Effects of exercise training on the cardiovascular system: Pharmacological approaches

Abstract

Physical exercise promotes beneficial health effects by preventing or reducing the deleterious effects of pathological conditions, such as arterial hypertension, coronary artery disease, atherosclerosis, diabetes mellitus, osteoporosis, Parkinson's disease, and Alzheimer disease. Human movement studies are becoming an emerging science in the epidemiological area and public health. A great number of studies have shown that exercise training, in general, reduces sympathetic activity and/or increases parasympathetic tonus either in human or laboratory animals. Alterations in autonomic nervous system have been correlated with reduction in heart rate (resting bradycardia) and blood pressure, either in normotensive or hypertensive subjects. However, the underlying mechanisms by which physical exercise produce bradycardia and reduces blood pressure has not been fully understood. Pharmacological studies have particularly contributed to the comprehension of the role of receptor and transduction signaling pathways on the heart and blood vessels in response to exercise training. This review summarizes and examines the data from studies using animal models and human to determine the effect of exercise training on the cardiovascular system.

Full text

Associate editor: Brain
Effects of exercise training on the cardiovascular system:
Pharmacological approaches
Angelina Zanesco
a,
⁎, Edson Antunes
b
a
Department of Physical Education, Institute of Bioscience, University of Sao Paulo State (UNESP), Rio Claro (SP), Brazil, Cep: 13506-900
b
Deparment of Pharmacology, Faculty of Medical Science, University of Campinas (UNICAMP), Campinas (SP), Brazil
Abstract
Physical exercise promotes beneficial health effects by preventing or reducing the deleterious effects of pathological conditions, such as arterial
hypertension, coronary artery disease, atherosclerosis, diabetes mellitus, osteoporosis, Parkinson's disease, and Alzheimer disease. Human
movement studies are becoming an emerging science in the epidemiological area and public health. A great number of studies have shown that
exercise training, in general, reduces sympathetic activity and/or increases parasympathetic tonus either in human or laboratory animals.
Alterations in autonomic nervous system have been correlated with reduction in heart rate (resting bradycardia) and blood pressure, either in
normotensive or hypertensive subjects. However, the underlying mechanisms by which physical exercise produce bradycardia and reduces blood
pressure has not been fully understood. Pharmacological studies have particularly contributed to the comprehension of the role of receptor and
transduction signaling pathways on the heart and blood vessels in response to exercise training. This review summarizes and examines the data
from studies using animal models and human to determine the effect of exercise training on the cardiovascular system.
© 2007 Elsevier Inc. All rights reserved.
Keywords: Exercise training; Adrenergic receptors; Muscarinic receptor; Nitric oxide; Cardiac tissues; Vascular smooth muscle
Abbreviations: ATP, adenosine triphosphate; cAMP, cyclic adenosine 3′5′-monophosphate; cGMP, 3′5′-guanosine monophophate; DAG, diacylglycerol; EDRF,
endothelium-derived relaxing factor; eNOS, endothelial NOS; iNOS, inducible NOS; IP3, inositol-1,4,5-triphosphate; nNOS, neuronal NOS; NO, nitric oxide; NOS,
NO synthase; PKC, protein kinase C; SOD, superoxide dismutase.
Contents
1. Introduction. ........................................... 307
2. Adrenergicandmuscarinicreceptorsandexercisetraining..................... 308
2.1. αand βadrenoceptors .................................. 308
3. Muscarinic cholinergic receptors and exercise .......................... 310
4. Adenosine receptors and physical training ............................ 310
5. Responsiveness of vascular smooth muscle and exercise training ................ 311
6. Erectile dysfunction and exercise................................. 313
7. Summary and conclusion..................................... 313
Acknowledgment ........................................... 314
References ............................................... 314
1. Introduction
A healthy lifestyle has been strongly associated with the
practice of regular physical activity. Evidence has shown that
Pharmacology & Therapeutics 114 (2007) 307 –317
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⁎Corresponding author.
E-mail address: azanesco@rc.unesp.br (A. Zanesco).
0163-7258/$ - see front matter © 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.pharmthera.2007.03.010

physically active subjects have more longevity with reduction
of morbidity and mortality. Physical exercise prevents or
reduces the deleterious effects of pathological conditions, such
as arterial hypertension, coronary artery disease, atherosclero-
sis, diabetes mellitus, osteoporosis, Parkinson's disease, and
Alzheimer disease (Kingwell, 2000; Sutoo & Akiyama, 2003;
Larson & Wang, 2004). Classical kinetic studies were based
exclusively in sports performance, but at present human move-
ment studies are becoming an emerging science in the epide-
miological area and public health.
Physical training produces significant alterations in auto-
nomic nervous system activity and/or changes in cellular
function resulting in marked modifications of the cardiovascular
system function (Krieger et al., 1998; Kingwell, 2000). Basic
sciences, such as physiology and biochemistry, have helped to
increase knowledge in the physical exercise field and its
association with cardiovascular benefits. Additionally, pharma-
cological studies have greatly contributed to the comprehension
of the role of receptor and transduction pathways in the heart
and blood vessels in response to exercise training. This review
summarizes and examines the data from studies using animal
models and human to determine the effect of exercise training
on the cardiovascular system.
