Preconditioned Rats Research Articles

Relationship between the activation of cyclic AMP responsive element binding protein and ischemic tolerance in the penumbra region of rat cerebral cortex

Application of a brief period of ischemia, i.e. preconditioning treatment of the middle cerebral artery territory, has been known to produce ischemic tolerance, reducing cerebral infarction volume in the penumbra region after lethal ischemia. However, little is known about the molecular mechanisms responsible for preconditioning-induced ischemic tolerance. In the present study, we examined the difference in the phosphorylation pattern of cyclic AMP responsive element binding protein (CREB) after 1 h of focal cerebral ischemia between preconditioned and non-preconditioned rats by immunohistochemistry and Western blotting. The phosphorylation of CREB in the penumbra region was more rapidly enhanced in the preconditioned rats than in the non-preconditioned rats after 1 h of ischemia. The result suggested that the immediate enhancement in the phosphorylation of CREB in the penumbra region prevented the spread of infarction in the preconditioned rats.

Preconditioning protects liver and lung damage in rat liver transplantation: Role of xanthine/xanthine oxidase

This study was designed to evaluate whether ischemic preconditioning could confer protection against liver and lung damage associated with liver transplantation. The effect of preconditioning on the xanthine/xanthine oxidase (XOD) system in liver grafts subjected to 8 and 16 hours of cold ischemia was also evaluated. Increased xanthine levels and marked conversion of xanthine dehydrogenase (XDH) to XOD were observed after hepatic cold ischemia. Xanthine/XOD could play a role in the liver and lung damage associated with liver transplantation. This assumption is based on the observation that inhibition of XOD reduced postischemic reactive oxygen species (ROS) generation and hepatic injury as well as ensuing lung inflammatory damage, including neutrophil accumulation, oxidative stress, and edema formation. Ischemic preconditioning reduced xanthine accumulation and conversion of XDH to XOD in liver grafts during cold ischemia. This could diminish liver and lung damage following liver transplantation. In the liver, preconditioning prevented postischemic ROS generation and hepatic injury as well as the injurious effects in the lung following liver transplantation. Administration of xanthine and XOD to preconditioned rats led to hepatic ROS and transaminase levels similar to those found after reperfusion and abolished the protective effect of preconditioning on the lung inflammatory damage. In conclusion, ischemic preconditioning reduces both liver and lung damage following liver transplantation. This endogenous protective mechanism is capable of blocking xanthine/XOD generation in liver grafts during cold ischemia. (H EPATOLOGY 2002;36:562-572.)

Ischemic preconditioning: a defense mechanism against the reactive oxygen species generated after hepatic ischemia reperfusion.

Preconditioning protects against both liver and lung damage after hepatic ischemia-reperfusion (I/R). Xanthine and xanthine oxidase (XOD) may contribute to the development of hepatic I/R. To evaluate whether preconditioning could modulate the injurious effects of xanthine/XOD on the liver and lung after hepatic I/R. Hepatic I/R or preconditioning previous to I/R was induced in rats. Xanthine and xanthine dehydrogenase/xanthine oxidase (XDH/XOD) in liver and plasma were measured. Hepatic injury and inflammatory response in the lung was evaluated. Preconditioning reduced xanthine accumulation and conversion of XDH to XOD in liver during sustained ischemia. This could reduce the generation of reactive oxygen species (ROS) from XOD, and therefore, attenuate hepatic I/R injury. Inhibition of XOD prevented postischemic ROS generation and hepatic injury. Administration of xanthine and XOD to preconditioned rats led to hepatic MDA and transaminase levels similar to those found after hepatic I/R. Preconditioning, resulting in low circulating levels of xanthine and XOD activity, reduced neutrophil accumulation, oxidative stress, and microvascular disorders seen in lung after hepatic I/R. Inhibition of XOD attenuated the inflammatory damage in lung after hepatic I/R. Administration of xanthine and XOD abolished the benefits of preconditioning on lung damage. Preconditioning, by blocking the xanthine/XOD pathway for ROS generation, would confer protection against the liver and lung injuries induced by hepatic I/R.

