Circulatory depression and ventricular arrhythmias induced by compound 48/80 in anaesthetized rats

The effects of graded doses of compound 48/80 on various cardiovascular and respiratory parameters were studied in pentobarbitone-anaesthetized rats. Following intravenous injections, this compound significantly depressed the mean blood pressure (MBP), left ventricular pressure (LVP) and d_LVP/dt_max, and caused ventricular tachycardia (VT) or fibrillation (VF) and death. Heart rate (HR) response were variable, and there were no marked changes in airway resistance or blood gases. Pretreatment of the animals with either cimetidine or diphenhydramine significantly prolonged the time of onset of VT/VF but failed to alter the changes in other circulatory variables. A combination of cimetidine and diphenhydramine significantly alleviated the decreases in MBP and LVP and prevented the occurrence of VT/VF. It is suggested that the circulatory depression and the occurrence of ventricular arrhythmias following the administration of compound 48/80 result from activation of H₁- and H₂-receptors by elevated blood histamine levels due to release of the amine from tissues.     

Zacopride缺血后适应抑制大鼠缺血/再灌注性心律失常

目的:探讨心肌内向整流钾通道(K_(ir))激动剂zacopride缺血后适应对大鼠缺血/再灌注性心律失常的影响及可能的电生理学机制。方法:SD大鼠Langendorff离体灌流心脏和在体麻醉大鼠冠状动脉左前降支结扎15 min后松扎15 min诱发缺血/再灌注性心律失常。在冠状动脉左前降支松扎前3 min给予zacopride,观察缺血后适应对再灌注性心律失常的影响。胶原酶法分离大鼠单个心室肌细胞,应用全细胞膜片钳技术观察zacopride对心室肌细胞缺氧/复氧致延迟后除极的影响和对细胞膜表面ATP敏感性钾通道(KATP)的影响。结果:大鼠离体心脏再灌注时预先给予0.1~10μmol/L zacopride可有效抑制再灌注性心律失常的发生。其中0.1μmol/L zacopride为最大效应浓度,可使期前收缩数减少,室速和室颤发生率均下降,持续时间均缩短;再灌前3 min将1μmol/L BaCl_2和0.1μmol/L zacopride同时灌流心脏,BaCl_2可部分逆转zacopride的保护效应(P0.01),表明zacopride的后适应保护与其增强K_(ir)电流的作用有关。在1.5~5μg/kg剂量范围内,zacopride对大鼠在体再灌注诱发的室速和室颤有明显抑制效应,但对期前收缩数无明显影响。1.5μg/kg zacopride抗心律失常的效应与阳性对照药利多卡因(7.5 mg/kg)相似。进一步研究发现zacopride可有效抑制缺氧/复氧所致心室肌细胞延迟后除极,降低其发生率(P0.01)。Zacopride的上述效应与K_(ATP)无关。结论:Zacopride对大鼠缺血/再灌注性心律失常的抑制作用是由激活心肌细胞K_(ir)介导的。激活K_(ir)并消除延迟后除极所诱发的触发性活动可能是zacopride缺血后适应的主要机制。     

Capsaicin prevents the adrenocorticotropin-induced improvement of cardiovascular function and survival in hemorrhage-shocked rats.

A volume-controlled hemorrhagic shock was produced in anesthetized rats by intermittent bleeding from an iliac vein over a period of 20-30 min, until the carotid mean arterial pressure (MAP) stabilized around 20-24 mmHg. In this condition, which caused the death of all saline-treated animals within 25-30 min, the intravenous (i.v.) bolus injection of the adrenocorticotropin fragment 1-24 (ACTH(1-24)) at a dose of 160 micrograms/kg promptly restored MAP, as well as pulse pressure, heart rate and respiratory function, and greatly prolonged the survival time. Capsaicin (125 mg/kg cumulatively, s.c., 1 week before) completely prevented the anti-shock effect of ACTH(1-24), which, on the other hand, was shared by i.v. [Nle11]-substance P (SP) (200-300 micrograms/kg). Finally the SP-antagonist [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-SP prevented the effect of ACTH(1-24). These results suggest that SP-containing nerve fibers are required for the effect of ACTH in hemorrhagic shock.     

