(Hypertension. 1995;25:1224-1231.)
© 1995 American Heart Association, Inc.
Articles |
-Adrenoceptor Modulation of Norepinephrine and ATP Release in Isolated Kidneys of Spontaneously Hypertensive Rats
From Medizinische Universitätsklinik Freiburg, Innere Medizin IV, and Pharmakologisches Institut (I.v.K.), Freiburg im Breisgau, Germany.
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Abstract The present study investigates sympathetic cotransmission and its
-adrenoceptor–mediated modulation in kidneys
of spontaneously hypertensive rats (SHR, 12 to 14 weeks) and
age-matched normotensive Wistar-Kyoto rats (WKY). In the presence of
cocaine and corticosterone, renal nerve stimulation at 1 Hz (30
seconds) induced a greater outflow of norepinephrine in SHR (4.2±0.2
pmol/g kidney) than in WKY (3.0±0.2 pmol/g kidney). The
2-adrenoceptor antagonist rauwolscine (0.01 to 1
µmol/L) increased the stimulation-induced norepinephrine outflow to a
greater extent in SHR than in WKY. In contrast, the
1-adrenoceptor antagonist prazosin (0.03 to 3 µmol/L)
increased the stimulation-induced norepinephrine outflow to a greater
extent in WKY than in SHR. This difference was not observed in the
presence of the P1-purinoceptor antagonist
8-(p-sulfophenyl)theophylline (100 µmol/L).
Stimulation at 4 Hz (30 seconds) induced an outflow of ATP (SHR,
12.7±3.3 pmol/g kidney; WKY, 16.7±2.1 pmol/g kidney; perfusion
solution without cocaine and corticosterone). Prazosin (0.03 µmol/L)
markedly reduced pressor responses to stimulation and inhibited the
induced ATP outflow by 60% to 70%. When prazosin (0.03 µmol/L) was
present, rauwolscine (0.1 µmol/L) increased the induced
outflow of norepinephrine and ATP and markedly enhanced
prazosin-resistant pressor responses. These pressor responses were
abolished by the P2-purinoceptor antagonist suramin (300
µmol/L). The results demonstrate an increased
2-adrenoceptor–mediated automodulation of
norepinephrine release in SHR kidneys caused by increased intrasynaptic
norepinephrine levels. 1-Adrenoceptor–mediated
transjunctional modulation of norepinephrine release by
endogenous adenosine is defective in SHR kidneys and may be
responsible for the greater norepinephrine release in this strain.
Norepinephrine and ATP are coreleased in SHR and WKY kidneys and both
mediate pressor responses to stimulation. The release of ATP is
identical in SHR and WKY and is, like that of norepinephrine, modulated
by 2-adrenoceptor–mediated autoinhibition.
Key Words: hypertension, experimental • kidney • norepinephrine • purines • sympathetic nervous system • rats, inbred SHR • receptors, adrenergic, alpha • receptors, purinergic
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
An enhanced activity of the sympathetic nervous system and in particular of the sympathetic nervous system of the kidney may play an important role in the pathogenesis of hypertension.1 2 3 4 An increased rate of renal norepinephrine release may result from an enhanced activity of the central nervous system to the kidneys5 as well as from altered local mechanisms. Sympathetic nerve endings possess prejunctional receptors that can be activated by endogenous substances or drugs to either enhance or inhibit norepinephrine release6 7 ; this is also true for the kidney.8 Previous studies in Wistar rat kidneys preincubated with [3H]norepinephrine have shown that neuronally released norepinephrine itself activates prejunctional
2-adrenoceptors to inhibit its own
release,9 10 as is known for other sympathetically
innervated tissues.6 7 Furthermore, activation of
postjunctional 1-adrenoceptors by neuronally
released norepinephrine or exogenously applied
1-adrenoceptor agonists induces in isolated kidneys the
formation of prostaglandins and adenosine, which then inhibit
norepinephrine release through activation of prejunctional
prostaglandin E2 and adenosine (P1) receptors,
respectively.11 12 Alterations in these prejunctional
control mechanisms may lead to enhanced transmitter release and thereby
contribute to the pathogenesis of hypertension in the spontaneously
hypertensive rat (SHR).13
Norepinephrine and ATP are cotransmitters in postganglionic sympathetic
neurons of various tissues and species,14 15 16 17 and there is
also evidence that -adrenoceptor blockade–resistant pressor
responses in the rat kidney are due to the sympathetic cotransmitter
ATP.18 19 Moreover, some functional experiments suggest
that ATP is responsible for a greater portion of sympathetic nerve
stimulation–induced pressor responses of isolated tail arteries and
kidneys in SHR than in normotensive Wistar-Kyoto rats
(WKY).19 20
We aimed in the present study to compare the role of
2-adrenoceptor–mediated autoinhibition, of
1-adrenoceptor–mediated transjunctional modulation as
well as of norepinephrine-ATP cotransmission in SHR and
WKY. For this purpose, we examined the effects of the preferential
2-adrenoceptor antagonist rauwolscine and the
preferential 1-adrenoceptor antagonist prazosin on the
renal nerve stimulation (RNS)–induced release of
endogenous norepinephrine and endogenous ATP as
well as on pressor responses to RNS in both SHR and WKY kidneys.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
SHR and WKY (both obtained from Savo, Kisslegg, Germany) 12 to 14 weeks of age (SHR, 92±3 days, n=48; WKY, 88±2 days, n=51) were used. Experiments were performed in accordance with institutional guidelines. Rats were weighed and anesthetized with sodium pentobarbital (60 mg/kg IP). Body weights of SHR and WKY were 307±4 g (n=48) and 311±5 g (n=51), respectively. Mean arterial pressure was measured intra-arterially by a cannula in the lower aorta and was significantly greater in SHR (96±3 mm Hg, n=43) than in WKY (56±2 mm Hg, n=40).
Kidneys were isolated and perfused with Krebs-Henseleit solution according to a method described previously.21 Bipolar platinum electrodes were placed around the renal arteries to stimulate the renal nerves. Perfusion pressure was monitored continuously with a Statham P23 Db pressure transducer (Gould Inc) coupled to a Watanabe pen recorder (Graphtec Corp).
