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(Hypertension. 1995;26:744.)
© 1995 American Heart Association, Inc.
Articles |
L-NAME Hypertension Alters Endothelial and Smooth Muscle Function in Rat Aorta
Prevention by Trandolapril and Verapamil
From the Division of Cardiology, Cardiovascular Research, University Hospital, Bern (C.F.K., P.M., H.T., T.F.L.), and Department of Research, Laboratory of Vascular Research, University Hospital, Basel (C.F.K., T.F.L.), Switzerland.
Correspondence to Thomas F. Lüscher, MD, Cardiology, University Hospital, Inselspital, CH-3010 Bern, Switzerland.
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionReferences |
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Abstract Nitric oxide is an important regulator of vascular function and blood pressure. Chronic administration of nitric oxide inhibitors provides a new model of hypertension with pronounced target organ damage. We investigated the effects of oral treatment with N
-nitro-L-arginine
methyl ester (L-NAME) for 6 weeks on vascular reactivity of the aorta
in Wistar-Kyoto rats. Certain rats received verapamil or
trandolapril in addition to L-NAME. Systolic blood pressure
increased in the L-NAME group (by 
80 mm Hg systolic) but not
in controls or rats treated with verapamil or trandolapril.
Isometric tension changes of aortic rings were recorded.
Endothelium-dependent relaxations to acetylcholine
were reduced in the L-NAME group (58±6% versus 104±1% in placebo,
P<.05) but were normalized by treatment with
verapamil or trandolapril. In contrast,
endothelium-independent relaxations to sodium
nitroprusside were not significantly reduced in L-NAME hypertension but
were slightly enhanced by trandolapril therapy (P<.05).
Acute in vitro incubation of vessels with the thromboxane
receptor antagonist SQ 30741 enhanced the relaxation to
acetylcholine (P<.05) in the L-NAME group only. In
quiescent rings, acetylcholine caused
endothelium-dependent contractions in particular
after in vitro incubation with L-NAME. These contractions tended to be
enhanced in L-NAME hypertension (23±4% versus 14±3% in the placebo
group; P=NS) and were significantly reduced after treatment
with verapamil or trandolapril (P<.05).
Contractions to norepinephrine and angiotensin
I and II were unaffected by L-NAME hypertension, whereas those to
endothelin-1 were reduced (P<.05). Thus, in the aorta,
L-NAME–induced hypertension is associated with impaired
endothelium-dependent relaxations, unmasking the
effects of endothelium-derived vasoconstrictor
prostanoids, and with a specific reduction of the contraction induced
by endothelin-1. Chronic antihypertensive therapy with
verapamil or trandolapril prevented this imbalance of
endothelium-dependent relaxations and contractions
and, in turn, normalized vascular function.
Key Words: endothelins • hypertension • L-NAME • verapamil
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The L-arginine nitric oxide (NO) pathway is an important regulatory system in the circulation.1 The endothelial form of the enzyme NO synthase is constitutively expressed and produces NO under basal conditions2 as well as in response to shear stress3 and receptor-operated agonists such as acetylcholine.4 5 6 7 NO is an endogenous nitrovasodilator produced in large conduit arteries as well in the resistance circulation. Inhibitors of NO synthesis such as L-monomethyl arginine (L-NMMA) or N
-nitro-L-arginine methyl ester
(L-NAME) cause endothelium-dependent contractions
in isolated arteries and inhibit
endothelium-dependent relaxations to a variety of
agonists.8 In perfused organs, these
inhibitors markedly reduce local blood flow,9
and when infused in vivo, they induce sustained systemic
arterial hypertension.10 11 12 13 More recently,
L-NAME has been added to the drinking water of experimental animals to
induce a marked and persistent hypertension.10 13 L-NAME–induced hypertension is of particular interest, not only because it involves a new mechanism for the development of hypertension but also because of the biological properties of NO. Indeed, NO not only is a potent vasodilator but also inhibits platelet function,1 14 15 monocyte adhesion,16 and perhaps vascular smooth muscle migration and proliferation.6 7 17 18 19 Since a deficiency of NO production or action has been involved in several disease states,1 20 21 chronic application of NO synthase inhibitors may represent a model of specific vascular dysfunction and hence of early vascular disease. Clinically, vascular disease leading to cardiovascular complications occurs almost exclusively in large conduit arteries such as the aorta, coronary, carotid, renal, and peripheral arteries. Since it is likely that drugs are most efficient in preventing and reversing early rather than late vascular alterations in hypertension, this model may be suitable to test the vascular protective effects of antihypertensive drugs in the context of NO deficiency.
Angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists exert vascular protective effects in cardiovascular diseases.22 23 24 Indeed, they are potent antihypertensive drugs alone or in combination. Furthermore, they reduce cardiovascular mortality in patients after myocardial infarction.23 In addition, calcium antagonists reduce new atherosclerotic lesions in patients with coronary artery disease.23 25 26 Hence, ACE inhibitors and calcium antagonists may be effective pharmacological tools to improve endothelial function in a state of selective NO deficiency.
To test this hypothesis, 6-week-old normotensive Wistar-Kyoto rats were treated for 6 weeks with the NO inhibitor L-NAME alone or in combination with verapamil or trandolapril in a dosage previously shown to be equally effective in lowering blood pressure.27
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Animals
Normotensive 6-week-old Wistar Kyoto rats (WKY; Iffa Credo) were held at the animal facilities of the University Hospital with free access to water and standard rat chow. Housing facilities and protocols were approved by the local authorities for animal research (Kommission für Tierversuche des Kantons Bern, Switzerland). Rats were assigned to four groups: the control group (fed with standard chow and water, referred to as placebo group), the L-NAME group (
50
mg · kg-1 · d-1
of L-NAME in the drinking water), the verapamil group
(100
mg · kg-1 · d-1
of verapamil in the chow and 50
mg · kg-1 · d-1
of L-NAME in the drinking water), and the trandolapril group (1
mg · kg-1 · d-1
of trandolapril and 50
mg · kg-1 · d-1
of L-NAME in the drinking water). The treatment lasted for 6 weeks and
was discontinued 2 or 3 days before the experiments. Food and water
intake were evaluated daily, and drug intake was calculated from that
(Table 1). Blood pressure was measured by
a tail-cuff method (model LE 5000, Letica) before the animals were
used for the following experiments at the age of 12 weeks (Table 1).
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Tissue Harvesting
Rats were anesthetized by an injection of thiopental (50
mg/kg body wt IP) and then were killed by opening of the carotid
artery. The chest and the abdomen were opened through a medial
sternotomy, and the aorta was excised and immediately placed into cold
(4°C) modified Krebs-Ringer bicarbonate solution (control solution,
in mmol/L: NaCl 118.6, KCl 4.8, CaCl2 2.5,
MgSO4 1.2, KH2PO4 1.2,
NaHCO3 25.1, edetate calcium disodium 0.026, and glucose
10.1). The thoracic aorta was then dissected free under a microscope
(Wild AG) and cut into rings 3.5 mm long.
Experimental Setup
The aortic rings were mounted horizontally between two
stirrups in organ chambers filled with 25 mL of control solution
(37°C; 95% O2/5% CO2). One stirrup
was connected to an anchor and the other to a force transducer (UTC2,
Gould Statham) for the recording of isometric tension. After a
30-minute equilibrium period, rings were progressively stretched until
the contractile response to KCl (100 mmol/L)/Krebs-Ringer solution (in
mmol/L: NaCl 23.0, KCl 100.0, CaCl2 2.5, MgSO4
1.2, KH2PO4 1.2, NaHCO3 25.1,
edetate calcium disodium 0.026, and glucose 10.1) was maximal. Optimal
tension for the vessels averaged 2.5±0.2 g. The aortic rings were
allowed to equilibrate for 30 minutes before the experiments.
Protocols
For endothelium-dependent relaxations,
vessels were studied in the presence or absence of SQ 30741 (a
thromboxane/endoperoxide receptor
antagonist, at 10-7
mol/L for 30 minutes27 28 ); rings were precontracted with
norepinephrine (10-7
mol/L) and then relaxed with acetylcholine
(10-9 to
10-4 mol/L). To study direct
relaxation of vascular smooth muscle, another series of experiments was
performed: Vessels were incubated for 30 minutes with L-NAME
(10-4 mol/L; an
inhibitor of NO formation29 ) and
indomethacin (10-5
mol/L; to inhibit prostaglandin formation30 ),
precontracted with norepinephrine
(10-7 mol/L), and then relaxed with
sodium nitroprusside (10-10 to
10-5 mol/L).
Endothelium-dependent contractions were tested in quiescent preparations: Aortic segments were incubated for 30 minutes with L-NAME (10-4 mol/L), alone or in combination with SQ 30741 (10-7 mol/L), and then acetylcholine (10-9 to 10-4 mol/L) was added. Control vessels without preincubation with the drugs were tested in parallel.
