Department of Pediatrics, Medical College of Wisconsin, Milwaukee 53226; and Research Services, Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Therapies to
prevent the onset or progression of pulmonary hypertension in newborns
have received little study compared with those in adult models. We
wanted to determine whether nifedipine treatment prevents the increased
pulmonary vascular resistance, blunted pulmonary vascular responses to
acetylcholine, and reduced lung endothelial nitric oxide synthase
(eNOS) amounts that we have found in a newborn model of chronic
hypoxia-induced pulmonary hypertension. Studies were performed with 1- to 3-day-old piglets raised in room air (control) or 10%
O2 (hypoxia) for 10-12 days. Some piglets from each group were given nifedipine (3-5 mg/kg sublingually three times a day). Pulmonary arterial pressure, pulmonary
wedge pressure, and cardiac output were measured in anesthetized
animals. Pulmonary vascular responses to acetylcholine and eNOS amounts
were assessed in excised lungs. The calculated value of the pulmonary
vascular resistance for nifedipine-treated hypoxic piglets (0.09 ± 0.01 cmH2O · ml1 · min · kg)
was almost one-half of the value for untreated hypoxic piglets (0.16 ± 0.01 cmH2O · ml
1 · min · kg)
and did not differ from the value for untreated control piglets (0.05 ± 0.01 cmH2O · ml
1 · min · kg).
Pulmonary arterial pressure responses to acetylcholine and whole lung
homogenate eNOS amounts were less for both nifedipine-treated and
untreated hypoxic piglets than for untreated control piglets. Nifedipine treatment attenuated pulmonary hypertension in chronically hypoxic newborn piglets despite the persistence of blunted responses to
acetylcholine and reduced lung eNOS amounts.
endothelium-dependent responses; neonatal pulmonary hypertension; dysfunctional endothelium; endothelial nitric oxide synthase; calcium-channel blockers
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
DESPITE THE PROBABILITY that the pathophysiology of pulmonary hypertension may differ between newborns and adults, newborn models of this disease have received relatively little study compared with adult models. To improve the understanding of the pathogenesis of neonatal pulmonary hypertension, our laboratory (4-6) developed a model of chronic hypoxia-induced pulmonary hypertension in newborn piglets. In addition to developing pulmonary hypertension, newborn piglets exposed to 10-12 days of chronic hypoxia exhibit blunted pulmonary arterial responses to the endothelium-dependent dilator acetylcholine and have reduced lung endothelial nitric oxide synthase (eNOS) amounts (5, 6). These latter findings suggest that impaired endothelial function might contribute to the pathogenesis of pulmonary hypertension in the newborn.
Devising therapies that might prevent the onset or progression of pulmonary hypertension has received particularly little attention in newborns in comparison to studies with adult animals. For example, treatment with calcium-channel blockers such as nifedipine has been shown to ameliorate the development of chronic hypoxia-induced pulmonary hypertension in adult animals (17), but the efficacy of these agents in preventing pulmonary hypertension in neonates has not been evaluated. Moreover, the mechanisms by which nifedipine attenuates the development of pulmonary hypertension in adults remain unknown. Because endothelial dysfunction is one potential cause of pulmonary hypertension (11, 20, 22), it is possible that nifedipine treatment ameliorates pulmonary hypertension, at least in part, by improving endothelial function. The purposes of the present study were to determine whether treatment with nifedipine would ameliorate the development of pulmonary hypertension in chronically hypoxic newborn piglets and prevent the altered endothelium-dependent responses that we have found in this newborn model. In addition, because reduced eNOS amounts might underlie altered endothelium-dependent responses in the lungs of chronically hypoxic newborn piglets (6), we evaluated eNOS amounts in whole lung homogenates from both nifedipine-treated and untreated control and chronically hypoxic piglets.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals. Newborn piglets (1-3 days old) were placed in chambers with either a room air environment (control; n = 13) or a hypoxic normobaric environment (chronic hypoxia; n = 24) for 10-12 days. Except for the case of one control piglet, two piglets were placed in each chamber. For the chronically hypoxic piglets, the normobaric hypoxic environment was produced by delivering compressed air and nitrogen to an incubator (Thermocare). The O2 content was regulated at 8-10% (PO2 60-72 Torr), and PCO2 was maintained at 3-6 Torr by absorption with soda lime. The chamber was opened two to three times a day for cleaning and to weigh the animals. The animals were fed ad libitum with an artificial sow milk replacer from a feeding device attached to the chamber. Piglets were randomly chosen from both groups (n = 5 control and 10 hypoxic) for nifedipine treatment (3-5 mg/kg sublingually three times a day). The dose of nifedipine was chosen because in pilot studies with chronically hypoxic piglets, we found that lower doses had no effect on pulmonary vascular resistance and that larger doses were associated with a high incidence of unexpected death. Some nifedipine-treated piglets were raised in the same chamber with an untreated animal from the same group (n = 3 control and 5 hypoxic). Because Fike et al. (6) previously found no differences in endothelium-dependent responses or lung eNOS amounts between control piglets raised on the farm and control piglets raised in a normoxic chamber, 11 untreated control animals were studied on the day of arrival from the farm at 11-15 days of age.
