Function of cyclo-oxygenase-1 and cyclo-oxygenase-2 in the ductus arteriosus from foetal lamb: differential development and change by oxygen and endotoxin

Relationship between gentamicin administration and ductal patency in very low birth weight infants

Background:

Patent ductus arteriosus (PDA) is associated with adverse clinical outcomes in very low birth weight (<1500g) infants.

Objective:

In our study, it was aimed to investigate the effect of gentamicin treatment, which is frequently used for early-onset sepsis on ductal patency.

Method:

We performed a single-center retrospective review of charts of preterm infants <32 weeks gestation with birth weight <1500 grams born between June 1, 2015, and December 31, 2019, at the neonatal intensive care unit. All infants underwent an echocardiogram (ECHO) at 72 hours. To determine the effect of gentamicin treatment on hemodynamically significant PDA (hsPDA), we compared the frequency and duration of gentamicin administration between infants with hsPDA and without hsPDA.

Results:

During the study period, 792 patients were evaluated. Gentamicin was given to more infants with hsPDA than to those without hsPDA (89.2 % vs. 64.6 %, p<0.001), and the duration of therapy was longer in those infants with hsPDA (7 days vs. 9 days, p<0.001). The area under the curve for duration of gentamicin was 0.772 (%95 CI: 0.742-0.804, P=0.0001), sensitivity: 59 (%95 CI: 53-65), specificity: 82 (%95 CI: 78-88), with a cut-off day for duration of gentamicin >7 days.

Conclusion:

In our study, it was found that ductal contraction decreased and hsPDA rate increased as the rate and duration of gentamicin increased.

Prolonged early antenatal indomethacin exposure is safe for fetus and neonate. J Matern Fetal Neonatal Med 2019;34:167-176. [PMID: 30905227 DOI: 10.1080/14767058.2019.1599351]

Objective: To evaluate fetal and neonatal safety of early-onset long-term antenatal indomethacin treatment (LIT) for short cervix.Methods: In this cohort study, women started LIT for short cervix (<25 mm) before completing 25 weeks. They followed a standardized regiment of oral indomethacin: 100 mg loading, 50 mg qid for 48 h, 25 mg qid until delivery or at 32 weeks gestational age (GA), whichever comes first. Weekly monitoring for oligohydramnios and ductus arteriosus (DA) constriction included confirmation of compliance with treatment/dose. This approach is established in our clinical practice. To identify LIT complications separate from prematurity, each neonate exposed to LIT were matched to two unexposed neonatal controls within ±3 days of GA of delivery and birth weight of ±10%. Odds ratios for neonatal variables included pulmonary hemorrhage, patent DA (PDA) requiring medical or surgical correction, necrotizing enterocolitis (NEC), spontaneous intestinal perforation (SIP), intraventricular hemorrhage (IVH) grade III-IV, other intracranial hemorrhage (ICH), neonatal mortality, calculated individually, and for total composite morbidity. Statistical determinants of neonatal morbidity were assessed using binary logistic regression. Exposure to LIT, maternal age, parity, BMI, GA at delivery, birth-weight (BW), neonatal gender, cord artery pH, and 5-min Apgar score were independent variables.Results: 166 LIT cases were matched with 332 controls. LIT median duration was 49 (3-108) days. Mean delivery GA was 34 weeks. LIT was stopped for 5 patients (2.9%) with oligohydramnios and 1 (0.6%) with DA constriction, without consequent morbidity. 71 cases (43%) completed LIT, stopping at 32 weeks. 95 stopped early for preterm premature ruptures of membranes (PPROM) (20%), active labor (11%) or patient choice (22%). Odds of any individual complication did not differ between treated cases and controls. LIT was not a statistical determinant of composite morbidity or any individual neonatal problem.Conclusion: Continuous early-onset indomethacin exposure, up to 15 weeks antenatally, did not increase fetal or neonatal complications. This level of safety is permissive to a randomized trial of indomethacin for the treatment of short cervix.

