From the Departamento de Fisiología, Facultad de Medicina, Murcia,
Spain (J.D.G., M.T.L., E.N., F.J.S.); and I Clinica Medica, University of
Pisa, Italy (L.G.).
Correspondence to F. Javier Salazar, Departamento de Fisiología, Facultad de Medicina, 30100 Murcia, Spain. E-mail salazar{at}fcu.um.es
Results obtained in previous studies performed in anesthetized
dogs suggest that an important interaction exists between NO and PG in
the acute regulation of renal hemodynamic and excretory
function.5 6 It was found that the renal effects
induced by acute intrarenal L-NAME administration are significantly
potentiated when PG synthesis is reduced. However, it is not known
whether there is an interaction between NO and PG in the prolonged
regulation of renal function. The objective of this study was to
determine, in conscious chronically instrumented dogs, whether the
effects induced by the prolonged administration of a
cyclooxygenase inhibitor on
arterial pressure and renal function are enhanced when NO
synthesis is reduced. The results obtained in this study may have
important clinical implications because, during aging and in
sodium-sensitive hypertension, NO synthesis seems to be
reduced7 and the intake of nonsteroidal
antiinflammatory drugs is frequent.8
Seven days before the experiments were started, the dogs were housed in
individual metabolic cages and fitted with harnesses that
contained arterial pressure transducers mounted at heart
level and a connector to the flow line. The arterial
pressure and flow lines were connected to an analog-to-digital data
collection system (Transonic, No. T208) and the data obtained
analyzed using an IBM personal computer. Use of the
transit-time flowmeter has been demonstrated to be a good method to
determine continuous changes in blood flow.9
During the experiments, the data from the recorder were obtained
every minute and subsequently averaged over a 20-hour period (12
PM to 8 AM).
Dogs were fed a sodium-deficient diet (H/D, Hill Pet Products) that
provided 5 to 7 mmol of sodium per day and were allowed free
access to tap water throughout the experiment. The venous catheter was
connected to a peristaltic pump for continuous infusion of isotonic
saline to maintain sodium intake constant at approximately 80
mmol/d. Saline was pumped through a disposable filter (0.22 µm,
Cathivex, Millipore) to prevent the formation of air bubbles and
possible contaminants from entering the venous system. The filters were
changed frequently throughout the study. The infusion tubing and both
the pressure and flow lines were protected with a flexible vacuum hose
that was attached to the harness. The dogs were allowed to move freely
in the cage but were unable to turn around completely.
Experimental Groups
Group 2 (n=8)
In preliminary experiments (n=6), it was found that meclofenamate
infusion during 6 consecutive days, at the dose used in this study,
reduced the urinary excretion of PGE2 and
6-keto-PGF1
Group 3 (n=8)
Group 4 (n=7)
Analytic Methods
Statistical Analysis
Group 2
Group 3
Group 4
Figure 2
The role of endogenous PG in the acute and long-term
regulation of arterial pressure and renal function has been
evaluated in many studies by the administration of
cyclooxygenase inhibitors (see
References 2 and 42 4 for review). It has been observed that acute PG
synthesis inhibition does not induce changes in arterial
pressure but may produce an increase in RVR and a decrease in sodium
and water excretion.5 6 10 In this study, the
prolonged PG synthesis inhibition induced changes in renal excretory
function, PRA, and plasma potassium levels that were similar to those
reported in studies in which a cyclooxygenase
inhibitor was administered during several days in animals
or humans with a normal sodium intake.2 4 11 12
However, the continuous decrease in RBF found in this study during
prolonged meclofenamate administration was unexpected because the dogs
had a normal sodium intake (
The effects of prolonged NO synthesis inhibition in conscious
dogs with the administration of pressor doses of L-NAME have also been
examined previously, with similar results to those obtained in this
study.13 14 These results suggest that
endogenous NO plays an important role in the regulation of
arterial pressure and renal function and that the long-term
pressure-natriuresis relationship is shifted to the right when NO
synthesis is reduced. Although highly speculative because the
glomerular hemodynamics have not been
examined, the fact that RBF decreased transitorily in our study without
changes in GFR suggests that NO is more important in regulating the
efferent than the afferent arteriole resistance. In support of this
idea, it has been reported that immunoreactivity to NOS I and NOS III
antibodies is greater in the efferent than in the afferent
arteriole.15
A weakness in this study is the lack of quantification of the amount of
NO synthesis inhibition. This weakness is similar to that in many
long-term studies performed with the administration of an NO synthesis
inhibitor13 14 16 17 18 19 20 21 22 because there
is not an easy way to evaluate the NO production in conscious
animals. However, the dose used was high enough to elicit an increase
in MAP and to enhance the renal vasoconstrictor and
antinatriuretic effects induced by the infusion of
a cyclooxygenase inhibitor. The
hypertension and renal vasoconstriction induced by the prolonged L-NAME
administration is most probably due to the reduction in NO synthesis
because L-NAME infusion induces a decrease in NOS
activity.18
The present work is the first study showing the renal effects of
prolonged systemic administration of a
cyclooxygenase inhibitor in animals in
which the systemic NO synthesis is diminished. The results obtained
suggest that, even when NO synthesis is reduced, endogenous
PGs do not play an important role in the maintenance of
arterial pressure because the meclofenamate infusion did
not induce a further increment in MAP in the L-NAMEtreated dogs.
