Pulmonary Hypertension In Newborn Piglets Research Articles

Rescue Treatment with L-Citrulline Inhibits Hypoxia-Induced Pulmonary Hypertension in Newborn Pigs.

Infants with cardiopulmonary disorders associated with hypoxia develop pulmonary hypertension. We previously showed that initiation of oral L-citrulline before and continued throughout hypoxic exposure improves nitric oxide (NO) production and ameliorates pulmonary hypertension in newborn piglets. Rescue treatments, initiated after the onset of pulmonary hypertension, better approximate clinical strategies. Mechanisms by which L-citrulline improves NO production merit elucidation. The objective of this study was to determine whether starting L-citrulline after the onset of pulmonary hypertension inhibits disease progression and improves NO production by recoupling endothelial NO synthase (eNOS). Hypoxic and normoxic (control) piglets were studied. Some hypoxic piglets received oral L-citrulline starting on Day 3 of hypoxia and continuing throughout the remaining 7 days of hypoxic exposure. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess NO production and eNOS dimer-to-monomer ratios (a measure of eNOS coupling). Pulmonary vascular resistance was lower in L-citrulline-treated hypoxic piglets than in untreated hypoxic piglets but was higher than in normoxic controls. NO production and eNOS dimer-to-monomer ratios were greater in pulmonary arteries from L-citrulline-treated than from untreated hypoxic animals but were lower than in normoxic controls. When started after disease onset, oral L-citrulline treatment improves NO production by recoupling eNOS and inhibits the further development of chronic hypoxia-induced pulmonary hypertension in newborn piglets. Oral L-citrulline may be a novel strategy to halt or reverse pulmonary hypertension in infants suffering from cardiopulmonary conditions associated with hypoxia.

Angiotensin II type 1 receptor blockade partially attenuates hypoxia-induced pulmonary hypertension in newborn piglets: relationship with the nitrergic system

The objective of this study was to observe possible interactions between the renin-angiotensin and nitrergic systems in chronic hypoxia-induced pulmonary hypertension in newborn piglets. Thirteen chronically instrumented newborn piglets (6.3 ± 0.9 days; 2369 ± 491 g) were randomly assigned to receive saline (placebo, P) or the AT1 receptor (AT1-R) blocker L-158,809 (L) during 6 days of hypoxia (FiO2 = 0.12). During hypoxia, pulmonary arterial pressure (Ppa; P < 0.0001), pulmonary vascular resistance (PVR; P < 0.02) and the pulmonary to systemic vascular resistance ratio (PVR/SVR; P < 0.05) were significantly attenuated in the L (N = 7) group compared to the P group (N = 6). Western blot analysis of lung proteins showed a significant decrease of endothelial NOS (eNOS) in both P and L animals, and of AT1-R in P animals during hypoxia compared to normoxic animals (C group, N = 5; P < 0.01 for all groups). AT1-R tended to decrease in L animals. Inducible NOS (iNOS) did not differ among P, L, and C animals and iNOS immunohistochemical staining in macrophages was significantly more intense in L than in P animals (P < 0.01). The vascular endothelium showed moderate or strong eNOS and AT1-R staining. Macrophages and pneumocytes showed moderate or strong iNOS and AT1-R staining, but C animals showed weak iNOS and AT1-R staining. Macrophages of L and P animals showed moderate and weak AT2-R staining, respectively, but the endothelium of all groups only showed weak staining. In conclusion, pulmonary hypertension induced by chronic hypoxia in newborn piglets is partially attenuated by AT1-R blockade. We suggest that AT1-R blockade might act through AT2-R and/or Mas receptors and the nitrergic system in the lungs of hypoxemic newborn piglets.

