Vol. 276, Issue 5, H1591-H1598, May 1999
The effects of mannitol, albumin, and cardioplegia enhancers
on 24-h rat heart
preservation
Gail
Dunphy1,
Helen Wilkinson
Richter2,
Masoud
Azodi1,
John
Weigand1,
Fereydoon
Sadri3,
Frank
Sellke4, and
Daniel
Ely1
Departments of 1 Biology and
2 Chemistry, The University of
Akron, Akron, Ohio 44325-3908;
3 BioPreserve Medical Corporation,
Redmond, Washington 98052; and
4 Division of Cardiothoracic
Surgery, Department of Medicine of Beth Israel-Deaconess Medical
Center and Harvard Medical School, Boston, Massachusetts 02215
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ABSTRACT |
During 24 h in vitro heart preservation and
reperfusion, tissue damage occurs that seriously reduces cardiac
function. Prevention of free radical production during preservation and
reperfusion of ischemic tissue using free radical scavengers is of
primary importance in maintaining optimal heart function in long-term preservation protocols. We examined whether mannitol (68 mM) and albumin (1.4 µM) in combination with other cardioplegia enhancers decreased free radical formation and edema and increased cardiac function during 24-h cold (5°C) heart preservation and warm
(37°C) reperfusion in the Langendorff-isolated rat heart. The
performance of mannitol-treated hearts was significantly decreased
compared with that of hearts without mannitol treatment after 24 h of
preservation with regard to recovery of diastolic pressure,
contractility (+dP/dt), relaxation
(
dP/dt), myocardial creatine
kinase release, coronary flow, and lipid peroxidation.
Albumin-treated hearts demonstrated higher cardiac function
(contractility and coronary flow especially) than hearts not treated
with albumin or hearts treated with mannitol, and this appears to be
due to the positive effects of increased cellular metabolism and the
enhancement of membrane stability.
organ preservation; free radicals; reperfusion injury; scavengers
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INTRODUCTION |
IN VITRO HEART PRESERVATION for 24 h produces unique
problems involving altered energy metabolism, cell organelle and
membrane damage, left ventricular dysfunction, and reperfusion injury. Recent studies have evaluated various cardioplegia solutions (10, 34)
and specific enhancers (2) that are intended to protect the heart from
preservation-induced injury. Several studies have also described
prevention of reperfusion damage through the use of chelators (6) and
enzymes (11, 32) selected to reduce the concentration of free radicals.
Additional problems are encountered after 24 h of heart preservation,
such as the short biological half-life of many enzymes that scavenge
free radicals, antigenicity of enzymes, and pH and dosage effects that
can accumulate during that period. We found that five additives to a
standard cardioplegia solution (insulin, ATP, corticosterone, pyruvate,
and the iron chelator deferoxamine) maintained 24-h rat heart
preservation at ~90% of function (8).
Several studies have suggested that albumin and mannitol may reduce
ischemic and reperfusion injury. The proposed mechanisms of action of
mannitol are the prevention of edema by hyperosmotic action (19, 26,
35) and the reduction of lipid peroxidation by scavenging hydroxyl
radicals (29, 33). The beneficial effects of mannitol appear to be dose
dependent, and the optimal mannitol dosage for reducing
ischemic-induced ventricular fibrillation was 50 mM (35).
Gronow et al. (12) showed that a dose of 1-10 mM mannitol
minimized edema and reduced malondialdehyde (MDA) formation (lipid
peroxidation index) in the postischemic kidney model; however,
unfavorable cell membrane effects were observed at higher doses (>60
mM). Magovern et al. (19) showed that mannitol produced greater
coronary flow and less edema after 60 min of hypothermia (27°C) and
cardioplegic arrest in rabbit hearts compared with those hearts treated
with isosmolar or hyperosmolar glucose. This study and others (22)
suggest that mannitol exerts its beneficial effects during early
reperfusion by reducing edema and possibly free radical formation.