Optimal Timing and Temperature for Hyperthermic Preconditioning in an Animal Model of Fecal Peritonitis

The impact of immune parameters in the mechanism of hyperthermia is yet to be explained. In this study, the optimal timing and temperature of thermal treatment for reversing the abnormal immunologic parameters obtained in a rat model of peritonitis were planned to be determined. Male Sprague-Dawley rats were grouped as sham, control peritonitis, and thermally treated rats at the time of peritonitis or 4 h prior to induction of peritonitis both at 40 and 42°C. Peritonitis was induced by the cecal ligation and perforation model. Eight hours after the induction of peritonitis, rats were sacrified and samples were taken for measurements of CD 4 + , CD 8 + , CD 11b , B cells, NK cells, and tumor necrosis factor f (TNF f ) and thiobarbituric acid-reactive substances (TBARS) levels. CD 4 + expression and B cell amount were decreased whereas TNF f levels, CD 8 + and CD 11b expression, and NK cell amount were found to be increased in the control peritonitis group when compared to the sham group. Peritonitis induction also increased TBARS levels in liver tissue. Hyperthermic preconditioning at either 40 or 42°C applied 4 h prior to peritonitis induction returned all parameters to their normal levels, which is similar to the results of the sham laparotomy group. The results of TNF f values in preconditioned rats were varied according to the temperature that was applied. The levels were increased at 40°C, whereas they showed a decline at 42°C. Hyperthermic preconditioning prevented the oxidative damage in liver as well as TNF f elevation, particularly at 42°C. Results from this study suggest that hyperthermic preconditioning 4 h prior to the onset of septic events may improve the adverse outcome in sepsis.

Ischaemic preconditioning in the rat brain: a longitudinal magnetic resonance imaging (MRI) study

Ischaemic preconditioning in rats was studied using MRI. Ischaemic preconditioning was induced, using an intraluminal filament method, by 30 min middle cerebral artery occlusion (MCAO), and imaged 24 h later. The secondary insult of 100 min MCAO was induced 3 days following preconditioning and imaged 24 and 72 h later. Twenty-four hours following ischaemic preconditioning most rats showed small sub-cortical hyperintense regions not seen in sham-preconditioned rats. Twenty-four hours and 72 h following the secondary insult preconditioned animals showed significantly smaller lesions (24 h = 112 +/- 31 mm(3), mean +/- standard error; 72 h = 80 +/- 35 mm(3)), which were confined to the striatum, than controls (24 h = 234 +/- 32 mm(3), p = 0.026; 72 h = 275 +/- 37 mm(3), p = 0.003). In addition during lesion maturation from 24 to 72 h post-secondary MCAO, preconditioned rats displayed an average reduction in lesion size as measured by MRI whereas sham-preconditioned rats displayed increases in lesion size; this is the first report of such differential lesion volume evolution in cerebral ischaemic preconditioning.

Fructose-1,6-biphosphate in rat intestinal preconditioning: involvement of nitric oxide

BACKGROUND AND AIMSInhibition of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by nitric oxide (NO) in intestinal preconditioning could modify the rate of formation of glycolytic intermediates. Fructose-1,6-biphosphate (F16BP) is a glycolytic intermediate that...

Role of Adenosine in Renal Protection Induced by a Brief Episode of Ischemic Preconditioning in Rats

The protective effect of a brief episode of ischemic preconditioning was examined at an early phase of ischemic-reperfusion injury in the rat kidney. Rats were subjected to 50 min of left renal artery occlusion followed by 120 min of reperfusion. Ischemic preconditioned rats were subjected to preconditioning with two cycles of 3-min ischemia and 5-min reperfusion (IPC). Ischemic-reperfusion injury led to a low recovery of the glomerular filtration rate (GFR). Overt morphological changes, consisting of blood trapping and tubular collapse, were seen. IPC improved the recovery of GFR and renal morphology. The IPC effect was not blocked by 8-(p-sulfophenyl)-theophylline (SPT), a non-selective adenosine receptor antagonist, by 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), a selective A1-receptor antagonist, or by 3,7-dimethyl-1-propargylxanthine (DMPX), a selective A2-receptor antagonist. Intravenous infusion of adenosine (30 μg/min per rat, for 5 min) prior to the 50-min occlusion improved the recovery of GFR, and this protection of GFR was blocked by SPT. Thus, both IPC and exogenous adenosine attenuated ischemic-reperfusion injury of the kidney. However, because three adenosine receptor antagonists failed to abolish the protective effect of IPC, there is no evidence to indicate that activation of adenosine receptors contributes to the IPC effect in the kidney.

