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Molecular and Cellular Biochemistry 186: 69–77, 1998.
© 1998 Kluwer Academic Publishers. Printed in the Netherlands.
Ischemic preconditioning in isolated perfused
mouse heart: Reduction in infarct size without
improvement of post-ischemic ventricular function
Lei Xi, Michael L. Hess and Rakesh C. Kukreja
Division of Cardiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, USA
Abstract
Genetically engineered mice provide an excellent tool to study the role of a particular gene in biological systems and will be
increasingly used as models to understand the signal transduction mechanisms involved in ischemic preconditioning (IP).
However, the phenomenon of IP has not been well characterized in this species. We therefore attempted to examine whether IP
could protect isolated mouse heart against global ischemia/reperfusion (GI/R) injury. Thirty adult mice hearts were perfused at
constant pressure of 55 mmHg in Langendorff mode. Following 20 min equilibration, the hearts were randomized into three
groups (n = 10/each): (1) Control Group; (2) IP2.5 Group: IP with two cycles of 2.5 min GI + 2.5 min R; (3) IP5 Group: IP with
5 min GI + 5 min R. All hearts were then subjected to 20 min of GI and 30 min R (37°C). Ventricular developed force was
measured by a force transducer attached to the apex. Leakage of CK and LDH was measured in coronary efflux. Infarct size
was determined by tetrazolium staining. Following sustained GI/R, infarct size was significantly reduced in IP2.5 (13.8 ± 2.3%),
but not in IP5 (20.1 ± 4.0%), when compared with non-preconditioned control (23.6 ± 3.8%) hearts. CK & LDH release was
also reduced in both IP2.5 and IP5 groups. No significant improvement in post-ischemic ventricular contractile function was
observed in either IP groups. We conclude that IP with repetitive cycles of brief GI/R is able to reduce myocardial infarct size
and intracellular enzyme leakage caused by a sustained GI/R in the isolated perfused mouse heart. This anti-necrosis
cardioprotection induced by IP was not associated with the amelioration of post-ischemic ventricular dysfunction. (Mol Cell
Biochem 186: 69–77, 1998)
Key words: isolated mouse heart, ischemia/reperfusion injury, myocardial infarction, preconditioning, cardioprotection,
ventricular function, signal transduction
Introduction
Since Murry et al. [1] first demonstrated the phenomenon in
1986 in a canine model, ischemic preconditioning (IP) has
been extensively studied by a number of investigators. The
potent endogenous cardioprotective effects afforded by IP,
especially in enhancing myocardial cellular survival against
irreversible damages caused by ischemia/reperfusion, have
been consistently found in different experimental models
including dogs [2–5], pigs [6], rabbits [7–12] and rats [13–
21] both in vitro and in vivo. However, the signal transduction
mechanisms involved in the early phase of IP remain unclear.
There has been controversy in such mechanisms particularly
across different animal species.
In recent years, the genetically engineered mice are being
used as unique tools to investigate the role of genes in the
biological systems. Transgenic mouse models have been
reported to study the role of heat shock protein 70 and
adenosine A1 receptor in myocardial protection [22–24].
These animals will be increasingly used to understand the
mechanisms of ischemic preconditioning at the molecular
level. However, the results from transgenic mice studies can
not be entirely extrapolated to other species unless we have
a thorough understanding of the cardiovascular physiology
in normal mouse. In this context, mouse differs from other
species in many ways. For example, the total body oxygen
consumption and myocardial oxidative capacity seem to be
very high in this species [25], which may have a major impact
Address for offprints: R.C. Kukreja, Division of Cardiology, Box 282, Medical College of Virginia, Richmond, VA 23298, USA
70
on the myocardial response to ischemia/reperfusion injury.
The activity of xanthine oxidoreductase enzyme, a major
source of free radicals, is much higher in mouse heart as
compared to other species [26]. Combined with its lack of
inhibition of mitochondrial adenosine triphosphatase (ATPase)
[27], the susceptibility of mouse heart to ischemia/ reperfusion
injury may be substantially increased. A recent study from our
laboratory [28, 29] demonstrated that, in contrast to some
previous reports in other species (rats or rabbits), whole body
heat shock failed to precondition the isolated mouse heart
despite induction of 72 kDa heat shock protein at 6 or 24 h
after the heat stress. These results suggest that mouse may
differ from other species in its response to stress. Moreover,
IP, which has been proved in virtually all studied mammalian
species, has not been well characterized in the mouse heart.
