Center for Anesthesia Research, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, 19104-4283
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
These studies document striking pulmonary vasoconstrictor response to nitric oxide synthase (NOS) inhibition in monocrotaline (MCT) pulmonary hypertension in rats. This constriction is caused by elevated endothelin (ET)-1 production acting on ETA receptors. Isolated, red blood cell plus buffer-perfused lungs from rats were studied 3 wk after MCT (60 mg/kg) or saline injection. MCT-injected rats developed pulmonary hypertension, right ventricular hypertrophy, and heightened pulmonary vasoconstriction to ANG II and the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA). In MCT-injected lungs, the magnitude of the pulmonary pressor response to NOS inhibition correlated strongly with the extent of pulmonary hypertension. Pretreatment of isolated MCT-injected lungs with combined ETA (BQ-123) plus ETB (BQ-788) antagonists or ETA antagonist alone prevented the L-NMMA-induced constriction. Addition of ETA antagonist reversed established L-NMMA-induced constriction; ETB antagonist did not. ET-1 concentrations were elevated in MCT-injected lung perfusate compared with sham-injected lung perfusate, but ET-1 levels did not differ before and after NOS inhibition. NOS inhibition enhanced hypoxic pulmonary vasoconstriction in both sham- and MCT-injected lungs, but the enhancement was greater in MCT-injected lungs. Results suggest that in MCT pulmonary hypertension, elevated endogenous ET-1 production acting through ETA receptors causes pulmonary vasoconstriction that is normally masked by endogenous NO production.
pulmonary circulation; pulmonary vascular resistance; endothelial function; nitric oxide
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
ALTERATIONS IN ENDOTHELIAL FUNCTION accompany pulmonary vascular diseases including hypertension (19). Endothelin (ET)-1 is a 21-amino acid peptide with potent vasoconstrictor (26) and smooth muscle mitogenic (5, 6) properties. The peptide is synthesized in pulmonary vascular endothelium, and although its role in normal regulation of vessel tone is unclear, it has recently been implicated in a variety of disease states, including pulmonary hypertension. Upregulation of ET-1 has been found in pulmonary vessels of patients with primary pulmonary hypertension (4) and idiopathic pulmonary fibrosis (21). In the rat model of pulmonary hypertension induced by exposure to hypoxic environment, pulmonary ET-1 and ETA- and ETB-receptor gene expression is upregulated (2, 10).
Nitric oxide (NO) mediates smooth muscle relaxation through stimulation of the soluble guanylate cyclase. NO synthase (NOS) uses L-arginine and molecular oxygen as substrates to synthesize NO in pulmonary vascular endothelium. All three of the known NOS isoforms have been localized in lung tissue (8, 16), and it is widely accepted that endogenous NOS III activity of pulmonary endothelial cells is an important modulator of pulmonary vascular tone. NOS enzymes are upregulated in chronic hypoxia (7, 9, 23, 27), and inhibition of NOS unmasks a marked pulmonary vasoconstriction in this model (1, 7, 14, 15) that appears to be mediated by ET-1 through both ETA and ETB receptors (15).
Here we present data that support the hypothesis that both endothelial NO and ET-1 production are elevated in monocrotaline (MCT)-induced pulmonary hypertension. Blocking of NOS unmasks a severe constriction that is caused by elevated endogenous ET-1 acting on ETA receptors. The magnitude of pressure increase in response to NOS inhibition correlates with the extent of pulmonary hypertension. It appears that two potent vasoactive compounds with opposite effects compete for control of pulmonary vascular tone in this model of pulmonary hypertension.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals. Virus-free male Sprague-Dawley rats obtained from Charles River were used for these experiments, and the protocols were approved by our institutional review board. MCT (Sigma) was dissolved in 1 N HCl. The pH was neutralized with 0.5 N NaOH, and the volume of the solution was adjusted with phosphate-buffered saline (PBS; pH 7.4) to achieve a concentration of 30 mg/ml. Animals (225-250 g) were given a single subcutaneous injection of MCT (60 mg/kg) or were given an equivolume injection of PBS (2 ml/kg). Studies were performed 20-21 days after MCT or sham injection.