Aminoglycoside-mediated relaxation of the ductus arteriosus in sepsis-associated PDA

Sepsis is strongly associated with patency of the ductus arteriosus (PDA) in critically ill newborns. Inflammation and the aminoglycoside antibiotics used to treat neonatal sepsis cause smooth muscle relaxation, but their contribution to PDA is unknown. We examined whether: 1) lipopolysaccharide (LPS) or inflammatory cytokines cause relaxation of the ex vivo mouse DA; 2) the aminoglycosides gentamicin, tobramycin, or amikacin causes DA relaxation; and 3) newborn infants treated with aminoglycosides have an increased risk of symptomatic PDA (sPDA). Changes in fetal mouse DA tone were measured by pressure myography in response to LPS, TNF-α, IFN-γ, macrophage-inflammatory protein 2, IL-15, IL-13, CXC chemokine ligand 12, or three aminoglycosides. A clinical database of inborn patients of all gestations was analyzed for association between sPDA and aminoglycoside treatment. Contrary to expectation, neither LPS nor any of the inflammatory mediators caused DA relaxation. However, each of the aminoglycosides caused concentration-dependent vasodilation in term and preterm mouse DAs. Pretreatment with indomethacin and N-(G)-nitro-L-arginine methyl ester did not prevent gentamicin-induced DA relaxation. Gentamicin-exposed DAs developed less oxygen-induced constriction than unexposed DAs. Among 488,349 infants who met the study criteria, 40,472 (8.3%) had sPDA. Confounder-adjusted odds of sPDA were higher in gentamicin-exposed infants, <25 wk and >32 wk. Together, these findings suggest that factors other than inflammation contribute to PDA. Aminoglycoside-induced vasorelaxation and inhibition of oxygen-induced DA constriction support the paradox that antibiotic treatment of sepsis may contribute to DA relaxation. This association was also found in newborn infants, suggesting that antibiotic selection may be an important consideration in efforts to reduce sepsis-associated PDA.

Differential renal adverse effects of ibuprofen and indomethacin in preterm infants: a review

OBJECTIVE

The objective of this study was to evaluate the extent of renal adverse effects caused by ibuprofen or indomethacin in order to choose the safer drug to administer to preterm infants.

METHODS

THE FOLLOWING THREE PARAMETERS OF RENAL FUNCTION WERE TAKEN INTO CONSIDERATION: 1) the urine output; 2) the serum creatinine concentration; and 3) the frequency of oliguria. The bibliographic search was performed using PubMed and Embase databases as search engines.

RESULTS

Urine output ranged from 3.5±1.2 to 4.0±1.4 mL/kg/h after ibuprofen treatment, and from 2.8±1.1 to 3.6±1.4 mL/kg/h after indomethacin treatment. The values for ibuprofen are significantly (P<0.05) higher than those for indomethacin. The serum creatinine concentrations ranged from 0.98±0.24 to 1.48±0.2 mg/dL after ibuprofen treatment, and from 1.06±0.24 and 2.03±2.10 mg/dL after indomethacin treatment. The values for ibuprofen are significantly (P<0.05) lower than those for indomethacin. The frequency of oliguria ranged from 1.0% to 9.6% (ibuprofen) and from 14.8% to 40.0% (indomethacin), and was significantly lower following ibuprofen than indomethacin administration. In infants with body weight lower than 1,000 g, oliguria appeared in 5% (ibuprofen) and 40% (indomethacin; P=0.02).

CONCLUSION

Indomethacin is associated with more severe renal adverse effects than ibuprofen. Ibuprofen is less nephrotoxic than indomethacin and should be used to treat patent ductus arteriosus in preterm infants. Immaturity increases the frequency of adverse effects of indomethacin.

Intrauterine inflammation as a risk factor for persistent ductus arteriosus patency after cyclooxygenase inhibition in extremely low birth weight infants

OBJECTIVES

To test the hypothesis that intrauterine inflammation increases prostaglandin production and may be a risk factor for persistent ductus arteriosus after therapy with indomethacin, a nonselective cyclooxygenase inhibitor.

STUDY DESIGN

Indomethacin therapy was started after confirming ductus arteriosus within 24 hours after birth in extremely low birth weight infants. After one cycle of therapy, infants with closed ductus were classified as responders, and those with patent ductus were classified as nonresponders. Multiple logistic regression analysis was used to determine important perinatal factors associated with persistent ductus arteriosus. Immunohistochemistry with cyclooxygenase antibodies and radioimmunoassay by 6-keto prostaglandin F(1α) kit were used to determine the relationship between intrauterine inflammation and ductal patency.