Aortic contractions to norepinephrine, endothelin-1, and angiotensin I and II were also analyzed. Norepinephrine (10-10 to 10-5 mol/L) was added to vessels with or without preincubation with SQ 30741 (10-7 mol/L for 30 minutes) and/or L-NAME (10-4 mol/L for 30 minutes). The same protocol was used with endothelin-1 (10-10 to 10-7 mol/L). Angiotensin I (10-7 mol/L) was tested with or without preincubation with the ACE inhibitor captopril (10-6 mol/L for 30 minutes). Angiotensin II was given with or without preincubation with SQ 30741 (10-7 mol/L for 30 minutes) or the AT2 receptor antagonist losartan (10-5 mol/L for 30 minutes31 ). In addition, contractions to endothelin-1 were studied with or without preincubation with bosentan (10-5 mol/L for 30 minutes), a combined endothelin (ETA/ETB) receptor antagonist.32
Drugs
The following drugs were used: acetylcholine hydrochloride,
angiotensin I, angiotensin II,
indomethacin, L-arginine, L-NAME,
L-norepinephrine, sodium nitroprusside (all
Sigma Chemical Co), endothelin-1 (Novabiochem), bosentan (F. Hoffmann
La Roche Ltd), SQ 30741, captopril (Squibb Institute for Medical
Research), and losartan (Merck, Sharp & Dohme–Chibret AG). All
concentrations of the drugs used are expressed as the final
concentration in the organ chamber.
Data Analysis
For statistical analyses, the concentration of the
substance evoking 50% contraction or relaxation (expressed as negative
log mol/L; pD2 value) and the maximal contraction or
relaxation (expressed as percentage of a previous contraction to an
agonist) were calculated. Contractions were expressed as percentage of
the response to KCl (100 mmol/L). Data are given as mean±SEM. In all
series of experiments, n is the number of rats from which the blood
vessels were obtained. Unpaired or paired Student’s t test
or ANOVA followed by Bonferroni’s correction for multiple comparisons
were used for statistical analysis. A two-tailed value of
P<.05 was considered to be statistically significant.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Experimental Animals
During the 6-week treatment period, all rats increased their body weight. Although there was no difference between the groups at the beginning of the study, at the end of the treatment the body weight of the placebo group was higher than that of the verapamil or trandolapril group (Table 1). In the L-NAME group, weight also tended to be lower than in the placebo group, but the difference was not significant. Systolic blood pressure was markedly increased in the L-NAME group compared with the placebo group (Table 1). Both antihypertensive treatments completely prevented this elevation of blood pressure. Heart rate was lower in all the groups that received L-NAME than in the placebo group, but particularly so in the verapamil-treated rats (Table 1).
Endothelial Function
Endothelium-Dependent Relaxation
In the placebo group, acetylcholine totally relaxed (104±1%)
aortic rings precontracted with norepinephrine (Figs 1 and 2). As expected, the 6-week treatment
with L-NAME reduced the endothelium-dependent
relaxations to 58±6% (P<.05 versus control). Trandolapril
completely restored (107±6%) this response, whereas
verapamil improved it significantly (86±8%; Figs 1 and 2).
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P<.05 vs respective SQ 30741 preincubation.In aortic rings of the L-NAME group, in vitro preincubation with the thromboxane/endoperoxide receptor antagonist SQ 30741 (10-7 mol/L) significantly enhanced the maximum relaxation to acetylcholine compared with the control condition (Fig 2). However, the maximum response remained reduced compared with the aortic rings of the placebo group pretreated with SQ 30741 (P<.05). As in the placebo group, in rats treated with verapamil or trandolapril, the response was not significantly affected by SQ 30741. In all the groups, the sensitivity of the aortic rings to acetylcholine concentration-response curves was similar (data not shown).
Endothelium-Independent Relaxation
The maximal relaxation to the nitrovasodilator sodium
nitroprusside was similar in all groups but minimally enhanced in the
trandolapril group (114±2%) compared with the L-NAME group (109±1%,
P<.05; Fig 3). Although pD2
values in the placebo (8.2±0.1), the L-NAME (7.9±0.1), and the
verapamil (8.3±0.1) groups did not differ statistically,
the sensitivity to sodium nitroprusside was enhanced in the
trandolapril group compared with the L-NAME group (8.6±0.1; fivefold
log shift; P<.05).
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Endothelium-Dependent Contractions
Acetylcholine caused very slight contractions in quiescent aortic
rings (between 0% and 5% of KCl 100 mmol/L), but this response was
markedly enhanced when NO production was acutely blocked by the
addition of L-NAME in the organ chambers for 30 minutes (Fig 4A). Coincubation of the vessels with
L-NAME and SQ 30741 almost abolished these contractions
(P<.05 versus corresponding L-NAME alone; Figs 4A and 4B),
suggesting that this contraction is mediated by a prostanoid. The
profile of acetylcholine-induced contraction in the different
conditions was the same among the groups, but the maximal responses
differed, as depicted in Fig 4B. Indeed, the
contractions to acetylcholine were most pronounced in the L-NAME group
(23±4% versus 14±3% in the placebo group, P=NS). Chronic
treatment with verapamil or trandolapril significantly
reduced these responses to 10±2% and 8±2%, respectively (Fig 4B).