Isolated, perfused lung. Rats were anesthetized with an intraperitoneal injection of 60 mg/kg of pentobarbital sodium. A ventral midline neck incision was made, and the trachea was isolated and intubated with a blunt 17-gauge stainless steel needle. The rats were ventilated with room air with a Harvard volume-controlled ventilator (10 ml/kg, 60 strokes/min).
The chest was opened via a midline sternotomy, and the heart and lungs
were exposed. Heparin (200 U) was injected into the left ventricle. A
suture (3-0 silk) was looped around the main pulmonary artery and ascending aorta and another was put around the
ventricles. The animal was exsanguinated by left ventricle puncture,
and blood was collected into a 15-ml modified polystyrene centrifuge
tube (Corning). The inspiratory gas was changed to a mixture of 21%
O2-5%
CO2-balance
N2 (normoxic gas mixture). A
large-bore cannula was inserted through the apex of the left ventricle,
advanced into the left atrium, and secured by suture. Another cannula
was secured in the main pulmonary artery through an incision in the
right ventricle. Perfusion of the lungs was initiated by pumping a
steady flow of perfusate into the pulmonary arterial
cannula, gradually increasing the rate to 0.06 ml · min1 · g
1.
The lungs were washed free of blood with ~50 ml of perfusate. Perfusate was then recirculated (total volume 50 ml) for the
duration of the experiment. The heart and lungs remained in
situ for the experiment. The blood that was collected
was spun at 2,500 rpm for 20 min, and the packed red blood cell
fraction (3.5-4 ml) was slowly added to perfusate.
A Masterflex pump (Cole Parmer) with a modified flow controller enabled a precisely calibrated regulation of flow. A 20-ml air reservoir or windkessel distal to the pump dampened pulsations to <0.1 cmH2O. Transducers placed near the cannulas allowed measurement of pulmonary arterial and left atrial pressures; left atrial pressure was kept at 0 cmH2O by adjusting the height of the reservoir. Pressures were recorded continuously on a Gould chart recorder. The perfusion apparatus was maintained at 37-39°C with a heat lamp.
Physiological salt solution contained the following (in mM): 131 NaCl,
4.7 KCl, 1.17 MgSO4, 22.61 NaHCO3, 1.18 KH2PO4,
3.2 CaCl2, and 10.0 glucose. In
addition, 1.6 mU/ml of insulin, 5 × 106 g/ml of meclofenamate,
and 4% (wt/vol) BSA were added to the perfusate. With the
addition of 3.5-4 ml of packed red blood cells, hematocrit in the
perfusate was 7-8%.
When pulmonary arterial pressure (PAP) stabilized (5-10 min after addition of red blood cells), a bolus (0.3 µg) of ANG II was injected upstream of the lung as a test for pulmonary vascular reactivity and to "prime" the vasomotor tone of the isolated lung preparation. The ANG II response was taken as the peak PAP recorded minus the pre-ANG II baseline PAP.
A 10- to 15-min stabilization period was allowed, after which the recorded PAP was taken as the baseline PAP for subsequent comparisons.
Effect of NOS inhibition. In 18 MCT-injected and 8 control (sham-injected) rats, the effect of NOS
inhibition on baseline PAP was evaluated. After equilibration, the NOS
inhibitor NG-monomethyl-L-arginine
(L-NMMA; Cyclopss Biochem, Salt
Lake City, UT) was added to the perfusate to a final concentration of 3 × 104 M. Effects were
recorded for 30 min.
Effect of ETA or
ETB antagonist after NOS
inhibition.
In 10 of the 18 MCT-treated rats used to study the effects of NOS
inhibition, the ability of either
ETA or ETB
blockade to reverse the
L-NMMA-induced constriction was
studied. After a 30-min perfusion with
L-NMMA, the
ETA-receptor antagonist BQ-123 (5 × 106 M) was added in
five lungs. In five other lungs, the
ETB antagonist BQ-788 (5 × 10
6 M; both from RBI,
Natick, MA) was added.
