| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Department of Anesthesiology, Baylor College of Medicine, Houston, Texas 77030; and 2 Department of Internal Medicine, Lund University Hospital, Lund, S-221 85 Sweden
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The effects of stimulating
P2Y1 or
P2Y2 purinoceptors on the
endothelium of isolated middle cerebral arteries (MCAs), third-order branches of the MCA (bMCAs), and penetrating arterioles (PAs) of the
rat were studied. After pressurization and development of spontaneous
tone (25% contraction), resting diameters for MCAs, bMCAs, and PAs
were 203 ± 5 (n = 50), 99 ± 2 (n = 42), and 87 ± 2 µm
(n = 53), respectively. Luminal
application of the P2Y1-selective agonist 2-methylthioadenosine 5'-triphosphate elicited
dose-dependent dilations (or loss of intrinsic tone) in MCAs but not in
bMCAs or PAs. The dilation in MCAs was completely blocked by removal of
the endothelium or by nitro-L-arginine methyl ester
(10
5 M), an inhibitor of NO
synthase. Luminal application of the
P2Y2-selective agonist ATP
elicited dilations in MCAs, bMCAs, and PAs. Removal of the endothelium
abolished the dilations in all vessel groups. Dilations in MCAs have
been shown to involve both NO and endothelium-derived hyperpolarizing
factor (EDHF). The dilations in bMCAs and PAs had a minor NO component
and prominent EDHF component; that is, 1) the dilations to ATP were not
diminished by the combined inhibition of NO synthase and
cyclooxygenase, 2) the dilations
were accompanied by significant hyperpolarizations of the vascular
smooth muscle (~15 mV), and 3) the
dilations were completely abolished by the calcium-activated potassium
channel blocker charybdotoxin. We concluded that the role of NO in
purinoceptor-induced dilations diminishes along the cerebrovascular
tree in the rat, whereas the role of EDHF becomes more prominent.
calcium-activated potassium channels; endothelium; vascular smooth muscle; P2Y2- and P2Y1-purinoceptor subtypes; nitric oxide; endothelium-derived hyperpolarizing factor
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
RECOGNITION OF the importance of P2 purinoceptors in vascular control, coupled with the identification of numerous receptor subtypes, has provided an important and fruitful frontier for studying the regulation of blood flow (1, 2, 10, 12, 16, 24, 29). The naturally occurring purine and pyrimidine phosphates ATP, ADP, and UTP can either dilate or constrict vessels, depending on the P2 subtype and their vascular location (smooth muscle or endothelium) (2, 29, 36).
Our laboratory has recently identified two P2 purinoceptors located on the endothelium of the rat middle cerebral artery (MCA). When stimulated, both of these receptor subtypes elicit dilation (36). The P2y (or P2Y1) subtype, sensitive to ADP, dilates by releasing nitric oxide (NO) from the endothelium (36) [henceforth, "NO" may refer to either NO gas or an NO-containing compound (32)]. On the other hand, the P2u (P2Y2) subtype, sensitive to ATP and UTP, dilates the rat MCA by releasing both NO and endothelium-derived hyperpolarizing factor (EDHF) (36, 37). Although these two subtypes have been identified for the MCA, it is not known whether these receptors function in a similar manner at more distal locations of the cerebrovascular tree. For this reason, we asked the following questions: 1) Does 2-methylthioadenosine 5'-triphosphate (2-MeS-ATP), a synthetic agonist selective for the P2Y1 subtype, dilate third- and fourth-order branches of the MCA (bMCAs) and penetrating arterioles (PAs)? 2) Does ATP, an agonist for the P2Y2 subtype, dilate bMCAs and PAs? 3) If either agonist were to produce a dilation, what is (are) the relaxing factor(s) released from the endothelium?
| |
METHODS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The Animal Protocol Review Committee at Baylor College of Medicine approved the experimental protocol. Male Long-Evans rats (250-350 g) were anesthetized with 3% isoflurane and decapitated. The brain was immediately removed and placed in cold (4°C) physiological saline solution (PSS). With the aid of a dissecting microscope, MCAs, bMCAs, and PAs were carefully harvested (3, 9, 19). Sections of these three vessel groups were mounted in an arteriograph (Living Systems, Burlington, VT) as previously described (3, 4). Micropipettes were inserted into both ends of each vessel and secured in place with nylon ties. Each vessel was bathed in PSS (37°C) equilibrated with a gas consisting of 20% O2-5% CO2-balance N2 (3, 4). The pH of the bath was ~7.40, PCO2 was ~35 mmHg, and PO2 was ~130 mmHg (3).
Luminal pressure was maintained at 85 mmHg for the MCAs and 60 mmHg for the bMCAs and PAs by raising reservoirs to the appropriate height above the vessels (3). These pressures were considered to be near the pressures experienced in vivo for each vessel type. Luminal perfusion was adjusted to ~100 µl/min in MCAs and 10-25 µl/min in bMCAs and PAs by setting the two reservoirs at different heights. These rates of flow produced a luminal shear stress (25 dyn/cm2 for all vessels) that was considered to be near the shear stress experienced in vivo (25). Pressure transducers on either side of the vessels provided a measurement of perfusion pressure. The vessels were magnified with an inverted microscope equipped with a video camera and monitor. Outside diameters of the vessels were measured directly from the video screen.