However, the administration of this cyclooxygenase
inhibitor produced a significant increase in RVR and a
decrease in UNaV, UV, and GFR in these dogs. These results suggest that
endogenous PGs modulate the antinatriuresis and renal
vasoconstriction induced by the prolonged NO synthesis reduction. The
greater renal vasoconstriction and increased sodium reabsorption
elicited by the simultaneous administration of L-NAME and
meclofenamate might be secondary to the decrease in NO and PG or to the
effects of other agents, such as Ang II. The Ang II effects on renal
vasculature and tubules would now be exerted without the modulating
actions of NO and PG, thus leading to an increase in RVR and a decrease
in sodium excretion. This concept is supported by the facts that PRA
was normal during the L-NAME and meclofenamate administration and the
renal hemodynamic and
antinatriuretic Ang II effects are significantly
potentiated when NO and PG synthesis are simultaneously
decreased.6 Several studies have also
demonstrated that the renal Ang II effects are enhanced when NO or PG
synthesis is reduced.10 23 24 The important
decrease in the renal ability to eliminate sodium and water during
simultaneous L-NAME and meclofenamate administration
suggests that the prolonged increment in sodium intake may induce the
development of a sodium-sensitive hypertension in situations in which
NO and PG synthesis are reduced. Indeed, it has been reported that NO
synthesis inhibition induces the development of a sodium-sensitive
hypertension.17 21
The reported effects of prolonged NO synthesis inhibition on PRA levels
are contradictory.13 16 19 21 22 One possible
reason for this discrepancy is the different doses of NO synthesis
inhibitors and different experimental protocols used. In
this study, PRA decreased on the first day of L-NAME infusion and then
increased, despite the fact that MAP remained elevated. It is possible
that two opposing mechanisms affect PRA. Increased arterial
pressure would tend to reduce renin release, while NO synthesis
reduction would enhance renin release. The PRA-reducing effect of
elevated arterial pressure appears to be the predominant
effect during the first day of L-NAME infusion. During the following
days, it appears that there is a balance between the effects.
The decrease of PRA and the hyperkalemia observed in
this study during the prolonged administration of a
cyclooxygenase inhibitor confirm the
results reported previously.2 4 11 12 The most
frequent explanation given for the hyperkalemia induced
by the cyclooxygenase inhibitors is a
suppression of renin and
aldosterone.4 11 12 25 However, the
decrease in renin release and possible aldosterone
suppression is not the only explanation for the
hyperkalemia elicited by the administration of a
cyclooxygenase inhibitor. In our study,
it was found in dogs with a reduced NO synthesis that meclofenamate
induces an increase in plasma potassium levels without changes in PRA.
The mechanism responsible for this effect is not readily apparent, but
it has been suggested that the hyperkalemia induced by
the cyclooxygenase inhibitors could be
secondary to a decrease in distal sodium delivery or to the activation
of a high-conductance K+ channel that has been
described in the collecting tubules.25
To summarize, the results obtained in this study suggest that the renal
hemodynamic and excretory functions may be more
sensitive to the prolonged administration of a
cyclooxygenase inhibitor in situations
in which NO production is reduced. In support of this
hypothesis, it has been observed that renal function declines promptly
in elderly patients with hypertension and mild renal
insufficiency25 ; it is known that the intake of
nonsteroidal antiinflammatory drugs is increased during aging and in
hypertensive patients,8 and finally it has been
suggested that NO production is reduced during aging and in
salt-sensitive hypertension.7
Received December 22, 1997;
first decision January 12, 1998;
accepted February 16, 1998.
