Developmental Changes in Prostaglandin E2 Receptor Subtypes in Porcine Ductus Arteriosus Possible Contribution in Altered Responsiveness to Prostaglandin E2 Mousumi Bhattacharya, PhD; Pierre Asselin, PhD; Pierre Hardy, MD; Anne-Marie Guerguerian, MD; Hitoshi Shichi, PhD; Xin Hou, MD, PhD; Daya R. Varma, MD, PhD; Asma`a Bouayad, MSc; Jean-Claude Fouron, MD; Ronald I. Clyman, MD; Sylvain Chemtob, MD, PhD Background—Prostaglandin E2 (PGE2) is important in ductus arteriosus (DA) patency, but the types of functional PGE2 receptors (EP) in the developing DA are not known. We postulated that age-dependent alterations in EP and/or their subtypes may possibly contribute to the reduced responsiveness of the newborn DA to PGE2. Methods and Results—We determined PGE2 receptor subtypes by competition binding and immunoblot studies on the DA of fetal ('75% and 90% gestation) and newborn (,45 minutes old) pigs. We studied the effects of EP receptor stimulation on cAMP signaling in vitro and on term newborn (,3 hours old) DA patency in vivo. Fetal pig DA expressed EP2, EP3, and EP4 receptors equivalently, but not EP1. In neonatal DA, EP1, EP3, and EP4 were undetectable, whereas EP2 density was similar in fetus and newborn. Prostaglandin-induced changes in cAMP mirrored binding data. 16,16-Dimethyl PGE2 and 11-deoxy PGE1 (EP2/EP3/EP4 agonist) produced more cAMP in fetus than newborn, but butaprost (selective EP2 agonist) caused similar cAMP increases in both; EP3 and EP4 ligands (M&B28767 and AH23848B, respectively) affected cAMP production only in fetus. After birth, administration of butaprost alone was as effective as 11-deoxy PGE1 and 16,16-dimethyl PGE2 in dilating DA in vivo. Conclusions—The data reveal fewer PGE2 receptors in the DA of the newborn than in that of the fetus; this may contribute to the decreased responsiveness of the DA to PGE2 in newborn. Because EP2 receptors seem to mediate the effects of PGE2 on the newborn DA, one may propose that a selective EP2 agonist may be preferred as a pharmacological agent to maintain DA patency in infants with certain congenital heart diseases. (Circulation. 1999;100:1751-1756.) Key Words: ductus arteriosus n receptors n prostaglandins n pediatrics
P
rostaglandins play a major role in maintaining patency of the fetal ductus arteriosus (DA).1,2 The marked sensitivity of the DA to prostaglandin E2 (PGE2) suggests that this is the most important prostanoid regulating vessel patency.3 PGE2 exerts its effects through a diverse group of receptors, classified as EP1, EP2, EP3, and EP4.4 Activation of EP1 increases inositol 1,4,5-triphosphate (IP3) formation and elicits vasoconstriction,5 stimulation of EP2 and EP4 increases cAMP and leads to vasodilation,4,6 and stimulation of EP3 decreases cAMP and opposes vasodilation.4 At present, the relative types and importance of EP receptors in the DA are uncertain. Pharmacological evidence suggests that the EP4 receptor is the predominant PGE2 receptor in the fetal rabbit DA.7 Conversely, genetic disruption of the EP4 receptor does not diminish DA patency in the fetal and neonatal mouse.8 However, the type of EP receptors expressed in higher species, and especially in the newborn, is