Protein complex formation with heat shock protein 90 in chronic hypoxia-induced pulmonary hypertension in newborn piglets

Aberrant interactions between heat shock protein (Hsp)90 and its client proteins could contribute to pulmonary hypertension. We tested the hypotheses that 1) the interaction between Hsp90 and its known client protein, endothelial nitric oxide synthase (eNOS), is impaired in pulmonary resistance arteries (PRAs) from piglets with pulmonary hypertension caused by exposure to 3 or 10 days of hypoxia and 2) Hsp90 interacts with the prostanoid pathway proteins prostacyclin synthase (PGIS) and/or thromboxane synthase (TXAS). We also determined whether Hsp90 antagonism with geldanamycin alters the agonist-induced synthesis of prostacyclin and thromboxane or alters PRA responses to these prostaglandin metabolites. Compared with normoxic piglets, less eNOS coimmunoprecipitated with Hsp90 in PRAs from hypoxic piglets. Despite reduced Hsp90-eNOS interactions, dilation to ACh was enhanced in geldanamycin-treated PRAs from hypoxic, but not normoxic, piglets. In PRAs from all groups of piglets, PGIS and TXAS coimmunoprecipitated with Hsp90. Geldanamycin reduced the ACh-induced synthesis of prostacyclin and thromboxane and altered responses to the thromboxane mimetic U-46619 in PRAs from all groups. Although geldanamycin enhanced responses to prostacyclin in PRAs from both groups of hypoxic piglets, geldanamycin had no effect on prostacyclin responses in PRAs from either group of normoxic piglets. Our findings indicate that Hsp90 influences both prostanoid and eNOS signaling in the pulmonary circulation of newborn piglets and that the impact of pharmacological inhibition of Hsp90 on these signaling pathways is altered during exposure to chronic hypoxia.

Effects of Intermittent Nebulization of NONOate, DPTA/NO, on Group B Streptococcus-Induced Pulmonary Hypertension in Newborn Piglets

Background: A single dose of NONOate attenuates pulmonary hypertension (PH) induced by group B Streptococcus (GBS) infusion and this is accompanied by a decrease in systemic vascular resistance (SVR). Objective: The objective of the study was to determine whether two doses of the NONOate sustain the attenuation in GBS-induced PH without further systemic compromise. Methods: 15 anesthetized newborn piglets were randomized to receive placebo (n = 8) or two doses of nebulized DPTA/NO (n = 7) at 15 and 75 min after GBS-induced PH. Pulmonary artery (Ppa) and systemic (Psa) pressures, cardiac output (CO) and arterial blood gases were obtained at baseline and every 15 min until 180 min during GBS infusion. Results: Ppa and pulmonary vascular resistance (PVR) decreased significantly after the first dose of nebulized DPTA/NO and this effect was maintained after the second dose. Psa and SVR decreased after the first dose of DPTA/NO to values close to baseline and no further changes in systemic circulation were observed with repeated treatment. PVR/SVR increased with GBS infusion, but decreased after the first dose of DPTA/NO and remained significantly lower for 180 min. CO was significantly higher in the DPTA/NO group. Changes in Ppa, PVR, Psa, SVR, and CO with GBS infusion were not modified by placebo infusion. PaCO₂, base deficit, and pH did not differ between groups. PaO₂ was significantly lower in the DPTA/NO group after the second dose. Conclusion: These data demonstrated that GBS-induced PH is attenuated with two doses of DPTA/NO without significant systemic effect. The vasodilatory effect is more pronounced in the pulmonary than in the systemic vasculature, as suggested by lower PVR/SVR in the DPTA/NO group. We speculate that NONOates may have a clinical application in the management of PH in neonates.

L-Citrulline ameliorates chronic hypoxia-induced pulmonary hypertension in newborn piglets

Newborn piglets develop pulmonary hypertension and have diminished pulmonary vascular nitric oxide (NO) production when exposed to chronic hypoxia. NO is produced by endothelial NO synthase (eNOS) in the pulmonary vascular endothelium using l-arginine as a substrate and producing l-citrulline as a byproduct. l-Citrulline is metabolized to l-arginine by two enzymes that are colocated with eNOS in pulmonary vascular endothelial cells. The purpose of this study was to determine whether oral supplementation with l-citrulline during exposure of newborn piglets to 10 days of chronic hypoxia would prevent the development of pulmonary hypertension and increase pulmonary NO production. A total of 17 hypoxic and 17 normoxic control piglets were studied. Six of the 17 hypoxic piglets were supplemented with oral l-citrulline starting on the first day of hypoxia. l-Citrulline supplementation was provided orally twice a day. After 10 days of hypoxia or normoxia, the animals were anesthetized, hemodynamic measurements were performed, and the lungs were perfused in situ. Pulmonary arterial pressure and pulmonary vascular resistance were significantly lower in hypoxic animals treated with l-citrulline compared with untreated hypoxic animals (P < 0.001). In vivo exhaled NO production (P = 0.03) and nitrite/nitrate accumulation in the perfusate of isolated lungs (P = 0.04) were significantly higher in l-citrulline-treated hypoxic animals compared with untreated hypoxic animals. l-Citrulline supplementation ameliorated the development of pulmonary hypertension and increased NO production in piglets exposed to chronic hypoxia. We speculate that l-citrulline may benefit neonates exposed to prolonged periods of hypoxia from cardiac or pulmonary causes.