After being mounted and pressurized, the vessels of all groups developed spontaneous tone by constricting to ~75% of the initial diameter over the course of 1 h. Experimental protocols were not initiated until the vessel diameters were stable over a period of 15 min.
Endothelial P2Y1 or P2Y2 purinoceptors were stimulated by adding 2-MeS-ATP or ATP, respectively, to the luminal perfusate (36). Only one concentration-response curve was conducted for each vessel to avoid the risk of tachyphylaxis. For removal of the endothelium, air was passed through the lumen of the vessel as previously described (21, 36).
In some vessels, membrane potential
(Em) was
measured in individual vascular smooth muscle cells using glass
microelectrodes filled with 3 M KCl (impedance from 55 to 75 M
).
Em measurements were made in pressurized, perfused bMCAs and PAs mounted in the arteriograph so that diameters could be simultaneously recorded (26,
34, 37). The potential difference between the glass microelectrode and
a reference electrode, placed in the bath of the arteriograph, was
measured using a Dagan 8700 Cell Explorer (Dagan, Minneapolis, MN) with
the output displayed on a Tektronix 5223 Digitizing Oscilloscope.
Micropipettes were made by pulling capillary tubing to a rapid taper
(tip diameter ~0.1 µm) using a model P-87 Brown-Flaming
micropipette puller (Sutter, San Francisco, CA). Primary criteria for a
successful impalement included a sharp drop in voltage from baseline on
entry of the microelectrode tip into the cell and no change in
microelectrode resistance after it exited the cell.
Em measurements
from several different smooth muscle cells were averaged to obtain a
single Em for a
given condition in a single vessel. The number of observations
(n) was the number of vessels
studied rather than the number of impalements.
Drugs and reagents. ATP, indomethacin, and nitro-L-arginine methyl ester (L-NAME) were purchased from Sigma Chemical (St. Louis, MO). S-nitroso-N-acetylpenicillamine (SNAP), 2-MeS-ATP, and charybdotoxin (ChTX) were purchased from Research Biochemicals International (Natick, MA). (Z)-1-{N-methyl-N-[6-(N-methylammoniohexyl)amino]}diazen-1-ium-1,2-diolate (MAHMA NONOate) was purchased from Alexis Biochemicals (San Diego, CA). Indomethacin was dissolved in a solution of Na2CO3 and distilled water, MAHMA NONOate was dissolved in 0.01 M NaOH, ChTX was dissolved in 150 mM NaCl, and all other reagents and drugs were dissolved in distilled water. The composition of the PSS used to bathe the vessels was previously described (3). ChTX, SNAP, and MAHMA NONOate were added to the extraluminal bath (smooth muscle side). The purinoceptor agonists ATP and 2-MeS-ATP were added to the PSS perfusing the lumen (endothelial side). L-NAME and indomethacin were added to both luminal and extraluminal compartments.
Statistical analysis.
All data are presented as means ± SE. For concentration-response
curves, the results are presented as percentages of the maximum diameter of the vessel and were calculated as
[(Ddrug 
Dbase)/(Dmax Dbase)] × 100, where
Dmax is the
maximum diameter of the vessel for the given pressure (85 mmHg for
MCAs, 60 mmHg for bMCAs and PAs),
Dbase is the
baseline diameter of the vessel before addition of dilator (or
agonist), and
Ddrug is the
diameter of the vessel after dilation.
Dmax is the
diameter of the vessel immediately after pressurization and before
development of spontaneous tone. Previous studies (26) in our lab have
shown that Dmax,
as calculated above, was identical to the diameter in
Ca2+-free buffer for a given pressure.
| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Resting diameters for MCAs, bMCAs, and PAs were 203, 99, and 87 µm,
respectively (Table 1). Dilations to the
luminal administration of ATP
(P2Y2 selective) in MCAs, bMCAs,
and PAs are shown in Fig. 1A.
Two-way repeated-measures ANOVA revealed that there was a significant
group difference (P = 0.0002), a
significant concentration effect (P < 0.0001), and a significant interaction between group and
concentration (P < 0.0001). A post
hoc Student-Newman-Keuls test revealed significant differences
(P < 0.05) between MCAs and bMCAs
and between MCAs and PAs. The EC50
values for the luminal application of ATP are shown in Table
2. Note that there was a 5- and 10-fold
difference (P < 0.05) in the
calculated EC50 values for the
bMCAs and PAs, respectively, compared with that for the MCAs.
|
|
|
Dilations to the luminal administration of 2-MeS-ATP
(P2Y1 selective) are shown in Fig.