Measurements in anesthetized animals.
On the day of study, all piglets were weighed and anesthetized with
ketamine (30 mg/kg im) and pentobarbital sodium (10 mg/kg iv).
Additional intravenous pentobarbital sodium was given as needed via an
ear vein to maintain anesthesia during placement of the catheters.
First, the trachea of the piglet was cannulated so that the animal
could be ventilated if necessary. Then, a catheter was placed into the
right femoral artery for monitoring systemic blood pressure and
arterial blood gases. Next, for most piglets
(n = 16 untreated control, 5 nifedipine-treated control, 13 untreated hypoxic, and 11 nifedipine-treated hypoxic), another catheter was placed through the
right external jugular vein into the pulmonary artery to monitor
pulmonary arterial pressure. To obtain pulmonary wedge pressure, the
pulmonary arterial catheter was advanced into a distal pulmonary
vessel. The zero reference for the vascular pressures was the
midthorax. To measure cardiac output by the thermodilution technique
(model 9520 thermodilution cardiac output computer, Edwards
Laboratory), a thermistor was placed into the aortic arch via the left
femoral artery and a catheter that served as an injection port was
placed into the left ventricle via the left carotid artery. Cardiac
output was measured at end expiration as the mean of three injections
of 3 ml of 0.9% saline (0°C). After blood gases were measured, all animals were given heparin (1,000 IU/kg iv) and additional anesthesia (3-5 mg/kg of pentobarbital sodium iv) and then exsanguinated. Most lungs were left in situ and used for perfusion as described in
Measurements in isolated perfused
lungs. A few lungs
(n = 1 untreated control and 1 untreated hypoxic) were immediately frozen in liquid nitrogen and
stored at 80°C for later analysis of eNOS as described in
Immunoblot analysis.
Measurements in isolated perfused lungs. For lung perfusion, the tracheal cannula was attached to a large-animal piston-type ventilator, and the lungs were ventilated with a normoxic gas mixture (17% O2, 6% CO2, and balance N2), with a tidal volume of 15-20 ml/kg and a respiratory rate of 15-20 breaths/min (mean airway pressure of 4-6 cmH2O). A midline sternotomy was performed, and a clamp was placed across the ductus arteriosus. Saline-filled cannulas were placed into the pulmonary artery and left atrium through incisions in the right and left ventricles. The diaphragm and all abdominal contents were removed. The vascular cannulas were connected to the perfusion circuit as previously described (4, 5). The perfusion circuit was filled with 100-200 ml of the animal's own blood collected during exsanguination (as described in Measurements in anesthetized animals) and mixed with 50-100 ml of 3% albumin-saline. The perfusion circuit included a rotary pump (model 7523-00, Cole Palmer Masterflex) that continuously circulated the perfusate from a reservoir through a bubble trap into the pulmonary arterial cannula, through the lungs to the left atrial cannula, and back to the reservoir. Pulmonary arterial, left atrial, and airway pressures were continuously monitored. The most dependent edge of the lung was used as the zero reference for vascular pressures.
