Effect of the thromboxane A2 receptor antagonist SQ 30,741 on ultimate myocardial infarct size, reperfusion injury and coronary flow reserve

We determined if the thromboxane A2 antagonist SQ 30,741 can reduce ultimate myocardial infarct size and reperfusion injury. Anesthetized dogs were subjected to left circumflex coronary artery occlusion for 90 min at which time reperfusion was instituted. In one study, SQ 30,741 (1 mg/kg + 1 mg/kg/hr) was given either 10 min postocclusion (n = 7) or 2 min (n = 9) before reperfusion along with their appropriate vehicle controls in a model of 90 min of occlusion and 5 hr of reperfusion. Infarct size was reduced 50% (P less than .05) when SQ 30,741 was given 10 min postocclusion and 30% (P less than .05) when given only during reperfusion. Flow reserve using maximally dilating doses of adenosine was determined 3 hr postreperfusion in vehicle (10 min postocclusion, n = 10), SQ 30,741 (10 min postocclusion, n = 6) and nonischemic (n = 5) animals. Maximal subendocardial flow was reduced during reperfusion in ischemic animals, but SQ 30,741 improved this compared to vehicle animals (400 +/- 95, 88 +/- 25 and 208 +/- 48 ml/min/100 g; nonischemic, vehicle, SQ 30,741 groups, respectively). To determine if myocardial salvage can be observed 24 hr postocclusion with SQ 30,741 or the cyclooxygenase inhibitor aspirin, dogs were given vehicle (n = 9), SQ 30,741 (10 min postocclusion up to 4 hr postreperfusion) or aspirin (n = 9, 40 mg/kg 30 min preocclusion) and infarct size was determined 24 hr postocclusion (90 min left circumflex coronary artery occlusion + reperfusion).(ABSTRACT TRUNCATED AT 250 WORDS)     

The new K+ channel opener Aprikalim (RP 52891) reduces experimental infarct size in dogs in the absence of hemodynamic changes.

The objective of the present study was to determine the effect of a novel K+ channel opener, Aprikalim (RP 52891; [trans-(-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothio-pyran carbothiamide-1-oxide]), on myocardial infarct size in barbital-anesthetized dogs subjected to 90 min of left circumflex coronary artery occlusion followed by 5 hr of reperfusion. To determine if RP 52891 is mediating its effects by opening adenosine triphosphate regulated potassium channels (KATP), glibenclamide, a KATP channel antagonist was used. Dogs were pretreated with vehicle, a nonhypotensive dose of RP 52891 (10 micrograms/kg + 0.1 microgram/kg/min i.v.), glibenclamide (1 mg/kg; i.v. bolus) or RP 52891 (10 micrograms/kg and 0.1 microgram/kg/min i.v.) after pretreatment with glibenclamide (1 mg/kg i.v. bolus). At the end of reperfusion, myocardial infarct size was determined by triphenyltetrazolium staining. There were no significant differences in systemic hemodynamics, myocardial oxygen demand, collateral blood flow or ischemic bed size among groups with the exception of an increase in coronary blood flow to the ischemic area at 3 and 5 hr of reperfusion in both RP-treated groups. However, myocardial infarct size, expressed as a percentage of the area at risk, was significantly (P less than .05) reduced (38%) by RP 52891 and significantly increased (38%) by glibenclamide (vehicle, 39 +/- 4%; RP 52891, 24 +/- 2%; and glibenclamide, 54 +/- 5%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of thromboxane receptor blockade on oxygen supply/consumption variables during reperfusion in the anesthetized dog

The thromboxane A2/PGH2 receptor antagonist SQ 30,741 has been previously shown to reduce infarct size and to improve subendocardial reflow. The purpose of this study was to determine the effect of SQ 30,741 on reperfusion O2 supply/consumption variables. Anesthetized open-chest dogs treated with vehicle or 1 mg/kg + 1 mg/kg/hr SQ 30,741, i.v. (starting 10 min after the onset of ischemia) were subjected to 90 min left circumflex coronary occlusion and 3 hr reperfusion. Regional myocardial blood flow (radioactive microspheres) and arterial and venous O2 saturations (microspectrophotometry) were determined. Animals treated with SQ 30,741 had significantly higher subendocardial reflow at 3 hr (48 +/- 6 ml/min/100 g) compared with vehicle (27 +/- 10 ml/min/100 g). At 3 hr postreperfusion, O2 extraction was significantly higher in the reperfused region compared with the nonischemic region, although extraction was not at maximal values. O2 extraction was similar in vehicle- and SQ 30,741-treated animals despite the near doubling of reflow into the subendocardial region with SQ 30,741. O2 consumption was significantly reduced in the reperfused subendocardial region (1.65 +/- 0.9 ml O2/min/100 g) in vehicle controls compared with the nonischemic subendocardial region (10.2 +/- 2.6 ml O2/min/100 g). SQ 30,741 significantly improved subendocardial reperfused regional O2 consumption (4.03 +/- 0.41 ml O2/min/100 g) compared with vehicle and this increase was proportional to the flow increment (no change in the O2 supply/consumption ratio). SQ 30,741 is thus increasing subendocardial reflow secondary to an increase in O2 consumption and the increased O2 consumption may be due to preservation of myocardial tissue.     

