Effects of ischemic preconditioning on the oxidative stress in small bowel autotransplantation

One determining factor in intestinal transplantation is the bowel's extreme sensitivity to ischemia-reperfusion injury. This study was meant to investigate the effect of ischemic preconditioning prior to autotransplantation. Total orthotopic intestinal autotransplantation was performed in 40 mongrel dogs. Four groups (GI-GIV) were established. In GI and GII grafts were stored in 4 degrees C Euro Collins and University of Wisconsin solutions. In GIII and GIV before preservation IPC was induced by 4 cycles (5-min ischemia + 10-min reperfusion). Three hours of preservation was followed by 1 hour of reperfusion. We determined oxidative stress markers in bowel tissue [reduced glutathione (GSH), superoxide dismutase (SOD)], oxygen free radicals (OFRs) (confocal microscopy), NF-kappa B (gel electrophoretic mobility shift assay), DNA damage (TUNEL). Cold preservation could not prevented against oxidative stress and resulted decrease of SOD activity significantly during reperfusion. In the preconditioned groups the elevated GSH and better preserved SOD activity indicated development of protection. Production of OFRs increased during reperfusion in non-preconditioned groups. Activation of NF-kappa beta was peaking by 1-3 hours following preconditioning. We detected more cells suffered DNA strand breaks in preconditioned groups. Our findings confirm that ischemic preconditioning prior to preservation can moderate the severity of oxidative stress and activate the endogenous celluar adaptation in bowel tissue.     

The effects of preconditioning on the oxidative stress in small-bowel autotransplantation

BACKGROUND: One determining factor in intestinal transplantation is the extreme sensitivity of the small bowel to ischemia-reperfusion injury. This study investigated the effect of ischemic preconditioning prior to autotransplantation. METHODS: Total orthotopic intestinal autotransplantation was performed in 40 mongrel dogs. In 4 groups (GI-GIV), grafts were stored for 3 hours in cold Euro Collins (GI,GIII) and University of Wisconsin (GII,GIV) solutions. In GIII and GIV, before preservation, preconditioning was induced by 4 cycles (5-min ischemia + 10-min reperfusion). Bowel samples were collected after laparotomy (control), at the end of preservation and reperfusion periods. We determined oxidative stress markers (reduced glutathione [GSH], superoxide dismutase [SOD]), production of oxygen free radicals, activity of nuclear factor-kappaB (NF-kappaB), and DNA damage. RESULTS: In the non-preconditioned groups, GSH concentration increased slightly, while SOD activity decreased significantly during reperfusion. In the preconditioned groups, GSH increased markedly, and better preservation of SOD was observed. The number of oxygen free radicals increased during reperfusion mainly in non-preconditioned groups. Activation of NF-kappaB peaked by 1 hour, and decreased 3 hours after preconditioning. We observed DNA-damaged cells in all groups. CONCLUSIONS: Our findings confirm that preconditioning prior to preservation can moderate the severity of oxidative stress and activate the endogenous cellular adaptation in bowel tissue.     

Changes and Effect of PACAP-38 on Intestinal Ischemia-Reperfusion and Autotransplantation

Tissue injury caused by cold preservation and reperfusion during small bowel transplantation remains an unsolved problem. Increasing evidence suggests that pituitary adenylate cyclase-activating polypeptide (PACAP) has protective effects in several ischemia-reperfusion (I/R) models. This study investigated the effect of PACAP-38 on oxidative stress in autotransplanted intestine. We established sham-operated, I/R, and autotransplanted groups in Wistar rats (n = 55). We applied ischemia for 1 (GI), 2 (GII), or 3 hours (GIII). In autotransplanted groups, we performed total orthotopic intestinal autotransplantation. Grafts were preserved in University of Wisconsin (UW) solution for 1 (GIV), 2 (GV), 3 (GVI), or 6 (GVII) hours and in PACAP-38-containing UW for 1 (GVIII), 2 (GIX), 3 (GX), or 6 (GXI) hours. Reperfusion lasted 3 hours in each group. Endogenous PACAP-38 values were measured by radioimmunoassay. Oxidative stress parameters malondialdehyde (MDA), reduced glutathione (GSH), and superoxide dismutase (SOD) were measured in tissue homogenates. Concentration of endogenous PACAP-38 significantly decreased in GI to GIII compared with the sham-operated animals following I/R periods (P < .05). Cold preservation in UW and reperfusion of the intestine increased the level of tissue MDA in GIV to GVII, which correlated with the duration of cold storage. The content of GSH decreased in GIV to GVII to levels that were significantly different between GIV and GVIII and between GVII and GXI. SOD activity decreased dramatically in GIV to GVII with significantly higher activity in GIX to GXI. Our findings confirmed that I/R decreased endogenous PACAP-38 concentration. Administration of PACAP-38 to UW solution mitigated the oxidative injury during intestinal autotransplantation.     