RESULTS

Forty-one infants were responders, and 37 infants were nonresponders. Responders were frequently small for gestational age; nonresponders frequently had lower gestational age, respiratory distress syndrome, and intrauterine inflammation. By multiple logistic regression analysis, respiratory distress syndrome and intrauterine inflammation were more frequent in nonresponders. Cyclooxygenase-1 expression in the umbilical arteries and plasma 6-keto prostaglandin F(1α) levels were higher in nonresponders.

CONCLUSIONS

Respiratory distress syndrome and intrauterine inflammation were independent risk factors for persistent ductus arteriosus after indomethacin therapy in extremely low-birth weight infants. Intrauterine inflammation may have a negative influence on ductus arteriosus closure via increased cyclooxygenase-1 activity.

Role of microsomal prostaglandin E synthase-1 (mPGES1)-derived PGE2 in patency of the ductus arteriosus in the mouse

Prostaglandin E2 (PGE2) plays a key role in the ductus arteriosus, prenatally by maintaining patency and postnatally by promoting tissue remodeling for closure. Here, by using near-term mouse fetuses with (wild-type, WT) and without microsomal PGE synthase-1 (mPGES1-/-), we have examined the importance of this enzyme for PGE2 formation and function. mPGES1-/- ductus, unlike WT ductus, contracted little, or not all, to indomethacin in vitro. Coincidentally, as evident from responses to NG-nitro-L-arginine methyl ester and zinc photoporphyrin, the mutant showed no significant enhancement of nitric oxide (NO)- and carbon monoxide (CO)-based relaxation. mPGES1 suppression differs, therefore, from cyclooxygenase (COX) suppression, whether genetically or pharmacologically induced, where NO is markedly up-regulated. In vivo, the ductus was patent, albeit occasionally with a narrowed lumen, in all mPGES1-/- fetuses. Conversely, postnatal closure progressed regularly in mPGES1-/- animals thanks to residual PGE2 originating via mPGES2. We conclude that mPGES1 is critical for PGE2 formation in the ductus but its loss does not entail compensatory up-regulation of other relaxing mechanisms. Accordingly, an mPGES1 inhibitor stands out as a prospective better tool, compared with the currently used COX inhibitors, for the management of premature infants with persistent ductus.

Maturation of the contractile response of the Emu ductus arteriosus

The avian embryo has a pair of ductus arteriosi that allow the blood to bypass the pulmonary circulation prior to the initiation of lung ventilation. Our objective was to characterize the factors regulating DA tone during the later stages of development in the emu embryo. We examined in vitro the reactivity of the emu ductus from day 39 through 49 of a 50-day incubation. Steady state tension was not altered by the COX inhibitor indomethacin or the nitric oxide synthase inhibitor L-NAME. However, prostaglandin E(2) (PGE(2)) produced a significant relaxation. Norephinephrine and U-46619 produced strong significant contractions in the emu DA and the adrenergic response matured with development. The contractile response to oxygen matured as the embryo developed with significant oxygen-induced contraction on days 45 and 49, but not on day 39 of incubation. The Kv channel inhibitor 4-aminopyridine induced the contraction of the day 48-49 ductus of similar magnitude as the oxygen-induced contraction. The oxygen-induced contraction was reversed by the reducing agent DTT and the electron transport chain inhibitor rotenone. These results suggest that while the emu DA responds to PGE(2), locally produced PGE(2) are not the important regulators of vessel tone. Additionally, relaxation upon addition of the mitochondria electron transport chain inhibitor rotenone suggests that the mitochondria might be acting as vascular oxygen sensors in this system through the production of reactive oxygen species to stimulate the oxygen-induced contraction in a similar fashion to mammals.

