Vol. 93, Issue 6, 1952-1958, December 2002
O
-mediated impairment of coronary arterial
relaxation is prevented by overnight treatment with 1 nM
-estradiol
David R.
Bell,
Kristen E.
Gochenaur, and
Jennifer
Hecht
Department of Cellular and Integrative Physiology,
Indiana University, School of Medicine, Fort Wayne, Indiana 46805
 |
ABSTRACT |
We tested the hypothesis that the
ability of coronary arteries to withstand functional damage from
superoxide (O
) is altered by exposure of the
arteries to a physiological concentration of 
-estradiol. Female
porcine coronary arterial rings were incubated in an
O2-CO2 incubator, under normoxic conditions, at
37°C for 22-24 h. Arteries were then placed in baths containing
a physiological salt solution at 37°C with 95% O2-5%
CO2 for isometric force recordings. In rings from 14 female
pigs, vasorelaxation to A-23187 and diethylamine-NONOate (DEA-NONOate) was determined with and without prior 15-min exposure to
400 µM pyrogallol. Sensitivity (
logM ED50) and maximum
relaxation to A-23187, but not DEA-NONOate, were significantly impaired
by exposure to pyrogallol (pyrogallol treated: 7.39 ± 0.09, 82 ± 5%; control: 7.76 ± 0.11, 99 ± 1%, means ± SE; P < 0.01 and P < 0.05, respectively). This effect was attenuated by concurrent exposure to
equimolar ascorbate. Arterial rings from 12 separate female pigs were
incubated for 22-24 h with or without 1 nM -estradiol before
pyrogallol exposure. -Estradiol significantly enhanced arterial
sensitivity to A-23187 and prevented pyrogallol impairment without
affecting DEA-NONOate responses. Therefore, superoxide-mediated endothelial damage and impaired endothelium-dependent relaxation of
coronary arteries are prevented by overnight exposure of the arteries
to a physiological concentration of -estradiol.
nitric oxide; vascular injury; oxygen radicals
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INTRODUCTION |
OUR LABORATORY HAS REPORTED
PREVIOUSLY (4) that endothelium-dependent,
NO-mediated relaxation of isolated porcine coronary arteries is
enhanced after direct overnight incubation of the arteries with 1 nM
-estradiol. This enhancement was related to an effect on the
arterial endothelium rather than on the responsiveness of the arterial
smooth muscle to NO and was not seen in arteries exposed acutely to 1 nM -estradiol or in arteries incubated overnight with either 1 nM
-estradiol or 1 nM -estradiol plus tamoxifen. Results from
studies by other investigators in experimental animals (1, 11,
15, 37) and humans (5, 11) have supported the
concept that long-term exposure to estrogen enhances the arterial endothelial NO system. It has been suggested that estrogen may be
responsible for the lower incidence and severity of cardiovascular disease in premenopausal women compared with age-matched postmenopausal women or men (26, 28, 38).
The vascular pathology associated with several cardiovascular diseases
involves overproduction of reactive oxygen species in the vascular wall
and surrounding tissues that can stimulate vascular smooth muscle cell
proliferation, damage the arterial endothelium, and render arteries
prospasmodic, proatherogenic, and prothrombotic (12, 14, 21,
24). Exposure to superoxide (O) and other
oxygen radicals impairs endothelium-dependent, NO-mediated
vasorelaxation, which is mediated through direct damage to the arterial
endothelium as well as from chemical reaction of NO with
O (20, 32). It has been suggested that
under certain conditions the reaction of NO with O
may actually result in accelerated arterial damage and pathology due to
the formation of peroxynitrite, lipoxides, and hydroxyl radicals
(3, 31). However, NO has been shown to inhibit
atherogenesis and ischemia-reperfusion injury, which are
pathological conditions associated with overproduction of superoxide
(6, 8, 22).
It is not known whether enhanced endothelial NO relaxation of porcine
coronary arteries after overnight exposure to estrogen results in an
artery whose reactivity is more or less susceptible to impairment by
subsequent exposure to O. Therefore, we utilized a
simple method for inducing partial, O-mediated, functional damage to isolated porcine coronary arteries to test the
hypothesis that overnight exposure of coronary arteries to a
physiological concentration of -estradiol alters their ability to
withstand functional damage from oxygen radicals.
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METHODS |
Superoxide arterial injury model.
