Application of high-dose propofol during ischemia
improves postischemic function of rat hearts:
effects on tissue antioxidant capacity1
Zhengyuan Xia, David V. Godin, and David M. Ansley
Abstract: Previous studies have shown that reactive oxygen species mediated lipid peroxidation in patients undergoing
cardiac surgery occurs primarily during cardiopulmonary bypass. We examined whether application of a high concen-
tration of propofol during ischemia could effectively enhance postischemic myocardial functional recovery in the set-
ting of global ischemia and reperfusion in an isolated heart preparation. Hearts were subjected to 40 min of global
ischemia followed by 90 min of reperfusion. During ischemia, propofol (12 µg/mL in saline) was perfused through the
aorta at 60 µL/min. We found that application of high-concentration propofol during ischemia combined with low-
concentration propofol (1.2 µg/mL) administered before ischemia and during reperfusion significantly improved
postischemic myocardial functional recovery without depressing cardiac mechanics before ischemia, as is seen when
high-concentration propofol was applied prior to ischemia and during reperfusion. The functional enhancement is asso-
ciated with increased heart tissue antioxidant capacity and reduced lipid peroxidation. We conclude that high-
concentration propofol application during ischemia could be a potential therapeutic and anesthetic strategy for patients
with preexisting myocardial dysfunction.
Key words: propofol, ischemia, heart, rat, oxidative stress.
Résumé : Des études antérieures ont montré que, chez les patients subissant une chirurgie cardiaque, la peroxydation
lipidique véhiculée par les espèces oxygénées radicalaires se produit surtout durant la circulation extracorporelle. Nous
avons examiné si l’application d’une forte concentration de propofol durant l’ischémie peut stimuler efficacement le ré-
tablissement de la fonction myocardique post-ischémique, dans le contexte d’une ischémie globale suivie d’une reperfu-
sion dans une préparation cardiaque isolée. Les cœurs ont été soumis à une ischémie globale de 40 min suivie d’une
reperfusion de 90 min. Durant l’ischémie, le propofol (12 µg/mL dans une solution physiologique salée) a été perfusé
par l’aorte à 60 µL/min. Nous avons constaté que l’application d’une forte concentration de propofol durant l’ischémie,
combinée à une faible concentration de propofol (1,2 µg/mL) administrée avant l’ischémie et durant la reperfusion, a
amélioré significativement le rétablissement de la fonction myocardique post-ischémique sans diminuer la mécanique
cardiaque pré-ischémique, comme cela a été observé lorsqu’une forte concentration de propofol a été appliquée avant
l’ischémie et durant la reperfusion. L’amélioration fonctionnelle est associée à une augmentation de la capacité anti-
oxydante du tissu cardiaque et à une diminution de la peroxydation lipidique. Nous concluons que l’application d’une
forte concentration de propofol durant l’ischémie pourrait être une stratégie anesthésique et thérapeutique potentielle
pour les patients ayant une dysfonction myocardique préexistante.
Mots clés : propofol, ischémie, cœur, rat, stress oxydatif.
[Traduit par la Rédaction]
Xia et al. 926
Oxidative stress has been strongly implicated in myocar-
dial ischemia–reperfusion injury (IRI) (Ambrosio and Tritto
1999; Toufektsian et al. 2001). Reactive oxygen species (ROS)
formation, primarily during reperfusion, was previously
thought responsible for IRI, but the importance of ROS for-
mation during ischemia has recently been emphasized. ROS-
induced oxidative stress occurs in patients following
systemic thrombolysis (Bell et al. 1990), percutaneous tran-
Can. J. Physiol. Pharmacol. 82: 919–926 (2004)doi: 10.1139/Y04-097© 2004 NRC Canada
Received 22 February 2004. Published on the NRC Research Press Web site at http://cjpp.nrc.ca on 20 November 2004.
Z. Xia2and D.V. Godin. Centre for Anesthesia and Analgesia, Department of Pharmacology and Therapeutics, University of
British Columbia, Vancouver, BC V6T 1Z3, Canada.
D.M. Ansley.3Centre for Anesthesia and Analgesia, Department of Pharmacology and Therapeutics, University of British
Columbia, Vancouver, BC V6T 1Z3, Canada and Department of Anesthesiology, University of British Columbia, Room 3200, 3rd
Floor JPP, 910 West 10th Ave., Vancouver, BC V5Z 4E3, Canada.