After connection to the perfusion circuit, the lungs were perfused for
30-60 min until a stable pulmonary arterial pressure was achieved.
The perfusate flow and left atrial pressure were adjusted to respective
levels of 50 ml · min1 · kg
1
and 0 cmH2O and were maintained
constant for the remainder of the study.
Changes in pulmonary arterial pressure in response to the
endothelium-dependent agent acetylcholine were then measured in some
lungs. Because baseline pulmonary arterial pressure is greater in
chronically hypoxic than in control animals (see Refs. 5 and 6 and
RESULTS), the pulmonary arterial
pressure in the control animals was elevated to a level comparable to
that in the chronically hypoxic animals by adding 1 M KCl to the
perfusate of the control lungs. Acetylcholine was added cumulatively to the reservoir to achieve concentrations of
109 to
10
6 M. The acetylcholine
responses were transient so that the pulmonary arterial pressure was
allowed to return to baseline between doses. After the response to
acetylcholine was measured, papaverine was added to the reservoir (300 µg/ml of perfusate) of most lungs and allowed to circulate for 20 min
to determine the contribution of vasomotor tone to pulmonary arterial
pressure. In a few other lungs (n = 5 untreated control and 2 untreated hypoxic), a similar protocol was
followed except that the responses to acetylcholine were not measured
before papaverine was added to the perfusate.
At the end of perfusion, some lungs from each group
(n = 4 untreated control, 5 nifedipine-treated control, 4 untreated hypoxic, and 4 nifedipine-treated hypoxic) were then immediately frozen in liquid
nitrogen and stored at 80°C for later analysis of eNOS as
described in Immunoblot analysis.
Immunoblot analysis. Tissue pieces
that did not contain large airways or large vessels were selected from
frozen perfused and unperfused lungs from treated and untreated piglets
from both the control (n = 4 perfused
and 1 unperfused untreated and 5 perfused nifedipine treated) and
chronically hypoxic (n = 4 perfused
and 1 unperfused untreated and 4 perfused nifedipine treated) groups. The tissue pieces were homogenized in 10 mM HEPES buffer containing 250 mM sucrose, 3 mM EDTA, and 1 mM phenylmethylsulfonyl fluoride, pH 7.4, on ice with three 15-s pulses of a Polytron blender, taking care to
avoid foaming of the homogenate. Protein concentration of the lung
homogenate was determined by the Bio-Rad protein assay. Each lung
homogenate was diluted with phosphate-buffered saline (PBS) to obtain a
protein concentration of 1 mg/ml. Forty microliters of each protein
concentration were solubilized in 40 µl of denaturing, reducing
buffer [Novex; 0.25 M Tris · HCl, 5%
(wt/vol) SDS, 2.5% (vol/vol) -mercaptoethanol, 10%
glycerol, and 0.05% bromphenol blue, pH 6.8], heated to 80°C
for 15 min, and centrifuged for 3 min at 5,600 g in a microfuge. Equal volumes (20 µl) of these supernatants were then applied to two Tris-glycine
precast 8% polyacrylamide gels (Novex) so that 10 µg of protein lung
homogenate samples were loaded on both gels. We used 10-µg protein
samples because Fike et al. (6) previously found that this amount of protein was within the dynamic range of our immunoblot analysis. Each
gel contained 10-µg protein samples from at least one
nifedipine-treated and one untreated lung from both the control and
chronically hypoxic groups. Furthermore, to normalize the results
between the two different blots, at least one lane of each gel was
loaded with 10 µg of protein from a lung homogenate that was
designated as the standard. Electrophoresis was carried out in 25 mM
Tris, 192 mM glycine, and 0.1% SDS (pH 8.3) at 125 V for 1.7 h. The
proteins were transferred from the gel to a nitrocellulose membrane
(Novex) at 10 V for 1 h in 25 mM Tris, 192 mM glycine, and 20%
methanol (pH 8.3). The membrane was incubated overnight at 4°C in
