(Stroke. 2001;32:1394.)
© 2001 American Heart Association, Inc.
Original Contributions |
Role of Endothelium in Shear Stress–Induced Constrictions in Rat Middle Cerebral Artery
From the Departments of Anesthesiology (R.M.B., M.L.S., S.P.M.), Molecular Physiology and Biophysics (R.M.B.), and Medicine (Division of Cardiovascular Sciences) (R.M.B.), Baylor College of Medicine, Houston, Tex.
Correspondence to Robert M. Bryan, Jr, PhD, Department of Anesthesiology, Baylor College of Medicine, One Baylor Plaza, Suite 434D, Houston TX 77030. E-mail rbryan{at}bcm.tmc.edu
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Background and Purpose—Luminal shear stress has been reported to constrict cerebral arteries and arterioles of several species. Although the endothelium is not required for this response, it is not known whether the endothelium enhances or attenuates shear stress–induced constrictions.
Methods—Middle cerebral arteries (MCAs) were isolated from male Long-Evans rats, mounted in a tissue bath, and pressurized to 80 mm Hg in the absence of luminal flow. In some MCAs, the endothelium was selectively loaded with fura 2 for the measurement of endothelial Ca2+ concentration. Luminal shear stress was increased by adjusting luminal flow while maintaining a constant intraluminal pressure.
Results—After the
development of spontaneous tone in MCAs without luminal flow, inside
diameters were 
190 µm. MCAs constricted 15% when luminal flow
was increased to produce a shear stress of 50
dyne/cm2. The shear stress–induced
constrictions were more pronounced in vessels without intact
endothelium. Scavenging reactive oxygen species with
4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron) or superoxide
dismutase/catalase significantly inhibited the shear stress–induced
constrictions in vessels with intact endothelium and in
vessels in which the endothelium had been removed. In
intact vessels, endothelial
Ca2+ increased 33 nmol/L (from 133±11 to
166±12 nmol/L) when shear stress was increased to 50
dyne/cm2. The presence of
NG-nitro-L-arginine
methyl ester (L-NAME), L-NAME+indomethacin, or
L-NAME+indomethacin+charybdotoxin had no significant
effect on the shear stress–induced constrictions in MCAs with intact
endothelium.
Conclusions—We conclude that the endothelium plays a role in attenuating the shear stress–induced constrictions in rat MCAs. The attenuation does not appear to be by release of NO, prostacyclin, or endothelium-derived hyperpolarizing factor. The endothelium apparently attenuates the constriction by an unknown dilating factor, by a dilating process, or simply by attenuating the mechanical force of the shear stress as it is transmitted to the abluminal side of the vessel.
Key Words: calcium • endothelium • fura 2 • middle cerebral artery • reactive oxygen species • rats
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Peripheral arteries and arterioles dilate when flow through the lumen of the vessel is increased. The mechanism involves sensing a mechanical deformation (resulting from shear stress) by the endothelium and releasing a relaxing factor (NO or prostacyclin).1 2 3 4 In cerebral vessels, the response to shear stress is somewhat more controversial. Shear stress has been reported to produce dilations, constrictions, or a combination of dilation and constriction depending on the level of shear stress (see Bryan et al5 for complete references). The controversy surrounding the effect in cerebral vessels could possibly be dependent on species, vessel size, or vessel location in the vascular tree.