Hearts from female pigs were obtained from local slaughterhouses
immediately after death and placed in physiological salt solution (PSS)
at 4°C (PSS, in mmol/l: 130 NaCl, 4.7 KCl, 14.9 NaHCO3,
5.5 dextrose, 1.18 KH2PO4, 1.17 MgSO4 · 7 H2O, 1.60 CaCl2 · 2 H2O, 0.03 CaNa2 EDTA). Hearts then were transferred to our laboratories, and the left anterior descending and circumflex coronary
arteries were carefully dissected free from the surrounding tissue and
washed with sterile PSS. With the use of sterile procedures, the artery
was cleaned of excess fat and connective tissue and cut into 2- to
4-mm-wide rings. For the following experiments, each pig served as its
own control. Rings were transferred under sterile conditions into
separate petri dishes containing sterile HEPES-buffered serum- and
phenol red-free DMEM with antibiotic. All dishes then were placed in an
O2-CO2 incubator for 22-24 h utilizing
standard procedures for cell and tissue cultures. As such, rings were
kept in a humidified environment, with temperature and CO2
concentration precisely controlled at 37°C and 5.0%, respectively.
After the incubation period, rings were removed from the dishes and
washed with PSS. Next, all rings were suspended between triangular
stainless steel hooks and a stationary support rod, transferred to
artery baths containing PSS at 37°C and pH 7.4, bubbled with 95%
O2-5% CO2, and connected to FT.03 force
transducers (Grass Instruments, Quincy, MA) for isometric force
recording (Grass P7 and Gould 2400S recorders). Rings were suspended at a passive tension of 10 g, previously determined to produce
maximum force generation in all treatment groups, and allowed to
equilibrate for not less than 90 min. Maximum contractile force was
determined in all rings by exposure to PSS containing equimolar
replacement of NaCl with 130 mM KCl. Next, prostaglandin synthesis was
blocked in the rings by exposure to 10
5 M meclofenamic
acid for 30 min followed by repeated rinses with PSS.
Exposure of arteries to superoxide was accomplished through the
auto-oxidation of pyrogallol added to the artery baths
(25). Preliminary experiments were conducted to find a
pyrogallol dose and time exposure that would reduce sensitivity (logM
ED50) and efficacy (% maximum relaxation) of relaxation to
A-23187 without totally abolishing endothelium-dependent relaxation of
the rings. In this manner, the experimental design would allow for the
possibility, a priori, that overnight incubation of the arteries with
estrogen could attenuate or exacerbate this impairment. A-23187 is a
direct, receptor-independent activator of endothelium constitutive
nitric oxide synthase (ecNOS) (29). In porcine
coronary artery rings pretreated with meclofenamate, A-23187 produces
dose-dependent relaxation that is entirely mediated by endothelial NO
(4). [Acetylcholine, the most common receptor-mediated
activator of ecNOS, is not an appropriate agonist of
endothelium-dependent relaxation of coronary arteries from pigs because
it produces marked endothelium-independent contraction, with little or
no relaxation of any type, in coronary arteries from that species (7).]
Preliminary experiments indicated that exposure of artery rings to 400 µM pyrogallol for 15 min resulted in the desired impairment of
A-23187 coronary arterial relaxation. Therefore, we documented the
effects of this exposure using coronary artery rings from 14 female
pigs. After the PSS rinses following treatment with meclofenamate,
rings were allowed to reequilibrate for 30 min. Half the rings were
then exposed to 400 µM pyrogallol for 15 min, followed by repeated
rinses with PSS. The remaining rings were not exposed to any agents
during this time and served as controls. All rings were then contracted
to ~35-45% of their individual KCl maximum with the thromboxane
analog U-46619. Dose-response relationships, from subthreshold to
maximum response, to A-23187 and the NO donor diethylamine-NONOate
(DEA-NONOate) were determined in all rings. DEA-NONOate spontaneously
releases NO when exposed to pH < 8.0 and thus serves as a source
of NO for the rings. This source has the advantage of avoiding required
intracellular bioconversion to produce NO, as is the case with
nitroglycerin, and does not possess the secondary, non-cGMP-mediated
vasodilator properties of sodium nitroprusside.
In separate experiments, coronary artery rings with endothelium from
seven additional mature female pigs were incubated in vehicle control
media overnight, suspended in artery baths, and exposed to KCl and
meclofenamate as described above. Half the rings were then exposed to
either 400 µM pyrogallol, 400 µM pyrogallol + 400 µM
ascorbic acid, or 400 µM ascorbic acid alone for 15 min followed by
repeated rinses with PSS. The remaining rings were not exposed to any
agents during this time and served as controls. Dose-response
relationships to A-23187 and DEA-NONOate were determined in all these
rings as described above.