1This paper is one of a selection of papers published in this Special Issue, entitled John H. McNeill Symposium.
2Present address: Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia,
Vancouver, BC V6T 1Z3, Canada.
3Corresponding author (email: email@example.com).
luminal coronary angioplasty (Buffon et al. 2000; Iuliano et
al. 2001), and coronary artery bypass surgery using extra-
corporeal circulation (Messent et al. 1997; Ansley et al.
2003). We recently identified a significant inverse correla-
tion between postoperative cardiac functional recovery and
the percent change in plasma levels of 15-F2t-isoprostane
reperfusion (Ansley et al. 2003). 15-F2t-IsoP is a novel
marker of lipid peroxidation and a reliable measure of
oxidative injury (Morrow and Roberts 1997). Although 15-
F2t-IsoP levels are elevated primarily during ischemia, the
pattern of its degradation during reperfusion appears to be
clinically relevant (Ansley et al. 2003). This suggests that
endogenous antioxidant capacity is reduced during myocar-
dial ischemia–reperfusion (Buffon et al. 2000), resulting in
the persistent intraoperative elevation of 15-F2t-IsoP during
reperfusion (Ansley et al. 2002, 2003), and this may be a
factor in postoperative cardiac dysfunction. Hence, the de-
velopment of an effective antioxidant therapy and (or) thera-
peutic regimen for the management of myocardial IRI,
including interventions during the ischemic phase, would be
of particular interest.
Despite the now generally accepted oxidative etiology of
myocardial injury associated with ischemia and post-
ischemic reperfusion, supplementation with the “traditional”
antioxidants vitamins E and C has yielded no beneficial ef-
fects in humans with major cardiovascular risk factors
(Chiabrando et al. 2002) or reduced myocardial injury after
cardiac surgery (Westhuyzen et al. 1997). Our previous work
has demonstrated that propofol, an intravenous anesthetic
agent frequently used during cardiac surgery and in postop-
erative sedation (Bryson et al. 1995), enhances red cell and
tissue antioxidant capacity both in vitro and in vivo (Ansley
et al. 1999; Runzer et al. 2002). We recently showed that
propofol, when applied before and during ischemia and early
reperfusion, enhanced myocardial antioxidant capacity and
resulted in improved postischemic cardiac function in the
isolated rat heart in a dose-dependent manner (Xia et al.
2003a). Its effect is prominent at a clinically achievable high
concentration of 12 µg/mL (67 µmol/L) (Ansley et al. 1999;
Xia et al. 2003a). This technique is promising but is associ-
ated with significant cardiac depression prior to ischemia
(Xia et al. 2003a, 2003b) and therefore is technically diffi-
cult to handle when applied to patients with reduced preop-
erative cardiac function.
We hypothesized that a high concentration of propofol ap-
plied during ischemia, combined with a low concentration of
propofol prior to ischemia and during reperfusion, could be
an effective approach to antioxidant supplementation that
would result in improved postischemic cardiac functional re-
covery. The hypothesis was tested in an isolated rat heart
model using 15-F2t-IsoP as a measure of oxidative injury.
This study was approved by the Committee of Animal
Care of the University of British Columbia. Animals were
cared for in accordance with the principles and guidelines of
the Canadian Council on Animal Care. Male Sprague–Dawley
rats (250–300 g) were anesthetized with pentobarbital
(70 mg/kg intraperitoneally) and heparinized with sodium
heparin (1000 IU/kg intraperitoneally). After median thora-
cotomy, hearts were quickly excised and immersed in ice-
cold Krebs–Henseleit (KH) solution to stop contractions.
Hearts were gently squeezed to remove residual blood to
prevent clot formation. Hearts were retrogradely perfused
via the aorta in a nonworking “Langendorff” preparation at a
constant flow rate of 10 mL/min using a peristaltic pump.
The perfusion flow rate (10 mL/min) was based on the result
of a pilot work that showed that hearts sham-perfused with-
out ischemia beat well and remain hemodynamically stable
for 150 min (the duration of the experiment) in our experi-
mental setup. Hearts were electrically paced at a rate of 300
beats/min prior to and following, but not during, the
ischemic period when hearts ceased to beat spontaneously.
