Effect of atrial dilatation on electrophysiologic properties and inducibility of atrial fibrillation

Introduction: Atrial dilatation may play an important role in the occurrence of atrial fibrillation (AF) in clinical situations. However, the electrophysiologic characteristics of dilated atria are still unclear. Methods and results: In 18 isolated Langendorff-perfused canine hearts (14.6 ± 2.2 kg), we measured atrial effective refractory periods (ERPs) at four different sites, conduction velocity and percentage of slow conduction on the right atrium (using a high-density electrode plaque), and assessed the inducibility of AF at the baseline (0 cm H₂O) and high (15 cm H₂O) atrial pressure. The atrial ERPs did not change significantly, but the dispersion of ERP increased significantly (40 ± 18 vs 25 ± 9 vs ms, p = 0.01) during high atrial pressure. The percentage of slow conduction (< 25 cm/s) over the mapping area, and the inducibility of AF increased during high atrial pressure (23.7 ± 10.2 % vs 32.1 ± 12.5 %, p = 0.02). The AF inducibility significantly correlated with the ERP dispersion (R = 0.75, p < 0.001) and maximal percentage of slow conduction (R = 0.88, p < 0.001). Furthermore, ERPs were significantly shorter in the induced AF group than those without induced AF (68 ± 17 vs 84 ± 16 ms, P < 0.05). Conclusions: The increased inhomogenity in atrial electrophysiological properties during atrial dilatation contributed to the inducibility of AF. Received: 26 November 2001?Returned for 1. revision: 2 January 2002?1. Revision received: 11 February 2002?Returned for 2. revision: 25 March 2002?2. Revision received: 6 May 2002?Returned for 3. revision: 10 June 2002?3. Revision received: 21 August 2002?Accepted: 11 September 2002     

Angiotensin inhibition and coronary autoregulation in a canine model of LV hypertrophy

In humans with hypertension and LV hypertrophy, beneficial effects of angiotensin inhibition may be associated with preserved autoregulatory capacity. We studied the effect of acute angiotensin converting enzyme (ACE) inhibition on coronary autoregulatory pressure-flow relations and transmural distribution of blood flow in sham and LV hypertrophy dogs. Heart/body weight ratio increased (p = 0.001) from 5.5 ± 0.7 in sham to 6.9 ± 0.5 in LV hypertrophy dogs. The lower coronary pressure limit (LPL) on the pressure-flow relation was 47 ± 2 mmHg in sham and 57 ± 6 mmHg (p = 0.001) in LV hypertrophy dogs; after acute ACE-inhibition the LPL was reduced to 40 ± 5 mmHg and 49 ± 6 mmHg (p = 0.001), respectively. Transmural distribution of blood flow was preserved at the LPL in both groups before and after acute ACE-inhibition. Concomitant blockade of prostaglandin and nitric oxide release and bradykinin catabolism had no additional effects on the LPL and distribution of blood flow. After acute ACE-inhibition in LV hypertrophy dogs, distribution of blood flow across the LV wall was preserved and subendocardial vascular reserve was maintained even though the LPL was significantly lower. Preservation of autoregulatory capacity by ACE inhibitors contributes to beneficial outcome in patients with hypertension and LV hypertrophy. Received: 2 October 2001, Returned for 1. revision: 17 October 2001, 1. Revision received: 20 December 2001, Returned for 2. revision: 2 January 2002, 2. Revision received: 14 January 2002, Accepted: 17 January 2002     