ATP-sensitive potassium channels (K ATP) in retina: a key role for delayed ischemic tolerance

The objectives of the present study were to determine the localization of K ATP channels in normal retina and to evaluate their potential roles in ischemic preconditioning (IPC) in a rat model of ischemia induced by increased intraocular pressure (IOP). Brown Norway rats were subjected to sublethal 3-, lethal 20- and 40-min ischemia and the functional recovery was evaluated using electroretinography. The time interval between ischemic insults ranged from 1 to 72 h. The effects of K ATP channel blockade on IPC protection were studied by treatment with 0.01% glipizide. IPC was mimicked by injection of K ATP channel openers of 0.01% (−)cromakalim or 0.01% P1060 72 h before 20-min ischemia. Co-expression of K ATP channel subunits Kir6.2/SUR1 was observed in the retinal pigment epithelium, inner segments of photoreceptors, outer plexiform and ganglion cell layers and at the border of the inner nuclear layer. In contrast to a 20- or 40-min ischemia, a 3-min ischemia induced no alteration of the electroretinogram (ERG) and constituted the preconditioning stimulus. An ischemic challenge of 40 min in preconditioned rats induced impairment of retinal function. However, animals preconditioned 24, 48 and 72 h before 20-min ischemia had a significant improvement of the ERG. (−)Cromakalim and P1060 mimicked the effect of IPC. Glipizide significantly suppressed the protective effects of preconditioning. In conclusion, activation of K ATP channels plays an important role in the mechanism of preconditioning by enhancing the resistance of the retina against a severe ischemic insult.

Brain ischemia alters platelet ATP diphosphohydrolase and 5'-nucleotidase activities in naive and preconditioned rats.

The effects of transient forebrain ischemia, reperfusion and ischemic preconditioning on rat blood platelet ATP diphosphohydrolase and 5'-nucleotidase activities were evaluated. Adult Wistar rats were submitted to 2 or 10 min of single ischemic episodes, or to 10 min of ischemia 1 day after a 2-min ischemic episode (ischemic preconditioning) by the four-vessel occlusion method. Rats submitted to single ischemic insults were reperfused for 60 min and for 1, 2, 5, 10 and 30 days after ischemia; preconditioned rats were reperfused for 60 min 1 and 2 days after the long ischemic episode. Brain ischemia (2 or 10 min) inhibited ATP and ADP hydrolysis by platelet ATP diphosphohydrolase. On the other hand, AMP hydrolysis by 5'-nucleotidase was increased after 2, but not 10, min of ischemia. Ischemic preconditioning followed by 10 min of ischemia caused activation of both enzymes. Variable periods of reperfusion distinctly affected each experimental group. Enzyme activities returned to control levels in the 2-min group. However, the decrease in ATP diphosphohydrolase activity was maintained up to 30 days of reperfusion after 10-min ischemia. 5'-Nucleotidase activity was decreased 60 min and 1 day following 10-min ischemia; interestingly, enzymatic activity was increased after 2 and 5 days of reperfusion, and returned to control levels after 10 days. Ischemic preconditioning cancelled the effects of 10-min ischemia on the enzymatic activities. These results indicate that brain ischemia and ischemic preconditioning induce peripheral effects on ecto-enzymes from rat platelets involved in nucleotide metabolism. Thus, ATP, ADP and AMP degradation and probably the generation of adenosine in the circulation may be altered, leading to regulation of microthrombus formation since ADP aggregates platelets and adenosine is an inhibitor of platelet aggregation.

Hyperthermic preconditioning protects against spinal cord ischemic injury

Background. Paraplegia can result from operations requiring transient occlusion of the descending thoracic aorta. The present study tested whether inducing hyperthermia in rats before aortic ischemia would be neuroprotective. Methods. Rats were randomly assigned to hyperthermic preconditioning (n = 27) or control (n = 32) groups. Eighteen hours before ischemia, the hyperthermic preconditioned rats were heated at 41°C for 15 minutes. Ten minutes of spinal ischemia were produced by balloon occlusion of the thoracic aorta. Neurologic performance scores were evaluated daily to 7 days after ischemia. The lumbar region of the spinal cord was removed for histologic grading. Results. The hyperthermic preconditioned animals had less permanent spinal cord injury compared with controls (29.6% versus 59.4%, p = 0.02), and the incidence of immediate paraplegia in the hyperthermic preconditioned group was significantly less than that in the control group (3.7% versus 28.1%, p = 0.03). Histologic scores correlated with the neurologic outcome at the time of sacrifice in rats with permanent spinal cord injury but not in those walking normally. Conclusions. We used a rat model of spinal cord ischemia and found that hyperthermic preconditioning before spinal cord ischemia resulted in improved clinical outcome.

