Am J Physiol Heart Circ Physiol 299: H379–H385, 2010.
First published May 28, 2010; doi:10.1152/ajpheart.00294.2010.
Long-term exercise training does not alter brachial and femoral artery
vasomotor function and endothelial phenotype in healthy pigs
Jaume Padilla,1 Sean C. Newcomer,2 Grant H. Simmons,1 Kurt V. Kreutzer,1 and M. Harold Laughlin1,3,4
1
Biomedical Sciences, University of Missouri, Columbia, Missouri; 2Health and Kinesiology, Purdue University, West
Lafayette, Indiana; and 3Department of Medical Pharmacology and Physiology and 4Dalton Cardiovascular Research Center,
University of Missouri, Columbia, Missouri
Submitted 23 March 2010; accepted in final form 26 May 2010
chronic exercise; peripheral conduit artery; endothelium
accepted that exercise training
exerts direct effects on the vascular wall, a concept recently
referred to as vascular conditioning (9, 12, 29). The beneficial
effects of exercise on conduit artery endothelial function are
primarily notable in subject populations with preexisting cardiovascular risk factors or disease, that is, in individuals with
compromised vascular function (11, 21, 23, 29). Conversely, in
sedentary but otherwise healthy subjects, there is conflicting
evidence regarding the influence of exercise training on endothelial function (11, 21, 23, 29). The disparity of results may be
partially explained by the time point at which assessments are
performed. In this regard, it is proposed in both healthy animals
and humans (9, 11, 29) that the endothelial adaptive response
in conduit arteries is training duration-dependent such that
prolonging the exercise training leads to normalization of
function, possibly as a result of an arterial remodeling (9, 11,
13, 14, 17, 19, 29). In the present investigation, we sought to
determine whether, indeed, endothelial function of skeletal
IT IS BECOMING INCREASINGLY
Address for reprint requests and other correspondence: J. Padilla, Dept. of
Biomedical Sciences, W102 Veterinary Medicine, 1600 E. Rollins Rd., Univ.
of Missouri, Columbia, MO 65211 (e-mail: [email protected]).
http://www.ajpheart.org
muscle arteries from pigs demonstrating the classic traininginduced adaptations were similar to that of sedentary animals.
With the goal of examining this question in a large data set
(n ⫽ 127), we conducted a retrospective analysis of data collected
in our laboratory during the past 2 decades. Specifically, we
compared in vitro brachial and femoral artery endotheliumdependent and -independent relaxation between a group of
healthy pigs that exercise-trained for 16 –20 wk and a group
that remained sedentary. No differences in vasomotor function
were detected between the 2 groups in either vessel, thus
supporting the concept that, in healthy animals, long-term
exercise training does not enhance endothelium-dependent
dilation in peripheral conduit arteries. Notwithstanding this
outcome, it may be incorrect to presume that the absence of a
training-induced adaptation in vasomotor function implies a
lack of change toward an atheroprotective endothelial phenotype. To unravel this question, in a subset of pigs, expression
of 18 proteins that are frequently altered in early atherosclerotic disease were measured from brachial and femoral artery
endothelial cell scrapes. We hypothesized that trained animals
would reveal a more antiatherogenic endothelial cell phenotype
than their sedentary but otherwise healthy counterparts.
METHODS
Experimental animals. Between 1992 and 2010, 669 pigs entered
our research program, which is devoted to the study of the cardiovascular effects of exercise. All pigs were used with protocols approved
by the Animal Care and Use Committee at the University of Missouri.