Potential for left ventricular assistance by latissimus dorsi myograft--sequential effects of electrical preconditioning on skeletal muscle fiber type, blood flow and metabolic status

In order to evaluate the possibility of left ventricular assistance by latissimus dorsi (LD) myograft, we have studied contractile property and fatigue rates of skeletal muscle ventricle (SMV) constructed using canine LD muscles. Twenty three dogs were divided into 3 groups depending on the conditioning protocol of LD muscles; Group I (Control n = 12), Group II (Vascular delay n = 4) and Group III (Vascular delay and electrical preconditioning n = 7). SMVs in GIII dogs generated sufficient pressure and forward flow in a hydraulic test system with muscle stimulation at a burst-frequency of 50 Hz (SMV pressure 131 +/- 42 mmHg, Stroke volume 7.0 +/- 3.0 ml/beat). Although SMVs in GI and GII dogs could sustain flow for only 4.0 +/- 1.1 minutes and 32.4 +/- 14.0 minutes, respectively, SMVs in GIII were able to pump continuously for 107.5 +/- 15.0 minutes (p less than 0.01, vs GI and GII). Thermography surface temperature mapping revealed marked improvement of blood distribution of LD muscles in GII and GIII dogs. Flow rates of thoracodorsal artery during SMV stimulation were GI: 10.0 +/- 3.1 ml/minute/LD 100 g, GII: 15.0 +/- 3.7 ml/minutes/100 g and GIII: 20.7 +/- 2.5 ml/minutes/100 g (p less than 0.01 vs GI). The ratio of oxygen consumption to lactate output was GI: 0.33 +/- 0.10, GII: 0.36 +/- 0.09 and GIII: 1.56 +/- 0.97 (p less than 0.01 vs GI, p less than 0.05 vs GII). Histochemical examination of LD muscles using alkaline ATPase stain revealed muscle fiber type transformation of GIII muscles. These results suggest electrically preconditioned LD muscles have sufficient contractile property for partial left ventricular assistance, and highly fatigue-resistant properties resulted from muscle fiber transformation, improved muscle perfusion and metabolic changes.     

Threshold level of NF-kB activation in small bowel ischemic preconditioning procedure

Ischemic preconditioning (IPC), which is obtained by exposure to brief periods of vascular occlusion, improves organ tolerance to prolonged ischemia. The aim of this study was to evaluate the threshold level of NF-kB activation in small intestine during an IPC procedure. Various intestinal IPC were performed on 20 Wistar rats in seven groups: group I (GI, nonpreconditioned); group II (GII, 1-minute ischemia and 1-minute reperfusion); group III (GIII, two cycles of 1-minute ischemia and 1-minute reperfusion); group IV (GIV, 2-minutes ischemia and 2-minutes reperfusion); group V (GV, two cycles of 2-minute ischemia and 2-minute reperfusion); group VI (GVI, 5-minute ischemia and 10-minute reperfusion); group VII (GVII, two cycles of 5-minute ischemia and 10-minute reperfusion). Bowel biopsies were collected after laparotomy (control) as well as at 30, 60, and 120 minutes following IPC. We determined the cytoplasmic and nuclear NF-kB by a chemiluminescence-based ELISA method. Our results showed low, constant NF-kB levels in GI. In the preconditioned groups (GII-GVII), NF-kB was significantly elevated at 30 minutes following IPC (P < .05 vs control). After 1 hour, NF-kB activity decreased to the control level. However, 2 hours after IPC both forms of NF-kB were elevated significantly again, which was independent of the number of IPC cycles (P < .05 vs control). Our experiments revealed that one cycle of 1-minute ischemia and 1-minute reperfusion is a critical threshold level for NF-kB activation during small bowel IPC. Longer and more IPC cycles did not result in further elevation of NF-kB activation.     