2.
Navar LG, Inscho EW, Majid SA, Imig JD,
Harrison-Bernard LM, Mitchell KD. Paracrine regulation of the renal
microcirculation. Physiol Rev. 1996;76:425536.
3.
Raij L, Baylis C. Glomerular actions of
nitric oxide. Kidney Int. 1995;48:2032.[Medline]
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4.
Romero JC, Knox FG. Mechanisms underlying
pressure-related natriuresis: the role of the
renin-angiotensin and prostaglandins systems:
state of the art lecture. Hypertension. 1988;11:724738.
5.
Salazar FJ, Llinás MT, González JD,
Quesada T, Pinilla JM. Role of prostaglandins and nitric
oxide in mediating renal response to volume expansion. Am J
Physiol. 1995;268:R1442R1448.
6.
Llinás MT, González JD, Nava E, Salazar
FJ. Role of angiotensin II in the renal effects induced by
nitric oxide and prostaglandin synthesis inhibition.
J Am Soc Nephrol. 1997;8:543550.[Abstract]
7.
Lüscher TF, Dohi Y, Tschudi M.
Endothelium-dependent regulation of resistance
arteries: alterations with aging and hypertension. J
Cardiovasc Pharmacol. 1992;19(suppl 5):S34S42.
8.
Houston MC. Nonsteroidal anti-inflammatory drugs and
anti-hypertensives. Am J Med. 1991;90(suppl
5A):S42S47.
9.
Wittmann U, Nafz B, Ehmke H, Kirchheim R, Persson PB.
Frequency domain of renal autoregulation in the conscious dog.
Am J Physiol. 1995;269:F317F322.
10.
Pinilla JM, Alberola A, González JD, Quesada T,
Salazar FJ. Role of prostaglandins on the renal effects of
angiotensin and interstitial pressure during
volume expansion. Am J Physiol. 1993;265:R1469R1474.
11.
Ruilope LM, Robles RG, Paya C, Rodicio JL, Romero JC.
Effects of long-term treatment with indomethacin on
renal function. Hypertension. 1986;8:677684.
12.
Clive DM, Stoff JS. Renal syndromes associated with
nonsteroidal antiinflammatory drugs. N Engl J Med. 1984;310:563572.[Medline]
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13.
Manning RD, Hu L. Nitric oxide regulates renal
hemodynamics and urinary sodium excretion in dogs.
Hypertension. 1994;23:619625.
14.
Granger JP, Novak J, Schnackenberg C, Williams S,
Reinhart GA. Role of renal nerves in mediating the hypertensive effects
of nitric oxide synthesis inhibition. Hypertension. 1996;27:613618.
15.
Bachmann S, Bosse HM, Mundel P. Topography of nitric
oxide synthesis by localizing constitutive NO synthases in mammalian
kidney. Am J Physiol. 1995;268:F885F898.
16.
Salazar FJ, Pinilla JM, López F, Romero JC,
Quesada T. Renal effects of prolonged synthesis inhibition of
endothelium-derived nitric oxide.
Hypertension. 1992;20:113117.
17.
Salazar FJ, Alberola A, Pinilla JM, Romero JC, Quesada
T. Salt-induced increase in arterial pressure during nitric
oxide synthesis inhibition. Hypertension. 1993;22:4955.
18.
Takase H, Moreau P, Küng CF, Nava E,
Lüscher TF. Antihypertensive therapy prevents
endothelial dysfunction in chronic nitric oxide
deficiency: effects of verapamil and trandolapril.
Hypertension. 1996;27:2531.
19.
Pollock DM, Polakowski JS, Divish BJ, Opgenorth TJ.
Angiotensin blockade reverses hypertension during long-term
nitric oxide synthase inhibition. Hypertension. 1993;21:660666.
20.
