Ischemic preconditioning improves liver microcirculation after ischemia/reperfusion

[Hemodynamic effects of N-acetylcysteine and ischemic preconditioning in a liver ischemia-reperfusion model]

The aim of the study was to investigate whether repeated ischemic preconditioning or N-acetylcysteine (NAC) prevents ischemic-reperfusion injury as determined by having favourable hemodynamic effects during reperfusion in canine livers.

METHODS

The control group ( n = 10) underwent 60 minutes of hepatic ischemia followed by 180 minutes reperfusion. In the NAC group ( n = 5) 150 mg kg -1 of NAC was administered intravenously before inducing ischemia. In the preconditioned group ( n = 5) animals received ischemic preconditioning (10 minutes of ischemia followed by 10 minutes of reperfusion repeated three times) before clamping the portal triad.

RESULTS

18 dogs survived the study period. One dog in the NAC group died due to circulatory failure unresponsive to inotropic drugs. The cardiac index and the intrathoracic blood volume index were significantly higher in the preconditioning group compared to the controls throughout the study period.

CONCLUSIONS

Repeated ischemic preconditioning might improve hemodynamic parameters, whereas we were unable to find any significant differences between the groups regarding N-acetylcysteine.

Ischemic preconditioning enhances regenerative capacity of hepatocytes in long-term ischemically damaged rat livers

BACKGROUND AND AIMS

Ischemic preconditioning (IPC) protects tissues against ischemia and reperfusion (I/R) injury. The aim of this study was to examine the impact of IPC on protection and regeneration of hepatocytes after prolonged I/R injury.

METHODS

A rat model of segmental (70%) hepatic ischemia was used to determine the effect of 10-min IPC preceding 40, 60, 90, or 120 min of liver ischemia. The effect was assessed by comparing cytolysis markers and necrotic areas of the liver, as well as the regenerative capacity of hepatocytes using the proliferating cell nuclear antigen labeling index (PCNA-LI) and weight of the ischemic liver lobe. Protein kinase B/Akt (Akt) and caspase-9 were investigated immunohistochemically to determine the effect of IPC on activation of survival and anti-apoptotic signals.

RESULTS

In the model of 40 min I/R, which resulted in focal necrosis of the liver, IPC significantly protected against I/R injury by reducing the area of focal necrosis, level of PCNA-LI and immunoreactivities to Akt and caspase-9. In contrast, IPC did not prevent ischemic damage in the 90- and 120-min ischemic model with massive liver necrosis. However, IPC enhanced the regenerative capacity of the remaining hepatocytes with higher levels of PCNA-LI, number of Akt-positive cells and mean weight of the liver lobe postoperatively than in the controls.

CONCLUSIONS

In a model of focal necrosis of the liver, IPC protected hepatocytes against I/R injury. In addition, in a model of massive necrosis, IPC maintained the regenerative capacity of the remaining hepatocytes by enhancing the survival signals.

Vascular Delay Revisited

The technique of vascular delay has been used by plastic surgeons for nearly 500 years and has proven useful for reliably transferring tissue and allowing for a greater volume of tissue to be reliably harvested. Delay procedures are an essential plastic surgical tool for a variety of aesthetic and reconstructive procedures. Despite the widespread use of vascular delay procedures, the mechanism by which this phenomenon occurs remains unclear. A number of groups have exhaustively examined microvascular changes that occur during vascular delay. Theories have been proposed ranging from the dilation of choke vessels to changes in metabolism and new blood vessel formation. Inherent in these theories is the concept that ischemia is able to act as the primary stimulus for vascular changes. The purpose of this review is to revisit the theories proposed to underlie the delay phenomenon in light of recent advances in vascular biology. In particular, the participation of bone marrow-derived endothelial progenitor cells in the delay phenomenon is explored. Greater understanding of the role these cells play in new blood vessel formation will be of considerable clinical benefit to high-risk patients in future applications of delay procedures.

