic and nitroglycerin-induced preconditioning

Previous studies have shown that the cardioprotective effect of ischemic preconditioning (IPC) can be mimicked pharmacologically with clinically relevant agents, including nitric oxide (NO) donors. However, whether pharmacological preconditioning shares the same molecular mechanism with IPC is not fully elucidated. The present study aimed to determine the activation of mitogen-activated protein kinases (MAPKs) (ERK1/2, p38 MAPK and p46/p54 JNKs) during ischemia and at reperfusion in nitroglycerin-induced preconditioning as compared to IPC and to correlate this with the conferred cardioprotection in anesthetized rabbits. Sixty minutes of intravenous administration of nitroglycerin was capable of inducing both early and late phase preconditioning in anesthetized rabbits, as it was expressed by the reduction of infarct size. Despite the cardioprotective effect conferred by both ischemic and nitroglycerin-induced preconditioning, there was a differential phosphorylation of MAPKs between the studied groups. p38 MAPK was activated early in ischemia in both ischemic and the early nitroglycerin-induced preconditioning while JNKs were markedly increased only after IPC. Furthermore, in these groups, ERK1/2 were activated during reperfusion. A different profile was observed in the late preconditioning induced by nitroglycerin with increased p38 MAPK and ERK1/2 phosphorylation during late ischemia. No activation of JNKs was observed at any time point in this group. It seems that activation of individual MAPK subfamilies depends on the nature of preconditioning stimulus. Returned for 1st revision: 18 November 2005 1st revision received: 3 January 2006 Returned for 2nd revision: 19 January 2006 2nd revision received: 6 February 2006 Returned for 3rd revision: 22 February 2006 3rd revision received: 1 March 2006     

Arrhythmogenic potential of positive inotropic agents

The clinical use of positive inotropic agents has been associated with increased mortality, with proarrhythmia speculated to be a contributing factor. This study compares the arrhythmogenic potential of six positive inotropic agents representing different mechanistic classes: the β-adrenergic agonist dobutamine, the adenylyl cyclase activator forskolin, the phosphodiesterase-III inhibitor milrinone, the cardiac glycoside ouabain, and the sodium channel agonists DPI 201-106 and BDF 9148. These agents were studied in dogs with anterior myocardial infarction using lower and higher dose i. v. regimens targeted to elicit 20–40% and 70–90% increases in LV+dP/dt, respectively. Precipitation of new ventricular arrhythmia by programmed ventricular stimulation was observed in all treatment groups. Incidences of new arrhythmia were comparable in the lower dose regimens, ranging from 16.7% (3/18 animals with BDF 9148) to 31.6% (6/19 animals with DPI 201-106), and in the higher dose regimens, ranging from 10.0% (1/10 animals with milrinone) to 27.7% (5/18 animals with DPI 201-106). The overall incidence of new ventricular arrhythmia ranged from 27.3% (3/11 animals with ouabain) to 47.4% (9/19 animals with DPI 201-106). No differences were observed in underlying infarct size or time from infarction to electrophysiologic study between subgroups of animals in which new arrhythmias were precipitated vs. those remaining non-responsive in any treatment group. The positive inotropic agents tested displayed diverse total group effects on heart rate, electrocardiographic intervals including QTc and ventricular refractoriness. Within individual treatment comparisons revealed a general but not universal pattern of greater ventricular refractory period values in newly inducible vs. non-inducible subgroups in the DPI 201-106, BDF 9148 and ouabain (low and high dose); milrinone and dobutamine (high dose) treatment groups. These findings indicate that regardless of underlying cellular mechanisms of action, the six positive inotropic agents tested all displayed comparable proarrhythmic potentials unrelated to underlying infarct size and time from infarction. This observation suggests the general shared property of increased myocardial contractility, potentially adversely affecting myocardial oxygen balance, myocardial perfusion and electrical stability in the setting of previous myocardial infarction, to be a common underlying cause for arrhythmogenesis. Additionally, alterations in ventricular refractoriness and repolarization may contribute significantly to proarrhythmia with some positive inotropic interventions. Received: 20 July 1999, Returned for 1. revision: 16 September 1999, 1. Revision received: 26 October 1999, Returned for 2. revision: 24 November 1999, 2. Revision received: 22 December 1999, Accepted: 6 January 2000