2. Adrenergic and muscarinic receptors and exercise training
The effect of exercise training on the sympathetic and para-
sympathetic activities has been studied in great detail by dif-
ferent groups (Frick et al., 1967; Lin & Horvath, 1972;
Scheuer & Tipton, 1977; Katona et al., 1982; Geenen et al.,
1988; Negrão et al., 1992; Grassi et al., 1994; Moore & Korzick,
1995; Shi et al., 1995; Collins & Di Carlo, 1997; Krieger et al.,
1998; O'Sullivan & Bell, 2000). In general, these studies have
shown that exercise training reduces sympathetic activity and/or
increases parasympathetic tonus, either in man or laboratory
animals, which are correlated with reduction in heart rate
(resting bradycardia) and blood pressure (Scheuer & Tipton,
1977; Paffenbarger et al., 1993; Fagard, 2001). However, the
underlying mechanisms by which physical exercise produces
bradycardia and reduces blood pressure have not yet been fully
understood.
The autonomic nervous system regulates directly the
contractility and frequency of the heart by chemical signals,
including neurotransmitters and hormones. Norepinephrine
released from autonomic sympathetic fibers produces positive
inotropic and chronotropic response acting through stimula-
tion of β-adrenoceptors (Lands et al., 1967; Feldman, 1987).
In addition, myocardial α-adrenoceptors participate in the
inotropic responses (Michel et al., 1989; Korzick et al., 2001).
On the other hand, acetylcholine released from parasympa-
thetic fibers produces negative inotropic and chronotropic
responses through stimulation of muscarinic receptors (Dorje
et al., 1991). Thus, changes in adrenergic and muscarinic
receptor population and function have been proposed as a
potential mechanism to explain some cardiovascular altera-
tions in response to exercise training, as detailed below and
shown in Tables 1 and 2.
2.1. αand βadrenoceptors
Adrenergic receptors were formerly classified into αand β
adrenoceptor (Ahlquist, 1948). Later, functional studies and
molecular biology techniques showed that either α-orβ-
adrenergic receptors can be subdivided into more subtypes
(Lands et al., 1967; Langer, 1974; Brodde, 1987) as detailed
below.
At least 3 distinct subtypes of βadrenoceptors have been
described, namely β
1
,β
2
, and β
3
(Stiles et al., 1984; Emorine
et al., 1989; Kaumann & Molenaar, 1997). βadrenoceptors
mediate many catecholamine actions in several tissues.
Specifically in the heart, activation of β-adrenoceptors stimulate
Gs-protein (stimulatory G-protein) that in turn promotes
activation of adenylyl cyclase, which catalyzes the conversion
of adenosine triphosphate (ATP) to cyclic adenosine 3′5′-
monophosphate (cAMP). The increment of cAMP levels acti-
vates protein kinase A, which phosphorylates several proteins
leading to an increase of intracellular Ca
2+
concentration result-
ing in positive chronotropic and inotropic responses (Rodbell,
1980; Birnbaumer, 1990).
Decrease in heart rate at rest and at submaximal work loads is
the hallmark of cardiovascular adaptation in response to long-
term exercise training. However, the mechanisms underlying
this phenomenon are not fully understood. An increase in
parasympathetic activity and/or diminished sympathetic activity
has been associated with training bradycardia. Since the actions
of catecholamines on the myocardial functions are mediated by
interactions with α- and β-adrenergic receptors, a number of
pharmacological studies have been carried out in cardiac tissues
to evaluate the role of this receptor population in the cardio-
vascular adaptation to physical training (see Tables 1 and 2, for
more details).
Classical pharmacological assays, using concentration–
response curves, have shown no alterations in cardiac β-
adrenoceptors from trained animals (Hughson et al., 1977;
Schaefer et al., 1992; Carroll, 2003; see Table 1 for more
details). Radioligand binding studies also failed to show
alterations in β-adrenergic receptor density after exercise
training (see Table 2 for more details), thus confirming the
functional assays (Williams, 1980; Moore et al., 1982; Williams
et al., 1984; Tomita et al., 1994; Roth et al., 1998; Favret et al.,
2001). In contrast, other radioligand-binding studies reported a
decrease in β-adrenoceptors number in cardiac tissue from
trained animals (Sylvestre-Gervais et al., 1982; Werle et al.,
1990; Plourde et al., 1991). It is noteworthy that in all these
studies the duration of exercise training per day was 2 hr as
compared to the studies cited above which exercise duration was
1 hr/day (see Table 2 for more details). Regarding the affinity of
the radioligand to the receptor, no changes were found in all
studies, indicating clearly that physical training does not affect
the receptor population subtypes present in cardiac tissues.
The activation of Gs protein and/or adenylyl cyclase is an
important pathway in cardiac β-adrenergic signal transduc-
tion to produce the positive chronotropic and inotropic re-
sponse. Thus, to assess the contribution of β-adrenergic signal
transduction in the training bradycardia, studies have been
308 A. Zanesco, E. Antunes / Pharmacology & Therapeutics 114 (2007) 307–317

performed to evaluate the Gs- and/or adenylyl cyclase-activity
in myocardial tissues, but conflicting data were found. Scarpace
et al. (1994) found that run exercise training for 9 weeks (60 min
5 days a week, 12.5% grade, 70% of maximum oxygen con-
sumption) in female young Fisher 344 rats (3 months) produced
a decrease in isoproterenol stimulated adenylyl cyclase activity
with no change in Gs-protein immunoreactivity. In contrast,
Roth et al. (1998) observed an increase of cAMP production in
myocardial tissues in male young Fisher 344 rats (4 months)
after 10 weeks of run training (60 min 5 days a week, 15% of
grade and 75% of initial maximal speed capacity). Tomita et al.