The proposed mechanisms of action for the beneficial effect of albumin
in cardioplegia solutions are the maintenance of a high osmotic
pressure and the reduction of free radical formation (27). However, the
effectiveness of mannitol and albumin during longer periods of
preservation (24 h) has not been ascertained. Therefore, the objective
of the following study was to determine the effectiveness of mannitol
and albumin with standard and enhanced cardioplegia during 24-h rat
heart preservation.
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MATERIALS AND METHODS |
Experimental groups.
Seven groups of rats (n = 6 rats/group) were tested for left ventricular function before and after
a 24-h heart preservation routine. Biochemical indicators of tissue
damage, release of creatine kinase, and MDA content of tissue were
evaluated at the end of the 24-h period. All cardioplegia solutions
contained the Krebs-Henseleit buffer (K) which was composed of (in mM)
119 NaCl, 15 KCl, 0.8 CaCl2, 5.2 MgCl2, 25 NaHCO3, 1.2 KH2PO4,
and 11 glucose. Some solutions contained the following enhancers, which
we have previously shown to be successful in 24-h preservation: 0.12 mM
corticosterone, 0.14 mM pyruvic acid, 10.4 µM ATP, and 24 U/l
insulin. We originally used 71 enhancers in the cardioplegia to benefit
heart function, and from those we were able to narrow down to five the
powerful additives that were necessary (9). Some solutions contained albumin (1.4 µM), some contained mannitol (68 mM), and some contained neither of these two additives (Table 1).
The seven groups consisted of two subgroups:
1) Krebs-Henseleit buffer (K),
Krebs-Henseleit buffer and albumin (KA), and Krebs-Henseleit buffer and
mannitol (KM); and 2) enhancers (E),
enhancers and albumin (EA), enhancers and mannitol (EM), and enhancers,
albumin, and mannitol (EAM). The K-group solutions do not contain the
enhancers, and the E-group solutions do contain the enhancers. In
RESULTS, group
K and group E are used
as controls for assessing the effects of albumin and mannitol on 24-h
cardioplegia. In addition, we assess the effect of the enhancers by
comparing group E (enhancers) with
group K (no enhancers).
Perfusion and storage of hearts.
Hearts from spontaneously hypertensive rats (SHR;
n = 43, wt 250-350 g) were
isolated and perfused using the Langendorff technique (25). SHR rats
were used because our laboratory has studied hypertension for over 20 years in these animals and we have a large database of physiological
phenotypes for comparison. Rats were injected with heparin (500 U) 5 min before anesthesia (50 mg/kg ip, Brevital, Eli Lilly, Indianapolis,
IN). Hearts were removed and rinsed in an ice-cold K solution (24)
containing 119 mM NaCl, 4.7 mM KCl, 2.5 mM
CaCl2, 1.2 mM
MgSO4, 25 mM
NaHCO3, 1.2 mM
KH2PO4,
14 mM glucose, and 1.4 µM albumin. Atria were trimmed, and the hearts
were attached by an aortic cannula to a hydrostatic perfusion
apparatus. Hearts were retrograde-perfused at 80 Torr, 37°C, with
the above K solution, which was bubbled with 95%
O2-5% CO2. A nonelastic water-filled
balloon was secured in the left ventricle, and the volume was adjusted
via a syringe to achieve a zero diastolic pressure as measured with a
pressure transducer (Statham model P23 Db) and physiograph (4-channel
recorder, Gould, Cleveland, OH). The hearts were paced at 240 beats/min
using bipolar pacing (Grass Instruments, Quincy, MA). Left ventricular
systolic and diastolic pressures were recorded at five balloon volumes (50-300 µl) yielding positive and negative first derivatives of left ventricular pressure with respect to time
(±dP/dt). Coronary perfusion
flow was determined at the midpoint balloon volume (150 µl) by
collection of the coronary effluent for 1 min.