The perfusion fluid (pH 7.4, temperature 37 °C) was KH
solution that contained 120 mmol/L NaCl, 20 mmol/L
1.25 mmol/L CaCl2, 1.17 mmol/L KH2PO4, and 8 mmol/L
glucose. The perfusate was bubbled with a mixture of 95%
O2and 5% CO2. The perfusate solution and the bath temper-
ature were maintained at 37 °C using a thermostatically con-
pressure (CPP) was measured via a side arm of the perfusion
cannula connected to a pressure transducer (Statham p23 ID;
Gould Electronics, Cleveland, Ohio). A latex water-filled
balloon fixed to a pressure transducer was inserted through
the mitral valve into the left ventricle for the determination
of left ventricular (LV) developed pressure (LVDP), which
was calculated by subtracting end-diastolic pressure (LVEDP)
from LV peak systolic pressure. LVEDP was adjusted to ap-
proximately 5 mmHg (1 mmHg = 133.322 Pa) before the
start of the experiment by adjusting the volume in the intra-
ventricular balloon and was held constant throughout the ex-
periment. Hearts were perfused within 30–40 s after
excision. Exclusion criteria included heart preparation times
longer than 60 s and (or) LVSP lower than 70 mmHg after
10 min of equilibration.
All hearts were initially equilibrated for 10 min (BS10),
and then they were randomly assigned to one of the three
experimental groups (n = 6 each): ischemia–reperfusion un-
treated control, high-concentration propofol applied during
propofol applied prior to and during ischemia and early
reperfusion (Hi-P(PIR) group). Control hearts were equili-
brated an additional 10 min prior to inducing global
ischemia for 40 min by stopping perfusion flow. Propofol
(1.2 or 12 µg/mL) was applied for 10 min in the Hi-P(I) and
Hi-P(PIR) groups prior to 40 min of global ischemia. Saline
(control) or 12 µg propofol/mL in saline was perfused
through the aorta at 60 µL/min using a minipump in both the
Hi-P(I) and Hi-P(PIR) groups during the ischemic interval.
KH or 1.2 µg propofol/mL in KH was perfused in the con-
trol group and in the Hi-P(I) group, respectively, during
90 min of reperfusion. Propofol at 12 µg/mL in KH was
perfused for the first 15 min of reperfusion and then at
5 µg/mL for 75 min in the Hi-P(PIR) group to minimize the
direct negative inotropic effects of propofol on myocytes
(Hamilton et al. 2000).
© 2004 NRC Canada
920 Can. J. Physiol. Pharmacol. Vol. 82, 2004
Baseline effluent perfusate was sampled at BS10 (i.e., af-
ter hearts were equilibrated for 10 min). Effluent samples
were collected during the first 30 min of ischemia and then
at 0.5 (Re-0.5), 5 (Re-5), 10 (Re-10), and 30 min (Re-30) of
reperfusion in the control and propofol-treated groups. Efflu-
ent samples were stored at –70 °C and were analyzed for
free 15-F2t-IsoP within 1 week of storage. LV function was
continuously monitored using a polygraph. At the end of the
90-min reperfusion period, hearts were immediately removed
from the cannula, frozen with liquid nitrogen, and stored at
–70 °C. Hearts were assayed for tissue thiobarbituric acid-
reactive substances (TBARS) within 48 h of storage, as pre-
viously described (Xia et al. 2003a, 2003b).
Heart tissue antioxidant capacity determination
Myocardial tissue antioxidant capacity was determined by
exposure of tissue homogenates to the peroxidizing agent
tertiary butyl hydroperoxide (t-BHP). The oxidation of tis-
sues by t-BHP results in the formation of numerous lipid by-
products, which form a chromogen when incubated with
thiobarbituric acid (TBA) and are therefore collectively
termed TBARS. Lower tissue antioxidant capacity will result
in a greater amount of TBARS formation in the presence of
t-BHP. The level of TBARS in the sample is estimated from
the absorbance at 532 nm. Heart tissue samples (300 mg)
were thawed and homogenized on ice in 3 mL of Tris–
EDTA buffer using a Polytron homogenizer for 30 s at 25%
power. The resulting homogenates were used for in vitro
forced peroxidation using t-BHP and subsequent determina-
tion of TBARS, as previously described (Runzer et al. 2002;
Xia et al. 2003a). In brief, 400 µL of tissue homogenate was
combined with 400 µL of t-BHP (in 0.9% saline – 2 mmol/L
sodium azide to produce final concentrations of t-BHP rang-
ing from 0.5 to 10 mmol/L). These suspensions were incu-
bated for 30 min at 37 °C and then 400 µL of cold 28%
(w/v) trichloroacetic acid – 0.1 mol/L sodium arsenite was
added. The mixture was centrifuged at 12 000g for 5 min at
4 °C and 800 µL of supernatant was removed and added to
400 µL of TBA (0.5% in 25 mmol/L NaOH). The samples
were boiled for 15 min and the absorbance at 532 nm was
measured spectrophotometrically. The TBARS formed at a t-
BHP concentration of 1 mmol/L was considered critical, as
it is a compromise between concentrations sufficiently high
to produce adequate levels of TBARS but sufficiently low to
avoid nonspecific bleaching of the color produced by the
Enzyme-linked immunoassay was used to measure free
15-F2t-IsoP levels according to the methods provided by the
manufacturer (Cayman Chemical, Ann Arbor, Mich.).