PBS containing 10% nonfat dried milk and 0.1% Tween 20 to block
nonspecific protein binding. To detect eNOS, the nitrocellulose
membrane was incubated for 1 h at room temperature with mouse
anti-human eNOS (Transduction Laboratories) diluted 1:500 in PBS
containing 0.1% Tween 20 and 1% nonfat dried milk (carrier buffer)
followed by incubation for 30 min at room temperature with a
biotinylated anti-mouse antibody (Vector Elite ABC kit, Vector
Laboratories) diluted 1:5,000 in the carrier buffer followed by
incubation for 30 min at room temperature with streptavidin-horseradish
peroxidase conjugate (Amersham) diluted 1:1,500 in PBS containing 0.1%
Tween 20. The nitrocellulose membrane was washed three times between
the first two incubations with the carrier buffer and three times with
the carrier buffer plus one time with PBS containing 0.1% Tween 20 after the final incubation. To visualize the biotinylated antibody, the
membranes were developed with enhanced chemiluminescence reagents
(Amersham), and the chemiluminescent signal was captured on X-Ray film
(Bio-Max MR, Kodak) with 1-min exposures. The bands for eNOS were
quantified with laser densitometry. The absorbance of the eNOS band for
the standard lung homogenate was used to normalize the peak absorbance of the eNOS bands on the gels.
Statistics. Data are presented as means ± SE. A one-way ANOVA with a multiple comparison test was used to compare the data between nifedipine-treated and untreated control and chronically hypoxic animals. P < 0.05 was indicative of significance.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
After 10-12 days of hypoxia, nifedipine-treated and untreated
chronically hypoxic piglets had higher hematocrits than both groups of
control piglets (Table 1). The
measured values of blood pH, PO2, and
PCO2 obtained during hemodynamic measurements in anesthetized piglets breathing room air were similar between all groups of piglets except for a slightly higher
PCO2 in the nifedipine-treated
control group (Table 1). For the perfused lungs, the hematocrits in
both groups of chronically hypoxic piglets were slightly higher than
the hematocrits in both groups of control piglets. The measured values
of pH, PO2, and
PCO2 in the perfusate of isolated
lungs from both the nifedipine-treated and untreated chronically
hypoxic piglets were not different from those in the control piglets
(Table 1).
|
Measurements of pulmonary arterial pressure, pulmonary wedge pressure,
left ventricular end-diastolic pressure, cardiac output, and aortic
pressure in the anesthetized piglets are shown in Table 2. Pulmonary arterial pressure was greater in the
untreated chronically hypoxic piglets than in the other three groups of
piglets. The pulmonary arterial pressure in the nifedipine-treated
group of chronically hypoxic piglets was intermediate in value between that in both groups of control piglets and that in untreated
chronically hypoxic piglets. Pulmonary wedge pressure did not
differ among nifedipine-treated chronically hypoxic, untreated control,
and nifedipine-treated control piglets but was less in these three groups than in the untreated chronically hypoxic piglets (Table 2).
Measurements of left ventricular end-diastolic pressure did not differ
significantly from measurements of pulmonary wedge pressure (Table 2)
and were used to calculate pulmonary vascular resistance if we were
unable to obtain a pulmonary wedge pressure. Cardiac output did not
differ between the untreated groups of control and hypoxic piglets but
was greater in the nifedipine-treated piglets than in their
corresponding group of untreated piglets (Table 2). The calculated
value of pulmonary vascular resistance [(pulmonary arterial
pressure pulmonary wedge pressure)/cardiac output] was
greater for the untreated chronically hypoxic piglets than for all the
other groups of piglets (Table 2, Fig.