Experimental Protocol (Part A)
The kidneys were perfused with drug-free Krebs-Henseleit
solution at 37°C and a flow rate of 4.2 mL/min per gram kidney
weight. Kidney weights were estimated from previous unpublished
experiments in which they were approximately 0.5% of the corresponding
body weights in both SHR and WKY. The perfusion solution was
continuously gassed with carbogen (5% CO2/95%
O2) and passed through a 0.8-µm filter before it reached
the kidneys. After a stabilization period of 60 minutes, a stimulation
at 5 Hz for 30 seconds (1-millisecond width, 50 V) was performed to
test the preparation viability. Subsequently, cocaine (10 µmol/L) and
corticosterone (20 µmol/L) were added to the perfusion solution to
prevent cellular norepinephrine uptake mechanisms. After 30 minutes, a
fraction collector (LKB) was used to collect 1-minute fractions of the
effluent into vials containing 167 µL of 1 mol/L HCl, 13.3 µL of
0.067 mol/L EDTA, and 3.3 µL of 1 mol/L
Na2SO3. Three electrical stimulation periods
(S1 through S3) at 1 Hz for 30 seconds
(1-millisecond duration, 50 V) were applied 2, 22, and 42 minutes after
the start of fraction collection. Drugs were added to the perfusion
solution at increasing concentrations 17 minutes before S2
and S3. When
8-(p-sulfophenyl)theophylline (8-SPT) was present
throughout the experiment, it was added to the perfusion solution 30
minutes before the start of fraction collection.
Determination of Endogenous Norepinephrine
The norepinephrine content in the samples was determined by
high-performance liquid chromatography with electrochemical detection
(HPLC-ECD) according to a method described by Halbrügge et
al.22 Briefly, the pH of the perfusate was adjusted to
8.4, and then the catecholamines were adsorbed onto alumina and eluted
by 250 µL of 0.1 mol/L HClO4. One hundred microliters was
injected into the HPLC system, which consisted of a pump (Waters 510,
Millipore Corp), an automatic injector (Waters WISP 712, Millipore),
and a reversed-phase column (ODS-Hypersil 5 µm, Bischoff) fitted with
a precolumn packed with C18 material (Millipore). The mobile phase was
delivered at 1 mL/min and consisted of (mmol/L)
Na2HPO4 15, citric acid 30, Na2EDTA
2, and (-)-octanesulfonic acid 2.77, as well as 12% methanol
(vol/vol); the pH was adjusted to 6.5 with 10 mol/L NaOH. The
norepinephrine content of the samples was determined by an
electrochemical detector (Waters 460, Millipore). The oxidation
potential was set at 0.7 V. The amount of norepinephrine
present in each sample was determined from a standard calibration
curve (20 to 10 000 pg norepinephrine) and corrected for recoveries
(average percent recovery of norepinephrine, 69±0.6%; n=418).
Calculations
RNS-induced norepinephrine outflow was determined as the
difference between the norepinephrine content present in the two
1-minute samples collected immediately after onset of stimulation and
the estimated spontaneous norepinephrine outflow. Spontaneous
norepinephrine outflow was taken as the norepinephrine content
present in the 1-minute sample collected before onset of
stimulation. S1 served as a reference stimulation, and the
RNS-induced norepinephrine outflow in S2 and S3
was expressed as a percentage of that in S1. Spontaneous
norepinephrine outflow during Sn (Rn) was
expressed as a percentage of that during S1. Pressor
responses to RNS were measured as the maximum increase in perfusion
pressure above basal perfusion pressure (millimeters of mercury).
Pressor responses during Sn were expressed as a percentage
of that during S1.
For further evaluation of drug effects on RNS-induced norepinephrine outflow and pressor responses, the respective Sn/S1 ratios were calculated as a percentage of the values determined in the corresponding control experiments.
Experimental Protocol (Part B)
The kidneys were perfused with drug-free Krebs-Henseleit
solution as described in part A. After a stabilization period of 60
minutes, 1-minute fractions of the effluent were collected and stored
on ice. There was one stimulation period (S1: at either 1
or 4 Hz for 30 seconds, 1-millisecond width, 50 V; applied 3 minutes
after the start of fraction collection). A second stimulation period
could not be applied because basal ATP outflow increased after a total
time of perfusion longer than 80 minutes. Drugs were added to the
perfusion solution 30 minutes before the start of fraction
collection.
Determination of Endogenous Norepinephrine and Endogenous ATP
Aliquots (1 mL) of the perfusate were immediately separated
after each experiment and kept at -20°C until determination of ATP
content. The remaining part of the fractions received 167 µL of 1
mol/L HCl, 13.3 µL of 0.067 mol/L EDTA, and 3.3 µL of 1 mol/L
Na2SO3, and norepinephrine was
determined as described above.
The ATP content of the perfusate was measured with the luciferase technique23 24 using the ATP bioluminescence FL-AAM assay kit (Sigma Chemical Co) and a Biolumat LB 9500 or LB 953 luminometer (Berthold). Blank values obtained with fresh Krebs-Henseleit solution were subtracted from each experimental value. For each single experiment an ATP standard was added to a collected fraction immediately after each experiment for determination of possible ATP breakdown in the perfusate. The amount of ATP present in each sample was determined from a standard calibration curve (0.1 to 5 nmol/L, obtained with Krebs-Henseleit solution as solvent) and corrected for recoveries (average percent "recovery" of ATP was 15±4%; n=98. This decrease in ATP content in the collected perfusate is likely to be due to enzymatic breakdown by soluble ATPases; such a breakdown of ATP has not been observed in experiments performed on human saphenous veins or guinea pig vasa deferentia [see Reference 2525 and I.v.K., unpublished observation, 1994]). Since suramin markedly interfered with the luciferin-luciferase assay,25 26 ATP outflow could not be determined in experiments with suramin. None of the other drugs used caused an interference with the ATP assay.
Calculations
The RNS-induced and spontaneous outflow of norepinephrine as
well as pressor responses to RNS were determined as described above
(part A). The RNS-induced outflow of ATP was determined as the
difference between the ATP content present in the four 1-minute
samples collected immediately after onset of stimulation and the
estimated spontaneous ATP outflow. The spontaneous ATP outflow was
assumed to decline linearly from the 1-minute interval before to the
1-minute interval 4 to 5 minutes after onset of stimulation. The
RNS-induced outflow of ATP and norepinephrine in S1 was
expressed as picomoles per gram kidney weight, and the spontaneous
outflow of ATP and norepinephrine during S1
(R1) was expressed as picomoles per gram kidney weight per
minute. Pressor responses during S1 were expressed as
millimeters of mercury. For evaluation of drug effects, S1
values in the presence of drugs were compared with S1
control values.