After these initial pressure-volume curves were recorded, the
cannulated hearts were removed from the hydrostatic apparatus and
connected to a pulsatile roller pump (Minipuls 2 pump, Gilson, Middleton, WI). The hearts were perfused at a flow rate of 2 ml/min through Tygon tubing (R3603) using one of the seven cardioplegic solutions (Table 1) saturated with 95%
O2-5%
CO2. Disposable 5-µm filters
(Gilson) were placed in the perfusion line immediately before entry
into the aorta. Each heart was placed in a plastic bag
(Saran) that was vented at the top to ensure moistness. The entire
apparatus was transferred to a cold chamber (5°C) for 24 h with
continuous recirculated perfusion. The pH of the perfusate was
continuously monitored and remained at 7.4 due to the bubbling of the
95% O2-5%
CO2 mixture.
After 24 h of cold storage, the heart was removed from the cold
chamber, reattached to the hydrostatic apparatus, and reperfused with
warm (37°C) K plus albumin (described above) to which mannitol (68 mM) was added. The mannitol was added to make the solution hyperosmolar
(330 mosM) to reduce edema (21). Pressure-volume curves and short-term
coronary flow were recorded again, and reperfusion fluid was collected
for creatine kinase analysis. Percentage measurements for the recovery
period were made at a midpoint balloon volume of 150 µl.
The data were not corrected for the difference in the final coronary
flow rates because, during the majority (99%) of the preservation
period, flow was held constant at 2 ml/min. During the preservation
period, the hearts were quiescent, and on reperfusion any arrhythmias
stopped when 37°C was reached. Occasionally a higher
voltage was used to maintain heart rate until 37°C was reached, and
then the voltage was turned down to normal (4 V). Hearts were
weighed before and after preservation to determine water accumulation.
After the final tests, the hearts were frozen (70°C) and
later used for MDA assays.
Reperfusion fluids were analyzed for creatine kinase using the Sigma
Diagnostics method (Sigma Diagnostics, St. Louis, MO, 20) that was
optimized by Szasz (28). Samples were either analyzed immediately for
creatine kinase or refrigerated (5°C) for no longer than 1 wk
before analysis. Our data suggest that for prolonged storage the
addition of 2.5 g/dl albumin is required to stabilize the enzyme (7).
Whole heart MDA was measured as an indicator of lipid peroxidation by
the thiobarbituric acid (TBA) method first developed by Kohn and
Liversedge (17) for brain tissue and later modified for other
biological tissues (4). Kosugi and Kikugawa (18) analyzed the potential
MDA reactive substances in peroxidized lipids and showed that the TBA
method measures lipid oxidation. There has been some controversy as to
the sensitivity of MDA as a marker for lipid peroxidation at low free
radical levels (3); however, we feel it provides an adequate marker in
24-h studies with elevated lipid peroxidation. In brief, the heart
tissue was prepared by first removing the aorta and cutting the heart
into pieces. The pieces were then placed in a large mortar, covered with liquid nitrogen, and ground into a fine powder. The powdered tissue was mixed with water (ratio of tissue to water 1:9 by mass) to
lyse the cells. The supernatant was added to a TBA-TCA solution and
heated for 1 h at 95°C. The supernatant was removed from the flocculent precipitate, and the absorbance was determined at 535 nm
against a sample blank containing all of the reaction constituents minus the TBA (4). The MDA concentrations were calculated from a
standard curve prepared with 1,1,3,3-tetramethoxypropane (Sigma).
Results were analyzed for significance by one-way ANOVA, followed by
the Student-Newman-Keuls method for pairwise multiple comparisons, and
are expressed as means ± SE. All experiments were performed
according to the guidelines of "The Principles of Laboratory Animal
Care" (NIH), and procedures were approved by the University of Akron
Animal Use and Care Committee.