Pigs were housed in rooms maintained at 20 –23°C with a 12:12-h
light-dark cycle. With the purpose to examine the influence of longterm exercise training on peripheral artery endothelial function in
healthy animals, we conducted a retrospective analysis of published
and unpublished data from our swine database. Specifically, we
selected data from pigs: 1) that were miniature Yucatan; 2) that were
12–14 mo old at time of death; 3) that were provided a standard diet
(Purina Lab Mini-Pig Chow; 8% of daily caloric intake derived from
fat); 4) that participated in a 16- to 20-wk exercise training program
(EX) or remained sedentary (SED); and 5) in which in vitro endothelium-dependent and -independent relaxation of brachial and/or femoral arteries was assessed. In the present study, data were obtained
from 127 pigs from which brachial (n ⫽ 113) and/or femoral arteries
(n ⫽ 89) were harvested. Out of the 113 brachial arteries, 59 were
derived from EX pigs (33 males, 26 females), and 54 were derived
from SED pigs (34 males, 20 females). Out of the 89 femoral arteries,
47 were derived from EX pigs (30 males, 17 females), and 42 were
derived from SED pigs (29 males, 13 females). It should be noted that
some data included here have been reported in previous studies (37,
38, 40) in which the pigs were used as controls against high-fat-fed
pigs. In a subset of 16 male pigs (8 EX, 8 SED), we measured protein
expression in endothelial cell scrapes from brachial and femoral
arteries. Furthermore, we used this subgroup of pigs to confirm our
0363-6135/10 Copyright © 2010 the American Physiological Society
H379
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Padilla J, Newcomer SC, Simmons GH, Kreutzer KV, Laughlin
MH. Long-term exercise training does not alter brachial and femoral
artery vasomotor function and endothelial phenotype in healthy pigs.
Am J Physiol Heart Circ Physiol 299: H379 –H385, 2010. First
published May 28, 2010; doi:10.1152/ajpheart.00294.2010.—Although the beneficial effects of exercise training on conduit artery
endothelial function are well-established in animals and humans with
compromised basal function, whether exercise exerts favorable effects
on a healthy endothelium is inconclusive. We sought to determine
whether long-term exercise training enhances endothelial function in
peripheral conduit arteries of healthy pigs. Using a retrospective
analysis of data collected in our laboratory (n ⫽ 127), we compared
in vitro brachial and femoral artery endothelium-dependent and -independent relaxation between a group of pigs that exercise-trained for
16 –20 wk and a group that remained sedentary. No differences in
vasomotor function were found between the 2 groups (P ⬎ 0.05).
Additionally, in a subset of pigs (n ⫽ 16), expression levels of 18
proteins that are typically associated with the atherosclerotic process
were measured by immunoblot analysis of endothelial cell scrapes
obtained from the brachial and femoral arteries. We found no differences (P ⬎ 0.05) in endothelial gene expression between these
exercise-trained and sedentary healthy pigs. These results indicate that
pigs exhibiting the classic training-induced adaptations do not demonstrate enhanced endothelium-dependent dilation nor reveal a more
atheroprotected endothelial cell phenotype in their brachial and femoral arteries than their sedentary but otherwise healthy counterparts.
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ENDOTHELIAL HEALTH IN EXERCISE-TRAINED VS. SEDENTARY PIGS
A
Fig. 1. A: photomicrograph showing immunoreactive staining for endothelial nitric oxide synthase
(eNOS) along the endothelial lining of an intact
femoral artery. B: photomicrograph demonstrating
loss of immunoreactivity to eNOS after scraping the
luminal surface of the artery to remove endothelium.
C: Western blot demonstrating enrichment of endothelial protein content with mechanical scraping of
the luminal surface (femoral artery). Note the increase in eNOS immunoreactivity between scraped
vessel, whole vessel, and endothelial scrape. EC,
endothelial cell.
Solutions and drugs for vasomotor experiments. Krebs bicarbonate
buffer solution contained 131.5 mM NaCl, 5.0 mM KCl, 1.2 mM
NaH2PO4, 1.2 mM MgCl2, 2.5 mM CaCl2, 11.2 mM glucose, 20.8
mM NaHCO3, 0.003 mM propranolol, and 0.025 mM EDTA. Solutions were aerated with 95% O2-5% CO2 (pH 7.4) and maintained at
37°C. All drugs and chemicals were purchased from Sigma.