not known. This is of particular relevance because responsiveness of the DA to PGE2 in the newborn is significantly less than that in the fetus.9,10 Because PGE2 acts on several distinct receptor subtypes, each coupled to different second messengers, we hypothesized that differences in the relative density and/or proportion of EP receptors could explain, at least in part, the differences in the responsiveness of the fetal and neonatal DA to PGE2.9,10 We therefore studied the expression of EP receptor subtypes and EP receptor signaling factors in the DA of fetal and newborn pigs. We also assessed the role of these receptors in the newborn in vivo. Our findings reveal that the DA of the fetal pig expresses negligible amounts of the EP1 receptor but does express the other 3 EP subtypes (EP2, EP3, EP4) in equivalent proportions. In the DA of the newborn pig, the density of PGE2 receptors is significantly reduced compared with that in the fetus because of complete loss of EP3 and EP4
Received March 16, 1999; revision received June 8, 1999; accepted June 14, 1999. From the Departments of Pharmacology and Therapeutics, McGill University (M.B., D.R.V., S.C.), and the Departments of Pediatrics and Pharmacology, Universite´ de Montre´al (P.A., P.H., A.-M.G., X.H., A.B., J.-C.F., S.C.), Montre´al, Quebec, Canada; the Department of Ophthalmology, Wayne State University, Detroit, Mich (H.S.); and the Department of Pediatrics, University of California at San Francisco (R.I.C.). Correspondence to Sylvain Chemtob, MD, PhD, FRCP(C), Research Center, Ste-Justine Hospital, 3175 Coˆte Ste-Catherine, Montre´al, Que´bec, Canada, H3T 1C5. E-mail
[email protected] © 1999 American Heart Association, Inc. Circulation is available at http://www.circulationaha.org
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receptors; however, the number of EP2 receptors remains unchanged, such that EP2 seems to mediate all PGE2dependent relaxation in the newborn DA.
Methods Animals DAs were removed from fetal pigs (78 to 90 and 100 to 105 days of gestation [term, 114 days]) and term newborn piglets (1.25 to 1.7 kg, killed within 45 minutes of vaginal birth with pentobarbital [120 mg/kg intracardiac] under halothane anesthesia). Tissues were immediately rinsed in ice-cold Krebs buffer (pH 7.4) of the following composition (mmol/L): NaCl 120, KCl 4.5, CaCl2 2.5, MgSO4 1.0, NaHCO3 27, KH2PO4 1.0, and glucose 10 and then frozen in liquid N2; we have shown that freezing does not affect PGE2 binding.11 A group of newborn piglets (,3 hours old) was used to study the effects of prostaglandin analogues on DA diameter in vivo.
EP Receptor Characterization Tissues were prepared for prostaglandin binding as described.11–13 Aliquots of DA homogenate (200 mg protein) were incubated at 37°C for 30 minutes with various concentrations of [3H]PGE2 (Amersham) in the presence or absence of 25 mmol/L 16,16dimethyl PGE2. The reaction was terminated with ice-cold 5 mmol/L Tris-HCl buffer (pH 7.4), the homogenate was filtered through Whatman GF/C glass filter disks, and the radioactivity was counted with a b-counter (Beckman LS 7500). Subtypes of PGE2 receptors were studied by displacement of bound [3H]PGE2 with 16,16dimethyl PGE2, AH6809 (Glaxo-Wellcome), butaprost (Bayer), M&B28,767 (Rhone-Poulenc Rorer), and sulprostone, 11-deoxy PGE1, and AH23848B (Glaxo-Wellcome).4 Receptor densities (Bmax), affinity constants (Kd), and concentrations of ligands that displace 50% of bound [3H]PGE2 (IC50) were determined from Scatchard plots and displacement curves with the computer programs Prism (GraphPad) and Ligand, respectively.14
Immunoblotting of EP Receptors Western blotting of EP1, EP3a, and EP4 receptors was conducted15 on DA membranes prepared as described13 and on cell lysates from human embryonic kidney (HEK) 293 cells (Invitrogen), which overexpress each of these receptors16 and hence were used as positive controls. After immunoblotting with EP1, EP3a, or EP4 specific polyclonal rabbit antibodies17 (1:1000; EP2 antibodies are not available), immunoreactive bands were visualized by chemiluminescence (Amersham) according to the manufacturer’s instructions.