El preacondicionamiento isquémico del hígado: de las bases moleculares a la aplicación clínica

Ischemia-reperfusion injury is produced when an organ is deprived of blood flow (ischemia), which is then restored (reperfusion). In certain circumstances, this injury leads to irreversible organ damage. Several therapeutic strategies have been used to reduce the severity of this injury. One of these strategies is the application of brief and repetitive episodes of ischemia-reperfusion before prolonged ischemia-reperfusion (ischemic preconditioning). In the present article we review the molecular mechanisms through which ischemic preconditioning confers protection against ischemia-reperfusion injury. The application of ischemic preconditioning during liver surgery is discussed, both in normothermic situations such as liver resection and in situations of low temperature such as liver transplantation.

Dynamic changes of post-ischemic hepatic microcirculation improved by a pre-treatment of phosphodiesterase-3 inhibitor, milrinone

BACKGROUND

Phosphodiesterase-3 inhibition has been shown to attenuate hepatic warm ischemia-reperfusion injury. The aim of this study was to investigate the effect of milrinone, phosphodiesterase-3 inhibitor, on post-ischemic microcirculation of rat livers by intravital microscopy.

MATERIALS AND METHODS

Male Wistar rats were randomly assigned to three groups; group A, milrinone pre-treatment; group B, ischemic pre-conditioning; and group C, no pre-treatment. All animals underwent a 60-min warm ischemia of the left lateral liver lobe. Microvascular perfusion and leukocyte-endothelial interaction were observed by intravital videomicroscopy. Hepatocellular viability and cellular damage were quantified by adenosine triphosphate tissue concentration as well as alanine aminotransferase and lactate dehydrogenase blood levels, respectively.

RESULTS

In groups A and B, cyclic AMP hepatic tissue concentration was elevated significantly. After reperfusion, microvascular perfusion in hepatic sinusoids was significantly better maintained, and the number of adherent leukocytes was reduced in sinusoids and in post-sinusoidal venules in these rats. Serum transaminase blood levels were suppressed significantly in these groups compared with controls.

CONCLUSION

The demonstrated improvement of hepatic microcirculation is certainly derived from milrinone induced cell protection in ischemia reperfusion of the liver. This effect is outlined by improved energy status and reduced liver enzyme liberation and mimics the effect of ischemic pre-conditioning.

Ischemic preconditioning prevents apoptotic cell death and necrosis in early and intermediate phases of liver ischemia-reperfusion injury in rats

Ischemic preconditioning (IPC) may be useful in attenuating the hepatic ischemia reperfusion (IR) syndrome by means of improving cell resistance to anoxia and reoxygenation and preventing cell death. Since there are insufficient data available regarding the chronology of preconditioning effects, we investigated the role of IPC, to test the hypothesis that liver protection would occur during the early and intermediate phases of the reperfusion period. Wistar rats (n = 72) were randomly assigned into six experimental groups, 12 animals each. A 40-min ischemia to the left lateral and median liver lobes was induced by selective hepatic pedicle clamping followed by 30 min or 240 min of reperfusion (IR30 and IR240). IPC groups (IPC30 and IPC240) underwent a 10 min of ischemia followed by 10 min of reperfusion preceding the definitive 40-min ischemic period. Sham-operated animals were followed for 30 and 240 min. Hepatic enzymes and histological evaluation were performed after the reperfusion period. Hepatic ischemia-reperfusion (IR30 and IR240) induced marked increases in liver enzymes levels after 30 min and particularly after 240 min. IPC effectively attenuated those enzymatic increases. Microvesicular steatosis was observed after 30 min, but not 240 min, of reperfusion in both IPC and IR livers. Necrosis was detected in 66.7% of IR240 and only in 8.3% of IPC240. Both hepatocyte and sinusoidal apoptosis were markedly attenuated by IPC. We conclude that IPC provided protection against hepatic ischemia reperfusion injury in early and intermediate phases of the reperfusion period, reducing hepatic enzymatic leakage and ameliorating hepatic apoptosis and necrosis.

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.

Ischaemic preconditioning in transplantation and major resection of the liver

BACKGROUND

Ischaemia-reperfusion injury (IRI) contributes significantly to the morbidity and mortality of transplantation and major resection of the liver. Its severity is reduced by ischaemic preconditioning (IP), the precise mechanisms of which are not completely understood. This review discusses the pathophysiology and role of IP in this clinical setting.