1B. The MCAs showed a pronounced
dilation to 2-MeS-ATP, whereas the bMCAs and PAs did not dilate at any concentration. There was a significant group effect
(P < 0.0001), concentration effect
(P < 0.0001), and interaction
between groups and concentration (P < 0.0001). The response to 2-MeS-ATP in MCAs was significantly
different from that in either bMCAs or PAs
(P < 0.05). After 2-MeS-ATP was
administered in bMCAs and PAs, the same vessels dilated to
104 M ATP (Fig.
1B). The calculated
EC50 for the 2-MeS-ATP-induced dilation in MCAs is shown in Table 2 and agrees with those reported by
previous studies (36). The EC50
for 2-MeS-ATP in MCAs is less than one-tenth
(P < 0.05) of the
EC50 for ATP (Table 2).
The effects of NO synthase inhibition
(105 M
L-NAME) on the dilations to ATP
in the three vessel groups are shown in Fig.
2, A-C. In addition, the effects of
removing the endothelium and the combined inhibition of NO synthase
(105 M
L-NAME) and cyclooxygenase
(105 M indomethacin) are
shown for the bMCAs (Fig. 2B) and
the PAs (Fig. 2C). These later
studies were previously conducted on the MCAs (36) and have therefore
been omitted here. There was a significant group effect
(P < 0.0001), concentration effect
(P < 0.0001), and interaction
between groups and concentration (P < 0.0001) for each vessel group (Fig. 2,
A-C). Inhibition of NO synthase
significantly increased the EC50
for the MCAs 10-fold (P < 0.05, Table 2) but had a lesser, but significant
(P < 0.05), effect in the bMCAs
(Table 2 and Fig. 2). Inhibition of NO synthase increased the
EC50 in the PAs by 60%; however,
statistical significance was not achieved (Table 2). Although NO was
apparently involved in the dilations for all vessel groups studied, its
significance apparently diminished distally along the vascular tree.
The combined inhibition of NO synthase and cyclooxygenase in MCAs (36)
and bMCAs (Fig. 2B) had very similar
effects on the dilation to that of NO synthase inhibition alone. Thus a
cyclooxygenase metabolite was not involved in the dilation. Note that
in our previous study of MCAs (36) UTP was used instead of ATP to
stimulate P2Y2 purinoceptors. The
effects of the combined inhibition in the PAs were different from those
in the MCAs and bMCAs. The combined inhibition of NO synthase and
cyclooxygenase in PAs appeared to actually potentiate the dilation to
ATP compared with NO inhibition alone. In fact, the group of PAs with
combined inhibition was significantly different from the control PAs
(P < 0.05 using
Student-Newman-Keuls).
|
Removal of the endothelium reduced the resting diameter of MCAs, bMCAs, and PAs by 16% (36), 7 ± 4% (n = 5, P = 0.19), and 4 ± 2% (n = 6, P = 0.045), respectively. Constrictions after removal of the endothelium in bMCAs and PAs were not as large as after L-NAME (Table 3), most likely because of the release of an endothelium-derived constricting factor (unpublished observation). In all three groups removal of the endothelium abolished the dilation to ATP (Ref. 36 and Fig. 2, B and C, P < 0.05 for each). After the endothelium was removed, the constriction produced by the luminal application of ATP in bMCAs and PAs (Fig. 2, B and C) was caused by stimulation of constrictor purinoceptors on the vascular smooth muscle (36).
Table 3 shows the effect of NO synthase
inhibition (105 M
L-NAME) on the diameters of the
three vessel groups. MCAs constricted significantly more to NO synthase
inhibition than either bMCAs or PAs (P < 0.05 for each). The constrictions produced in bMCAs or PAs by the
administration of L-NAME plus
indomethacin were not different from those produced by
L-NAME alone (data not shown).
|
Figure 3 demonstrates that ChTX abolished
the non-NO component of the dilation in bMCAs and PAs (Fig. 3,
A and
B). For both bMCAs and PAs, there
was a significant group effect (P < 0.0001), concentration effect (P < 0.0001), and interaction between groups and concentration
(P < 0.0001). Similarly, ChTX
abolished the non-NO component of the dilation to
P2Y2 stimulation (using UTP) in
MCAs (37).
|
Figure 4 shows mean diameters and
Em in bMCAs (Fig.
4A) and PAs (Fig.
4B) before and after
dilations to 105 M ATP in
vessels treated with L-NAME
(105 M) and indomethacin
(105 M). Diameter and
Em were measured
simultaneously from each vessel. Both vessel groups dilated
significantly after the administration of
105 M ATP
[P = 0.002 (n = 4) for bMCAs;
P = 0.006 (n = 5) for PAs]. The
dilations were accompanied by a significant hyperpolarization of the
vascular smooth muscle [18 mV in bMCAs
(P = 0.0002); 14 mV in PAs
(P = 0.0006)]. In PAs
not treated with either L-NAME or indomethacin, the dilations were accompanied by a 13 ± 2-mV (n = 4, P = 0.0097) hyperpolarization (data
not shown).
|
The effects of two NO donors, SNAP and MAHMA NONOate, on the three
vessel types are shown in Fig. 5,
A and
B, respectively. For both SNAP and
MAHMA NONOate there were significant group effects (P < 0.0001), concentration effects
(P < 0.0001), and interactions between groups and concentration (P < 0.0001) (2-way repeated-measures ANOVA). Each group was
significantly different from the other two groups
(P < 0.05) by post hoc
Student-Newman-Keuls testing. SNAP produced larger dilations in MCAs
than in bMCAs, whereas PAs did not dilate. The dilator effects of SNAP
diminished in a distal direction along the cerebrovascular tree.