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Relation Between Contractions and Relaxations
The vessels of the placebo group exhibited strong
endothelium-dependent relaxations but only weak
endothelium-dependent contractions. Interestingly,
the opposite was observed for aortic rings coming from rats chronically
treated with L-NAME. The two antihypertensive treatments shifted this
relation toward the placebo conditions, with trandolapril achieving a
more complete prevention of the alterations observed in L-NAME–treated
rats. With the four groups, it was therefore possible to obtain a
linear relation between the maximal
endothelium-dependent contraction and relaxation,
suggesting a functional balance between these two
antagonistic endothelial influences on
vascular tone (r=.79; Fig 5).
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Contractile Responses
Contractions to KCl 100 mmol/L
Absolute contractions to KCl were comparable in the placebo, the
L-NAME, and the verapamil groups, whereas aortic rings of
the trandolapril group contracted less to KCl (Table 2).
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Endothelin-1
The maximal contractions and the sensitivity to endothelin-1 were
reduced in the L-NAME group compared with the placebo group (Fig 6A and Table 3; P<.05),
whereas both antihypertensive treatments prevented these changes in
endothelin responses. Acute in vitro preincubation of the aortic rings
with L-NAME alone enhanced maximal contractions only in the placebo and
L-NAME groups (Fig 6B). The sensitivity to endothelin-1
(pD2 value) was also increased by acute in vitro
preincubation with L-NAME in all groups (Table 3). When
SQ 30741 was added in vitro in addition to L-NAME, the enhanced
contractility of the vessels to endothelin-1 in the
presence of L-NAME alone was abolished, and the preparations contracted
similarly to their respective controls in all groups except in the
L-NAME groups, in which the inhibition was not complete (Fig 6B). Preincubation with SQ 30741 alone slightly
diminished maximal endothelin-1 contractions (P<.05 in the
placebo group only).
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Preincubation of the vessels with bosentan (10-5 mol/L) completely inhibited the contractions to endothelin-1 (maximal contraction was 0±0% for placebo group, 1±1% for L-NAME, 3±3% for verapamil, and 10±7% for trandolapril; P=NS versus each other; P<.05 for all versus control vessels; data not shown).
Norepinephrine
Norepinephrine produced concentration-dependent
contractions that were comparable between the placebo and the
L-NAME–treated rats (Table 2). Maximal contractions to
norepinephrine were enhanced in the trandolapril and the
verapamil groups. Similarly, the sensitivity to
norepinephrine was enhanced in the verapamil
group compared with the placebo and with the L-NAME groups
(P<.05, data not shown).
In vitro preincubation of the aortic rings with L-NAME alone or in combination with SQ 30741 increased the norepinephrine-induced maximal contractions (Table 2) as well as the sensitivity (pD2, data not shown) to this agonist in all four groups. In vitro preincubation with SQ 30741 alone, however, did not affect maximal contractions to norepinephrine (Table 2) and had no important effect on the sensitivity.
Angiotensin
Contractions to angiotensin I were similar in all
groups, and captopril significantly reduced these contractions,
particularly in the L-NAME– and trandolapril-treated rats
(P<.05 versus placebo for both groups; data not shown).
Angiotensin II produced similar contractions in the
placebo, L-NAME, and verapamil groups, but the response was
enhanced in the trandolapril group (P<.05). Preincubation
with SQ 30741 did not significantly affect the contractions to
angiotensin II, whereas losartan
(10-5 mol/L) completely blocked the
effects of the peptide (data not shown).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The present study demonstrates that NO-deficient hypertension induced by chronic oral administration of L-NAME in the rat is associated with marked functional alterations of the endothelium and vascular smooth muscle of large conduit arteries such as the aorta. Antihypertensive therapy with either verapamil or trandolapril prevented the increase in blood pressure in this model of hypertension and improved or normalized the vascular dysfunction induced by L-NAME.
NO is a well-established regulator of the cardiovascular system.4 5 6 29 33 As reported previously,10 11 12 13 the oral administration of a potent inhibitor of NO synthase led to a marked and sustained hypertension and to a decrease in heart rate (which is most likely mediated via the baroreflex34 ). Appropriate inhibition of NO synthase in this model is documented not only by the marked hypertension but also by direct measurements of NO synthase activity in the kidney (unpublished observation). Coadministration of verapamil or trandolapril together with the inhibitor of NO production prevented the increase in blood pressure in these animals and reduced heart rate further, probably because of the known negative chronotropic effects of verapamil and the inhibitory effects of ACE inhibitors, such as trandolapril, on the sympathetic nervous system.
L-NAME–induced hypertension is of particular interest because it allows in vivo study of the effects of prolonged NO deficiency. Rats with L-NAME–induced hypertension usually die after 8 to 11 weeks, possibly of spinal infarcts,35 renal failure, and other forms of target organ damage.21 This is surprising, because rats with spontaneous hypertension are able to live up to an age of 70 weeks36 despite a similar blood pressure increase. Hence, the vascular dysfunction associated with L-NAME–induced hypertension may serve as a model of vascular disease. In this context, the endothelium is of particular interest because it is a source of relaxing and contracting factors as well as mediators able to interfere with platelet function and vascular smooth muscle proliferation.