Alcohol and the risk of myocardial infarction

Epidemiological studies have repeatedly demonstrated a beneficial effect of moderate alcohol consumption on the incidence of coronary heart disease, myocardial infarction and overall mortality. The latter increases with excessive alcohol consumption. Although most epidemiological studies demonstrate a beneficial effect of alcohol consumption independent from the specific kind of alcoholic beverage, there is increasing evidence that wine and in particular red wine might contain pharmacological substances, which prevent atherosclerosis and myocardial infarction independent from the wine ethanol. Pathophysiological mechanisms mediating these beneficial effects include effects of wine phenols and tannins on LDL-cholesterol oxidation status, thrombocyte aggregation, endothelial function and smooth muscle cell proliferation. Identification and characterization of the pharmacologically active substances might provide the stage for the development of new substances to be used in the prevention of coronary artery disease and myocardial infarction. Received: 14 August 2000, Returned for 1. revision: 6 September 2000, 1. Revision received: 23 November 2000, Returned for 2. revision: 5 December 2000, 2. Revision received: 21 December 2000, Accepted: 8 January 2001     

Inhibition of apoptotic responses after ischemic stress in isolated hearts and cardiomyocytes

Recent findings on the induction of anti-apoptotic gene expression in ischemic/reperfused hearts encouraged us to investigate whether ischemic/reperfused hearts may be protected against apoptosis induction. To analyze this hypothesis we performed studies on isolated perfused hearts of rat. For apoptosis induction, hearts were perfused with the NO donor (±)-S-nitroso-N-acetylpenicillamine (SNAP, 10 μM) for 30 minutes. Four hours thereafter apoptosis was detected by DNA laddering and TUNEL assay. Under normoperfusion SNAP induced 5.5 ± 1.4 TUNEL-positive myocytes per tissue section (vs. 1.8 ± 0.5 in controls). But when hearts were subjected to 20 minutes of no flow ischemia, which was sufficient for energy depletion of the hearts without inducing severe necrotic or apoptotic cell death, reperfusion in the presence of SNAP did not induce apoptosis. To analyze if this mode of protection is a property of the cardiomyocytes, we performed corresponding experiments on ventricular cardiomyocytes of rat. Again, under normoxic conditions SNAP (100 (μM) increased the number of TUNEL-positive cells to 12.6 ± 4.9 % (vs. 5.4 ± 0.7 % in controls). But when SNAP was added after 3 h of simulated ischemia, which was sufficient for energy depletion of the cells without inducing apoptotic cell death, the number of apoptotic cells did not increase. The ischemia-induced protection of hearts and cardiomyocytes goes along with an increased expression of several anti-apoptotic genes, mainly of the bcl-2 family. This indicates that ischemic conditions induce an anti-apoptotic gene program in cardiomyocytes, which may also be responsible for the observed anti-apoptotic actions in the intact ischemic/reperfused myocardium. Received: 20 March 2002, Returned for 1. revision: 8 April 2002, 1. Revision received: 30 April 2002, Returned for 2. revision: 21 May 2002, 2. Revision received: 29 May 2002, Returned for 3. revision: 29 May 2002, 3. Revision received: 6 June 2002, Accepted: 12 June 2002 Correspondence to: Dr. G. Taimor     

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     

Beta-adrenergic receptors and intracellular signalling pathway in stunned and non-ischemic regions of pig myocardium

The β-adrenergic pathway may have a role in the pathophysiology of ischemic syndromes characterised by reversible left ventricular dysfunction, such as myocardial stunning and other clinical conditions of unstable angina or coronary spasms, or chronic reversible left ventricular dysfunction, which might be a consequence of repeated events of short-term ischemia (“repetitive stunning”). A partial-to-total occlusion of the left anterior descending coronary artery in pigs was used to induce short periods of ischemia (total ischemic time 12 ± 2 min). Hypokinesis and dyskinesis of the myocardium were considered signs of myocardial dysfunction. We found a maintained function of the β-adrenergic signalling system. Density and affinity of β-adrenergic receptors were not different in stunned and non-ischemic regions, nor were cyclic AMP and cyclic GMP intracellular contents and ratio, nor well as the ratio of stimulatory/inhibitory G protein a subunits. Our findings are in agreement with a maintained β-adrenergic signalling system in the pathophysiology of chronic reversible left ventricular dysfunction. Received: 25 September 2000 / Returned for 1. revision: 9 October 2000 / 1. Revision received: 22 November 2000 / Returned for 2. revision: 7 December 2000 / 2. Revision received: 8 January 2001 / Accepted: 11 January 2001     