Attenuated cyclooxygenase-2 expression contributes to patent ductus arteriosus in preterm mice

Patent ductus arteriosus (DA) is the second most common congenital heart defect, the incidence of which is increased in premature infants, although mechanisms responsible are not clear. Our previous studies with genetic or pharmacological inactivation of cyclooxygenase-2 (COX-2) in mice, emphasized the importance of this enzyme in normal DA closure. The current study was designed to determine whether reduced COX-2 expression contributes to patent DA in preterm mice. Real-time PCR analysis indicated that COX-2 expression in the fetal mouse DA significantly increased with advancing gestational age. Furthermore, we observed a significant induction in COX-2 expression in the DA at 3 h after birth at full-term gestation. In contrast, COX-2 expression was significantly attenuated in the DA of preterm neonatal mice. DA closure was incomplete in preterm mice at 3 h postpartum, a time-point when the DA of full-term neonates was completely remodeled. Additionally, COX-2 expression was significantly attenuated in the DA of mice deficient in the prostanoid receptor EP4, which also show a patent DA phenotype, suggesting the importance of this receptor for the induction of COX-2 required for DA closure. Overall, these studies suggest that attenuated expression of COX-2 may contribute to increased patent DA at preterm gestation.

Changing expression of cyclooxygenases and prostaglandin receptor EP4 during development of the human ductus arteriosus

Programmed proliferative degeneration of the human fetal ductus arteriosus (DA) in preparation for its definite postnatal closure has a large developmental variability and is controlled by several signaling pathways, most prominently by prostaglandin (PG) metabolism. Numerous studies in various mammalian species have shown interspecies and developmental differences in ductal protein expression of cyclooxygenase (COX) isoforms and PG E receptor subtypes (EP1-4). We examined COX1, COX2, and EP4 receptor protein expression immunohistochemically in 57 human fetal autopsy DA specimens of 11-38 wk of gestation. According to their histologic maturity, specimens were classified into four stages using a newly designed maturity score that showed that histologic maturity of the DA was not closely related to gestational age. COX1 expression was found in all DA regions and rose steadily during development. COX2 staining remained weak throughout gestation. EP4 receptor staining increased moderately during gestation and was limited to the intima and media. In conclusion, histologic maturity classification helps to address developmentally regulated processes in the fetal DA. Concerning prostaglandin metabolism our findings are in line with animal studies, which assigned COX1 the predominant role in the DA throughout gestation. EP4 receptor presumably plays a key role for active patency of the human DA in the third trimester.

Ontogeny of chicken ductus arteriosus response to oxygen and vasoconstrictors

The present study aimed to characterize the contractile reactivity of the chicken ductus arteriosus (DA) from the last stage of prenatal development and throughout the perinatal period. Isolated DA rings from 15-day, noninternally-pipped 19-day, and externally-pipped 21-day embryos were studied using myograph techniques. On embryonic day 15, the chicken DA did not respond to O(2) (0 to 21%), norepinephrine (NE), or phenylephrine (Phe) but contracted in response to high-K(+) solution, the inhibitor of voltage-gated channels 4-aminopyridine, U-46619, and endothelin (ET)-1. These responses increased with advancing incubation age. Contractile responses to O(2), NE, and Phe were present in the 19- and 21-day embryo. Oxygen-induced contraction was restricted to the pulmonary side of the DA and was augmented by the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine methyl ester and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one and reduced by the peptidic ET(A) and ET(B)-receptor antagonist PD-142,893. Transmural electrical stimulation of nerves, the nonselective cyclooxygenase (COX) inhibitor indomethacin, the COX-1 inhibitor valeryl salicylate, the COX-2 inhibitor nimesulide, the inhibitor of ATP-sensitive K(+) channels glibenclamide, and the inhibitor of Ca(2+)-activated K(+) channels tetraethylammonium did not cause contraction of the DA rings at any age. We conclude that transition to ex ovo life is accompanied by dramatic changes in chicken DA reactivity. At 0.7 incubation, excitation-contraction and pharmacomechanical coupling for several contractile agonists are already present, whereas the constrictor effects of O(2) and cathecolamines appear later in development and are located in the pulmonary side of the DA.

Role of the cyclooxygenase pathway in the protection against postischemic stunning in conscious sheep

OBJECTIVE

There are controversial reports in conscious animals regarding the role of cyclooxygenase-2 in late preconditioning (LP). This study analyzed the effect of COX-2 involvement in non-preconditioned hearts (NP) and in mediation of LP protection against stunning in conscious sheep submitted to a prolonged reversible ischemia.