1). Most importantly, the pulmonary vascular resistance was the same in the
nifedipine-treated chronically hypoxic piglets as in the untreated group of control piglets (Table 2, Fig. 1).
|
|
In the perfused lungs, left atrial pressure and perfusate flow were the
same in all groups and were maintained constant throughout the study so
that changes and differences in pulmonary arterial pressure,
respectively, represent changes and differences in pulmonary vascular
resistance. Note that the baseline pulmonary arterial pressure did not
differ between the nifedipine-treated and the corresponding group of
untreated piglets (Table 3) and that the baseline
pulmonary arterial pressure was greater in both groups of hypoxic
piglets than in either group of control piglets (Table 3). After the
addition of KCl, the pulmonary arterial pressure in the control groups
was raised to a level comparable to that in the hypoxic groups (Table
3). Addition of all doses of acetylcholine resulted in similar
decreases in pulmonary arterial pressure in the nifedipine-treated
piglets as in the corresponding groups of untreated piglets (Table 3,
Fig. 2). The response to all but the lowest dose of
acetylcholine was less in both the nifedipine-treated and untreated
groups of hypoxic lungs compared with either group of control lungs
(Table 3, Fig. 2). The addition of papaverine and removal of vasomotor
tone resulted in a pulmonary arterial pressure in the
nifedipine-treated group of chronically hypoxic piglets that was less
than the pulmonary arterial pressure in the untreated group of
chronically hypoxic piglets and that did not differ from the pulmonary
arterial pressure in either the treated or untreated group of control
piglets (Fig. 3).
|
|
|
One of the immunoblot analyses for eNOS in the whole lung homogenates
is shown in Fig. 4. In both the nifedipine-treated and untreated groups of control and chronically hypoxic lungs, the antibody
to eNOS detected eNOS at an apparent molecular mass of 135 kDa as determined from an exponential fit of molecular-mass standards.
Figure 5 shows the mean data for the absorbance of the
eNOS bands as determined by laser densitometry for the whole lung
homogenates from the untreated and nifedipine-treated control and the
untreated and nifedipine-treated chronically hypoxic lungs and shows
that absorbance of the eNOS bands was less for the lungs from both the
nifedipine-treated and untreated chronically hypoxic piglets compared
with that for the lungs from the untreated control piglets.
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In agreement with the findings of previous studies by Fike and colleagues (4-6), in this study we show that when exposed to 10-12 days of chronic hypoxia, newborn piglets develop pulmonary hypertension. Also in agreement with previous studies by Fike and colleagues (5, 6), the chronically hypoxic piglets exhibit blunted pulmonary vascular responses to the endothelium-dependent dilator acetylcholine and have reduced amounts of lung eNOS. A new finding is that the pulmonary vascular resistance in newborn piglets treated with nifedipine during chronic hypoxia did not differ from that in control piglets. This finding is consistent with the results of a study in adult models of pulmonary hypertension (17) and indicates that treatment with nifedipine ameliorates the development of pulmonary hypertension in our newborn model. Another new finding in this study is that the pulmonary arterial responses to acetylcholine were blunted and eNOS amounts were reduced in the lungs from chronically hypoxic piglets regardless of whether or not they were treated with nifedipine. This latter finding indicates that mechanisms other than an improvement in endothelial function or restoration of lung eNOS amounts underlie the ameliorative effect of nifedipine.
Although pulmonary vascular resistances in nifedipine-treated hypoxic and untreated control piglets did not differ in this study, the in vivo pulmonary arterial pressure was greater in the nifedipine-treated chronically hypoxic piglets than in the control piglets (Table 2). In addition, in the perfused lungs, the baseline pulmonary arterial pressure was greater in the nifedipine-treated hypoxic piglets than in the control piglets. This latter finding can be attributed to the influence of vasomotor tone in the isolated lung preparation because there was no diffference between pulmonary arterial pressures in nifedipine-treated hypoxic and untreated control lungs once the vasomotor tone was removed (Fig. 3). In regard to the in vivo measurements, it is probable that the measurement of pulmonary arterial pressure was affected by differences in left atrial pressure and cardiac output. Moreover, even though not as low as in the control piglets, the pulmonary arterial pressure in the nifedipine-treated hypoxic piglets was less than that in the untreated hypoxic piglets. This latter finding clearly indicates that although pulmonary hypertension was not completely prevented, nifedipine treatment inhibited the development of the disorder.