Statistics
All data are given as arithmetic mean±SEM and were analyzed by
unpaired Student's t test. When the effects of drug
treatments in SHR were compared with those in WKY, data were further
analyzed by two-way ANOVA. Probability levels of less than .05 were
considered statistically significant.
Drugs and Vehicles
The Krebs-Henseleit solution had the following composition
(mmol/L): NaCl 118, KCl 4.7, CaCl2 2.5, MgSO4
0.45, NaHCO3 25, KH2PO4 1.03,
D-(+)-glucose 11.1, Na2EDTA 0.067, and
ascorbic acid 0.07. The following drugs were purchased:
(±)-norepinephrine HCl, tetrodotoxin, and corticosterone from Sigma;
cocaine HCl from Merck; ATP disodium salt from Boehringer
Mannheim; rauwolscine HCl from Roth; and 8-SPT from Research
Biochemicals Inc. The following drugs were kindly donated: prazosin HCl
and 5-bromo-6-[2-imidazoline-2-ylamino]-quinoxaline tartrate salt (UK
14304) by Pfizer; and suramin hexasodium salt by Bayer. Drugs were
dissolved in distilled water before being diluted with Krebs-Henseleit
solution, except prazosin (0.5 mL glycerol, 3.5 mL 5% glucose, 6 mL
distilled water) and corticosterone (absolute ethanol).
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
SHR and WKY kidneys were isolated and perfused with Krebs-Henseleit solution. Pressor responses to RNS as well as RNS-induced outflow of norepinephrine and in some experiments of ATP were measured.
RNS-Induced Norepinephrine Outflow and Pressor Responses to RNS
In the presence of cocaine and corticosterone, RNS at 1 Hz for 30
seconds induced a significantly greater norepinephrine outflow in SHR
(4.18±0.18 pmol/g kidney, n=34) than in WKY (2.97±0.16 pmol/g kidney,
n=38) kidneys. However, in the presence of the
P1-purinoceptor antagonist 8-SPT (100 µmol/L), the
RNS-induced norepinephrine outflow was similar in SHR (5.53±0.63
pmol/g kidney, n=10) and WKY (6.05±0.94 pmol/g kidney, n=12)
kidneys.
The spontaneous norepinephrine outflow present in the 1-minute sample collected before the onset of stimulation was small and almost identical in SHR (0.22±0.02 pmol/g kidney per minute, n=34) and WKY (0.21±0.02 pmol/g kidney per minute, n=38) kidneys. 8-SPT (100 µmol/L) did not alter the spontaneous norepinephrine outflow in either SHR (0.12±0.04 pmol/g kidney per minute, n=10) or WKY (0.18±0.04 pmol/g kidney per minute, n=12) kidneys.
Pressor responses to RNS at 1 Hz were significantly greater in SHR (22±2.4 mm Hg, n=34) than in WKY (16±1.5 mm Hg, n=38) kidneys. In the presence of 8-SPT, pressor responses to RNS were 29±6.7 mm Hg (n=10) in SHR and 18±4.2 mm Hg (n=12) in WKY kidneys.
Basal perfusion pressure was significantly greater in SHR (42±1.0 mm Hg, n=96) than in WKY (35±0.8 mm Hg, n=102) kidneys.
The RNS-induced norepinephrine outflow was reproducible at the second (S2) and third (S3) stimulation periods. The mean Sn/S1 ratios in the control experiments were 1.04±0.06 (S2/S1) and 1.14±0.06 (S3/S1) (n=11) in SHR and 1.05±0.06 (S2/S1) and 1.25±0.06 (S3/S1) (n=12) in WKY kidneys. In the presence of 8-SPT, the Sn/S1 control ratios were not different from those in the absence of 8-SPT. Pressor responses to RNS were also reproducible at S2 and S3 (data not shown).
Effects of Rauwolscine on RNS-Induced Norepinephrine Outflow and
Pressor Responses to RNS at 1 Hz
Rauwolscine (0.01 to 1 µmol/L) concentration dependently
increased RNS-induced norepinephrine outflow (Fig 1A)
and pressor responses to RNS (Fig 1B) in SHR and WKY kidneys.
Rauwolscine (1 µmol/L) increased RNS-induced norepinephrine outflow
and pressor responses to RNS to a significantly greater extent in SHR
than in WKY kidneys (Fig 1A and 1B). Rauwolscine did not alter
spontaneous norepinephrine outflow and basal perfusion pressure.
|
) and
Wistar-Kyoto rat (WKY, 
) kidneys. There were three stimulation
periods (S1 through S3, each at 1 Hz for
30 seconds, 1-millisecond width, 50 V). Rauwolscine was added in
increasing concentrations 17 minutes before S2 and
S3. Results are expressed as ratios
Sn/S1 (S2/S1,
S3/S1) and are given as percentages of the
ratios of the corresponding controls. Mean±SEM is shown of 4 to 12
experiments. +Significant difference between SHR and WKY, ANOVA,
P<.05; *significant difference compared with control,
Student's t test, P<.05.
Effects of Prazosin on RNS-Induced Norepinephrine Outflow and
Pressor Responses to RNS at 1 Hz and its Interaction With 8-SPT
Prazosin (0.03 to 3 µmol/L) concentration dependently increased
RNS-induced norepinephrine outflow in SHR and WKY kidneys (Fig 2A). Prazosin (0.3 µmol/L) induced a significantly
greater increase in RNS-induced norepinephrine outflow in WKY than in
SHR kidneys (Fig 2A).
|
In SHR and WKY kidneys, 0.03 µmol/L prazosin markedly reduced pressor responses to RNS (Fig 2B). However, prazosin at higher concentrations of 0.3 to 3 µmol/L did not reduce pressor responses further. In contrast, pressor responses in the presence of 0.3 and 3 µmol/L prazosin were higher than those in the presence of 0.03 µmol/L prazosin (Fig 2B).
The P1-purinoceptor antagonist 8-SPT (100 µmol/L) added 32 minutes before S1 did not alter the release-enhancing effect of prazosin in SHR kidneys (Fig 3A) but significantly reduced the facilitatory effect of prazosin (0.3 µmol/L) in WKY kidneys (Fig 3B). Thus, in the presence of 8-SPT (100 µmol/L) prazosin increased RNS-induced norepinephrine outflow in SHR and WKY kidneys to an identical extent.
|
, prazosin in the
presence of 8-SPT in SHR kidneys (A); and 
, prazosin in the
presence of 8-SPT in WKY kidneys (B). +Significant difference between
prazosin alone and prazosin in the presence of 8-SPT, ANOVA,
P<.05; *significant difference compared with control,
Student's t test, P<.05.Prazosin at 0.03 to 0.3 µmol/L did not alter spontaneous norepinephrine outflow (Rn/R1), but prazosin at 3 µmol/L slightly increased it compared with control in SHR (0.99±0.23 [n=5] versus 0.82±0.27 [n=11]) and WKY (1.19±0.09 [n=6] versus 0.88±0.21 [n=13]) kidneys. Prazosin did not alter basal perfusion pressure.