Prevention of recurrent life-threatening ventricular arrhythmias by temporary cardiac pacing

Overdrive pacing has been applied in 26 patients to prevent frequent recurrent ventricular fibrillation (VF) and ventricular tachycardia (VT) occurring in the setting of ventricular extrasystole of 2-5 degrees graded by Lown. These patients had 3-47 recurrent attacks of VF and VT (11.4 +/- 2.4) which were not prevented with antiarrhythmic agents. Overdrive pacing was continued for 2-236 hours (21.3 +/- 3.7) and appeared to be effective in 23 (88.4%) of the 26 patients including those with prolonged QT intervals. Atrial pacing was more effective than ventricular overdriving and required stimulation at a slower rate. Antiarrhythmic therapy and overdrive pacing in combination were more effective than both used independently. Suppression of ventricular extrasystole and prevention of life-threatening arrhythmias were achieved by increasing the heart rate by 23.2 +/- 4.5 beats/min.     

Cardiac arrest in Stockholm with special reference to the ambulance organization

During a one-year period all patients with cardiac arrest (CA) taken care of by three ambulances were studied. An incidence of 110 cardiac arrests/100,000 inhabitants/year was found. The majority of CAs affected the elderly and occurred during the day in their homes. The majority of CAs were witnessed but cardiopulmonary resuscitation (CPR) had been initiated by bystanders in only a few cases. The ambulance arrived within a mean time of 7.7 +/- 4.0 min. Forty-eight per cent of the CA patients showed ventricular tachycardia or ventricular fibrillation (VT/VF) on ambulance arrival. Patients with a prolonged ambulance delay showed a lower incidence of VT/VF than patients with a short delay. Patients in whom CPR had been initiated by bystanders showed a significantly higher incidence of VT/VF (67%) than unattended patients (45%). Bystander CPR was furthermore associated with an increased incidence of VT/VF in patients with prolonged ambulance delay. VT/VF was present at the time when the ambulance arrived in 86% of the CA patients who had received CPR from a bystander and were reached within 8 min by the ambulance.     

基于短时心率变异性信号两种熵测度的过速型室性心律失常的预测分析

目的:过速型室性心律失常［持续性室性心动过速或心室纤颤（VT/VF）］是心脏猝死的主要诱因,测试VT/VF发生前心率变异性信号是否有明显改变可作为VT和VF发生的提前预报信号。方法:以78名患者体内心脏复律除颤器记录的VT/VF事件发生前心率变异性信号（VT/VF序列）和来自同一患者的正常窦性节律（CON序列）组成的135个样本对作为实验序列。通过预处理消除实验序列的伪差、异位心搏等干扰,采用两种基于熵的非线性复杂度测度——样本熵和逐点多尺度熵（PPMSE）,分析VT和VF发生前十几分钟的VT/VF序列,以及心率增加和减小的VT/VF序列复杂性,并采用PPMSE方法讨论了接近VT/VF发生时VT/VF序列复杂性变化。结果:与正常对照组CON序列相比,在一定匹配容差内,VT/VF发生前心率变异性信号的样本熵明显减小（r<0.25×SD, P<0.000 5）,心率增加的VT/VF序列减小更显著（r<0.3×SD, P<0.000 1）;VT/VF序列的PPMSE在越接近VT/VF发生时刻减小越显著,提取的CI指数存在显著差异（如1~30尺度,N=986、500、250时,P=1.5×10-2、P=4.3×10-3、P=1.3×10-5）,心率增加的VT/VF序列区分性能更好。结论:过速型心律失常的自然发作并不是突发现象,在其发作前或许存在某种生理预兆,两种熵测度可能是短时预报恶性室性心律失常事件的有效非线性参数。     

Anti-arrhythmic effect of diosgenin in reperfusion-induced myocardial injury in a rat model: activation of nitric oxide system and mitochondrial KATP channel