Enzyme-linked immunoassay provides a sensitive measure
for 15-F2t-IsoP with a limit of quantification as low as
3.9 pg/mL. In brief, effluent samples were removed from
−70 °C storage and thawed on ice. Fifty-microlitre standards
and samples were added in duplicate to the 96-well plate
provided in the kit followed by addition of 15-F2t-IsoP
acetycholinesterase tracer and antibody. The prepared plates
were then incubated overnight at room temperature. On the
next day, the plates were washed five times with wash buffer
followed by addition of Ellman’s reagent. After optimal de-
velopment, the plates were read at 405 nm and the values of
the unknowns were expressed as picograms of 15-F2t-IsoP
per millilitre of effluent. The samples were coded and the in-
vestigator responsible for 15-F2t-IsoP assays was blinded un-
til the completion of the assay.
All data are presented as mean ± SEM. 15-F2t-IsoP and
hemodynamic data were compared by two-way ANOVA
with Bonferroni’s correction (GraphPad Prism). One-way re-
peated ANOVA and Tukey’s multiple comparison test were
applied for within-group comparison. Correlation analysis
was performed by the Pearson test. A value of p < 0.05
(two-tailed) was considered statistically significant.
Tissue antioxidant capacity
Heart tissue TBARS formation following in vitro peroxide
challenge at 1 mmol/L t-BHP was significantly higher in the
control group than in the propofol treatment groups (Fig. 1),
indicating that tissue antioxidant capacity was lower in un-
treated hearts compared with hearts treated with Hi-P(I) and
Hi-P(PIR). Tissue TBARS formation in the Hi-P(PIR) group
was significantly lower than in the Hi-P(I) group (p < 0.01).
15-F2t-IsoP generation during ischemia–reperfusion
As shown in Fig. 2, baseline (BS10) 15-F2t-IsoP values
did not differ among groups. 15-F2t-IsoP levels increased
during ischemia (p < 0.01 vs. BS10) and remained elevated
at Re-0.5 (p < 0.05 vs. BS10) in all the three experimental
groups. Effluent 15-F2t-IsoP release during ischemia was
significantly lowerin the
2.8 pg/mL) than in the untreated control group (67.0 ±
4.7 pg/mL). Similarly, F2t-IsoP release at Re-0.5 was signifi-
cantly lower in the Hi-P(PIR) group (11.3 ± 2.8 pg/mL) than
in the untreated control group (22.7 ± 2.4 pg/mL). Values of
F2t-IsoP release during ischemia (51.7 ± 8.3 pg/mL) and at
Re-0.5 (17.5 ± 1.8 mg/mL) in the Hi-P(I) group were rela-
tively lower than the corresponding values in the untreated
© 2004 NRC Canada
Xia et al.921
Fig. 1. Formation of TBARS, a measure of tissue antioxidant ca-
pacity, in heart tissue (represented as absorbance at 532 nm) in
the presence of 1 mmol/L t-BHP. Hearts were assayed for in vi-
tro TBARS formation after 90 min of reperfusion following
40 min of ischemia. Values are mean ± SEM. *p < 0.05; **p <
0.01 vs. control; +p < 0.01 vs. Hi-P(PIR).