In middle cerebral arteries (MCAs) from the cat and rat and penetrating arterioles from the rat, luminal flow constricted the vessels in a shear stress–dependent manner.5 6 Additionally, flow constricted rabbit cerebral vessels during some but not all conditions.7 8 The shear stress–dependent constriction persisted even after removal of the endothelium. The role of the endothelium is complicated in that it is not needed for a shear stress–induced constriction to occur, but endothelia are the cells that directly experience deformation by shear stress.5 6 Neither NO nor cyclooxygenase metabolites (ie, prostacyclin) appeared to be involved with the response in endothelium-intact cat MCAs. The exact role of the endothelium in the shear stress–induced constrictions remains largely unknown, especially when rat cerebral vessels are considered. Consequently, it is possible that the endothelium attenuated the constriction, enhanced the constriction, or had no effect on the response. Attenuation of the shear stress–induced constriction could be a result of the release of NO, prostacyclin, endothelium-derived hyperpolarizing factor (EDHF), or reactive oxygen species (ROS). Enhancement of the shear stress–induced constriction could be a result of constricting factors such as ROS. The rationale for considering ROS is that endothelial cells in culture generate ROS when exposed to shear stress.9 10 11 Furthermore, ROS have been reported to either dilate or constrict cerebral vessels.6 12 13
The purpose of the present study was to determine the role of endothelium in the shear stress–induced constriction in the rat middle cerebral artery. Specifically, we tested the following hypotheses: (1) ROS that are produced by the endothelium as a result of shear stress either attenuate or enhance the shear stress–induced constriction. (2) Endothelium attenuates the shear stress–induced constrictions in rat MCAs by releasing NO, prostacyclin, or EDHF.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Harvesting and Mounting Vessels
The Animal Protocol Review Committee at Baylor College of Medicine approved the experimental protocol. Male Long-Evans rats (250 to 350 g) were anesthetized with 3% isoflurane and decapitated. The brain was immediately removed and placed in cold (4°C) physiological saline solution (PSS). MCAs were carefully harvested and mounted in a vessel chamber maintained at 37°C.14 Micropipettes were inserted into both ends of each vessel, and the vessel was secured with nylon ties. Luminal pressure was set at 80 mm Hg by raising 2 reservoirs that were connected to the micropipettes.14 The vessels were bathed in PSS that was equilibrated with a gas consisting of 20% O2/5% CO2, with a balance of N2. The pH of the bath was
7.40,
PCO2
was 35 mm Hg, and
PO2
was 130
mm Hg.14 Flow through the lumen of the vessels was produced by a variable-speed syringe pump (model 22, Harvard Apparatus) (see Bryan et al5 for diagram and more details). Pressure transducers on either side of the vessel chamber provided a measurement of perfusion pressure. Before mounting of the vessel, the resistance of the tubing and micropipettes on either side of the vessel was measured. From the resistances of the micropipettes, an algorithm was used to determine the upstream pressure and downstream pressure necessary to maintain a luminal pressure of 80 mm Hg.5 After initiating or increasing luminal flow, the output reservoir was appropriately lowered as calculated by the algorithm.
The vessels were magnified with an inverted microscope
equipped with a video camera and monitor. Inside diameters of the
vessels were measured manually from the video screen or from videotape
made at the time of the study. After they were mounted and pressurized,
the vessels of all groups developed spontaneous tone (18% to 20%).
Experimental protocols were not initiated until the vessel diameters
were stable over a period of 15 minutes.
Shear stress was calculated by use of the following
equation1 5 15 16 :
t=4
Q/
r3, where t is shear stress in
dyne/cm2, is viscosity, Q is flow, and r
is the inside radius of the vessel. In all studies, we attempted to set
a flow to produce a given shear stress. Because the diameter changed
when flow was altered, adjustments in flow were made 3 times to
approach the target shear stress.
The presence of intact endothelium in
cerebral vessels was verified by luminal administration of ATP, an
agonist for P2Y2 receptors. ATP dilates cerebral
arteries and arterioles via an endothelium-dependent
mechanism involving NO and
EDHF.17 18 19
In some arteries, the endothelium was damaged by
passing air through the lumen of the vessel as previously
described.14 17 18
The absence of dilation to luminally applied ATP indicated that the
endothelium had been successfully removed. Vessels
denuded of endothelium dilated in response to the NO
donor,
S-nitroso-N-acetylpenicillamine
(SNAP), indicating that the vascular smooth muscle was intact. In
studies in which the endothelium was damaged or in
which NO synthase was inhibited with
NG-nitro-L-arginine
methyl ester (L-NAME), the vessels constricted 20% of the resting
diameter.19 SNAP was added
to these vessels to dilate them back to the diameter before L-NAME
treatment or damage to the endothelium. In another
group of MCAs, endothelial cell rigidity was increased
by exposing the luminal surface to glutaraldehyde
(0.025%) for 20 seconds. This procedure has been reported to increase
the shear modulus of the endothelium by
>10-fold.20
Measurement of Endothelial
Ca2+ With Use of Fura 2
Ca2+ concentrations in the
cytoplasm of the endothelium and vessel diameter were
simultaneously measured as previously
described.21 Briefly, fura
2-AM (0.67 µmol/L final concentration) was added to the luminal
perfusate. After 5 minutes of exposure, the vessel was washed
to remove extracellular fura 2-AM, and an additional 30 minutes for was
allowed for intracellular deesterification of the fura 2-AM to fura 2.