Ischemic preconditioning and liver tolerance to warm or cold ischemia: experimental studies in large animals

BACKGROUND: In the rodent, ischemic preconditioning (IPC) has been shown to improve the tolerance of the liver to ischemia-reperfusion under normothermic or hypothermic conditions. The aim of the present study was to test this hypothesis in a dog model, which may be more relevant to the human. METHODS: Beagle dogs were used in two distinct animal models of hepatic warm ischemia and orthotopic liver transplantation (hypothermic ischemia). IPC consisted of 10 minutes of ischemia followed by 10 minutes of reperfusion. In the first model, livers were exposed to 55 minutes prolonged warm ischemia and reperfused for 3 days (n = 6). In the second model, livers were retrieved and preserved for 48 hours at 4 degrees C in University of Wisconsin solution, transplanted, and reperfused without immunosuppression for 7 days (n = 5). In each model, nonpreconditioned animals served as controls (n = 5 in each group). Also, isolated dog hepatocytes were subjected to warm and cold storage ischemia-reperfusion to model the animal transplant studies using IPC. RESULTS: In the first model (warm ischemia), IPC significantly decreased serum aminotransferase activity at 6 and 24 hours post-reperfusion. After 1 hour of reperfusion, preconditioned livers contained more adenosine triphosphate and produced more bile and less myeloperoxidase activity (neutrophils) relative to controls. In the second model (hypothermic preservation), IPC was not protective. Finally, IPC significantly attenuated hepatocyte cell death after cold storage and warm reperfusion in vitro. CONCLUSIONS: IPC is effective in large animals for protecting the liver against warm ischemia-reperfusion injury but not injury associated with cold ischemia and reperfusion (preservation injury). However, the IPC effect observed in isolated hepatocytes suggests that preconditioning for preservation is theoretically possible.     

Differences in prolonged ischemia length using ischemic preconditioning in the rabbit heart. Tolerable limitation time for surgically induced myocardial ischemia during normothermic cardiac operation

BACKGROUND: To determine the effect of the tolerable limitation time of prolonged ischemia after ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart. METHODS: White rabbits (n=30) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 min; 30 min global ischemia hearts (30GI) received 30 min global ischemia and 120 min reperfusion; IPC+30GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 30 min global ischemia; 20 min global ischemia hearts (20GI) received 20 min global ischemia and 120 min reperfusion; IPC+20GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 20 min global ischemia. RESULTS: Infarct size in the 30GI hearts was 33.5+/-4.0% and 1.7+/-0.5% in the control hearts. The 20GI hearts and IPC+30GI hearts decreased infarct size, as compared with the 30GI hearts (13.0+/-1.8% and 16.6+/-1.7%, respectively; p<0.001, 20GI vs 30GI; p<0.01, IPC+30GI vs 30GI; p>0.05, 20GI vs IPC+30GI) but did not enhance postischemic functional recovery. The IPC+20GI hearts (3.5+/-0.6%) significantly decreased infarct size as compared with the 20GI hearts (p<0.05, IPC+20GI vs 20GI), and there was no significant difference between the IPC+20GI and the control hearts (p>0.05), but the IPC+20GI hearts did not enhance postischemic functional recovery. CONCLUSIONS: A 20 min ischemia may be the tolerable limitation time of prolonged ischemia after ischemic preconditioning in an isolated rabbit heart model.     

Pharmacological preconditioning with the adenosine triphosphate-sensitive potassium channel opener pinacidil