(1994) showed that run training for 10 weeks, twice daily,
6 days a week, 20% of grade, did not change basal and
isoproterenol-stimulated adenylyl cyclase in hamsters. These
studies show that adaptive response to training is a complex
phenomenon and many variables should be considered to make
comparison among data including age, sex, and animal species.
Regarding the α-adrenergic receptors, at least 6 distinct α-
adrenoceptor genes have been cloned, 3 α
1
genes (α
1A
,α
1B
,
α
1D
), and 3 α
2
genes (α
2A
,α
2B
,α
2C
;Ford et al., 1994). It is
known that stimulation of α
1
-adrenergic receptors regulates 4
effector systems. The primary signal transduction of α
1
-
adrenergic receptors involves the activation of phospholipase
C through the Gq-protein which generates 2 second messenger
diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP3). IP3
promotes the mobilization of Ca
2+
from endoplasmic stores and
activation of myosin light chain kinase which phosphorylates
the light chain of myosin, and in conjunction with actin initiates
the contraction response (Lomasney et al., 1991; Webb, 2003).
The stimulation of α
1
-adrenergic receptors in the myocar-
dium promotes positive inotropic response by activation of Gq-
protein which activates the phospholipase C pathway leading to
generation of the second messengers IP3 and DAG. This latter
messenger activates protein kinase C (PKC) which increases
Ca
2+
intracellular concentration (Korzick, 2003). The increase
of Ca
2+
intracellular through phosphorylation of several protein
by PKC along with calcium mobilization by IP3 produce
cardiac excitation–contraction response generating positive
inotropy (Vago et al., 1989; Johnson et al., 1996).
To investigate the effect of exercise training on the inotropic
response mediated by α
1
-adrenergic receptors in cardiac tissues
studies have been carried out in different rat strains (see Tables 1
and 2 for more details). Similar to the findings involving β-
adrenergic receptors studies, controversial findings related to
α
1
-adrenergic receptors-mediated cardiac inotropy in response
to exercise training have been found. An increase of inotropic
responses mediated by α
1
-adrenoceptors in rat isolated heart
after run exercise training was reported (Korzick & Moore,
1996; Korzick et al., 2004). On the other hand, radioligand
binding studies showed a decrease (Williams et al., 1984) and
Table 1
Effects of run training program on the sensitivity of isolated cardiac tissues from animals
Duration (weeks) Intensity (VO
2max
/slope) Frequency Agonists Species Type of study Sensitivity Reference
10 NM 0% grade 45 min 5 days/week NE ACh SD rats male Right atria β:( ) Muscarinic: Hughson et al., 1977
12–16 NM 8% grade 2 hr/day 5 days/week ISO SD rats male Right and left atria β:( )Schaefer et al., 1992
12 NM 60 min 5 days/week ISO Rabbit, female Isolated heart β:( )Carroll, 2003
12 70% VO
2
max 10% grade 60 min 5 days/week Phe F344 rats, male Isolated heart α
1
:↑Korzick et al., 2004
VO
2max
, maximum oxygen consumption; Slope: grade of treadmill inclination; NM, not mentioned in the study; NE, norepinephrine; ISO, isoproterenol; Phe,
phenylephrine; ACh, acetylcholine. SD, Sprague Dawley rats; ( ), no changes of functional response mediated by β-adrenergic or muscarinic receptors; ↑, increase of
functional response mediated by α
1
-adrenergic receptors.
Table 2
Effects of exercise training in the receptor density from myocardial tissue
Stimulus Duration
(weeks)
Intensity
(VO
2max
/slope)
Frequency Receptor Species Receptor density
(B
max
)
Reference
Swim 8 NM 75 min 5 days/week β-AR,
Muscarinic
Male CD rats ( )Williams, 1980
Run 15 NM 5% grade 60 min 5 days/week β-AR Female SD rats ( )Moore et al., 1982
Swim 14 NM 90 min 5 days/week α-, β-AR
Muscarinic
Male CD rats,
Female Wistar rats
β:( )α/muscarinic:
↓
Williams et al., 1984
Run 10 NM 20%grade Twice daily/6 days/week β-AR Male F1B hamsters ( ) Tomita et al., 1994
Run 10 75% max speed 15% grade 60 min 5 days/week β-AR F 344 rats Male ( )Roth et al., 1998
Run 10 80% VO
2max
10% grade 60 min 5 days/week α-, β-AR
Muscarinic
Male SD rats β:( )α/Muscarinic:
↑
Favret et al., 2001
Run 10 NM 8% grade Twice daily/60 min
5 days/week
β-AR Male Wistar rats ↓Sylvestre-Gervais et al.,
1982
Swim 6 NM 2 h/day 5–6 days/week β-AR Male SD rats ↓Werle et al., 1990
Run 10 NM 8% grade Twice a day 60 min β-AR Male Wistar rats ↓Plourde et al., 1991
Run 12 NM 10% grade 60 min 5 days/week α-AR Male F 344 rats ↑Korzick & Moore, 1996
VO
2max
, maximum oxygen consumption; slope, grade of treadmill inclination; NM, not mentioned in the study; ( ), no changes in the receptor density; ↓, decrease in
the receptor density.