Endothelium-dependent relaxations were reduced in L-NAME hypertensive rats compared with controls. This impairment could not be explained by changes in the sensitivity of vascular smooth muscle to NO, since the endothelium-independent relaxations to sodium nitroprusside—which, like NO, exerts its action via activation of guanylyl cyclase and formation of cGMP37 —were unchanged. It is obvious that in this model the release of NO must be reduced. However, this may not be the only reason for the impaired endothelium-dependent relaxations in this model. The endothelium, particularly in the aorta38 and cerebral blood vessels39 of the rat, also produces contracting factors derived from the cyclooxygenase-1 pathway, such as prostaglandin H2 and thromboxane A2. The present study confirms that acetylcholine is a stimulus for the release of prostaglandin H2 or another constrictor prostanoid from the aortic endothelium. Indeed, particularly after in vitro incubation with L-NAME to limit the production of NO, acetylcholine evoked contractions (previously shown to be endothelium dependent1 36 ) in aortas of control rats, which could be blocked by the thromboxane receptor antagonist SQ 30741. Interestingly, this endothelial release of constrictor prostanoids tended to be enhanced in L-NAME–treated rats. Furthermore, endothelium-dependent relaxations were significantly augmented (albeit not normalized) after in vitro incubation of aortas obtained from L-NAME hypertensive rats with a thromboxane receptor antagonist.28 36 Both prostaglandin H2 and thromboxane A2 are agonists of the thromboxane receptor, which induces contraction in vascular smooth muscle cells. Hence, it appears that both a reduced production of NO and an enhanced release of endothelium-derived vasoconstrictor prostanoids contribute to the impaired endothelium-dependent relaxations to acetylcholine in the aorta of L-NAME hypertensive rats.
Interestingly, chronic treatment with either verapamil or trandolapril markedly augmented (in the case of verapamil) or normalized (in the case of trandolapril) the relaxations to acetylcholine in L-NAME–treated rats. Trandolapril slightly but significantly enhanced the sensitivity of the aortas to sodium nitroprusside, whereas verapamil did not affect the response to the nitrovasodilator. Under certain conditions, calcium antagonists may increase the sensitivity to sodium nitroprusside. Although studies in spontaneously hypertensive rats and porcine coronary arteries sometimes show a higher sensitivity to the nitrovasodilator,40 41 others, such as Novosel et al,27 using stroke-prone spontaneously hypertensive rats, did not find any difference between calcium antagonist–treated rats and control animals. Hence, a slight increase in the sensitivity of aortic vascular smooth muscle to NO may explain why trandolapril had a more pronounced effect than verapamil but cannot explain the main beneficial effect shared by both drugs. Indeed, both verapamil and trandolapril markedly reduced endothelium-dependent contractions to acetylcholine. This effect of the drugs is at variance with a previous chronic study from our group in stroke-prone spontaneously hypertensive rats, in which neither trandolapril nor verapamil had any effect on endothelium-dependent contractions to acetylcholine.27 Hence, it appears that the antihypertensive drugs reduce the formation of endothelium-derived vasoconstrictor prostanoids in L-NAME hypertension. It cannot be excluded, however, that an enhanced production or a decreased breakdown of NO also contributes to their beneficial effect. Indeed, the balance between acetylcholine-stimulated endothelium-derived relaxing and contracting factors was restored by verapamil and especially by trandolapril, as depicted in Fig 5. Another possible explanation is that antihypertensive treatments could favor the activation of alternative endothelium-dependent vasodilator mechanisms, since the NO synthesis was blunted due to the presence of L-NAME.
Contractions to norepinephrine and the angiotensins were not significantly altered in L-NAME hypertensive rats. Surprisingly, verapamil therapy augmented the sensitivity and maximal response to norepinephrine, and trandolapril therapy the maximal response to the catecholamine. It must be kept in mind, however, that all the chronically supplied drugs were withdrawn a few days before the experiments. These effects therefore represent chronic adaptations to the therapy and do not represent direct acute effects of verapamil and trandolapril. As expected, the response to angiotensin II was augmented only in the trandolapril group, possibly due to an upregulation of angiotensin II receptors with prolonged blockade of ACE and hence low levels of the natural agonist at the receptor.