Therefore, the purpose of the present investigation was to
demonstrate that the classic IP could also afford an early
phase of cardioprotection in the isolated perfused mouse heart
against ischemia/reperfusion injury. We measured multiple
end-points such as myocardial infarct size, ventricular
contractile function, and intracellular enzyme release to
ensure a more comprehensive assessment of the potential
cardioprotection in the globally ischemic isolated mouse
hearts.
Materials and methods
Animals
Adult male outbred ICR mice (body weight 26–42 g) were
supplied by Harlan Sprague Dawley Co. (Indianapolis, IN).
The animals were allowed to readjust the new housing
environment for at least 3 days before any experiment.
Standard rodent food and water were freely accessible to the
animals. All animal experiments were conducted under the
guidelines on humane use and care of laboratory animals
for biomedical research published by the U.S. National
Institutes of Health (NIH Publication No.85-23, revised
1985) and the experimental protocols were approved by the
Animal Welfare Committee of Medical College of Virginia/
Virginia Commonwealth University.
Langendorff isolated perfused heart preparation
The animals were anesthetized with sodium pentobartital
(100 mg/kg with 33 IU heparin, i.p.) and hearts were quickly
removed from the thorax and placed into a small dish
containing ice-cold modified Krebs-Henseleit (K-H) solution
containing heparin. Under an illuminated magnifier, the
aortic opening of mouse heart was immediately cannulated
and tied on a 20 gauge stainless steel blunt needle. The heart
was retrogradely perfused with the K-H solution containing
(in mM) NaCl 118, NaHCO3 24, CaCl2 2.5, KCl 4.7, KH2PO4
1.2, MgSO4 1.2, Glucose 11, EDTA 0.5 at a constant
pressure of 55 mmHg in the non-recirculating Langendorff
mode. The K-H solution was pre-filtered by a micro-filter
(0.45 µm diameter, Millipore Corp.) and constantly gassed
with 95% O2–5% CO2 (pH 7.35–7.43). The perfusion solution
was warmed through a water-jacketed glass cylinder/heat
exchanger system with a warming/cooling bath (Brinkmann)
and was constantly circulated by a water pump. The heart
temperature was monitored continuously by a thermo-
couple thermometer (Cole-Palmer, Model 8112-10) with
a Type K micro-probe and maintained at 37 ± 0.2°C. The
ambient temperature around the heart was also kept at
37°C throughout the experiment using a heating lamp and
monitored by a digital thermometer (Fisher Scientific,
Model 15-077-8D). During the no-flow ischemia, K-H
buffer was periodically applied on the heart surface in order
to keep it moisturized.
Assessment of ventricular function
Soon after the start of perfusion, a force-displacement
transducer (Grass, Model FT03) was attached to the apex of
mouse heart through a rigid, light weight stainless metal hook
with No. 5 surgical thread and a low-resistance pulley. The
resting tension of the heart was initially adjusted to 0.3 g as
used by Plumier et al. [23] and kept without readjustment
thereafter. The ventricular force was recorded by a polygraph
(Beckman, R-511A) connected to the force transducer. The
preamplifier and coupler were calibrated and balanced. The
force transducer was calibrated prior to each experiment with
four known amount of weights i.e., 0.2, 0.3, 0.5, 1.0 g. The
coronary flow rate was calculated by collecting the efflux
perfusate within certain time period. The hearts were not
electrically paced.
Ischemia/reperfusion protocol
A detailed illustration of the ischemia/reperfusion protocol
is shown in Fig. 1. In brief, after a 20 min equilibration period,
heart rate, ventricular force and coronary flow were measured
and recorded. The global ischemia (GI) was achieved by
clamping the aortic inflow line whereas reperfusion (R) was
accomplished by re-opening the aortic line. Thirty mouse
hearts were randomly subjected to one of the following three
experimental protocols (n = 10/each): (1) Control Group: no
ischemic preconditioning (IP); (2) IP2.5 Group: IP with two
cycles of 2.5 min GI + 2.5 min R; (3) IP5 Group: IP with 5
min GI + 5 min R. All of the hearts were then challenged by
a sustained 20 min GI followed by 30 min R.
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Three hearts (i.e. 9% of the total 33 perfused mouse hearts)
were excluded from further data analysis due to the presence
of any of the following undesirable situations: (1) a significant
time delay in aortic cannulation; or (2) damage of aorta during
the process of cannulation; and (3) sustained arrhythmia during
the 20 min stabilization period.