BACKGROUND: Ischemic preconditioning (IPC) decreases infarct size after global or regional ischemia. Potassium channel openers also precondition but are subject to dose-limiting vasodilation. We compared the mechanical and electrophysiological effects of ischemic and pharmacological preconditioning in an isolated rabbit heart model. METHODS: Rabbit hearts were preconditioned with either 10 micromol/L pinacidil alone (P-), 10 micromol/L pinacidil with 10 micromol/L phenylephrine (P+), or two cycles of global ischemia and reperfusion (IPC) before 1 hour of LAD occlusion. Left ventricular pressure, epicardial monophasic action potential duration (APD) and coronary flow were monitored throughout. Infarct size was determined at the end of reperfusion. RESULTS: Regional ischemia uniformly decreased APD (p<0.05). During reperfusion, APDs were prolonged beyond preischemic values in all preconditioned groups (p<0.05). P- and P+ reduced the incidence of fibrillation. P- significantly increased coronary flow (+15%, p = 0.001), whereas IPC and P+ did not. However, IPC and P- significantly decreased systolic function (p<0.05) but P+ did not. In addition, IPC depressed diastolic function (p<0.05) but P- and P+ did not. Infarct size was reduced by all methods (p<0.05). CONCLUSIONS: Pinacidil presents a safe and effective alternative to IPC for preserving the heart during regional ischemia. Its coronary vasodilatory effects are safely and effectively reversed by the addition of phenylephrine.     

Selective mitochondrial adenosine triphosphate-sensitive potassium channel activation is sufficient to precondition human myocardium

OBJECTIVES: Recently, the mitochondrial adenosine triphosphate-sensitive potassium channel has been suggested to be the final common effector of myocardial preconditioning. The purpose of this study is to determine whether selective mitochondrial adenosine triphosphate-sensitive potassium channel activation alone can precondition human myocardium from an ischemia/reperfusion insult. METHODS: Isolated human right atrial trabeculae were placed in tissue baths, paced, and subjected to 30 minutes of normothermic hypoxia (ischemia) followed by 45 minutes of reoxygenation (reperfusion). Trabeculae were preconditioned with a selective mitochondrial adenosine triphosphate-sensitive potassium channel opener (diazoxide 30 micromol/L) or a nonselective purinergic agonist, adenosine (125 micromol/L), for 5 minutes (adenosine) followed by a 10-minute washout period. Developed force at end reperfusion (mean +/- standard error) was compared with baseline, and tissue creatine kinase and adenosine triphosphate levels were measured after ischemia/reperfusion. RESULTS: Trabeculae subjected to ischemia/reperfusion exhibited 30% +/- 2% of baseline developed force, whereas trabeculae subjected to selective adenosine triphosphate-sensitive potassium channel opening (diazoxide) and nonselective purinergic agonist (adenosine) recovered to 55% +/- 7% and 46% +/- 3% of baseline developed force, respectively. Tissue creatine kinase activity was preserved in both the diazoxide- and adenosine-treated trabeculae (5.4 +/- 12 and 5.4 +/- 14 micromol/L per gram wet tissue) compared with ischemia/reperfusion (1.8 +/- 0.2 U/mg wet tissue). Adenosine triphosphate levels at end reperfusion were also increased in the trabeculae treated with selective (diazoxide) and nonselective (adenosine) adenosine triphosphate-sensitive potassium channel opener (4.1 +/- 0.01 and 4. 4 +/- 0.2 micromol/L per gram wet tissue) compared with trabeculae subjected to ischemia/reperfusion (1.5 +/- 0.1 micromol/L per gram wet tissue). CONCLUSIONS: These results suggest that selective mitochondrial adenosine triphosphate-sensitive potassium channel activation preconditions human myocardium and the protection conferred is equal to that of adenosine preconditioning. Targeted openers of mitochondrial adenosine triphosphate- sensitive potassium channels promote constructive protection of myocellular energy levels, contractile function, and cellular viability in human myocardium after ischemia/reperfusion.     

Amrinone preconditioning in the isolated perfused rabbit heart

BACKGROUND: Ischemic preconditioning (IPC) reduces infarct size in experimental preparations. IPC, however, is not without detrimental effects. We studied amrinone as a possible alternative to IPC. METHODS: Isolated perfused rabbit hearts were given a 5-minute infusion of 10 micromol/L amrinone followed by a 5-minute washout (n = 6). The anterior descending artery was then occluded for 1 hour and reperfused for 1 hour. Six hearts underwent IPC, with two episodes of 5-minute global ischemia followed by 5-minute reperfusion before LAD occlusion; eight control hearts received no preconditioning. Left ventricular pressure and ischemic zone epicardial monophasic action potentials were continuously monitored. RESULTS: IPC but not amrinone reduced peak pressure before anterior descending artery occlusion. Peak pressure fell significantly during ischemia and reperfusion in all hearts. End diastolic pressure rose significantly during reperfusion in control and IPC hearts but not in amrinone hearts. Action potentials shortened during ischemia in all hearts. They returned to preocclusion values in control hearts but lasted beyond preocclusion values in IPC and amrinone hearts. Both the incidences of ventricular fibrillation and infarct size were significantly reduced in amrinone hearts but not in IPC hearts. CONCLUSIONS: Amrinone is not only a useful inotropic agent but is also a superior preconditioning agent when compared to IPC.     