309A. Zanesco, E. Antunes / Pharmacology & Therapeutics 114 (2007) 307–317

an increase (Favret et al., 2001)inα-adrenoceptor density in
myocardial tissues from trained rats as compared to sedentary
animals. Exercise training did not affect the affinity of
radioligand (K
D
) for α-adrenergic receptors in any of these
studies (see Table 2 for more details).
In view of all these studies, no conclusive data have been found
relating the responsiveness and/or density of α-andβ-adrenergic
receptors and their signal transduction pathway after an exercise
training program. The reasons for these discrepancies could be
related to the differences in duration, intensity, and frequency of
the training program employed in each study (see Tables 1 and 2
for more details). Indeed, to evaluate the effect of exercise training
on functional responses and/or receptor density, it is important to
consider the total volume of an exercise training program which is
based upon the frequency, intensity, and duration. Thus, these 3
parameters are fundamental in kinesiology for understanding the
alterations that exercise training could provoke in cellular
function and/or molecular structures.
Duration of physical training can be divided in short-term
(b7 days) and long-term (N1 week) of exercise program. Short-
term duration is commonly related to functional adaptations to
physical training whereas long-term duration is correlated to the
health benefits that chronic exercise training promotes. The
intensity of an exercise training program can be determined by
several biochemical parameters, including plasma lactate
threshold, tissue metabolic enzymes, and maximum oxygen
uptake. Maximum oxygen consumption (VO
2max
) is an accurate
measurement of the intensity of physical exercise on the cardio-
respiratory system and is a highly reproducible characteristic of
the aerobic power of a training program (Astrand, 1976;
Scheuer & Tipton, 1977; Mercier et al., 1999). Thus, VO
2max
is
a crucial parameter to provide the intensity of the exercise
training employed in each experimental protocol. Based on
VO
2max
values, the levels of intensity of exercise training can be
divided in low (25–60% of VO
2max
), moderate (65–85% of
VO
2max
), and high intensity (90–100% of VO
2max
)(ACSM,
1998). Thus, the lack of a standardization of the intensity of
exercise in the majority of reports makes difficult an interpre-
tation and comparison of results obtained in those studies. The
frequency of an exercise training program is related to the
amount of the days of week that the physical exercise is per-
formed. This parameter was quite similar in the majority of
the cited studies, employing 5 days a week. However, the
duration of each training session was variable among the
studies, 6–16 weeks (see Tables 1 and 2 for more details).
3. Muscarinic cholinergic receptors and exercise
Acetylcholine released from parasympathetic fibers can
stimulate 2 major types of receptors, named nicotinic and
muscarinic receptors. Muscarinic receptors belong to the class
of G protein-coupled receptor and are widely distributed
throughout the periphery and the central nervous system
(Caulfield, 1993). Five subtypes of muscarinic cholinergic
receptors have been detected by molecular cloning, named M
1
,
M
2
,M
3
,M
4
, and M
5
. In cardiac tissue, the stimulation of the
subtype M
2
muscarinic receptor by acetylcholine promotes an
activation of a Gi protein with resultant inhibition of adenylyl
cyclase and/or activation of receptor-operated K
+
channels
leading to negative chronotropic and inotropic response (Kubo
et al., 1986).
It is well known that exercise training provokes a resting
bradycardia either in human or in laboratory animals. Although
the majority of studies showed an increase of parasympa-
thetic activity after exercise training, other studies failed to show a
positive relationship between trainingbradycardia and increase in
parasympathetic drive (Katona et al., 1982; Maciel et al., 1985;
Bonaduce et al., 1998). In an attempt to clarify the influence of
parasympathetic activity on the reduction of heart rate after
exercise training, pharmacological studies were carried out to
investigate the contribution of muscarinic cholinergic receptors in
this phenomenon (see Tables 1 and 2 for more details).
An early study using rat isolated right atria showed that run
training for 10 weeks did not affect the negative chronotropic
responses mediated by muscarinic–cholinergic receptors
(Hughson et al., 1977). On the other hand, radioligand binding
assays revealed conflicting findings. Williams (1980), studying
the muscarinic-cholinergic receptor in crude cardiac mem-
branes, did not find alterations in number or affinity of this
receptor in heart tissue from 8-week swimming trained rats.
In contrast, a swim training program for 14 weeks in male and
female rats produced a significant decrease in muscarinic
cholinergic receptor number without changes in the affinity for
this receptor population (Williams et al., 1984). Recently, a
well-conducted study using run training program at an intensity
of 80% of VO
2max
for 10 weeks showed an up-regulation of
muscarinic cholinergic receptors in rat right ventricles mem-
branes (Favret et al., 2001). Therefore, as mentioned above
concerning the relationship between exercise training and
adrenergic receptors-mediated responses, the total volume of
exercise training (duration, intensity, and frequency) should be
well controlled to obtain more conclusive data about the role of
muscarinic–cholinergic receptors in the training bradycardia
(see Tables 1 and 2 for more details).
4. Adenosine receptors and physical training
Adenosine is a nucleotide derived from ATP breakdown that
exerts a variety of physiological actions in cardiovascular, renal,
pulmonary, and immune systems (Ralevic & Burnstock, 1998).
Specifically, in cardiovascular function, adenosine promotes
vasodilatation and negative chronotropic and inotropic
effects in several species (Berne, 1963; West & Belardinelli,
1985; Olsson & Pearson, 1990). At least 4 subtypes of
adenosine receptors are found in the heart, namely A
1
,A
2a
,
A
2b
, and A
3
receptors (Collins and Hourani, 1993; Meester
et al., 1998). The negative chronotropic actions of adenosine are
attributed to A
1
and A
3
adenosine receptor subtypes (Ribeiro &
Sebastiäo, 1986). Additionally, a cardioprotective effect of
adenosine in response to hypoxia, ischaemia, and augmented
metabolic demand in ventricular myocardium has been
demonstrated (Mullane & Bullough, 1995; Cross et al., 2002).