Endothelial cell phenotype: immunoblot analysis. In a subset of
male pigs (n ⫽ 16), expression levels of 18 proteins that are frequently
altered in association with early atherosclerotic changes were measured from brachial and femoral artery endothelial cell scrapes. We
selected markers of endothelium-derived dilators, antioxidant pathways, prooxidant pathways, and inflammation. Immediately following
death, arteries were opened longitudinally and pinned. Laemmli
buffer was applied on the endothelial surface, and, using a blade, the
endothelial cell layer was gently scraped as described previously (4,
25). This method of scraping the luminal surface yields an endothelial
enriched sample, as demonstrated in Fig. 1 and previously by others
(6, 16, 27).
Total protein contents of arterial scrapes were measured using the
NanoOrange protein assay. Protein samples from endothelial scrapes
(10 ␮g/lane) were loaded on a 12-lane 5–12% NuPAGE Bis-Tris
gradient gels, electrophoresed at 200 V for 50 min, and transferred at
34 V for 60 min to a polyvinylidene difluoride membrane (HybondECL; Amersham). Brachial and femoral artery samples from the
exercise and sedentary groups were loaded on the same gel in an
alternating pattern. The membranes were blocked in 5% nonfat milk
and TBST (20 mM Tris·HCl, 137 mM NaCl, and 0.1% Tween 20) at
room temperature for 1 h. Overnight, the membrane was incubated
with the primary antibody against endothelial nitric oxide synthase
(eNOS; 1:1,000; BD Transduction), p47phox (1:500; BD Transduction), SOD-1 (1:5,000; Stressgen), SOD-2 (1:2,000; Stressgen),
SOD-3 (1:4,000; Stressgen), catalase (1:5,000; Sigma), phosphoreNOS (1:250; BD Transduction), Akt (1:500; Cell Signaling), phosphor-Akt (1:250; Cell Signaling), arginase 1 (1:1,000; BD Transduction), cyclooxygenase-1 (COX-1; 1:1,000; Santa Cruz Biotechnology), angiotensin AT1 (1:150; Santa Cruz Biotechnology), AT2
(1:1,000; Santa Cruz Biotechnology), VCAM-1 (1:250; Santa Cruz
Biotechnology), p67phox (1:500; BD Transduction), Rac1 (1:1,000;
Cytoskeleton), heat shock protein HSP90 (1:1,000; BD Transduction),
Whole Vessel
B
C
eNOS
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previous findings (34) that 1-yr-old Yucatan pigs that are fed a
standard diet do not exhibit signs of atherosclerotic disease. All
brachial and femoral arteries from this subset revealed 0% Sudan IV
staining, a marker of atherosclerotic lesions (data not shown). This
observation is vital because the objective of the present study was to
examine the effects of exercise training on endothelial function and
phenotype in healthy (disease-free) peripheral conduit arteries.
Training program. All pigs were familiarized with running on a
motorized treadmill and then randomly assigned to either an exercise
or sedentary group. The exercise group completed a 16- to 20-wk
endurance training program as described previously (24, 30, 40).
Briefly, intensity and duration of exercise bouts increased steadily so
that by week 10 of training the pigs ran 85 min/day, 5 days/wk. The
85-min training bouts consisted of a 5-min warm-up, a 15-min sprint
run at 6 – 8 mile/h (mph), a 60-min endurance run at 4 – 6 mph, and a
5-min cool-down. Pigs assigned to the sedentary group were restricted
to their enclosures (2 ⫻ 4-m pens) and did not exercise. At the
conclusion of the intervention, both groups of pigs performed a graded
intensity treadmill exercise test to exhaustion (20). In our laboratory,
the efficacy of the training program is evaluated from measurements
of endurance time on the treadmill, heart-to-body weight ratio, and
citrate synthase activity assay as index of skeletal muscle oxidative
capacity (31).
In vitro assessment of endothelium-dependent and -independent
relaxation. Procedures used to assess vasoactive responses of arterial
rings have been published previously in detail (39, 40). Pigs from the
exercise training group were killed 16 –24 h following the last bout of
exercise. Immediately following death, brachial and femoral arteries
were harvested, trimmed of fat and connective tissue, and sectioned
into 2- to 3-mm rings in cold Krebs bicarbonate buffer solution.