Does adenosine administration during the early reperfusion period affect ischemic preconditioning?

We hypothesized that the adenosine administration during the early reperfusion period might affect ischemic preconditioning (IPC) and might reduce infarct size and enhance post-ischemic functional recovery. Twenty-four anesthetized rabbits underwent 30 min. normothermic global ischemia with 120 min. reperfusion in a buffer-perfused isolated, paced heart model and divided into four groups. Global ischemic hearts (GI, n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n=6) were subjected to perfusion without ischemia. Ischemic preconditioned hearts (IPC, n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. IPC + Ado hearts (n=6) received IPC and adenosine administration (100 m mol/L) during 3 min. early reperfusion period. Post-ischemic functional recovery was better in IPC + Ado hearts as compared to GI and IPC hearts, but the effect of post-ischemic functional recovery in IPC + Ado hearts became weaker during 120 min. reperfusion after prolong ischemic insult. Infarct size wre 1.0 ± 0.3% in Control hearts, 32.9 ± 5.1% in GI hearts, 13.8 ± 1.3% in IPC hearts and 8.1 ± 0.9% in IPC + Ado hearts. Infarct size in IPC hearts was significantly decreased (p<0.01) as compared to GI hearts. The reduction rate against myocardial necrosis in IPC + Ado hearts versus GI hearts was higher as compared to IPC hearts versus GI hearts (p<0.001, IPC+Ado hearts vs GI hearts; p<0.01, IPC hearts vs GI hearts; p = ns, IPC + Ado hearts vs Control hearts). These data suggest that adenosine administration during the early reperfusion period reinforce IPC effect and reduce myocardial reperfusion injury. Cardiomyoprotective effects of IPC and exogenous adenosine are exerted during early reperfusion after coronary occlusion in the isolated perfused rabbit hearts.     

Intestinal ischemic preconditioning in rats and NF-kappaB activation

Cold preservation prior to small-bowel transplantation can moderate tissue injury, although it is unable to protect the bowel graft from acute reperfusion injury. One method to reduce oxidative stress is ischemic preconditioning (IPC). The limited data regarding IPC of the bowel encouraged us to investigate the key factor in this process, i.e., the activation of nuclear factor-kappa binding (NF-kB) in bowel tissue. The intestine was preconditioned by various cycles of IPC on rats. Activation of NF-kB was detected by a chemiluminescence-based ELISA method. Our findings showed that NF-kB level was elevated significantly 30 min after IPC. One hour following IPC, NF-kB decreased to control level; 2 h after IPC, the level significantly increased again. These changes were independent of the number of IPC cycles. Our experiments with various IPC cycles revealed that even a very short IPC cycle was able to activate the IPC cascade in small-bowel tissue.     

Influence of Pituitary Adenylate Cyclase-Activating Polypeptide on the Activation of Mitogen Activated Protein Kinases Following Small Bowel Cold Preservation

Cold preservation prior to small bowel transplantation can moderate tissue oxidative injury. This stress triggers several intracellular pathways via mitogen activated protein (MAP) kinases. MAP kinases include the extracellular signal related kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAP kinase. Pituitary adenylate cyclase-activating polypeptide (PACAP) plays a central role in intestinal physiology. We sought to investigate the effect of PACAP on the activation of MAP kinases during cold preservation of the small bowel. Total orthotopic intestinal autotransplantation was performed on 40 Wistar rats. Perfused grafts were stored in University of Wisconsin (UW) solution for 1 (GI), 2 (GII), 3 (GIII), or 6 hours (GIV) without or with 30 PACAP, namely 1 (GV), 2 (GVI), 3 (GVII), or 6 hours (GVIII). After 3 hours of reperfusion in all groups, the activation of MAP kinases were measured using immunocytochemistry of small bowel tissue. Among the UW preserved grafts (GI-GIV), phosphorylated ERK1/2 level were decreased, while phosphorylated JNK1/2 and p38 MAP kinase activation were elevated compared with control levels. In GV-GVIII PACAP we observed enhanced phospho-ERK1/2 appearance with decreased JNK and p38 MAP kinase activity at the end of the reperfusion periods. We concluded that cold preservation decreased phosphorylated ERK1/2 levels and increased JNK1/2 and p38 MAP kinase activities, which meant that cold storage triggered apoptotic cell death. In contrast, PACAP treatment induced signalling pathways protective against oxidative injury by MAP kinases in bowel tissue.     