In view of the actions of adenosine receptors on the heart, our
group was the first to examine the effects of exercise training on
310 A. Zanesco, E. Antunes / Pharmacology & Therapeutics 114 (2007) 307–317

the negative chronotropic response mediated by adenosine
receptors, using rat isolated right atria. The run training pro-
gram was performed 5 days a week for 8 weeks, at an intensity
of 60–70% of VO
2max
. Concentration–response curves for A
1
and A
3
selective adenosine agonists in the presence of atropine
and propranolol were performed. Our findings showed no
association between the training bradycardia and the negative
chronotropic response mediated by adenosine receptor stimu-
lation, thus excluding the participation of this receptor in this
phenomenon (Priviero et al., 2004).
5. Responsiveness of vascular
smooth muscle and exercise training
Originally, Furchgott and Zawadzki (1980) discovered that
endothelial cells release a vascular smooth muscle relaxing
factor that was named endothelium-derived releasing factor
(EDRF). Later, Ignarro et al. (1987) and Palmer et al. (1987)
revealed that EDRF was nitric oxide (NO; or a related com-
pound) that is synthesized from the amino acid L-arginine by the
enzyme NO synthase (NOS). Three isoforms of NOS, termed
endothelial NOS (eNOS), neuronal NOS (nNOS), and inducible
NOS (iNOS) have been recognized (Moncada et al., 1991).
NO has been implicated in a variety of cellular functions,
such as vasodilatation, inhibition of platelet aggregation,
immune function, cell growth, neurotransmission, metabolic
regulation, and excitation–contraction coupling. The produc-
tion of NO is regulated by humoral (hormones, autacoids) and
physical stimuli (shear stress; Vanhoutte, 2003).
The stimulation of endothelial cells by agonists, such as
bradykinin and acetylcholine, leads to the increase of intra-
cellular concentration of calcium ions with generation of Ca
2+
–
calmodulin complex which in turn activates eNOS. The activity
of the NOS requires also cofactors such as reduced nicotin-
amide-adenine-dinucleotide phosphate (NADP) and 5,6,7,8
tetrahydrobiopterin. NO diffuses to the vascular smooth
muscle cells and promotes relaxing response by stimulating
the cytosolic enzyme, soluble guanylate cyclase, which cata-
lyzes the production of cyclic 3′5′-guanosine monophophate
(cGMP), leading to an increased of extrusion of Ca
2+
from
cytosol in vascular smooth muscle and consequently inhibition
of the contractile machinery (Moncada et al., 1991).
Vascular shear stress is a result of increased blood flow in
the vessel wall, and it is described as a potent stimulator of NO
production from endothelium (Traub & Berk, 1998; Boo & Jo,
2003). Physical exercise is a powerful stimulus to increase
blood flow in vascular beds and consequently the beneficial
effects of physical training on cardiovascular diseases are
strongly associated with increase in NO production and/or NO
bioavailability induced by shear stress. The exact mechanisms
by which shear stress induced by exercise training promotes
increases in NO levels are not fully understood. It is postulated
that shear stress induces increase NO production by up-
regulation of eNOS gene expression in endothelial cells through
activation of protein tyrosine kinase pathway (Sessa et al., 1994;
Kingwell, 2000; Grahan & Rush, 2004; Higashi & Yoshizumi,
2004). Recently, several investigators have studied the
mechanisms by which physical training modulates gene
expression in endothelial cells. Evidence showed that shear
stress stimulates mechanosensors present in endothelial cells,
including caveolin, ion channels, G proteins, and integrins.
These mechanosensors are coupled to complex biochemical
signal pathways, such as Ras/MEK/ERK, c-Src, and PI3K/Akt,
which in turn regulate eNOS gene expression, thus increasing
NO production (Traub & Berk, 1998).
Evidence shows that the improvement of the vascular
relaxing response to muscarinic agonist acetylcholine might be
related to an increase in NO bioavailability as consequence of an
up-regulation of antioxidant enzymes system. The antioxidant
defense systems consists of enzymes, such as superoxide
dismutase (SOD), catalase, and glutathione peroxidase, and
nonenzymes, including vitamins and flavonoids (Droge, 2002).
The antioxidant enzymes are scavengers of reactive oxygen
species (ROS), causing an increase of NO bioavailability to the
vascular smooth muscle and enhancement of endothelium-
dependent vasodilatation (Dimmler et al., 1999; Davis et al.,
2001, 2003). Cells produce free radicals and ROS as con-
sequence of physiological metabolic processes, and an efficient
antioxidant defense system exist to neutralize ROS production.
An imbalance of ROS production and antioxidant system can
cause cellular damages that have been associated with several
pathological conditions, such as hypertrophy of vascular cells,
joint inflammation, diabetes, arterial hypertension, atheroscle-
rosis, ischaemia–reperfusion injury, and thrombo-embolic
events (Touyz & Schiffrin, 2004). Recently, aerobic exercise
training at moderate intensity has been associated with increase
in antioxidant enzymes expression in both human (Linke et al.,
2005; Javier et al., 2006) and laboratory animals (Fukai et al.,
2000; Rush et al., 2002; Chang et al., 2004). Indeed, results from
our laboratory showed that an increase of SOD expression of
∼20% is associated with improvement of relaxing response to
acetylcholine after 4 or 12 weeks of run training program in
isolated rat aorta (personal communication).