Effect of pretreatment with combined ETA
plus ETB antagonists or
ETA alone.
In four MCT-treated rat lungs, the ability of combined
ETA plus
ETB blockade to inhibit
L-NMMA-induced pulmonary
vasoconstriction was examined. The
ETA-selective antagonist BQ-123 (5 × 106 M) and
ETB-selective antagonist BQ-788 (5 × 10
6 M) were added
to perfusate 15 min before addition of
L-NMMA.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Pulmonary hypertension and right ventricular
hypertrophy. Injection of rats with MCT led to
pulmonary hypertension and right ventricular hypertrophy. The RV/(LV+S)
(Fig.
1A)
for all animals used in these studies was 0.288 ± 0.006 for
sham-injected rats (n = 14) and 0.487 ± 0.015 for MCT-injected rats (n = 36; P < 0.0001). Isolated lung vascular resistance normalized
by body weight (Fig. 1B) was
elevated in MCT-injected rat lungs (506 ± 43 cmH2O · min · g · ml1;
n = 36) compared with sham-injected
lungs (307 ± 27 cmH2O · min · g · ml
1;
P < 0.005;
n = 14).
|
Response to ANG II. Isolated lungs
from MCT-injected rats exhibited heightened responsiveness to ANG
II (Fig.
2A). The
change in PAP over baseline in response to a bolus injection of 0.3 µg of ANG II was 20.2 ± 2.6 cmH2O in MCT-injected lungs
(n = 36) and 3.9 ± 0.4 cmH2O in sham-injected lungs
(P < 0.0001;
n = 14).
|
Response to L-NMMA.
Addition of the NOS inhibitor
L-NMMA to perfusate increased
baseline PAP in MCT-injected lungs (Fig.
2B); however, there was wide
variability in the magnitude of the response. After 30 min of perfusion
with 3 × 104 M
L-NMMA, change in PAP over
baseline was 12.8 ± 3.2 cmH2O
in MCT-injected lungs (n = 28) and 1.6 ± 0.4 cmH2O in sham-injected lungs (P < 0.0001;
n = 14).
|
|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A reasonable explanation for the results presented here is that both endogenous endothelial NO and ET-1 production are elevated in MCT pulmonary hypertension, and the extent of upregulation is proportional to the severity of pulmonary hypertension. Endogenous NO production masks a constriction that would ensue from elevated ET-1 production acting on ETA receptors. This constriction is unmasked by inhibition of NOS. It thus appears that two potent vasoactive compounds of opposite effects are upregulated and oppose each other for control of pulmonary vascular tone.
In the chronic hypoxia rat model of pulmonary hypertension, NOS inhibition also leads to significant elevation of pulmonary vascular resistance compared with that in control lungs (1, 6, 14, 15). Oka et al. (15) searched for a vasoconstrictor that was suppressed by endogenous NO production, but they could not attribute their results to ET-1 or any common constrictor. More recently, however, the same group (14) found combined ETA and ETB receptor-mediated ET-1 constriction unmasked by NOS inhibition. The authors hypothesized that their conflicting results are due to differences in blood versus buffer perfusion.
Our observations of hyperresponsiveness to NOS inhibition in MCT pulmonary hypertension originally led to the hypothesis that the mechanism was mediated through ETB receptors. ETB receptors localized on vascular endothelium and smooth muscle mediate both vasoconstriction and vasorelaxation, the latter apparently through a coupling with stimulated NO release (24). We reasoned that NOS inhibition eliminated this relaxation pathway and thus unmasked a vasoconstrictor response. However, addition of the selective ETB-receptor antagonist BQ-788 failed to affect the L-NMMA-induced vasoconstriction (Fig. 4). On the other hand, blockade of ETA receptors with BQ-123 significantly reversed the constriction caused by NOS inhibition. On the basis of these data, it appears that NOS inhibition in MCT pulmonary hypertension unmasks vasoconstriction by endothelin acting on the ETA receptor.