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RESULTS |
The results of the cardioplegia comparisons are summarized in Table
2. The percent recovery of contractility
(+dP/dt) and relaxation
(dP/dt) after 24 h of
preservation for each group is shown in Figs.
1 and 2,
respectively. The results for both contractility and relaxation were
similar. The addition of albumin (KA) or mannitol (KM) to the Krebs
buffer had no significant effect in the Krebs groups (K). The addition
of albumin to the E group (EA) produced a large increase in the percent
recovery of contractility (P < 0.05). The enhanced mannitol-containing solution (EM) showed a decrease
in the percent recovery (P < 0.05).
When both albumin and mannitol were added to the enhancers (EAM), the
positive albumin effect and the negative mannitol effect canceled each
other out, and group EAM was not
significantly different from group E. Group E and group
K showed about the same contractility.
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Fig. 1.
Left ventricular contractility
(+dP/dt) recovery (%) in each
treatment group after 24-h heart preservation. K, Krebs-Henseleit
solution; KA, Krebs + albumin; KM, Krebs + mannitol; E, enhancers; EA,
enhancers + albumin; EM, enhancers + mannitol; EAM, enhancers + albumin + mannitol. Values are means ± SE.
* P < 0.05, ** P < 0.01 compared with
group E.
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Fig. 2.
Left ventricular relaxation
(dP/dt) recovery (%) in each
treatment group after 24-h heart preservation. Values are means ± SE. * P < 0.05 compared with
group E.
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The percent recovery of coronary flow is shown in Fig.
3. As previously described, the
addition of albumin (KA) or mannitol (KM) to the K solution had no
significant effect in the K groups. The addition of albumin in the E
group (EA) produced a large (49%) increase in the percent recovery of
coronary flow (P < 0.05). The
addition of mannitol (EM) gave the same result as the control (E), as
did the addition of both albumin and mannitol. The percent recovery of
group E was similar to that of
group K (51% and 61%, respectively).
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Fig. 3.
Percent coronary flow recovery in each treatment group after 24-h heart
preservation. Values are means ± SE.
* P < 0.05 compared with
group E.
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The change in diastolic pressure (Torr) is shown in Fig.
4. In all groups the diastolic pressure
increased after 24 h. In the K groups, the addition of albumin (KA) had
no effect, but mannitol (KM) produced a very large increase (120%) in
diastolic pressure (P < 0.01). In
the E groups, the addition of albumin (EA) greatly reduced (69%) the
postcardioplegia diastolic pressure increase
(P < 0.01). The addition of mannitol
(EM) had no effect, although the addition of both albumin and mannitol
(EAM) gave a small nonsignificant decrease (24%), i.e., the mannitol
counteracted some of the positive effect of the albumin in
group EAM. The addition of enhancers
to the K solution (group E vs.
group K) caused a large increase
(78%) in the postcardioplegia diastolic pressure (P < 0.05).
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Fig. 4.
Left ventricular diastolic pressure (actual increase in pressure
compared with initial time 0 value) in
each treatment group after 24-h heart preservation. Values are means ± SE. * P < 0.05 for E vs.
K; ** P < 0.01 for EA vs. E
and for KM vs. K.
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The percent recovery of systolic pressure is shown in Fig.
5. There were no significant differences
among the K groups. Groups EA and
EM showed a significant reduction
(15%) compared with group E
(P < 0.05), and
group EAM showed a larger decrease in
function (22%, P < 0.01).
Group E had a 33% increase in
systolic function compared with group
K (P < 0.05). There
was no significant difference among any of the groups in percent mass
gain (Fig. 6).
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Fig. 5.
Left ventricular systolic pressure recovery (percentage of initial
time 0 value) for each treatment group
after 24-h heart preservation. Values are means ± SE.
* P < 0.05 for E vs. K, for EA
vs. E, and for EM vs. E; ** P < 0.01 for EAM vs. E.
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Fig. 6.