Effect of -estradiol on pyrogallol-mediated impairment of
coronary arterial reactivity.
Coronary arterial rings from 12 additional mature female pigs were used
to examine whether impaired coronary arterial reactivity after exposure
to pyrogallol is altered by prior overnight exposure to estrogen. Rings
were incubated in tissue culture media as described above except that
half of the rings from each pig were incubated for 22-24 h with
109 M 17-estradiol. The remaining rings received
estrogen vehicle (0.01% ethanol). Rings were then prepared for
isometric force recordings, maximum contraction to KCl was determined,
and rings were treated with meclofenamate as described above.
Half the rings from the estrogen- and vehicle-treated groups were
exposed to 400 µM pyrogallol for 15 min, whereas the remaining rings
from each group were not exposed to any agent during this interval. Dose-response relationships to A-23187 and DEA-NONOate were determined in all rings as described above.
DEA-NONOate used in this study was obtained from Cayman Chemicals, Ann
Arbor, MI. All other chemicals used in these experiments were obtained
from Sigma Chemical, St. Louis, MO.
Data analysis.
In all experiments, individual pigs served as their own controls and
responses to all agents were recorded as the average response of two
rings per treatment type per pig. Sensitivity of the coronary rings was
expressed as the log M half-maximal effective dose (ED50)
value determined by probit transformation and linear regression of the
dose-response relationship. Differences among the means of treatment
groups were tested by a paired t-test with the Bonferroni
correction for multiple comparisons. Any alteration in responses to
A-23187 were to be compared with responses to DEA-NONOate in coronary
artery rings from the same pig. This comparison was made to determine
whether any alteration in endothelium-dependent relaxation
caused by a treatment was a reflection of altered endothelial function
related to NO or, instead, was a reflection of altered arterial smooth
muscle responsiveness to NO.
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RESULTS |
Responses of porcine coronary arteries to A-23187 with and without
prior exposure to pyrogallol are depicted in Fig.
1. Exposure to 400 µM pyrogallol for 15 min resulted in a significant decrease in sensitivity and maximum
relaxation to A-23187 (Table 1). In contrast, sensitivity and maximum relaxation to DEA-NONOate were not
significantly altered by prior exposure to pyrogallol (Table 1 and Fig.
2).
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Fig. 1.
Relaxation responses of porcine coronary arterial rings
to cumulative 1/2 log doses of A-23187 with and without prior
exposure to 400 µM pyrogallol for 15 min. Rings were precontracted
with U-46619 to a similar percentage of their individual KCl maximum
before administration of A-23187. Pyrogallol impaired relaxation to
A-23187 compared with control rings. Values are means ± SE of the
mg force remaining after each dose as expressed per mg force of initial
precontraction to U-46619. Pyrogallol, rings exposed to 400 µM
pyrogallol for 15 min and then rinsed with PSS before relaxation by
A-23187; Control, rings not exposed to any agents during pyrogallol
exposure in test rings; n = 14 pigs, from which rings
were obtained. * P < 0.05 vs. control.
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Fig. 2.
Relaxation responses of porcine coronary arterial rings
to cumulative 1/2 log doses of diethylamine-NONOate
(DEA-NONOate) with and without prior exposure to 400 µM pyrogallol
for 15 min. Rings were precontracted with U-46619 to a similar
percentage of their individual KCl maximum before administration of
DEA-NONOate. Values are means ± SE of the mg force remaining
after each dose as expressed per mg force of initial precontraction to
U-46619; n = 14 pigs. There were no significant
differences in the responses between the Pyrogallol and Control
groups.
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Subsequent experiments with this pyrogallol injury model yielded
similar results in coronary arteries from seven additional female
pigs (Figs. 3 and
4 and Table
2). This experiment also demonstrated
that the impaired A-23187 relaxation after pyrogallol exposure was
attenuated by concurrent exposure to equimolar concentration of
ascorbic acid. Responses to rings treated with ascorbate + pyrogallol did not differ significantly from those treated with ascorbate alone.
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Fig. 3.