The expression of heat shock protein 60 in myocardium of patients with chronic atrial fibrillation

Objective Cardiomyocytes respond to stress with the expression of different heat shock proteins (HSP). HSP60 is induced by various stress factors. The aim of this study was to investigate the expression of HSP60 in human atrial fibrillation (AF). Method Right atrial samples from 14 patients undergoing elective cardiac surgery were excised and immediately frozen in liquid nitrogen. Eight patients had chronic AF and six patients were in sinus rhythm. The HSP60 protein level was determined by SDS-PAGE, Western blot and quantified by optical densitometry according to the immunoreactive bands of actin. Results In myocardial samples from patients with chronic AF, we found a more than 2.5-fold increase in HSP60 expression compared to atrial myocardium of patients in sinus rhythm. Conclusion This result indicates an up regulation of HSP60 in response to chronic atrial fibrillation Received: 31 October 2001, Returned for 1. revision: 20 Novemver 2001, 1. Revision received: 12 December 2001, Returned for 2. revision: 3 January 2002, 2. Revision received: 25 January 2002, Accepted: 6 February 2002     

Lentiviral vectors for delivery of genes into neonatal and adult ventricular cardiac myocytes in vitro and in vivo

Vectors based on lentiviruses such as human immunodeficiency virus (HIV) type-1 have many advantages for gene therapy, including the ability to infect non-dividing cells, long-term transgene expression and the absence of induction of an inflammatory/immune response. This study was initiated to determine whether lentiviruses would efficiently transfer genes to both neonatal and adult cardiac cells in culture and, by direct injection, to the heart in vivo. A three-plasmid expression system, including a packaging defective helper construct, a plasmid coding for a heterologous (VSV-G) envelope protein and a vector construct harboring reporter genes –E-GFP (enhanced green fluorescent protein) and puro (puromycin-resistance protein) was used to generate pseudotyped HIV-1 particles by transient transfection of human embryonic kidney 293T cells. We demonstrated efficient gene transfer into neonatal and adult cardiac myocytes in vitro and identified conditions in which virtually 100 % of cultured neonatal and 70 % of adult cardiac myocytes express the reporter gene. Transduction of adult cardiac myocytes with high titre lentiviral vectors did not affect the cell number, morphology or viability compared to untransduced cells. We delivered HIV-1-based vectors to the intact heart by direct injection. Hearts transduced with pseudotyped HIV-1 vectors showed levels of transgene expression comparable to that achieved by adenovirus vectors. This study demonstrates for the first time that lentivirus-based vectors can successfully transduce adult cardiomyocytes both in vitro and in vivo, and opens up the prospect of lentivirus-based vectors becoming an important gene delivery system in the cardiovascular field. Received: 1 October 2001, Returned for 1. revision: 18 October 2001, 1. Revision received: 19 November 2001, Returned for 2. revision: 6 December 2001, 2. Revision received: 13 February 2002, Accepted: 6 March 2002     

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     

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     

Selectin-mediated rolling of neutrophils is essential for their activation and retention in the reperfused coronary system

Neutrophil adhesion to coronary endothelium is a key event for cardiac reperfusion injury. Adhesion is proposed to be a multi-step event, consisting of selectin-mediated rolling, chemotactic activation, and subsequent integrin-mediated firm attachment. However, it is not clear whether this sequence also occurs in the coronary circulation with its unique hemodynamic properties (turbulent flow, flow reversal). We have studied neutrophil adhesion in the coronary system of isolated perfused guinea pig hearts under basal and reperfusion conditions (15 min global ischemia). Adhesion was manipulated by an anti-CD18 antibody (blocking firm adhesion) and fucoidin (reducing rolling). Neutrophil behavior during coronary passage was assessed by measurement of CD11b expression, forward scatter (FSC, indicating polarization), and sideward scatter (SSC, measure for granularity) via flow cytometry. Adhesion rose from 21 % (basal) to 35 % after ischemia. Anti-CD18 decreased adhesion to 11 % and 14 %, respectively; fucoidin altered only the postischemic increase (23 %). CD11b was unchanged by passage through the non-ischemic coronaries, but rose postischemically (139 % increase). CD18 blockade did not reduce the postischemic rise of CD11b, while fucoidin was inhibitory (24 % increase). FSC did not differ between controls and ischemic hearts in any group, while SSC decreased most in postischemic hearts after CD18 blockade. Blockade of rolling and of firm attachment both reduce neutrophil retention, while only inhibition of rolling reduces intracoronary activation. Thus, rolling seems to be mandatory for endothelial-leukocyte communication in the coronary system. Received: 22 February 2002, Returned for revision: 22 March 2002, Revision received: 17 May 2002, Accepted: 4 June 2002     