NADPH oxidases and reactive oxygen species at different stages of chronic hypoxia-induced pulmonary hypertension in newborn piglets

Recently, we reported that reactive oxygen species (ROS) generated by NADPH oxidase (NOX) contribute to aberrant responses in pulmonary resistance arteries (PRAs) of piglets exposed to 3 days of hypoxia (Am J Physiol Lung Cell Mol Physiol 295: L881-L888, 2008). An objective of the present study was to determine whether NOX-derived ROS also contribute to altered PRA responses at a more advanced stage of pulmonary hypertension, after 10 days of hypoxia. We further wished to advance knowledge about the specific NOX and antioxidant enzymes that are altered at early and later stages of pulmonary hypertension. Piglets were raised in room air (control) or hypoxia for 3 or 10 days. Using a cannulated artery technique, we found that treatments with agents that inhibit NOX (apocynin) or remove ROS [an SOD mimetic (M40403) + polyethylene glycol-catalase] diminished responses to ACh in PRAs from piglets exposed to 10 days of hypoxia. Western blot analysis showed an increase in expression of NOX1 and the membrane fraction of p67phox. Expression of NOX4, SOD2, and catalase were unchanged, whereas expression of SOD1 was reduced, in arteries from piglets raised in hypoxia for 3 or 10 days. Markers of oxidant stress, F(2)-isoprostanes, measured by gas chromatography-mass spectrometry, were increased in PRAs from piglets raised in hypoxia for 3 days, but not 10 days. We conclude that ROS derived from some, but not all, NOX family members, as well as alterations in the antioxidant enzyme SOD1, contribute to aberrant PRA responses at an early and a more progressive stage of chronic hypoxia-induced pulmonary hypertension in newborn piglets.

L‐Citrulline Inhibits Chronic Hypoxia‐Induced Pulmonary Hypertension in Newborn Piglets

Decreased Nitric Oxide (NO) production may contribute to the development of chronic hypoxia‐induced PHT. NO is produced from arginine by nitric oxide synthase. Citrulline is metabolized to arginine and may increase the amount of arginine available for NO production. Our goal was to determine if supplementation with L‐citrulline inhibits chronic hypoxia‐induced PHT in newborn pigs. Two day old pigs were kept in hypoxia (H, n=15) or normoxia (controls, C, n=5) for 10 days. Some (n=5) H pigs received oral L‐citrulline (0.13 mg/kg/dose bid). Catheters were placed to measure pulmonary artery pressure (Ppa), left ventricular end diastolic pressure, cardiac output by thermodilution and exhaled NO concentration (ppb). Ppa (cm H2O) and pulmonary vascular resistance (PVR, cmH2O.ml−1.min−1.kg−1) were higher in untreated H (Ppa 39±3, PVR 0.13±0.01) than C (Ppa 21±3, PVR 0.04±0.01) piglets. Ppa and calculated PVR in citrulline‐treated H (Ppa 27±1, PVR 0.07±0.004) did not differ from C. Values for exhaled NO were lower in untreated H (1.5 ±0.2) than C (3.4±0.6) but did not differ between citrulline‐treated H (2.5±0.4) and C pigs. Thus, L‐citrulline increases NO production and inhibits the development of PHT in piglets exposed to 10 days chronic hypoxia. We speculate that enteral supplementation with L‐citrulline may limit pulmonary vascular changes in neonates who have prolonged periods of hypoxia. Supported: AHA‐SE Affil

Voltage-gated K+ channels at an early stage of chronic hypoxia-induced pulmonary hypertension in newborn piglets

