Bon Ohta

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.

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 stretch induced by increased left ventricular diastolic pressure preconditions isolated perfused hearts of normotensive and spontaneously hypertensive rats

Objective: The aim of our study was to determine whether myocardial stretch (non-ischemic stress) could precondition isolated perfused hearts of both normotensive Wister-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).Methods: The perfused hearts in Langendorff mode were subjected to 30 min of global no-flow ischemia followed by 30 min of reperfusion. Left ventricular developed pressure (LVDP) and end-diastolic pressure (LVEDP) were measured. In the control group, LVEDP was set at 10 mmHg. In the stretch group, LVEDP was increased to 30 or 60 mmHg for 5 min before 30 min of ischemia. In the ischemic preconditioning group, the hearts were exposed to two cycles of a 5-min period of ischemia before 30 min of ischemia. Myocardial lactate contents were measured at the baseline and at the end of the 60 mmHg stretch.Results: Hemodynamic parameters of LVDP and LVEDP at 30 min of reperfusion improved in the stretch group (LVEDP at 60 mmHg) and the ischemic preconditioning group. Coronary flow did not decrease during the stretch. Recovery of the coronary flow during reperfusion was better in the stretch and ischemic preconditioning groups. Postischemic contractile function was better in WKY rats than in SHR. Myocardial lactate contents at the end of 60 mmHg stretch were negligible. Conclusions: Myocardial stretch induced by increasing LVEDP preconditioned isolated perfused hearts of both WKY rats and SHR, via mechanisms not involving myocardial ischemia during stretch.

Impact of cardiopulmonary resuscitation duration on neurologically favourable outcome after out-of-hospital cardiac arrest: A population-based study in Japan

BACKGROUND The optimal cardiopulmonary resuscitation (CPR) duration for patients with out-of-hospital cardiac arrest (OHCA) remains unclear. We aimed to assess the association between CPR duration and outcome after OHCA. METHODS This prospective, population-based observational study conducted in Osaka, Japan enrolled 6981 adult patients with non-traumatic witnessed OHCA who achieved return of spontaneous circulation (ROSC) from January 2005 through December 2012. CPR duration was defined as the time of CPR initiation by emergency medical service personnel to the ROSC in pre-hospital settings or after hospital admission. The primary outcome was one-month survival with neurologically favourable outcome (cerebral performance category scale 1 or 2). RESULTS Overall, median CPR duration was 25min (interquartile range: 15-34) and the proportion of neurologically favourable outcome was 12.5% (875/6,981). The proportion of neurologically favourable outcome among the CPR duration ≥31min group was significantly lower compared with that among the 0-5min group (55.1% [320/581] versus 2.2% [54/2424], adjusted odds ratio [AOR] 0.04; 95% confidence interval [CI] 0.03-0.05 in all patients, 78.4% [240/306] versus 11.4% [30/264], AOR 0.04; 95% CI 0.02-0.06 in the shockable group, 29.1% [80/275] versus 1.1% [24/2160], and AOR 0.03; 95% CI 0.02-0.05 in the non-shockable group). The cumulative proportion for neurologically favourable outcome reached 99% after 44, 41, and 43min of CPR in all patients, the shockable group, and the non-shockable group, respectively. CONCLUSION The proportion of patients with neurologically favourable outcome declined with increasing CPR duration, but some OHCA patients could benefit from prolonged CPR duration >30min.

Hospital characteristics and favourable neurological outcome among patients with out-of-hospital cardiac arrest in Osaka, Japan☆

OBJECTIVE To assess the association between favourable neurological outcome and hospital characteristics such as hospital volume and number of critical care centres (CCMCs) after out-of-hospital cardiac arrest (OHCA). METHODS This retrospective, population-based observational study conducted in Osaka Prefecture, Japan included adult patients with OHCA, aged ≥18 years who were transported to acute care hospitals between January 2005 and December 2012. We divided acute care hospitals into CCMCs or non-CCMCs, the latter of which were divided into the following three groups according to the annual average number of transported OHCA cases: low-volume (≤10 cases), middle-volume (11-39 cases), and high-volume (≥40 cases) groups. Random effects logistic regression models, with hospital treated as a random effect, were used to assess factors potentially associated with a favourable neurological outcome. RESULTS A total of 44,474 patients were eligible. The proportions of favourable neurological outcome from OHCA were 0.9% (31/3559) in the low-volume group, 1.2% (106/9171) in the middle-volume group, 1.6% (222/14,007) in the high-volume group, and 4.3% (766/17,737) in the CCMC group (P<0.001). In the multivariable analysis, transport to CCMCs was significantly associated with favourable neurological outcome, compared with transport to non-CCMCs (adjusted odds ratio 1.63; 95% confidence interval, 1.60-1.66). Among the non-CCMC group, there was no significant relationship between hospital volume and favourable neurological outcome. CONCLUSIONS In this population, transport of OHCA patients to CCMCs led to significantly higher one-month survival rates with favourable neurological outcome from OHCA, whereas no significant association was noted among the hospitals with different volumes.

Effects of glibenclamide and nicorandil in post-ischaemic contractile dysfunction of perfused hearts in normotensive and spontaneously hypertensive rats

Objective We have demonstrated previously that nicorandil, an ATP-sensitive potassium channel opener, improved postischaemic contractile dysfunction of perfused hearts in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats dose-dependently. This study aimed to characterize the effect of glibenclamide, an ATPsensitive potassium channel blocker, and nicorandil in postischaemic contractile dysfunction of SHR and WKY rats Methods The perfused hearts were subjected to 30 min of global ischaemia and then 30 min of reperfusion. Administration of 10 or 50µmol/l glibenclamide or of a combination of glibenclamide and 300 µmol/l nicorandil was performed for 10 min before the ischaemia. The left ventricular developed pressure and end-diastolic pressure were measured Results Postischaemic contractile function was better in WKY rats than it was in SHR. Neither glibenclamide nor a combination of glibenclamide and nicorandil influenced the postischaemic contractile function or increased the incidence of reperfusion arrhythmias. The recoveries of coronary flow and heart rate after reperfusion were poor and the incidence of reperfusion arrhythmias was low in SHR Conclusions These results suggest that nicorandil improves postischaemic contractile dysfunction via a mechanism involving ATP-sensitive potassium channel opening both in SHR and in WKY rats. The hypertensive hearts were more susceptible to cardiac reperfusion dysfunction, compared with normal hearts

Cardioprotective effect of taurine on calcium paradox in streptozotocin-induced diabetic rat hearts.

Through the modification of Ca2+ metabolism, taurine is known to have several beneficial physiological actions, including antiarrhythmic18, positive inotropic2–4, and membrane stabilizing effects7. In addition, it has been reported that taurine protects the heart against Ca2+ paradox-induced myocardial injury9. However, it is unclear whether taurine has a similar cardioprotective effect in diabetic hearts, which exhibit a number of alterations in metabolism. Diabetes mellitus is a disorder of carbohydrate, lipid, and protein metabolism affecting many organs. In addition to contractile abnormalities, previous studies revealed disturbances in function of subcellular organelles in diabetic hearts, including impaired glucose utilization, mitochondrial dysfunction, and depressed Na+-Ca2+ Na+-H+ exchange activities12, 17, 22.