Haloperidol catalepsy consolidation in the rat as a model of neuromodulatory integration

Haloperidol, a non-selective D 2 dopamine antagonist, both in vitro (1 μM) and in vivo (2.5 mg/kg i.p.), induced a long-term potentiation of K +-induced Ca 2+-dependent release of endogenous noradrenaline and dopamine in rat brain cortical slices, by increasing the content of noradrenaline and dopamine known to be controlled by dopamine auto- and heteroreceptors. Haloperidol administration (2.5 mg/kg i.p.) evoked catalepsy and increased the content of noradrenaline and dopamine in the same structures of the brain. Haloperidol catalepsy consolidated without any additional learning and could be retrieved up to two weeks later by placing the animals in the test box. The catalepsy is disordered and retrieved only in the test box. The catalepsy was more intense on day 14 than on day 7. Injection of haloperidol immediately after conditioning evened the reflex retrieval on the following days. Moreover, learning increased the intensity of catalepsy in animals tested on the day of injection. Repeated testing of the reflex on the following days led to specific modifications of catalepsy retrieval. Pre-conditioned rats exhibited maximal catalepsy when tested immediately after being placed in the test box. These results suggest that both the processes of long-term potentiation and catalepsy consolidation are mediated by the same type of receptors, long-term modulation-inducing receptors. Endogenous neuromodulators, acting non-specifically or diffusely via their respective long-term modulation-inducing receptors, can initiate and consolidate generalized states which form the basis for emotional and motivational states.

Endotoxin-induced renal failure. I. A role for altered renal microcirculation.

The pathogenesis of sepsis-induced renal failure is multifactorial and only partially understood. In these studies we evaluated intrarenal microcirculatory changes during endotoxemia and the potential role of nitric oxide (NO) and endothelin in these changes. In anesthetized rats endotoxin infusion [lipopolysaccharide (LPS), Escherichia coli serotype 0127:B8; 10 mg/kg/h] resulted in hypotension and a transient enhancement of renal blood flow, with cortical vasodilation and a loss of outer medullary vasodilatory response to hypotension. The initial cortical vasodilation was abolished by the NO synthase inhibitor NG-nitro-L-arginine methyl ester, but not by indomethacin. Direct NO measurements disclosed a gradual rise in cortical NO, despite the waning vasodilatory effect, suggesting antagonizing vasoconstrictive stimuli. In rats pretreated by LPS (1 mg/kg i.p. 1 day earlier) the renal blood flow was reduced to 55% of that of controls. Moreover, the vasodilatory response to LPS infusion was converted into profound cortical and medullary vasoconstriction. In these preconditioned rats the endothelin receptor antagonist bosentan evoked a vasodilatory response and attenuated the vasoconstrictive reaction to LPS infusion. The infusion of another LPS (E. coli serotype 0111:B4) exerted predominant and protracted renal vasodilation without hypotension. In conclusion, different LPS exert diverse systemic and renal hemodynamic responses. The 0127:B8 serotype attenuates renal medullary vasodilation during hypotension, exerts transient cortical vasodilation, and following repeated exposure induces profound renal vasoconstriction. NO and endothelin participate in LPS-induced vascular responses that may predispose to hypoxic tubular damage.

Modification of oxidative stress in response to intestinal preconditioning.

Previous studies have demonstrated that intestinal preconditioning protects the organ from ischemia reperfusion damage. Xanthine oxidase mediating free radical generation contributes to the development of injury associated to ischemia reperfusion. Thus, any process able to modulate the oxygen free radical generation system could attenuate the injury. Also, it is known that nitric oxide is implicated in the preconditioning response. The aim of this work is to determine: (1) the effect of intestinal preconditioning on the xanthine oxidase system, (2) the relevance of this system in the development of injury, and (3) its relationship with nitric oxide. For this purpose, we have determined the activity of the xanthine dehydrogenase/xanthine oxidase system, the levels of its substrate (xanthine), and end-product (uric acid) and oxidant stress status in rat small intestine subjected to ischemic pre-conditioning. The effects of nitric oxide inhibition have also been evaluated. Results show that the percentage of xanthine dehydrogenase to xanthine oxidase conversion, xanthine, uric acid concentration, lipoperoxides, and reduced glutathione were significantly reduced in preconditioned rats irrespectively of nitric oxide inhibition. In summary, this work shows that oxidative stress in intestinal preconditioning is reduced as consequence of the diminished conversion of xanthine dehydrogenase to xanthine oxidase, and also as a consequence of the reduced availability of xanthine.