Because SNAP does not spontaneously release NO, the results in Fig.
5A could lead to an erroneous
conclusion regarding the ability of the bMCAs and PAs to dilate to NO.
SNAP requires a reducing environment for the liberation of NO that may
be absent in the smaller vessels (5, 30). Therefore, we administered
MAHMA NONOate, a compound that spontaneously releases NO (20). MAHMA
NONOate dilated the three vessel groups. Whereas the PAs dilated at a
lower concentration of NO, they did not dilate to the same degree
(expressed as %maximum) as the MCAs or bMCAs (Fig.
5B).
|
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Our laboratory has previously determined that the endothelium of the rat MCA possesses both P2Y1- and P2Y2-purinoceptor subtypes (36). When stimulated, the P2Y1 purinoceptors dilated by the synthesis and release of NO and the P2Y2 purinoceptors dilated by the release of both EDHF and NO (36, 37). The purpose of the present investigation was to determine whether arterial and arteriolar segments distal to the MCA had the same potential to dilate via these endothelial purinergic receptors.
We report that luminal applications of 2-MeS-ATP, a synthetic agonist selective for the P2Y1 subtype, dilated the MCAs but not the more distal segments studied (bMCAs and PAs, Fig. 1B). We suggest that either the P2Y1 purinoceptors are absent from the endothelium of these smaller vessel segments or, if present, the P2Y1 purinoceptors do not function in a dilator capacity.
On the other hand, the luminal application of ATP, an agonist for the P2Y2 subtype, dilated all vessel segments studied. However, the EC50 in the MCA was one-fifth and one-tenth of that for bMCAs and PAs, respectively (Table 2 and Fig. 1A). This greater sensitivity to ATP in the MCAs was apparently caused by a more pronounced NO component at lower ATP concentrations in the MCA.
There are two possible reasons why bMCAs and PAs had greater EC50 values (or decreased sensitivity) to ATP compared with that of the MCAs and why these same two vessel groups did not dilate to 2-MeS-ATP. First, less NO from the endothelium was reaching the bMCAs and PAs. Second, the vascular smooth muscle in the bMCAs and PAs was less sensitive to NO than that in the MCAs. Because the bMCAs and PAs were either more sensitive or equally sensitive to NO (as liberated from the spontaneous donor MAHMA NONOate, Fig. 5B), the latter reason must be ruled out. Therefore, less NO was reaching the vascular smooth muscle in bMCAs and PAs than in MCAs. Possibly, less NO was being produced by the endothelium of the smaller cerebral vessels.
It is interesting to note that, in the PAs,
L-NAME alone appeared to
attenuate the dilation at
105 M ATP (Fig.
2C), whereas, at the same ATP
concentration, the combination of
L-NAME and indomethacin appeared
to potentiate the dilation. We suggest that, in addition to the release
of dilators from the endothelium, ATP also produced the release of
constrictor prostanoids in PAs and, hence, that this was the reason for
the enhanced dilation after inhibition of cyclooxygenase in the
presence of L-NAME.
Finally, we sought to determine the mechanism for the L-NAME-insensitive component of the ATP-mediated dilation. In the MCAs, the L-NAME-insensitive component of the dilation after stimulation of endothelial P2Y2 purinoceptors (using UTP) has been shown to be EDHF (37). EDHF is defined as a relaxant, released from the endothelium, that is distinct from both NO and prostaglandins and that dilates vessels by hyperpolarizing the vascular smooth muscle (28). The hyperpolarization is the result of activation of potassium channels (for comprehensive reviews, see Refs. 8, 15, 17, 28, and 35). EDHF may not be a single agent but rather a diverse class of agents, all of which open potassium channels (8, 28). The chemical identity of EDHF is in question and may vary with species and/or vessel. Candidates for EDHF include 1) epoxyeicosatrienoic acid, a cytochrome P-450 metabolite of arachidonic acid; 2) anandamide, an endogenous agonist of the cannabinoid receptors; 3) hydrogen peroxide; 4) hydroxyl radicals; 5) superoxide anions; 6) carbon monoxide; or 7) potassium ions (6, 8, 13, 18, 28, 31, 38). Alternatively, the "EDHF effect" may not involve a chemical compound per se but rather myoendothelial junctions that allow the electrical coupling between the endothelium and vascular smooth muscle (7).