Thus, the beneficial effects of physical exercise in the
relaxing response to agonists, particularly acetylcholine, are
associated with increase in NO production in endothelial cells
and/or increase in NO bioavailability for vascular smooth
muscle by up-regulation of eNOS or antioxidant enzymes,
respectively (see Table 3 for more details).
Exercise training has been described as an important
nonpharmacological tool in the management arterial hyperten-
sion and atherosclerotic process (Kingwell, 2000; Higashi &
Yoshizumi, 2004; Marsh & Coombes, 2005). Thus, the
beneficial effects of exercise training are strongly associated
with the properties of NO to regulate vascular tone and platelet
aggregation. Regarding the vascular tone regulation, the
majority of research relating exercise training to endothelial
function showed an improvement of the vasodilatation response
evoked by agonists such as acetylcholine, either in spontane-
ously hypertensive animals (Yen et al., 1995; Chen et al., 1996,
1999; Grahan & Rush, 2004) or in normotensive animals (Wang
et al., 1993; Sun et al., 1994; Delp & Laughlin, 1997; McAllister
& Laughlin, 1997; Choate et al., 2000; Woodman et al., 2005).
Data are summarized in Table 3. On the other hand, other studies
311A. Zanesco, E. Antunes / Pharmacology & Therapeutics 114 (2007) 307–317

failed to show a direct correlation between increased NO pro-
duction and improvement of endothelium-dependent dilation
after exercise training (Oltman et al., 1992; McAllister et al.,
1996; Jasperse & Laughlin., 1999; Henderson et al., 2004; see
Table 4 for more details).
In human, a positive relationship between physical activity
and NO formation was also found in athletes and nonathletes
(Jungersten et al., 1997). Furthermore, it has been consistently
demonstrated that endurance athletes have a higher basal level
of nitrite/nitrate in both plasma or urine excretion as compared
to untrained volunteers (Bode-Boger et al., 1994; Poveda et al.,
1997; Schena et al., 2002; Banfi et al., 2006; Tordi et al., 2006).
Regarding the oxidant enzymes, Grahan and Rush (2004)
found a reduction of pro-oxidant enzyme levels in exercised
animals suggesting that various pathways exist in regulating NO
bioavailability in vascular vessel. It is noteworthy that in all
studies the relaxing responses to sodium nitroprusside were
unaltered by exercise training showing that the major effect of
exercise training program is closely related to endothelial cells.
Although measurements of NO production and eNOS acti-
vity have been used as markers to investigate the effects of the
physical exercise in the vascular blood vessels, it should be kept
in mind that the regulation of vascular tone is a complex
phenomenon. Thus, multiple interactions exist between the
stimulus of an agonist and the vascular response including the
affinity of receptor agonist, metabolism of drugs, existence of
antioxidant and prooxidant enzymes in the cell, participation of
small molecules in the pathway signal transduction, and the
contribution of several protein regulators in the phosphorylation
process. Considering the variety of the receptors and signaling
pathways present in the vascular smooth muscle and endothelial
cells to trigger the relaxing response, the evaluation of exercise
training on the responsiveness of vascular blood vessel is a
complex issue and more investigations are required. In addition,
it should be pointed out that the differences in the blood vessel
tree can contribute to the nonconclusive data related to the effect
of physical exercise and vascular relaxing response.
Regarding contractile responses mediated by α-adrenocep-
tors, experiments have found no change (Edwards et al., 1985,
Rogers et al., 1991; Sun et al., 1994; Jasperse & Laughlin, 1999;
Choate et al., 2000; Laughlin et al., 2001), an increase
(McAllister & Laughlin, 1997), or a decrease (Parker et al.,
1994; Jansakul, 1995; Oltman et al., 1995; Chen et al., 1996;
McAllister et al., 1996; Jansakul & Hirupan, 1999; Chies et al.,
2004) in vascular contractile responses to adrenergic agonists in
trained animals (see Table 5 for more details). It should be
emphasized that some pharmacological methodology limita-
tions exist in these studies. First, norepinephrine was used as an
α-adrenergic agonist without concomitant β-adrenoceptors
blockade. Second, neuronal and extraneuronal uptake inhibitors
for catecholamines were not added to the tissue bath during the
concentration–response curves to norepinephrine. Third, when
the appropriate α-adrenergic agonist phenylephrine was used, it
was not stated whether propranolol, a nonselective β-
Table 4
Effects of run training in the vascular response for bradykinin (BK), isoproterenol (ISO), adenosine (ADO) and endothelin-1 (ET)
Duration Intensity (VO
2max
)/slope Frequency Species Arteries Responses Reference
11 weeks NM, 20% grade 70 min 5 days/week ♂Dog Coronary ↓β(ISO) Rogers et al., 1991
12 weeks NM 85 min ♀swine coronary ↑(ADO/BK) Parker et al., 1994
16–20 weeks NM, 10% grade 85 min 5 days/week ♀swine Femoral, brachial, mesenteric,
renal, hepatic
() (BK) McAllister et al., 1996
7 days NM 2 × day, 60 min ♀swine Femoral, brachial ( ) (BK) McAllister & Laughlin, 1997
13–21weeks NM, 10% grade 85 min ♂swine Femoral, brachial ( ) (ET/BK) Laughlin et al., 2001
16 weeks NM 60 min 5 days/week ♂swine Coronary ( ) (BK) Henderson et al., 2004
16 weeks NM 60 min 5 days/week ♂swine Brachial ( ) (BK) Woodman et al., 2005
VO
2max
, maximum oxygen consumption; slope, grade of treadmill inclination; NM, not mentioned in the study; SHR, spontaneously hypertensive rats; SD, Sprague-
Dawley; ♀, female; ♂, male.