Navarro-Cid J, Maeso R, Rodrigo E, Muñoz-Garcia
R, Ruilope LM, Lahera V, Cachofeiro V. Renal and vascular consequences
of the chronic nitric oxide synthase inhibition: effects of
antihypertensive drugs. Am J Hypertens. 1996;9:10771083.[Medline]
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21.
Yamada SS, Sassaki AL, Fujihara CK, Malheiros DM, De
Nucci G, Zatz R. Effect of salt intake and inhibitor dose
on arterial hypertension and renal injury induced by
chronic nitric oxide blockade. Hypertension. 1996;27:11651172.
22.
Zanchi A, Schaad NC, Osterheld MC, Grouzmann E,
Nussberger J, Brunner HR, Waeber B. Effects of chronic NO synthase
inhibition on renin-angiotensin system and sympathetic
nervous system. Am J Physiol. 1995;268:H2267H2273.
23.
Llinás MT, González JD, Salazar FJ.
Interactions between angiotensin and nitric oxide in the
renal response to volume expansion. Am J Physiol. 1995;269:R504R510.
24.
Olsen ME, Hall JE, Montani JP, Cornell JE. Protection
of preglomerular vessels from angiotensin II
vasoconstriction by renal prostaglandins. J
Hypertens. 1985;3(suppl 3):S255S258.
25.
Schlondorff D. Renal complications of nonsteroidal
anti-inflammatory drugs. Kidney Int. 1993;44:643653.[Medline]
[Order article via Infotrieve]
© 1998 American Heart Association, Inc.
Scientific Contributions
Role of Nitric Oxide and Prostaglandins in the Long-term Control of Renal Function
![]()
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
AbstractPrevious studies have
reported evidence of an important interaction between nitric oxide (NO)
and prostaglandins in the acute regulation of renal
function. The objective of this study was to determine in conscious
dogs whether the renal effects of the prolonged administration of a
cyclooxygenase inhibitor are enhanced
when NO synthesis is reduced. Meclofenamate infusion (5 µg ·
kg-1 · min-1) during 4 consecutive
days (n=8) elicited a continuous decrease (P<0.05) in
renal blood flow and plasma renin activity and a transitory decrease in
sodium excretion.
NG-Nitro-L-arginine methyl ester
(L-NAME) infusion (5 µg · kg-1 ·
min-1) during 6 days (n=8) produced a significant increase
in arterial pressure and a transitory decrease
(P<0.05) in both renal blood flow and plasma renin
activity. The simultaneous inhibition of NO and
prostaglandin synthesis (n=7) led to an increase in
arterial pressure and a decrease in renal blood flow
similar to those observed during the administration of either L-NAME or
meclofenamate. In contrast, this simultaneous inhibition
produced a decrease in glomerular filtration rate, which
was not observed in the previous groups, and also induced an increase
in renal vascular resistance and a decrease in sodium excretion greater
(P<0.05) than those found during the inhibition of
either NO or prostaglandins. Only a transitory decrease in
plasma renin activity was found during meclofenamate infusion in this
group. The results of this study present new evidence that the
renal vasoconstrictor and antinatriuretic effects
induced by the prolonged infusion of a
cyclooxygenase inhibitor are
significantly enhanced when NO synthesis is reduced. These results
suggest that renal function may be more sensitive to the prolonged
administration of a cyclooxygenase
inhibitor in situations where NO production is
reduced.
Key Words: vasoconstriction nitric oxide prostaglandins sodium plasma renin activity
![]()
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
The role of NO and PG
in the acute and long-term regulation of arterial pressure
and renal function has been examined in many studies (see References 1
through 41 2 3 4 for review). It has been reported that acute and long-term NO
synthesis inhibition induces a significant elevation in
arterial pressure and RVR and a decrease in the renal
excretory ability.1 2 3 The results obtained
during the acute administration of a cyclooxygenase
inhibitor are contradictory, but it is generally accepted
that it can induce small changes in RVR and sodium
excretion.2 4 The effects of the prolonged PG
synthesis inhibition on renal function have been evaluated, but changes
in RBF during the first days of cyclooxygenase
inhibition have been only partly examined.2 4
![]()
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Animal Preparation
Experiments were performed in 29 female conscious chronically
instrumented dogs (16 to 22 kg). Surgery was performed under aseptic
conditions, and the experiments were designed according to the
Guiding Principles in the Care and Use of Laboratory Animals
approved by the Council of the American
Physiological Society. The dogs were surgically
instrumented under anesthesia induced with pentobarbital
(0.4 mL/kg) and maintained with a 1.5% to 2%
halothane/O2 mixture. Tygon catheters were
inserted through the femoral vessels into the abdominal aorta, distal
to the origins of the renal arteries, and the inferior vena
cava. The arterial catheter was used for
arterial pressure monitoring and blood sample collections,
and the venous catheter was used for infusion of various solutions. A
transit-time flow probe (4R, Transonic Systems) was implanted on the
left renal artery for the measurement of RBF. The catheters and cable
connected to the probe were tunneled subcutaneously, exteriorized
between the scapulae, and placed in neck collars. The dogs were allowed
to recover from surgery for at least 2 weeks before any experiments
were performed. Antibiotic prophylaxis was initiated before surgery and
maintained throughout the experiment.