METHODS

Six groups were considered: NP: 12 min ischemia and 120 min reperfusion; LP consisting of six periods of 5 min-ischemia-5 min reperfusion 24 h before the 12 min ischemia; NP and LP with either the non-selective COX-1 and COX-2 inhibitor, aspirin (20 mg/kg), or the specific COX-2 inhibitor, celecoxib (3 mg/kg) before the 12 min ischemic period.

RESULTS

Mean postischemic wall thickening fraction (as % of preischemic values) improved from 49.6 +/- 4.0% in NP to 72.5 +/- 3.5% in LP (p < 0.01) and a similar protection was obtained with aspirin and celecoxib in NP hearts (p < 0.01). Neither aspirin nor celecoxib administration prior to the prolonged ischemia on day 2 abrogated LP improvement of postischemic dysfunction. Moreover, LP with aspirin improved the protective response (80.7 +/- 2.6%) over that obtained with aspirin in NP hearts (66.6 +/- 4.7%, p < 0.05). This effect was not obtained with celecoxib.

CONCLUSIONS

Aspirin and celecoxib showed that COX-2 has a detrimental effect on mechanical cardioprotection in NP hearts of conscious sheep submitted to a prolonged reversible ischemia, and does not seem to participate as mediator of LP. Aspirin revealed a similar COX-1 deleterious action, since only when both COX-1 and COX-2 were inhibited, LP was put in evidence adding functional improvement over that obtained in NP hearts treated with aspirin.

Constriction of the ductus arteriosus by selective inhibition of cyclooxygenase-1 and -2 in near-term and preterm fetal rats

We studied the transplacental ductal constrictive effects of a selective cyclooxygenase (COX)-1 inhibitor (SC560), six selective COX-2 inhibitors including rofecoxib, and a non-selective COX inhibitor (indomethacin). Each drug was administered to the pregnant rats, and fetal ductus arteriosus (DA) was studied with a whole-body freezing method. The inner diameter ratio of the DA to the main pulmonary artery (DA/PA) was 1.02+/-0.03 (mean+/-S.E.M.) in controls. Every drug constricted the DA dose-dependently. In preterm rats on the 19th day of gestation, 10mg/kg of SC560, rofecoxib and indomethacin caused ductal constriction, with DA/PA reduced to 0.76+/-0.02, 0.80+/-0.03 and 0.75+/-0.02, respectively. In near-term on the 21st day, 10mg/kg of them caused ductal constriction, with DA/PA to 0.74+/-0.04, 0.26+/-0.02 and 0.33+/-0.05. In conclusion, both COX-1 and COX-2 selective inhibitors constrict fetal DA. They are not better alternatives for the fetus than non-selective COX inhibitors for tocolysis.

Gene transfer of prostaglandin synthase maintains patency of the newborn lamb arterial duct

In congenital heart disease with left- or right-sided obstruction, prostaglandin E (PGE)1 or PGE2 is infused to maintain ductus arteriosus (DA) patency. We hypothesized that transfection of the DA with PGE synthase would lead to a greater production of PGE2 in situ and, hence, patency of the DA. The cDNA for human prostaglandin synthase was sequenced and ligated into a eukaryotic expression vector. The negative control was created by ligating the cDNA encoding the bacterial protein chloramphenicol acetyltransferase into the same plasmid. Transfection (600 microg DNA) was achieved in lambs within the first 24 h of life using the hemagglutinating virus of Japan (HVJ)-liposome transfection method with a custom-made, basket-weave-perforated catheter. Echocardiography was performed to assess DA patency until the time of sacrifice. To confirm expression of the transgene, PGE2 concentration was measured in organ culture of the DA by immunoassay and by Western immunoblotting of homogenized DA tissue. Patency of the DA was demonstrated by color Doppler in all the lambs (7/7) in which the PGE synthase was delivered, whereas functional closure was seen in the control group (6/6). The PGE2 concentration in the culture medium of the explanted DA in the treatment group was 3-fold higher than that of the control groups. Western immunoblotting confirmed the presence of PGE synthase in the treatment group. Gene transfer of PGE synthase to the DA is feasible and will maintain patency for at least 1 wk.