As in MCAs, the L-NAME-insensitive component of the dilation to P2Y2-purinoceptor stimulation in the bMCAs and PAs is EDHF. First, it is endothelium dependent because removal of the endothelium abolished the dilation (Fig. 2, B and C). Second, the relaxing factor was neither NO nor a cyclooxygenase metabolite (Fig. 2, B and C). Third, the dilation was completely blocked in both bMCAs and PAs by ChTX, a potassium-channel blocker with selectivity for the calcium-activated potassium channel type (37) (Fig. 3). Finally, the dilations were accompanied by hyperpolarization of the vascular smooth muscle (Fig. 4). Hence, the L-NAME-insensitive component of the ATP-mediated dilations in bMCAs and PAs fit all the criteria for EDHF. Therefore, EDHF is a major component of the dilation to P2Y2-purinoceptor stimulation in MCAs (37), bMCAs (present study), and PAs (present study).
Our results showing the involvement of EDHF in smaller cerebral vessels
are, for the most part, different from those of other in vivo and in
vitro studies. To our knowledge, only three laboratories have
previously published studies involving the mechanism of
endothelium-mediated dilations elicited by purine phosphates in
cerebral vessels distal to the MCA. In general, those studies have
reported that endothelium-mediated dilations elicited by the naturally
occurring purine phosphates or their synthetic analogs were abolished
by NO synthase inhibitors (22, 23, 27, 33). Rosenblum et al. (33)
reported that, in addition to NO synthase inhibition, inhibition of
cyclooxygenase could abolish the dilations elicited by ADP and
2-MeS-ATP in mouse pial arterioles in vivo. Furthermore, the same
authors reported that dilations produced by 
,
-methyleneadenosine
5'-triphosphate (AMP-CPP), a P2X-selective agonist, were not
affected by cyclooxygenase inhibition and were attenuated by 50% after
inhibition of NO synthase (33). The relaxing factor responsible for the
remaining component of the dilation was not determined. Interestingly,
Janigro et al. (22, 23) reported that the dilations induced by the
luminal administration of ATP in PAs of the rat were abolished after NO synthase inhibition with
nitro-L-arginine (0.1 or 1 mM)
but not N-monomethyl-L-arginine
(0.1 mM). According to these other studies, EDHF is not involved, with
the possible exception of the dilations elicited by AMP-CPP in mice
pial arterioles.
There are at least two possible explanations for this apparent discrepancy between the previously reported results and our present data. First, the mechanism for dilation when endothelial P2Y2 purinoceptors are stimulated could be related to the rate of luminal flow (or shear stress on the endothelium). At different shear stresses, different mechanisms (i.e., NO vs. EDHF) could be involved with the dilations to ATP. There is precedence for flow affecting responses to extraluminally applied ATP in the rat PAs (11). However, the shear stresses in our study and those of Janigro et al. (22, 23) are comparable and close to what would be considered physiological. A second possibility is that different relaxing factors are involved with male Long-Evans rats (the strain used in this study) from those with male Sprague-Dawley rats [the strain used in the other studies (22, 23, 27)]. In this respect, we have found that the dilations elicited by ACh in the femoral artery of Long-Evans rats did not involve EDHF, whereas the dilation elicited by the same agonist in the femoral artery of Sprague-Dawley rats had EDHF as a component (unpublished observation). Whether a difference in relaxing factors in smaller cerebral vessels of different strains of rats exists is not presently known.
One interesting concept evolving from our studies is the apparent decrease in the role of NO in distal vessels. However, it must be pointed out that this conclusion may only apply to rats, more specifically to Long-Evans rats (see preceding paragraph). This idea is based on three findings of this study. First, 2-MeS-ATP, which elicits dilation in the MCA through the synthesis and release of NO, is without effect in the bMCAs and PAs. Second, the constriction produced by NO synthase inhibition with L-NAME is significantly less in the bMCAs and PAs (13% constriction for either) than in the MCA (22% constriction) (Table 3). This latter finding is in agreement with a previous study showing that NO plays a greater role in larger cerebral arteries than in arterioles in setting the resting or basal tone (14). Third, the NO component of the ATP-mediated dilation is reduced along the cerebrovascular tree (Fig. 2 and Table 2). There exists a concept in peripheral vessels that NO is the more prominent relaxing factor in larger arteries and EDHF is the more prominent relaxing factor in smaller arteries and arterioles (17). We suggest that the same holds true in the cerebral circulation of male Long-Evans rats.
In summary, we have demonstrated that 2-MeS-ATP, a P2Y1-selective agonist, elicits an NO-mediated dilation in the MCAs of Long-Evans rats but not in bMCAs or PAs. Furthermore, ATP, a P2Y2-selective agonist, elicits dilations in all three vessel segments; however, the dilations in the MCA occur at a lower threshold concentration because of a more pronounced NO component of the dilation. Finally, in the Long-Evans rat, the role of NO in agonist-induced dilations diminishes along the cerebrovascular tree as EDHF becomes the more prominent relaxing factor released from the endothelium. The heterogeneity of the dilator response to the P2-purinoceptor agonists underscores the coordination and division of labor involved with maintaining blood flow to diverse brain regions. Although the reason for the heterogeneity of vascular control is not well understood, it is reasonable to assume that such a strategy provides a distinct advantage in circulatory control.
| |
ACKNOWLEDGEMENTS |
|---|
These studies were supported by National Institute of Neurological Disorders and Stroke Grants P01-NS-27616 and R01-NS-37250 and National Heart, Lung, and Blood Institute Training Grant T32-HL-07816.
| |
FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: R. M. Bryan, Jr., Department of Anesthesiology, Rm. 434D, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 (E-mail: rbryan{at}bcm.tmc.edu).