Had we used higher doses of nifedipine as in a study with chronically hypoxic adult rats (17), we might have achieved even greater reductions in pulmonary vascular resistance in the hypoxic piglets. However, the dose that we used is high compared with common clinical usage in newborns (1, 7), and in pilot studies, we found that larger doses than these were not well tolerated by the newborn piglets. The mechanism by which nifedipine treatment inhibits the development of pulmonary hypertension in either our newborn model or adult models remains unknown. Of course, part of the difficulty in determining the mechanism underlying the ameliorative effect of nifedipine is the lack of understanding of the pathogenesis of pulmonary hypertension in either newborns or adults. Endothelial dysfunction is one potential cause of pulmonary hypertension (11, 20, 22). Another possibility is that either in association with or separate from endothelial dysfunction, decreased production of endothelium-derived vasodilators such as nitric oxide could contribute to the development of pulmonary hypertension (11, 20, 22). Although the findings of Fike and colleagues (5, 6) and those of others (16, 19, 21) are supportive of the preceding mechanisms as a cause of neonatal pulmonary hypertension, our findings in the present study are also notable for providing evidence that mechanisms other than an improvement in endothelial function or restoration of lung eNOS amounts underlie the ameliorative influence of nifedipine. Indeed, one logical possibility is that nifedipine provided the reduction in smooth muscle tone, i.e., vasodilatory effect, that the dysfunctional pulmonary vascular endothelium and/or reduced lung eNOS could not.
The ability of nifedipine to reduce pulmonary arterial pressure and inhibit hypoxic pulmonary vasoconstriction from a smooth muscle cell vasorelaxant effect has been previously proposed as a mechanism for preventing pulmonary hypertension in chronically hypoxic adult animals (9, 17). That nifedipine can be an effective pulmonary vasodilator even in the nonhypoxic newborn pulmonary circulation is suggested by the slightly lower pulmonary vascular resistance in the nifedipine-treated than in the untreated control piglets (Fig. 1, Table 2). In addition to blockade of smooth muscle cell calcium channels, the vasodilatory effect of nifedipine could result from altered production of vasoactive agents. For example, nifedipine inhibited the production of the vasoconstrictor thromboxane by cultured rabbit aortic endothelial cells (13). Yet, it is important to note that despite effectively lowering pulmonary arterial pressure, not all smooth muscle cell vasodilators have been shown to inhibit the development of chronic hypoxia-induced pulmonary hypertension (17). The ability of nifedipine to ameliorate pulmonary hypertension might be more complex than can be explained by smooth muscle cell dilation.
One possibility is that nifedipine has an inhibitory effect on smooth muscle cell proliferation (12). Another possibility is that nifedipine modulates metabolism of collagens within the extracellular matrix (15). Both of these effects would help maintain a lower pulmonary vascular resistance by preventing the pulmonary vascular remodeling associated with chronic hypoxia-induced pulmonary hypertension (17, 18). The mechanism for these effects could involve a decrease in intracellular calcium concentration due to the inhibition of voltage-gated L-type calcium channels. That is, nifedipine might ameliorate pulmonary vascular wall changes by inhibiting the calcium-triggered transcription of a myriad of genes (14). Additional pathways independent of calcium may also be involved (3).
Supportive of the potential for the above-noted protective effects of nifedipine, other investigators (17) found that nifedipine treatment inhibited pulmonary vascular remodeling in chronically hypoxic adult animals. Because we did not perform morphometry, we do not know with certainty that nifedipine prevented the pulmonary vascular remodeling that we (4) and others (8) have found in chronically hypoxic newborn piglets. However, our finding that with removal of vasomotor tone, the pulmonary vascular resistance in isolated lungs from nifedipine-treated hypoxic piglets did not differ from that in untreated control piglets provides evidence that the pulmonary vascular bed does not differ structurally in these two groups of piglets (Fig. 3). In addition, consistent with our previous findings (4), structural remodeling is the most likely explanation for the persistently greater pulmonary arterial pressure in the untreated hypoxic lungs than in all other groups of lungs even with removal of vasomotor tone (Fig. 3).