Estimation of creatine kinase (CK) and lactate
dehydrogenase (LDH) release
Coronary effluent was collected from the isolated perfused
mouse hearts at the end of a 20 min stabilization period; 1
min prior to the 20 min sustained global ischemia as well as
5, 10, 20, 30 min during the reperfusion. The LDH and CK
measurements were done spectrophotometrically (Shimadzu,
Model UV160U) using kits supplied by Sigma Chemical Co.
(St. Louis, MO). The activities of enzymes were expressed
as units per liter and also normalized against coronary flow
rate and heart weight (U/min/g wet weight).
Measurement of myocardial infarct size
At the end of ischemia/reperfusion, the heart was removed
from the Langendorff perfusion apparatus and immediately
frozen and stored in a freezer overnight. Next morning, the
frozen hearts were cut from apex to base into 8 transverse
slices of approximately equal thickness (~0.8 mm). The
slices were placed into a small cell culture dish and then
incubated in 10% triphenyl-tetrazolium chloride (TTC) in
phosphate buffer (Na2HPO4 88 mM, NaH2PO4 1.8 mM, pH
7.8) at room temperature for 30 min. The development of
the red formazan pigment in living tissues relies on the
presence of lactate dehydrogenase or NADH while failure
to stain red indicates a loss of these constituents from
necrotic tissue. After staining, the TTC buffer was replaced
by 10% formaldehyde, the slices were fixed for the next 4–
6 h before the areas of infarct tissue were determined by
computer morphometry (Bioquant System IV). The risk area
was the sum of total ventricular area minus cavities. The
infarct size was calculated and presented as percentage of
risk area.
Data analysis and statistics
All measurements are expressed as mean ± S.E.M. Data from
the three experimental groups were analyzed by one-way
ANOVA. If a significant value of F was obtained, the Student-
Newman-Keuls test was used for pair-wise comparisons.
Paired t-test was used to compare any pair of pre- and post-
Fig. 1. Experimental protocol of ischemia/reperfusion in isolated perfused mouse hearts. Hearts were randomized into three groups (n = 10/each group): (1)
Control: no preconditioning; (2) IP2.5: preconditioning with two cycles of 2.5 min global ischemia and 2.5 min reperfusion; (3) IP5: preconditioning with
one cycle of 5 min global ischemia and 5 min reperfusion. All hearts were subjected to 20 min global ischemia and 30 min reperfusion. Cardiac function and
leackage of intracellular enzymes (CK and LDH) were determined at the indicated time points. Myocardial infarct size was measured at the end of 30 min
reperfusion.
72
treatment values. A probability value of < 0.05 was considered
significant.
Results
Morphometric and the pre-ischemia baseline values of
cardiac hemodynamic and contractile parameters from the
three experimental groups are summarized in Table 1. There
was no significant difference among the groups for any of the
parameters.
Ventricular contractile function
The time course of ventricular developed force and rate-force
product during pre-ischemic as well as reperfusion period are
shown in Fig. 2A and B. The repeated brief ischemia/
reperfusion episodes (IP2.5) caused a consistent overshoot
in cardiac contractile function as indicated by a significant
increase in ventricular developed force (p < 0.05). On the
other hand, a single cycle of IP (IP5) did not significantly alter
the ventricular function. Following the 20 min sustained
global ischemia, the ventricular developed force significantly
decreased in the control and IP groups at 5 min after reperfusion
(0.13 ± 0.05, 0.17 ± 0.08, 0.12 ± 0.05 g in control, IP2.5, and
IP5, respectively, Fig. 2A). The contractile function was not
significantly improved at any time point during the rest of the
reperfusion period. A similar trend in the changes in the rate-
force product was also observed (Fig. 2B). No significant
differences in both resting tension (Fig. 3A) and heart rate
(Fig. 3B) were found between control and IP groups at any
time point throughout the experimental protocol (p > 0.05,
n = 10/each group).
Intracellular enzymes (CK and LDH) leakage
Figure 4 shows the time course of CK (A) and LDH (B) release
in the coronary effluent of isolated hearts during pre-IP, post-
IP and following 20 min ischemia and 30 min of reperfusion
period. Pre-IP CK values (U/L) were 4.9 ± 1.2, 5.1 ± 0.8, 8.8
± 2.2 in control, IP2.5, and IP5 respectively which were not
significantly different from the post-IP values (3.5 ± 0.6, 4.6
± 1.6, 4.7 ± 1.2, respectively, p > 0.05). At 5 min of reperfusion,
CK efflux increased significantly in the control group to 129.6
± 50.2, but not in both IP groups (36.5 ± 15.7 for IP2.5; 16.3
± 4.4 for IP5). Although the mean values of the enzyme efflux
were remarkably higher in the control group (Fig. 4A) as
Table 1. Morphometric characters of the mice and the baseline values of
hemodynamic and contractile parameters of the isolated perfused mouse
hearts at the end of 20 min stabilizing period.