Received 22 January 1999; accepted in final form 25 March 1999.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Abbracchio, M. P.,
and
G. Burnstock.
Purinoceptors: are there families of P2X and P2Y purinoceptors?
Pharmacol. Ther.
64:
445-475,
1994[Medline].
2.
Boarder, M. R.,
G. A. Weisman,
J. T. Turner,
and
G. F. Wilkinson.
G protein-coupled P2 purinoceptors: from molecular biology to functional responses.
Trends Pharmacol. Sci.
16:
133-139,
1995[Medline].
3.
Bryan, R. M., Jr.,
M. Y. Eichler,
M. W. G. Swafford,
T. D. Johnson,
M. S. Suresh,
and
W. F. Childres.
Stimulation of 2 adrenoceptors dilates the rat middle cerebral artery.
Anesthesiology
85:
82-90,
1996[Medline].
4.
Bryan, R. M., Jr.,
M. L. Steenberg,
M. Y. Eichler,
T. D. Johnson,
M. W. G. Swafford,
and
M. S. Suresh.
Permissive role of NO in 2-adrenoceptor-mediated dilations in rat cerebral arteries.
Am. J. Physiol.
269 (Heart Circ. Physiol. 38):
H1171-H1174,
1995
5.
Butler, A. R.,
F. W. Flitney,
and
D. L. H. Williams.
NO, nitrosonium ions, nitroxide ions, nitrosothiols and iron-nitrosyls in biology: a chemist's perspective.
Trends Pharmacol. Sci.
16:
18-22,
1998.
6.
Campbell, W. B.,
D. Gebremedhin,
P. F. Pratt,
and
D. R. Harder.
Identification of epoxyeicosatrienoic acids as endothelium-derived hyperpolarizing factors.
Circ. Res.
78:
415-423,
1996
7.
Chaytor, A. T.,
W. H. Evans,
and
T. M. Griffith.
Central role of heterocellular gap junctional communication in endothelium-dependent relaxations of rabbit arteries.
J. Physiol. (Lond.)
508:
561-573,
1998
8.
Cohen, R. A.,
and
P. M. Vanhoutte.
Endothelium-dependent hyperpolarization. Beyond nitric oxide and cyclic GMP.
Circulation
92:
3337-3349,
1995
9.
Dacey, R. G., Jr.,
and
B. R. Duling.
A study of rat intracerebral arterioles: methods, morphology, and reactivity.
Am. J. Physiol.
243 (Heart Circ. Physiol. 12):
H598-H606,
1982.
10.
Dalziel, H. H.,
and
D. P. Westfall.
Receptors for adenine nucleotides and nucleosides: subclassification, distribution, and molecular characterization.
Pharmacol. Rev.
46:
449-466,
1994[Medline].
11.
Dietrich, H. H.,
Y. Kajita,
and
R. G. Dacey, Jr.
Local and conducted vasomotor responses in isolated rat cerebral arterioles.
Am. J. Physiol.
271 (Heart Circ. Physiol. 40):
H1109-H1116,
1996
12.
Dubyak, G. R.,
and
C. el-Moatassim.
Signal transduction via P2-purinergic receptors for extracellular ATP and other nucleotides.
Am. J. Physiol.
265 (Cell Physiol. 34):
C577-C606,
1993
13.
Edwards, G.,
K. A. Dora,
M. J. Gardener,
C. J. Garland,
and
A. H. Weston.
K+ is an endothelium-derived hyperpolarizing factor in rat arteries.
Nature
396:
269-272,
1998[Medline].
14.
Faraci, F. M.
Role of endothelium-derived relaxing factor in cerebral circulation: large arteries vs. microcirculation.
Am. J. Physiol.
261 (Heart Circ. Physiol. 30):
H1038-H1042,
1991
15.
Feletou, M.,
and
P. M. Vanhoutte.
Endothelium-derived hyperpolarizing factor.
Clin. Exp. Pharmacol. Physiol.
23:
1082-1090,
1996[Medline].
16.
Fredholm, B. B.,
M. P. Abbracchio,
G. Burnstock,
J. W. Daly,
T. K. Harden,
K. A. Jacobson,
P. Leff,
and
M. Williams.
Nomenclature and classification of purinoceptors.
Pharmacol. Rev.
46:
143-156,
1994[Medline].
17.
Garland, C. J.,
F. Plane,
B. K. Kemp,
and
T. M. Cocks.
Endothelium-dependent hyperpolarization: a role in the control of vascular tone.
Trends Pharmacol. Sci.