Cyclooxygenase isoenzymes and patency of ductus arteriosus

Prenatal patency of the ductus arteriosus is maintained mainly by prostaglandin (PG) E(2). Accordingly, the vessel is endowed in its muscular component with a complete, cyclooxygenase (COX) and PGE synthase (PGES), system for the synthesis of the compound. COX1 is better expressed than COX2, particularly in the premature, but COX2 is more extensively coupled with microsomal PGES (mPGES). No evidence was obtained of either COX being coupled with cytosolic PGES (cPGES). Functionally, these data translate into a differential constrictor response of the ductus to dual, COX1/COX2, vs. COX2-specific inhibitors (indomethacin vs. L-745,337), with the latter being less effective specifically prior to term. This difference, however, subsides upon treatment with endotoxin and the attendant upregulation of COX2 and mPGES. Furthermore, when studied separately, COX1 and COX2 prove to be unevenly responsive to indomethacin, and an immediate and fast developing contraction of the vessel occurs only when COX2 is inhibited. Deletion of either COX gene results into upregulation of NO synthase, and a similar compensatory reaction is expected when enzymes are suppressed pharmacologically. We conclude that PGE(2) and NO can function synergistically in keeping the ductus patent. This arrangement provides a possible explanation for failures of indomethacin or ibuprofen treatment in the management of the prematurely born infant with persistent ductus. Coincidentally, it opens the way to new therapeutic possibilities being based on interference with the NO effector or a more selective disruption, possibly having mPGES as a target, of the PGE(2) synthetic cascade.

An EP4 receptor agonist prevents indomethacin-induced closure of rat ductus arteriosus in vivo

Indomethacin exerts a strong tocolytic effect by suppressing uterine contractions mediated by prostaglandins. However, indomethacin also induces in utero closure of fetal ductus arteriosus (DA), leading to serious neonatal consequences. Using rats, we tested the effect of an agonist for a subtype of prostaglandin E2 receptor (EP4), ONO-AE1-437 and its prodrug ONO-4819, as a DA dilator during indomethacin treatment. In vitro, ONO-AE1-437 exhibited a potent dilatory effect on DA against O(2)- and indomethacin-induced contractions in a concentration-dependent manner. In vivo, rat dams were given indomethacin (10 mg/kg, p.o.) alone or with ONO-4819 (0.3 micrograms/kg/h, s.c.) on d 21 of gestation and pups were delivered 4 h later through cesarean section to evaluate the ratio of diameter of DA to that of pulmonary artery. Pups from dams with no drug had DA/PA ratio of 0.9 +/- 0.05, whereas those from dams with indomethacin alone had a decreased ratio of 0.2 +/- 0.03. When ONO-4819 was co-administered to the dams, the ratio recovered significantly to 0.7 +/- 0.06. The administration of ONO-4819 to the dams did not induce any increase in the uterine activity. These results suggest that administration of an EP4 agonist in addition to indomethacin might prevent adverse reactions of indomethacin on fetal DA without restricting its tocolytic effects.

Response of fetal prostanoids, nitric oxide, and ductus arteriosus to the short- and long-term antenatal administration of celecoxib, a selective cyclo-oxygenase-2 inhibitor, in the pregnant rabbit

OBJECTIVE

The purpose of this study was to test the hypothesis that the maternal administration of therapeutic doses of celecoxib would not affect ductus arteriosus patency or alter renal and hepatic prostanoids in the fetal rabbit.

STUDY DESIGN

Pregnant rabbits received celecoxib from 13 to 20 days (celecoxib-A), from 13-28 days (celecoxib-B), or vehicle from 13 to 28 days by gavage. Fetal serum and lung tissue were analyzed for nitric oxide oxidation products. Fetal plasma, liver, and kidney were analyzed for prostaglandin levels.

RESULTS

The ductus arteriosus was patent in both treatment groups. Celecoxib induced elevations of plasma prostaglandin E(2) production. In celecoxib-B liver and kidney, the 6-keto-prostaglandin F(1alpha) and prostaglandin F(2alpha) levels were increased, and the prostaglandin E(2) and thromboxane B(2) levels were decreased substantially.

CONCLUSION

This preliminary evaluation demonstrates that the maternal administration of celecoxib does not influence fetal ductus arteriosus patency adversely in rabbits.