The addition of fura 2-AM through the lumen at the above concentration
and duration selectively loads the
endothelium.21
Therefore, the fluorescence signal is derived exclusively from
the endothelium, and the calculated
Ca2+ concentration represents only
the
endothelium.21
For Ca2+ measurements, the vessels were
illuminated with excitation light alternating between wavelengths of
340 and 380 nm with the use of a xenon arc lamp, appropriate filters,
and a filter changer (Intracellular Imaging). Additionally, red light
from a separate lamp was used to transilluminate the vessels for
diameter measurements. The light was collected with a quartz objective
(x10, numerical aperture 0.5, Nikon) and subsequently split and
filtered with a dichroic mirror. The red light was diverted to a
charge-coupled device for diameter measurements, and the remainder was
diverted to a photomultiplier after passing through a 510-nm narrow
bandpass filter. Intensities of the 510-nm fluorescence light
were used to quantify intracellular Ca2+
according to the following equation:
[Ca2+]i=ß(R-Rmin)Kd/(Rmax-R),
where [Ca2+]i is
the intracellular Ca2+ concentration in the
endothelium, ß is the ratio of the 380-nm
fluorescence intensity for
Ca2+-unbound fura 2 over
Ca2+-bound fura 2, R is the ratio of light
intensity at 510 nm when excited at 340 nm to the intensity when
excited at 380 nm (340/380 ratio) at a given condition (ie, shear
stress), Rmin is the 340/380 ratio at zero
[Ca2+]i,
Rmax is the 340/380 ratio when
[Ca2+]i was
sufficiently high to saturate fura 2, and
Kd is
282 nmol/L. ß, Rmin, and
Rmax were determined in a separate group of
vessels as previously
described.21
Drugs and Reagents
ATP, 2-methylthio-ATP (MeSATP),
indomethacin, 4,5-dihydroxy-1,3-benzene disulfonic acid
(Tiron), charybdotoxin, and L-NAME were purchased from Sigma Chemical
Co. SNAP was purchased from Research Biochemicals Inc. Catalase was
purchased from ICN Biochemicals. Superoxide dismutase (SOD) was
purchased from Calbiochem). Fura 2-AM (50 µg) was purchased from
TefLabs and dissolved in 75 µL dimethyl sulfoxide (containing 14%
pluronic solution).
PSS consisted of the following (mmol/L)14 : NaCl 119, NaHCO3 24, KCl 4.7, KH2PO4 1.18, MgSO4 1.17, CaCl2 1.6, glucose 5.5, and EDTA 0.026.
Statistical Analysis
All data are presented as mean±SE. For
statistical analysis, the 1- or 2-way repeated-measures ANOVA
was used with a post hoc Tukey test (where appropriate) for comparison
of individual groups and individual data points. The acceptable level
of significance was defined as P<0.05.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Figure 1A
shows absolute changes in diameter of the
rat MCAs when luminal shear stress was increased in control MCAs and in
MCAs treated with a scavenger of ROS, Tiron (10 mmol/L) or SOD
(200 U/mL)/catalase (140 U/mL) (SOD/cat). Note that for each group, the
MCAs were allowed to develop spontaneous tone in the absence of luminal
flow. The SOD/cat group had a mean inner diameter that was greater than
that in the control or Tiron group; however, there was no group
difference (P=0.11, 2-way
repeated-measures ANOVA). Furthermore, because the MCAs were randomized
and because there was no significant effect of SOD/cat on the vessel
diameter, this increased mean diameter was due to chance alone. The
magnitude of constriction due to shear stress for the Tiron and SOD/cat
groups was less than that for the control group. This can be clearly
seen in
Figure 1B, where the same data were plotted as percent
change in inner diameter. For the results in
Figure 1B, there was a significant group effect
(P=0.01), a significant shear
stress effect (P<0.001), and a
significant interaction between groups and shear stress
(P<0.001). The control group
was significantly different from the Tiron group
(P=0.02) and the SOD/cat group
(P=0.04, Tukey test). Thus,
scavenging ROS significantly reduced the constriction that was due to
luminal shear stress. Flows required to achieve a shear stress of 50
dyne/cm2 were 108±19 µL/min for the
control group (n=8), 144±22 µL/min for the Tiron group (n=6), and
190±20 µL/min for the SOD/cat group (n=6).