Protection from myocardial ischemia/reperfusion injury by a positive allosteric modulator of the A₃ adenosine receptor

Adenosine is increased in ischemic tissues where it serves a protective role by activating adenosine receptors (ARs), including the A? AR subtype. We investigated the effect of N-{2-[(3,4-dichlorophenyl)amino]quinolin-4-yl}cyclohexanecarboxamide (LUF6096), a positive allosteric modulator of the A? AR, on infarct size in a barbital-anesthetized dog model of myocardial ischemia/reperfusion injury. Dogs were subjected to 60 min of coronary artery occlusion and 3 h of reperfusion. Infarct size was assessed by macrohistochemical staining. Three experimental groups were included in the study. Groups I and II received two doses of vehicle or LUF6096 (0.5 mg/kg i.v. bolus), one administered before ischemia and the other immediately before reperfusion. Group III received a single dose of LUF6096 (1 mg/kg i.v. bolus) immediately before reperfusion. In preliminary in vitro studies, LUF6096 was found to exert potent enhancing activity (EC?? 114.3 ± 15.9 nM) with the canine A? AR in a guanosine 5'-[γ-[3?S]thio]triphosphate binding assay. LUF6096 increased the maximal efficacy of the partial A? AR agonist 2-chloro-N?-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide and the native agonist adenosine more than 2-fold while producing a slight decrease in potency. In the dog studies, administration of LUF6096 had no effect on any hemodynamic parameter measured. Pretreatment with LUF6096 before coronary occlusion and during reperfusion in group II dogs produced a marked reduction in infarct size (～50% reduction) compared with group I vehicle-treated dogs. An equivalent reduction in infarct size was observed when LUF6096 was administered immediately before reperfusion in group III dogs. This is the first study to demonstrate efficacy of an A? AR allosteric enhancer in an in vivo model of infarction.     

Nicotinic acid, free fatty acids and myocardial function during coronary occlusion and reperfusion in the dog

The effect of nicotinic acid on regional myocardial blood flow, percentage of segment shortening and myocardial uptake of free-fatty acids during a 15-min occlusion of the left anterior descending coronary artery and 3-hr reperfusion period was compared to a saline-treated control group. Nicotinic acid (2.4 mumol/kg/min i.v.) was infused 30 min before and throughout the occlusion period. Heart rate, arterial blood pressure and left ventricular systolic and end diastolic pressures were not different during occlusion and reperfusion in the nicotinic acid or saline-treated groups. However, left ventricular dP/dt, an index of global myocardial function and percentage of segment shortening in the ischemic region were greater during occlusion and reperfusion after nicotinic acid. Even though myocardial blood flow was unaltered in the normal or ischemic region during nicotinic acid infusion, subendocardial blood flow during reperfusion was enhanced significantly when compared to the control group. Nicotinic acid also decreased free-fatty acid uptake by the heart during occlusion which returned gradually to the pretreatment control during 3 hr of reperfusion. Thus, the improvement in percentage of segment shortening, dP/dt and subendocardial blood flow during reperfusion may be related to the ability of nicotinic acid to reduce free-fatty acid uptake by the heart during coronary occlusion.     