The inotropic response of the isolated,perfused, working rat heart to norepinephrine is attenuated by inhibition of nitric oxide

Experiments on isolated, perfused, working left ventricular (LV) hearts of 66 female Wistar rats were done to examine whether nitric oxide (NO) influences the effects of norepinephrine (NE) on coronary flow as well as on contraction and relaxation. Functional parameters were monitored before and after application of NE at a concentration of 3 × 10⁻⁸ M in the absence and presence of the nitric oxide synthase (NOS) inhibitor L-nitro-arginine (L-NA) at a concentration of 1 × 10⁻⁴ M and of the spontaneous NO donor sodium (Z)-1-(N,N-diethylamino) diazen-1-ium-1,2-diolat (DEA/NO) at a concentration of 1 × 10⁻⁷ M. In control experiments, heart rate was varied by electrical stimulation between 200 and 400 beats/min. Within this range of heart rates, coronary flow and cardiac output remained constant, while stroke volume, LV peak pressure and LV dP/dt_max decreased with increasing heart rate. NE increased coronary flow from 7.6 ± 0.4 to 9.8 ± 0.7 ml/min and induced the well-known positive chronotropic and inotropic effects. DEA/NO increased coronary flow; however, the inotropic and lusitropic parameters were not affected. Simultaneous infusion of NE with DEA/NO further increased coronary flow from 9.8 ± 0.7 to 12.1 ± 0.8 ml/min without a significant effect on any other functional parameter. When NOS was inhibited by L-NA, the positive inotropic effect of NE was attenuated. Cardiac output, however, was increased, while coronary flow did not change significantly. Under these conditions, NE increased dP/dt_max by 65.5 ± 5.8% (from 2999 ± 97 to 4929 ± 230 mmHg/s) compared with an increase by 92.8 ± 6.7% (from 3770 ± 82 to 7234 ± 211 mmHg/s) under control conditions. Application of DEA/NO reversed the attenuated inotropic response, but relaxation remained partially impaired. Thus, the presence of NO seems to be necessary for the inotropic effect of NE to become manifest. Received: 9 February 2001, Returned for 1. revision: 22 February 2001, 1. Revision received: 25 May 2001, Returned for 2. revision: 12 June 2001, 2. Revision received: 20 July 2001, Returned for 3. revision: 2 August 2001, Accepted: 20 August 2001     

Heart rate adjustment of magnetic field map rotation in detection of myocardial ischemia in exercise magnetocardiography