RNS-Induced Outflow of ATP and Norepinephrine and Pressor Responses
to RNS at 1 and 4 Hz
Pressor responses resistant to blockade by prazosin were further
investigated. The RNS-induced outflow of ATP and norepinephrine as well
as pressor responses to RNS were measured. Fig 4 shows
the time course for one experimental group.
|
RNS at 1 Hz for 30 seconds induced an ATP outflow that was similar in SHR (1.58±1.74 pmol/g kidney, n=12) and WKY (3.88±2.94 pmol/g kidney, n=11) kidneys. Since the RNS-induced ATP outflow was variable and small compared with the spontaneous ATP outflow (SHR, 8.73±1.66 pmol/g kidney per minute, n=12; WKY, 14.27±2.13 pmol/g kidney per minute, n=11), further experiments were performed at a stimulation frequency of 4 Hz. RNS at 4 Hz for 30 seconds induced an ATP outflow that was much greater than at the lower stimulation frequency and that was again similar in SHR and WKY kidneys (Fig 5A).
|
In this series of experiments the RNS-induced norepinephrine outflow tended to be increased in SHR compared with WKY kidneys (Fig 5B). The spontaneous norepinephrine outflow present in the 1-minute sample collected before the onset of stimulation was similar in SHR (0.09±0.02 pmol/g kidney per minute, n=24) and WKY (0.11±0.03 pmol/g kidney per minute, n=24) kidneys.
As observed at a stimulation frequency of 1 Hz, at 4 Hz pressor responses were also significantly greater in SHR compared with WKY kidneys (Fig 5C).
Effects of Tetrodotoxin, Prazosin, Rauwolscine, and Suramin on
RNS-Induced Outflow of Norepinephrine and ATP and Pressor Responses
to RNS at 4 Hz
Tetrodotoxin (1 µmol/L) abolished the RNS-induced outflow of ATP
and norepinephrine and pressor responses to RNS in SHR and WKY kidneys
(Fig 5A through 5C). Prazosin (0.03 µmol/L) did not alter the
RNS-induced norepinephrine outflow (Fig 5B) but significantly reduced
RNS-induced ATP outflow and pressor responses to RNS (Fig 5A and 5C) in
SHR and WKY kidneys. Rauwolscine (0.1 µmol/L) given in addition to
prazosin (0.03 µmol/L) markedly enhanced RNS-induced outflow of
norepinephrine (approximately 2.8-fold compared with values in the
presence of prazosin alone) and ATP (approximately 2.4- to 3.8-fold) as
well as prazosin-resistant pressor responses to RNS (approximately 3.0-
to 3.8-fold) in both groups. These pressor responses were then
abolished by the P2-purinoceptor antagonist suramin (300
µmol/L) given in addition to prazosin (0.03 µmol/L) and rauwolscine
(0.1 µmol/L) (Fig 5C). Suramin had no significant effect on the
RNS-induced norepinephrine outflow. Since suramin interfered with the
ATP assay, the RNS-induced ATP outflow in the presence of suramin could
not be determined.
None of the drugs altered the spontaneous outflow of norepinephrine and ATP and basal perfusion pressure, except suramin, which slightly enhanced basal perfusion pressure by 16±4 mm Hg (n=3) in SHR and 13±4 mm Hg (n=3) in WKY kidneys.
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The aim of the present study was to investigate the modulation of norepinephrine and ATP release from SHR and WKY isolated kidneys. RNS-induced outflow of endogenous norepinephrine and ATP was determined by HPLC-ECD and by the luciferin-luciferase technique, respectively.
Previous studies comparing sympathetic neurotransmission in SHR and WKY isolated kidneys obtained conflicting results. The stimulation-induced norepinephrine outflow has been reported to be increased,27 28 29 30 decreased,19 31 or unchanged32 33 in isolated SHR kidneys compared with WKY kidneys. The density of renal sympathetic innervation and hence the amount of norepinephrine released by the kidneys may change with age.34 Ages of the rats used in the above-cited studies differed markedly, and this may partly explain the controversial results. Another reason may be the method used for the determination of the outflow of norepinephrine. In most of the studies [3H]norepinephrine release was measured as a marker of endogenous norepinephrine. When in the present experiments performed with rats at an age of 12 to 14 weeks the renal nerves were stimulated at 1 Hz, the stimulation-induced endogenous norepinephrine outflow was significantly greater in SHR than in WKY kidneys. Similar data have been obtained previously for SHR and WKY kidneys at this age in a study also measuring endogenous norepinephrine outflow,35 whereas another earlier study from our laboratory using [3H]norepinephrine as a marker of endogenous norepinephrine had not been able to reveal a difference in sympathetic neurotransmission of SHR and WKY kidneys (12 to 14 weeks).32 The measurement of endogenous norepinephrine by HPLC-ECD seems to be the more appropriate approach for the study of the pathophysiology of hypertension in this model.
Prejunctional 2-Adrenoceptor–Mediated
Autoinhibition
The most important modulatory system of norepinephrine release at
the sympathetic neuroeffector junction is
2-autoinhibition.6 7 Accordingly, in the
present study the 2-adrenoceptor antagonist
rauwolscine markedly increased the RNS-induced outflow of
endogenous norepinephrine in SHR and WKY kidneys. The
facilitatory effect of rauwolscine was more pronounced in SHR kidneys.
One possible explanation could be that rauwolscine has different
affinities at the 2-autoreceptors present in SHR and
WKY kidneys. However, a previous study in which rauwolscine antagonized
the inhibitory effect of UK 14304 in SHR and WKY kidneys with identical
affinity estimates35 rules out this possibility.