Protective effect of melanocortin peptides in rat myocardial ischemia

The influence of the melanocortin peptide ACTH-(1-24) (adrenocorticotropin) on the consequences of short-term coronary ischemia (5 min) followed by reperfusion, and the effect of the long-acting melanocortin [Nle(4),D-Phe(7)]alpha-melanocyte-stimulating hormone (NDP-MSH) on the damage induced by a permanent coronary occlusion, were investigated in anesthetized rats. Ischemia was produced by ligature of the left anterior descending coronary artery. Reperfusion-induced arrhythmias [ventricular tachycardia (VT), ventricular fibrillation (VF)] and survival rate within the 5 min following reperfusion, blood levels of free radicals detected 2 min after reperfusion by electron spin resonance spectrometry, and amount of healthy myocardial tissue, measured 72 h after permanent coronary occlusion on immunohistologically stained serial sections, were evaluated. Postischemic reperfusion induced VT in all saline-treated rats, and VF and death in a high percentage of animals (87%). In rats treated i.v. (2.5 min after coronary occlusion) with ACTH-(1-24) (0.16-0.48 mg/kg) there was a significantly dose-dependent reduction in the incidence of arrhythmias and lethality. Ischemia/reperfusion caused a large increase in free radical blood levels; treatment with ACTH-(1-24) (0.48 mg/kg i.v.) almost completely prevented this increase. In rats subjected to permanent coronary occlusion, the amount of healthy myocardial tissue was much reduced in saline-treated rats, while in rats treated s.c. with NDP-MSH (0.27 mg/kg every 12 h) it was significantly higher. The present data demonstrate, for the first time, an unforeseen property of melanocortin peptides, i.e., their ability to significantly reduce both heart ischemia/reperfusion injury and size of the ischemic area induced by permanent coronary occlusion.     

Effects of KR-33028, a novel Na+/H+ exchanger-1 inhibitor, on ischemia and reperfusion-induced myocardial infarction in rats and dogs

The present study was performed to evaluate the cardioprotective effects of KR-33028, a novel Na+/H+ exchanger subtype 1 (NHE-1) inhibitor, in rat and dog models of coronary artery occlusion and reperfusion. In anesthetized rats subjected to a 45-min coronary occlusion and a 90-min reperfusion, KR-33028 at 5 min before occlusion (i.v. bolus) dose-dependently reduced myocardial infarct size from 58.0% to 46.6%, 40.3%, 39.7%, 33.1%, and 27.8% for 0.03, 0.1, 0.3, 1.0, and 3.0 mg/kg respectively (P < 0.05). In anesthetized beagle dogs that underwent a 1.0-h occlusion followed by a 3.0-h reperfusion, KR-33028 (3 mg/kg, i.v. bolus) markedly decreased infarct size from 45.6% in vehicle-treated group to 16.4% (P < 0.05), and reduced the reperfusion-induced release in creatine kinase myocardial band isoenzyme (MB), lactate dehydrogenase, troponin-I, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase. In separate experiments to assess the effects of timing of treatment, KR-33028 (1 mg/kg, i.v. bolus) given 10 min before or at reperfusion in rat models also significantly reduced the myocardial infarct size (46.3% and 44.1% respectively) compared with vehicle-treated group. In all studies, KR-33028 caused no significant changes in any hemodynamic profiles. In an isolated rat heart model of hypothermic cardioplegia, KR-33028 (30 mum), which was added to the heart preservation solution (histidin-tryptophan-ketoglutarate) during hypothermic cardioplegic arrest, significantly improved the recovery of left ventricular developed pressure, heart rate and dP/dt(max) after reperfusion. Taken together, these results indicate that KR-33028 significantly reduced the myocardial infarction induced by ischemia and reperfusion in rats and dogs, without affecting hemodynamic profiles.     

Effect of diltiazem on infarct size, reperfusion flow and flow reserve: the effect of timing of treatment

This study was performed to determine if improved subendocardial reflow seen with diltiazem pretreatment after left circumflex coronary (LCX) occlusion is due to a direct vasodilatory effect of diltiazem on the reperfused bed or due to an increased flow maximum or reserve. In the first part of this study anesthetized dogs were subjected to saline or diltiazem (infused starting before, 10 min after LCX occlusion or 2 min before reperfusion; 0.18 mg/kg + 0.45 mg/kg/hr i.v. for all groups) treatment with a 90-min LCX occlusion and 5-hr reperfusion and myocardial blood flow and infarct size were determined at the end of the experiment. In the second part, maximal flow using intracoronary adenosine was determined at 1 and 3 hr postreperfusion in the ischemic bed when pretreated with saline or diltiazem. Myocardial infarct size was reduced significantly only in animals pretreated with diltiazem compared to saline-treated animals. At 1-hr postreperfusion, subendocardial flow (microspheres) was significantly higher only with diltiazem pretreatment compared to the saline group (100 +/- 17 vs. 54 +/- 8 ml/min/100 g, respectively) and subendocardial reperfusion flows were negatively correlated to infarct size (r = 0.97, P less than .05). Thus, diltiazem only improves reflow and infarct size when infused before occlusion and this improved reflow does not occur via a direct vasodilator action of diltiazem. When maximal vasodilating doses of adenosine were given, flow in the ischemic region was nearly identical for saline and diltiazem pretreated groups despite higher preadenosine flows in the diltiazem group (higher resting flow occurred at the expense of the existing flow reserve).(ABSTRACT TRUNCATED AT 250 WORDS)     