Table 3
Effect of exercise training in the relaxing responses for acetylcholine
Duration Intensity (VO
2max
)/slope Frequency Species Arteries Responses Reference
12 weeks⁎⁎ NM 60 min/day ♂SHR Thoracic aorta mesenteric ↑Yen et al., 1995
19 weeks⁎⁎ NM 60 min 5 days/week ♂SHR Thoracic aorta carotic ↑aorta ( ) carotid Chen et al., 1996
8–11 weeks⁎⁎ NM 60 min 5 days/week ♂SHR Mesenteric hindlimb flow ↑flow Chen et al., 1999
6 weeks⁎⁎ 70% VO
2max
4.5%grade 45 min 5 days/week ♂SHR Thoracic aorta ↑Grahan & Rush, 2004
7 days⁎⁎ NM 2 h/day ♂dogs Coronary flow ↑Wang et al., 1993
4–10 weeks⁎⁎ NM, 15% grade 60 min ♂rats Abdominal aorta ↑Delp & Laughlin, 1997
16 weeks⁎⁎ NM 60 min 5 days/week ♂swine Brachial ↑Woodman et al., 2005
12 weeks⁎⁎ NM, 0% grade 85 min 5 days/week ♀swine Coronary ( ) pEC
50
Oltman et al., 1992
2–4 weeks⁎⁎ NM, 2% grade 38 min 5 days/week ♂Wistar rats Gracilis muscle ↑Sun et al., 1994
10–12weeks⁎⁎ NM, 20% grade 60 min 5 days/week ♂SD rats Soleus ( ) Jasperse & Laughlin., 1999
13–21weeks⁎⁎ NM, 10% grade 85 min ♂swine Femoral, brachial ( ) Laughlin et al., 2001
6 weeks⁎NM 90 min 5 days/week ♂guinea pig Saphenous ↑Choate et al., 2000
⁎⁎, run training; ⁎, swim training; VO
2max
, maximum oxygen consumption; slope, grade of treadmill inclination; NM, not mentioned in the study; ACh, acetylcholine;
SHR, spontaneously hypertensive rats; SD, Sprague-Dawley; ♀, female; ♂, male.
312 A. Zanesco, E. Antunes / Pharmacology & Therapeutics 114 (2007) 307–317

adrenoceptor antagonist, was added to the tissue bath before
obtaining the full concentration–response curves. All these
limitations bring discrepancies into these studies involving the
contractile responses mediated by α-adrenoceptors.
Therefore, a well-controlled exercise training program, use
of appropriate agonists, measurements of the enzymes and the
second messengers involved in the transduction signaling
pathways may provide a better comprehension of the effects
of exercise training in the cardiovascular system.
6. Erectile dysfunction and exercise
Erectile dysfunction is a public health problem, and it is now
established that some vascular diseases such as hypercholes-
terolemia, diabetes mellitus, and arterial hypertension can
interfere with the intricate vascular mechanisms underlying
normal erection. Thus, alterations of penile arterial cell function
may be the basis for the understanding of the prevalence of
erectile dysfunction. Penile erection is a neurovascular pheno-
menon that requires dilation of penile vasculature, relaxation of
smooth muscle, increased intracavernosal blood flow, and
normal veno-occlusive function. The degree of contraction of
corpus cavernosum smooth muscle determines the function
states of penile flaccidity, tumescence, erection, or detumes-
cence. The balance between contractile and relaxant effects is
controlled by central and peripheral mechanisms and involves
neurotransmitters and other endogenous agents. It is now
accepted that NO from both nitrergic nerve and sinusoidal
endothelium plays a fundamental role in the corpus cavernosum
relaxations and hence the erectile process (Andersson, 2001).
Several groups have demonstrated that NO inhibitors block the
corpus cavernosum relaxation induced by electrical field
stimulation in a variety of animals species including rabbit
(Ignarro et al., 1990), dogs (Hedlund et al., 1995), horse (Recio
et al., 1998), monkey (Okamura et al., 1998), rat (Hedlund et al.,
1999), mice (Gocmen et al., 1998), and humans (Holmquist
et al., 1991; Kim et al., 1991; Pickard et al., 1991). On the other
hand, PDE5 inhibitors, such as sildenafil, have been shown to
increase the cGMP levels in corpus cavernosum leading to an
improvement of the erectile responses (Gibson, 2001).