Furthermore, the exact subclassification of prejunctional
2-autoreceptors using a series of -adrenoceptor
antagonists has demonstrated that in both strains these receptors are
of the 2D-adrenoceptor subtype.35 It is
therefore rather likely that the greater facilitatory effect of
rauwolscine in SHR kidneys simply depends on the interruption of a more
pronounced autoinhibition due to higher intrasynaptic levels of
norepinephrine in this strain. The intrasynaptic levels of
norepinephrine seem to differ despite the fact that the tissue content
of norepinephrine is similar in SHR and WKY kidneys at this
age.32 Differences in norepinephrine uptake seem not to be
responsible for this phenomenon, since in our experiments the cellular
uptake mechanisms for norepinephrine were blocked by cocaine and
corticosterone.
Transjunctional 1-Adrenoceptor–Mediated Modulation
of Norepinephrine Release
The preferential 1-adrenoceptor antagonist prazosin
increased the RNS-induced outflow of endogenous
norepinephrine to a significantly greater extent in WKY than in SHR
kidneys. The facilitatory mechanisms of prazosin on norepinephrine
release are complex.9 10 11 12 Prazosin has been shown to have
some affinity at 2D-adrenoceptors that may contribute to
its release-enhancing effect.10 In addition,
1-adrenoceptor–mediated transjunctional mechanisms
are involved in the facilitatory effect of prazosin.12 In
this respect, one important modulator of renal norepinephrine release
is adenosine. It is released upon RNS by activation of postjunctional
1-adrenoceptors in rabbit kidney and has been shown to
inhibit norepinephrine release.36 37 Evidence for
adenosine-mediated inhibition of norepinephrine release has
also been obtained in Wistar rat kidneys.12 The
P1-purinoceptor antagonist 8-SPT increased the
norepinephrine outflow evoked by the first stimulation period in both
species. This has been observed previously12 and is likely
to be due to a tonic outflow of endogenous adenosine, which inhibits
norepinephrine release. Furthermore, 8-SPT significantly diminished the
prazosin-induced facilitation of norepinephrine release in WKY kidneys.
This suggests that in WKY kidneys the effect of prazosin was in part
due to a transjunctional 1-adrenoceptor–mediated
adenosine mechanism. In contrast, 8-SPT did not alter at all the
facilitatory effect of prazosin in SHR kidneys. The
facilitatory effect of prazosin in the presence of 8-SPT (100
µmol/L) was then identical in SHR and WKY kidneys. Taken together,
these results suggest that the 1-adrenoceptor–mediated
transjunctional modulation of norepinephrine release by
endogenous adenosine functions less efficiently in SHR than
in WKY kidneys, thus leading to an enhanced norepinephrine release in
this strain. Others have investigated a possible role of adenosine in
sympathetic neurotransmission in SHR. Ekas et al30 have
reported that exogenous adenosine inhibited
[3H]norepinephrine release more potently in SHR
than in WKY kidneys (19 to 21 weeks). A more potent effect of adenosine
could be due to supersensitive prejunctional inhibitory adenosine
receptors and/or the upregulation of adenosine receptors due to lower
endogenous adenosine levels in SHR kidneys. However, in
several studies on isolated tail arteries38 and mesentery
arteries39 40 of SHR, exogenous adenosine has been found
to be less potent as a neuromodulator compared with WKY arteries. In
agreement with the last observations, the affinity of adenosine to
adenosine receptors has been shown to be reduced in SHR.41
The mechanism responsible for the defective
1-adrenoceptor–mediated transjunctional adenosine
modulation of norepinephrine release in SHR kidneys is not known and is
currently under investigation.
Norepinephrine-ATP Cotransmission
The preferential 1-adrenoceptor antagonist prazosin
at 0.03 µmol/L markedly reduced pressor responses to RNS. However,
higher concentrations of prazosin (0.3 and 3 µmol/L) did not further
reduce these pressor responses to RNS but instead increased them
substantially. Similar observations have been made in the rat
mesenteric vasculature,42 in which prazosin at lower
concentrations (0.03 µmol/L) reduced the RNS-induced increase in
perfusion pressure but prazosin at higher concentrations (1 µmol/L)
did not. These prazosin-resistant pressor responses seem not to be due
to neuronally released norepinephrine activating vasoconstrictor
1-adrenoceptors, since prazosin was used in a
concentration 100 times higher than its pA2 value at
1-adrenoceptors.43 44 There is the
theoretical possibility that neuronally released norepinephrine has
activated vasoconstrictor 2-adrenoceptors.
Vasoconstrictor responses to exogenous -adrenoceptor agonists in the
rat isolated kidney in the absence of other drugs are exclusively
mediated by 1-adrenoceptors.44 A small
population of vasoconstrictor 2-adrenoceptors can be
demonstrated in this preparation only in the presence of exogenous
angiotensin II.44 Such a secondary role of vasoconstrictor
2-adrenoceptors regulating renal blood flow has also
been confirmed previously in the rat in vivo,45 where
presumably substantial levels of angiotensin II are present.
However, the 2-adrenoceptor antagonist rauwolscine did
not reduce, but in contrast even enhanced pressor responses to nerve
stimulation in the presence of prazosin. This excludes a role of
postjunctional 2-adrenoceptors in the pressor responses.
Therefore, another nonadrenergic neurotransmitter seems to be involved,
most likely ATP, and this possibility was investigated in further
experiments.
In SHR and WKY kidneys, RNS (4 Hz, 30 seconds) induced a marked
vasoconstriction and the release of a considerable and similar amount
of endogenous ATP. The sodium channel blocker tetrodotoxin,
which prevents the propagation of action potentials, abolished pressor
responses to RNS as well as the RNS-induced outflow of norepinephrine
and ATP, which suggests the neuronal origin of both norepinephrine and
ATP. However, in other tissues, such as the rat tail
artery,46 the rabbit aorta,47 the guinea pig
vas deferens,23 25 26 48 the rat vas
deferens,49 and the human saphenous vein,24
ATP release from nonneuronal cells caused by activation of
1-adrenoceptors by endogenous norepinephrine
has been demonstrated. Accordingly, when pressor responses were
markedly reduced in the presence of 0.03 µmol/L prazosin, the
RNS-induced ATP outflow was inhibited by 71% and 61% in SHR and WKY
kidneys, respectively, whereas this low prazosin concentration did not
alter the RNS-induced norepinephrine outflow in both groups. Thus, the
major source of ATP is nonneuronal cells such as smooth muscle and
endothelial cells, which release ATP on 1-adrenoceptor
activation.
In the presence of prazosin at 3 µmol/L, in contrast to the findings
at 0.03 µmol/L prazosin, pressor responses to RNS (1 Hz) were almost
as high as in the absence of 1-adrenoceptor blockade.