Antioxidant LY231617 enhances electrophysiologic recovery after global cerebral ischemia in dogs

OBJECTIVE: The potent antioxidant LY231617 (2,6-bis(1,1-dimethylethyl)-4-[[(1-ethyl)amino]methyl]phenol hydrochloride) is cytoprotective in models of focal and global cerebral ischemia. We tested the hypothesis that administration of LY231617, before the insult, would improve recovery of cerebral electrical activity and metabolic function after transient global cerebral ischemia by improving cerebral blood flow (CBF) during the reperfusion period. DESIGN: Randomized, controlled, prospective study. SETTING: Research laboratory at a university teaching hospital. SUBJECTS: Twenty-four male beagle dogs. INTERVENTIONS: All experiments were performed under pentobarbital anesthesia and controlled conditions of normoxia, normocarbia, and normothermia. Twelve control dogs received 20 mL/kg saline (vehicle) bolus into the right atrium and 0.01 mL/kg/min i.v., beginning 20 mins before 13 mins of global cerebral ischemia (by aortic occlusion). The dogs in the drug-treated group received LY231617 as a 10-mg/kg bolus 20 mins before ischemia and 5 mg/kg/hr throughout reperfusion (n = 12). CBF was measured using radiolabeled microspheres. MEASUREMENTS AND MAIN RESULTS: Total CBF, cerebral oxygen consumption, and somatosensory evoked potentials (SEP) were measured during 240 mins of reperfusion. CBF was similar in both vehicle- and LY231617-treated animals at baseline and throughout the experimental period. In all animals, SEP became isoelectric between 60 and 100 secs after cross-clamping of the ascending aorta. SEP amplitude recovery was significantly higher in drug-treated animals compared with controls (73%+/-15% vs. 39%+/-14% [mean+/-SEM] from baseline at 120 mins [p<.05] and 86%+/-12% vs. 49%+/-14% from baseline at 240 mins [p< .05]). CONCLUSIONS: LY231617 improves recovery of cerebral electrical function after complete transient global ischemia via mechanisms unrelated to cerebral circulatory effects.     

Mechanisms of the cardioprotective actions of WEB-2170, bepafant, a platelet activating factor antagonist, in myocardial ischemia and reperfusion.

The cardioprotective effects of WEB-2170, a specific platelet activating factor (PAF) receptor antagonist, were investigated in a feline model of myocardial ischemia (MI) and reperfusion. Either WEB-2170 (1-mg/kg bolus plus 2 mg/kg/hr) or its vehicle (0.9% NaCl) was administered 1 hr after left anterior descending coronary artery occlusion (i.e., 30 min before reperfusion). The cardiac area-at-risk (AAR) was similar in MI-reperfused (MI + R) cats given either WEB-2170 (31.5 +/- 3.6%) or vehicle (27.8 +/- 2.8%). However, in cats receiving only the vehicle, 1.5 hr of ischemia plus 4.5 hr of reperfusion resulted in significant myocardial injury (necrotic tissue/AAR, 37.7 +/- 4.5%), high plasma creatine kinase activity (29.4 +/- 4.1 I.U./micrograms of protein) and a marked decrease in endothelium-dependent relaxation in isolated left anterior descending coronary arteries to acetylcholine (33 +/- 4% of U-46619-induced vasocontraction) with no change in endothelium-independent relaxation to NaNO2 (91 +/- 1%). In contrast, MI + R cats treated with WEB-2170 developed significantly less myocardial necrosis (necrotic tissue/AAR, 12.0 +/- 2.8%, P less than .001), lower plasma creatine kinase activity (16.5 +/- 4.1 I.U./micrograms of protein, P less than .01) and enhanced vascular relaxation to acetylcholine (53 +/- 4.1%, P less than .01) compared to MI + R cats given only the vehicle. Furthermore, the addition of WEB-2170 to PMN suspensions in vitro significantly inhibited (P less than .01) PAF-induced polymorphonuclear leukocyte (PMN) adherence to endothelial cells (12 +/- 2.4 cells/field vs. 27 +/- 2.6 in the control group).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of three different A1 adenosine receptor antagonists on infarct size and multiple cycle ischemic preconditioning in anesthetized dogs