Our finding that lung eNOS amounts were reduced in the lungs of hypoxic piglets regardless of nifedipine treatment merits some additional comments. Oxygen tension and shear stress are two stimuli that have been shown to regulate eNOS expression (2, 10). In the chronically hypoxic piglet model, oxygen tension changes but so do a number of determinants of shear stress including pulmonary arterial pressure, cardiac output, and hematocrit. Whether any or all of these stimuli are responsible for the reduced eNOS observed in the lungs of chronically hypoxic piglets remains unknown. Of these stimuli, it is of interest that findings in fetal lambs with pulmonary hypertension due to in utero closure of the ductus arteriosus support the notion that prolonged in vivo exposure to elevated pulmonary arterial pressure decreases lung eNOS in immature animals (16, 21). In this regard, the reason that lung eNOS amounts remained reduced despite nifedipine treatment could be due to the failure of nifedipine to completely reduce pulmonary arterial pressure in the hypoxic piglets to the level of control animals. Other possibilities are that the potential to restore lung eNOS by lowering pulmonary arterial pressure was offset by a direct effect of hypoxia or by some other effect of the nifedipine treatment such as increased cardiac output.
In summary, we found that nifedipine-treatment attenuated the development of pulmonary hypertension in a newborn model and that the effectiveness of the treatment was not due to an improvement in endothelial dysfunction nor to preventing a reduction in lung eNOS amounts. It seems logical that the presence of endothelial dysfunction and decreased lung eNOS amounts increase the likelihood that there will be worsening of the pulmonary hypertensive process so that counteracting, reversing, or preventing these alterations remains a reasonable therapeutic target that requires further exploration.
![]() |
ACKNOWLEDGEMENTS |
---|
This work was supported in part by a Children's Hospital of Wisconsin Foundation Grant and a March of Dimes Birth Defects Foundation Research Grant.
![]() |
FOOTNOTES |
---|
Present address of and address for reprint requests and other correspondence: C. D. Fike, Dept. of Pediatrics, Wake Forest Univ. Baptist Medical Center, Medical Center Blvd., Winston-Salem, NC 27157-1081.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Received 4 November 1998; accepted in final form 23 April 1999.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Brownlee, J. R.,
R. H. Beekman,
and
A. Rosenthal.
Acute hemodynamic effects of nifedipine in infants with bronchopulmonary dysplasia and pulmonary hypertension.
Pediatr. Res.
24:
186-190,
1988[Abstract].
2.
Davies, P. F.
Flow-mediated endothelial mechanotransduction.
Physiol. Rev.
75:
519-560,
1995
3.
Eickelberg, O.,
M. Roth,
and
L.-H. Block.
Effects of amolodipine on gene expression and extracellular matrix formation in human vascular smooth muscle cells and fibroblasts: implications for vascular protection.
Int. J. Cardiol.
62, Suppl. 2:
S31-S37,
1997[Medline].
4.
Fike, C. D.,
and
M. R. Kaplowitz.
Effect of chronic hypoxia on pulmonary vascular pressures in isolated lungs of newborn pigs.
J. Appl. Physiol.
77:
2853-2862,
1994
5.
Fike, C. D.,
and
M. R. Kaplowitz.
Chronic hypoxia alters nitric oxide-dependent pulmonary vascular responses in lungs of newborn pigs.
J. Appl. Physiol.
81:
2078-2087,
1996
6.
Fike, C. D.,
M. R. Kaplowitz,
C. J. Thomas,
and
L. D. Nelin.
Chronic hypoxia decreases nitric oxide production and endothelial nitric oxide synthase in newborn pig lungs.
Am. J. Physiol.
274 (Lung Cell. Mol. Physiol. 18):
L517-L526,
1998
7.
Garson, A., Jr.
(Editor).
The Science and Practice of Pediatric Cardiology. Baltimore, MD: Williams and Wilkins, 1998, p. 2251
8.
Haworth, S. G.,
and
A. A. Hislop.
Effect of hypoxia on adaptation of the pulmonary circulation to extra-uterine life in the pig.