Group 1 (n=6)
Only isotonic saline was infused throughout the experiment and
24 urine samples were measured between 8:30 and 9 AM each
day. Samples for the measurement of GFR (24-hour creatinine
clearance), plasma sodium and potassium concentrations, osmolality, and
hematocrit were drawn daily, 22 hours after the last feeding. In
addition, blood samples were obtained on days 1, 4, 7, 8, and 10 of the
experiment to analyze PRA.
After a control period of 3 days, a continuous IV infusion of
meclofenamate (5 µg · kg-1 ·
min-1) was started and maintained during 4
consecutive days. A recovery period of 3 days was allowed after the
meclofenamate infusion was finished. Urinary and blood samples were
taken in the same fashion as those obtained in group 1. Blood samples
to determine PRA were drawn during the control period (day 1), on the
first and last days of meclofenamate infusion (days 4 and 7), and
during the recovery period (days 8 and 10).
. These PGs were measured using a
commercially available radioimmunoassay (New England Nuclear). The
urinary excretion rate of PGE2 and
6-keto-PGF1
decreased (P<0.05)
from 172±18 and 443±44 pg/min in the control period to 52±12 and
40±3 pg/min, respectively, on the third day of meclofenamate
administration. No side effects (eg, diarrhea or vomiting) were
observed in these experiments during the first 4 days of meclofenamate
infusion. Only 2 dogs had diarrhea by the sixth day of meclofenamate
infusion.
L-NAME (5 µg · kg-1 ·
min-1 IV) was infused during 6 consecutive days
after a control period of 3 days. A recovery period of 3 days was
allowed after the L-NAME infusion was finished. Urinary and blood
samples were taken in the same fashion as those obtained in group 1,
with the difference that blood samples to analyze PRA were
drawn during the control period (day 1), on the first and last days of
L-NAME infusion (days 4 and 9), and during the recovery period (days 10
and 12).
A similar protocol to that of group 3 was performed, with the
difference that a meclofenamate infusion (5 µg ·
kg-1 · min-1 IV)
was started 48 hours after that of L-NAME (5 µg ·
kg-1 · min-1 IV).
L-NAME and meclofenamate administration was maintained for 6 and 4
days, respectively. The objective was to reduce only NO synthesis
during 2 days (days 4 and 5) and to reduce simultaneously
NO and PG synthesis during 4 consecutive days (days 6 through 9). A
recovery period of 3 days was allowed after the infusion of L-NAME and
meclofenamate was finished. Plasma samples to analyze PRA were
drawn during the control period (day 1), on the first day of L-NAME
infusion (day 4), on the first and last days of the
simultaneous inhibition of NO and PG synthesis (days 6 and
9), and during the recovery period (days 10 and 12).
Sodium and potassium concentrations in the urine and plasma were
measured by flame photometry (Instrumentation Laboratories). GFR was
determined by the clearance of endogenous
creatinine. Creatinine was measured with a
photocolorimetric method (Boehringer-Mannheim).
PRA was measured using a commercially available radioimmunoassay
(RENCTK P2721, Sorin Biomedica). RVR was calculated as the ratio of MAP
to RBF.
Data are expressed as mean±SE. Significance of differences in
values of each day compared with to the control period was evaluated
using a one-way ANOVA for repeated measures and the Fisher test for
multiple comparisons. The significant difference between the same
experimental day in different groups was calculated with a two-way
ANOVA and the Duncan test. P<0.05 was considered
significant.