In contrast to the other vasoconstrictors studied, L-NAME–induced hypertension was associated with a specific reduction of the response to endothelin-1, as it has been observed previously in other forms of hypertension in the aorta36 42 43 44 and in mesenteric resistance arteries42 but not in renal arteries.45 46 Since bosentan, a combined ETA/ETB-receptor antagonist,32 prevented the response to endothelin-1, the contractions involved activation of specific ET receptors. In L-NAME hypertension, increased plasma endothelin levels occur at least under acute conditions47 ; hence, agonist-induced receptor downregulation—such as occurs in atherosclerotic vascular disease48 —may be involved in this form of hypertension. Interestingly, both verapamil and trandolapril normalized the response to endothelin-1. This suggests that the drugs either reduce vascular endothelin production and/or that the reduction in pressure is crucial for the normalization of the response to endothelin-1, as has been observed in other studies with chronic nifedipine therapy in spontaneously hypertensive rats.49
Endothelin-1 can activate endothelial receptors. Most commonly, these receptors are linked to vasodilators such as NO or prostacyclin. Also in this study, acute inhibition of NO synthesis with L-NAME markedly augmented the response to endothelin-1. Although this is consistent with the concept that endothelin-1 releases NO and in turn partially blunts its own response, our results as well as experiments of others give room to another interpretation of the data. Under certain conditions, endothelin-1 also appears to be able to release vasoconstrictors such as thromboxane A2 from the endothelium.50 Indeed, in the rat, thromboxane receptor antagonists blunt the response to endothelin-1 in preparations with endothelium only.50 Similarly, in this study the thromboxane receptor antagonist SQ 30741 reduced the enhanced response to endothelin-1 induced by L-NAME in most groups and reduced the contractions to endothelin-1 in control rats. Hence, thromboxane A2 or another prostanoid appears to contribute to endothelin-1–induced contractions in the aorta of the rat.
In conclusion, L-NAME hypertension is associated with marked alterations of the endothelial and vascular smooth muscle function of large conduit arteries such as the aorta. These changes may contribute importantly to the end-organ damage seen early in the disease process of this model of hypertension. Verapamil and trandolapril were able to prevent these vascular alterations, suggesting that they might also be able to exert protective effects against end-organ damage in conditions associated with NO deficiency.
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Acknowledgments |
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This study was supported by the Swiss National Foundation (grant 32-32541.91), Schweizerische Mobiliar Insurance, Bern, Switzerland, and Knoll AG, Ludwigshafen, Germany. Dr C.F. Küng holds a stipend of the Senglet Foundation, Basel, Switzerland. Dr P. Moreau holds a fellowship from the Medical Research Council of Canada. Dr Joseph Gries and Dr Michael Kirchengast, Knoll AG, Ludwigshafen, Germany, kindly supplied verapamil and trandolapril for these studies and helped with pilot studies for the selection of the dosages used.
Received March 13, 1995; first decision April 10, 1995; accepted July 6, 1995.
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References |
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|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Lüscher TF, Vanhoutte PM. The Endothelium: Modulator of Cardiovascular Function. Boca Raton, Fla: CRC Press; 1990:1-255.
2. Moncada S, Palmer R, Higgs E. Nitric oxide: physiology, pathophysiology and pharmacology. Pharmacol Rev. 1991;43:109-142. [Medline] [Order article via Infotrieve]
3.
Joannides R, Häfeli W, Linder L, Richard V,
Bakkali E, Thuillez C, Lüscher T. Nitric oxide is
responsible for flow-dependent dilatation of human
peripheral conduit arteries in vivo.
Circulation. 1995;91:1314-1319.
4. Furchgott R, Zawadzki J. The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature. 1980;299:373-376.
5. Palmer RM, Ferrige AG, Moncada S. Nitric oxide release accounts for the biological activity of endothelium-derived relaxing factor. Nature. 1987;327:524-526. [Medline] [Order article via Infotrieve]
6. Palmer R, Ashton D, Moncada S. Vascular endothelial cells synthesize nitric oxide from L-arginine. Nature. 1988;333:664-666. [Medline] [Order article via Infotrieve]
7.
Yang Z, Von Segesser L, Bauer E, Stulz P, Turina M,
Lüscher T. Different activation of the
endothelial L-arginine and
cyclooxygenase pathway in the human internal
mammary artery and saphenous vein. Circ
Res. 1991;68:52-60.
8.
Rees D, Palmer R, Moncada S. The role of
endothelium-derived nitric oxide in the regulation
of blood pressure. Proc Natl Acad Sci U S A. 1989;86:3375-3378.
9.
Meyer P, Flammer J, Lüscher T. Local
action of the renin angiotensin system in the porcine
ophthalmic circulation: effects of ACE-inhibitors and
angiotensin receptor antagonists.
Invest Ophthalmol Vis Sci. 1995;36:555-562.
10. Gardiner S, Kemp P, Bennett T, Palmer R, Moncada S. Nitric oxide synthase inhibitors cause sustained, but reversible, hypertension and hindquarters vasoconstriction in Brattleboro rats. Eur J Pharmacol. 1992;213:449-451. [Medline] [Order article via Infotrieve]
11.