cAMP Assay The effects of PGE2 analogues on cAMP were determined.12,13 Briefly, DA homogenates (100 mg protein) were incubated in an assay mixture (100 mL) containing 10 mmol/L Tris-HCl buffer (pH 8.0), 1 mmol/L ATP, 7.5 mmol/L MgCl2, 15 mmol/L creatine phosphate, 185 U/mL creatine phosphokinase, 200 mg/mL aspirin, 0.5 mmol/L EGTA, 0.5 mmol/L 3-isobutyl-1-methylxanthine, 1 mmol/L dithiothreitol, 1 mmol/L benzamidine, 0.1 mmol/L phenylmethylsulfonyl fluoride, and 100 mg/mL soybean trypsin inhibitor in the presence or absence of test agents at 37°C for 10 minutes. The reaction was terminated with 200 mL acidic ethanol. After centrifugation, cAMP was measured by radioimmunoassay (Diagnostic Products).
Surgical Preparation and Echocardiography Newborn pigs (between 1.5 and 2 hours after delivery; 1.3 to 1.7 kg) were prepared to test the effects of specific EP receptor agonists on DA patency; in the piglet, the DA closes completely by 4 to 6 hours of age.18 We were not able to perform in vivo studies on fetal pigs because facilities were not available to operate on sows. The newborn piglets were anesthetized with halothane (2%) for 15 minutes during tracheostomy and catheterization of the umbilical
vein and artery, and anesthesia was discontinued after surgery. Animals were ventilated with air with a Harvard small-animal respirator, maintained on a-chloralose (50 mg/kg bolus followed by 10 mg z kg21 z h21 infusion), and paralyzed with pancuronium (0.1 mg/kg); body temperature was maintained at 38°C. The surgical procedure was completed within 15 minutes, and piglets were allowed to stabilize for an additional 30 minutes. Echocardiographic measurements were performed with an Acuson 128 XP/10C real-time ultrasound imaging system using 7.5- and 5-MHz transducers duplexed with a range-gated Doppler as previously described19,20; Doppler signals were filtered by 100-Hz highpass filter. The DA was visualized through a left second intercostal parasternal approach. Measurements of the DA diameter were repeated 3 times. The smallest diameter of the DA lumen was monitored until it reached 0.6 to 0.8 mm in diameter. Experimental drugs were then injected, and the smallest diameter was measured every minute for the next 10 to 25 minutes. Animals (3 to 4 per treatment) were randomly assigned to receive 10-minute infusions of saline (1 mL, controls) or 0.083 mg z kg21 z min21 of EP receptor agonists; the doses used have been shown previously to be effective in vivo.21 The effect of EP receptor agonists on DA patency was also tested in animals pretreated with indomethacin (3 mg/kg IV for 5 minutes), once the DA diameter reached 0.6 to 0.9 mm (within 20 minutes).
Statistical Analysis Data were analyzed by Student’s t test and by 2-way ANOVA factoring for time and treatment; means tests were compared by the Tukey-Kramer method. Statistical significance was set at P,0.05. Data are expressed as mean6SEM.
