Single or multiple brief periods of ischemia (preconditioning) have been shown to protect the myocardium from infarction after a subsequent more prolonged ischemic insult. To test the hypothesis that preconditioning is the result of opening ATP-sensitive potassium (KATP) channels, a selective KATP channel antagonist, glibenclamide, was administered before or immediately after preconditioning in barbital-anesthetized open-chest dogs subjected to 60 minutes of left circumflex coronary artery (LCX) occlusion followed by 5 hours of reperfusion. Preconditioning was elicited by 5 minutes of LCX occlusion followed by 10 minutes of reperfusion before the 60-minute occlusion period. Glibenclamide (0.3 mg/kg i.v.) or vehicle was given 10 minutes before the initial ischemic insult in each of four groups. In a fifth group, glibenclamide was administered immediately after preconditioning. In a final series (group 6), a selective potassium channel opener, RP 52891 (10 jig/kg bolus and 0.1 ,ug/mg/min i.v.) was started 10 minutes before occlusion and continued throughout reperfusion. Transmural myocardial blood flow was measured at 30 minutes of occlusion, and infarct size was determined by triphenyltetrazolium staining and expressed as a percent of the area at risk. There were no significant differences in hemodynamics, collateral blood flow, or area at risk between groups. The ratio of infarct size to area at risk in the control group (28+±6%) was not different from the group pretreated with glibenclamide in the absence of preconditioning (31±6%). Preconditioning produced a marked reduction (p<0.002) in infarct size (28±6% to 6+2%), whereas glibenclamide administered before or immediately after preconditioning completely abolished the protective effect (28±6% and 30±8%, respectively). RP 52891 also produced a significant (p<0.03) reduction (28+6% to 13+±3%) in infarct size. These results suggest that myocardial preconditioning in the canine heart is mediated by activation of KATP channels and that these channels may serve an endogenous myocardial protective role. (Circulation Research 1992;70:223-233) Single or multiple brief periods of ischemia that produce reversible myocyte injury have been shown to limit infarct size after a subsequent more sustained ischemic period.1 This phenomenon has been termed preconditioning and has been shown to occur in a variety of animal species including dogs,1-3 rabbits,4 rats,5 and pigs.6 Recently, Deutsch et a17 have presented evidence that preconditioning also occurs in patients subjected to repeated episodes of percutaneous transluminal coronary angioplasty.

Abstract-Glycogen synthase kinase (GSK) inhibition produced by ischemic preconditioning has been previously shown to be regulated through phosphatidylinositol-3 kinase (PI3K). Therefore, we determined whether opioid-induced cardioprotection (OIC) occurs during reperfusion by altering GSK phosphorylation through PI3K and target of rapamycin (TOR). Furthermore, we determined if selective GSK inhibitors, SB216763(SB21) or SB415286(SB41), emulate OIC. Rats were treated with the nonselective opioid agonist, morphine (MOR, 0.3 mg/kg), the ␦-selective opioid agonist BW373U86 (BW, 1 mg/kg), or the GSK inhibitors, SB21 (0.6 mg/kg) or SB41(1.0 mg/kg), either 10 minutes before ischemia or 5 minutes before reperfusion. Five minutes before opioid or SB21 treatment, some rats received either the PI3K inhibitor wortmannin (15 g/kg) or LY294002 (0.3 mg/kg) or the TOR inhibitor rapamycin (3 g/kg). Key Words: reperfusion Ⅲ glycogen synthase kinase Ⅲ phosphatidylinositol-3 kinase Ⅲ target of rapamycin Ⅲ opioids

Ischemic preconditioning (IPC) is the phenomenon whereby brief periods of ischemia have been shown to protect the myocardium against a sustained ischemic insult. The result of IPC may be manifest as a marked reduction in infarct size, myocardial stunning, or incidence of arrhythmias. While many substances and pathways have been proposed to play a role in the signal transduction mediating the cardioprotective effect of IPC, overwhelming evidence indicates an intimate involvement of the ATP-sensitive potassium channel (K ATP channel) in this process. Initial hypotheses suggested that the surface or sarcolemmal K ATP (sarcK ATP) channel mediated the cardioprotective effects of IPC. However, much research has subsequently supported a major role for the mitochondrial K ATP channel (mitoK ATP) as the one involved in IPC-mediated cardioprotection. This review presents evidence to support a role for the sarcK ATP or the mitoK ATP channel as either triggers and/or downstream mediators in the phenomenon of IPC.

Ischemic or myocardial preconditioning (IPC) is a phenomenon whereby brief periods of ischemia have been shown to protect the myocardium against a more sustained ischemic insult. The result of IPC may be manifest as a marked reduction in infarct size, myocardial stunning, or incidence of cardiac arrhythmias. Whereas many endogenous neurotransmitters, peptides, and hormones have been proposed to play a role in the signal transduction pathways mediating the cardioprotective effect of IPC, nearly universal evidence indicates the involvement of the ATP-sensitive potassium (KATP) channel. Initial evidence suggested that the surface or sarcolemmal KATP (sarcKATP) channel triggered or mediated the cardioprotective effects of IPC; however, more recent findings have suggested a major role for a mitochondrial site or possibly a mitochondrial KATP channel (mitoKATP). This review presents evidence that supports a role for these two channels as a trigger and/or downstream mediator in the phenomenon of IPC or pharmacologically induced PC as well as recent evidence that suggests the involvement of a mitochondrial calcium-activated potassium (mitoKca) channel or the electron transport chain in mediating the beneficial effects of IPC or pharmacologically induced PC.