|
Figure 2 shows the effects of SOD/cat treatment on the
shear stress–induced constriction in MCAs after the
endothelium had been removed by the passage of air
through the lumen (see Methods). Removal of the
endothelium was verified by the absence of a dilation
to luminally applied ATP. The absolute diameters are shown in
Figure 2A, and the percent changes of the diameters as a
function of shear stress are shown in
Figure 2B. Even after the removal of the
endothelium, MCAs significantly constricted to the
luminal shear stress (P=0.001
and P=0.03 for absolute change
[Figure 2A] and percent change
[Figure 2B], respectively). After removal of the
endothelium, SOD/cat completely abolished the shear
stress–induced constriction in endothelium-denuded
MCAs.
|
The effect of shear stress on diameter and
endothelial Ca2+ (measured
simultaneously from each MCA) is shown in
Figure 3. The inside diameter progressively decreased
from 200±18 to 180±18 µm (n=5,
P<0.001) when the shear stress
was increased from 0 to 50 dyne/cm2. In the
same MCAs, endothelial Ca2+
increased 33 nmol/L, from 133±10 to 166±12 nmol/L, over the same
shear stress range (P=0.01).
The insert in
Figure 3 shows an enlarged plot of the
Ca2+ change in the
endothelium with increasing shear stress.
Figure 3 also shows the diameter and
Ca2+ change when
3x10-6 mol/L
MeSATP was administered luminally. MeSATP dilates rat MCAs through the
activation of NO synthase by increasing endothelial
Ca2+.18 21
The 33-nmol/L increase in Ca2+ as a result
of shear stress (50 dyne/cm2) is
considerably less than the increase of 376 nmol/L that resulted when
the MCAs were dilated after the addition of MeSATP
(Figure 3). Using data from a previous study, we estimate
that a 33-nmol/L increase in endothelial
Ca2+ could dilate MCAs through the
stimulation of NO synthase by only 2% or less (S.P. Marrelli,
unpublished data, 2000, and
Marrelli21 ).
|
The effect of removing the endothelium on
the shear stress–induced constriction is shown in
Figure 4. Increasing luminal shear stress by
increasing flow through the lumen constricted intact MCAs
(Figure 4A) (n=4,
P<0.001). After the flow was
stopped and the MCAs were allowed to dilate, a similar response to
shear stress was repeated
(Figure 4A). The insert in
Figure 4A expresses the data as percent change in the
diameter of the MCAs, where the baseline was the inner diameter without
flow (0 dyne/cm2). There was no significant
difference between the first response (control) and the second response
(time control). After an initial response to shear stress in another
group of MCAs, air was passed through the lumen of each vessel to
damage the endothelium. Because damaging the
endothelium significantly constricted the cerebral
vessels, SNAP, an NO donor, was added to the extraluminal bath to
dilate the vessel to near its original diameter before removal of the
endothelium. After damage to the
endothelium, the response of the MCAs to shear stress
was enhanced (P=0.04, n=5)
(Figure 4B), indicating that the endothelium
attenuated the constrictor response to the shear stress.