control group, but the difference did not reach statistical sig-
nificance (p = 0.1). Levels of 15-F2t-IsoP decreased rapidly
after reperfusion in all the three groups and these did not
statistically differ from baseline values at Re-5 (p > 0.05). It
is noteworthy that 15-F2t-IsoP in the Hi-P(I) group appeared
to decrease more rapidly after Re-0.5 than in the untreated
and Hi-P(PIR) groups. At Re-10, 15-F2t-IsoP in the Hi-P(I)
group (5.5 ± 0.5 pg/mL) completely returned to its baseline
value (5.5 ± 0.5 pg/mL) and was significantly lower than the
corresponding value in the untreated group (Fig. 2). In con-
trast, the 15-F2t-IsoP release in the untreated and the Hi-
P(PIR) groups remained considerably higher than the
corresponding baseline values up to Re-10, although the dif-
ference did not reach statistical significance (p > 0.05).
Contracture development during ischemia
Increases in LVEDP are indicative of contracture (ventric-
ular stiffness) of isolated hearts during ischemia (“ischemic
contracture”). The LVEDP increased progressively during
ischemia in the untreated control group (Fig. 3A). LVEDP
was significantly lower in Hi-P(PIR) compared with the un-
treated control (p < 0.05 or p < 0.01, Hi-P(PIR) vs. control
after ischemia 30 min and onwards). LVEDP was similar for
the first 25 min in (Hi-P(I)) and Hi-P(PIR) groups. After
30 min of ischemia, the magnitude of LVEDP in the Hi-P(I)
group became relatively higher than that in the Hi-P(PIR)
group but lower than that in the untreated control group.
However, the differences did not reach statistical signifi-
cance (p > 0.05). The latency to the onset of contracture was
significantly increased in both the Hi-P(PIR) group (22.7 ±
2.4 min) and the Hi-P(I) group (23.3 ± 1.4 min) as compared
with that in the untreated control group (15.3 ± 1.0 min)
(Fig. 3B). Of interest is the fact that the time to maximum
LVEDP was significantly longer in the Hi-P(I) group (37.8 ±
0.4 min), but not in the Hi-P(PIR) group (35.8 ± 2.7 min),
compared with the untreated control group (31.3 ± 2.9 min)
Functional response to ischemia and reperfusion
One of the main effects of propofol on functional recovery
during reperfusion was a difference in LVEDP (increases in
the latter being an indicator of reperfusion-induced increase
in “ventricular stiffness”). During reperfusion, LVEDP in the
untreated control group increased over time and peaked at
66.5 ± 11.0 mmHg at Re-90. Hi-P(I) significantly attenuated
the increase of LVEDP at Re-30 and onwards as compared
with the untreated control group (p < 0.05 or p = 0.01 vs.
control). However, LVEDP in the Hi-P(I) group increased to-
ward the end of reperfusion. At Re-90, LVEDP in the Hi-
P(I) group (25.4 ± 8.9 mmHg) was higher than that in the
Hi-P(PIR) group (7.2 ± 1.1 mmHg) (p < 0.05). In the Hi-
P(PIR) group, there was no evidence of an increase in ven-
tricular stiffness during the experiment.
During reperfusion, maximum recovery in LVDP occurred
at Re-30 in all the three groups (Fig. 4A). LVDP in the un-
© 2004 NRC Canada
922 Can. J. Physiol. Pharmacol. Vol. 82, 2004
Fig. 2. 15-F2t-IsoP release during ischemia and reperfusion.
BS10 indicates 10 min after equilibration, Ische indicates
ischemia (samples were collected during the first 30 min of
ischemia); Re-0.5, Re-5, Re-10, and Re-30 indicate 0.5, 5, and
10 min after reperfusion, respectively. Values are mean ± SEM.
*p < 0.05 or p < 0.01 vs. control; #p < 0.05 or p < 0.01 vs.