Signals from the intestinal microbiota are important for normal host physiology; alteration of the microbiota (dysbiosis) is associated with multiple disease states. We determined the effect of antibiotic-induced intestinal dysbiosis on circulating cytokine levels and severity of ischemia/reperfusion injury in the heart. Treatment of Dahl S rats with a minimally absorbed antibiotic vancomycin, in the drinking water, decreased circulating leptin levels by 38%, resulted in smaller myocardial infarcts (27% reduction), and improved recovery of postischemic mechanical function (35%) as compared with untreated controls. Vancomycin altered the abundance of intestinal bacteria and fungi, measured by 16S and 18S ribosomal DNA quantity. Pretreatment with leptin (0.12 μg/kg i.v.) 24 h before ischemia/reperfusion abolished cardioprotection produced by vancomycin treatment. Dahl S rats fed the commercially available probiotic product Goodbelly, which contains the leptin-suppressing bacteria Lactobacillus plantarum 299v, also resulted in decreased circulating leptin levels by 41%, smaller myocardial infarcts (29% reduction), and greater recovery of postischemic mechanical function (23%). Pretreatment with leptin (0.12 μg/kg i.v.) abolished cardioprotection produced by Goodbelly. This proof-of-concept study is the first to identify a mechanistic link between changes in intestinal microbiota and myocardial infarction and demonstrates that a probiotic supplement can reduce myocardial infarct size.

Previous results from our laboratory have suggested that opioid receptors are involved in ischemic preconditioning (PC) in rat heart. Furthermore, other investigators have suggested that mu- and delta-opioid receptors mediate analgesia and hypoxic cerebral vasodilatation via opening of ATP-sensitive K+ (KATP) channels. Thus, the purpose of the present study was to test the hypothesis that activation of opioid receptors mimics the cardioprotective effect of ischemic PC and that this effect is produced by activation of KATP channels in the rat heart. Anesthetized open-chest Wistar rats were subjected to six different protocols. All groups were subjected to 30 minutes of occlusion and 2 hours of reperfusion. Ischemic PC was elicited by three 5-minute occlusion periods interspersed with 5 minutes of reperfusion. Similarly, morphine-induced PC was elicited by three 5-minute drug infusions (100 micrograms/kg i.v. ) interspersed with 5-minute drug-free periods before the prolonged 30-minute occlusion. Infarct size (IS) as a percentage of the area at risk (AAR) was determined by triphenyltetrazolium staining. Ischemic PC and morphine infusions resulted in similar reductions in IS/AAR from 56 +/- 5% to 11 +/- 3% and 12 +/- 5%, respectively (P < .05). Administration of glibenclamide (0.3 mg/kg i.v.), a KATP channel antagonist, or naloxone (3 mg/kg i.v.), a nonselective opioid receptor antagonist, both blocked the cardioprotective effects of morphine. These results indicate that opioid receptor stimulation results in a reduction in infarct size similar to that produced by ischemic PC. The effect of morphine is most likely mediated via an opioid receptor-KATP channel-linked mechanism in the rat heart, since glibenclamide abolished its protection.

The purpose of the present study was to investigate a possible role of opioid receptors in ischemic preconditioning (PC). To test this hypothesis, anesthetized, open-chest, male Wistar rats were subjected to five different protocols. In group I, the control group was subjected to 30 min of left coronary artery occlusion and 2 h of reperfusion. In group II, ischemic PC was elicited by three 5-min occlusion periods interspersed with 5 min of reperfusion. In group III, naloxone (NL, 3 mg/kg iv), a nonselective opioid antagonist, was given to nonpreconditioned rats 10 min before the 30-min occlusion period. Finally, NL was administered 10 min before preconditioning (NL + PC, group IV) or immediately after the last 5-min preconditioning period (PC + NL, group V). Infarct size (IS) as a percentage of the area at risk (AAR) (IS/AAR) was determined by 2,3,5-triphenyltetrazolium chloride staining. PC resulted in a marked reduction in myocardial IS from 45 +/- 5 to 8 +/- 1 (P < 0.05). NL treatment before or immediately after PC abolished this protective effect; however, NL had no effect on IS in non-PC rats. These results are the first to support the hypothesis that activation of opioid receptors may play an important role in ischemic PC in the rat myocardium.

We examined the role of the sarcolemmal and mitochondrial K(ATP) channels in a rat model of ischemic preconditioning (IPC). Infarct size was expressed as a percentage of the area at risk (IS/AAR). IPC significantly reduced infarct size (7 +/- 1%) versus control (56 +/- 1%). The sarcolemmal K(ATP) channel-selective antagonist HMR-1098 administered before IPC did not significantly attenuate cardioprotection. However, pretreatment with the mitochondrial K(ATP) channel-selective antagonist 5-hydroxydecanoic acid (5-HD) 5 min before IPC partially abolished cardioprotection (40 +/- 1%). Diazoxide (10 mg/kg iv) also reduced IS/AAR (36.2 +/- 4.8%), but this effect was abolished by 5-HD. As an index of mitochondrial bioenergetic function, the rate of ATP synthesis in the AAR was examined. Untreated animals synthesized ATP at 2.12 +/- 0.30 micromol x min(-1) x mg mitochondrial protein(-1). Rats subjected to ischemia-reperfusion synthesized ATP at 0.67 +/- 0.06 micromol x min(-1) x mg mitochondrial protein(-1). IPC significantly increased ATP synthesis to 1.86 +/- 0.23 micromol x min(-1) x mg mitochondrial protein(-1). However, when 5-HD was administered before IPC, the preservation of ATP synthesis was attenuated (1.18 +/- 0.15 micromol x min(-1) x mg mitochondrial protein(-1)). These data are consistent with the notion that inhibition of mitochondrial K(ATP) channels attenuates IPC by reducing IPC-induced protection of mitochondrial function.