![]()
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
Group 1
It can be observed in Figures 1
and 2
that, as expected, MAP, GFR, RBF, and
UNaV did not change when only isotonic saline was infused. No
significant changes were found throughout the experiment in PRA (Figure 3
), UV, hematocrit, and plasma sodium and
potassium concentrations.

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Figure 1. Changes in MAP, GFR, and RBF during the
administration of vehicle (NaCl, 0.9%) or meclofenamate (MECLO, 5
µg · kg-1 · min-1) for 4
consecutive days (days 4 through 7). *P<0.05 vs average
of the 3-day control period.

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Figure 2. Changes in UNaV in response to the administration
of vehicle (NaCl, 0.9%) or meclofenamate (MECLO, 5 µg ·
kg-1 · min-1) during 4 consecutive
days (days 4 through 7) (top) and in response to the administration of
L-NAME for 6 consecutive days (days 4 through 9) or to the
simultaneous administration of L-NAME (5
µg · kg-1 · min-1,
days 4 through 9) and meclofenamate (days 6 through 9) (bottom).
*P<0.05 vs average of the 3-day control period.

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Figure 3. Changes in PRA during the administration of
meclofenamate (MECLO, 5 µg · kg-1 ·
min-1) or L-NAME (5 µg · kg-1
· min-1). PRA was measured during the control period, on
days 1 and 4 of meclofenamate administration, on days 1 and 6 of L-NAME
administration, and during the first and third days of the recovery
period (RECOV) in both studies. *P<0.05 vs control
period.
Figure 1
illustrates the effects of meclofenamate infusion on MAP,
GFR, and RBF. It can be observed that MAP and GFR did not change
throughout the experiment and that meclofenamate infusion induced a
continuous decrease in RBF (P<0.05) that remained
significant even during the 3 days of recovery. RVR increased from
0.44±0.11 (control period) to 0.53±0.12 and 0.66±0.10
mm Hg · mL-1 ·
min-1 on the first and last days, respectively,
of meclofenamate infusion. UNaV decreased (P<0.05) on only
the first and last days of meclofenamate administration and returned to
control levels (81±5 mmol/d) during the recovery period (Figure 2
). The response of UV was similar to that of UNaV. PRA decreased
(P<0.05) on the first and last days of meclofenamate
infusion and increased to control levels (0.7±0.1 ng Ang I ·
mL-1 · h-1)
thereafter (Figure 3
). As expected, plasma sodium concentration did not
change and plasma potassium levels increased (P<0.05) with
meclofenamate administration (5.0±0.1 versus 4.4±0.1 mmol/L in
the control period). Plasma potassium remained slightly elevated
(P<0.05) on the third day of the recovery period
(4.7±0.1 mmol/L). Hematocrit did not change throughout the
experiment.
Figure 4
shows the changes in MAP,
GFR, and RBF induced by L-NAME. MAP increased (P<0.05) from
98±4 to 110±5 mm Hg on the first day and remained elevated
during the 6 days that NO synthesis was reduced. GFR did not change
throughout the experiment, and RBF decreased (P<0.05) on
only the first day of L-NAME infusion (225±18 versus 251±10 mL/min in
the control period) (Figure 4
). UNaV (Figure 2
), UV, hematocrit, and
plasma sodium and potassium concentrations did not change throughout
the experiment. Figure 3
shows that PRA decreased (P<0.05)
on the first day of L-NAME infusion (0.2±0.1 ng Ang I ·
mL-1 · h-1) and
then increased to levels not different from those found in the control
period (0.8±0.2 ng Ang I · mL-1 ·
h-1).

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Figure 4. Changes in MAP, GFR, and RBF during the
administration of L-NAME for 6 consecutive days (days 4 through 9) or
the simultaneous administration of L-NAME (5 µg ·
kg-1 · min-1, days 4 through 9) and
meclofenamate (MECLO, days 6 through 9). *P<0.05 vs
average of the 3-day control period.