A(1) adenosine receptor (AR) antagonists are effective diuretic agents that may be useful for treating fluid retention disorders including congestive heart failure. However, antagonism of A(1)ARs is potentially a concern when using these agents in patients with ischemic heart disease. To address this concern, the present study was designed to compare the actions of the A(1)AR antagonists CPX (1,3-dipropyl-8-cyclopentylxanthine), BG 9719 (1,3-dipropyl-8-[2-(5,6-epoxynorbornyl)]xanthine), and BG 9928 (1,3-dipropyl-8-[1-(4-propionate)-bicyclo-[2,2,2]octyl]xanthine) on acute myocardial ischemia/reperfusion injury and ischemic preconditioning (IPC) in an in vivo dog model of infarction. Barbital-anesthetized dogs were subjected to 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion, after which infarct size was assessed by staining with triphenyltetrazolium chloride. IPC was elicited by four 5-min occlusion/5-min reperfusion cycles produced 10 min before the 60-min occlusion. Multiple-cycle IPC produced a robust reduction ( approximately 65%) in infarct size; this effect of IPC on infarct size was not abrogated in dogs pretreated with any of the three AR antagonists. Surprisingly, in the absence of IPC, pretreatment with CPX or BG 9928 before occlusion or immediately before reperfusion resulted in significant reductions ( approximately 40-50%) in myocardial infarct size. However, treatment with an equivalent dose of BG 9719 had no similar effect. We conclude that the A(1)AR antagonists BG 9719, BG 9928, and CPX do not exacerbate cardiac injury and do not interfere with IPC induced by multiple ischemia/reperfusion cycles. We discuss the possibility that the cardioprotective actions of CPX and BG 9928 may be related to antagonism of A(2B)ARs.     

Early Recovery of Regional Performance in Salvaged Ischemic Myocardium following Coronary Artery Occlusion in the Dog

Although numerous agents have been shown experimentally to protect ischemic myocardium, a critical unanswered question is whether function is preserved in the salvaged tissue. Accordingly, 38 openchest dogs had measurements of percent segment length shortening (%SS) and velocity of segment length shortening either in midmyocardial or subepicardial and subendocardial ischemic segments before and after 60 min of left anterior descending coronary artery occlusion during 5 h of reperfusion; 10 additional dogs were subjected to 3 h of coronary occlusion followed by 72 h of reperfusion. 15 min after coronary artery occlusion, radiolabeled microspheres were injected into the left atrium for measurement of regional myocardial blood flow, and dogs were treated with 1 mg/kg i.v. (n = 23) of an anti-inflammatory drug, flurbiprofen or an equal volume of saline (n = 25). The ischemic myocardium-at-risk for necrosis was determined by injecting methylene blue dye into the left atrium with the coronary artery reoccluded at the end of the reperfusion period, slicing the left ventricle into thin transverse sections, and measuring the areas of each slice that were not perfused (pink unstained tissue) by methylene blue. The quantity of necrotic tissue in each transverse section was measured by planimetry after incubation of the slices in triphenyltetrazolium chloride, and by direct histological examination in dogs with 72 h of reperfusion.     

Cl-IB-MECA [2-chloro-N6-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide] reduces ischemia/reperfusion injury in mice by activating the A3 adenosine receptor

We used pharmacological agents and genetic methods to determine whether the potent A(3) adenosine receptor (AR) agonist 2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide (Cl-IB-MECA) protects against myocardial ischemia/reperfusion injury in mice via the A(3)AR or via interactions with other AR subtypes. Pretreating wild-type (WT) mice with Cl-IB-MECA reduced myocardial infarct size induced by 30 min of coronary occlusion and 24 h of reperfusion at doses (30 and 100 mug/kg) that concomitantly reduced blood pressure and stimulated systemic histamine release. The A(3)AR-selective antagonist MRS 1523 [3-propyl-6-ethyl-5[(ethylthio)carbonyl]-2-phenyl-4-propyl-3-pyridine-carboxylate], but not the A(2A)AR antagonist ZM 241385 [4-{2-7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl}phenol], blocked the reduction in infarct size provided by Cl-IB-MECA, suggesting a mechanism involving the A(3)AR. To further examine the selectivity of Cl-IB-MECA, we assessed its cardioprotective effectiveness in A(3)AR gene "knock-out" (A(3)KO) mice. Cl-IB-MECA did not reduce myocardial infarct size in A(3)KO mice in vivo and did not protect isolated perfused hearts obtained from A(3)KO mice from injury induced by global ischemia and reperfusion. Additional studies using WT mice treated with compound 48/80 [condensation product of p-methoxyphenethyl methylamine with formaldehyde] to deplete mast cell contents excluded the possibility that Cl-IB-MECA was cardioprotective by releasing mediators from mast cells. These data demonstrate that Cl-IB-MECA protects against myocardial ischemia/reperfusion injury in mice principally by activating the A(3)AR.     