Gardiner S, Compton A, Bennett T, Palmer R, Moncada
S. Control of regional blood flow by
endothelium-derived nitric oxide.
Hypertension. 1990;15:486-492.
12. Chyu K, Guth P, Ross G. Effect of N-omega-nitro-L-arginine methyl ester on arterial pressure and on vasodilator and vasoconstrictor responses: influence of initial vascular tone. Eur J Pharmacol. 1992;212:159-164. [Medline] [Order article via Infotrieve]
13. Calver A, Collier J, Moncada S, Vallance P. Effect of local intra-arterial NG-monomethyl-L-arginine in patients with hypertension: the nitric oxide dilator mechanism appears abnormal. J Hypertens. 1992;10:1025-1031. [Medline] [Order article via Infotrieve]
14. Radomski M, Palmer R, Moncada S. Endogenous nitric oxide inhibits human platelet adhesion to vascular endothelium. Lancet. 1987;2:1057-1058. [Medline] [Order article via Infotrieve]
15. Radomski M, Palmer R, Moncada S. Comparative pharmacology of endothelium-derived relaxing factor, nitric oxide and prostacyclin in platelets. Br J Pharmacol. 1987;92:181-187. [Medline] [Order article via Infotrieve]
16.
Clozel M, Kuhn H, Hefti F, Baumgartner H.
Endothelial dysfunction and
subendothelial monocyte macrophages in
hypertension: effect of angiotensin converting enzyme
inhibition. Hypertension. 1991;18:132-141.
17. Dubey R, Lüscher T. Nitric oxide inhibits angiotensin II-induced migration of rat aortic smooth muscle cell. J Clin Invest. 1995; 96:141-149.
18. Dzau V, Gibbons G. Vascular remodelling: mechanisms and implications. J Cardiovasc Pharmacol. 1993;21(suppl 1):S1-S5.
19. Garg U, Hassid A. Nitric oxide generating vasodilators and 8-bromo-cyclic guanosine monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells. J Clin Invest. 1989;83:1774-1777.
20. Baylis C, Mitruka B, Deng A. Chronic blockade of nitric oxide synthesis in the rat produces systemic hypertension and glomerular damage. J Clin Invest. 1992;90:278-281.
21. Arnal J, Warin L, Michel J. Determinants of aortic cyclic guanosine monophosphate in hypertension induced by chronic inhibition of nitric oxide synthase. J Clin Invest. 1992;90:647-652.
22.
Clozel M, Kuhn H, Hefti F. Effects of
angiotensin converting enzyme inhibitors and of
hydralazine on endothelial function in
hypertensive rats. Hypertension. 1990;16:532-540.
23. Lichtlen PR, Hugenholtz PG, Rafflenbeul W, Hecker H, Jost S, Deckers JW, INTACT Group Investigators. Retardation of angiographic progression of coronary artery disease by nifedipine: results of the International Nifedipine Trial on Antiatherosclerotic Therapy (INTACT). Lancet. 1990;335:1109-1113. [Medline] [Order article via Infotrieve]
24.
Powell JS, Clozel JP, Muller RK, Kuhn H, Hefti F,
Hosang M, Baumgartner HR. Inhibitors of
angiotensin-converting enzyme prevent myointimal
proliferation after vascular injury. Science. 1989;245:186-188.
25. Borhani N, Miller S, Brugger S, Schnaper H, Craven T, Bond M, Khoury S, Flack J, MIDAS Research Group. MIDAS: hypertension and atherosclerosis: a trial of the effects of antihypertensive drug treatment on atherosclerosis. J Cardiovasc Pharmacol. 1992;19:S16-S20.
26. Bond M, Purvis C, Mercouri M. Antiatherogenic properties of calcium antagonists. J Cardiovasc Pharmacol. 1991;17:S87-S92.
27. Novosel D, Lang M, Noll G, Lüscher T. Endothelial dysfunction in aorta of the spontaneously hypertensive, stroke-prone rat: effects of therapy with verapamil and trandolapril alone and in combination. J Cardiovasc Pharmacol. 1994;24:979-985. [Medline] [Order article via Infotrieve]
28.
Auch-Schwelk W, Katusic ZS, Vanhoutte PM.
Thromboxane A2 receptor antagonists inhibit
endothelium-dependent contractions.
Hypertension. 1990;15:699-703.