METHODS

A Medline search was performed using the keywords 'ischaemic preconditioning', 'ischaemia-reperfusion injury', 'transplantation' and 'hepatic resection'. Additional articles were obtained from references within the papers identified by the Medline search.

RESULTS AND CONCLUSION

The mechanisms underlying hepatic IRI are complex, but IP reduces the severity of such injury in several animal models and in recent human trials. Increased understanding of the cellular processes involved in IP is of importance in the development of treatment strategies aimed at improving outcome after liver transplantation and major hepatic resection.

Ischemic preconditioning impairs liver regeneration in extended reduced-size livers

OBJECTIVE

To evaluate the effect of ischemic preconditioning (IPC) in an experimental setting of extended liver resection with 30 minutes of inflow occlusion in rats.

SUMMARY BACKGROUND DATA

IPC has been proven an effective strategy against hepatic ischemia-reperfusion injury in both animal and human studies. However, decreased protective effects in terms of transaminase levels were found in patients with larger resection volume, questioning the benefit of IPC in case of small liver remnants.

METHODS

Rats undergoing 90% hepatectomy under strict inflow occlusion for 30 minutes were subjected to either receive or not receive an IPC period (5 minutes of ischemia followed by 30 minutes of reperfusion). In addition to 10-day survival rate, laser Doppler flowmetry of hepatic blood flow and fluorescence microscopic analysis of the hepatic microcirculation were performed to assess the effect of IPC on initial microvascular reperfusion of liver remnants after 90% resection. Moreover, regeneration capacity of livers undergoing IPC and 70% resection was studied over 7 days by means of histology and immunohistochemistry.

RESULTS

Ten-day survival of rats which underwent IPC and 90% hepatectomy was 0 out of 10 animals versus 1 out of 10 animals without IPC. Hemodynamic and microcirculatory analysis revealed signs of hyperperfusion during initial reperfusion of preconditioned liver remnants in 90% hepatectomized animals. In addition to increased transaminase levels, IPC impaired hepatic proliferative response after 70% organ resection, as indicated by both a significant reduction in mitotic figures and Ki-67 nuclear staining of hepatocytes, as well as a decrease in restitution of liver mass.

CONCLUSIONS

Though portal hypertension reflecting shear stress has been reported to trigger liver regeneration, remnant liver tissue after major hepatectomy may not benefit from hyperperfusion-induced trigger for cell cycle entry but is rather dominated from hyperperfusion-induced local organ injury. Further studies are required to finally judge on the harmfulness of IPC in extended liver resection.

Ischemic preconditioning impairs liver regeneration in extended reduced-size livers

OBJECTIVE

To evaluate the effect of ischemic preconditioning (IPC) in an experimental setting of extended liver resection with 30 minutes of inflow occlusion in rats.

SUMMARY BACKGROUND DATA

IPC has been proven an effective strategy against hepatic ischemia-reperfusion injury in both animal and human studies. However, decreased protective effects in terms of transaminase levels were found in patients with larger resection volume, questioning the benefit of IPC in case of small liver remnants.

METHODS

Rats undergoing 90% hepatectomy under strict inflow occlusion for 30 minutes were subjected to either receive or not receive an IPC period (5 minutes of ischemia followed by 30 minutes of reperfusion). In addition to 10-day survival rate, laser Doppler flowmetry of hepatic blood flow and fluorescence microscopic analysis of the hepatic microcirculation were performed to assess the effect of IPC on initial microvascular reperfusion of liver remnants after 90% resection. Moreover, regeneration capacity of livers undergoing IPC and 70% resection was studied over 7 days by means of histology and immunohistochemistry.

RESULTS

Ten-day survival of rats which underwent IPC and 90% hepatectomy was 0 out of 10 animals versus 1 out of 10 animals without IPC. Hemodynamic and microcirculatory analysis revealed signs of hyperperfusion during initial reperfusion of preconditioned liver remnants in 90% hepatectomized animals. In addition to increased transaminase levels, IPC impaired hepatic proliferative response after 70% organ resection, as indicated by both a significant reduction in mitotic figures and Ki-67 nuclear staining of hepatocytes, as well as a decrease in restitution of liver mass.