Ischemic preconditioning reduces peripheral oxidative damage associated with brain ischemia in rats.

Brain ischemia followed by reperfusion causes neuronal death related to oxidative damage. Furthermore, it has been reported that subjects suffering from ischemic cerebrovascular disorders exhibit changes in circulating platelet aggregation, a characteristic that might be important for their clinical outcome. In the present investigation we studied tert-butyl hydroperoxide-initiated plasma chemiluminescence and thiol content as measures of peripheral oxidative damage in naive and preconditioned rats submitted to forebrain ischemia produced by the 4-vessel occlusion method. Rats were submitted to 2 or 10 min of global transient forebrain ischemia followed by 60 min or 1, 2, 5, 10 or 30 days of reperfusion. Preconditioned rats were submitted to a 10-min ischemic episode 1 day after a 2-min ischemic event (2 + 10 min), followed by 60 min or 1 or 2 days of reperfusion. It has been demonstrated that such preconditioning protects against neuronal death in rats and gerbils submitted to a lethal (10 min) ischemic episode. The results show that both 2 and 10 min of ischemia cause an increase of plasma chemiluminescence when compared to control and sham rats. In the 2-min ischemic group, the effect was not present after reperfusion. In the 10-min ischemic group, the increase was present up to 1 day after recirculation and values returned to control levels after 2 days. However, rats preconditioned to ischemia (2 + 10 min) and reperfusion showed no differences in plasma chemiluminescence when compared to controls. We also analyzed plasma thiol content since it has been described that sulfhydryl (SH) groups significantly contribute to the antioxidant capacity of plasma. There was a significant decrease of plasma thiol content after 2, 10 and 2 + 10 min of ischemia followed by reperfusion when compared to controls. We conclude that ischemia may cause, along with brain oxidative damage and cell death, a peripheral oxidative damage that is reduced by the preconditioning phenomenon.

Pre-conditioning to global cerebral ischemia changes hippocampal acetylcholinesterase in the rat.

This study shows the effect of transient global cerebral ischemia (ISC) on hippocampal acetylcholinesterase (AChE) activity. Naive adult Wistar rats received either a brief (2 min) or a long (10 min) ischemic episode by the four-vessel occlusion method. Pre-conditioned rats received double ischemia: a 10 min episode inflicted 24 h after a 2 min event, a condition known to confer cytoprotection to CA1 pyramidal cells of hippocampus. 2 min of ischemia caused an increase in acetylcholinesterase activity both immediately and 30 min after the episode, however enzyme activity was significantly decreased after 24 h of reperfusion. 10 min of ischemia caused an increase in activity both 60 min and 24 h after ischemia. Conversely, pre-conditioned rats displayed lower activity both immediately and 60 min after ischemia. Our results suggest that: a) neuronal death, that follows 10 min of ischemia, is associated to a late increase in acetylcholinesterase activity; b) pre-conditioning is related to diminished acetylcholinesterase activity. This is in agreement with previous evidence that acetylcholinesterase inhibition and maintenance of acetylcholine levels are beneficial for cell surviving after cerebral ischemia.

Hypoxic preconditioning and hypoxic-ischemic brain damage in the immature rat: pathologic and metabolic correlates.