Effect of 400 µM pyrogallol and ascorbate on relaxation
responses of porcine coronary arterial rings to cumulative 1/2 log doses of A-23187. Rings were examined after 15-min exposures to 400 µM pyrogallol, 400 µM ascorbate, or 400 µM pyrogallol + 400 µM ascorbate. Rings were precontracted with U-46619 to a similar
percent of their individual KCl maximum before administration of
A-23187. Pyrogallol impaired relaxation to A-23187 compared with
control rings. This effect was attenuated by concurrent exposure to
ascorbate. Responses after exposure to ascorbate + pyrogallol were
not significantly different from responses after ascorbate alone.
Values are means ± SE of the mg force remaining after each dose
as expressed per mg force of initial precontraction to U-46619. Asc.
Acid, rings exposed to 400 µM ascorbic acid for 15 min and then
rinsed with PSS before relaxation by A-23187; Asc. Acid + Pyrog.,
rings exposed to 400 µM ascorbic acid and 400 µM pyrogallol for 15 min and then rinsed with PSS before relaxation by A-23187;
n = 7 pigs per group. * P < 0.05 vs. control.
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Fig. 4.
Effect of 400 µM pyrogallol and ascorbate on relaxation
responses of porcine coronary arterial rings to cumulative 1/2 log doses of DEA-NONOate. Rings were examined after 15-min exposures to
400 µM pyrogallol, 400 µM ascorbate, or 400 µM pyrogallol + 400 µM ascorbate. Rings were precontracted with U-46619 to a similar
percentage of their individual KCl maximum before administration of
DEA-NONOate. Values are means ± SE of the mg force remaining
after each dose as expressed per mg force of initial precontraction to
U-46619; n = 7 pigs per group. There were no
significant differences in the responses among the groups.
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The effects of direct overnight exposure of arterial rings from 12 additional mature female pigs to 1 nM -estradiol, on relaxation to
A-23187 with and without prior exposure to pyrogallol, are depicted in
Fig. 5 and Table
3. Overnight incubation with 1 nM -estradiol significantly enhanced sensitivity of rings to A-23187. Greater mean relaxation was observed at every dose of A-23187, and
enhanced sensitivity to A-23187 was observed in all
-estradiol-treated rings in all pigs. Maximum relaxation and
sensitivity of the coronary artery rings to A-23187 was significantly
reduced by acute exposure to pyrogallol. In contrast, maximum
relaxation and sensitivity to A-23817 after acute exposure to
pyrogallol was not impaired in rings incubated overnight with 1 nM
-estradiol compared with control rings. Overnight treatment of rings
with -estradiol did not affect responses of rings to DEA-NONOate,
with or without prior treatment with pyrogallol (Fig.
6; Table 3).
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Fig. 5.
Relaxation responses of porcine coronary arterial rings
to cumulative 1/2 log doses of A-23187. Rings were incubated for
22-24 h in either 1 nM -estradiol or estradiol vehicle.
Responses to A-23187 in rings from both of these groups were then
examined with and without prior exposure to 400 µM pyrogallol for 15 min. Rings were precontracted with U-46619 to a similar percent of
their individual KCl maximum before administration of A-23187. BE2,
rings incubated overnight with 1 nM -estradiol and not exposed to
any agents during pyrogallol exposure in test rings; BE2 + Pyrog.,
rings incubated overnight with 1 nM -estradiol and subsequently
exposed to 400 µM pyrogallol for 15 min and then rinsed with PSS
before relaxation by A-23187. Overnight incubation of rings with
estradiol enhanced responses to A-23187. Pyrogallol impaired relaxation
to A-23187 in rings incubated overnight with estradiol vehicle but not
in those incubated overnight with 1 nM -estradiol. Values are
means ± SE of the mg force remaining after each dose as expressed
per mg force of initial precontraction to U-46619; n = 12 pigs per group. * P < 0.05 vs. control.
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Fig. 6.
Relaxation responses of porcine coronary arterial rings
to cumulative 1/2 log doses of DEA-NONOate. Rings were incubated
for 22-24 h in either 1 nM -estradiol or estradiol vehicle.
Responses to DEA-NONOate in rings from both of these groups were then
examined with and without prior exposure to 400 µM pyrogallol for 15 min. Rings were precontracted with U-46619 to a similar percentage of
their individual KCl maximum before administration of DEA-NONOate.
Values are means ± SE of the mg force remaining after each dose
as expressed per mg force of initial precontraction to U-46619. There
were no significant differences among the groups; n = 12 pigs per group.