Aims We studied the capability of heart rate (HR) adjusted change in multichannel magnetocardiogram (MCG) to detect exercise-induced ischemia. Methods and results The MCG and 12-lead ECG were recorded simultaneously during supine exercise testing in 17 healthy controls and 24 patients with single vessel coronary artery disease (CAD). In the MCG analysis, we plotted the orientation of the magnetic field map (MFM) against the HR in each cardiac cycle during recovery. A regression line was fitted to the data and the line slope (degrees/bpm) was determined. In the ECG, the ST-segment depression vs HR (ST/HR) slope was evaluated. The HR adjusted MFM rotation was more extensive in the pooled CAD group, and in all subgroups with different stenosed vessel, than in the control group at the ST-segment (1.5 ± 2.1°/bpm vs 0.29 ± 0.25°/bpm, p < 0.0005) and at the T-wave apex (0.95 ± 0.81°/bpm vs 0.24 ± 0.25°/bpm, p < 0.0005). Areas under the receiver operating characteristic curves of the HR adjusted MFM rotation at the ST-segment (88.5 %) and the T-wave (86.0 %) were higher than the ones without HR adjustment (75.5 % and 68.1 %, respectively), and higher than the area of ST/HR slope in the ECG (80.2 %). Conclusion HR adjusted MFM rotation detects transient ischemia independent of the stenosed vessel. HR adjustment improves the performance of the MCG in ischemia detection by the analysis of the ST-segment and the T-wave. The MCG was superior to the 12-lead ECG. Received: 5 April 2001, Returned for 1. revision: 7 May 2001, 1. Revision received: 25 May 2001, Returned for 2. revision: 12 June 2001, 2. Revision received: 18 June 2001, Accepted: 20 June 2001     

Defective suppression of the aldosterone biosynthesis during stroke permissive diet in the stroke-prone phenotype of the spontaneously hypertensive rat

Previous studies have shown that short-term high salt intake unmasks blunted plasma aldosterone suppression in stroke-prone spontaneously hypertensive rats (SHRsp). The aim of this study was to evaluate the response of aldosterone biosynthesis and production to a sustained exposure to the stroke-permissive Japanese-style diet (JD) in young stroke-prone and stroke-resistant SHRs. For this purpose, 6-week old male rats from both strains were divided into 2 dietary groups and received regular diet (SHR = 37, SHRsp = 32) or the JD and 1% saline to drink (SHR = 34, SHRsp = 30) for 4 weeks. All measurements were carried out at the end of the dietary periods. After JD, plasma aldosterone levels were significantly decreased in SHR (from 357.8±57 to 163.3±31.5 pg/ml, p < 0.05) but markedly increased in SHRsp (from 442±56.5 to 739±125.7 pg/ml, p < 0.05). Consistently, the adrenal aldosterone synthase expression was reduced by JD in SHR (p < 0.05), whereas it was even slightly raised by JD in SHRsp so that, at the end of JD, aldosterone synthase mRNA was 5-fold higher in SHRsp than in SHR. Urinary sodium excretion (mEq/24h) achieved lower levels in SHRsp, so that fractional excretion of sodium was 80.2±9% in SHR and 40.3±8% in SHRsp (p < 0.05) in balance studies performed at the end of JD. These different responses of mineralocorticoid biosynthesis and urinary sodium excretion to JD were not accounted for by different adaptions of the renin-angiotensin and atrial natriuretic peptide systems, of serum potassium levels, or of adrenal 11β-hydroxylase expression in the two strains. Systolic blood pressure was comparable in both strains throughout the experiment. These results demonstrate enhanced aldosterone biosynthesis, associated with reduced urinary excretion of sodium in response to JD in SHRsp before the onset of stroke. This abnormality may play a role in the higher susceptibility of stroke of this model. Received: 1 March 1999, Returned for 1. revision: 22 March 1999, 1. Revision received: 7 June 1999, Returned for 2. revision: 28 June 1999, 2. Revision received: 4 August 1999, Returned for 3. revision: 10 September 1999, 3. Revision received: 28 October 1999, Accepted: 17 November 1999     

Mechanisms involved in coronary artery dilatation during respiratory acidosis in the isolated perfused rat heart

A rat Langendorff heart preparation, perfused at constant pressure, was used to evaluate the role of K_ATP channels in respiratory acidosis-induced coronary hyperemia. Prior administration of glibenclamide, an inhibitor of K_ATP channels, reduced basal flow rates and eliminated the hyperemia associated with hypercapnia. These results implicate K_ATP channels as a functional link in the respiratory acidosis-induced increase in coronary flow. Received: 28 June 1999, Returned for revision: 11 August 1999, Revision received: 28 August 1999, Accepted: 29 September 1999     