Our purpose was to determine whether smooth muscle cell membrane properties are altered in small pulmonary arteries (SPA) of piglets at an early stage of pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. A microelectrode technique was used to measure smooth muscle cell membrane potential (E(m)) in cannulated, pressurized SPA (100- to 300-microm diameter). SPA responses to the voltage-gated K(+) (K(V)) channel antagonist 4-aminopyridine (4-AP) and the K(V)1 family channel antagonist correolide were measured. Other SPA were used to assess amounts of K(V)1.2, K(V)1.5, and K(V)2.1 (immunoblot technique). E(m) was more positive in SPA of chronically hypoxic piglets than in SPA of comparable-age control piglets. The magnitude of constriction elicited by either 4-AP or correolide was diminished in SPA from hypoxic piglets. Abundances of K(V)1.2 were reduced, whereas abundances of both K(V)1.5 and K(V)2.1 were unaltered, in SPA from hypoxic piglets. At least partly because of reduced amounts of K(V)1.2, smooth muscle cell membrane properties are altered such that E(m) is depolarized and K(V) channel family function is impaired in SPA of piglets at an early stage of chronic hypoxia-induced pulmonary hypertension.

Intratracheal administration of sildenafil and surfactant alleviates the pulmonary hypertension in newborn piglets

To study systemic and pulmonary effects of low-dose sildenafil with surfactant in newborn piglets with pulmonary hypertension (PHT) induced by thromboxane A(2) analog (U46619). Piglets (1-3 days, 1.7-2.5 kg) were mechanically ventilated and prepared for the continuous measurement of mean systemic and pulmonary arterial pressures (MAP and PAP, respectively), heart rate and pulmonary artery flow (as cardiac output). Following stabilization, PHT was induced by intravenous U46619 infusion (0.2-0.8 microg/kg/min) for 120 min. Piglets were randomized for intratracheal administration of surfactant (BLES, 4 ml/kg) with saline (n=6) or sildenafil (0.05 mg/kg, n=6) given after 60 min of U46619 treatment. Temporal changes of hemodynamic measurements were analyzed by two-way ANOVA. There was progressive PHT induced by U46619 (161% of baseline), with increased PAP and pulmonary vascular resistance and decreased cardiac output. Surfactant and sildenafil combined improved PAP along with reduced pulmonary vascular resistance. Cardiac output was higher with surfactant and sildenafil combined than surfactant alone. No significant changes in heart rate, stroke volume, MAP and systemic vascular resistance were observed. Ratio of PAP:MAP was lowered with surfactant and sildenafil combined. Systemic oxygen consumption was not different between groups but the oxygen extraction ratio was higher than baseline in surfactant alone (P<0.05). Adding low-dose sildenafil to surfactant is effective in alleviating the progressive PHT developed in newborn piglets induced by thromboxane A(2). Intratracheal sildenafil may be a useful therapeutic adjunct to critically ill neonates with PHT.

Superoxide and Chronic Hypoxia-Induced Pulmonary Hypertension in Newborn Piglets

Free radicals, including superoxide, O2−, have been implicated in the pathogenesis of certain types of pulmonary hypertension. Yet, the role of O2− in chronic hypoxia-induced pulmonary hypertension in newborns is unknown. Moreover, there is little information regarding the influence of chronic hypoxia on the expression of O2− enzymatic scavenging systems, such as the cytosolic copper/zinc containing enzyme, superoxide dismutase (SOD)-1 or mitochondrial manganese SOD (SOD-2). Our purpose was to determine whether O2− is involved with the abnormal constrictor responses that develop in resistance pulmonary arteries (RPAs) of newborn pigs exposed to 3 days of hypoxia.

Sildenafil and an early stage of chronic hypoxia‐induced pulmonary hypertension in newborn piglets