This study was designed to investigate the anti-arrhythmic effect of diosgenin preconditioning in myocardial reperfusion injury in rat, focusing on the involvement of the nitric oxide (NO) system and mitochondrial ATP-dependent potassium (mitoK_ATP) channels in this scenario. After isolation of the hearts of male Wister rats, the study was conducted in an isolated buffer-perfused heart model. Global ischemia (for 30 min) was induced by interruption of the aortic supply, which was followed by 90-min reperfusion. Throughout the experiment, the electrocardiograms of hearts were monitored using three golden surface electrodes connected to a data acquisition system. Arrhythmias were assessed based on the Lambeth convention and were categorized as number, duration and incidence of ventricular tachycardia (VT), ventricular fibrillation (VF), and premature ventricular complexes (PVC), and arrhythmic score. Additionally, lactate dehydrogenase (LDH) levels in coronary effluent were estimated colorimetrically. Diosgenin pre-administration for 20 min before ischemia reduced the LDH release into the coronary effluent, as compared with control hearts (P < 0.05). In addition, the diosgenin-receiving group showed a lower number of PVC, VT and VF, a reduced duration and incidence of VT and VF, and less severe arrhythmia at reperfusion phase, in comparison with controls. Blocking the mitoK_ATP channels using 5-hydroxydecanoate as well as inhibiting the NO system through prior administration of l-NAME significantly reduced the positive effects of diosgenin. Our finding showed that pre-administration of diosgenin could provide cardioprotection through anti-arrhythmic effects against ischemia–reperfusion (I/R) injury in isolated rat hearts. In addition, mitoK_ATP channels and NO system may be the key players in diosgenin-induced cardioprotective mechanisms.     

Epicardial propranolol administration for ventricular arrhythmias in dogs: matrix formulation and characterization.

The effect of propranolol on the prevention of ventricular tachycardia/fibrillation (VT/VF) due to acute coronary ischaemia was studied in dogs. A series of propranolol-polymer controlled release matrices in slab configuration using various polyurethanes and a polyurethane-silicone rubber copolymer were formulated and characterized. In general, drug release in vitro occurred with an initial burst phase followed by an exponentially declining delivery rate; the silicone rubber containing copolymer preparation had more sustained release properties than did pure polyurethane matrices. In the animal studies, dogs underwent 5-hourly 10 min complete occlusions of the left anterior descending coronary artery (LAD), followed by 50 min normal perfusion. During non-drug occlusions VT occurred at a frequency of 1.22 +/- 0.12 episodes/min. A propranolol-polyurethane matrix (30% w/w, 28-42 mg) was placed on the ischaemic zone of the left ventricular epicardium immediately after the fifth occlusion. After an hour of drug delivery a sixth occlusion took place. The number of arrhythmia episodes both before and after drug were quantified and compared. The time to ventricular fibrillation (when present) and the mean blood pressure were also assessed. The drug patch delivered propranolol at a dose of 140 +/- 45 micrograms/kg by the conclusion of the 1 h study period. Therapeutic drug levels were achieved in the peripheral blood samples (8.7-43.7 ng/ml) and were enhanced in coronary venous samples (360.9-556.2 ng/ml). Reduction of blood pressure and proarrhythmic events following epicardial controlled release propranolol administration were noted but were not statistically significant. Arrhythmia episodes before and after propranolol were not found to be significantly different (VT/min 1.02 +/- 0.31 and 1.22 +/- 0.12).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ruthenium red-induced transition from ventricular fibrillation to tachycardia in isolated rat hearts:: possible involvement of changes in mitochondrial calcium uptake