It has been reported that immature rats subjected to cerebral hypoxia-ischemia sustain less brain damage if they are previously exposed to systemic hypoxia compared with animals not exposed to prior hypoxia. Accordingly, neuropathologic and metabolic experiments were conducted to confirm and extend the observation that hypoxic preconditioning protects the perinatal brain from subsequent hypoxic-ischemic brain damage. Six-day postnatal rats were subjected to systemic hypoxia with 8% oxygen at 37 degrees C for 2.5 h. Twenty-four hours later, they were exposed to unilateral cerebral hypoxia-ischemia for 2.5 h, produced by unilateral common carotid artery ligation and systemic hypoxia with 8% oxygen. Neuropathologic analysis, conducted at 30 days of postnatal age, indicated a substantial reduction in the severity of brain damage in the preconditioned rats, such that only 6 of 14 such animals exhibited cystic infarction, but all 13 animals without prior preconditioning exhibited infarction (p < 0.001). Measurement of cerebral glycolytic and tricarboxylic acid intermediates and high-energy phosphate reserves at the terminus of and at 4 and 24 h following hypoxia-ischemia showed no differences in the extent of alterations in the preconditioned and nonpreconditioned immature rats. A difference was seen in the restitution of high-energy stores during the first 24 h of recovery from hypoxia-ischemia, with a more optimal preservation of these metabolites in the preconditioned animals, reflecting the less severe ultimate brain damage. Accordingly, the neuroprotection afforded to the preconditioned animals was not the result of any differences in the extent of anaerobic glycolysis, tissue acidosis, or depletion in high-energy reserves during hypoxia-ischemia but rather the result of other mechanisms that improved the metabolic status of the immature brain during the early hours of reperfusion following hypoxia-ischemia.

Nucleotide hydrolysis in rats submitted to global cerebral ischemia: A possible link between preconditioning and adenosine production

Adenosine, an endogenous neuroprotective agent, can be produced in the synaptic cleft from adenosine triphosphate (ATP) hydrolysis via the concerted action of two enzymes: ATP diphosphohydrolase and 5'-nucleotidase. The aim of the present study was to investigate such enzymatic activities in the hippocampus of rats subjected to single (2- or 10-minute) or double (2+10 minute, with a 24-hour interval in between, named preconditioned group) ischemic episodes. Ischemia was produced by four-vessel occlusion method. Histological analysis showed no cell death in 2-minute ischemia, and up to 90% of pyramidal CA(1) cell loss in the 10-minute ischemic group. As predicted, double ischemic rats displayed a significant cytoprotective effect (around 60%). Preconditioned rats presented a delayed enhancement in ATP diphosphohydrolase activity (for ATP and adenosine diphosphate hydrolysis) after 48 hours of reperfusion. 5'-nucleotidase activity was increased immediately after ischemic insult (for all groups) and after a late reperfusion period (48 hours). We suggest that preconditioning causes delayed changes in enzymatic activities that would conceivably lead to increased adenosine production. This effect could be related to cytoprotection seen in preconditioned rats.

Does protein kinase C play a role in ischemic preconditioning in rat hearts?

Protein kinase C (PKC) has been implicated in the cardioprotective effects of ischemic preconditioning in rabbits, but whether it plays a role in rats is unknown. We tested this preconditioning PKC theory by assessing whether the inhibition of PKC with calphostin C, a potent and specific inhibitor of PKC, can block the preconditioning effects in this model. Four groups of rats were studied: 1) control + vehicle, 2) control + calphostin C, 3) preconditioning + vehicle, and 4) preconditioning + calphostin C. All rats underwent 90 min of coronary occlusion followed by 4 h of reperfusion; in addition, preconditioned rats underwent three 3-min episodes of ischemia and 5 min of reperfusion before the 90 min of ischemia. Two injections of vehicle or calphostin C (0.1 mg/kg) were administered in intravenous boluses 29 min and 3 min before the 90-min coronary occlusion, i.e., one dose was given 5 min before preconditioning, and another dose was given between preconditioning and the sustained 90 min of ischemia in preconditioned rats. After 4 h of reperfusion, the area at risk (AR) was delineated by dye injection and area of necrosis was assessed by triphenyltetrazolium chloride staining. The electrocardiogram was recorded for the incidence of ventricular tachycardia (VT) and ventricular fibrillation. AR was similar in all four groups. In the nonpreconditioned control rats receiving vehicle, myocardial infarct size expressed as a percentage of the AR averaged 45.7 +/- 1.7%. Pretreatment with calphostin C had no effect on infarct size (48.9 +/- 3.4%) in nonpreconditioned control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine deaminase inhibition is not cardioprotective in the rat