Data from perfused normal rat lungs suggest that both ETA and ETB blockade are required to inhibit ET-1-induced pulmonary vasoconstriction. Sato et al. (22) found that although BQ-788 alone had no inhibitory effect, combined BQ-788 plus BQ-123 was more effective than BQ-123 alone in blunting ET-1-induced increases in pulmonary vascular resistance. Because ETB receptors play an important role in the pulmonary clearance of ET-1 (3), Sato et al. (22) proposed that elimination of this clearance function by BQ-788 could explain their results. If ET-1 vasoconstriction is mediated by both ETA and ETB receptors, then an apparent lack of effect of BQ-788 might be explained as a balance between suppression of ETB-mediated vasoconstriction and an enhanced ETA constriction, made possible by increased circulating levels of ET-1.
Our data in Fig. 4 demonstrate that vasoconstriction caused by NOS inhibition in MCT pulmonary hypertension is reversed by ETA blockade but is unaffected by ETB block. However, it remains possible that ETB receptors play a complementary role similar to that demonstrated by Sato et al. (22) in normal rat lungs. Therefore, we compared ETA-receptor antagonism alone with combined ETA- and ETB-receptor antagonism on the inhibition of L-NMMA-induced pulmonary vasoconstriction. As demonstrated in Fig. 5, pretreatment with combined BQ-123 plus BQ-788 completely prevented the increase in resistance caused by NOS inhibition. However, pretreatment with BQ-123 alone was equally effective in preventing the increase in pulmonary vascular resistance.
It thus appears that in the MCT model of pulmonary hypertension, vasoconstriction induced by NOS inhibition is mediated exclusively through the ETA receptors. This contrasts with normal rat lung and the chronic hypoxia model, in which constriction is mediated by mixed ETA and ETB receptors. It is possible that a change in the role of ET receptors occurs in rat lungs after MCT injection; however, any elaboration on this point would be purely speculative without further investigation.
Our data in Fig. 4 showing a reversal of the increase in PAP after addition of BQ-123 are consistent with the report by Warner et al. (28). These authors demonstrated a slow reversal in established (systemic) constrictor response to ET-1 infusion after addition of BQ-123. The time course in pressure increase after ET-1 infusion and subsequent pressure decrease after BQ-123 are both similar to the time courses shown in Fig. 4. Warner et al. suggested that a large molar excess of receptor antagonist prevents new binding of ET-1 after receptor externalization. Thus the observed slow reversal of established constriction is most likely explained as a function of the rate of receptor recycling. Newly externalized receptors are bound by the antagonist BQ-123 rather than by ET-1; therefore, vasoconstriction is diminished over time.
In these experiments, we found a significant correlation in MCT-treated lungs between the severity of pulmonary hypertension and responses to NOS inhibition (Fig. 3). This suggests enhanced vasoactivity in response to MCT as the severity of hypertension increases. It is not known if this represents a change in function or is a consequence of pulmonary vascular remodeling. For example, it is possible that neomuscularization of previously nonmuscular small pulmonary arteries is responsible for this observed enhanced agonist response.
It should also be pointed out that these studies do not address the important issue of cause and effect; that is, whether upregulation of ET is involved in the pathogenesis of MCT pulmonary hypertension or is secondary to it. ET is a vascular smooth muscle mitogen (6); however, these studies do not shed light on whether upregulation of ET-1 is implicated in vascular remodeling in this model of pulmonary hypertension.
Further insight might be gained by correlating the time course of ET upregulation after MCT injection with pulmonary vascular remodeling. We chose to study rats 3 wk after MCT injection, as have numerous other investigators. At this time point, pulmonary hypertension is well developed, but mortality is low. Pulmonary vascular reactivity varies with time after MCT injection (20, 25); therefore, it is reasonable to expect that NOS and ET-1 regulation differ at other time points.