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DISCUSSION |
Pyrogallol is an auto-oxidizing source of O
(29, 39) that has been used as an agent to induce damage
from reactive oxygen species in in vitro arterial bath and other
preparations (19, 53). Exogenous generation of superoxide in isolated artery bath preparations has been shown to impair subsequent endothelium-dependent relaxations in the arteries through physical damage to the arterial endothelium (23) that can
be mitigated by concurrent exposure to ascorbate used as an
O scavenger (44). In our study, acute
exposure of isolated porcine coronary arteries to pyrogallol resulted
in an impairment of subsequent endothelium-dependent, NO-mediated
vasorelaxation that could be attenuated by concurrent exposure to
ascorbate. This impairment could not have been due to quenching of
O by NO released by A-23187 because the pyrogallol
was not present in the artery baths during the A-23187 dose-response
determination. We believe the results of our experiment are consistent
with the concept that superoxide generated from pyrogallol initiated
events that resulted in functional damage to the endothelium of
isolated porcine coronary arteries.
This pyrogallol-mediated damage, however, did not appear to extend to
the underlying arterial smooth muscle. We did not intend, nor expect,
to produce a superoxide arterial injury model that selectively affected
the arterial endothelium. However, this result is not unreasonable
because pyrogallol, acting as an exogenous source of superoxide, would
be expected to act at the outer portions of the isolated artery ring
first. Thus any superoxide generated by pyrogallol would affect the
vascular endothelium and adventitia initially. Furthermore, these
tissue layers would act indirectly to delay any damage to underlying
vascular smooth muscle in the ring. During our preliminary studies, we
experimented with exposing arteries to different pyrogallol
concentration and time exposure combinations. We found that time and/or
concentration exposures greater than those used in the present
experiments too often resulted in severe or total inhibition of
arterial relaxation to A-23187, whereas doses and time exposures less
than those used presently too often produced no impairment of A-23187
responses (data not shown). Because such results negate the possibility
that one could detect, respectively, whether overnight exposure to
estrogen exacerbated or attenuated arterial injury after exposure to
pyrogallol, we did not use pyrogallol exposures different from 400 µM
and 15 min in this study.
Our study has shown that overnight exposure of isolated porcine
coronary arteries to a physiological concentration of -estradiol produces a direct effect on the vessel itself that both enhances endothelium-dependent, NO-mediated relaxation and protects this type of
relaxation from the effects of exposure to pyrogallol. Furthermore, the
effect of -estradiol appears to be mediated through actions on the
arterial endothelium because vasorelaxant responses of the rings to
exogenous NO were not affected. Although the direct effect of overnight
incubation of arteries with estradiol to enhance endothelium-dependent,
NO-mediated relaxation has been reported previously (4),
this study demonstrates that such treatment also protects these
arteries from superoxide-mediated damage.
This study was not designed to examine the underlying mechanisms of
this protection, but evidence exists in the literature for several
possibilities. Exposure to estrogen may enhance the intrinsic oxidant
defense capacity of an artery or the arterial endothelium. Estrogen
provides protection of arteries from ischemia-reperfusion injury (19) and preserves endothelial function while
limiting low-density lipoprotein oxidation in
hypercholesterolemic swine (18). Both these conditions are
associated with increased superoxide and reactive oxygen species load,
although the mechanisms underlying the effects of estrogen in these
conditions are not known. However, Barbacanne et al. (2)
have reported that superoxide production, as measured by both
chemiluminescence and electron spin resonance spectroscopy, is
significantly reduced in bovine cultured endothelial cells after
exposure to 1 nM ethinyl estradiol for 48 h. In addition, Si et
al. (33) have reported recently that levels of superoxide dismutase and catalase as well as the mRNA for these enzymes are increased in cultured endothelial cells that have been exposed to 1 nM
-estradiol for 24 h. An enhancement of arterial defenses against reactive oxygen species after estrogen exposure could provide a
measure of protection against an exogenous assault from O as well as enhance arterial relaxation to A-23187
(23, 32). However, it is not known whether this effect is
seen in isolated arteries incubated with estrogen, such as those used
in our study, nor whether such an effect on the biochemical level in
cultured cells translates to a functional alteration in intact blood vessels.
The endothelium can be a source of O (10,
27). Wagner et al. (39) have shown that the
superoxide-generating enzyme NADPH oxidase is downregulated in cultured
endothelial cells after direct long-term exposure to 1 nM
-estradiol. It might be expected that such an effect of estrogen
affords some protection against oxygen radical-mediated vascular
injury. This effect may even enhance relaxation of arteries to NO
generators such as A-23187 by reducing the removal of NO through its
reaction with O. However, it is difficult to imagine
how such an effect could protect arteries from an exogenously supplied
source of O such as that employed in our study. It
is reasonable to assume that any reduction in intrinsic
O generation in estrogen-treated rings would have a
minimal impact on the total O load experienced by
the rings in the artery baths while being exposed to pyrogallol.