Angiotensin II-induced upregulation of MAP kinase phosphatase-3 mRNA levels mediates endothelial cell apotosis

Angiotensin II (Ang II) is central to the pathobiology of atherosclerosis. In endothelial cells (EC), Ang II induces apoptosis. The MAP kinase ERK1/2 plays a key role in regulating cell survival. We therefore investigated the effect of Ang II on ERK1/2. Incubation of EC with Ang II led to the dephosphorylation of ERK1/2 (43 % of control). To characterize the phosphatase involved, we investigated the effect of Ang II on MAP kinase phosphatase expression. Ang II induced MAP kinase phosphatase-3 (MKP-3) mRNA levels to about 2-fold, whereas MKP-1 expression was not affected. Transfection with a dominant negative MKP-3 construct (dnMKP-3mt) prevented the Ang II-induced ERK1/2 dephosphorylation and apoptosis in EC (p < 0.001). ERK1/2 inactivation has been shown to result in the dephosphorylation and proteasomal degradation of the antiapoptotic protein Bcl-2. Ang II induced the degradation of Bcl-2 wild type, whereas the dephosphorylation-resistant Bcl-2 construct mimicking phosphorylation by ERK1/2 was resistant to Ang II stimulation. These results indicate that Ang II-induced apoptosis signaling in human EC is mediated via MKP-3-dependent dephosphorylation of ERK1/2, which in turn leads to the degradation of Bcl-2. Received: 11 April 2001, Returned for revision: 9 May 2001, Revision received: 30 May 2001, Accepted: 1 June 2001     

Effects of different inotropic interventions on myocardial function in the developing rabbit heart

The development of the mammalian heart is characterized by substantial changes in myocardial performance. We studied the ontogeny of myocardial function with and without various inotropic interventions in the developing isolated, antegrade-perfused rabbit heart (2d, 8d, 14d, 28d, n = 96). Myocardial function was related to the protein expression of the sarcolemmal Na⁺-Ca²⁺ exchanger and to the sarcoplasmic Ca²⁺-ATPase. In neonatal hearts an age-dependent increase in maximal developed pressure velocity (dP/dt_max) by 45 % and peak negative pressure velocity (dP/dt_min) by 75 % within days 2 to 8 were observed. In response to inotropic intervention with isoproterenol, ouabain, calcium and the Na⁺-channel modulator BDF 9148, dP/dt_max and dP/dt_min increased in a concentration dependent manner. Significant differences between neonatal, juvenile and adult hearts could be demonstrated in a repeated measurement ANOVA model on the concentration-response curves for BDF 9148 (dP/dt_max and dP/dt_min), ouabain (dP/dt_min) and calcium (dP/dt_min), but not for isoproterenol. At the maximum isoproterenol concentration of 1 μmol/l, the increase in dP/dt_max and dP/dt_min was significantly higher in adult compared to neonatal hearts (t-test, p < 0.01). The significant decline of the Na⁺-Ca²⁺ exchanger protein expression from neonatal (1822 ± 171) to adult hearts (411 ± 96 S.E.M. [units per 20 μg protein], p < 0.01) was related to an increase in myocardial function (dP/dt_max r = 0.63, p < 0.01, dP/dt_min r = 0.62, p < 0.01). Contractility, relaxation and the observed positive inotropic effects were in general significantly lower in neonatal compared to adult hearts. In the individual heart an increase in contractility and relaxation was related to a decrease in Na⁺-Ca²⁺ exchanger expression. Received: 22 May 2000, Returned for 1. revision: 21 June 2000, 1. Revision received: 27 November 2000, Returned for 2. revision: 19 December 2000, 2. Revision received: 2 January 2001, Returned for 3. revision: 17 January 2001, 3. Revision received: 25 May 2001, Accepted: 11 June 2001     

Coronary blood flow control is impaired at rest and during exercise in conscious diabetic dogs