These studies address a question regarding the acute interaction between NOS activity and ET-1 release. We investigated the possibility that inhibition of endothelial NO production was related to the stimulation of ET-1 release. The data in Fig. 6 demonstrate that this is not the case; the measured ET-1 levels in perfusate were elevated (compared with control lungs) before L-NMMA addition and did not increase in response to L-NMMA. Thus it appears in this model that ET-1 vasoconstriction is masked by endogenous NO release. Eliminating the vasodilator effect of NO unmasks an underlying ET-1-mediated constriction.
Strong evidence exists for NOS III upregulation in the chronic hypoxia model of pulmonary hypertension (7, 9, 23, 27). In both acute and chronic hypoxic pulmonary hypertension, ET-1 is upregulated as well (2, 10). In the MCT model of pulmonary hypertension, recent studies documented enhanced NOS III localization (18) and increased NO production (25). In MCT-injected rats, ET-1 precursor mRNA is upregulated (13), and Matthew et al. (12) found elevated ET-1 levels in large pulmonary arteries. Although their data suggested that NOS may be downregulated because endothelium-dependent relaxation was inhibited, a study by Madden et al. (11) supported enhanced pulmonary NO production in MCT-injected rats. Our data support both NO (indirectly) and ET-1 (directly) upregulation.
Markedly elevated NO levels upregulate ETA receptors and enhance ET-1 affinity in cultured (systemic) smooth muscle cells (17). Others have also demonstrated functional interactions between ET-1 and NO in pulmonary vessels (29). Increasing evidence suggests that interactions among opposing vasoactive compounds may be involved in both normal and pathophysiological regulation of vascular tone.
The physiological significance of this dual upregulation is not known. Clearly, elevated endothelial NO production in this model serves to maintain active vasorelaxation and prevent the possibility of edema formation resulting from greatly elevated smooth muscle tone. Another possible function of this dual upregulation is suggested by the hypoxic response data (Fig. 7). These data demonstrate that the modulating effect of NO on HPV is greater in pulmonary hypertensive compared with control rats. This could have a significant effect on the regulation of ventilation-to-perfusion ratios and consequently on active maintenance of gas-exchange efficiency.
![]() |
ACKNOWLEDGEMENTS |
---|
This work was supported by National Heart, Lung, and Blood Institute Grant HL-09040.
![]() |
FOOTNOTES |
---|
Present address of and address for reprint requests: H. F. Frasch, National Institute for Occupational Safety and Health, MS 3030, 1095 Willowdale Rd., Morgantown, WV 26505-2888.
Received 29 December 1997; accepted in final form 26 October 1998.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Barer, G.,
C. Emery,
A. Stewart,
D. Bee,
and
P. Howard.
Endothelial control of the pulmonary circulation in normal and chronically hypoxic rats.
J. Physiol. (Lond.)
463:
1-16,
1993[Abstract].
2.
Elton, T. S.,
S. Oparil,
G. R. Taylor,
P. H. Hicks,
R.-H. Yang,
H. Jin,
and
Y. F. Chen.
Normobaric hypoxia stimulates endothelin-1 gene expression in the rat.
Am. J. Physiol.
263 (Regulatory Integrative Comp. Physiol. 32):
R1260-R1264,
1992
3.
Fukuroda, T.,
T. Fujikawsa,
S. Ozaki,
K. Ishikawa,
M. Yanno,
and
M. Nishikibe.
Clearance of circulating endothelin-1 by ETB receptors in rats.
Biochem. Biophys. Res. Commun.
199:
1461-1465,
1994[Medline].
4.
Giaid, A.,
M. Yanagisawa,
D. Langleben,
R. P. Michel,
R. Levy,
H. Shennib,
S. Kimura,
T. Masaki,
W. P. Duguid,
and
D. J. Stewart.
Expression of endothelin-1 in the lungs of patients with pulmonary hypertension.
N. Engl. J. Med.
328:
1732-1739,
1993
5.
Hassoun, P. M.,
V. Thappa,
M. J. Landman,
and
B. L. Fanburg.
Endothelin 1: mitogenic activity on pulmonary artery smooth muscle cells and release from hypoxic endothelial cells.
Proc. Soc. Exp. Biol. Med.