CONCLUSIONS

Though portal hypertension reflecting shear stress has been reported to trigger liver regeneration, remnant liver tissue after major hepatectomy may not benefit from hyperperfusion-induced trigger for cell cycle entry but is rather dominated from hyperperfusion-induced local organ injury. Further studies are required to finally judge on the harmfulness of IPC in extended liver resection.

Ischemic preconditioning and intermittent clamping improve murine hepatic microcirculation and Kupffer cell function after ischemic injury

The aim of this study was to evaluate whether the protective effect of intermittent clamping and ischemic preconditioning is related to an improved hepatic microcirculation after ischemia/reperfusion injury. Male C57BL/6 mice were subjected to 75 or 120 min of hepatic ischemia and 1 or 3 hours of reperfusion. The effects of continuous ischemia, intermittent clamping, and ischemic preconditioning before prolonged ischemia on sinusoidal perfusion, leukocyte-endothelial interactions, and Kupffer cell phagocytic activity were analyzed by intravital fluorescence microscopy. Kupffer cell activation was measured by tissue levels of tumor necrosis factor (TNF)-alpha, and the integrity of sinusoidal endothelial cells and Kupffer cells were evaluated by electron microscopy. Continuous ischemia resulted in decreased sinusoidal perfusion rate and phagocytic activity of Kupffer cell, increased leukocyte-endothelial interactions and TNF-alpha levels. Both protective strategies improved sinusoidal perfusion, leukocyte-endothelial interactions and phagocytic activity of Kupffer cells after 75-minutes of ischemia, and intermittent clamping also after 120 minutes ischemia. TNF-alpha release was significantly reduced and sinusoidal wall integrity was preserved by both protective procedures. In conclusion, both strategies are protective against ischemia/reperfusion injury by maintaining hepatic microcirculation and decreasing Kupffer cell activation for clinically relevant ischemic periods, and intermittent clamping appears superior for prolonged ischemia.

Protection of the liver by ischemic preconditioning: a review of mechanisms and clinical applications

Ischemic preconditioning refers to the endogenous mechanism of protection against a sustained ischemic insult following an initial, brief ischemic stimulus. Ischemia-reperfusion injury of the liver is a major cause of morbidity and mortality in liver surgery and transplantation and ischemic preconditioning is a promising strategy for improving the outcome of liver surgery. The preconditioning phenomenon was first described in a canine model of myocardial ischemia-reperfusion injury in 1986 and since then has been shown to exist in other organs including skeletal muscle, brain, kidneys, retina and liver. In the liver, the preconditioning effect has been demonstrated in rodents and a recent study has demonstrated human clinical benefits of preconditioning during hemihepatectomies. Ischemic preconditioning has been described as an adaptive response and although the precise mechanism of hepatoprotection from preconditioning is unknown it is likely to be a receptor-mediated process. Several hypotheses have been proposed and this review assesses possible mechanisms of ischemic preconditioning and its role in hepatic surgery and liver transplantation. The future lies in defining the mechanisms of the ischemic preconditioning effect to allow drug targeting to induce the preconditioning response.

Role of ischemic preconditioning and the portosystemic shunt in the prevention of liver and lung damage after rat liver transplantation

BACKGROUND

This study evaluates whether surgical strategies such as the portosystemic shunt and ischemic preconditioning can protect against hepatic and pulmonary injury associated with liver transplantation.

METHODS

The effect of the portosystemic shunt, ischemic preconditioning, and both surgical procedures together were evaluated in rat liver transplantation. Alanine aminotransferase, hyaluronic acid levels in plasma, adenosine triphosphate and nucleotide levels in liver and edema, malondialdehyde levels, and myeloperoxidase activity were measured 24 hr posttransplantation. Plasmatic tumor necrosis factor (TNF) levels were measured as a possible proinflammatory factor responsible for hepatic and pulmonary damage associated with liver transplantation.

RESULTS

Hepatocyte and cell endothelial damage were observed in liver grafts subjected to 8 hr of cold ischemia. This was associated with increased plasma TNF levels and lung inflammatory response. Portosystemic shunt application in the recipient protected endothelial cells but did not confer an effective protection from hepatocyte damage or reduce the increased plasma TNF levels and lung damage after liver transplantation. However, preconditioning of the donor liver conferred protection against both the endothelial cell and hepatocyte damage observed after liver transplantation. Preconditioning also attenuated the increased plasma TNF release and pulmonary damage. The combination of both surgical strategies resulted in levels of liver injury, TNF, and lung damage similar to those seen after liver transplantation.