As pointed out above, NO is a potent vasodilator regulating a
number of vascular cell functions. Additionally, it well known
that shear stress induced by physical exercise promotes an
increase of NO production and/or NO bioavailability. Several
investigators have shown that exercise training in both humans
and laboratory animals improves the endothelial function and
ameliorates several cardiovascular disorders. Specifically,
epidemiological studies have associated lowering in blood
pressure, blood glucose, and cholesterol concentration with
improvement of the erectile function in man (Muller et al., 1991;
Aranda et al., 2004). It is surprising, however, that no studies had
been carried out to investigate the influence of physical training
in the erectile dysfunction until Claudino et al. (2004) showed
that run training for 8 weeks increases the relaxing responses in
rat corpus cavernosum from healthy animals through the NO-
cGMP signaling pathway activation. Additional studies of our
laboratory have shown that physical preconditioning markedly
restores the reduced relaxation response of corpus cavernosum
for the muscarinic agonist acetylcholine and electrical field
stimulation in rats made hypertensive by long-term NO blockade
(Zanesco et al., 2005; Claudino et al., 2006). Since hypercho-
lesterolemia and diabetes mellitus are strongly associated with
erectile dysfunction in humans, we are now investigating the
effect of exercise training in the relaxing response of rat corpus
cavenorsum in these disorders.
7. Summary and conclusion
Regular physical exercise is currently an important inter-
vention to prevent and/or to manage cardiovascular diseases and
other disorders. Specifically, the beneficial cardiovascular
effects of physical training have been associated with alterations
Table 5
Effect of exercise training in the vascular responsiveness for norepinephrine (NE) and phenylephrine (Phe)
Duration Intensity
(VO
2max
/slope)
Frequency Species Arteries Responses Reference
12 weeks⁎⁎ NM 60 min/day ♂SHR Aorta/mesenteric ↓(NE) Yen et al., 1995
7 days⁎⁎ NM 2× day, 60 min ♀swine Femoral/brachial ↑(NE) McAllister & Laughlin, 1997
11 weeks⁎⁎ NM, 20% grade 70 min 5 days/week ♂dog Coronary ( ) (NE/Phe) Rogers et al., 1991
12 weeks⁎⁎ 0% grade 85 min 5 days/week ♀swine Coronary ( ) (NE) Oltman et al., 1992
16–20 weeks⁎⁎ NM, 10% grade 85 min 5 days/week ♀swine Femoral, brachial,
mesenteric, renal, hepatic
( ) (NE) McAllister et al., 1996
12–16 weeks⁎⁎ 60% VO
2
max 60 min 5 days/week ♂SHR/ ♂Wistar rats Aorta, femoral, renal ( ) (NE) Edwards et al., 1985
12–16 weeks⁎⁎ 70% VO
2
max 70 min ♂SD rats Aorta, femoral, renal ( ) (NE) Edwards et al., 1985
2–4 weeks⁎⁎ NM, 2% grade 38 min 5 days/week ♂Wistar rats Gracilis muscle ( ) (NE) Sun et al., 1994
10–12 weeks⁎⁎ NM, 20% grade 60 min 5 days/week ♂SD rats Soleus ( ) (NE) Jasperse & Laughlin., 1999
13–21 weeks⁎⁎ NM, 10% grade 85 min ♂swine Femoral, brachial ( ) (NE) Laughlin et al., 2001
12 weeks⁎⁎ NM 85 min ♀swine Coronary ↓(NE) Parker et al., 1994
21 days⁎NM 90 min every day ♂Wistar rats Thoracic aorta ↓(Phe) Jansakul, 1995
28–33 days⁎NM 90 min every day ♂Wistar rats Superior mesenteric ↓(Phe) Jansakul & Hirupan, 1999
5 weeks⁎NM 30 min 5 days/week ♂Wistar rats Mesenteric ↓(Phe) Chies et al., 2004
6 weeks⁎NM 90 min 5 days/week ♂guinea pig Saphenous ( ) (Phe) Choate et al., 2000
⁎⁎, run training; ⁎, swim training; VO
2max
, maximum oxygen consumption; slope, grade of treadmill inclination; NM, not mentioned in the study; SHR, spontaneously
hypertensive rats; SD, Sprague-Dawley; ♀, female; ♂, male.
313A. Zanesco, E. Antunes / Pharmacology & Therapeutics 114 (2007) 307–317

in autonomic nervous system and endothelial cells. However,
the exact mechanisms by which physical exercise produces
these alterations are not fully understood. Several pharmaco-
logical studies have been performed to investigate the effect of
exercise training using classical approaches, such as concen-
tration–response curves and radioligand binding assays, to
analyze the receptor–drug interaction and biochemical mea-
surements of second messengers and their signal transduction
pathways. However, no conclusive data related to the role of
adrenergic and muscarinic–cholinergic receptors in response to
exercise training have been found. The reasons for these
discrepancies are multiple. First, the intensity, duration, and
frequency of exercise training have not been well controlled.
Second, nonappropriate pharmacological tools (agonists and
antagonist) were used to evaluate the efficacy and affinity of the
drug–receptor interaction. Third, inhibitors of metabolism of
catecholamines, effective inhibition of drug removal process,
and when necessary blockers of β-adrenergic receptor have not
been used in tissues bath to avoid misinterpretation of the
concentration–response curves. Furthermore, the complexity of
stimulus–response mechanisms in endothelial cells with a
variety of signal pathways mediating the relaxing response
makes it difficult to delineate a specific mechanism by which
exercise training can produces beneficial effects in the vascular
smooth muscle response. Thus, it is desirable an association
between experts in kinesiology and pharmacology to performed
well-controlled physical training programs and careful phar-
macological analysis of drug receptor interaction experiments in
order to get more conclusive data relating physical training and
pharmacological studies.
Acknowledgment
A. Zanesco and E. Antunes are supported by grants from
the Fundação de Amparo a Pesquisa do Estado de Sao Paulo
(FAPESP).
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