Devising therapies that might prevent the onset or progression of pulmonary hypertension in newborns has received little attention. Our major objective was to determine whether sildenafil, a selective phosphodiesterase inhibitor, prevents the development of an early stage of chronic hypoxia-induced pulmonary hypertension in newborn pigs. Another objective was to determine whether sildenafil causes pulmonary vasodilation without systemic vasodilation in piglets with chronic pulmonary hypertension. Piglets were raised in room air (control, n = 5) or 10-11% O(2) (hypoxic, n = 17) for 3 days. Some piglets (n = 4) received oral sildenafil, 12 mg/kg/day, throughout exposure to hypoxia. All piglets were anesthetized and catheterized, and pulmonary arterial pressure (Ppa), pulmonary wedge pressure (Pw), aortic pressure (Ao), and cardiac output (CO) were measured. Then for some piglets raised in hypoxia for 3 days, a single oral sildenafil dose (3 mg/kg, n = 6) or placebo (n = 5) was given, and hemodynamic measurements were repeated. For piglets raised in hypoxia for 3 days, mean Ppa and calculated PVR were elevated above respective values in control piglets. Mean Ppa and PVR did not differ between piglets that received sildenafil throughout exposure to hypoxia and those that did not. For piglets with chronic hypoxia-induced pulmonary hypertension that received a single oral dose of sildenafil, mean Ppa and PVR decreased, while mean Pw, CO, mean Ao, and systemic vascular resistance remained the same. All hemodynamic measurements were unchanged after placebo. Oral sildenafil did not influence the early stage of chronic hypoxia-induced pulmonary hypertension in newborn piglets. However, a single oral dose of sildenafil caused pulmonary vasodilation, without systemic vasodilation, in piglets with chronic hypoxia-induced pulmonary hypertension, which may have therapeutic implications.

Effects of a Nebulized NONOate, DPTA/NO, on Group B Streptococcus–Induced Pulmonary Hypertension in Newborn Piglets

NONOates are chemical compounds that are stable as solids but generate nitric oxide (NO) in aqueous solutions. When nebulized or instilled intratracheally, NONOates can attenuate pulmonary hypertension in adult animals with lung injury. To assess the effect of a nebulized NONOate, DPTA/NO, on group B Streptococcus (GBS)-induced pulmonary hypertension in newborn piglets, we studied 20 anesthetized and mechanically ventilated piglets (4-10 d). They were randomly assigned to receive nebulized placebo solution or DPTA/NO (100 mg) 15 min after sustained pulmonary hypertension. Pulmonary artery and wedge, systemic, and right atrial pressures; cardiac output; and arterial blood gases were obtained at baseline and every 15 min during 120 min of continuous GBS infusion (6 x 10(8) CFU/min). Methemoglobin levels were measured at baseline and 60 min. A significant decrease in pulmonary artery pressure, pulmonary vascular resistance (PVR), systemic arterial pressure, and systemic vascular resistance (SVR) was observed after DPTA/NO nebulization (p <0.001). Whereas the increase in PVR/SVR observed after GBS infusion was sustained for 120 min in the placebo group, this ratio decreased after DPTA/NO nebulization and remained significantly lower throughout the study period (p <0.01). Cardiac output, arterial blood gases, and methemoglobin values did not differ between groups. These data demonstrate that the pulmonary hypertension induced by GBS infusion is markedly attenuated by DPTA/NO nebulization. The lower PVR/SVR observed in the treated group indicates that the vasodilatory effect of NONOate is more pronounced in the pulmonary than systemic vasculature. Therefore, NONOates may have clinical application in the management of pulmonary hypertension secondary to sepsis in neonates.

The Effect of a Nebulized NO Donor, DPTA/NO, on Acute Hypoxic Pulmonary Hypertension in Newborn Piglets

NONOates, novel NO donors, are complexes of NO with nucleophiles which spontaneously and nonenzymatically release NO in aqueous solution. This study sought to determine the cardiopulmonary effects of the nebulized NONOate dipropylenetriamine (DPTA)/NO in newborn piglets with acute hypoxia-induced pulmonary hypertension. Twenty sedated and mechanically ventilated piglets (4–10 days old) exposed to hypoxia (Fi_O2 = 0.14) were randomly assigned to receive nebulized saline as placebo (PL) or DPTA/NO (75 mg) after 30 min of hypoxia. Pulmonary artery (P_pa) and wedge pressures, systemic (P_sa) and right atrial pressures, cardiac output (CO) and arterial blood gas were measured at baseline and every 15 min for 2 h. Methemoglobin levels were measured at baseline and 1 h after drug nebulization. Data (means ± SD) were analyzed by repeated-measures analysis of variance. Acute hypoxia resulted in an increase in P_pa and pulmonary vascular resistance (PVR), which was significantly attenuated by DPTA/NO nebulization as compared to the PL group (p < 0.0001). Changes in P_sa, CO, systemic vascular resistance (SVR), arterial blood gas and methemoglobin levels were not different between groups. In contrast to the increase in PVR/SVR observed during hypoxia in the PL group, there was a significant decrease in this ratio after NONOate administration (p < 0.0001). These data show that acute hypoxic pulmonary hypertension in newborn piglets is markedly attenuated by NONOate nebulization. This response is predominantly in the pulmonary vasculature as the PVR/SVR was significantly lower in the treated group. We speculate that NONOates may have clinical application in the treatment of persistent pulmonary hypertension of the newborn.