Exposure of arteries to estrogen has been reported to upregulate their
NO synthase and NO-generating capacity (13, 15, 17, 36).
Such an effect could enhance responsiveness of estrogen-treated arteries to A-23187. However, the possibility that this effect alone
could also account for the increased ability of our estrogen-treated arteries to withstand oxygen radical assault is problematic. Using simplistic stoichiometry, one could postulate that, by increasing the
amount of NO produced, an artery could quench O while still leaving NO available to relax the underlying smooth muscle.
However, in our study the arteries were exposed to pyrogallol in the
basal, unstimulated state. It is difficult to imagine that basal NO
production was enhanced by overnight exposure to -estradiol such
that two arteries could quench the O generated from
400 µM pyrogallol in a 50-ml bath. Furthermore, one cannot simply
treat NO and O as mutually quenching reactants
without consideration for the products that are formed from the
reaction of the two radicals. NO is known to react with
O at diffusion-limited rates to generate
peroxynitrite, which is highly reactive and damaging to tissues
(3, 31). Therefore, exposing an artery to
O after an enhancement of its NO-generating capacity
could, theoretically, exacerbate superoxide-mediated injury. We allowed
for such a possibility in our experimental design by selecting a level
of O-mediated inhibition of A-23187 vasorelaxation
that was submaximal, thereby allowing for observation that treatment of
our arteries with estrogen might result in more or less functional
deficit in vasoreactivity after exposure to O.
However, the formation of significant quantities of peroxynitrite or
other damaging species from NO and O is highly
dependent on the concentration of the reactants present. It is quite
clear from the results of our study that overnight exposure of
arteries to estrogen did not result in additional damage to the
vessels after exposure to O. In fact, the
O-mediated reduction in A-23187 responses was
actually attenuated by overnight incubation of the arteries with
-estradiol. Therefore, it seems unlikely that our estrogen-treated
arteries produced damaging levels of peroxynitrite or subsequent
chemical species once exposed to exogenous O. This
is perhaps not surprising in that, although NO reacts rapidly with
O to form peroxynitrite, peroxynitrite in turn
reacts very rapidly with CO2. This process converts
peroxynitrite to nitrate while regenerating CO2, making
CO2 catalytic for the inactivation of peroxynitrite
(30, 35). The concentration of CO2 produced within living cells and used in artery baths is more than sufficient to
drive this reaction (30, 35).
Regardless of the underlying mechanisms, the possibility that estrogen
protects arteries from superoxide-mediated injury, if extrapolated to
the human population, has potentially far-reaching implications. The
difference in the incidence of cardiovascular disease between men and
premenopausal women is more than 4:1, with the difference between these
groups from heart attack alone at more than 40:1. It is difficult to
imagine how a simple enhancement of endothelium-dependent relaxation to
NO alone can account for such large differences. It is possible,
therefore, that the enhanced endothelium-dependent, NO-mediated
arterial relaxation, observed by us and other investigators, after
exposure to estrogen is simply a reflection of an overall upregulation
of the endothelial NO system and NO bioavailability. In this context,
enhanced vasorelaxation is observed because that is what is being
examined by the investigator, but it is other properties of NO, either
individually or collectively, that impart cardiovascular protection to
premenopausal women. Protection of the vasculature against oxygen
radical injury would appear to be a particularly high-impact mode of
cardiovascular protection in that increased oxygen radical load is a
common feature in the pathology of many different cardiovascular
diseases. In this context, such a common protective mechanism might be
able to create the type of large epidemiological differences in
cardiovascular disease and myocardial infarction between men and
premenopausal women.
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ACKNOWLEDGEMENTS |
This research was supported by a Grant-In-Aid to D. R. Bell
from the August Tomusk Foundation.
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FOOTNOTES |
Address for reprint requests and other correspondence:
D. R. Bell, Cellular and Integrative Physiology, Indiana
Univ., School of Medicine, 2101 Coliseum Boulevard East, Fort Wayne, IN
46805-1499 (E-mail: bell{at}ipfw.edu).
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
September 13, 2002;10.1152/japplphysiol.00615.2002
Received 9 July 2002; accepted in final form 20 August 2002.
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