Results PGE2 Receptors in Fetal and Newborn DA [3H]PGE2 bound specifically to fetal and newborn DA membranes. Maximum binding of [3H]PGE2 to the fetal DA was similar at both gestational ages studied (78 to 90 days: 34.962.5 fmol/mg protein, n53; 100 to 105 days: 35.163.1 fmol/mg protein, n53). Maximum specific binding of [3H]PGE2 was 3-fold greater in fetal than newborn DA (Figure 1A and 1B and Table 1); the Kd did not differ between the fetus and newborn. In fetal DA membrane preparations (Figure 1C), butaprost (EP2 agonist), M&B28,767 (EP3 agonist), sulprostone (EP1/ EP3 receptor agonist), and AH23848B (EP4 antagonist) caused an equivalent displacement of [3H]PGE2 (Figure 1C and 1E and Table 2); 11-deoxy PGE1 (EP2/EP3/EP4 agonist) displaced virtually all [3H]PGE2, but the EP1 antagonist AH6809 was ineffective (Figure 1C and 1E and Table 2). In contrast to fetal DA, [3H]PGE2 bound to newborn DA membranes was no longer displaced by M&B28,767, sulprostone, or AH23848B (Figure 1D). Butaprost and 11-deoxy PGE1 were the only PGE2 analogues (along with 16,16dimethyl PGE2) capable of fully displacing [3H]PGE2 from the newborn DA (Figure 1D and Table 2). IC50 values of ligands tested were comparable to those reported in other porcine tissues.11,12 Results indicate the presence of EP2, EP3, and EP4 in fetal DA. In the immediate postnatal newborn, EP3 and EP4 are absent, without significant change in the number of EP2 receptors (Figure 1E); this is reflected by the reduced [3H]PGE2 binding in the newborn DA (Figure 1A and 1B and Table 1).
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Figure 1. Representative curves of specific binding and displacement of [3H]PGE2 on DA membranes of fetal and newborn pigs. A, Saturation isotherm of specifically bound [3H]PGE2. Because maximum binding in fetuses at 78 to 90 and 100 to 105 days of gestation was similar, fetal tissues from both ages were combined in figures referring to fetus. B, Scatchard analysis of saturation isotherms in A. C and D, Displacement of specifically bound [3H]PGE2 (8 nmol/L) in DA of fetal (C) and neonatal (D) pigs by 16,16-dimethyl PGE2 ( f ), EP1 antagonist AH6809 ( ), EP2 agonist butaprost (F), EP3 agonist M&B28,767 ( ƒ ), EP1/EP3 agonist sulprostone ( ‚ ), EP4 antagonist AH23848B (E), and EP2/EP3/EP4 agonist 11-deoxy PGE1 ( Œ ). E, Estimated Bmax of specific EP receptors was calculated as maximum binding of PGE23proportion of EP subtypes derived from indicated ligands.
Expression of EP1, EP3a, and EP4 Immunoreactive Protein in DA of Fetal and Newborn Pig The DA of the fetal pig, but not of the newborn, expressed EP3a (55-kDa band) and EP4 (63-kDa band) immunoreactive protein consistent with binding data (Figure 2); EP2 antibodies are unavailable.
PGE2 Analogue–Induced Production of cAMP PGE2 receptor– coupled changes in cAMP generation were also consistent with the binding data. 16,16-Dimethyl PGE2 TABLE 1. Maximum Binding and Affinity Constant of [3H]PGE2 on DA Membranes From Fetal and Newborn Pigs Variables
Fetus
Newborn
Bmax, fmol/mg protein
34.962.5
12.361.6*
Kd, nmol/L
10.863.0
6.162.3
Values are the mean6SEM of 3 or 4 experiments, each performed in duplicate. Because Bmax in fetus 78 to 90 and 100 to 105 days of gestation was similar, fetal tissue from both ages were combined for all tables. *P,0.01 vs corresponding value for fetus.
and 11-deoxy PGE1 (EP2/EP3/EP4 agonist) produced a comparable dose-dependent increase in cAMP synthesis, which was greater in fetus than in newborn (Table 3). In fetal DA, butaprost (EP2 agonist) stimulated cAMP production in a concentration-dependent manner. The EP3 agonist M&B28,767 and EP1/EP3 agonist sulprostone had no effect on cAMP formation by themselves but reduced forskolin-induced cAMP synthesis; this suggests that EP3 is coupled to inhibition of cAMP formation. Because no selective EP4 agonist is currently available, we estimated the effects attributed to EP4, as we previously reported,12 by subtracting the increase in cAMP produced by the combination of 16,16-dimethyl PGE2 and EP4 antagonist AH23848B (which would stimulate all of the EP receptors except EP4) from the increase in cAMP produced by 16,16-dimethyl PGE2 alone (which stimulates all EP receptors). In the fetal DA, AH23848B decreased the cAMP production induced by 16,16-dimethyl PGE2 but not that stimulated by butaprost (Table 3).