16:
23-30,
1995[Medline].
18.
Gebremedhin, D.,
Y. H. Ma,
J. R. Falck,
R. J. Roman,
M. VanRollins,
and
D. R. Harder.
Mechanism of action of cerebral epoxyeicosatrienoic acids on cerebral arterial smooth muscle.
Am. J. Physiol.
263 (Heart Circ. Physiol. 32):
H519-H525,
1992
19.
Golding, E. M.,
C. S. Robertson,
and
R. M. Bryan, Jr.
Comparison of the myogenic response in rat cerebral arteries of different calibers.
Brain Res.
785:
293-298,
1998[Medline].
20.
Hrabie, J. A.,
J. R. Klose,
D. A. Wink,
and
L. K. Keefer.
New nitric oxide-releasing zwitterions derived from polyamines.
J. Org. Chem.
58:
1472-1476,
1993.
21.
Ignacio, C. S.,
P. E. Curling,
W. F. Childres,
and
R. M. Bryan, Jr.
Nitric oxide-synthesizing perivascular nerves in the rat middle cerebral artery.
Am. J. Physiol.
273 (Regulatory Integrative Comp. Physiol. 42):
R661-R668,
1997
22.
Janigro, D.,
T. S. Nguyen,
E. L. Gordon,
and
H. R. Winn.
Physiological properties of ATP-activated cation channels in rat brain microvascular endothelial cells.
Am. J. Physiol.
270 (Heart Circ. Physiol. 39):
H1423-H1434,
1996
23.
Janigro, D.,
T. S. Nguyen,
J. Meno,
G. A. West,
and
H. R. Winn.
Endothelium-dependent regulation of cerebrovascular tone by extracellular and intracellular ATP.
Am. J. Physiol.
273 (Heart Circ. Physiol. 42):
H878-H885,
1997
24.
Khakh, B. S.,
and
C. Kennedy.
Adenosine and ATP: progress in their receptors' structures and functions.
Trends Pharmacol. Sci.
19:
39-41,
1998[Medline].
25.
Lipowsky, H. H.
Shear stress in the circulation.
In: Flow-Dependent Regulation of Vascular Function, edited by J. A. Bevan,
G. Kaley,
and G. M. Rubanyi. New York: Oxford Univ. Press, 1995, p. 28-45.
26.
Marrelli, S. P.,
A. Khorovets,
T. D. Johnson,
W. F. Childres,
and
R. M. Bryan, Jr.
P2 purinoceptor-mediated dilations in the rat middle cerebral artery after ischemia/reperfusion.
Am. J. Physiol.
276 (Heart Circ. Physiol. 45):
H33-H41,
1999
27.
Mayhan, W. G.
Endothelium-dependent responses of cerebral arterioles to adenosine 5'-diphosphate.
J. Vasc. Res.
29:
353-358,
1992[Medline].
28.
Mombouli, J. V.,
and
P. M. Vanhoutte.
Endothelium-derived hyperpolarizing factor(s): updating the unknown.
Trends Pharmacol. Sci.
18:
252-256,
1997[Medline].
29.
Olsson, R. A.,
and
J. D. Pearson.
Cardiovascular purinoceptors.
Physiol. Rev.
70:
761-845,
1990
30.
Pfeiffer, S.,
A. Schrammel,
K. Schmidt,
and
B. Mayer.
Electrochemical determination of S-nitrosothiols with a Clark-type nitric oxide electrode.
Anal. Biochem.
258:
68-73,
1998[Medline].
31.
Randall, M. D.,
S. P. H. Alexander,
T. Bennett,
E. A. Boyd,
J. R. Fry,
S. M. Gardiner,
P. A. Kemp,
A. I. McCulloch,
and
D. A. Kendall.
An endogenous cannabinoid as an endothelium-derived vasorelaxant.
Biochem. Biophys. Res. Commun.
229:
114-120,
1997.
32.
Rosenblum, W. I.
Endothelium-derived relaxing factor in brain blood vessels is not nitric oxide.
Stroke
23:
1527-1532,
1992
33.
Rosenblum, W. I.,
G. H. Nelson,
and
S. Murata.
Endothelium-dependent dilation by purines of mouse brain arterioles in vivo.
Endothelium
1:
287-294,
1994.
34.
Stekiel, W. J.,
S. J. Contney,
and
J. H. Lombard.
Small vessel membrane potential, sympathetic input, and electrogenic pump rate in SHR.
Am. J. Physiol.
250 (Cell Physiol. 19):
C547-C556,
1986
35.
Vanhoutte, P. M.,
M. Feletou,
C. M. Boulanger,
U. Hoffner,
and
G. M. Rubanyi.
Existence of multiple endothelium-derived relaxing factors.
In: Endothelium-Derived Hyperpolarizing Factor, edited by P. M. Vanhoutte. Amsterdam: Harwood, 1996, p. 1-10.
36.
You, J. P.,
T. D. Johnson,
W. F. Childres,
and
R. M. Bryan, Jr.
Endothelial-mediated dilations of rat middle cerebral arteries by ATP and ADP.