Fig. 3. Effects of different propofol regimen on LVEDP, reflect-
ing myocardial contracture (ventricular stiffness), (A) during
ischemia (ischemic contracture), (B) ischemic contracture onset
time, and (C) the time to maximal ischemic contracture. Values
are mean ± SEM (n = 6) for all groups. *p < 0.05; **p < 0.01
vs. control; p > 0.05, Hi-P(I) vs. Hi-P(PIR).
treated control group, however, decreased progressively
thereafter. In both the Hi-P(I) and the Hi-P(PIR) groups, a
significantly attenuated decease in LVDP was observed after
Re-30. At Re-90, LVDP in the untreated control group, but
not in the Hi-P(I) and Hi-P(PIR) groups, was lower than its
baseline value (p < 0.05) (Fig. 4A). At Re-90, the LVDP
percent recovery over baseline values was higher in both the
Hi-P(I) and the Hi-P(PIR) groups compared with the un-
treated group control (p < 0.05) (Fig. 4B). Application of
12 µg propofol/mL (Hi-P(PIR)), but not 1.2 µg/mL (Hi-
P(I)), for 10 min before ischemia was associated with a sig-
nificant decrease in LVDP during this interval (p < 0.01,
preischemia vs. BS10 in the Hi-P(PIR) group).
Since one of the major goals of this study was to optimize
the long-term protective effects of propofol, administration
of propofol was not discontinued during reperfusion. This
mimicked the clinical study of propofol, which aimed to in-
crease myocardial antioxidant status during cardiopulmonary
bypass surgery (Ansley et al. 1999). Also, propofol may be
primarily used for postoperative sedation after cardiac sur-
gery (De Hert et al. 2003). Continued application of pro-
pofol during reperfusion, however, makes it inappropriate to
compare postischemic LVDP values in the propofol treat-
ment groups directly with that in the untreated control group
because of the potential confounding negative inotropic ef-
fect of propofol. The within-group percent change of LVDP
from Re-30 to Re-60 (i.e., changes of LVDP after its maxi-
mum postischemic recovery at Re-30) and (or) from Re-60
to Re-90 (the later phase of reperfusion in this study) best
reflected the postischemic myocardial function preservation
at different experimental conditions. Therefore, it could
serve as a meaningful index for comparison between groups.
The percent decrease in LVDP from Re-30 to Re-60 in Hi-
P(I) (–2.0% ± 2.8%) was less than in the untreated control
group (–15.4% ± 2.8%) (p < 0.01) or in the Hi-P(PIR) group
(–11.8% ± 2.3%) (p < 0.05) (Fig. 5A). During late
reperfusion, the percent decrease in LVDP was least in the
Hi-P(PIR) group compared with the untreated control group
(p < 0.05) but comparable with that in the Hi-P(I) group (p =
0.1, Hi-P(PIR) vs. Hi-P(I)) (Fig. 5B).
Coronary perfusion pressure
CPP increased significantly atRe-60 in the untreated con-
trol group (p < 0.05 vs. BS10). Hi-P(PIR), but not Hi-P(I),
prevented the increase in CPP seen in the untreated control
group. The CPP value at Re-90 in the Hi-P(PIR) group was
lower than those in the untreated control and Hi-P(I) groups.
A negative correlation was obtained between tissue
TBARS formation and percent changes of LVDP from Re-
60 to Re-90 (r = –0.70, p = 0.003, n = 18).
Transient myocardial dysfunction immediately following
coronary artery bypass surgery is a well-documented phe-
nomenon that may significantly affect patient outcome
(Mangano 1985; Breisblatt et al. 1990) despite improve-
© 2004 NRC Canada
Xia et al. 923
Fig. 4. (A) LVDP and (B) LVDP recovery at Re-90 as a percent-
age of baseline (BS10) values. Pre-isch indicates preischemia;
Re-10, Re-30, Re-60, and Re-90 indicate 10, 30, 60, and 90 min
of reperfusion following 40 min of global myocardial ischemia.
Values are mean ± SEM. *p < 0.05 or p < 0.01 vs. control; #p <
0.05 or p < 0.01 vs. BS10.
Fig. 5. Percent changes of LVDP (A) from 30 to 60 min of
reperfusion and (B) from 60 to 90 min of reperfusion. Values are
mean ± SEM. *p < 0.01 (Fig. 5A) or p < 0.05 (Fig. 5B) vs.
control; +p < 0.05 vs. Hi-P (PIR).
ments in operative techniques and methods of myocardial
protection. Preoperative cardiac function appears to be an
important factor. For instance, a preoperative ejection frac-
tion greater than 55% was associated with moderate dys-
function immediately after cardiopulmonary bypass, whereas
an ejection fraction less than 45% was associated with more
severe postoperative myocardial
1985). Therefore, the development of an effective therapeu-
tic regimen specifically targeting individual patient popula-
tions with varying disease severity is critical.