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Competing Agents 16,16-Dimethyl PGE2 AH6809
Newborn
% Inhibition of Binding
IC50, nmol/L
% Inhibition of Binding
IC50, nmol/L
10060
3164
10060
28.562.5
,1
11-Deoxy PGE1
9466
Butaprost M&B28,767 Sulprostone AH23848B
ND
,1
ND
3065.0
9664
3865.5
3262*
157612
9861
18769.6
4263
260613
,1
ND
4364
128613
,1
ND
3262
150506323
,1
ND
Values are mean6SEM of 3 to 5 experiments, each performed in duplicate. Concentration of [3H]PGE2 was 8 nmol/L. ND indicates not determined (inhibition of binding was too low for accurate calculation of IC50). *P,0.01 vs corresponding value in newborn.
In the newborn DA, butaprost increased cAMP generation to values comparable to those in the fetus (Table 3); M&B28,767, sulprostone, and AH23848B had no effect on cAMP production.
Effects of EP Receptor Agonists on DA Diameter In Vivo We examined the effects of EP receptor agonists (17-phenyltrinor PGE2 [EP1]; butaprost [EP2]; M&B28,767 [EP3]; sulprostone [EP1/EP3]; and 11-deoxy PGE1 [EP2/EP3/EP4]) on patency of the newborn DA in vivo (Figure 3). 16,16Dimethyl PGE2 dilated both the untreated, spontaneously closing (Figure 3A) and the indomethacin-constricted DA (Figure 3B). Butaprost and 11-deoxy PGE1 dilated the constricting DA as seen with 16,16-dimethyl PGE2 (Figure 3); cessation of infusion of these PGE2 analogues resulted in constriction of the DA. In contrast, 17-phenyl-trinor PGE2, M&B28,767, and sulprostone did not affect DA diameter; 2-
Figure 2. Immunoblot of EP1, EP3a, and EP4 receptor proteins (arrows) in DA of fetal (F) and newborn (N) pigs and in cell lysates from HEK 293 cells overexpressing EP1, EP3a, and EP4 receptors separately (positive controls). Molecular weight protein markers (kDa) are on right.
to 3-fold higher infusion rates of the EP1 and EP3 agonists also had no effects (data not shown). Hence, the vasodilatory effects of PGE2 in the newly born seem to be accounted for by action on EP2.
Discussion Previous pharmacological studies have suggested that EP4 is the dominant (relaxant) PGE2 receptor in the fetal rabbit DA.7 In the mouse, however, disruption of the EP4 gene did not affect ductal patency,8 suggesting possible species differences. We therefore set out to characterize the EP receptors in the DA of the fetus and newborn of a higher species, namely the pig. Using binding and displacement, immunoblot, and stimulation of second-messenger cAMP, our studies revealed that the number and types of PGE2 receptors differ between fetal and immediate postnatal newborn DA. There was a 3-fold higher density of PGE2 receptors and a greater PGE2-induced increase in cAMP in the fetus than in the newborn (Table 3); a rise in cAMP is usually associated with vasorelaxation.6 We identified EP2, EP3, and EP4 receptors in the fetal pig DA; EP1 receptor was undetectable (Figures 1 and 2). In the newborn DA, we observed a decrease in PGE2 binding due to a loss of EP3 and EP4 receptors (Figures 1C through 1E and 2); the number of EP2 receptors was essentially the same in the fetus and newborn. As a result, the EP2 receptor appeared to mediate the vasorelaxant effects of PGE2 on the full-term neonatal DA (Figure 3). The mechanism(s) responsible for the birth-related decrease in PGE2 receptors in the DA are currently unknown. We have previously observed that the loss of DA responsiveness to PGE2 is directly related to the degree of postnatal DA constriction.9 However, a role for hypoxia to explain the selective loss of EP3 and EP4 is unlikely. Our data on [3H]PGE2 binding, immunoreactivity, and cAMP generation in newborn were obtained on DA of animals ,45 minutes after birth. Although a 50% ductal constriction occurs over this time period,18 the partial pressure of oxygen also rises markedly immediately after birth; as a result, the DA tunica media may not develop significant hypoxia during this time
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TABLE 3. Effects of PGE2 Analogues and Forskolin on Net cAMP Synthesis on DA From Fetal and Newborn Pigs Net cAMP synthesis, pmol z mg protein21 z min21 Agent
Fetus
Newborn
16,16-Dimethyl PGE2 0.05 mmol/L
0.860.2
0.560.2
16,16-Dimethyl PGE2 0.1 mmol/L
1.560.2
0.8560.1*
16,16-Dimethyl PGE2 1 mmol/L
2.260.3
1.2560.2*
11-Deoxy PGE1 0.1 mmol/L
1.460.2
0.860.1*
2.0560.3
1.060.2*
11-Deoxy PGE1 1 mmol/L Butaprost 0.1 mmol/L
0.660.1‡
Butaprost 1 mmol/L
0.660.2
1.2560.4
1.560.4
1.360.3
1.4560.4
Sulprostone 1 mmol/L
,0.1
,0.1
M&B28,767 1 mmol/L
0.260.1†
Butaprost 1 mmol/L1AH23848B 10 mmol/L
,0.1
Forskolin 0.1 mmol/L
19.060.6
15.061.4
Forskolin 0.1 mmol/L1M&B28,767 1 mmol/L
15.961.1§
14.861.6
Forskolin 0.1 mmol/L1Sulprostone 1 mmol/L
15.761.0§
13.762.0
AH23848B 10 mmol/L
0.260.1†
,0.1
AH23848B 10 mmol/L116,16-dimethyl PGE2 0.1 mmol/L
0.660.05‡
0.960.05
AH23848B 10 mmol/L116,16-dimethyl PGE2 1 mmol/L
0.9560.2†
1.2560.3
Values are mean6SEM of 4 or 5 experiments, each performed in duplicate. The net maximum stimulated production of cAMP was corrected for basal (unstimulated) synthesis of cAMP, which was 4.160.7 pmol z mg protein21 z min21 for newborn and 2.960.6 pmol z mg protein21 z min21 for fetus. *P,0.05 vs values in fetus; †P,0.05 vs corresponding values with 16,16dimethyl PGE2 (1 mmol/L); ‡P,0.05 vs corresponding values with 16,16-dimethyl PGE2 (0.1 mmol/L); §P,0.05 vs corresponding values with forskolin alone.