29. Rees D, Palmer R, Hodson H, Moncada S. A specific inhibitor of nitric oxide formation from L-arginine attenuates endothelium-dependent relaxation. Br J Pharmacol. 1989;96:418-424. [Medline] [Order article via Infotrieve]
30. Moncada S, Vane J. Pharmacology and endogenous roles of prostaglandin, endoperoxides, thromboxane A2 and prostacyclin. Pharmacol Rev. 1978;30:293-331. [Medline] [Order article via Infotrieve]
31. Timmermanns P, Wong P, Chiu A, Herblin W, Benfield P, Carini D, Wexler R, Saye J, Smith R. Angiotensin II receptors and angiotensin II receptor antagonists. Pharmacol Rev. 1993;45:205-251. [Medline] [Order article via Infotrieve]
32. Clozel M, Breu V, Burri K, Cassal JM, Fischli W, Gray GA, Hirth G, Löffler BM, Müller M, Neidhart W, Ramuz H. Pathophysiological role of endothelin revealed by the first orally active endothelin receptor antagonist. Nature. 1993;365:259-261.
33. Bredt DS, Hwang PM, Glatt CE, Löwenstein C, Reed RR, Snyder SH. Cloned and expressed nitric oxide synthase structurally resembles cytochrome P-450 reductase. Nature. 1991;351:714-718. [Medline] [Order article via Infotrieve]
34.
Shi X, Andresen J, Potts J, Foresman B, Stern S, Raven
P. Aortic baroreflex control of heart rate during hypertensive
stimuli: effect of fitness. J Appl
Physiol. 1993;74:1555-1562.
35. Blot S, Arnal J-F, Xu Y, Gray F, Michel J-B. Spinal cord infarcts during long term inhibition of nitric oxide synthesis in rats. Stroke. 1994;25:1666-1673. [Abstract]
36.
Küng CF, Lüscher TF. Different
mechanisms of endothelial dysfunction with aging and
hypertension in rat aorta. Hypertension. 1995;25:194-200.
37. Rapoport RM, Draznin MB, Murad F. Endothelium-dependent relaxation in rat aorta may be mediated through cyclic GMP-dependent protein phosphorylation. Nature. 1983;306:174-176. [Medline] [Order article via Infotrieve]
38.
Lüscher TF, Boulanger CM, Dohi Y, Yang ZH.
Endothelium-derived contracting factors.
Hypertension. 1992;19:117-130.
39.
Mayhan WG, Faraci FM, Heistad DD. Responses of
cerebral arterioles to adenosine 5'-diphosphate,
serotonin, and the thromboxane analogue U-46619
during chronic hypertension. Hypertension. 1988;12:556-561.
40.
Gray G, Clozel M, Clozel J, Baumgartner H.
Effects of calcium channel blockade on the aortic intima in
spontaneously hypertensive rats.
Hypertension. 1993;22:569-576.
41. Küng C, Tschudi M, Noll G, Clozel J, Lüscher T. Differential effects of the calcium antagonist mibefradil in epicardial and intramyocardial coronary arteries. J Cardiovasc Pharmacol. 1995;26:312-318. [Medline] [Order article via Infotrieve]
42. Lüscher TF, Dohi Y, Tschudi M. Endothelium-dependent regulation of resistance arteries: alterations with aging and hypertension. J Cardiovasc Pharmacol. 1992;19(suppl):34-42.
43. Schini V, Kim N, Vanhoutte P. The basal and stimulated release of EDRF inhibits the contractions evoked by endothelin-1 and endothelin-3 in aortae of normotensive and spontaneously hypertensive rats. J Cardiovasc Pharmacol. 1991;17:S267-S271.
44. Lüscher TF, Dohi Y, Tanner FC, Boulanger C. Endothelium-dependent control of vascular tone: effects of age, hypertension and lipids. Basic Res Cardiol. 1991;86(suppl):143-158.
45.
Seo B, Lüscher TF. ETA and
ETB receptors mediate contraction to endothelin-1 in renal
artery of aging SHR: effects of FR139317 and bosentan.
Hypertension. 1995;25:501-506.
46.
Masaki T, Kimura S, Yanagisawa M, Goto K.
Molecular and cellular mechanism of endothelin regulation: implications
for vascular function. Circulation. 1991;84:1457-1468.
47.
Richard V, Hogie M, Clozel M, Löffler B, Thuillez
C. In vivo evidence of an endothelin-induced vasopressor
tone after inhibition of nitric oxide synthesis in rats.
Circulation. 1995;91:771-775.
48. Winkles JA, Alberts GF, Brogi E, Libby P. Endothelin-1 and endothelin receptor mRNA expression in normal and atherosclerotic human arteries. Biochem Biophys Res Commun. 1993;191:1081-1088. [Medline] [Order article via Infotrieve]
49. Dohi Y, Criscione L, Pfeiffer K, Lüscher T. Angiotensin blockade or calcium antagonists normalize endothelial dysfunction in hypertension: studies in perfused mesenteric resistance arteries. J Cardiovasc Pharmacol. 1994;24:372-379. [Medline] [Order article via Infotrieve]
50.
Taddei S, Vanhoutte P. Role of
endothelium in endothelin-evoked contractions in
the rat aorta. Hypertension. 1993;21:9-15.
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