The principal findings of the present study are that
(i) 1.2 µg propofol /mL applied before ischemia and during
reperfusion in combination with 12 µg propofol/mL during
global ischemia significantly improved postischemic cardiac
functional recovery and (ii) postischemic myocardial func-
tion during the very early phase of reperfusion (up to 60 min
in this model) was better preserved with Hi-P(I) than with
Hi-P(PIR). The present study provided additional evidence
that propofol protection against myocardial IRI was attribut-
able, at least in part, to its ability to enhance tissue antioxi-
dant capacity and reduce ROS-mediated lipid peroxidation.
The present study highlights the necessity to undertake anti-
oxidant interventions during the ischemic phase.
Recent experimental studies show that volatile anesthetics
can exert cardioprotective effects directly via precondition-
ing (anesthetic preconditioning) or indirectly via enhancing
ischemic preconditioning (Novalija et al. 2003a, 2003b;
Kevin et al. 2003; Zaugg et al. 2002). Brief exposure of the
heart to volatile anesthetics before ischemia may lead to de-
creased formation of ROS during ischemia and subsequent
reperfusion (Novalija et al. 2003a, 2003b; Kevin et al. 2003).
This would seem to be a promising approach. It should be
noted, however, that volatile anesthetic mediated anesthetic
preconditioning primarily requires the generation of ROS in
advance (i.e., before ischemia) as a trigger of myocardial
preconditioning (Novalija et al. 2003a, 2003b; Kevin et al.
2003). Theoretically, the additional generation of ROS in a
population with preexisting high degrees of oxidative stress,
for example, chronic heart failure (McMurray et al. 1993;
Moskowitz and Kukin 1999), may stimulate an increased
amounts of ROS (involving radical-induced radical release)
that overwhelm endogenous antioxidant defenses, resulting
in extensive lipid peroxidation and cellular destruction
(Zorov et al. 2000).
The intravenous anesthetic propofol has antioxidant activ-
ity in vitro at concentrations as low as 1–10 µm/L (0.2–
1.8 µg/mL), and the addition of propofol to human plasma
significantly increased the plasma antioxidant capacity in
vivo (Murphy et al. 1992). Its use in cardiac surgery at
plasma concentrations in the range of 2–4 µg/mL (11–
22 µm/L) failed to produce significant cardioprotection com-
pared with volatile anesthesia (De Hert et al. 2002, 2003).
Volatile anesthetics, but not propofol at targeted plasma con-
centrations of 2–4 µg/mL, significantly reduced plasma lev-
els of postischemic myocardial troponin I (De Hert et al.
2002, 2003). At this concentration, however, propofol could
only be expected to increase the plasma total radical antioxi-
dant potential by less than 5%–10% (Murphy et al. 1992)
and this would not be functionally significant. Higher plasma
concentrations of propofol are likely needed to significantly
enhance the plasma total radical antioxidant potential. How-
ever, propofol accumulates in biomembranes very rapidly,
so that it may be able to augment the antioxidant defense of
tissues and, more specifically, lipophilic membrane environ-
ments more efficiently. We previously showed that propofol
in large dose (200 µg·kg–1·min–1during cardiopulmonary-
bypass) resulted in an average plasma concentration of
11.8 µg/mL and significantly enhanced human red blood cell
antioxidant capacity (Ansley et al. 1999). Sayin et al. (2002)
further observed that propofol can significantly reduce hu-
man myocardial lipid peroxidation during coronary artery
bypass surgery when applied at a dosage up to 6 mg·kg–1·h–1
(100 µg·kg–1·min–1). We would estimate that this resulted in
a plasma concentration of about 5 µg/mL according to our
previous experience (Ansley et al. 1999). However, propofol
at concentrations of 5 µg/mL or higher applied before myo-
cardial ischemia significantly impairs cardiac mechanics
(Xia et al. 2003a). Therefore, application of high-dose pro-
pofol prior to inducing global myocardial ischemia may not
be suitable for those patients with impaired preoperative
Propofol applied at a concentration of 1.2 µg/mL before
ischemia in the Hi-P(I) group did not depress LVDP. The
choice of 1.2 µg/mL (approximately 6.7 µmol/L) was based
on the observation that propofol at levels of 10 µmol/L or
higher produces a concentration-dependent reduction in
evoked contraction on rat ventricular myocytes in vitro
(Hamilton et al. 2000). This is close to the lowest clinically
relevant blood concentration of propofol that could produce
an anesthetic effect when used concomitantly with narcotics
(Wessen et al. 1993). The blood concentration of propofol
on awakening from surgical propofol anesthesia is reported
to be 0.8–1.0µg/mL (Wessen et al. 1993; Servin et al. 1993).