199:
165-170,
1991[Abstract].
6.
Hirata, Y.,
Y. Takagi,
Y. Fukuda,
and
R. Marumo.
Endothelin is a potent mitogen for rat vascular smooth muscle cells.
Atherosclerosis
78:
225-228,
1989[Medline].
7.
Isaacson, T. C.,
V. Hampl,
E. K. Weir,
D. P. Nelson,
and
S. L. Archer.
Increased endothelium-derived NO in hypertensive pulmonary circulation of chronically hypoxic rats.
J. Appl. Physiol.
72:
933-940,
1993.
8.
Kobzik, L.,
D. S. Bredt,
C. J. Lowenstein,
J. Drazen,
B. Gaston,
D. Sugarbaker,
and
J. S. Stamler.
Nitric oxide synthase in human and rat lung: immunocytochemical and histochemical localization.
Am. J. Respir. Cell Mol. Biol.
9:
371-377,
1993[Medline].
9.
Le Cras, T. D.,
C. Xue,
A. Rengasamy,
and
R. A. Johns.
Chronic hypoxia upregulates endothelial and inducible NO synthase gene and protein expression in the rat lung.
Am. J. Physiol.
270 (Lung Cell. Mol. Physiol. 14):
L164-L170,
1996
10.
Li, H.,
S.-J. Chen,
Y.-F. Chen,
Q. C. Meng,
J. Durand,
S. Oparil,
and
T. S. Elton.
Enhanced endothelin-1 and endothelin receptor gene expression in chronic hypoxia.
J. Appl. Physiol.
77:
1451-1459,
1994
11.
Madden, J. A.,
P. A. Keller,
J. S. Choy,
T. A. Alvarez,
and
A. D. Hacker.
L-Arginine-related responses to pressure and vasoactive agents in monocrotaline-treated rat pulmonary arteries.
J. Appl. Physiol.
79:
589-593,
1995
12.
Matthew, R.,
G. A. Zeballos,
H. Tun,
and
M. H. Gewitz.
Role of nitric oxide and endothelin-1 in monocrotaline-induced pulmonary hypertension in rats.
Cardiovasc. Res.
30:
739-746,
1995[Medline].
13.
Miyauchi, T.,
R. Yorikane,
S. Sakai,
T. Sakurai,
M. Okada,
M. Nishikibe,
M. Yano,
I. Yamaguchi,
Y. Sugishita,
and
K. Goto.
Contribution of endogenous endothelin-1 to the progression of cardiopulmonary alterations in rats with monocrotaline-induced pulmonary hypertension.
Circ. Res.
73:
887-897,
1993[Abstract].
14.
Muramatsu, M.,
D. M. Rodman,
M. Oka,
and
I. F. McMurtry.
Endothelin-1 mediates nitro-L-arginine vasoconstriction of hypertensive rat lungs.
Am. J. Physiol.
272 (Lung Cell. Mol. Physiol. 16):
L807-L812,
1997
15.
Oka, M.,
K. Hasunuma,
S. A. Webb,
T. J. Stelzner,
D. M. Rodman,
and
I. F. McMurtry.
EDRF suppresses an unidentified vasoconstrictor mechanism in hypertensive lungs.
Am. J. Physiol.
264 (Lung Cell. Mol. Physiol. 8):
L587-L597,
1993
16.
Pollock, J. S.,
M. Nakane,
L. D. K. Buttery,
A. Martinez,
D. Springall,
J. M. Polak,
U. Föstermann,
and
F. Murad.
Characterization and localization of endothelial nitric oxide synthase using specific monoclonal antibodies.
Am. J. Physiol.
265 (Cell Physiol. 34):
C1379-C1387,
1993
17.
Redmond, E. M.,
P. A. Cahill,
R. Hodges,
S. Zhang,
and
J. V. Sitzmann.
Regulation of endothelin receptors by nitric oxide in cultured rat vascular smooth muscle cells.
J. Cell. Physiol.
166:
469-479,
1996[Medline].
18.
