Recombinant human superoxide dismutase enhances the effect of inhaled nitric oxide in persistent pulmonary hypertension.

We investigated the pulmonary vascular effects of superoxide dismutase (SOD) alone and in combination with inhaled nitric oxide (iNO) in newborn lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. In in vitro experiments, pretreatment with SOD significantly enhanced vascular relaxation in response to the NO donor S-nitrosyl-acetylpenicillamine (SNAP) in fifth-generation pulmonary arteries isolated from lambs with PPHN. In vivo treatment of fully instrumented newborn lambs with a single intratracheal dose of recombinant human CuZn SOD (rhSOD; 5 mg/kg) produced selective dilation of the pulmonary circulation. Further studies, of the combination of rhSOD and iNO, showed enhancement of the pulmonary vascular effects of iNO after brief periods of inhalation of 5 ppm and 80 ppm NO. We conclude that rhSOD reduces pulmonary vascular resistance and facilitates the action of iNO in a lamb model of PPHN. This suggests that rhSOD may prove to be an effective adjunctive treatment for newborns with PPHN.     

Superoxide dismutase improves oxygenation and reduces oxidation in neonatal pulmonary hypertension

RATIONALE: Hyperoxic ventilation in the management of persistent pulmonary hypertension of the newborn (PPHN) can result in the formation of reactive oxygen species, such as superoxide anions, which can inactivate nitric oxide (NO) and cause vasoconstriction and oxidation. OBJECTIVE: To compare the effect of intratracheal recombinant human superoxide dismutase (rhSOD) and/or inhaled NO (iNO) on systemic oxygenation, contractility of pulmonary arteries (PAs), and lung reactive oxygen species (isoprostane, 3-nitrotyrosine) levels in neonatal lambs with PPHN. METHODS: Six newborn lambs with PPHN (induced by antenatal ductal ligation) were killed at birth. Twenty-six PPHN lambs were ventilated for 24 h with 100% O(2) alone (n = 6) or O(2) combined with rhSOD (5 mg/kg intratracheally) at birth (n = 4), rhSOD at 4 h of age (n = 5), iNO (20 ppm, n = 5), or rhSOD + iNO (n = 6). Contraction responses of fifth-generation PAs to norepinephrine and KCl, lung isoprostane levels, and 3-nitrotyrosine fluorescent intensity were measured. RESULTS: Systemic oxygenation was impaired in PPHN lambs and significantly improved (up to threefold) in both rhSOD groups with or without iNO. Oxygenation improved more rapidly with the combination of rhSOD + iNO compared with either intervention alone. Norepinephrine- and KCl-induced contractions and lung isoprostane levels were significantly increased by 100% O(2) compared with nonventilated newborn lambs with PPHN. Both rhSOD and iNO mitigated the increased PA contraction response and lung isoprostane levels. Intratracheal rhSOD decreased the enhanced lung 3-nitrotyrosine fluorescence observed with iNO therapy. CONCLUSION: Intratracheal rhSOD and/or iNO rapidly increase oxygenation and reduce both vasoconstriction and oxidation in newborn lambs with PPHN. This has important implications for clinical trials of rhSOD and iNO in newborn infants with PPHN.     

Pulmonary hypertension alters soluble guanylate cyclase activity and expression in pulmonary arteries isolated from fetal lambs

The nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling pathway plays an important role in the pulmonary vascular transition at birth. We studied pulmonary arteries and veins isolated from normal late-gestation fetal lambs and from fetal lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. We additionally used double immunolabeling and immunoblot analysis to determine relative vascular contents of endothelial nitric oxide synthase (NOS-III) and soluble guanylate cyclase (sGC). Cyclic GMP content and sGC activity were significantly lower in arteries from hypertensive lambs than controls. A rank order for contents of both soluble guanylate cyclase and NOS-III was observed by both immunolabeling and immunoblotting: Control vein = Hypertensive vein > Control artery > Hypertensive artery. Our data demonstrate that the relative expression of sGC correlates well with the relative expression of NOS-III, and indicate the potential importance of soluble guanylate cyclase in the regulation of the perinatal pulmonary circulation. These data may help us understand vascular mechanisms producing PPHN, as well as patterns of response to exogenous NO.     

Type I nitric oxide synthase is decreased in the fetal pulmonary circulation of hypertensive lambs

The nitric oxide (NO)/guanosine 3',5'-cyclic monophosphate (cGMP) pathway plays an essential role in mediating pulmonary vasodilatation during transition of the pulmonary circulation at birth. We used immunoblot analysis (Western) and semiquantitative immunohistochemistry to study the presence, distribution, and relative amounts of type I nitric oxide synthase (NOS-I). Immunoblots were performed on normal fetal sheep lungs, whereas immunohistochemistry for NOS-I was compared between lungs from normal fetal lambs vs. fetal lambs with persistent pulmonary hypertension of the newborn (PPHN) induced by ligation of the ductus arteriosus.Western blot analysis using a polyclonal antibody detected NOS-I protein in homogenates of normal fetal sheep lungs. Abundant NOS-I immunoreactivity was observed exclusively in the precapillary resistance vessels, i.e., terminal bronchiole-associated arteries (TA) and respiratory bronchiole-associated arteries (RA) in normal fetal lung. In marked contrast, immunoreactivity for NOS-I was significantly reduced in the TA and RA of hypertensive lungs.We conclude that there is a heterogeneous distribution of NOS-I in the normal fetal sheep lung, but that NOS-I staining is significantly reduced in lambs with PPHN.     