|
Figure 5 shows the effects of
10-5 mol/L
L-NAME (NO synthase inhibitor) alone or in combination with
10-5 mol/L
indomethacin (cyclooxygenase
inhibitor) on the constriction to luminal shear stress. In
each of the panels, there was an initial control response (solid bars)
during which luminal shear stress was adjusted to 30
dyne/cm2. After returning the shear stress
to 0 dyne/cm2 by stopping flow, shear stress
was adjusted to 50 dyne/cm2 for 5
minutes, and the shear stress was again removed. The experimental
condition (or time control) was then imposed, and the response to a
shear stress of 30 and 50 dyne/cm2 was
repeated as described above (stippled bars in
Figure 5). SNAP was added to each vessel in the experimental
condition to restore the diameter to near the original baseline,
because removal of the endothelium or L-NAME treatment
constricted the MCAs by 15%. From left to right, the panels in
Figure 5 are as follows: the time control (n=8), the
response in the presence of
10-5 mol/L
L-NAME (n=9), the response in the presence of
10-5 mol/L
L-NAME and 10-5
mol/L indomethacin (n=8), and the response after damage
to the endothelium (denude) (n=8). The only condition
showing a significant effect was after damage to the
endothelium
(P=0.004).
Figure 6 shows a similar study in which the
experimental condition was
L-NAME+indomethacin+charybdotoxin (100 nmol/L) (n=6
each for time control and experimental groups). Charybdotoxin is an
inhibitor of the
Ca2+-activated
K+ channels. SNAP was added to each vessel
in the experimental condition to restore the diameter to near the
original baseline. As the studies show in
Figure 5, the presence of
L-NAME+indomethacin+charybdotoxin did not affect the
response compared with the control response. There was a tendency in
the study shown in
Figure 6 for the second response (time control) to be
diminished compared with the original response. A similar finding
applied to the time control and L-NAME groups in
Figure 5.
|
|
Figure 7 shows the effects of increasing the rigidity
of endothelial cells with a 20-second luminal exposure
to 0.025%
glutaraldehyde20
(n=4 for each group) on the constrictor response to luminal shear
stress. Although the MCAs still constricted to increased shear stress
after glutaraldehyde treatment, the response was not as
prominent as the response in control vessels
(Figure 7A, statistical interaction between
glutaraldehyde treatment and shear stress,
P<0.001).
Figure 7B shows the response in the control condition and
after glutaraldehyde treatment when the diameter was
plotted as percent change. Although glutaraldehyde
treatment attenuated the constrictor response, it did not diminish the
endothelial response to
10-5 mol/L ATP,
indicating that the dilator function of the endothelium
was intact (see insert).
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Previous studies have demonstrated that luminal flow (shear stress) constricted MCAs from the cat and rat and penetrating arterioles from the rat.5 6 Additionally, flow constricted rabbit cerebral vessels during some but not all conditions.7 8 The majority of the constriction occurred over the range of shear stress (<50 dyne/cm2) experienced during normal physiological conditions.22 The mechanism for the constriction appears to involve integrin binding (specifically, ß3 integrin), depolarization of the vascular smooth muscle, and an increase in cytoplasmic Ca2+.5 6 Flow-induced constrictions persisted after removal of the endothelium.5 6 This observation may not seem logical on initial consideration because the cells receiving the mechanical stimuli were not required for the response to occur. In a previous paper, we speculated that the forces at the luminal surface of the endothelium are transmitted through the cytoskeletal matrix to mechanoreceptors on the extraluminal side of the endothelium.5 23
Although the endothelium is not needed for the shear stress–induced constrictions in cerebral vessels, it was not known whether the endothelium enhances, attenuates, or does not affect rat cerebral arteries. Therefore, the purpose of the present study was to better define the role of the endothelium in shear stress–induced constrictions. We tested the hypotheses that (1) ROS that are produced by the endothelium as a result of shear stress either attenuate or enhance the shear stress–induced constriction, and (2) the endothelium attenuates the shear stress–induced constriction by releasing NO, prostacyclin, or EDHF. From these studies, we report 2 findings: (1) ROS are involved in the shear stress–induced constriction in the rat MCA. (2) The endothelium attenuated the constrictor response to shear stress.