Experimental Groups Control IP 2.5 IP 5
Body Weight (g) 31.0 ± 1.1 33.3 ± 1.3 32.7 ± 0.9
Heart Wet Weight (mg) 248 ± 10 264 ± 11 265 ± 7
Heart Rate (bpm) 387 ± 14 351 ± 14 387 ± 10
Coronary Flow (ml/min) 1.93 ± 0.21 1.56 ± 0.16 1.65 ± 0.24
Resting Tension (g) 0.21 ± 0.03 0.17 ± 0.02 0.18 ± 0.02
Developed Force (g) 0.48 ± 0.10 0.51 ± 0.04 0.60 ± 0.06
Rate-Force Product 186 ± 39 179 ± 18 231 ± 22
(g × bpm)
Values are mean ± S.E.M. (n = 10 / each group). IP 2.5 = mouse heart subjected
to two cycles of 2.5 min ischemia and 2.5 min reperfusion; IP 5 = mouse
heart subjected to 5 min ischemia and 5 min reperfusion. No significant
difference was found among the experimental groups for any of the
parameters.
Fig. 2. Effect of ischemic preconditioning (IP) on ventricular contractile
function of the isolated perfused mouse hearts before and after IP as well as
the subsequent 20 min no-flow global ischemia and reperfusion. (A) time
course of ventricular developed force, and (B) time course of rate-force
product. Despite a consistent functional overshoot observed after IP in IP2.5
group (* means p < 0.05), no significant difference for both functional
parameters was observed between control and IP groups at any time point
during the 30 min reperfusion period (p > 0.05, n = 10/each group).
73
compared with the IP groups, the difference failed to reach
the statistical significance between IP2.5 and control groups
due to the high variability within the group. Such a difference
between control and IP groups was also observed in the
release of LDH (Fig. 4B). A similar trend in the release of
CK (A) and LDH (B) release was found when the values were
expressed in terms of wet heart weight (Fig. 5).
The pre-ischemic baseline of coronary flow was 1.93 ±
0.21, 1.56 ± 0.16, 1.65 ± 0.24 (ml/min) for control, IP2.5, IP5
respectively. At the end of reperfusion, the level of coronary
flow decreased to 1.62 ± 0.16 in control group, but increased
to 1.93 ± 0.21 in IP2.5 and 1.98 ± 0.24 in IP5, although these
changes were not statistically significant (p > 0.05).
Myocardial infarct size
Figure 6 presents the average infarct sizes for the three
experimental groups. The mean values of the area at risk were
not significantly different between the three groups. After 20
min global ischemia and 30 min reperfusion, a substantial
amount of the ventricular muscle was irreversibly damaged
in the control and IP5 hearts, but much less in IP2.5 hearts.
The pale color infarct zone was predominantly seen in
endocardial area. The infarct size calculated as percentage of
the risk area was 23.6 ± 3.8% in control, reduced significantly
to 13.8 ± 2.3% in IP2.5 group (p < 0.05). In contrast, the infarct
size in IP5 was 20.1 ± 4.0% which was not significantly
different from the control hearts.
Discussion
The major findings of the present study are summarized as
follows: (1) the phenomenon of ‘classic’ or the early phase
Fig. 3. Effects of ischemic preconditioning (IP) on resting tension (A) and
heart rate (B) before and after 20 min no-flow global ischemia (IS). No
significant difference for both parameters was found between Control and
IP groups at any time point (p > 0.05, n = 10/each group).
Fig. 4. Leakage of intracellular enzymes CK (A) and LDH (B) in coronary
efflux from the isolated perfused mouse hearts subject to 20 min global
ischemia and 30 min reperfusion. * indicates a significantly higher enzyme
release as compared to pre-IP basal value and # indicates a significantly
lower enzyme release as compared to control group (mean ± S.E.M., p <
0.05, n = 10/each group) at the time point of 5 min reperfusion.
74
ischemic preconditioning does exist in the isolated mouse
heart despite its species-specific energetic such as high heart
rate and lack of inhibition of mitochondria ATPase; (2) two
cycles of IP with 2.5 min ischemia and 2.5 min reperfusion
are necessary to induce the anti-infarct cardioprotection in
the mouse hearts; (3) the IP-induced myocardial stunning was
not a key element in the induction of cardioprotection in the
isolated mouse hearts; (4) The anti-necrosis cardioprotection
induced by IP was not associated with the amelioration of
post-ischemic ventricular dysfunction.