The present study highlights the importance of applying
antioxidant therapy during ischemia. We determined that Hi-
P(I) was equally as effective as Hi-P(PIR) in delaying the
onset time of ischemic contracture and facilitating post-
ischemic myocardial functional recovery. This effect likely
is attributable to the effects of high-dose propofol on preser-
vation or enhancement of tissue antioxidant capacity during
ischemia and to a much lesser degree to the low-
concentration propofol (1.2 µg/mL) applied before ischemia
and after reperfusion. Propofol at concentrations up to
10 µmol/L were shown not to reduce ROS formation and
failed to facilitate postischemic functional recovery in iso-
lated reperfused rat hearts (Tamaki et al. 2001). Indeed, in-
creasing evidence shows that production of ROS during
ischemia may actually exceed ROS production during
reperfusion of the ischemic heart during cardiac surgery
(Clermont et al. 2002; Ulus et al. 2003; Ansley et al. 2003).
It is of particular clinical relevance that Hi-P(I) proved to
be superior to Hi-P(PIR) in maintaining LVDP from Re-30
to Re-60. This is a critical period during which patients are
expected to be separated from cardiopulmonary bypass.
However, successful weaning from cardiopulmonary bypass
is difficult to achieve for patients with preexisting cardiac
dysfunction prior to surgery (Hardy and Belisle 1993).
While inotropic support may help wean these patients from
cardiopulmonary bypass, the long-term beneficial effect of
inotropic support is uncertain because it may increase myo-
cardial oxygen demand and decrease the oxygen supply vs.
© 2004 NRC Canada
924 Can. J. Physiol. Pharmacol. Vol. 82, 2004
© 2004 NRC Canada
Xia et al.925
demand ratio. This might be detrimental, especially when
applied during early reperfusion when the heart is very frag-
ile. Dobutamine, a routinely used inotrope, exacerbates
postischemic myocardial dysfunction in isolated rat hearts
(Pantos et al. 2003). The Hi-P(I) approach could minimize
the need for inotropic use in this case. The Hi-P(PIR) ap-
proach is associated with better LV relaxation (lower
reperfusion LVEDP) than Hi-P(I) and relatively less reduc-
tion in LVDP towards the end of Re-90. It may be a suitable
approach for patients with relatively normal preoperative
cardiac function where prolonged durations of aortic cross-
clamping and cardiopulmonary bypass are anticipated. The
Hi-P(I) approach, on the other hand, may be suitable for pa-
tients with preoperative cardiac dysfunction undergoing car-
In summary, the present study confirms and extends our
previous observations that propofol enhances antioxidant
capacity and reduces oxidant stress associated with posti-
schemic myocardial dysfunction. The ischemic interval is an
important target of antioxidant intervention. Other actions of
propofol, including preservation of high-energy phosphates
(Mathur et al. 1999) and the inhibition of mitochodrial
permeability transition, directly (Sztark et al. 1995) or indi-
ischemia–reperfusion (Kowaltowski et al. 2001) could also
be involved. In addition, the reduction in “ventricular stiff-
ness” observed in this study might be attributable, at least in
part, to propofol’s property in inhibiting cardiac L-type cal-
cium current (Yang et al. 1996) during myocardial ischemia–
reperfusion. Propofol dilation of coronary arteries, as evi-
denced by the significantly lower CPP during later
reperfusion seen in the Hi-P(PIR) group, but not in the Hi-
P(I) group, is not likely a major mechanism of its cardiac
protection in this model. Application of high-dose propofol
during ischemia and low-dose propofol before and after
reperfusion may provide a useful anesthetic regimen for car-
diac surgery in patients with preexisting cardiac dysfunction.
inoxidative stress during
The authors gratefully acknowledge Drs. Thomas K.H.
Chang, Ernest Puil, and Jiazhen Gu for providing helpful ad-
vice and assistance. Z. Xia is the recipient of a fellowship
from the Centre for Anesthesia and Analgesia, Department
of Pharmacology and Therapeutics, Faculty of Medicine,
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