Cyclooxygenase-1 and cyclooxygenase-2 in the mouse ductus arteriosus: individual activity and functional coupling with nitric oxide synthase

1. Prenatal patency of the ductus arteriosus is maintained by prostaglandin (PG) E(2), conceivably in concert with nitric oxide (NO). Local PGE(2) formation is sustained by cyclooxygenase-1 (COX1) and cyclooxygenase-2 (COX2), a possible exception being the mouse in which COX1, or both COXs, are reportedly absent. Here, we have examined the occurrence of functional COX isoforms in the near-term mouse ductus and the possibility of COX deletion causing NO upregulation. 2. COX1 and COX2 were detected in smooth muscle cells by immunogold electronmicroscopy, both being located primarily in the perinuclear region. Cytosolic and microsomal PGE synthases (cPGES and mPGES) were also found, but they occurred diffusely across the cytosol. COX1 and, far more frequently, COX2 were colocalised with mPGES, while neither COX appeared to be colocalized with cPGES. 3. The isolated ductus from wild-type and COX1-/- mice contracted promptly to indomethacin (2.8 micro M). Conversely, the contraction of COX2-/- ductus to the same inhibitor started only after a delay and was slower. 4. N(G)-nitro-L-arginine methyl ester (L-NAME, 100 micro M) weakly contracted the isolated wild-type ductus. Its effect, however, increased three- to four-fold after deleting either COX, hence equalling that of indomethacin. 5. In vivo, the ductus was patent in all mice foetuses, whether wild-type or COX-deleted. Likewise, no genotype-related difference was noted in its postnatal closure. 6. We conclude that the mouse ductus has a complete system for PGE(2) synthesis comprising both COX1 and COX2. The two enzymes respond differently to indomethacin but, nevertheless, deletion of either one results in NO upregulation. PGE(2) and NO can function synergistically in keeping the ductus patent.

Prenatal effects of DuP-697-the irreversible, highly selective cyclooxygenase-2 inhibitor

DuP-697 (5-bromo-2-(4-fluorophenyl)-3-[4-(methylsulfonyl)phenyl]-thiophene), like celecoxib and rofecoxib, is a vicinal diaryl heterocycle highly selective cyclooxygenase-2 (COX-2) inhibitor. The aim of the study was to evaluate prenatal tolerability of DuP-697. The drug was administered orally in Tween 80 water suspension once a day to pregnant Wistar rats, on Days 7-18 of gestation. The initial dose, similar to the rat antipyretic dose, was set at 0.05 mg/kg. The middle dose, 3.5 mg/kg, corresponded to the rat anti-inflammatory and analgesic dose. The high dose was set at 35.0 mg/kg. Control animals received Tween 80 water suspension. On Day 21 of gestation, fetuses were delivered by laparotomy and double stained with alcian blue and alizarin red S or examined using the Wilson technique. Intrauterine growth retardation occurred in the groups exposed to the middle and highest dose of DuP-697. Minimal reactive and degenerative hepatic changes were found in both drug-exposed and control groups. Skeletal malformations were seen occasionally in all drug-treated and control groups. A significant increase in skeleton variations, such as delayed and asymmetrical ossification, was observed in fetuses exposed to the highest drug dose when compared with the control. These changes were not increased (P<0.1) in the middle drug-dose group. The experimentally-derived NOAEL for developmental toxicity was 0.05 mg/kg, and the corresponding LOAEL was 3.5 mg/kg.

ChTX induces oscillatory contraction in guinea pig trachea: role of cyclooxygenase-2 and PGE2

We examined the possible role of cyclooxygenase (COX) in charybdotoxin (ChTX)-induced oscillatory contraction in guinea pig trachea. Involvement of prostaglandin E(2) (PGE(2)) in ChTX-induced oscillatory contraction was also investigated. ChTX (100 nM) induced oscillatory contraction in guinea pig trachea. The mean oscillatory frequency induced by ChTX was 10.7 +/- 0.8 counts/h. Maximum and minimum tensions within ChTX-induced oscillatory contractions were 68.4 +/- 1.8 and 14.3 +/- 1.7% compared with K(+) (72.7 mM) contractions. ChTX-induced oscillatory contraction was completely inhibited by indomethacin, a nonselective COX inhibitor. Valeryl salicylate, a selective COX-1 inhibitor, did not significantly inhibit this contraction, whereas N-(2-cyclohexyloxy-4-nitro-phenyl)-methanesulfonamide, a selective COX-2 inhibitor, abolished this contraction. Exogenously applied arachidonic acid enhanced ChTX-induced oscillatory contraction. SC-51322, a selective PGE receptor subtype EP(1) antagonist, significantly inhibited ChTX-induced oscillatory contraction. Exogenously applied PGE(2) induced only a slight phasic contraction in guinea pig trachea, but PGE(2) induced strong oscillatory contraction after pretreatment with indomethacin and ChTX. Moreover, ChTX time-dependently stimulated PGE(2) generation. These results suggest that ChTX specifically activates COX-2 and stimulates PGE(2) production and that ChTX-induced oscillatory contraction in guinea pig trachea is mediated by activation of EP(1) receptor.