Post-ischemic ventricular contractile function
It remains controversial whether the early phase of ischemic
preconditioning affords significant beneficial effects against
myocardial dysfunction. In in situ model, some investigators
demonstrated IP-induced improvement of myocardial wall
motion associated with a smaller infarct size following
transient coronary occlusion in rabbits [3], whereas Ovize et
al. [30] showed that regional myocardial contractility was not
preserved in the preconditioned canine hearts subjected to a
60 min regional ischemia. On the other hand, in isolated
perfused heart model, a number of investigators [14, 15, 17,
20, 31] have shown a dramatic improvement of the ventricular
contractile function afforded by IP in rat or rabbit hearts
following a sustained global ischemia. However, many other
researchers [10, 11, 16, 19, 32] have failed to observe the
similar functional improvement in a comparable experimental
model and protocol. In the present study, we did not observe
a significant difference in ventricular developed force, heart
rate, rate-force product, and resting tension between control
and preconditioned hearts (Figs 2 and 3) throughout the 30
min reperfusion period. The lack of IP-induced improvement
of post-ischemic ventricular function is in accordance with
the preliminary reports in globally ischemic isolated mouse
hearts which also showed no or very limited improvement in
the ventricular function afforded by IP [33, 34].
Infarct size and intracellular enzymes leakage
The powerful anti-infarct effects afforded by ischemic
preconditoning have been consistently found by numerous
investigators using different experimental models in several
species (see Introduction for details). The present study
confirms that the phenomenon of ‘classic’ or the early phase
ischemic preconditioning (IP) does exist in the isolated mouse
heart. The percentage of infarct size reduction (41.5%)
observed in the present study is very similar to the preliminary
reports by Sumeray and Yellon [34] who demonstrated a
42.1% reduction in infarct size in the preconditioned mouse
hearts after 30 min global ischemia and 30 min reperfusion.
A similar preliminary report by Gabel et al. [33] demonstrated
that IP significantly attenuated the drop of pH in the isolated
perfused mouse myocardium. We believe that the attenuation
of tissue acidosis may be accountable at least partially to
the infarct size reduction observed in the present study.
Similarly, leakage of intracellular enzymes (CK and LDH)
was remarkably decreased in both IP groups compared with
control group (Figs 4 and 5), providing additional evidence
of the cardioprotective effects induced by IP. The increase in
post-ischemic coronary flow in the preconditioned hearts may
also play a beneficial role in maintaining an adequate
perfusion condition to the myocardium. In the present study,
IP with two cycles of I/R (IP2.5) was able to reduce myocardial
infarct size significantly, whereas a single cycle of I/R (IP5)
failed to induce a significant anti-infarct cardioprotection. It
is possible that shorter ischemic episodes of preconditioning
Fig. 5. Leakage of intracellular enzymes CK (A) and LDH (B) in coronary
efflux. Values are normalized as unit per min per gram of heart wet weight.
* indicates a significantly higher enzyme release as compared to pre-IP
basal value and # indicates a significantly lower enzyme release as compared
to control group (mean ± S.E.M., p < 0.05, n = 10/each group) at the time
point of 5 min reperfusion.
75
are more effective in triggering the signal transduction
cascade in the mouse heart as compared to other species.
Since brief episodes of ischemia and reperfusion may elicit
bursts of oxygen-derived free radicals, it is reasonable to
speculate that they may serve as important stimulus activating
certain endogenous antioxidant cardioprotective mechanisms,
although further investigations should be done in order to
prove such a hypothesis. This finding is also in agreement
with the previous reports demonstrating cardioprotective
effects after 3-cycle of IP but not 1-cycle of IP in the in situ
rat hearts [13]. However, this was in contrast with the
previous studies from our laboratory where we were able to
precondition rat heart after a single bout of 5 min ischemia
and 10 min reperfusion in vivo [21, 35].
Myocardial stunning and preconditioning
Brief episodes of ischemia/reperfusion used in IP could cause
myocardial stunning in some experimental models. However,
it is controversial whether such an IP-induced myocardial
stunning is a key element responsible for the cardioprotection
afforded by IP against the subsequent sustained ischemia.
Evidence has been reported to either prove [6, 36] or refute
[37, 38] a role played by stunning in the phenomenon of
ischemic preconditioning.