Activation of beta2-adrenergic receptor plays a pivotal role in generating the protective effect of ischemic preconditioning in rat hearts

BACKGROUND: Ischemic preconditioning (IPC) protects hearts against ischemia by reducing infarct size. However, IPC does not preserve cardiac function, such as left ventricular peak developed pressure (LVPDP). Moreover, IPC fails to protect the post-myocardial infarct (MI) heart. DESIGN: Rat hearts were transfected with beta2-adrenergic receptor (B2AR) cDNA by the hemagglutinating virus of Japan-liposome method. After the gene transfer, the hearts were perfused in a Langendorff mode and preconditioned with two cycles of 5 min of ischemia and reperfusion. After 20 min of global ischemia, the hearts were reperfused under aerobic conditions for 90 min. LVPDP was measured as an indicator of the cardiac function. RESULTS: LVPDP of ischemic hearts was well preserved by the combination treatment of IPC and gene transfer of B2AR, but not IPC or gene transfer of B2AR alone. Moreover, the treatment was beneficial to even the post-MI heart. On the contrary, gene transfer of beta-adrenergic receptor kinase 1 (BARK1) reduced the protective effect of IPC. We also found that the mRNA ratio of B2AR and BARK1 was well correlated with the preservation of the LVPDP. CONCLUSIONS: The combination treatment of IPC and gene transfer of B2AR protects cardiac function against ischemia and it shows the beneficial effect also in post-MI hearts.     

L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts.

OBJECTIVE: Ischaemic or pharmacological preconditioning with L-arginine has been reported to be insufficient for optimal cardioprotection. The ability of nitric oxide (NO) to enhance ischaemic preconditioning was assessed, and the role of L-arginine-induced ischaemic preconditioning in myocardial protection was determined. METHODS: Isolated rat hearts were prepared and divided into six groups: control hearts (control, n=6) were perfused without global ischaemia at 37 degrees C for 160 min; global ischaemia hearts (GI, n=6) were subjected to ischaemia for 20 min and reperfusion for 120 min; ischaemic preconditioned hearts (IP, n=6) received 2 min of zero-flow global ischaemia followed by 5 min reperfusion, before 20 min of global ischaemia; L-arginine hearts (ARG, n=6) received 1 mmol/l L-arginine for 5 min, before 20 min of global ischaemia; ischaemic preconditioning plus nitro-L-arginine methyl ester hearts (IP+L-NAME, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 3 mmol/l L-NAME in Krebs-Henseleit buffer, before 20 min of global ischaemia; and ischaemic preconditioning plus L-arginine hearts (IP+ARG, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 1 mmol/l L-arginine in Krebs-Henseleit buffer. Haemodynamic parameters and coronary flow were recorded continuously. Nitrites and nitrates (NOx) were measured 5 and 60 min after reperfusion, and infarct size was also determined. RESULTS: In the IP+ARG group, significant amelioration and preservation of left ventricular peak developed pressure and coronary flow was observed compared with the GI, IP, ARG and IP+L-NAME groups. Infarct size in the IP+ARG group was reduced significantly compared with that in the GI, IP, ARG and IP+L-NAME groups. Significant preservation of NOx was observed during reperfusion in the IP+ARG group compared with the GI group. CONCLUSIONS: Inhibition of NO synthase with L-NAME had little impact on ischaemic preconditioning, suggesting that endogenous NO is not a major mediator of ischaemic preconditioning. Nevertheless, enhancement of the effects of ischaemic preconditioning can be achieved with L-arginine, a precursor of NO, improving post-ischaemic functional recovery and infarct size in the isolated rat heart.     