Impaired NO signaling in small pulmonary arteries of chronically hypoxic newborn piglets.

We performed studies to determine whether chronic hypoxia impairs nitric oxide (NO) signaling in resistance level pulmonary arteries (PAs) of newborn piglets. Piglets were maintained in room air (control) or hypoxia (11% O(2)) for either 3 (shorter exposure) or 10 (longer exposure) days. Responses of PAs to a nonselective NO synthase (NOS) antagonist, N(omega)-nitro-L-arginine methylester (L-NAME), a NOS-2-selective antagonist, aminoguanidine, and 7-nitroindazole, a NOS-1-selective antagonist, were measured. Levels of NOS isoforms and of two proteins involved in NOS signaling, heat shock protein (HSP) 90 and caveolin-1, were assessed in PA homogenates. PAs from all groups constricted to L-NAME but not to aminoguanidine or 7-nitroindazole. The magnitude of constriction to L-NAME was similar for PAs from control and hypoxic piglets of the shorter exposure period but was diminished for PAs from hypoxic compared with control piglets of the longer exposure period. NOS-3, HSP90, and caveolin-1 levels were similar in hypoxic and control PAs. These findings indicate that NOS-3, but not-NOS 2 or NOS-1, is involved with basal NO production in PAs from both control and hypoxic piglets. After 10 days of hypoxia, NO function is impaired in PAs despite preserved levels of NOS-3, HSP90, and caveolin-1. The development of NOS-3 dysfunction in resistance level PAs may contribute to the progression of chronic hypoxia-induced pulmonary hypertension in newborn piglets.

The role of endothelin converting enzyme inhibition during group B streptococcus-induced pulmonary hypertension in newborn piglets.

An endothelin-converting enzyme mediates the conversion from low-potency pro-endothelin to potent endothelin-1 (ET-1). Increased ET-1 levels have been observed in pulmonary hypertension of various etiologies in infants. We hypothesized that increased ET-1 levels induce pulmonary hypertension during group B Streptococcus (GBS) infusion, and this can be attenuated by the administration of an endothelin-converting enzyme inhibitor (ECEI). Twenty-two unanesthetized, chronically instrumented newborn piglets received a continuous infusion of GBS (3.5 x 10(8) colony-forming units/kg/min) while exposed to 100% O2. They were randomly assigned to receive a placebo (PL) or an ECEI (phosphoramidon, 30 mg/kg i.v.) 15 min after sustained pulmonary hypertension. Comparison of hemodynamic measurements and arterial blood gases at baseline and over the first 210 min from the onset of pulmonary hypertension was performed between groups. GBS infusion caused significant increases in mean pulmonary artery pressure, pulmonary vascular resistance (PVR), systemic vascular resistance (SVR), and PVR/SVR, and significant decreases in cardiac output, pH, and base excess. After the administration of ECEI, a significant reduction in pulmonary artery pressure (p < 0.0001), PVR (p < 0.001), and PVR/SVR (p < 0.01) and an improvement in cardiac output (p < 0.01) were observed during GBS infusion. The decrease in pH (p < 0.001) and base excess (p < 0.001) during GBS infusion was less marked after the administration of ECEI compared with the PL. Plasma ET-1 levels were obtained in 20 additional piglets; levels were significantly lower in the ECEI compared with PL after 3 h of GBS infusion (p < 0.02). All animals in the ECEI group survived the study period as opposed to 25% survival in the PL group (p < 0.001). These data suggest that the increased circulating ET-1 levels mediate, in part, the GBS-induced pulmonary hypertension.

Exhaled NO is reduced at an early stage of hypoxia-induced pulmonary hypertension in newborn piglets.