Ischemia-induced alterations in myocardial (Na+ + K+)-ATPase and cardiac glycoside binding.

The effects of ischemia on the canine myocardial (Na+ + K+)-ATPase complex were examined in terms of alterations in cardiac glycoside binding and enzymatic activity. Ability of the myocardial cell to bind tritiated ouabain in vivo was assessed after 1, 2, and 6 h of coronary occlusion followed by 45 min of reperfusion, and correlated with measurements of in vitro (Na+ + K+)-ATPase activity and in vitro [3H]ouabain binding after similar periods of ischemia. Regional blood flow alterations during occlusion and reperfusion were simultaneously determined utilizing 15 mum radioactive microspheres to determine the degree to which altered binding of ouabain might be flow related. Anterior wall infarction was produced in 34 dogs by snaring of confluent branches of the left coronary system. Epicardial electrograms delineated ischemic and border zone areas. Coronary reperfusion after 2 and 6 h of occlusion was associated with impaired reflow of blood and markedly impaired uptake of [3H]ouabain in ischemic myocardium. In both groups, in vivo [3H]ouabain binding by ischemic tissue was reduced out of proportion to the reduction in flow. Despite near-complete restoration of flow in seven dogs occluded for 1 h and reperfused, [3H]ouabain remained significantly reduced to 58 +/- 9% of nonischemic uptake in subendocardial layers of the central zone of ischemia. Thus, when coronary flow was restored to areas of myocardium rendered acutely ischemia for 1 or more hours, ischemic zones demonstrated progressively diminished ability to bind ouabain. To determine whether ischemia-induced alteration in myocardial (Na+ + K+)-ATPase might underlie these changes, (Na+ + K+)-ATPase activity and [3H]ouabain binding were measured in microsomal fractions from ischemic myocardium after 1, 2, and 6 h of coronary occlusion. In animals occluded for 6 h, (Na+ + K+)-ATPase activity was significantly reduced by 40% in epicardial and by 35% in endocardial layers compared with nonischemic myocardium. Comparable reductions in in vitro [3H]ouabain binding were also demonstrated. Reperfusion for 45 min after occlusion for 6 h resulted in no significant restoration of enzyme activity when compared to the nonreperfused animals. In six animals occluded for 2 h, a time at which myocardial creatine phosphokinase activity remains unchanged, (Na+ + K+)-ATPase activity was reduced by 25% compared with nonischemic enzyme activity. In five dogs occluded for 1 h, (Na+ + K+)-ATPase activity in ischemic myocardium was unchanged from control levels. We conclude that reduced regional myocardial blood flow, local alterations in cellular milieu, and altered glycoside-binding properties of (Na+ + K+)-ATPase all participate in the reduction of cardiac glycoside binding observed after reperfusion of ischemic myocardium. In addition, after 2 or more hours of severe ischemia, myocardial (Na+ + K+)-ATPase catalytic activity is significantly reduced despite incubation in the presence of optimal substrate concentrations.     

Alpha adrenergic contributions to dysrhythmia during myocardial ischemia and reperfusion in cats.