The first of our findings is the involvement of ROS in the
shear stress–induced constriction in the rat MCA. The source of these
ROS does not appear to be the endothelium. The
rationale for testing the hypothesis was derived from previous
observations that endothelial cells in culture generate
ROS when exposed to shear
stress.9 10 11
ROS have been reported to either dilate or constrict cerebral
vessels.6 12 13
Furthermore, a previous study implicated ROS in the shear stress
response, but the source (endothelium or vascular
smooth muscle) was not
determined.6 Our studies also
indicated that ROS were involved and that their source was not the
endothelium. We base this conclusion on the
observations that shear stress–induced constrictions were attenuated
with ROS scavengers not only in endothelium-intact MCAs
(Figure 1
) but also in endothelium-denuded
MCAs
(Figure 2). Because ROS were generated in the absence of
endothelium, it logically follows that the
endothelium was likely not the source. Thus, the
endothelium does not attenuate or potentiate the shear
stress–induced constriction by generating ROS. Although ROS seem to be
involved (Madden and
Christman6 and the
present study), they do not appear to be generated by the
endothelium; the apparent source of the ROS is the
vascular smooth muscle.
The second of our findings is that the
endothelium attenuates the constrictor response to
shear stress. The attenuation was not due to the release of NO,
prostacyclin, or EDHF. Determination of whether the
endothelium enhances, attenuates, or does not affect
the shear stress–induced constriction has not been
straightforward.5 6
In general, the strategy to assess the role of
endothelium is to compare the response for a given
condition (shear stress in this case) in
endothelium-intact cerebral vessels with the response
to the same condition in endothelium-denuded vessels.
However, removal of the endothelium constricts vessels
15% because of the concomitant removal of
endothelium-derived NO. The contractile state of a
vessel often dictates the magnitude of response for a stimulus. That
is, vessels that are already partially constricted after removal of the
endothelium may not constrict as much to luminal shear
stress as do endothelium-intact vessels. To overcome
this limitation, we added an NO donor, SNAP, in the present study
to restore the original diameter before removal of the
endothelium. When this was done, it was clear that the
endothelium attenuated the constrictor response to
luminal shear stress
(Figures 4 and far right bar graph of
Figure 5).
The attenuation (or dilator influence) of the
endothelium on the shear stress–induced response was
not due to the release of NO, prostacyclin, or EDHF from the
endothelium
(Figures 5 and 6). The results from the present study
leave us with the following question: what endothelial
component is responsible for the attenuated response? We offer 2
possible explanations to this question. First, there could be an
unknown dilating factor being released from the
endothelium or some unknown dilating process involving
the endothelium. The dilator process would serve to
offset and, thus, attenuate the constriction produced by the shear
stress. Second, the mechanical force of the shear stress could have
been attenuated as it was transmitted across the
endothelium to the vascular smooth muscle. It is
reasonable to believe that the mechanoreceptors responsible for the
shear stress–induced constriction are on the vascular smooth
muscle.5 6 A direct
stimulation of these mechanoreceptors by shear forces in
endothelium-denuded MCAs would be more efficient than
indirect stimulation when the endothelium is intact.
Consistent with this idea is the observation that the
constrictor response to luminal shear stress was attenuated after
increasing the rigidity of the endothelium
(Figure 7).16
Given that dilator mechanisms involving the endothelium
other than NO, prostacyclin, or EDHF are not known, we tentatively
conclude that an attenuation of the mechanical forces across the
endothelium could account for the attenuated shear
stress–induced constriction by the
endothelium.
We also demonstrated that shear stress on the
endothelium increased cytoplasmic
Ca2+ in endothelium by 33
nmol/L (from 133 nmol/L at rest to 166 nmol/L at 50
dyne/cm2)
(Figure 3). From previous studies, we calculate that this
increase in endothelial Ca2+
would have only minor effects, if any, in producing dilations through
the release of NO or EDHF from the
endothelium21
(S.P. Marrelli, unpublished data, 2000). However, it must be noted that
in peripheral vessels shear stress can stimulate NO release
through a pathway not directly involving
Ca2+ as a second
messenger.24 Thus, the
absence of a major increase in endothelial
Ca2+ does not rule out the involvement of an
endothelial relaxing factor. However, the minor
increase in endothelial Ca2+
(Figure 3) in combination with the studies in which
inhibitors were used
(Figures 5 an 6) does rule out the involvement of known
relaxing factors in attenuating the shear stress–induced
contraction.