Resta, T. C.,
R. J. Gonzales,
W. G. Dail,
T. C. Sanders,
and
B. R. Walker.
Selective upregulation of arterial endothelial nitric oxide synthase in pulmonary hypertension.
Am. J. Physiol.
272 (Heart Circ. Physiol. 41):
H806-H813,
1997
19.
Rodman, D. M.,
and
N. Voelkel.
Regulation of vascular tone.
In: The Lung: Scientific Foundations, edited by R. G. Crystal,
and J. B. West. New York: Raven, 1991, p. 1105-1119.
20.
Rosenberg, H. C.,
and
M. Rabinovitch.
Endothelial injury and vascular reactivity in monocrotaline pulmonary hypertension.
Am. J. Physiol.
255 (Heart Circ. Physiol. 24):
H1484-H1491,
1988
21.
Saleh, D.,
K. Furukawa,
M.-S. Tsao,
A. Maghazachi,
B. Corrin,
M. Yanagisawa,
P. J. Barnes,
and
A. Giaid.
Elevated expression of endothelin-1 and endothelin-converting enzyme-1 in idiopathic pulmonary fibrosis: possible involvement of proinflammatory cytokines.
Am. J. Respir. Cell Mol. Biol.
16:
187-193,
1997[Abstract].
22.
Sato, K.,
M. Oka,
K. Hasunuma,
M Ohnishi,
K Sato,
and
S. Kira.
Effects of separate and combined ETA and ETB blockade on ET-1-induced constriction in perfused rat lungs.
Am. J. Physiol.
269 (Lung Cell. Mol. Physiol. 13):
L668-L672,
1995
23.
Shaul, P. W.,
A. J. North,
T. S. Brannon,
K. Ujiie,
L. B. Wells,
P. A. Nisen,
C. J. Lowenstein,
S. H. Snyder,
and
R. A. Star.
Prolonged in vivo hypoxia enhances nitric oxide synthase type I and type III gene expression in adult rat lung.
Am. J. Respir. Cell Mol. Biol.
13:
167-174,
1995[Abstract].
24.
Tsukahara, H.,
H. Ende,
H. I. Magazine,
W. F. Bahou,
and
M. S. Goligorsky.
Molecular and functional characterization of the non-isopeptide-selective ETB receptor in endothelial cells. Receptor coupling to nitric oxide synthase.
J. Biol. Chem.
269:
21778-21785,
1994
25.
Yamaguchi, K.,
Y. Kanai,
K. Asano,
T. Takasugi,
T. Tanaka,
M. Yasuoka,
and
Y. Hosoda.
Temporal alterations of endothelial-vasodilator functions in lung injury induced by monocrotaline.
Respir. Physiol.
107:
47-58,
1997[Medline].
26.
Yanagisawa, M.,
H. Kurihara,
S. Kimura,
Y. Tomobe,
M. Kobayashi,
Y. Mitsui,
Y. Yazaki,
K. Goto,
and
T. Masaki.
A novel potent vasoconstrictor peptide produced by vascular endothelial cells.
Nature
332:
411-415,
1988[Medline].
27.
Xue, C.,
A. Rengasamy,
T. D. Le Cras,
P. A. Koberna,
G. C. Dailey,
and
R. A. Johns.
Distribution of NOS in normoxic vs. hypoxic rat lung: upregulation of NOS by chronic hypoxia.
Am. J. Physiol.
267 (Lung Cell. Mol. Physiol. 11):
L667-L678,
1994
28.
Warner, T. D.,
G. H. Allcock,
and
J. R. Vane.
Reversal of established responses to endothelin-1 in vivo and in vitro by the endothelin receptor antagonists, BQ-123 and PD 145065.
Br. J. Pharmacol.
112:
207-213,
1994[Abstract].
29.
Zellers, T. M.,
J. McCormick,
and
Y. Wu.
Interaction among ET-1, endothelium-derived nitric oxide, and prostacyclin in pulmonary arteries and veins.
Am. J. Physiol.
267 (Heart Circ. Physiol. 36):
H139-H147,
1994