Percent mass gain recovery of initial time
0 value compared with 24-h preservation value. Values
are means ± SE; no significant differences.
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The postpreservation efflux of creatine kinase is shown in Fig.
7. In the K groups, the addition of albumin
(KA) or (KM) mannitol had no significant effect. In the E groups,
albumin (EA) produced a substantially reduced (37%,
P < 0.05) creatine kinase value, whereas mannitol (EM) had no effect; the combination of albumin and
mannitol (EAM) had no effect. The addition of enhancers
to group K caused a nonsignificant
increase in the creatine kinase efflux.
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Fig. 7.
Creatine kinase levels (U/g heart) released to the perfusate in each
treatment group on reperfusion after 24-h preservation. Values are
means ± SE. * P < 0.05 for
EA vs. E.
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The production of MDA in heart tissue is shown in Fig.
8. In the K groups, the addition of albumin
(KA) caused a large decrease (39%, P < 0.01) in MDA, but there was no significant difference with the
addition of mannitol (KM). In contrast, in the E groups, the addition
of mannitol (EM) produced an increase in MDA (60%, P < 0.05), and the addition of both
albumin and mannitol (EAM) produced an even larger increase in MDA
(116%, P < 0.01). The addition of
enhancers to the K solution reduced MDA production (31%,
P < 0.05).
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Fig. 8.
Myocardial malondialdehyde values in each treatment group after 24-h
heart preservation. Values are means ± SE.
* P < 0.05 for E vs. K and for
EM vs. E; ** P < 0.05 for KA
vs. K and for EAM vs. E.
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DISCUSSION |
The effects of albumin in 24-h preservation.
In summary, albumin enhanced heart function through its role as an
antioxidant and increased cell metabolism protection after increased
energy supply provided by the enhancers. In the absence of the
enhancers, albumin in K (group KA) had no
effect on any of the physiological parameters with the exception of a
reduction in MDA. In stark contrast, albumin produced marked
improvement in four of the parameters in the presence of the enhancers
(group EA). The improvements of these
parameters are not due to the enhancers alone, because their addition
to K produced no or only slightly negative changes in the physiological
parameters (group E vs. group
K). Clearly, there is a synergistic effect between
albumin and one or more of the enhancers: insulin, pyruvate, ATP, and corticosterone.
What are the expected actions of the enhancers on the heart? Insulin
stimulates muscle cells to take up glucose: the administration of
insulin can increase the rate of passive-mediated glucose transport into the cells by an order of magnitude. This increase in cellular glucose will stimulate metabolism via the glycolytic pathway, where the
overall reaction is (30)
Under
anaerobic conditions, NAD+ is
regenerated when NADH reduces pyruvate to lactate, although under
aerobic conditions mitochondrial oxidation of NADH yields three ATPs.
During preservation, the cellular oxygen levels are below normal so
that substantial pyruvate will be consumed in reducing
NAD+, although the production of
ATP will be reduced. The addition of pyruvate and ATP to the perfusate
can compensate for the losses of pyruvate and ATP required for cell
function, provided they can cross the cell membrane. A deficit of
glucocorticoids, such as corticosterone (e.g., in disease states such
as Addison's disease), is characterized by hypoglycemia, muscle
weakness, Na+ loss,
K+ retention, and impaired cardiac
function; the addition of corticosterone may compensate for membrane
stabilization and energy loss during cardioplegia. In summary, the
expected actions of the enhancers are stimulation of metabolism in the
heart muscle cells by insulin, pyruvate, and ATP and regulation of cell
functions by corticosterone. As noted above, the observed actions when
just the enhancers were added to the K solution were essentially nil or
slightly negative with regard to the physiological function parameters.