Vasomotor reactivity was examined with the rings stretched to the
length that produced maximal active tension. Before dose-response
curves were initiated, arterial rings were preconstricted with PGF2␣
(30 ␮M). Endothelium-dependent relaxation was assessed by using
bradykinin (10⫺11 to 10⫺6 M), whereas endothelium-independent
relaxation was assessed with sodium nitroprusside (SNP; 10⫺10 to
10⫺4 M). After each dose-response protocol, the bicarbonate buffer
solution was replaced to wash out the drug, and arterial segments were
allowed 1 h to stabilize before initiation of the next protocol.
ENDOTHELIAL HEALTH IN EXERCISE-TRAINED VS. SEDENTARY PIGS
submaximal exercise (P ⬍ 0.0001). In addition, exercise training increased citrate synthase activity of the deltoid muscle,
and the medial, lateral, long, and accessory heads of the triceps
brachii muscle by approximately 15– 40% (P ⬍ 0.001). These
data confirm that pigs in the exercise group exhibited the
classic training-induced adaptations.
Bradykinin elicited a concentration-dependent relaxation of
the brachial (Fig. 2A) and femoral (Fig. 3A) artery rings that
was not different between the exercise and sedentary groups
(P ⬎ 0.05). Similarly, SNP-induced relaxation of brachial (Fig.
2B) and femoral (Fig. 3B) artery rings did not differ between
groups. Because the lack of differences between exercisetrained and sedentary groups occurred in both male and female
pigs (P ⬎ 0.05), data were pooled across sex. Together, these
data indicate that exercise training does not increase endothelium-dependent and -independent relaxation in healthy pigs.
Although there was an absence of a group-by-sex interaction,
we detected a main effect of sex on bradykinin-induced relaxation of the brachial (P ⬍ 0.05), but not femoral (P ⬎ 0.05),
artery when pooling across groups (Fig. 4, A and C). Specifically, brachial arteries from male pigs exhibited greater endothelium-dependent relaxation compared with female arteries.
Conversely, SNP-induced relaxation was greater (P ⬍ 0.05) in
brachial and femoral arteries from female pigs compared with
arteries from males (Fig. 4, B and D).
Furthermore, in the subset of pigs, expression of proteins of
interest in brachial (Fig. 5) and femoral (Fig. 6) artery endothelial scrapes was not different (P ⬎ 0.05) between exercise
(n ⫽ 8) and sedentary (n ⫽ 8) groups. Although it may appear
caveolin-1 (1:250; BD Transduction), and MDA (1:1,000; Abcam).
This was followed by 1-h incubation with a horseradish peroxidaseconjugated secondary antibody (1:2,500). Positive controls were included in all gels. Analysis of protein was performed with chemiluminescence and quantified by densitometry through the use of Kodak
4000R Imager and Molecular Imagery Software.
Statistical analysis. All values are means ⫾ SE. Dose-response
curves were analyzed by two-way ANOVA with repeated measures
on one factor (dose). Between-group differences in plasma cholesterol, body and heart weights, treadmill performance, skeletal muscle
citrate synthase activity, brachial and femoral artery ring characteristics, and protein expression were determined by using an independent
t-test. For all statistical tests, significance was set at 0.05. Statistical
analyses were performed with SPSS 17.0. (SPSS, Chicago, IL).
RESULTS
Following the 16 –20 wk intervention, total plasma cholesterol (EX ⫽ 64.5, SED ⫽ 67.3 mg/dl), low-density lipoprotein
cholesterol (EX ⫽ 25.9, SED ⫽ 29.1 mg/dl), high-density
lipoprotein cholesterol (EX ⫽ 34.0, SED ⫽ 32.4 mg/dl), and
triglycerides (EX ⫽ 40.1, SED ⫽ 44.6 mg/dl) were not
different between exercise and sedentary groups (P ⬎ 0.05).