Integration of the non-genomic and genomic actions of estrogen. Membrane-initiated signaling by steroid to transcription and cell biology

Estrogen binds to receptors that translocate to the plasma membrane and to the nucleus. The rapid, non-genomic actions of this sex steroid are attributed to membrane action, while gene transcription occurs through nuclear receptor function. However, gene transcription can also result from estrogen signaling initiated at the membrane, but the relative importance of this mechanism is not known. In vascular endothelial cells (EC), estradiol (E(2)) activates several kinase cascades, including phosphatidylinositol 3-phosphate (PI3K)/Akt, a signaling pathway that impacts EC biology. We determined here by DNA microarray that 40-min exposure to E(2) significantly increased 250 genes in EC, up-regulation that was substantially prevented by the PI3K inhibitor, LY294002. This coincided with maximum E(2)-induced PI3K activity at 15-30 min. An important vascular gene strongly up-regulated by E(2) in our array produces cyclooxygenase-2 (Cox-2). In cultured EC, E(2) induced both Cox-2 gene expression and new Cox-2 protein synthesis by 40 and 60 min, respectively, and rapidly stimulated the secretion of prostaglandins PGI(2) and PGE(2). The up-regulation of gene expression reflected transcriptional transactivation, shown using Cox-2 promoter/luciferase reporters in the EC. Soluble inhibitors or dominant negative constructs for PI3K and Akt prevented all these actions of E(2). Functionally, EC migration was induced by the sex steroid, and this was significantly reversed by NS-398, a Cox-2 inhibitor. Gene transcription and cell biological effects of estrogen emanate from rapid and specific signaling, integrating cell surface and nuclear actions of this steroid.

Prostanoid receptors: ontogeny and implications in vascular physiology

Prostanoids exert significant effects on circulatory beds. They play a role in the response of the vasculature to adjustments in perfusion pressure and oxygen and carbon dioxide tension, and they mediate the actions of numerous factors. The role of prostanoids in governing circulation of the perinate is suggested to surpass that in the adult. Prostanoids are abundantly generated in the perinate. They have been implicated in autoregulation of blood flow as studied in brain and eyes. Prostaglandins are also dominant regulators of ductus arteriosus tone. The effects of these autacoids are mediated through specific G protein-coupled receptors. In addition to the pharmacological characterization of the prostanoid receptors, important advances in understanding the biology of these receptors have been made in the last decade. Their cloning and the development of animals with disrupted genes of these receptors have been very informative. The involvement of prostanoid receptors in the developing subject, especially on brain and ocular vasculature and on ductus arteriosus, has also begun to be investigated; the expression of these receptors changes with development. Some but not all of the ontogenic changes in these receptors are attributed to homologous regulation. Interestingly, in the process of elucidating their effects, functional perinuclear prostaglandin E2 receptors have been uncovered. This article reviews prostanoid receptors and addresses implications on the developing subject with attention to vascular physiology.

New developments in the management of preterm labor

Current management of preterm labor has not changed the incidence of preterm delivery; therefore, significant research effort has been concentrated on the search for new methods of management. New tocolytics like inhibitors of cyclooxygenase 2 and nitric oxide donors have been tested in animal models and in preliminary clinical trials with promising results. Inhibition of cervical ripening may be one alternative to tocolysis. This new approach has a potential to be a valuable method of management of preterm labor if human studies confirm the promising results reported in animals. Growing evidence suggests that premature delivery may be associated with infection or fetal growth abnormalities, with dire consequences to the fetus. If these associations are to be included in risk and benefit assessment, then inhibition of preterm labor may prove to be detrimental to the fetus.