INTRODUCTION: Ventricular tachycardia (VT) is considered to be the most common precursor of ventricular fibrillation (VF) and sudden cardiac death. However, the mechanisms underlying the transition from VT to VF remain unclear despite more than a century of study. Here, we investigated whether perfusion of the heart with blockers of mitochondrial Ca(2+) uniporter changed the macrodynamics of the heart between VT and VF. METHODS: The experiments were performed using Langendorff perfused isolated rat hearts in which left ventricular pressure (LVP) and left ventricular cardiomyogram (LVCMG) were measured. Sustained VT or VF was induced by burst pacing of the left ventricular muscles. RESULTS: During pacing-induced sustained VF, perfusion of the heart with ruthenium red (RR) or Ru 360, blockers of mitochondrial Ca(2+) uniporter, resulted in the reversible conversion of VF to VT. In contrast, during pacing-induced sustained VT, perfusion of the heart with spermine, an activator of mitochondrial Ca(2+) uptake, resulted in the reversible conversion of VT to VF, and the effect was antagonized by cotreatment with RR. In addition, RR-induced conversion of VF to VT was antagonized by cotreatment with S(-)-Bay K8644 (Bay K), an activator of L-type Ca(2+) channels, suggesting that the inactivation of L-type Ca(2+) channels was responsible for the RR-induced effect on the macrodynamics of hearts. In fact, perfusion with verapamil, an antagonist of L-type Ca(2+) channels, during pacing-induced sustained VF, resulted in the conversion of VF to VT. CONCLUSION: This study demonstrated that perfusion of isolated rat hearts with blockers of Ca(2+) uptake by mitochondria resulted in the reversible conversion of pacing-induced sustained VF to VT, suggesting that changes in mitochondrial Ca(2+) uptake were possibly involved in the transition between VT and VF.     

Effect of carvedilol on neuronal survival and poly(ADP-ribose) polymerase activity in hippocampus after transient forebrain ischemia

Carvedilol a beta-adrenoreceptor antagonist with potent antioxidant properties raises high expectations in therapy of ischemia. In this study the effect of carvedilol on neuronal survival after transient forebrain ischemia in gerbils was investigated. The role of poly(ADP-ribose) polymerase (PARP-1) in this process was evaluated. Our data indicated that carvedilol administered subcutaneously in a dose of 7 or 70 mg/kg b.w. directly after 5 min of transient forebrain ischemia protects significant population of neurons in hippocampal area CA1, but has no effect after induction of prolonged 10 min ischemia. Carvedilol significantly decreased PARP activity in hippocampus that was markedly increased after both 15 min and 4 days of reperfusion following 5 min of ischemia. Moreover, carvedilol prevented NAD+ depletion after ischemic-reperfusion insult. These results indicated that carvedilol protects neurons against death and suggested that suppression of PARP activity during reperfusion could be involved in this process.     

Clearance of endotoxin from blood of rabbits injected with staphylococcal toxic shock syndrome toxin-1.

This study was undertaken to examine some of the properties of staphylococcal toxic shock syndrome toxin 1 (TSST-1) with regard to the clearance of endotoxin from blood. The concentration of endotoxin in blood was measured by using a chromogenic limulus test and modified perchloric acid method. When TSST-1, which produces fever in rabbits, was injected (100 ng/ml or 100 micrograms/ml per kg) intravenously (i.v.) into the animals, no measurable level of endotoxin was detected in the blood. In control animals, which were given 5 micrograms of endotoxin per ml per kg i.v., endotoxin could be detected in the blood at rapidly declining levels. These results suggested that TSST-1 might not lead bacterial endotoxin from other body sites into the blood. When the animals were given TSST-1 (1 to 100 ng/ml per kg) i.v. and then endotoxin (5 micrograms/ml per kg) i.v. 4 h later, endotoxin was detected in the blood at a high level, depending on the dose of TSST-1 injected. These results showed that TSST-1 inhibited the clearance of endotoxin in the blood; this clearance is thought to be mainly done by the reticuloendothelial system. In the animals given TSST-1 (100 ng/ml per kg) and endotoxin (5 micrograms/ml per kg) simultaneously, the endotoxin level in the blood was found to be higher than that in control animals given endotoxin only but lower than that in the animals given TSST-1 and then endotoxin at the same doses.     

Antiarrhythmic and arrhythmogenic effects of L-carnitine in ischemia and reperfusion

