Yasuhiro Yamahara

Energy metabolism after ischemic preconditioning in streptozotocin-induced diabetic rat hearts

OBJECTIVES The aim of this study was to compare the cardioprotective effects of preconditioning in hearts from streptozotocin-induced diabetic rats with its effects in normal rat hearts. BACKGROUND The protective effect of ischemic preconditioning against myocardial ischemia may come from improved energy balance. However, it is not known whether preconditioning can also afford protection to diabetic hearts. METHODS Isolated perfused rat hearts were either subjected (preconditioned group) or not subjected (control group) to preconditioning before 30 min of sustained ischemia and 30 min of reperfusion. Preconditioning was achieved with two cycles of 5 min of ischemia followed by 5 min of reperfusion. RESULTS In the preconditioned groups of both normal and diabetic rats, left ventricular developed pressure, high energy phosphates, mitochondrial adenosine triphosphatase and adenine nucleotide translocase activities were significantly preserved after ischemia-reperfusion; cumulative creatine kinase release was smaller during reperfusion; and myocardial lactate content was significantly lower after sustained ischemia. However, cumulative creatine kinase release was less in the preconditioned group of diabetic rats than in the preconditioned group of normal rats. Under ischemic conditions, more glycolytic metabolites were produced in the diabetic rats (control group) than in the normal rats, and preconditioning inhibited these metabolic changes to a similar extent in both groups. CONCLUSIONS The present study demonstrates that in both normal and diabetic rats, preservation of mitochondrial oxidative phosphorylation and inhibition of glycolysis during ischemia can contribute to preconditioning-induced cardioprotection. Furthermore, our data suggest that diabetic myocardium may benefit more from preconditioning than normal myocardium, possibly as a result of the reduced production of glycolytic metabolites during sustained ischemia and the concomitant attenuation of intracellular acidosis.

Release kinetics of cardiac troponin T in coronary effluent from isolated rat hearts during hypoxia and reoxygenation

SummaryA newly developed troponin T (TnT) test for the detection of myocardial cell necrosis has been reported to be very efficient in the detection of acute myocardial infarction. The aim of the present study was to determine whether cardiac TnT in coronary effluent from isolated heart perfused with albumin-free perfusion medium could be detected using the enzyme-linked immuno-sorbent assay developed by Katus et al. Isolated rat hearts were perfused according to the method of Langendorff. Coronary flow rate was measured by timed collection of the coronary perfusate that dripped from the hearts during 5 h of hypoxia (protocol A) or 4 h of hypoxia followed by 1 h of reoxygenation (protocol B). Creatine kinase (CK) and lactate dehydrogenase (LD) levels were compared with that of TnT. Myocardial adenine nucleotides were measured by HPLC. There was a strong correlation between TnT levels in albumin-free coronary effluent and TnT levels in coronary effluent diluted 1:1 with 5% bovine serum albumin (r=0.996, N=72). The coefficients of correlation between TnT and CK or LD during hypoxia and reoxygenation were 0.891 (N=88) and 0.871 (N=88), respectively. The coefficient of correlation between CK and LD was 0.993 (N=88). There were no significant differences in either the decrease of coronary flow or the increase of TnT content between the hearts in the two protocols. There was no significant correlation between ΣTnT and energy charge of adenine nucleotides. These results indicate that cardiac TnT levels can be easily measured in albumin-free coronary effluent of isolated heart preparations. Like CK and LD, TnT is a good indicator for detecting myocardial cell damage. However, the release kinetics of TnT seem to be different than those of CK and LD. After 4 h of hypoxia, 1 h of reoxygenation has no effect on coronary flow rate or release of TnT. ΣTnT did not determine energy charge at the end of hypoxia or reoxygenation.

Release kinetics and correlation with hemodynamic dysfunction of cardiac troponin T in coronary effluent from isolated rat hearts during reperfusion.

SummaryPreviously, we reported that cardiac troponin T (TnT) can be detected and measured in coronary effluent from isolated rat hearts during hypoxia. The present study was designed to evaluate the release kinetics of TnT from post-ischemic rat hearts. Using the Langendorff technique, the hearts were reperfused for 4h after 20 min or 60 min of global ischemia. Coronary flow was measured by timing the collection of the coronary perfusate that dripped from the hearts, and left ventricular pressure (LVP) was monitored continuously during the experiments. The amount of TnT released in 1 min was compared with the release of creatine kinase (CK) and lactate dehydrogenase (LD). The release kinetics of CK and LD showed a monophasic pattern and the levels at 4 h after reperfusion returned to baseline levels. By contrast, the release kinetics of TnT showed a small peak followed by a larger and more sustained peak. There were good negative correlations between developed pressure of LVP and both Σ TnT and the amount of TnT released within 1 min at 4 h after reperfusion. These results indicate that the release kinetics of TnT is different from that of CK and LD during reperfusion, and further that cardiac TnT is a useful indicator of myocardial cell damage and can be used to evaluate the degree of myocardial cell damage in both the early and late phase of acute myocardial infarction.

Kinetics of frequency-dependent conduction delay by class I antiarrhythmic drugs in human atrium.

We investigated use-dependent prolongation of interatrial conduction time (IACT) by class I antiar-rhythmic drugs in 16 patients. Changes in IACT at the initiation of atrial pacing were used to evaluate the onset kinetics. We examined recovery kinetics by giving a single extra stimulus with a varying coupling interval after discontinuing train stimulation. Time constants of the onset kinetics were 1.52 ± 0.15/n(fast) and 0.087 ± 0.031/ n(slow) for mexiletine, 0.075 ± 0.015/n for aprindine, 0.078 ± 0.019/n for disopyramide, and 0.050 ± 0.006/n for pilsicainide. The recovery time constants were 203 ± 66 ms for mexiletine, 1,021 ± 162 ms for aprindine, 993 ± 101 ms for disopyramide, and 2,930 ± 569 ms for pilsicainide. Class I antiarrhythmic drugs produced use-dependent IACT prolongation in humans, with characteristic kinetics for each agent similar to that of depression of the maximum upstroke velocity of cardiac action potential (Vmax) reported in in vitro studies.