It can be observed in Figures 2
and 4
that the response of MAP,
GFR, RBF, and UNaV to L-NAME infusion during 2 days is similar to
that observed in group 3. The simultaneous NO and PG
synthesis inhibition induced an increase in MAP that was similar to
that elicited by the inhibition of NO alone (Figure 4
) and a decrease
in RBF that was similar to that produced by the reduction of PG
synthesis alone (Figures 1
and 4
). However, the increment of
RVR in this group was greater (P<0.05) during the 4 days
that PG and NO synthesis were simultaneously reduced
(0.73±0.05 versus 0.40±0.03 mm Hg ·
mL-1 · min-1 in
the control period) than in the groups in which only NO or PG synthesis
was inhibited. Another important difference regarding the results found
during the inhibition of either NO or PG synthesis is that there was a
significant decrease (P<0.05) in GFR during both the third
(31±5 mL/min) and fourth (29±7 mL/min) days of the
simultaneous NO and PG synthesis reduction (Figure 4
). GFR
increased to control levels (45±6 mL/min) during the first day of the
recovery period but decreased again (P<0.05) on the second
and third days of this period (Figure 4
).
shows that UNaV remained decreased during the 4 days that NO
and PG synthesis were reduced and returned to control levels during the
recovery period. Cumulative sodium balance during the 4 days of
meclofenamate infusion was greater (P<0.05) in this group
(148±24 mmol) than in group 2 (54±18 mmol). The changes in
UV were similar to those of UNaV. As shown in Figure 5
, PRA decreased (P<0.05) on
the first day of the simultaneous NO and PG synthesis
inhibition (0.2±0.1 ng Ang I · mL-1
· h-1) and returned to control levels
(0.8±0.2 ng Ang I · mL-1 ·
h-1) on the last day of L-NAME and meclofenamate
infusion. Plasma sodium concentration did not change throughout the
experiment. Plasma potassium levels increased (P<0.05)
during simultaneous NO and PG synthesis reduction (4.9±0.1
versus 4.2±0.1 mmol/L) and remained elevated (P<0.05)
during the recovery period (4.7±0.1 mmol/L). Hematocrit was
diminished (0.31±0.01) during the last day of the
simultaneous L-NAME and meclofenamate administration
compared with the control period (0.35±0.01, P<0.05).

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Figure 5. Changes in PRA during the first and fourth days of
simultaneous meclofenamate (MECLO, 5 µg ·
kg-1 · min-1) and L-NAME (5 µg
· kg-1 · min-1) administration and
the first and third days of the recovery period (RECOV).
*P<0.05 vs control period.
![]()
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
This study reports for the first time that the renal
vasoconstrictor and antinatriuretic effects induced
by the prolonged administration of a cyclooxygenase
inhibitor are enhanced when NO production is
reduced. The simultaneous inhibition of NO and PG synthesis
induced an increase in RVR and a decrease in GFR and sodium excretion
that were greater than those induced by the reduction in either NO or
PG synthesis alone. Another novel finding is that the administration of
a cyclooxygenase inhibitor does not
produce a prolonged decrease in PRA when NO synthesis is reduced.
Finally, this is the first study in which RBF has been continuously
measured during the first days of administering a
cyclooxygenase inhibitor. It was
observed that the prolonged PG synthesis inhibition induces a
significant decrease in RBF.
80 mmol/d) and PRA was not
elevated. These results suggest that endogenous PGs play an
important role in the long-term regulation of RBF.
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Selected Abbreviations and Acronyms
Ang II
=
angiotensin II
GFR
=
glomerular filtration rate
L-NAME
=
NG-nitro-L-arginine methyl ester
MAP
=
mean arterial pressure
NO(S)
=
nitric oxide (synthase)
PG
=
prostaglandin
PRA
=
plasma renin activity
RBF
=
renal blood flow
RVR
=
renal vascular resistance
UNaV
=
urinary sodium excretion
UV
=
urine flow rate
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Acknowledgments
This study was supported by grants from the Fondo de
Investigaciones Sanitarias (FIS, 96/1329) of Spain and the Training and
Mobility Program of the European Community (ERBCHRXCT940645).
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References
Top
Abstract
Introduction
Methods
Results
Discussion
References
1.
Romero JC, Lahera V, Ruilope LM. Role of nitric
oxide on the intrarenal regulation of nephron function and its
relevance to hypertension. In: Laragh JH, Brenner BM, eds.
Hypertension: Pathophysiology, Diagnosis and Management. New
York, NY: Raven Press, Ltd; 1995:13851404.
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