Isolated rat hearts were subjected to 30-min coronary artery occlusion followed by 120-min reperfusion. The hearts (n=8–12) were perfused with Krebs-Henseleit solution enriched with L-carnitine (0.5, 2.5 and 5 mM) for 10 min before and after ischemia or reperfusion and for the whole period of ischemia and reperfusion. Two-hour perfusion with L-carnitine during ischemia/reperfusion markedly (p<0.05) and dose-dependently decreased the incidence of ventricular tachycardia (VT, maximum 65%). The incidence of reperfusion ventricular fibrillation (VF) also decreased from 63% (control) to 17% in hearts perfused with 5 mM L-carnitine, as reflected by a significant (p<0.05) decline in VF duration from 218±99 sec in control to 19±19 sec. Perfusion of etomoxir (palmitoylcarnitinetransferase-1 inhibitor) along with L-carnitine reversed the antiarrhythmogenic action of L-carnitine. Interestingly, short time preischemic administration of L-carnitine produced a concentration-dependent arrhythmogenic effects on both ischemia and reperfusion-induced arrhythmias. These results show that L-carnitine produced a protective effect against reperfusion arrhythmias only when it was perfused for the whole period of the experiment. This protective action was reversed by concomitant use of etomoxir, suggesting that the efficacy of L-carnitine is due to its mitochondrial action but cannot be solely attributed to increased fatty acid oxidation. Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 146, No. 8, pp. 175–178, August, 2008     

Inhibitory effect of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on the micturition reflex in rat.

The effect of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an alpha-amino-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptor antagonist, on bladder contractions was examined under isometric conditions in urethane anesthetized rats. Intravenous administration of CNQX (33 ng-50 micrograms/kg) inhibited or abolished bladder contraction. Before complete inhibition, the frequency of bladder contractions was reduced without altering the amplitude or duration. Intrathecal administration of CNQX (2 ng/kg-11 micrograms/kg) similarly inhibited bladder contractions. In contrast, CNQX did not affect bladder contractions in chronically spinalized animals (6.7 ng/kg-400 micrograms/kg i.v.), or contractions evoked by stimulation of the decentralized pelvic nerve (1-100 micrograms/kg i.v.).     

Role of enkephalins in the mechanism of anti-arrhythmia effects of adaptation in acute myocardial ischemia]

Adaptation of rats to cold and physical exercise prevented ventricular fibrillation (VF) caused by the occlusion of the left anterior coronary artery. In the heart of adapted rats with acute myocardial ischemia, myocardial enkephalins increased whereas the level of cAMP declined as compared to nonadapted animals. Injection of dalargin before the occlusion of the coronary artery in rats prevented both VF and a decrease of VF threshold. The peptide averted the rise of cAMP content in the heart during acute myocardial ischemia. The data obtained suggest that the rise of endogenous myocardial enkephalins may have an important role in antiarrhythmic action of adaptation. It is assumed that antiarrhythmic effect of enkephalins may be related to the restriction of sympathetic influence on the heart.     

Serum transforming growth factor-beta1 as a risk stratifier of sudden cardiac death

Sudden cardiac death prematurely claims the lives of some 7 million each year worldwide. It occurs primarily in patients with an underlying structural cardiac abnormality, and regardless of the type of the underlying pathology (heart failure, dilated and hypertrophic cardiomyopathies, myocardial infarction and aging), death is almost always caused by ventricular tachycardia (VT) which rapidly degenerates to ventricular fibrillation (VF). Implantable cardioverter defibrillator is an effective but expensive therapy for preventing SCD, and finding a reasonably specific, sensitive and cost-effective risk stratification tool for patients at high risk of sudden cardiac death will have great clinical utility in preventing premature sudden cardiac death. Increased myocardial fibrosis has been shown to develop in a wide range of cardiac diseases all manifesting increased risk of VT and VF. Clinical and experimental studies attribute a major role for fibrosis in the initiation of VT, VF and sudden cardiac death. Transforming growth factor-beta1 (TGF-beta1) has been shown to promote myocardial tissue fibrosis and perhaps more importantly in cardiac conditions associated with increased myocardial fibrosis are shown to be positively correlated with increased serum levels of TGF-beta1. In the present hypothesis we suggest that monitoring the serum levels of TGF-beta1 may be a cost-effective risk stratifier to identify patients at high risk of sudden cardiac death caused by VT and VF.     