What are the normal functions of albumin and what pathways are there
for synergism between albumin and one or more of the enhancers? Albumin
is a water-soluble protein that makes up about one-half of the
blood-serum protein. In addition to regulation of osmotic pressure,
albumin plays an important membrane transport function (30). Steroids
such as corticosterone can be transported in the blood and be made
accessible to cells in complex with albumin. Albumin binds free fatty
acids in the blood; when the fatty acid concentration is too large,
they form micelles that act as detergents to disrupt protein and
membrane structure (30). Human albumin has specific sites
for binding of copper ions. Albumin can scavenge hypochlorous acid and
thereby prevent damage to
1-protease (15). Albumin can
inhibit peroxidation (14), exhibit antioxidant capacity (13), decrease
lipoxygenase activity (31), and act as a coenzyme for tissue-repair
enzymes. In general, proteins such as albumin probably play a
protective role in vivo by acting as "sacrificial antioxidants"
(15).
As noted above, the addition of albumin alone to the K solution had no
effect on the physiological parameters, but the production of MDA was
reduced. This is consistent with albumin simply acting as a sacrificial
antioxidant, although the reduction in peroxidation was not sufficient
to be reflected in the physiological parameters measured.
For groups
E and EA, the expected
actions of the enhancers and of albumin and their observed synergism
suggest the following conclusions. The enhancers, particularly insulin,
pyruvate, and ATP, stimulate metabolism in the heart muscle cells. This
is both good and bad. The stimulation of metabolism should increase the viability of the cells; however, when metabolism was increased, the
oxygen deficit in the already-ischemic cells was increased. Thus in
group E hearts the positive and
negative effects essentially cancel each other out with regard to the
physiological parameters, except in the percentage of coronary flow
recovery and diastolic pressure increase, where small negative effects
were observed (group E vs.
group K). A decrease in MDA
appeared, just as for group KA, which
can be attributed in group
E to insulin acting as a sacrificial
oxidant. When albumin was introduced, the negative effects were offset,
whereas the positive effects were unmasked. Why is this so? One
potential mechanism is that the increased rate of metabolism stimulated
by the enhancers produced increased free radical production with
concomitant increases in lipid peroxidation pathways: thus the very
slight negative effect of the enhancers on the physiological
parameters. The addition of albumin gave protection from the negative
effects of lipid peroxidation, expected from the above discussion, thus
allowing the positive effects of increased cellular metabolism to
emerge. Albumin acts as a competing sacrificial oxidant and thereby
protects the insulin concentration, thus promoting an increase in
metabolism above that seen in group
E. This increase in metabolic rate for
group EA results in an increase in the
number of viable cells, reflected in the physiological parameters by a
concomitant increase in the absolute amount of peroxidation, which is
reflected in the slightly increased MDA. In addition to promoting an
increased metabolic rate, albumin should enhance the positive effects
of corticosterone by promoting its transmembrane mobility. The
seemingly contradictory result of slightly (nonsignificantly) increased
MDA production and decreased creatine kinase release might be explained
in that MDA reflects the cumulative 24-h biochemical peroxidation,
creatine kinase reflects the structural cell damage on reperfusion, and severe cell damage has not yet occurred.
The effects of mannitol on physiological parameters in 24-h
preservation.
In summary, mannitol decreased heart performance when interacting with
the enhancers most likely by reducing energy substrates to the cells
and potentially causing cell damage in the long term. In the absence of
the enhancers, mannitol in K (group KM) had no effect on any of the physiological parameters except for a large
increase in diastolic pressure indicative of increased heart stiffness,
which was probably due to injury rather than edema because there were
no significant differences between groups in water gain.
As with albumin (group
KA), mannitol
produced a decrease in MDA. In the presence of the enhancers, mannitol
greatly reduced the contractility and relaxation, and significantly
reduced systolic pressure recovery (group
EM). These responses were not due to the enhancers
alone because they produced little change in the physiological
parameters (E vs. K). Clearly, as with albumin, there was a synergism
between mannitol and one or more of the enhancers, only it was a
negative synergism with mannitol.