Although body weights were not different between groups
(EX ⫽ 36.6, SED ⫽ 37.2 kg; P ⬎ 0.05) at termination of the
study, heart weight (EX ⫽ 201.2, SED ⫽ 170.8 g) and
heart-to-body weight ratio (EX ⫽ 5.5, SED ⫽ 4.6) were
greater (P ⬍ 0.0001) in the exercise group compared with the
sedentary group. Furthermore, following the intervention, exercise pigs increased endurance time on the treadmill by 43%
(P ⬍ 0.0001) and revealed lower heart rates during rest and
AJP-Heart Circ Physiol • VOL
Fig. 3. Bradykinin (A) and sodium nitroprusside (B) induced relaxation of
femoral artery rings in exercise-trained (n ⫽ 47) vs. sedentary (n ⫽ 42) pigs
(means ⫾ SE). SE are not apparent because they are smaller than the symbols.
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Fig. 2. Bradykinin (A) and sodium nitroprusside (B) induced relaxation of
brachial artery rings in exercise-trained (n ⫽ 59) vs. sedentary (n ⫽ 54) pigs
(means ⫾ SE). SE are not apparent because they are smaller than the symbols.
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ENDOTHELIAL HEALTH IN EXERCISE-TRAINED VS. SEDENTARY PIGS
Fig. 4. Bradykinin and sodium nitroprusside induced
relaxation of brachial (A and B) and femoral artery (C
and D) in male vs. female pigs (means ⫾ SE). SE are
not apparent because they are smaller than the symbols.
DISCUSSION
Using a large data set, the present study confirms that, in
healthy adult male and female swine, long-term exercise training does not increase endothelium-dependent dilation of peripheral conduit arteries. Contrary to our hypothesis, we demonstrated that exercise-trained pigs do not reveal a more
antiatherogenic endothelial cell phenotype compared with sedentary but otherwise healthy pigs. Furthermore, we also report
that male pigs exhibit enhanced endothelium-dependent relax-
2.0
1.5
1.0
0.5
Fig. 5. Brachial artery endothelial expression
of proteins that are considered antiatherogenic
(A) and proatherogenic (B) in exercise-trained
(n ⫽ 8) vs. sedentary (n ⫽ 8) pigs (means ⫾
SE). All P ⬎ 0.05. P-, phosphorylated;
HSP90, heat shock protein 90; AT, angiotensin; COX-1, cyclooxygenase-1; MDA, malondialdehyde.
0.0
2.0
1.5
1.0
0.5
0.0
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as if trends for a group difference existed for certain proteins,
it should be noted that the lowest P value was 0.138 (SOD-3 in
femoral artery; Fig. 6A). Therefore, these data suggest that
exercise training in healthy pigs does not markedly alter
endothelial expression of the selected 18 genes. Importantly,
this subset of pigs were representative of the entire study
sample in that no differences in vasomotor function were found
between the exercise and sedentary groups (P ⬎ 0.05). Moreover,
the classic training-induced adaptations, as reported above, were
also confirmed in this subgroup of pigs (P ⬍ 0.05).
ENDOTHELIAL HEALTH IN EXERCISE-TRAINED VS. SEDENTARY PIGS
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2.0
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1.0
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0.0
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ation in the brachial but not femoral artery compared with
female pigs.