Effects of repeated ischemia on release kinetics of troponin T, creatine kinase, and lactate dehydrogenase in coronary effluent from isolated rat hearts

We studied the release kinetics of cardiac troponin T (TnT) from coronary effluent in a re-stenosis model of 13 isolated rat hearts. After a 20-min period of global ischemia, we reperfused the hearts for 60 min according to the method of Langendorff. A second period of global ischemia was then induced for 5 min (protocol A) or 20 min (protocol B), followed by a second 60-min period of reperfusion. Coronary flow was measured by a timed collection of the coronary effluent. Levels of TnT in the effluent were compared to those of creatine kinase (CK) and lactate dehydrogenase (LD). Levels of TnT increased after the second global ischemia, but no differences were found in the released levels of TnT between protocols A and B. However, the amounts of CK and LD released in protocol B were much greater than those released in protocol A. These studies indicate that the release kinetics of TnT are different from that of CK and LD during reperfusion. It appears that after the initial ischemic damage to TnT, subsequent ischemia causes damage to TnT regardless of the duration of the insult, whereas the damage to sarcolemma is dependent on the duration of the ischemia.

Effects of ischemic preconditioning on the release of cardiac troponin T in isolated rat hearts.

SummaryThe aim of this study was to examine the effect of ischemic preconditioning on the releases of cardiac troponin T (TnT) during reperfusion in isolated rat hearts. Experiments were done on 22 rat hearts, which were perfused according to the method of Langendorff and were divided into the control group (n=14) and the preconditioning group (n=8). Double 5 min of ischemia each followed by 5 min reflow were applied as ischemic preconditioning. After 20 min of global ischemia, the releases of TnT, creatine kinase (CK), and lactate dehydrogenase (LD) in coronary effluent and the left ventricular developed pressure (LVP) were measured during 60 min of reperfusion. Ischemic preconditioning significantly suppressed the amounts of TnT released during reperfusion, as with those of CK and LD, and also improved contractile dysfunction (nine hearts in which ventricular fibrillation was sustained were excluded from the evaluation for hemodynamics), though the release kinetics of TnT was different from that of CK and LD. There were good inverse relationships between the LVP and the total amounts of TnT released during reperfusion period (Σ TnT) or TnT levels at 60 min of reperfusion. Cardiac TnT can be used as a useful biochemical marker for hemodynamics and myocardial damage after reperfusion.

Myocardial stunning with partial aneurysmal formation generated during the recovering process of tachycardia-induced cardiomyopathy

We report a rare case of tachycardia-induced cardiomyopathy with apical stunning followed by partial aneurysmal formation. A 66-year-old male was admitted because of dyspnea and palpitation. Electrocardiogram showed persistent tachycardia due to atrial flutter. Echocardiography and left ventriculography showed severely diffuse hypokinesis with ejection fraction (EF) of 25%. Coronary arteries were normal. Heart failure responded well to conventional medical treatments. On day 9, persistent ST-segment elevation was disclosed before the ablation for atrial flutter. He was asymptomatic and free from the elevation of myocardial enzymes in laboratory data. (201)Tl scintigraphy showed slight hypoperfusion at a narrow site of the apex, whereas (123)I-betamethyl-iodophenyl-pentadecanoic acid scintigraphy revealed complete defect in the apical area. Left ventriculography showed akinesis at the localized site in the apex and mild hypokinesis in the basal area, with EF of 43%. However, no abnormalities were detected in coronary arteries during the ST-segment elevation. After 3 months, left ventriculography revealed the aneurysmal formation at a part of the apex, with EF of 50%, although the apical movement was improved. Moreover, coronary spasm was not induced by the intracoronary injection of ergonovine. In this case, a mechanism similar to Tako-Tsubo cardiomyopathy was speculated for the apical stunning.

Effect of nicorandil on cardiac dysfunction during reperfusion in normotensive and spontaneously hypertensive rats.

The cardioprotective effect of nicorandil, an opener of ATP-sensitive potassium channels, was studied in the isolated perfused hearts of the spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto (WKY) rat. The hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. Controls received no drug. In the nicorandil group, the hearts were treated with 0.03 to 0.3 mmol/L nicorandil for 15 min before ischemia. Left ventricular developed pressure (LVDP) and end diastolic pressure (LVEDP) at 30 min of reperfusion were significantly lower and larger, respectively, in SHR than in WKY rats. Nicorandil improved LVDP and decreased LVEDP at 30 min of reperfusion in both SHR and WKY rats dose-dependently. The hypertensive heart in the early stage is already susceptible to reperfusion-cardiac dysfunction. Nicorandil has a beneficial effect on the post-ischemic dysfunction in both SHR and WKY rats.

Electrophysiological effects of flecainide acetate on stretched guinea pig left atrial muscle fibers

SummaryThe electrophysiological effects of flecainide acetate (3×10−6 M) on stretched atrial tissue were investigated using guinea-pig left atrial muscle fibers. Before stretching, the resting membrane potential was not affected by flecainide at 1 Hz, although the overshoot potential (Eov) and the action potential duration at 50% repolarization (APD50) were slightly but significantly decreased by 2±1 mV and 2±1 msec, respectively. The effective refractory period (ERP) was increased by 3±1 msec. The reduction of