This fact points to the possibility that ATP release is modulated
through prejunctional 2-adrenoceptors and that these
receptors are blocked by the high concentration of
prazosin.42 And indeed, when prazosin (0.03 µmol/L) was
present (to block 1-adrenoceptor–mediated
vasoconstriction and nonneuronal ATP release), the
2-adrenoceptor antagonist rauwolscine (0.1 µmol/L)
markedly enhanced the RNS-induced outflow of norepinephrine and ATP in
SHR and WKY kidneys. Moreover, at the same time rauwolscine (0.1
µmol/L) also markedly enhanced prazosin-resistant pressor responses
to RNS. These pressor responses were entirely due to ATP because they
were abolished by the P2-purinoceptor antagonist
suramin.50 This ATP is likely to be derived from
sympathetic nerve fibers because the neurotoxin
6-hydroxydopamine has been shown to block pressor
responses in rat kidneys.19 It cannot be excluded from the
present experiments that a part of the ATP outflow detected in the
presence of rauwolscine and prazosin is nonneuronal in origin, because
neuronally released ATP itself may have activated postjunctional
P2-purinoceptors to induce nonneuronal ATP
release.23 25 However, the simultaneous enhancement by
rauwolscine of RNS-induced prazosin-resistant ATP outflow and pressor
responses demonstrates that the neuronal release of ATP, as that of its
cotransmitter norepinephrine, is modulated by
2-autoinhibition. Such an 2-adrenoceptor
modulation of norepinephrine-ATP cotransmission has been
observed previously in several tissues, such as the guinea pig vas
deferens51 52 and the mesentery artery of
rabbits53 and dogs.54 There is no evidence
for a different degree of modulation of norepinephrine and ATP release
by 2-autoinhibition in rat kidneys, in contrast to some
findings in guinea pig vas deferens and synaptosomes prepared from
guinea pig myenteric plexus.25 48 55
ATP release, ATP-mediated pressor responses to RNS, and
2-adrenoceptor modulation of ATP release do not differ
between kidneys of SHR and WKY aged 12 to 14 weeks at a stimulation
frequency of 4 Hz. In comparison, in a previous study performed with
rats at an age of 5 to 6 weeks and at a lower stimulation frequency of
1 Hz, the purinergic component of pressor responses was found to be
more pronounced in SHR than in WKY kidneys.19 This
suggests that ATP may play a significant role in the developing but not
the established stage of hypertension. Nevertheless, this is the first
study demonstrating nerve stimulation–induced ATP release and its
physiological consequences in rat isolated kidney.
|
Acknowledgments |
|---|
The study was supported by the Deutsche Forschungsgemeinschaft (Ru 401/1-3; SFB 325).
|
Footnotes |
|---|
Reprint requests to L.C. Rump, Medizinische Universitätsklinik Freiburg, Innere Medizin IV, Hugstetter Str. 55, D-79106 Freiburg i. Br., FRG.
Received October 24, 1994; first decision December 5, 1994; accepted February 3, 1995.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Liard JF. Renal denervation delays blood pressure increase in the spontaneously hypertensive rat. Experientia. 1977;33:339-340. [Medline] [Order article via Infotrieve]
2. Katholi R. Renal nerves in the pathogenesis of hypertension in experimental animals and humans. Am J Physiol. 1983;14:F1-F4.
3. Esler M, Lambert G, Jennings G. Increased regional sympathetic nervous activity in human hypertension: causes and consequences. J Hypertens. 1990;8(suppl 7):S53-S57.
4. Oparil S. Pathophysiology of hypertension. Curr Opin Nephrol Hypertens. 1993;2:253-257.
5. Lundin S, Ricksten SE, Thoren P. Renal sympathetic activity in spontaneously hypertensive rats and normotensive controls, as studied by three different methods. Acta Physiol Scand. 1984;120:265-272. [Medline] [Order article via Infotrieve]
6. Starke K. Regulation of noradrenaline release by presynaptic receptor systems. Rev Physiol Biochem Pharmacol. 1977;77:1-124. [Medline] [Order article via Infotrieve]
7.
Starke K, Göthert M, Kilbinger H.
Modulation of neurotransmitter release by presynaptic
autoreceptors. Physiol Rev. 1989;69:864-989.
8. Rump LC, Schollmeyer P. Modulation der renalen Transmitterfreisetzung durch präsynaptische Rezeptoren. Klin Wochenschr. 1989;67:865-869. [Medline] [Order article via Infotrieve]
9.
Rump LC, Majewski H. Modulation of
norepinephrine release through 1- and
2-adrenoceptors in rat isolated kidney. J
Cardiovasc Pharmacol. 1987;9:500-507. [Medline]
[Order article via Infotrieve]
10.
Bohmann C, Schollmeyer P, Rump LC.
2-Autoreceptor subclassification in rat isolated
kidney by use of short trains of electrical stimulation.
Br J Pharmacol. 1993;108:262-268. [Medline]
[Order article via Infotrieve]
11.
Rump LC, Majewski H. Methoxamine inhibits
noradrenaline release in rat isolated kidney through
release of prostaglandins and direct activation of inhibitory
prejunctional 1-adrenoceptors. J
Cardiovasc Pharmacol. 1987;10(suppl 4):147-149.
12.
Bohmann C, Schollmeyer P, Rump LC. Methoxamine
inhibits noradrenaline release through activation of
1- and 2-adrenoceptors in rat isolated
kidney: involvement of purines and prostaglandins. Naunyn
Schmiedebergs Arch Pharmacol. 1993;347:273-279. [Medline]
[Order article via Infotrieve]
13. Lokhandwala MF, Eikenburg DC. Presynaptic receptors and alterations in norepinephrine release in spontaneously hypertensive rats. Life Sci. 1983;33:1527-1542. [Medline] [Order article via Infotrieve]
14. Burnstock G. The changing face of autonomic neurotransmission. Acta Physiol Scand. 1986;126:67-91. [Medline] [Order article via Infotrieve]
15. Burnstock G. Co-transmission. Arch Int Pharmacodyn. 1990;304:7-33.
16. von Kügelgen I, Starke K. Noradrenaline-ATP co-transmission in the sympathetic nervous system. Trends Pharmacol Sci. 1991;12:319-324. [Medline] [Order article via Infotrieve]
17. Hoyle CHV. Transmission: purines. In: Burnstock G, Hoyle CHV. Autonomic Neuroeffector Mechanisms. Chur, Switzerland: Harwood; 1992:367-407.
18.