Antifibrillatory effect of GYKI-23107 in induced ventricular vulnerability by local cooling and programmed stimulation in canine models

We tested GYKI-23107 a new agent with local anaesthetic activity, in experimentally induced life-threatening ventricular arrhythmias in pentobarbitone-anaesthetized dogs. By a cooling test and programmed stimulation ventricular fibrillation was induced before and after drug administration (8 mg/kg i.v., n = 14 and 20 mg/kg i.d., n = 12). Comparative experiments were carried out with lidocaine (10 mg/kg). In this lidocaine-treated group, ventricular fibrillation could be produced at 27.7 +/- 6.6 (S.D.) min, n = 12, while after GYKI-23107 ventricular fibrillation occurred at 46.6 +/- 10.7 min, n = 14. The new compound was well absorbed from the intestines; after i.d. administration it could prevent or reduce the onset of lethal arrhythmia for more than 40 min. Its i.d. efficacy correlated well with that of i.v. administration. GYKI-23107 appears to be a safe and potent long-acting agent against ventricular dysrhythmias. It may be a promising and valuable alternative to currently available antiarrhythmic agents. The strong antifibrillatory action observed in ischaemic canine heart (n = 5) both after i.v. or i.d. administration is of special importance.     

Involvement of postsynaptic alpha 2-adrenoceptors and guanine nucleotide-binding protein in guanabenz-induced cardiovascular suppressant effects in the rat

In adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium, pretreatment with the catecholamine-depleting agent, reserpine (150 micrograms, i.c.v.) significantly antagonized the hypotensive and negative inotropic and chronotropic effects of guanabenz, either given intravenously (100 micrograms/kg) or microinjected bilaterally (5 micrograms) into the nucleus reticularis gigantocellularis (NRGC), a medullary site of action for this centrally acting antihypertensive agent. Pretreating animals with microinjection of the selective norepinephrine neurotoxin, DSP4 (50 micrograms), into the bilateral NRGC, on the other hand, did not appreciably blunt the cardiovascular suppressive actions of the aminoguanidine compound. I.c.v. administration of pertussis toxin (2.5 micrograms), which potentially blocks the action of two guanine nucleotide-binding proteins (Gi and Go), significantly antagonized the circulatory inhibitory effects of guanabenz (100 micrograms/kg, i.v.). More specifically, this blocking effect was still apparent upon microinjecting pertussis toxin (250 ng) into the bilateral NRGC. These data suggest that both pre- and postsynaptic alpha 2-adrenoceptors, and a pertussis toxin sensitive G-protein(s) (Gi and/or Go), in the NRGC are crucial to the expression of the cardiovascular suppressant actions of guanabenz.     

基于压力相平面推导的τ和K在评价离体缺血/再灌注大鼠心脏左心室舒张功能中的作用

目的:应用分析和比较基于压力相平面(PPP)推导的心室等容舒张期时间常数)(和室腔僵硬度常数(K)在离体大鼠心脏缺血/再灌注过程中的变化,探讨其在评价左心室舒张功能异常中的价值。方法:采用SD大鼠心肌不同时程缺血/再灌注模型,分别计算出LVEDP、-(dp/dt)max、和K。同时,检测冠脉流出液中的乳酸脱氢酶(LDH),并进行心肌电镜观察。结果:在再灌注过程中,在各缺血组均明显高于空白对照组(P0.05),K在各缺血组均明显低于空白对照组(P0.05);而且,随着缺血时间延长,更高,K更低(P0.05)。除了缺血15min组,其余各组LDH含量在再灌注10min和20min时均高于空白对照组(P0.05);缺血45min组和缺血60min组LDH含量在再灌注10min和20min时均高于缺血30min组(P0.05)。随着缺血时间延长,心肌超微结构发生异常改变。结论:基于PPP推导的和K可以作为定量评价离体大鼠心脏缺血/再灌注过程中的左心室舒张功能的指标,还可以反映缺血/再灌注损伤的严重程度。     

Increased vulnerability to ischemia/reperfusion-induced ventricular tachyarrhythmias by pre-ischemic inhibition of nitric oxide synthase in isolated rat hearts.