Altered nitric oxide (NO) production could contribute to the pathogenesis of hypoxia-induced pulmonary hypertension. To determine whether parameters of lung NO are altered at an early stage of hypoxia-induced pulmonary hypertension, newborn piglets were exposed to room air (control, n = 21) or 10% O(2) (hypoxia, n = 19) for 3-4 days. Some lungs were isolated and perfused for measurement of exhaled NO output and the perfusate accumulation of nitrite and nitrate (NOx-), the stable metabolites of NO. Pulmonary arteries (20-600-microm diameter) and their accompanying airways were dissected from other lungs and incubated for NOx- determination. Abundances of the nitric oxide synthase (NOS) isoforms endothelial NOS and neural NOS were assessed in homogenates of PAs and airways. The perfusate NOx- accumulation was similar, whereas exhaled NO output was lower for isolated lungs of hypoxic, compared with control, piglets. The incubation solution NOx- did not differ between pulmonary arteries (PAs) of the two groups but was lower for airways of hypoxic, compared with control, piglets. Abundances of both eNOS and nNOS proteins were similar for PA homogenates from the two groups of piglets but were increased in airway homogenates of hypoxic compared with controls. The NO pathway is altered in airways, but not in PAs, at an early stage of hypoxia-induced pulmonary hypertension in newborn piglets.

Arachidonic acid metabolites and an early stage of pulmonary hypertension in chronically hypoxic newborn pigs.

Our purpose was to determine whether production of arachidonic acid metabolites, particularly cyclooxygenase (COX) metabolites, is altered in 100-400-microm-diameter pulmonary arteries of piglets at an early stage of pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. A cannulated artery technique was used to measure responses of 100-400-microm-diameter pulmonary arteries to arachidonic acid, a prostacyclin analog, or the thromboxane mimetic. Radioimmunoassay was used to determine pulmonary artery production of thromboxane B(2) (TxB(2)) and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha)), the stable metabolites of thromboxane and prostacyclin, respectively. Assessment of abundances of COX pathway enzymes in pulmonary arteries was determined by immunoblot technique. Arachidonic acid induced less dilation in pulmonary arteries from hypoxic than in pulmonary arteries from control piglets. Pulmonary artery responses to prostacyclin and were similar for both groups. 6-Keto-PGF(1alpha) production was reduced, whereas TxB(2) production was increased in pulmonary arteries from hypoxic piglets. Abundances of both COX-1 and prostacyclin synthase were reduced, whereas abundances of both COX-2 and thromboxane synthase were unaltered in pulmonary arteries from hypoxic piglets. At least partly due to altered abundances of COX pathway enzymes, a shift in production of arachidonic acid metabolites, away from dilators toward constrictors, may contribute to the early phase of chronic hypoxia-induced pulmonary hypertension in newborn piglets.

Nitric Oxide in the Early Phase of Hypoxia-Induced Pulmonary Hypertension in Newborn Piglets † 1764

Nitric Oxide in the Early Phase of Hypoxia-Induced Pulmonary Hypertension in Newborn Piglets † 1764

Lipoxygenase and cyclooxygenase blockade by BW755C does not prevent the secondary phase of septic pulmonary hypertension

The infusion of Group B β hemolytic streptococci (GBS) in newborn animals generates a dual phase pulmonary hypertensive response. The initial, acute phase responds to cyclooxygenase or thromboxane inhibition, and appears to be thromboxane mediated. The second phase is characterized by a more moderate rise in pulmonary vascular resistance, accompanied by an increase in microvascular permeability. It has been speculated that this phase may be leukotriene mediated. In an attempt to clarify this, we have studied and compared the effects of the thromboxane synthetase inhibitor, Dazmegrel (DAZ), and the combined cyclooxygenase/lipoxygenase inhibitor, BW755C, on the cardiopulmonary hemodynamics of the secondary phase of GBS induced pulmonary hypertension in newborn piglets. Ten piglets were infused with GBS, and all animals developed a significant increase in pulmonary artery pressure (to 39 ± 5 and 36 ± 5 mmHg for DAZ and BW755C animals respectively). After one hour of GBS, either DAZ or BW755C was administered. Data were collected for another two hours following drug administration. GBS infusion was continued throughout. Both DAZ and BW755C were associated with transient, acute reductions in pulmonary artery pressure (to 22 ± 5 and 22 ± 8 mmHg, respectively). However, after 60 minutes, PAP again began to rise in both groups (PAP 30 ± 5 and 30 ± 11 mmHg respectively by 240 minutes). There were no differences between the groups at any time. These data do not support a significant role for lipoxygenase products in mediating the secondary phase of septic pulmonary hypertension.