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We have previously reported that postresuscitation myocardial dysfunction is accompanied by the release of cytochrome c and caspase-3 activation. We now investigated the role of caspase-3 activation by examining whether such process prompts apoptotic DNA fragmentation, whether caspase-3 inhibition attenuates myocardial dysfunction, and whether myocardial protective effects of sodium-hydrogen exchanger isoform-I (NHE-1) inhibition involve caspase-3 inhibition using a rat model of ventricular fibrillation (VF) of closed-chest resuscitation. Resuscitation after 4 or 8 min of untreated VF caused significant reductions in left ventricular stroke work index averaging 23% of sham control rats at 4 h postresuscitation. Left ventricular dysfunction was accompanied by increases in cytosolic cytochrome c, decreases in pro- and cleaved caspase-9 fragments, increases in 17-kDa caspase-3 fragments, and increases in caspase-3 activity indicating the activation of the mitochondrial apoptotic pathway but without evidence of apoptotic DNA fragmentation. In addition, levels of heat shock protein 70 were increased and levels of X-linked inhibitor of apoptosis protein and [alpha][beta]-crystallin were preserved, all of which can exert antiapoptotic effects. In a separate series, the caspase-3 inhibitor z-Asp-Glu-Val-Asp chloromethyl ketone given before the induction of VF failed to prevent postresuscitation myocardial dysfunction despite reductions in caspase-3 activity (2.3 [+ or -] 0.5 vs. 1.3 [+ or -] 0.5 pmol fluorophore AFC released x mg [protein.sup.-1] x [min.sup.-1]; P < 0.03). Treatment with the NHE-1 inhibitor cariporide had no effect on caspase-3 activity. Accordingly, in this rat model of VF and severe postresuscitation myocardial dysfunction, activation of caspase-3 did not lead to DNA fragmentation or contribute to myocardial dysfunction. Concomitant activation of intrinsic antiapoptotic mechanisms could play a protective role downstream to caspase-3 activation. ventricular fibrillation; cardiopulmonary resuscitation; apoptosis; ventricular function

[Ca.sup.2+] overload and reactive oxygen species can injure mitochondria during ischemia and reperfusion. We hypothesized that mitochondrial injury occurs during cardiac resuscitation, causing release of cytochrome c to the cytosol and bloodstream while activating apoptotic pathways. Plasma cytochrome c was measured using reverse-phase HPLC and Western immunoblotting in rats subjected to 4 or 8 min of untreated ventricular fibrillation and 8 min of closed-chest resuscitation followed by 240 min of postresuscitation hemodynamic observation. A sham group served as control. Plasma cytochrome c rose progressively to levels 10-fold higher than in sham rats 240 min after resuscitation (P < 0.01), despite reversal of whole body ischemia (decreases in arterial lactate). Cytochrome c levels were inversely correlated with left ventricular stroke work (r = -0.40, P = 0.02). Western immunoblotting of left ventricular tissue demonstrated increased levels of 17-kDa cleaved caspase-3 fragments in the cytosol. Plasma cytochrome c was then serially measured in 12 resuscitated rats until the rat died or cytochrome c returned to baseline. In three survivors, cytochrome c rose slightly to [less than or equal to] 2 [micro]g/ml and returned to baseline within 96 h. In nine nonsurvivors, cytochrome c rose progressively to significantly higher maximal levels [4.6 (SD 2.0) vs. 1.6 (SD 0.3) [micro]g/ml, P = 0.029] and at faster rates [0.7 (SD 0.5) vs. 0.1 (SD 0.1) [micro]g * [ml.sup.-1] * [h.sup.-1], P = 0.046] than in survivors. Plasma cytochrome c may represent a novel in vivo marker of mitochondrial injury after resuscitation from cardiac arrest that relates inversely with survival outcome. apoptosis; biological markers; cardiopulmonary resuscitation; myocardial ischemia; ventricular fibrillation

When given during closed-chest restiscitation, cariporide (4-isopropyl-methylsulfonylbenzoyl-guanidine methanesulfonate; a selective inhibitor of the N[a.sup.+]/[H.sup.+] exchanger isoform-1) enables generation of viable perfusion pressures with less depth of compression. We hypothesized that this effect results from greater blood flows generated for a given depth of compression. Two series of 14 rats each underwent 10 min of untreated ventricular fibrillation followed by 8 min of chest compression before defibrillation was attempted. Compression depth was adjusted to maintain an aortic diastolic pressure (ADP) between 26 and 28 mmHg in the first series and between 36 and 38 mmHg in the second series. Within each series, rats were randomized to receive caripolide (3 mg/kg) or NaCl (0.9%; control) before chest compression was started. Blood flow was measured using 15-[micro]m fluorescent microspheres. Less depth of compression was required to maintain the target ADP when cariporide was present in both series 1 (13.6 [+ or -] 1.2 vs. 16.6 [+ or -] 1.2 mm; P < 0.001) and series 2 (15.3 [+ or -] 1.0 vs. 18.9 [+ or -] 1.5 mm; P < 0.001). Despite less compression depth, the cardiac index in cariporide-treated rats was comparable to control rats in series 1 (11.1 [+ or -] 0.7 vs. 11.3 [+ or -] 1.4 ml* [min.sup.-1] * [kg.sup.-1]; P = not significant) but higher in series 2 (15.5 [+ or -] 2.3 vs. 9.9 [+ or -] 1.4 ml * [min.sup.-1] * [kg.sup.-1]; P < 0.05). Increases in compression depth (from series 1 to series 2) increased myocardial, cerebral, and adrenal blood flow in cariporide-treated rats. We conclude that cariporide enhances the efficacy of closed-chest resuscitation by leftward shift of the flow-depth relationship. ventricular fibrillation; cardiopulmonary restiscitation; defibrillation; sodium-hydrogen antiporter; fluorescent microspheres

The underlying mechanism of cell injury during ischemia and reperfusion is complex and timesesnsitive. Some processess develop coincidentally with the onset of ischemia and during reperfusion leading to abnormalities in energy metabolism, acid base status, and intracellular ion homeostasis. Other processes develop later and encompass activation of various signalling pathways that have deleterious or beneficial effects on specific effectors, but associated with sustained disruption of energy production contractile dysfunction and activation of apoptotic pathways. Discussion on the various cell mechanisms resposible for cell injury is beyond the scope of this review. However, pertinent to our discussion is the mounting evidence pointing to mitochondria as key target organelles of reperfusion injury. [ABSTRACT FROM AUTHOR]