Alpha compared to beta adrenergic contributions to dysrhythmias induced by left anterior descending coronary occlusion and by reperfusion were assessed in chloralose-anesthetized cats (n = 96). Alpha receptor blockade with either phentolamine or prazosin significantly reduced the number of premature ventricular complexes during coronary reperfusion (321 +/- 62-14 +/- 10 premature ventricular complexes, P less than 0.001), abolished early ventricular fibrillation (from 25% in controls to 0%), and prevented the increase in idioventricular rate seen with coronary reperfusion. However, beta-receptor blockade was without effect. Ventricular dysrhythmias induced by coronary occlusion alone (without reperfusion) were attenuated markedly by alpha-receptor blockade under conditions in which perfusion (measured with radiolabeled microspheres) within ischemic zones was not affected. Alternative sympatholytic interventions including pretreatment with 6-hydroxydopamine to deplete myocardial norepinephrine from 8.8 +/- 1.4 to 0.83 +/- 0.2 ng/mg protein and render the heart unresponsive to tyramine (120 microgram/kg) attenuated dysrhythmias induced by both coronary occlusion and reperfusion in a fashion identical to that seen with alpha-receptor blockade. Although efferent sympathetic activation induced by left stellate nerve stimulation increased idioventricular rate from 66 +/- 6 to 144+/- 7 beats/min (P less than 0.01) before coronary occlusion, this response was blocked by propranolol but not by phentolamine. In contrast, during reperfusion the increase in idioventricular rate induced by left stellate nerve stimulation (to 203 +/- 14) was not inhibited by propranolol but was abolished by phentolamine (79 +/- 10). Intracoronary methoxamine (0.1 microM) in animals depleted of myocardial catecholamines by 6-hydroxydopamine pretreatment did not affect idioventricular rate before coronary occlusion. However, early after coronary reperfusion, methoxamine increased idioventricular rate from 33 +/- 7 to 123 +/- 21 beats/min (P less than 0.01). Thus, enhanced alpha-adrenergic responsiveness occurs during myocardial ischemia and appears to be primary mediator of the electrophysiological derangements and resulting malignant dysrhythmias induced by catecholamines during myocardial ischemia and reperfusion.     

七氟醚预处理延迟相对大鼠心肌缺血再灌注损伤的保护作用

[目的]探讨七氟醚预处理延迟相对大鼠心肌缺血再灌注(IR)损伤的保护作用.[方法]将18只健康成年雄性大鼠随机分成3组:假手术组(C组)、缺血再灌注组(IR组)和七氟醚组(S组).C组仅开胸并分离冠状动脉左前降支,但不阻断血流150 min;IR组行冠状动脉左前降支阻断30 min,再灌注120 min; S组予以吸入...     

硫化氢预处理延迟相对大鼠心肌缺血再灌注损伤的保护作用

【目的】探讨硫化氢预处理延迟相对大鼠心肌缺血再灌注（IR）损伤的保护作用。【方法】将30只健康成年Sprague-Dawley雄性大鼠随机分成3组：假手术组（S组）、缺血再灌注组（IR组）和硫化氢组（H组）。S组仅开胸并分离左冠状动脉前降支;IR组行左冠状动脉前降支阻断30rain,再灌注120min;H组予以静脉注射硫氢化钠（NaHS）0．05mg／kg,给药后24h同IR组处理。各组分别于缺血前10min（T1）、缺血30min（T2）、再灌注60min（T3）、120min（T4）四个时点记录血流动力学变化。再灌注结束后测心梗面积。【结果】与IR组比,H组血流动力学改善,心肌梗死面积减少（P〈0．05）。【结论】硫化氢预处理延迟相对大鼠缺血再灌注心肌具有保护作用。     

Delayed cardioprotective effects of exercise in dogs are aminoguanidine sensitive: possible involvement of nitric oxide

Dogs were subjected to exercise on a treadmill, using a protocol in which the speed and slope were increased every 3 min, and which elevated both heart rate (to a mean of 198+/-14 beats.min(-1)) and mean arterial blood pressure (to 150+/-4 mmHg). Then, 24 or 48 h later, the dogs were anaesthetized with a mixture of alpha-chloralose and urethane and subjected to a 25 min occlusion of the left anterior descending coronary artery. The control dogs (instrumented but not exercised) were subjected to the same procedure. In some dogs the nitric oxide synthase inhibitor aminoguanidine (50 mg.kg(-1); intravenous) was administered 30 min before occlusion. Baroreflex sensitivity (BRS) was determined by the rapid bolus injection of phenylephrine 60 min before, and again 3 min after, the onset of occlusion. Exercise markedly reduced the consequences of coronary artery occlusion 24 h (but not 48 h) later, without modifying myocardial tissue blood flow. In the exercised dogs there were reductions in arrhythmia severity [ventricular fibrillation (VF) during occlusion, 0%; survival from the combined ischaemia/reperfusion insult, 70%] compared with controls (VF during occlusion, 36%; survival, 9%). BRS was preserved during occlusion in the exercised dogs (before occlusion, 1.60+/-0.54 ms.mmHg(-1); 3 min after occlusion, 1.37+/-0.4 ms.mmHg(-1)), but not in controls (before occlusion, 1.28+/-0.29 ms.mmHg(-1); 3 min after occlusion, 0.45+/-0.12 ms.mmHg(-1); P<0.05), and other ischaemic changes (inhomogeneity of electrical activation and changes in the ST-segment, recorded over the ischaemic region) were also less marked in the exercised dogs. Exercise-induced cardioprotection was abolished by aminoguanidine (VF during occlusion, 25%; survival, 0%). The results show that even a single period of exercise affords delayed protection against ischaemia/reperfusion-induced VF and other ischaemic changes. Since this protection is abolished by aminoguanidine, and since (inducible) NO synthase activity was elevated 3-fold in left ventricular samples 24 h after exercise, we suggest that this protection is mediated by nitric oxide.     