In summary, we have shown that the generation of ROS can account for at least part of the constriction in rat MCAs as a result of shear stress. The endothelium does not appear to be the source of the ROS. By a process of elimination, the vascular smooth muscle is the likely source. The endothelium attenuates the shear stress–induced constriction. Although shear stress increases cytoplasmic Ca2+ in the endothelium, the Ca2+ increase is not sufficient to stimulate the release of NO, prostacyclin, or EHDF.
|
Acknowledgments |
|---|
This work was supported by Public Health Service grant RO1 NS-37250.
Received December 7, 2000; revision received February 8, 2001; accepted February 27, 2001.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
1. Koller A, Sun D, Kaley G. Role of shear stress and endothelial prostaglandins in flow- and viscosity-induced dilation of arterioles in vitro. Circ Res. 1993;72:1276–1284.
2.
Koller A, Sun D,
Huang A, Kaley G. Corelease of nitric oxide and
prostaglandins mediates flow-dependent dilation of rat
gracilis muscle arterioles. Am J
Physiol. 1994;267:H326–H332.
3.
Kuo L, Davis MJ,
Chilian, WM. Endothelium-dependent, flow-induced
dilation of isolated coronary arterioles.
Am J Physiol. 1990;259:H1063–H1070.
4.
Kuo L, Chilian WM,
Davis MJ. Interaction of pressure- and flow-induced responses in
porcine coronary resistance vessels.
Am J Physiol. 1991;261:H1706–H1715.
5. Bryan RM Jr, Marrelli SP, Steenberg ML, Schildmeyer LA, Johnson TD. The effects of luminal shear stress on cerebral arteries and arterioles. Am J Physiol. 2001;280:H2011–H2022.
6. Madden JA, Christman NJ. Integrin signaling, free radicals, and tyrosine kinase mediate flow constriction in isolated cerebral arteries. Am J Physiol. 1999;277:H2264–H2271.
7.
Bevan JA, Wellman
GC. Intraluminal flow-initiated hyperpolarization
and depolarization shift the membrane potential of arterial
smooth muscle toward an intermediate level.
Circ Res. 1993;73:1188–1192.
8.
Thorin-Trescases N,
Bevan JA. High levels of myogenic tone antagonize the dilator response
to flow of small rabbit cerebral arteries.
Stroke. 1998;29:1194–1200.
9.
Yeh LH, Park YJ,
Hansalia RJ, Ahmed IS, Deshpande SS, Goldschmidt-Clermont PJ, Irani K,
Alevriadou BR. Shear-induced tyrosine phosphorylation
in endothelial cells requires Rac1-dependent
production of ROS. Am J
Physiol. 1999;276:C838–C847.
10. Hsieh HJ, Cheng CC, Wu ST, Chiu JJ, Wung BS, Wang DL. Increase of reactive oxygen species (ROS) in endothelial cells by shear flow and involvement of ROS in shear-induced c-fos expression. J Cell Physiol. 1998;175:156–162.[Medline] [Order article via Infotrieve]
11.
Chiu JJ, Wung BS,
Shyy JY, Hsieh HJ, Wang DL. Reactive oxygen species are involved in
shear stress–induced intercellular adhesion molecule-1 expression in
endothelial cells.
Arterioscler Thromb Vasc Biol. 1997;17:3570–3577.
12.
Sobey CG, Heistad
DD, Faraci FM. Mechanisms of bradykinin-induced cerebral vasodilatation
in rats: evidence that reactive oxygen species activate
K+ channels.
Stroke. 1997;28:2290–2294.
13.
Wei EP, Kontos
HA, Beckman JS. Mechanisms of cerebral vasodilation by superoxide,
hydrogen peroxide, and peroxynitrite.
Am J Physiol. 1996;271:H1262–H1266.
14. Bryan RM Jr, Eichler MY, Swafford MWG, Johnson TD, Suresh MS, Childres WF. Stimulation of a2 adrenoceptors dilates the rat middle cerebral artery. Anesthesiology. 1996;85:82–90.[Medline] [Order article via Infotrieve]
15. Lipowsky HH. Shear stress in the circulation. In: Bevan JA, Kaley G, Rubani GM, eds. Flow-Dependent Regulation of Vascular Function. New York, NY: Oxford University Press; 1995.