This study tested whether diabetes mellitus impairs coronary blood flow control sufficiently to alter the balance between myocardial oxygen delivery and metabolism. Dogs (n = 7) were instrumented with catheters in the aorta and coronary sinus, and with a flow transducer on the circumflex coronary artery. Coronary blood flow, myocardial oxygen consumption (MVO₂), heart rate and aortic pressure were measured at rest and during treadmill exercise before and after induction of diabetes with alloxan monohydrate (40 – 60 mg/kg). Arterial plasma glucose concentration increased from 4.6 ± 0.2 mM in non-diabetic, control dogs to 20.2 ± 2.3 mM one week after alloxan injection. In non-diabetic control dogs, exercise increased MVO₂ 3.1-fold, coronary blood flow 2.7-fold, and heart rate 2.4-fold. Coronary venous PO₂ decreased from 19.4 ± 0.6 mmHg at rest to 14.7 ± 0.7 mmHg during exercise. Diabetes significantly attenuated exercise coronary hyperemia and reduced coronary venous PO₂ at rest (15.6 ± 0.5 mmHg) and during exercise (12.6 ± 0.8 mmHg). Diabetes also significantly reduced myocardial oxygen delivery at each level of exercise. Acute hyperglycemia alone did not alter exercise-induced coronary vasodilation or reduce coronary venous PO₂. These findings demonstrate that experimental diabetes attenuates functional coronary hyperemia and impairs the balance between coronary blood flow and myocardial metabolism. However, this deleterious effect is not related to acute hyperglycemia but to the chronic disease process of diabetes mellitus. Received: 19 July 2001, Returned for 1. revision: 20 August 2001, 1. Revision received: 17 October 2001, Returned for 2. revision: 19 October 2001, 2. Revision received: 2 November 2001, Accepted: 5 November 2001     

Xanthine oxidase contributes to preconditioning's preservation of left ventricular developed pressure in isolated rat heart: developed pressure may not be an appropriate end-point for studies of preconditioning

Studies of preconditioning frequently use the isolated rat heart model in which recovery of post-ischemic function is the end-point. However, function following an episode of ischemia/reperfusion represents a composite of both stunning, which is related to free radical production and is not attenuated by preconditioning, and tissue salvage, the primary effect of preconditioning. Brief ischemia/reperfusion is also known to diminish adenosine release during subsequent ischemia by a mechanism independent of preconditioning's anti-infarct effect. Reduced purine release would diminish generation of free radicals by xanthine oxidase in rat heart and thus produce less stunning. In this paradigm preserved post-ischemic function in rat heart might look similar to salvage by preconditioning, but its mechanism would be quite different and not be relevant to the xanthine oxidase-deficient human heart. This hypothesis was tested in isolated rat hearts. Control or ischemically preconditioned hearts were subjected to 30 min of global ischemia and 60 min of reperfusion, either in the presence or absence of 25 μmol/l allopurinol, an inhibitor of xanthine oxidase. In non-preconditioned hearts allopurinol increased left ventricular developed pressure after 60 min of reperfusion from 26 ± 5 mmHg in control hearts to 47 ± 7 mmHg, whereas developed pressure in preconditioned hearts following reperfusion was 59 ± 5 mmHg and was unaffected by allopurinol. Developed pressure in non-preconditioned hearts treated with allopurinol was midway between that for untreated control and preconditioned hearts suggesting that at least 50 % of the recovery of developed pressure in preconditioned hearts may be related to free radical-induced stunning. In xanthine oxidase-deficient rabbit hearts, return of function was not different between non-preconditioned and preconditioned hearts. Therefore, post-ischemic developed pressure in the rat is significantly affected by purine-dependent stunning, and, hence, may be an unreliable marker of tissue salvage and also a poor index of what might be cardioprotective in man. Received: 2 May 2001, Returned for 1. revision: 25 May 2001, 1. Revision received: 13 June 2001, Returned for 2. revision: 18 June 2001, 2. Revision received: 11 July 2001, Accepted: 18 July 2001     

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