Schwartz DD, Malik KU. Renal periarterial nerve
stimulation-induced vasoconstriction at low stimulation frequencies is
primarily due to release of a purinergic transmitter in the
rat. J Pharmacol Exp Ther. 1989;250:764-771.
19. Rump LC, Wilde K, Schollmeyer P. Prostaglandin E2 inhibits noradrenaline release and purinergic pressor responses to renal nerve stimulation at 1 Hz in isolated kidneys of young spontaneously hypertensive rats. J Hypertens. 1990;8:897-908. [Medline] [Order article via Infotrieve]
20.
Vidal M, Hicks PE, Langer SZ. Differential
effects of ,ß-methylene ATP on responses to nerve stimulation in
SHR and WKY tail arteries. Naunyn Schmiedebergs Arch
Pharmacol. 1986;332:384-390. [Medline]
[Order article via Infotrieve]
21. Rump LC, Wilde K, Bohmann C, Schollmeyer P. Effects of the novel dopamine DA2-receptor agonist carmoxirole (EMD 45609) on noradrenergic and purinergic neurotransmission in rat isolated kidney. Naunyn Schmiedebergs Arch Pharmacol. 1992;345:300-308. [Medline] [Order article via Infotrieve]
22. Halbrügge T, Gerhard T, Ludwig J, Heidbreder E, Graefe KH. Assay of catecholamines and dihydroxyphenylethylene glycol in human plasma and its application in orthostasis and mental stress. Life Sci. 1988;43:19-26. [Medline] [Order article via Infotrieve]
23. von Kügelgen I, Starke K. Release of noradrenaline and ATP by electrical stimulation and nicotine in guinea-pig vas deferens. Naunyn Schmiedebergs Arch Pharmacol. 1991;344:419-429. [Medline] [Order article via Infotrieve]
24. Rump LC, von Kügelgen I. A study of ATP as a sympathetic cotransmitter in human saphenous vein. Br J Pharmacol. 1994;111:65-72. [Medline] [Order article via Infotrieve]
25.
Driessen B, von Kügelgen I, Starke K.
Neural ATP release and its
2-adrenoceptor-mediated modulation in guinea-pig vas
deferens. Naunyn Schmiedebergs Arch Pharmacol. 1993;348:358-366. [Medline]
[Order article via Infotrieve]
26. von Kügelgen I, Starke K. Corelease of noradrenaline and ATP by brief pulse trains in guinea-pig vas deferens. Naunyn Schmiedebergs Arch Pharmacol. 1994;350:123-129. [Medline] [Order article via Infotrieve]
27.
Collis MG, Demey C, Vanhoutte PM. Renal vascular
reactivity in the young spontaneously hypertensive rat.
Hypertension. 1980;2:45-52.
28.
Ekas RD, Steenberg ML, Lokhandwala MF.
Increased -adrenoceptor-mediated regulation of
noradrenaline release in the isolated perfused kidney of
spontaneously hypertensive rats. Clin Sci. 1982;63:309-311.
29.
Ekas RD, Steenberg ML, Woods MS, Lokhandwala MF.
Presynaptic - and ß-adrenoceptor stimulation and
norepinephrine release in the spontaneously hypertensive rat.
Hypertension. 1983;5:198-204.
30. Ekas RD, Steenberg ML, Lokhandwala MF. Increased norepinephrine release during sympathetic nerve stimulation and its inhibition by adenosine in the isolated perfused kidney of spontaneously hypertensive rats. Clin Exp Hypertens A. 1983;5:41-48. [Medline] [Order article via Infotrieve]
31.
Vanhoutte PM, Browning D, Coen E, Verbeuren TJ,
Zonnekeyn L, Collis MG. Decreased release of norepinephrine in
the isolated kidney of the adult spontaneously hypertensive
rat. Hypertension. 1982;4:251-256.
32. Rump LC, Wilde K, Schollmeyer P. Prostaglandin E2 inhibits and indomethacin enhances noradrenaline release in isolated kidneys of adult spontaneously hypertensive rats. Br J Clin Pharmacol. 1990;30(suppl 1):S165-S167.
33. Verbeuren TJ, Herman AG. Study of prejunctional beta-adrenoceptors in kidneys of normotensive and hypertensive rats using the new beta-adrenoceptor blocking drug tertatolol. Am J Nephrol. 1986;6(suppl 2):30-35.
34.
Donohue SJ, Stitzel RE, Head RJ. Time course of
changes in the norepinephrine content of tissues from spontaneously
hypertensive and Wistar Kyoto rats. J Pharmacol Exp
Ther. 1988;245:24-31.
35.
Bohmann C, Schaible U, Schollmeyer P, Rump LC.
2D-Adrenoceptors modulate renal
noradrenaline release in normotensive and spontaneously
hypertensive rats. Eur J Pharmacol. 1994;271:283-292. [Medline]
[Order article via Infotrieve]
36. Hedqvist P, Fredholm BB. Effects of adenosine on adrenergic transmission: prejunctional inhibition and postjunctional enhancement. Naunyn Schmiedebergs Arch Pharmacol. 1976;293:217-223. [Medline] [Order article via Infotrieve]
37.
Fredholm BB, Hedqvist P. Release of the
3H-purines from [3H]-adenine labelled rabbit
kidney following sympathetic nerve stimulation and its inhibition by
-adrenoceptor blockade. Br J Pharmacol. 1978;64:239-245. [Medline]
[Order article via Infotrieve]
38. Illes P, Rickmann H, Brod I, Bucher B, Stoclet J-C. Subsensitivity of presynaptic adenosine A1-receptors in caudal arteries of spontaneously hypertensive rats. Eur J Pharmacol. 1989;174:237-251. [Medline] [Order article via Infotrieve]
39. Kamikawa Y, Cline WH, Su C. Diminished purinergic modulation of the vascular adrenergic neurotransmission in spontaneously hypertensive rats. Eur J Pharmacol. 1980;66:347-353. [Medline] [Order article via Infotrieve]
40. Kubo T, Su C. Effects of adenosine on [3H]norepinephrine release from perfused mesenteric arteries of SHR and renal hypertensive rats. Eur J Pharmacol. 1983;87:349-352. [Medline] [Order article via Infotrieve]
41. Matias A, Zimmer FJ, Lorenzen A, Keil R, Schwabe U. Affinity of central adenosine A1 receptors is decreased in spontaneously hypertensive rats. Eur J Pharmacol. 1993;244:223-230. [Medline] [Order article via Infotrieve]
42. Yamamoto R, Cline WH Jr, Takasaki K. Reassessment of the blocking activity of prazosin at low and high concentrations on sympathetic neurotransmission in the isolated mesenteric vasculature of rats. J Auton Pharmacol. 1988;8:303-309. [Medline] [Order article via Infotrieve]
43.