Many compounds structurally similar to
D-glucose, including
D-mannitol, inhibit glucose
transport across the cell membrane. The addition of mannitol to the
perfusate would be expected to introduce competitive inhibition of
glucose uptake into the heart muscle cells, which may not be so
important in the short term, but in long-term perfusions it could lead
to cell exhaustion. Many studies have shown enhanced cardiac recovery
when mannitol was administered during short-term
ischemia-reperfusion. The positive effects observed in the
various systems included reduced MDA production (5, 19), arterial
vasodilation (23), prevention of cell swelling (22, 26, 29), improved
energy metabolism (12), and decreased reperfusion-induced arrhythmias
(10, 35). At higher mannitol concentrations (>50 mM) and longer
times, cell dehydration, membrane damage, and increased capillary
permeability have been reported (1).
Some of the long-term effects of mannitol can be understood on the
basis of its metabolic effects vis-à-vis inhibition of glucose
uptake by the cells. In group KM, the
increase in stiffness indicated by the large diastolic pressure
increase can be attributed to damage resulting from "starvation"
of the muscle cells over a 24-h period; the reduction in MDA observed
arises either from the reduced metabolic rate or from sacrificial
antioxidant behavior by the mannitol.
What about the negative synergism between mannitol and the enhancers?
This can be observed by examining the effect of the enhancers of
group EM with respect to
group KM. With the addition of the
enhancers, mannitol had a much more negative effect on the heart. The
rate of glucose uptake by the heart muscle cell should be much larger
in groups containing the enhancers because of the insulin; however,
when mannitol is present, it competitively inhibits the glucose uptake.
For the group EM, this means increased mannitol concentrations inside the cell, as well as perhaps decreased glucose. But clearly, extra tissue damage occurs with
enhancers and mannitol, and so it seems reasonable to assume that the
damage arises from the mannitol inside the cell, which is stimulated by
the insulin. Interestingly, the percent mass gain for the
group EM was the smallest of all the
groups; however, the difference was not significant. Mannitol has been
used as an agent to prevent edema in perfused organs, but does the
mannitol cause dehydration of some cells? As the mannitol accumulates
in the cell it may suppress any further influx of glucose and lead to
cell starvation. Blocking of glucose uptake by mannitol may not matter
for short time periods, and its control of osmotic pressure is
beneficial, but for 24-h preservation mannitol appears harmful.
In conclusion, we have shown that mannitol (68 mM) does not offer added
protection to cardioplegia during 24 h of cold storage in rat heart. In
contrast, albumin (1.4 µM) improved heart preservation and in
combination with the enhancers (insulin, ATP, corticosterone, and
pyruvic acid) offers the best combination of additives of the solutions
tested. Our cardioplegia with enhancers and albumin preserved heart
function equal to or better than that of the CP-11EB solution and
intermittent perfusion intervals in cold rat heart (36); however, an
iron chelator added to the cardioplegia preserves heart function even
more (8). Hisatomi et al. (16) also found that albumin
improved 6-h cold rat heart preservation at very high concentrations
(2% and 5% did, but 7% did not). This beneficial effect may be due
to synergism between the enhancers and albumin influencing myocardial
glucose metabolism.
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ACKNOWLEDGEMENTS |
The authors thank Fieke Bryson for animal maintenance, Dean
Petrinec for technical assistance, Dr. Michael Dunphy for editing, and
Linda Bordenkircher and Sarah Francis for typing the manuscript.
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FOOTNOTES |
This project was made possible by grants from the State of Ohio
Academic Challenge and Research Challenge Programs and The University
of Akron and by National Heart, Lung, and Blood Institute Grant
R15-HL-41779-01A2 (to H. Richter).
Address for reprint requests and other correspondence: D. L. Ely, Dept.
of Biology, Univ. of Akron, Akron, OH 44325-3908 (E-mail:
Ely1{at}uakron.edu).
Received 30 July 1998; accepted in final form 13 January 1999.
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