Effect of diltiazem on regional oxygenation of reperfused myocardium

Reperfusion after 2 hr of experimental ischemia results in reduced blood flow to the reperfused region, as well as elevated regional O2 extraction in that region. The aim of the present study was to determine whether diltiazem, administered during reperfusion, can improve regional blood flow and lower O2 extraction in the previously occluded region. In open-chest anesthetized dogs, 2-hr occlusion of the left anterior descending coronary artery was followed by a 4-hr period of reperfusion. In 7 of the 15 animals, diltiazem (0.45 micrograms/kg/min) was infused i.v. during the reperfusion period; this was preceded by a loading dose of 0.18 micrograms/kg 10 min before release. Small artery and vein O2 saturations obtained microspectrophotometrically were combined with regional blood flow measurements using radioactive microspheres to determine regional myocardial O2 consumption. In both groups, coronary occlusion lowered regional flow to a similar level. After a 4-hr reperfusion, flow to the subendocardial region of treated hearts was significantly greater than that to the untreated reperfused myocardium (75.6 +/- 46.4 vs. 40.3 +/- 25.8 ml/min/100 g), and did not differ from the preocclusion level. The subendocardium/subepicardium flow ratio was reversed in occluded and untreated reperfused myocardium (subendocardium flow less than subepicardium flow), but was not reversed in treated reperfused regions. Myocardial oxygen extraction was 11.0 +/- 2.4 ml of O2/100 ml of blood in the untreated reperfused subendocardium, and was significantly decreased to 8.5 +/- 0.9 ml of O2/100 ml in the treated subendocardium. The proportion of individual veins having O2 saturations below 25% was significantly reduced by diltiazem treatment from 45.2 to 22.7%.(ABSTRACT TRUNCATED AT 250 WORDS)     

A novel and orally active poly(ADP-ribose) polymerase inhibitor, KR-33889 [2-[methoxycarbonyl(4-methoxyphenyl) methylsulfanyl]-1H-benzimidazole-4-carboxylic acid amide], attenuates injury in in vitro model of cell death and in vivo model of cardiac ischemia

Blocking of poly(ADP-ribose) polymerase (PARP)-1 has been expected to protect the heart from ischemia-reperfusion injury. We have recently identified a novel and orally active PARP-1 inhibitor, KR-33889 [2-[methoxycarbonyl(4-methoxyphenyl)-methylsulfanyl]-1H-benzimidazole-4-carboxylic acid amide], and its major metabolite, KR-34285 [2-[carboxy(4-methoxyphenyl)methylsulfanyl]-1H-benzimidazole-4-carboxylic acid amide]. KR-33889 potently inhibited PARP-1 activity with an IC(50) value of 0.52 +/- 0.10 microM. In H9c2 myocardial cells, KR-33889 (0.03-30 microM) showed a resistance to hydrogen peroxide (2 mM)-mediated oxidative insult and significantly attenuated activation of intracellular PARP-1. In anesthetized rats subjected to 30 min of coronary occlusion and 3 h of reperfusion, KR-33889 (0.3-3 mg/kg i.v.) dose-dependently reduced myocardial infarct size. KR-34285, a major metabolite of KR-33889, exerted similar patterns to the parent compound with equi- or weaker potency in the same studies described above. In separate experiments for the therapeutic time window study, KR-33889 (3 mg/kg i.v.) given at preischemia, at reperfusion or in both, in rat models also significantly reduced the myocardial infarction compared with their respective vehicle-treated group. Furthermore, the oral administration of KR-33889 (1-10 mg/kg p.o.) at 1 h before occlusion significantly reduced myocardial injury. The ability of KR-33889 to inhibit PARP in the rat model of ischemic heart was confirmed by immunohistochemical detection of poly(ADP-ribose) activation. These results indicate that the novel PARP inhibitor KR-33889 exerts its cardioprotective effect in in vitro and in vivo studies of myocardial ischemia via potent PARP inhibition and also suggest that KR-33889 could be an attractive therapeutic candidate with oral activity for several cardiovascular disorders, including myocardial infarction.