Adenosine receptor activation has been assumed to play a role in the cardioprotective effect of ischemic preconditioning. The actions of adenosine are terminated by the naturally occurring substance adenosine deaminase. We determined whether 2′-deoxycoformycin (DCF), a potent inhibitor of adenosine deaminase, could mimic the effect of preconditioning in nonpreconditioned rats and potentiate the salutary effect of preconditioning in preconditioned rats. We assessed the effect of DCF on myocardial infarct size and the incidence of ventricular arrhythmias in four groups of anesthetized rats: control (nonpreconditioned) + vehicle, control + DCF, preconditioned + vehicle, and preconditioned + DCF. All rats underwent 90 minutes of coronary artery occlusion followed by 4 hours of reperfusion, while preconditioned rats received three cycles of 3-minute episodes of ischemia and 5 minutes of reperfusion before the 90-minute occlusion. Following 4 hours of reperfusion, area at risk was determined by intravenous injection of blue dye during a brief coronary occlusion, and area of necrosis was determined by incubation of heart slices in triphenyltetrazolium chloride. In the nonpreconditioned control rats receiving vehicle, myocardial infarct size expressed as a percentage of the area at risk averaged 44.8 ± 7.6%. Pretreatment with DCF had no effect on infarct size (49.4 ± 4.9%) in the nonpreconditioned control rats. Both the preconditioned + vehicle (19.2 ± 7.8%) and the preconditioned + DCF (17.9 ± 5.1%) groups had a significant reduction in infarct size ( p < 0.05 versus control + vehicle and control + DCF), with no significant difference in infarct size between the two preconditioned groups. The incidence of ventricular tachycardia (VT) during the 90 minutes of ischemia was significantly attenuated in both preconditioned groups ( p < 0.05 versus controls). However, DCF caused no difference in the incidence of VT in either control animals or in preconditioned rats compared with vehicle. The incidence of ventricular fibrillation (VF) during ischemia was significantly higher in the control + DCF group (85.7%) versus the other three groups in which no VF occurred. Thus DCF, an inhibitor of adenosine deaminase, was not cardioprotective in this rat model of ischemia and reperfusion.

The cardioprotective effects of ischemic 'preconditioning' are not mediated by adenosine receptors in rat hearts.

Adenosine receptor activation has been proposed to explain the cardioprotective effect of ischemic preconditioning in rabbit hearts. We tested this hypothesis in a rat model by assessing whether administration of an adenosine antagonist could block the protective effect of preconditioning and whether adenosine is able to reduce infarct size in rat hearts when given before sustained coronary occlusion. We assessed the effects of the adenosine antagonist 8-(p-sulfophenyl)theophylline (SPT) and adenosine on myocardial infarct size and the incidence of ventricular arrhythmias in five groups of rats: control (nonpreconditioned)+vehicle, control+SPT, preconditioned+vehicle, preconditioned+SPT, and control (nonpreconditioned)+adenosine. All rats underwent 90 minutes of coronary artery occlusion followed by 4 hours of reperfusion while preconditioned rats underwent three 3-minute episodes of ischemia, each separated by 5 minutes of reperfusion before sustained occlusion. The area at risk was determined by intravascular injection of blue dye during coronary artery occlusion, and infarct size was determined by incubation of heart slices in triphenyltetrazolium chloride. In the nonpreconditioned control rats receiving vehicle, myocardial infarct size expressed as a percentage of the area at risk averaged 55.2 +/- 4.8%. Pretreatment with SPT and adenosine had no effect on infarct size (52.2 +/- 3.1% and 52.6 +/- 3.8%, respectively) in the nonpreconditioned control animals compared with the control animals that received vehicle. Both the preconditioned+vehicle (16.4 +/- 4.3%) and the preconditioned+SPT (18.3 +/- 5.2%) groups had a significant reduction in infarct size (p < 0.01 versus control+vehicle, control+SPT, and control+adenosine), with no difference in infarct size between the two preconditioned groups. The incidence of ventricular tachycardia was significantly decreased in both the preconditioned+vehicle (10%, p < 0.05) and the preconditioned+SPT (25.0%, p < 0.05) groups when compared with the control+vehicle (100%), control+SPT (100%), and control+adenosine groups (100%). There was, however, no significant difference in the incidence of ventricular tachycardia between the preconditioned+vehicle and the preconditioned+SPT groups. Because the adenosine antagonist SPT failed to abolish the cardioprotective effects of preconditioning and intravenous adenosine was unable to protect the hearts, it is unlikely that the mechanism of preconditioning is mediated by adenosine receptors in the rat model.