CONCLUSIONS

These findings indicate that ischemic preconditioning could be a preferred treatment to reduce hepatic and pulmonary damage associated with liver transplantation. However, this strategy may not be effective in several clinical situations requiring a portosystemic shunt.

Ischemic preconditioning protects from hepatic ischemia/reperfusion-injury by preservation of microcirculation and mitochondrial redox-state

BACKGROUND/AIMS

Ischemic preconditioning (IP) is known to protect hepatic tissue from ischemia-reperfusion injury. However, the mechanisms involved are not fully understood yet.

METHODS

Using intravital multifluorescence microscopy in the rat liver, we studied whether IP exerts its beneficial effect by modulating postischemic Kupffer cell activation, leukocyte-endothelial cell interaction, microvascular no-reflow, mitochondrial redox state, and, thus, tissue oxygenation.

RESULTS

Portal triad cross-clamping (45 min) followed by reperfusion induced Kupffer cell activation, microvascular leukocyte adherence, sinusoidal perfusion failure (no-reflow) and alteration of mitochondrial redox state (tissue hypoxia) (P<0.05). This resulted in liver dysfunction and parenchymal injury, as indicated by decreased bile flow and increased serum glutamate dehydrogenase (GLDH) levels (P<0.05). IP (5 min ischemia and 30 min intermittent reperfusion) was capable to significantly reduce Kupffer cell activation (P<0.05), which was associated with a slight attenuation of leukocyte adherence. Further, IP markedly ameliorated sinusoidal perfusion failure (P<0.05), and, thereby, preserved adequate mitochondrial redox state (P<0.05). As a consequence, IP prevented the decrease of bile flow (P<0.05) and the increase in serum GLDH levels (P<0.05).

CONCLUSIONS

IP may exert its beneficial effects on hepatic ischemia-reperfusion injury by preserving mitochondrial redox state, which is guaranteed by the prevention of reperfusion-associated Kupffer cell activation and sinusoidal perfusion failure.

Effect of ischemic preconditioning on hepatic microcirculation and function in a rat model of ischemia reperfusion injury

Ischemic preconditioning (IPC) may protect the liver from ischemia reperfusion injury by nitric oxide formation. This study has investigated the effect of ischemic preconditioning on hepatic microcirculation (HM), and the relationship between nitric oxide metabolism and HM in preconditioning. Rats were allocated to 5 groups: 1. sham laparotomy; 2. 45 minutes lobar ischemia followed by 2-hour reperfusion (IR); 3. IPC with 5 minutes ischemia and 10 minutes reperfusion before IR; 4. L-arginine before IR; and 5. L-NAME + IPC before IR. HM was monitored by laser Doppler flowmeter. Liver transaminases, adenosine triphosphate, nitrites + nitrates, and guanosine 3'5'-cyclic monophosphate (cGMP) were measured. Nitric oxide synthase (NOS) distribution was studied using nicotinamide adeninine dinucleotide phosphate (NADPH) diaphorase histochemistry. At the end of reperfusion phase, in the IR group, flow in the HM recovered partially to 25.8% of baseline (P < .05 versus sham), whereas IPC improved HM to 49.5% of baseline (P < .01 versus IR). With L-arginine treatment, HM was 31.6% of baseline (NS versus IR), showing no attenuation of liver injury. In the preconditioned group treated with L-NAME, HM declined to 10.2% of baseline, suggesting not only a blockade of the preconditioning effect, but also an exacerbated liver injury. Hepatocellular injury was reduced by IPC, and L-arginine and was increased by NO inhibition with L-NAME. IPC also increased nitrate + nitrate (NOx) and cGMP concentrations. NOS detected by NADPH diaphorase staining was associated with hepatocytes and vascular endothelium, and was induced by IPC. IPC induced NOS and attenuated HM impairment and hepatocellular injury. These data strongly suggest a role for nitric oxide in IPC.