Cardiovasc. Res.
16:
293-303,
1982[Medline].
9.
McMurtry, I. F.,
A. B. Davidson,
J. T. Reeves,
and
R. F. Grover.
Inhibition of hypoxic pulmonary vasoconstriction by calcium antagonists in isolated rat lungs.
Circ. Res.
38:
99-104,
1976[Abstract].
10.
McQuillan, G.,
K. Leung,
P. A. Marsden,
S. K. Kostyk,
and
S. Kourembanas.
Hypoxia inhibits expression of eNOS via transcriptional and posttranscriptional mechanisms.
Am. J. Physiol.
267 (Heart Circ. Physiol. 36):
H1921-H1927,
1994
11.
Morin, F. C., III,
and
K. R. Stenmark.
Persistent pulmonary hypertension of the newborn.
Am. J. Respir. Crit. Care Med.
151:
2010-2032,
1995[Medline].
12.
Nikol, S.,
T. Y. Huehns,
and
B. Hofling.
Novel uses and potential for calcium antagonists in revascularization.
Eur. Heart J.
18, Suppl. A:
A105-A109,
1997[Medline].
13.
Ramadan, F. M.,
G. R. Upchurch,
B. A. Keagy,
and
G. Johnson.
Endothelial cell thromboxane production and its inhibition by a calcium-channel blocker.
Ann. Thorac. Surg.
49:
916-919,
1990[Abstract].
14.
Roche, E.,
and
M. Prentki.
Calcium regulation of immediate-early response genes.
Cell Calcium
16:
331-338,
1994[Medline].
15.
Roth, M.,
O. Eickelberg,
E. Kohler,
P. Erne,
and
L. Block.
Ca2+ channel blockers modulate metabolism of collagens within the extracellular matrix.
Proc. Natl. Acad. Sci. USA
93:
5478-5482,
1996
16.
Shaul, P. W.,
I. S. Yuhanna,
Z. German,
Z. Chen,
R. H. Steinhorn,
and
F. C. Morin III.
Pulmonary endothelial NO synthase gene expression is decreased in fetal lambs with pulmonary hypertension.
Am. J. Physiol.
272 (Lung Cell. Mol. Physiol. 16):
L1005-L1012,
1997
17.
Stanbrook, H. S.,
K. G. Morris,
and
I. F. McMurtry.
Prevention and reversal of hypoxic pulmonary hypertension by calcium antagonists.
Am. Rev. Respir. Dis.
130:
81-85,
1984[Medline].
18.
Stenmark, K. R.,
J. Fasules,
D. M. Hyde,
N. F. Voelkel,
J. Henson,
A. Tucker,
H. Wilson,
and
J. T. Reeves.
Severe pulmonary hypertension and arterial adventitial changes in newborn calves at 4,300 m.
J. Appl. Physiol.
62:
821-830,
1987
19.
Tulloh, R. M. R.,
A. A. Hislop,
P. J. Boels,
J. Deutsch,
and
S. G. Haworth.
Chronic hypoxia inhibits postnatal maturation of porcine intrapulmonary artery relaxation.
Am. J. Physiol.
272 (Heart Circ. Physiol. 41):
H2436-H2445,
1997
20.
Vender, R. L.
Chronic hypoxic pulmonary hypertension: cell biology to pathophysiology.
Chest
106:
236-243,
1994[Medline].
21.
Villamor, E.,
T. D. Le Cras,
M. P. Horan,
A. C. Halbower,
R. M. Tuder,
and
S. H. Abman.
Chronic intrauterine pulmonary hypertension impairs endothelial nitric oxide synthase in the ovine fetus.
Am. J. Physiol.
272 (Lung Cell. Mol. Physiol. 16):
L1013-L1020,
1997
22.
Voelkel, N. F.,
and
R. M. Tuder.
Cellular and molecular mechanisms in the pathogenesis of severe pulmonary hypertension.
Eur. Respir. J.
8:
2129-2138,
1995
HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Visit Other APS Journals Online |