Is ischemic preconditioning of the kidney clinically relevant?

BACKGROUND: Renal ischemic preconditioning (IPC) is a phenomenon whereby a brief period of ischemia and reperfusion (I/R) provides tolerance to subsequent periods of ischemia. IPC has been demonstrated to protect rodent kidneys during I/R. The applicability to large mammals, including human beings, is unclear. The objective of this study was to determine if renal IPC has a beneficial effect in a large animal model of warm I/R and hypothermic preservation injury, which occurs with renal allografting. METHODS: Renal ischemia (45 minutes) and reperfusion was studied in untreated dogs and in dogs receiving IPC (10-minute/10-minute I/R). IPC was administered immediately before I/R (early IPC) or 24 hours before I/R (delayed IPC). In another group of dogs, pharmacologically induced IPC was attempted with local intra-arterial administration of dipyridamole (2.4 mg/kg/min) to increase local adenosine concentrations. Finally, IPC was induced in kidneys before harvest, cold stored for 24 hours in University of Wisconsin flush solution, and subsequently reperfused for 4 hours in allogeneic recipients. Renal functional parameters, including vascular resistance, glomerular filtration rate, urine production, oxygen consumption, and proximal tubular fluid reabsorption, were monitored during the reperfusion period and were compared with the control ischemic group. RESULTS: Renal function significantly declined during I/R, relative to the nonischemic contralateral kidney but was not different with any form of IPC, relative to the ischemic control group not treated with IPC. IPC pretreatment also did not affect the preservation injury observed in cold-stored kidneys reperfused after transplantation. CONCLUSIONS: It is concluded that IPC has no significantly measurable effects in warm or hypothermic renal I/R injury in large animals. The clinical usefulness of IPC in human renal ischemic conditions remains uncertain.     

Ischaemic preconditioning causes increased myocardial vascular resistance but no myocardial contractility changes in pigs after OPCAB

The coronary vascular resistance (CVR) after off pump coronary bypass (OPCAB) surgery has never been clarified and ways of preventing stunning are wanted. We wished to investigate the effect of ischaemic preconditioning (IPC) on the CVR and stunning in the postoperative period after OPCAB. In 20 pigs (80 kg), 7 piezo-electric crystals were placed on the left ventricle to assess global and local myocardial contractility. Coronary vascular resistance was measured as the relation between perfusion pressure and coronary artery blood flow. IPC was obtained in ten pigs with one period of 10 min of coronary occlusion, followed by 15 min of reperfusion and 20 min of ischaemia. Ten control animals were exposed to 20 min of ischaemia only. Reperfusion was allowed for 120 min. The CVR was higher in the IPC group (measured by the slopes of the curves in the reperfusion period) (IPC: -0.33 (CI: (-0.62)-(-0.03)); Control: 0.31 (CI: (-0.03)-(0.67)), P<0.005. There was no difference in the local myocardial contractility (slopes of the curves in the reperfusion period) (IPC: -0.004+/-0.01; Control: -0.005+/-0.01). In conclusion, there was no alteration in myocardial contractility, but increased CVR in the early reperfusion period in animals preconditioned before sustained ischaemia.     

Calcium preconditioning, but not ischemic preconditioning, bypasses the adenosine triphosphate-dependent potassium (KATP) channel.