16. Shimoda LA, Norins NA, Jeutter DC, Madden JA. Flow-induced responses in piglet isolated cerebral arteries. Pediatr Res. 1996;39:574–583.[Medline] [Order article via Infotrieve]
17.
You J, Johnson
TD, Marrelli SP, Mombouli JV, Bryan RM Jr. P2u receptor–mediated
release of endothelium-derived relaxing factor/nitric
oxide and endothelium-derived hyperpolarizing factor
from cerebrovascular endothelium in rats.
Stroke. 1999;30:1125–1133.
18.
You JP, Johnson
TD, Childres WF, Bryan RM Jr. Endothelial-mediated
dilations of rat middle cerebral arteries by ATP and ADP.
Am J Physiol. 1997;273:H1472–H1477.
19. You J, Johnson TD, Marrelli SP, Bryan RM Jr. Functional heterogeneity of endothelial P2 purinoceptors in the cerebrovascular tree of the rat. Am J Physiol. 1999;277:H893–H900.
20.
Melkumyants AM,
Balashov SA, Khayutin VM. Control of arterial lumen by
shear stress on endothelium.
News Physiol Sci. 1995;10:204–210.
21. Marrelli SP. Selective measurement of endothelial or smooth muscle [Ca2+]i in pressurized/perfused cerebral arteries with fura-2. J Neurosci Methods. 2000;97:145–155.[Medline] [Order article via Infotrieve]
22.
Kroll MH, Hellums
JD, McIntire LV, Schafer AI, Moake JL. Platelets and shear stress.
Blood. 1996;88:1525–1541.
23. Davies PF, Barbee KA, Volin MV, Robotewskyj A, Chen J, Joseph L, Griem ML, Wernick MN, Jacobs E, Polacek DC, et al. Spatial relationships in early signaling events of flow-mediated endothelial mechanotransduction. Annu Rev Physiol. 1997;59:527–549.[Medline] [Order article via Infotrieve]
24.
Fleming I, Busse R. Signal transduction of eNOS activation. Cardiovasc Res. 1999;43:532–541.
This article has been cited by other articles:
 |
|
 |
|
  L. E. Rasmussen, P. M. Vanhoutte, B. L. Jensen, and O. Skott Continuous flow augments reactivity of rabbit carotid artery by reducing bioavailability of NO despite an increase in release of EDHF Am J Physiol Heart Circ Physiol, October 1, 2006; 291(4): H1521 - H1528. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. D. Prisby, M. K. Wilkerson, E. M. Sokoya, R. M. Bryan Jr., E. Wilson, and M. D. Delp Endothelium-dependent vasodilation of cerebral arteries is altered with simulated microgravity through nitric oxide synthase and EDHF mechanisms J Appl Physiol, July 1, 2006; 101(1): 348 - 353. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Andresen, N. I. Shafi, and R. M. Bryan Jr. Endothelial influences on cerebrovascular tone J Appl Physiol, January 1, 2006; 100(1): 318 - 327. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. G. Zani and H. G. Bohlen Transport of extracellular L-arginine via cationic amino acid transporter is required during in vivo endothelial nitric oxide production Am J Physiol Heart Circ Physiol, October 1, 2005; 289(4): H1381 - H1390. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. K. Wilkerson, L. A. Lesniewski, E. M. Golding, R. M. Bryan Jr., A. Amin, E. Wilson, and M. D. Delp Simulated microgravity enhances cerebral artery vasoconstriction and vascular resistance through endothelial nitric oxide mechanism Am J Physiol Heart Circ Physiol, April 1, 2005; 288(4): H1652 - H1661. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Miura, J. J. Bosnjak, G. Ning, T. Saito, M. Miura, and D. D. Gutterman Role for Hydrogen Peroxide in Flow-Induced Dilation of Human Coronary Arterioles Circ. Res., February 7, 2003; 92 (2): e31 - e40. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||