INTRODUCTION: The relationship between vulnerability to reperfusion-induced ventricular tachyarrhythmias, such as ventricular tachycardia (VT) and fibrillation (VF), and the endogenous activity of nitric oxide synthase (NOS) has not been well documented. The objective of the present study was to clarify whether the vulnerability to reperfusion-induced VT/VF changes with preishemic, sustained inhibition of NOS. METHODS: The experiments were performed using Langendorff-perfused isolated rat hearts, in which left ventricular pressure (LVP) and left ventricular cardiomyograms (LVCMGs) were measured. RESULTS: A pre-ischemic, sustained inhibition of NOS resulted in an increased vulnerability to reperfusion-induced VT/VF, and the increase was markedly attenuated by co-treatment with L-arginine or by post-ischemic treatment with 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of tetrahydrobiopterin (BH(4)) synthesis. We then tried to elucidate whether nitric oxide (NO) and superoxide were produced during reperfusion, and ATP-sensitive potassium channels (K(ATP)), especially mitochondrial ATP-sensitive potassium channels (mitoK(ATP)), are involved in the increased vulnerability. Post-ischemic inhibition of NOS and treatment with a NO scavenger attenuated the increased vulnerability to reperfusion-induced VT/VF, but post-ischemic treatment with a superoxide scavenger did not. In addition, post-ischemic treatment with S-nitroso-N-acetyl-DL-penicillamine (SNAP), a NO donor, or with diazoxide, a selective opener of mitoK(ATP), increased the VT/VF duration during reperfusion. The increased vulnerability to VT/VF was attenuated by the treatment with a selective mitoK(ATP) blocker. CONCLUSION: The results suggest that a pre-ischemic, sustained inhibition of NOS increases the vulnerability to reperfusion-induced VT/VF, and the NO-mitoK(ATP) pathway is one of the possible factors contributing to the increased vulnerability to VT/VF.     

Benzodiazepines protect hippocampal neurons from degeneration after transient cerebral ischemia: an ultrastructural study

The ability of full and partial benzodiazepine receptor agonists to prevent DNA fragmentation and neuronal death after transient cerebral ischemia was investigated in the Mongolian gerbil. Diazepam (10mg/kg, i.p.) or the partial agonist imidazenil (3mg/kg, i.p.) was administered 30 and 90min after transient forebrain ischemia produced by occlusion of the carotid arteries for 5min. Treatment with diazepam completely protected CA1b hippocampal pyramidal neurons in 94% of the animals and partially protected pyramidal neurons in 6% of the animals, as assessed with a standard Nissl stain three and four days after ischemia. DNA fragmentation was examined by the terminal dUTP nick-end labeling (TUNEL) reaction. Prior to cell death, there were no TUNEL-positive neurons in area CA1b. By three days after ischemia, when neuronal degeneration was nearly complete, 14 out of 16 gerbils exhibited a positive TUNEL reaction throughout area CA1b stratum pyramidale. In 13 out of 14 gerbils treated with diazepam, no TUNEL-positive neurons were observed in this region. Imidazenil was less effective than diazepam with respect to both neuroprotection and prevention of DNA fragmentation. Three days after ischemia, six out of eight gerbils treated with imidazenil showed partial to complete neuroprotection. Imidazenil completely prevented DNA fragmentation in only one of the animals; varying degrees of TUNEL reaction persisted in the remainder. To determine whether the neurons protected by diazepam had a normal ultrastructure, gerbils were killed two to 30 days after ischemia and the hippocampal neurons in area CA1b were examined by electron microscopy. Within the first 48h after ischemia, early cytoplasmic changes of varying degrees (e.g., vacuolation, rough endoplasmic reticulum stacking, swollen mitochondria) and electron-dense dendrites were observed in gerbils not treated with diazepam. Degeneration was nearly complete by three days after ischemia. In contrast, pyramidal neuron ultrastructure appeared normal in gerbils that exhibited complete area CA1b neuroprotection (defined at the light microscope level) by diazepam when studied two, seven or 30 days after ischemia. In gerbils with partial protection of area CA1b, most of the remaining neurons exhibited varying degrees of necrosis when studied 30 days after ischemia. No apoptotic bodies were observed.We conclude that: (i) diazepam can fully protect CA1 pyramidal cells from the toxic effects of transient cerebral ischemia; (ii) when diazepam affords only partial neuroprotection, the residual CA1 pyramidal cells exhibit ultrastructural abnormalities consistent with necrotic damage; and (iii) diazepam is a more efficacious neuroprotectant than the partial benzodiazepine receptor agonist, imidazenil.