In the present study, we did not observe significant stunning
following either one cycle of 5 min ischemia and 5 min
reperfusion (IP5) or two cycles of 2.5 min ischemia and 2.5
min reperfusion (IP2.5). Therefore, it appears that myocardial
stunning does not play a role in reducing infarct size in the
preconditioned hearts. In contrast, to our surprise, IP2.5
caused a consistent overshoot in cardiac contractile function
as indicated by the increase of ventricular developed force
(Fig. 2). We do not know mechanisms inducing the up-
regulation of ventricular function could also promote the anti-
infarct effects observed in the IP2.5 group.
Critique of methodology
In the present study, we used a Langendorff mode isolated
perfused mouse heart model which is similar to the documented
studies in transgenic [22–24, 39, 40] or normal [34, 41] mice.
We perfused the murine hearts at a constant pressure of 55
mmHg which was within the physiological range of 50–55
mmHg suggested by Ng et al. [41] for perfusing the mouse
heart. This perfusion pressure is similar to that used by
Yoshida et al. [39] but different from Marber et al. [22] who
perfused mouse hearts at 80 mmHg. Although most studies
successfully demonstrated a reduction in infarct size and/or
improved functional recovery following ischemia/reperfusion
Fig. 6. Effects of ischemic preconditioning on infarct size (mean ± S.E.M.) in the isolated perfused mouse myocardium after 20 min no-flow global
ischemia and 30 reperfusion. There is no difference between any pair of the experimental groups (n = 10/each group) for Risk Area (% of Total Area) (see
B). However, the Infarct Size (% of Risk Area) was significantly reduced in IP2.5 (* means p < 0.05) but not in IP5 group as compared with control group
(see A).
76
in transgenic animals [22, 39, 40], the magnitude of these
parameters were highly inconsistent among various studies.
For example, the infarct size in the globally ischemic mouse
hearts ranged from ~8 to ~60% following a 20 or 30 min
ischemia [22, 28, 34, 39, 40]. Clearly, there are substantial
differences in the experimental approaches and conditions
among various research groups and further studies are needed
to resolve these issues.
Species-specific myocardial energetics
We further speculate that the increased susceptibility of
mouse heart to ischemia may contribute in part to the
following three species-specific myocardial energetic
factors: (1) a significantly elevated total body oxygen
consumption (4 folds > human, dog, pig) and myocardial
oxidative capacity (2 folds > human, dog, pig) [25]; (2) a
lack of inhibition of mitochondria adenosine triphosphatase
(ATPase), an enzyme which consumes 35–50% of ATP
during myocardial ischemia [27, 42]; (3) a higher level of
xanthine oxydoreductase, an enzyme which is the source for
oxygen free radicals during ischemia/reperfusion injury in
the cardiac muscle [26, 43, 44]. Liu and Downey [13] were
the first group to report the IP phenomenon in rat - a species
with a fast beating heart similar to mouse. They ruled out
an obligatory role played by ATPase in IP and proposed an
increased threshold of IP in rat hearts.
Conclusion
The present study has confirmed the existence of ischemic
preconditioning in the normal mouse heart. This anti-necrosis
cardioprotection induced by ischemic preconditioning was
not associated with the amelioration of post-ischemic
ventricular dysfunction. To date, the exact mechanism of the
classic IP remains elusive, although a number of receptors,
end-effectors, or mediating pathways have been suggested to
be related to the signal transduction cascade including: (1)
Adenosine receptors [7, 17, 20]; (2) α-adrenergic receptors
[9, 18]; (3) Protein kinase C pathway [8, 9]; (4) ATP-sensitive
potassium channels [4, 21]; and more recently (5) tyrosine
phosphorylation [45–47]. Further studies are necessary to
demonstrate if the mechanism(s) of preconditioning in the
mouse heart is similar to those reported in other species.
Studies on transgenic or knockout mice would eventually
help in dissecting the specific target genes that lead to
cardioprotective effects of preconditioning. Knowledge of the
mechanisms involved in the preconditioning in mouse heart
may help in developing some clinically relevant therapeutic
and preventive approaches.
Acknowledgements
This research was supported in part by NHLBI grant HL-51045
(to R.C. Kukreja); L. Xi was supported by a postdoctoral
fellowship from NIH training grants (HL-07537 & HL-
07580). The authors are grateful to G.P. Matherne and J.P.
Headrick at University of Virginia for their expert advice on
the isolated perfused mouse heart model; to J.E. Levasseur
and Y-Z Qian for their technical assistance.
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