A plethora of research indicates that habitual exercise improves endothelial function in peripheral conduit arteries of
patients with heart failure, coronary artery disease, hypertension, hypercholesterolemia, obesity, diabetes, and aging (11,
21, 23, 29). These beneficial effects of exercise training on the
peripheral circulation have also been demonstrated in animal
models of cardiovascular risk or disease (14). For example,
studies in hypercholesterolemic pigs reveal that exercise training markedly preserves or restores endothelium-dependent
dilation of skeletal muscle arteries (37, 38, 40). At the opposite
end of the spectrum, studies in healthy animals and humans
indicate that exercise training does not consistently cause
increases in endothelial function (11, 14, 21, 23, 29). The
discrepancies in these findings may be attributed to the time
point at which measurements of endothelial function are performed. In fact, although it may appear counterintuitive, the
animal literature has long supported the proposal that short- but
not long-term exercise training improves conduit artery endothelial function (14, 17). The actual profile of the time course
of vascular adaptations during training has also been recently
described in healthy humans (32, 33). In a series of longitudinal studies involving multiple repeated measurements, Tinken
and colleagues (32, 33) established that endothelial function at
the brachial and popliteal arteries improves rapidly (2 wk) from
the start of exercise training and returns to baseline levels (at 8
wk) as dilatory capacity increases. As previously proposed for
coronary arteries (17), these data from Tinken and coworkers
(32, 33) support the notion that remodeling of conduit arteries
AJP-Heart Circ Physiol • VOL
may partly displace the need for acutely responsive vasodilatory mechanisms (9, 11, 14, 17, 19, 29). It is currently believed
that during long-term exercise training, as the conduit arteries
remodel and enlarge, shear stress during exercise bouts may
become normalized, thus resulting in the return of endothelial
function to basal levels (9, 11, 13, 14, 17, 19, 29). However,
further research is necessary to establish to what extent arterial
remodeling induced by training can alter wall shear stress at
rest and during exercise. Taken together, it is proposed that, in
sedentary but otherwise healthy animals and humans, the
endothelial adaptive responses in conduit arteries occur very
early in the training process, and as the exercise program
continues these functional changes tend to disappear. Indeed,
the present retrospective analysis of data from our swine
database supports the latter portion of this contention; that is,
long-term exercise training does not alter endothelium-dependent dilation in healthy peripheral conduit arteries. A previous
study from our laboratory (22) using the same porcine model
showed that 1 wk of exercise training does increase brachial
artery sensitivity to bradykinin. Interestingly, this effect was
not detected in the femoral artery. Given that blood flows to
muscles served by the brachial artery are more uniformly
elevated than those supplied by the femoral artery, it is possible
that this differential vascular adaptation to short-term training
is due to a greater brachial than femoral artery exposure to
shear stress during the exercise bouts (22).
These findings in healthy pigs and those in humans do not
appear to parallel observations made in healthy rats in which
endothelium-dependent dilation of the aorta increases as the
duration of the exercise training program progresses (7, 8). The
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Fig. 6. Femoral artery endothelial expression
of proteins that are considered antiatherogenic (A) and proatherogenic (B) in exercisetrained (n ⫽ 8) vs. sedentary (n ⫽ 8) pigs
(means ⫾ SE). All P ⬎ 0.05.
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ENDOTHELIAL HEALTH IN EXERCISE-TRAINED VS. SEDENTARY PIGS
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throughout the entire arterial tree. Endothelial phenotypic heterogeneity between beds (18) (e.g., conduit vs. resistant vessels) may dictate the adaptability of vascular cells to a given
stimulus (26). In this regard, data from Green et al. (10) and
Tinken et al. (33) suggest that, in healthy humans, the time
course of endothelial adaptations to repeated episodes of shear
stress is variable throughout the vasculature. Specifically, it
appears that in conduit arteries (e.g., brachial), endotheliumdependent dilation is initially enhanced followed by normalization to baseline levels (33), whereas in the microvasculature
(e.g., forearm skin), improvements in vasomotor function are
sustained without indication of succeeding normalization (10, 36).
The present data demonstrate that brachial artery bradykinin-induced relaxation is slightly but significantly greater in
male vs. female pigs, a difference that was not detected in the
femoral artery. Previous studies conducted in humans have
indicated that sex differences in endothelial function are agedependent, with older women exhibiting a more pronounced
attenuation in brachial artery function (15). Our data indicate
that, in pigs, sex-related differences may appear earlier in life.
More interestingly, for the first time, our study suggests that the
sex effect on endothelium-dependent dilation may be vesselspecific, an observation that will warrant further investigation.
Furthermore, similar to studies in humans (3), we found that
endothelium-independent relaxation is augmented in females
compared with males, thus suggesting that females exhibit
greater smooth muscle sensitivity than males. The present sex
differences should be, however, interpreted with caution given
that the death of female pigs was not standardized according to
the menstrual cycle. Although no studies in swine have systemically examined the impact of the menstrual cycle on
vasomotor function, data in humans strongly suggest that
vascular function is altered throughout the menstrual cycle
with the peak function occurring during the late follicular
phase before ovulation (1).