period. In support of this inference, tissues from 15-minuteold newborn animals exhibited [3H]PGE2 binding properties similar to those of piglets 30 to 45 minutes old (data not shown). Another more likely explanation for the changes in EP receptor profile after birth relates to the sharp increase in PGE2 concentrations in both the DA and the circulating plasma during the perinatal period.3,20,22,23 We have previously observed that EP3 and EP4 receptors in cerebral and ocular vessels can be altered by high levels of circulating PGE2 concentrations in the perinatal period.12,13 EP2 receptors, conversely, do not appear to be regulated by PGE2 concentrations.12 We speculate that the EP receptors in the DA also may undergo this same type of homologous downregulation during the perinatal period when plasma PGE2 levels peak at the end of labor.24 Although PGE2 levels decrease immediately after birth to reach fetal values by 1 to 2 hours,24 this time period is insufficient to reverse the downregulation of PGE2 receptors.13 A reduction in PGE2 receptors associated with a decrease in PGE2-induced cAMP formation in the immediately postnatal newborn is consistent with and may contribute to the reduced responsiveness to PGE2 of the newborn DA compared with that of the fetus.9,10 In the present study, we
Figure 3. Effects of PGE2 receptor agonists on DA diameter in newborn pigs. A, DA diameter in newborn pigs after infusion of saline (E), 16,16-dimethyl PGE2 ( f ), EP2/EP3/EP4 agonist 11-deoxy PGE1 ( Œ ), EP1 agonist 17-phenyl-trinor PGE2 ( M ), EP2 agonist butaprost (F), EP3 agonist M&B28,767 ( ƒ ), or EP1/EP3 agonist sulprostone (‚); diameter of aorta at isthmus was 5.860.9 mm. Effects of agents were studied when DA closed spontaneously to reach a diameter of 0.6 to 0.8 mm (at '2.5 to 3 hours old). Shaded area along abscissa corresponds to period of PGE2 analogue infusion (0.083 mg z kg21 z min21 IV). B, DA diameter of newborn pigs (1.5 hours old) first treated with indomethacin (INDO, 3 mg/kg IV) and subsequently infused with saline (E), 16,16-dimethyl PGE2 (f), 17-phenyl-trinor PGE2 ( M ), butaprost (F), or M&B28,767 ( ƒ ). Shaded area along abscissa corresponds to period of PGE2 analogue infusion (0.083 mg z kg21 z min21 IV). Arrow points to time of administration of indomethacin. Effects of PGE2 analogues were determined on DA when it reached a diameter similar to that in A. Ductal diameter was measured by echocardiogram as described in Methods section. Values are mean6SEM of 3 to 4 experiments for each agent. *P,0.05 vs corresponding values for saline, 17-phenyltrinor PGE2, M&B28,767, and sulprostone (ANOVA and TukeyKramer method).
focused on ontogenic changes in PGE2 receptors in the DA. Other mechanisms are also likely to participate in this age-dependent altered responsiveness of the DA to PGE2.9,10 These include developmental changes in the rates of prostaglandin production, uptake, and degradation as well as in prostaglandin-coupled signal transduction and relaxant mechanisms, and the role of increasing oxygen tension on ductal
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function,25 which has been debated26; these various aspects need to be examined separately. In summary, the present study demonstrates a developmental alteration of EP receptors in the DA. However, changes in EP receptor profile in DA of the prematurely born newborn remain to be determined. The present study also provides a physiological basis for the potential use of more selective EP receptor ligands to control DA patency and potentially diminish the side effects associated with nonselective PGE therapy.27 For example, one could suggest specific therapies for maintaining ductal patency in infants with congenital heart disease, such as selective EP2 agonists, and possibly reduce PGE2-mediated fever due to EP3 stimulation.28 In the future, selective EP receptor antagonists targeted toward inflammation,29 fever,28 and pain21 in the pregnant subject will also need to be evaluated for their effects on the fetal DA.
Acknowledgments This study was supported by grants from the Medical Research Council of Canada, the Heart and Stroke Foundation of Quebec, and the Fonds de la Recherche en Sante´ du Que´bec, and from the US Public Health Service, NIH, NHLBI HL-46691. The authors thank Hendrika Fernandez and Manon Lessard for their technical assistance. M. Bhattacharya and Dr Hardy are recipients of Doctoral Research and Fellowship Awards, respectively, from the Medical Research Council of Canada.
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Developmental Changes in Prostaglandin E2 Receptor Subtypes in Porcine Ductus Arteriosus : Possible Contribution in Altered Responsiveness to Prostaglandin E2 Mousumi Bhattacharya, Pierre Asselin, Pierre Hardy, Anne-Marie Guerguerian, Hitoshi Shichi, Xin Hou, Daya R. Varma, Asmàa Bouayad, Jean-Claude Fouron, Ronald I. Clyman and Sylvain Chemtob Circulation. 1999;100:1751-1756 doi: 10.1161/01.CIR.100.16.1751 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1999 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. Online ISSN: 1524-4539
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