Wilson VG, Brown CM, McGrath JC. Are there more
than two types of -adrenoceptors involved in physiological
responses? Exp Physiol. 1991;76:317-346. [Abstract]
44.
Rump LC, Rist W, Schollmeyer P. Vasoconstrictory
2-adrenoceptors in SHR kidneys. J
Hypertens. 1992;10(suppl 4):S57.
45.
Wolff DW, Colindres RE, Strandhoy JW. Unmasking
sensitive 2-adrenoceptor-mediated renal vasoconstriction
in conscious rats. Am J Physiol. 1989;257:F1132-F1139.
46. Westfall DP, Sedaa K, Bjur RA. Release of endogenous ATP from rat caudal artery. Blood Vessels. 1987;24:125-127. [Medline] [Order article via Infotrieve]
47.
Sedaa KO, Bjur RA, Shinozuka K, Westfall DP.
Nerve and drug-induced release of adenine nucleosides and
nucleotides from rabbit aorta. J Pharmacol Exp Ther. 1990;252:1060-1067.
48.
Sperlágh B, Vizi ES. Is the neuronal ATP
release from guinea-pig vas deferens subject to
2-adrenoceptor-mediated modulation?
Neuroscience. 1992;51:203-209. [Medline]
[Order article via Infotrieve]
49. Vizi ES, Burnstock G. Origin of ATP release in the rat vas deferens: concomitant measurement of [3H]noradrenaline and [14C]ATP. Eur J Pharmacol. 1988;158:69-77. [Medline] [Order article via Infotrieve]
50. Dunn PM, Blakeley AGH. Suramin: a reversible P2-purinoceptor antagonist in the mouse vas deferens. Br J Pharmacol. 1988;93:243-245. [Medline] [Order article via Infotrieve]
51.
Sneddon P, Westfall DP. Pharmacological
evidence that adenosine triphosphate and noradrenaline are
co-transmitters in the guinea-pig vas deferens. J Physiol
(Lond). 1984;347:561-580.
52. Stjärne L, Åstrand P. Relative pre- and postjunctional roles of noradrenaline and adenosine 5'-triphosphate as neurotransmitters of the sympathetic nerves of guinea-pig and mouse vas deferens. Neuroscience. 1985;14:929-946. [Medline] [Order article via Infotrieve]
53.
von Kügelgen I, Starke K.
Noradrenaline and adenosine triphosphate as co-transmitters of
neurogenic vasoconstriction in rabbit mesenteric artery.
J Physiol (Lond). 1985;367:435-455.
54.
Muramatsu I, Ohmura T, Oshita M. Comparison
between sympathetic adrenergic and purinergic transmission in the dog
mesenteric artery. J Physiol (Lond). 1989;411:227-243.
55. Hammond JR, MacDonald WF, White TD. Evoked secretion of [3H]noradrenaline and ATP from nerve varicosities isolated from the myenteric plexus of the guinea pig ileum. Can J Physiol Pharmacol. 1988;66:369-375.[Medline] [Order article via Infotrieve]
This article has been cited by other articles:
 |
|
 |
|
  O. Vonend, A. Okonek, J. Stegbauer, S. Habbel, I. Quack, and L. C. Rump Renovascular effects of sympathetic cotransmitters ATP and NPY are age-dependent in spontaneoulsy hypertensive rats Cardiovasc Res, May 1, 2005; 66(2): 345 - 352. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Luo, G. D. Fink, K. J. Lookingland, J. A. Morris, and J. J. Galligan Impaired function of {alpha}2-adrenergic autoreceptors on sympathetic nerves associated with mesenteric arteries and veins in DOCA-salt hypertension Am J Physiol Heart Circ Physiol, April 1, 2004; 286(4): H1558 - H1564. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Stegbauer, V. Oberhauser, O. Vonend, and L. C. Rump Angiotensin-(1-7) modulates vascular resistance and sympathetic neurotransmission in kidneys of spontaneously hypertensive rats Cardiovasc Res, February 1, 2004; 61(2): 352 - 359. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. A. Brindikova, N. Bourcier, B. Torres, D. Pchejetski, M. Gekle, G. V. Maximov, V. Montminy, P. A. Insel, S. N. Orlov, and P. Isenring Purinergic-induced signaling in C11-MDCK cells inhibits the secretory Na-K-Cl cotransporter Am J Physiol Cell Physiol, December 1, 2003; 285(6): C1445 - C1453. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. W. Inscho P2 receptors in regulation of renal microvascular function Am J Physiol Renal Physiol, June 1, 2001; 280(6): F927 - F944. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. N. Thomas, B. Tomlinson, and J. A. J. H. Critchley Modulation of Blood Pressure and Obesity With the Dopamine D2 Receptor Gene TaqI Polymorphism Hypertension, August 1, 2000; 36(2): 177 - 182. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Nishiyama, D. S. A. Majid, K. A. Taher, A. Miyatake, and L. G. Navar Relation Between Renal Interstitial ATP Concentrations and Autoregulation-Mediated Changes in Renal Vascular Resistance Circ. Res., March 31, 2000; 86(6): 656 - 662. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. OBERHAUSER, O. VONEND, and L. C. RUMP Neuropeptide Y and ATP Interact to Control Renovascular Resistance in the Rat J. Am. Soc. Nephrol., June 1, 1999; 10(6): 1179 - 1185. [Abstract] [Full Text]
|
|
|
|
|
|
D. S. A. MAJID, E. W. INSCHO, and L. G. NAVAR P2 Purinoceptor Saturation by Adenosine Triphosphate Impairs Renal Autoregulation in Dogs J. Am. Soc. Nephrol., March 1, 1999; 10(3): 492 - 498. [Abstract] [Full Text]
|
|
|
|
|
|
T. J. Jones, G. Dunphy, A. Milsted, and D. Ely Testosterone Effects on Renal Norepinephrine Content and Release in Rats With Different Y Chromosomes Hypertension, November 1, 1998; 32(5): 880 - 885. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. H. Cha, T. Sekine, and H. Endou P2 purinoceptor localization along rat nephron and evidence suggesting existence of subtypes P2Y1 and P2Y2 Am J Physiol Renal Physiol, June 1, 1998; 274(6): F1006 - F1014. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||