BACKGROUND: Recent evidence has implicated the KATP channel as an important mediator of ischemic preconditioning (IPC). Indeed, patients taking oral sulfonylurea hypoglycemic agents (i.e., KATP channel inhibitors) for treatment of diabetes mellitus are resistant to the otherwise profoundly protective effects of IPC. Unfortunately, many cardiopulmonary bypass patients, who may benefit from IPC, are chronically exposed to these agents. Calcium preconditioning (CPC) is a potent form of similar myocardial protection which may or may not utilize the KATP channel in its mechanism of protection. The purpose of this study was to determine whether CPC may bypass the KATP channel in its mechanism of action. If so, CPC may offer an alternative to IPC in patients chronically exposed to these agents. METHODS: Isolated rat hearts (n = 6-8/group) were perfused (Langendorff) and received KATP channel inhibition (glibenclamide) or saline vehicle 10 min prior to either a CPC or IPC preconditioning stimulus or neither (ischemia and reperfusion, I/R). Hearts were subjected to global warm I/R (20 min/40 min). Postischemic myocardial functional recovery was determined by measuring developed pressure (DP), coronary flow (CF), and compliance (end diastolic pressure, EDP) with a MacLab pressure digitizer. RESULTS: Both CPC and IPC stimuli protected myocardium against postischemic dysfunction (P < 0.05 vs I/R; ANOVA with Bonferroni/Dunn): DP increased from 52 +/- 4 (I/R) to 79 +/- 2 and 83 +/- 4 mmHg; CF increased from 11 +/- 0.7 to 17 +/- 2 and 16 +/- 1 ml/min; and EDP decreased (compliance improved) from 50 +/- 7 to 27 +/- 5 and 31 +/- 7 mmHg. However, KATP channel inhibition abolished protection in hearts preconditioned with IPC (P < 0.05 vs IPC alone), but not in those preconditioned with CPC (P > 0.05 vs CPC alone). CONCLUSIONS: (1) Both IPC and CPC provide similar myocardial protection; (2) IPC and CPC operate via different mechanisms; i.e., IPC utilizes the KATP channel whereas CPC does not; and (3) CPC may offer a means of bypassing the deleterious effects of KATP channel inhibition in diabetic patients chronically exposed to oral sulfonylurea hypoglycemic agents.     

山茛菪碱对大鼠移植肝脏保护作用的实验研究

目的 利用山莨菪碱具有稳定细胞膜和抗氧自由基损伤的作用,在低温保存期间用山茛菪碱对移植肝脏进行保护,从百改善移植肝脏的质量。方法 建立大鼠下腔静脉内分流法自体原位肝移植动物模型。动态观察肝脏氧自由基及酶学的变化。结果 实验组用山茛菪碱可减少再灌注后脂质过氧化物酶（ＬＰＯ０的增加,超氧化物歧化酶（ＳＯＤ）和谷胱甘肽过氧化物酶的下降,丙氨酸转氨酶乳酸脱氢酶的升高,与对照组比较,Ｐ〈０．０１。     

Ischemic preconditioning improves preservation with cold blood cardioplegia in valve replacement patients.

OBJECTIVE: The purpose of this study was to test the hypothesis that ischemic preconditioning improves myocardial protection in valve replacement patients undergoing cold-blood cardioplegic arrest and to study the mechanisms of human myocardial ischemic preconditioning initially. METHODS: Forty patients who required double valve replacement were studied. After the institution of cardiopulmonary bypass, 20 patients were preconditioned with two cycles of 3 min of aortic cross-clamping and 2 min of reperfusion before cardioplegic arrest (group IP). Twenty patients were not preconditioned as controls (group C). All hearts were arrested with 4 degrees C cold-blood cardioplegic solution. During perioperation, the blood samples were collected from coronary sinus and radial artery, which were used to measure calcitonin gene-related peptide (CGRP) and creatine kinase-MB (CK-MB). The right atrial myocardial tissue was collected to measure superoxide dismutase/malondialdehyde (T-SOD/MDA) and to observe myocardial ultrastructure. Hemodynamic date were measured. RESULTS: After reperfusion for 30 min, myocardial MDA was significantly lower in group IP than in group C (2.6+/-0.2 vs. 3.8+/-0.3 nM/mg) and T-SOD was significantly higher in group IP than in group C (13.1+/-12.1 vs. 9.2+/-1.2 IU/mg). Ischemic preconditioning significantly increased the production of myocardial CGRP just after preconditioning (92.0+/-4.1 vs. 52.3+/-4.5 pg/ml) and the begin of reperfusion (95.3+/-3.8 vs. 61.2+/-4.9 pg/ml), and deduced the release of CK-MB at 12 h post-reperfusion (77.5+/-9.2 vs. 136.5+/-8.9 IU/l). Preconditioning also improved cardiac function at 30 min and 12 h after reperfusion (cardiac index 2.8+/-0.3 vs. 2.3+/-0.2 l/min per m2 and 2.9+/-0.1 vs. 2.4+/-0.2 l/min per m2). CONCLUSIONS: Ischemic preconditioning enhance cardioplegic protection in valve replacement patients. The possible protective mechanism was that ischemic preconditioning decreased the production of oxygen free radicals.