Am. J. Physiol.
273 (Heart Circ. Physiol. 42):
H1472-H1477,
1997
37.
You, J. P.,
T. D. Johnson,
S. P. Marrelli,
J. V. Mombouli,
W. F. Childres,
and
R. M. Bryan, Jr.
P2u-receptor-mediated release of nitric oxide and endothelium-derived hyperpolarizing factor from cerebrovascular endothelium.
Stroke
30:
1125-1133,
1999
38.
Zakhary, R.,
S. P. Gaine,
J. L. Dinerman,
M. Ruat,
N. A. Flavahan,
and
S. H. Snyder.
Heme oxygenase 2: endothelial and neuronal localization and role in endothelium-dependent relaxation.
Proc. Natl. Acad. Sci. USA
93:
795-798,
1996
This article has been cited by other articles:
|
|
 |
|
  J. Chen, R. F. Crossland, M. M. Z. Noorani, and S. P. Marrelli Inhibition of TRPC1/TRPC3 by PKG contributes to NO-mediated vasorelaxation Am J Physiol Heart Circ Physiol, July 1, 2009; 297(1): H417 - H424. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. L. Ellsworth, C. G. Ellis, D. Goldman, A. H. Stephenson, H. H. Dietrich, and R. S. Sprague Erythrocytes: Oxygen Sensors and Modulators of Vascular Tone Physiology, April 1, 2009; 24(2): 107 - 116. [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]
|
|
|
|
|
|
J. You, E. M. Golding, and R. M. Bryan Jr. Arachidonic acid metabolites, hydrogen peroxide, and EDHF in cerebral arteries Am J Physiol Heart Circ Physiol, September 1, 2005; 289(3): H1077 - H1083. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. M. Faraci, C. Lynch, and K. G. Lamping Responses of cerebral arterioles to ADP: eNOS-dependent and eNOS-independent mechanisms Am J Physiol Heart Circ Physiol, December 1, 2004; 287(6): H2871 - H2876. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. G. Konduri, I. Bakhutashvili, R. Frenn, I. Chandrasekhar, E. R. Jacobs, and A. K. Khanna P2Y purine receptor responses and expression in the pulmonary circulation of juvenile rabbits Am J Physiol Heart Circ Physiol, July 1, 2004; 287(1): H157 - H164. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Miyagi and J. H. Zhang {alpha},{beta}-Methylene ATP enhances P2Y4 contraction of rabbit basilar artery Am J Physiol Heart Circ Physiol, April 1, 2004; 286(4): H1546 - H1551. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. J. Gonzales, D. N. Krause, and S. P. Duckles Testosterone suppresses endothelium-dependent dilation of rat middle cerebral arteries Am J Physiol Heart Circ Physiol, February 1, 2004; 286(2): H552 - H560. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Ospina, S. P. Duckles, and D. N. Krause 17{beta}-Estradiol decreases vascular tone in cerebral arteries by shifting COX-dependent vasoconstriction to vasodilation Am J Physiol Heart Circ Physiol, June 5, 2003; 285(1): H241 - H250. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. M. Golding, S. P. Marrelli, J. You, and R. M. Bryan Jr Endothelium-Derived Hyperpolarizing Factor in the Brain: A New Regulator of Cerebral Blood Flow? Stroke, March 1, 2002; 33(3): 661 - 663. [Full Text] [PDF]
|
|
|
|
|
|
L. A. Schildmeyer and R. M. Bryan Jr. Effect of NO on EDHF response in rat middle cerebral arteries Am J Physiol Heart Circ Physiol, February 1, 2002; 282(2): H734 - H738. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. L. Xu, R. A. Santizo, H. M. Koenig, and D. A. Pelligrino Chronic estrogen depletion alters adenosine diphosphate-induced pial arteriolar dilation in female rats Am J Physiol Heart Circ Physiol, November 1, 2001; 281(5): H2105 - H2112. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. M. Golding and T. E. Kepler Role of estrogen in modulating EDHF-mediated dilations in the female rat middle cerebral artery Am J Physiol Heart Circ Physiol, June 1, 2001; 280(6): H2417 - H2423. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. M. Bryan Jr., S. P. Marrelli, M. L. Steenberg, L. A. Schildmeyer, and T. D. Johnson Effects of luminal shear stress on cerebral arteries and arterioles Am J Physiol Heart Circ Physiol, May 1, 2001; 280(5): H2011 - H2022. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. C. Ngai, E. F. Coyne, J. R. Meno, G. A. West, and H. R. Winn Receptor subtypes mediating adenosine-induced dilation of cerebral arterioles Am J Physiol Heart Circ Physiol, May 1, 2001; 280(5): H2329 - H2335. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Horiuchi, H. H. Dietrich, S. Tsugane, and R. G. Dacey Jr. Analysis of purine- and pyrimidine-induced vascular responses in the isolated rat cerebral arteriole Am J Physiol Heart Circ Physiol, February 1, 2001; 280(2): H767 - H776. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