Protective effect of ischemic preconditioning against intermittent warm-ischemia-induced liver injury

BACKGROUND

Although ischemic preconditioning (IPC) has been reported to protect the liver from injury when subjected to continuous hepatic ischemia, whether IPC protects rat livers against ischemia-reperfusion (I/R) injury after intermittent ischemia has not been elucidated.

MATERIALS AND METHODS

Five groups of Wistar rats were subjected to intermittent hepatic ischemia (I) comprising 15-min ischemia and 5-min reperfusion three times with or without prior IPC (10-min ischemia and 10-min reperfusion), 45-min continuous ischemia (C) with or without IPC, and sham operation. Serum transaminase and lactic acid levels, hepatic tissue energy charges, and hepatic blood perfusion were measured after reperfusion. Plasma tumor necrosis factor-alpha (TNF-alpha) levels were determined after reperfusion for 120 min. Histological and apoptotic findings were evaluated after reperfusion for 180 min.

RESULTS

IPC significantly reduced serum transaminase levels after continuous and intermittent ischemia (IPC + C, 1107 vs C, 2684 IU/l; IPC + I, 708 vs I, 1859 IU/l). After hepatic ischemia without IPC, apoptosis and necrosis with increased plasma TNF-alpha levels were observed. IPC protected livers from injury by interfering with the increase in plasma TNF-alpha (IPC + I, 27.6 vs I, 64.8 pg/ml; IPC + C, 21.6 vs C, 49.3 pg/ml). This resulted in the attenuation of hepatic necrosis after continuous ischemia and significantly reduced necrosis and apoptosis after intermittent ischemia.

CONCLUSIONS

IPC exerts a greater protective effect against hepatic I/R injury after intermittent hepatic ischemia than after continuous hepatic ischemia.

Ischemic preconditioning by brief extremity ischemia before flap ischemia in a rat model

Ischemic preconditioning is a protective endogenous mechanism to reduce ischemia/reperfusion injury and is defined as a brief period of ischemia the authors term "preclamping." This is followed by tissue reperfusion and is believed to increase the ischemic tolerance. The objective of this study was to determine whether acute remote ischemic preconditioning, which has been reported to be successful for other organs, such as the heart, kidney, intestine, and liver, will also result in an enhancement of survival in flaps, and whether remote ischemic preconditioning is as effective as preclamping. Forty male Wistar rats were divided into four experimental groups. An extended epigastric adipocutaneous flap (6 x 10 cm) was raised, based on the left superficial epigastric artery and vein. In the control group, a 3-hour flap ischemia was induced. In the preclamping group, a brief ischemia of 10 minutes was induced by clamping the flap pedicle, followed by 30 minutes of reperfusion. Ischemia of the right hind limb was induced in the femoral ischemia group by clamping the femoral artery and vein for 10 minutes after flap elevation. The limb was then reperfused for 30 minutes. Thereafter, flap ischemia was induced as in the control group. A similar protocol was used in the tourniquet group. A tourniquet was used to induce hind-limb ischemia. The experiment was then performed as in the femoral ischemia group. Mean flap necrosis area was assessed for all groups on the fifth postoperative day using planimetry software. Average flap necrosis area was 68.2 +/- 18.1 percent in the control group, 11 +/- 8.38 percent in the preclamping group, 12.5 +/- 5.83 percent in the femoral ischemia group, and 24 +/- 11.75 percent in the tourniquet group. All preconditioned animals demonstrated a significantly lower area of flap necrosis than the control group (p < 0.001, one-way analysis of variance, post hoc Tukey's test). The data show that ischemic preconditioning and enhancement of flap survival can be achieved not only by preclamping of the flap pedicle but also by induction of an ischemia/reperfusion event in a body area distant from the flap before harvest. These findings indicate that remote ischemic preconditioning is a systemic phenomenon, leading to an enhancement of flap survival. The exact mechanism is not yet completely understood. The data suggest that remote ischemic preconditioning could be performed simultaneously with flap harvest in the clinical setting, resulting in an improved flap survival without prolongation of the operation. This may decrease the rate of partial flap loss or fat necrosis, especially in high-risk groups such as smokers, those with irradiated tissues, and obese patients.