In summary, the present investigation indicates that pigs
exhibiting the classic training-induced adaptations do not demonstrate enhanced endothelium-dependent dilation nor reveal a
more atheroprotected endothelial cell phenotype than their
sedentary, but otherwise healthy, counterparts. This is the first
study comprehensively characterizing brachial and femoral
artery vasomotor function and endothelial phenotype in exercise-trained and sedentary pigs. Furthermore, we report for the
first time that the sex effect on endothelium-dependent dilation
is vessel-specific, with brachial but not femoral arteries from
male pigs exhibiting enhanced function compared with females
pigs.
ACKNOWLEDGMENTS
We gratefully acknowledge the expert technical assistance of Pam Thorne,
Jennifer Casati, Ann Melloh, and David Harah.
GRANTS
This work was supported by National Heart, Lung, and Blood Institute
Grants HL-52490 and HL-36088 (to M. H. Laughlin).
DISCLOSURES
No conflicts of interest, financial or otherwise, are declared by the author(s).
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effects of body size on cardiovascular hemodynamics should
be considered when interpreting these contrasting data. Differences in vessel sizes between species, relative to differences in
arterial blood flows, largely impact vascular shear stress such
that resting and exercise-induced shear in rat arteries is ⬃4fold greater than shears observed in large mammals and humans (5). These inherent differences between species may
contribute to the divergence in vascular adaptations to training.
The measurement of endothelium-dependent dilation is established as a surrogate marker for overall endothelial health
and, in the human literature, has been referred to as the
barometer for cardiovascular risk (35). Given that regulation of
vascular tone is only one of the many functions of the endothelium (2), it is essential to recognize that endothelial alterations may not always be manifested with changes in endothelium-dependent dilation. With this in mind, we believe that it
may be presumptuous to assume that the absence of a traininginduced adaptation in vasomotor function implies a lack of
change toward an atheroprotective endothelial phenotype. To
address this issue, in a subset of exercise-trained and sedentary
healthy pigs, expression levels of 18 proteins that are frequently associated with early atherosclerotic disease were measured from brachial and femoral artery endothelial enriched
samples. Contrary to our premise, there were no differences in
the magnitude of expression for any of the measured proteins.
Furthermore, in the same subset of pigs, none of the histological markers that were assessed in the vascular wall (immunohistochemical staining for macrophage scavenger receptor A,
nitrotyrosine, and MDA as well as intima-media thickness)
revealed differences between exercise-trained and sedentary
animals (data not shown). Together, these data suggest that, in
healthy pigs, endurance training does not modulate vascular
gene expression.
The current finding that exercise training has no effect on
endothelial function/phenotype in healthy animals, contrasted
with previous observations from diseased animals and humans
in which exercise exerts a beneficial impact (11, 14, 21, 23,
29), supports the concept that there may be an interaction
between endothelial health and exercise (14). That is, it is
plausible that the endothelium is not amendable with long-term
exercise unless impairment or disease is present. In other
words, when endothelial function/phenotype is near optimal
levels, as in healthy arteries, improvements may not occur as a
result of a “ceiling effect.”
When interpreting the present results, we acknowledge that
the beneficial effects of exercise might be apparent in the
expression of genes that have yet to be identified as crucial and
therefore were not included in our analysis. In this regard, we
are currently directing efforts toward globally examining the
impact of training on endothelial cell phenotype with the use of
genome-wide microarray analysis of gene expression. It is also
possible that the magnitude of variability in protein expression
among pigs, as evidenced by the large error bars (Figs. 5 and
6), impeded the potential for detecting the effects of exercise.
Accordingly, we believe that further research should evaluate
the effectiveness of exercise on maintaining a healthy endothelial phenotype in a longitudinal design. Such an approach
would require the involvement of cutting-edge techniques
capable of in vivo endothelial cell sampling (28). Last, we
recognize that the lack of adaptations in large peripheral
arteries does not imply an absence of vascular changes
ENDOTHELIAL HEALTH IN EXERCISE-TRAINED VS. SEDENTARY PIGS
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