Hyperoxia increases phosphodiesterase 5 expression and activity in ovine fetal pulmonary artery smooth muscle cells

In the pulmonary vasculature, cGMP concentrations are regulated in part by a cGMP-dependent phosphodiesterase (PDE), PDE5. Infants with persistent pulmonary hypertension of the newborn (PPHN) are often mechanically ventilated with high oxygen concentrations. The effects of hyperoxia on the developing pulmonary vasculature and PDE5 are largely unknown. Here, we demonstrate that exposure of fetal pulmonary artery smooth muscle cells (FPASMCs) to high levels of oxygen for 24 hours leads to decreased responsiveness to exogenous NO, as determined by a decreased intracellular cGMP response, increased PDE5 mRNA and protein expression, as well as increased PDE5 cGMP hydrolytic activity. We demonstrate that inhibition of PDE5 activity with sildenafil partially rescues cGMP responsiveness to exogenous NO. In FPASMCs, hyperoxia leads to increased oxidative stress without increasing cell death. Treatment of normoxic FPASMCs with H2O2 is sufficient to induce PDE5 expression and activity, suggesting that reactive oxygen species mediate the effects of hyperoxia in FPASMCs. In support of this mechanism, a chemical antioxidant, N-acetyl-cysteine, is sufficient to block the hyperoxia-mediated increase in PDE5 expression and activity and rescue cGMP responsiveness to exogenous NO. Finally, ventilation of healthy neonatal sheep with 100% O2 for 24 hours leads to increased PDE5 protein expression in the resistance pulmonary arteries and increased PDE5 activity in whole lung extracts. These data suggest that PDE5 expression and activity play a critical role in modulating neonatal pulmonary vascular tone in response to common clinical treatments for PPHN, such as oxygen and inhaled NO.     

Adenosine is a pulmonary vasodilator in newborn lambs.

We investigated the systemic and pulmonary vascular effects of adenosine and determined plasma adenosine levels in pulmonary circulation in 12 newborn lambs during normoxia and during alveolar hypoxia (10% O2, 5% CO2, and 85% N2). Lambs were instrumented at 7 days of age with catheters in the descending aorta, main pulmonary artery, and right and left atria, and a flow transducer around the main pulmonary artery, and were studied following a 3-day recovery. Adenosine or an equal volume of normal saline (control) was infused into the right atrial line in doses ranging from 0.01 to 2.5 mumol/kg/min. In normoxic lambs, adenosine caused a significant decrease in pulmonary vascular resistance and increase in heart rate in doses of 0.15 to 2.5 mumol/kg/min and a decrease in systemic vascular resistance, with increase in cardiac output in doses of 0.3 to 2.5 mumol/kg/min. Baseline plasma adenosine levels in pulmonary artery and left atrium decreased significantly during alveolar hypoxia. Adenosine infusion in hypoxic lambs caused decreases in pulmonary artery pressure and pulmonary vascular resistance at all the doses tested. Aortic pressure and systemic vascular resistance decreased, and heart rate and cardiac output increased at doses greater than or equal to 0.3 mumol/kg/min in hypoxic lambs during adenosine infusion. The pulmonary vascular effects of adenosine in hypoxic lambs were attenuated by prior treatment of animals with aminophylline. Thus, adenosine appears to be an important regulator of pulmonary vascular response to hypoxia in newborn lambs. Its vasodilator effects were specific for pulmonary circulation when it was infused in doses less than or equal to 0.15 mumol/kg/min into the right atrium and appear to be mediated by P1 purinergic receptors.     

Effect of positive end-expiratory pressure on pulmonary vascular pressure-flow characteristics in canine endotoxin shock.

The vascular pulmonary pressure-flow (P-Q degree) relationships were studied in anesthetized dogs in order to characterize the distribution of total resistance in the pulmonary bed with respect to incremental resistance and critical closure prior to and after endotoxin insult. Incremental resistance was computed as the slope of the P-Q degree relation, whereas critical closure was referred to as the extrapolated pressure intercept at zero flow. P-Q degree coordinates were obtained by varying Q degree through graded inflation of right atrial balloon. The gradients across the arterial segment (Pa = Ppa - Pc) and across the venous segment (Pv = Pc - Pw) of the pulmonary vasculature were defined by the computation of effective capillary pressure (Pc) obtained from the analysis of the transient decay of pulmonary artery pressure (Ppa) toward wedge pressure (Pw) after arterial occlusion. Six group E dogs were infused with endotoxin at a rate of 0.25 microgram/kg min, while six additional animals served as control (group C). Endotoxin induced increases in flow resistance from 0.056 to 0.096 mm Hg/ml/min/kg due to arterial vasoconstriction and increases in critical closure from 2.3 to 8.4 mm Hg due to a venous waterfall. Before and after endotoxin insult, we assessed effects of each of three levels of static lung inflation (PEEP) on P-Q degree relationships.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased superoxide generation is associated with pulmonary hypertension in fetal lambs: a role for NADPH oxidase

Ligation of the ductus arteriosus in utero produces pulmonary hypertension and vascular remodeling in fetal and newborn lambs. However, the mechanisms producing these vascular changes are not well defined. Because reactive oxygen species (ROS) have been implicated as mediators of smooth muscle cell proliferation, we hypothesized that increased formation of ROS may be involved in the pathophysiology of pulmonary hypertension after in utero ductal ligation. Using ethidium fluorescence, we demonstrated an increase in superoxide levels after 9 days of ductal ligation compared with control lungs (P<0.05) that was localized to the adventitia and smooth muscle cells of hypertensive vessels. SOD-1 and SOD-2 protein levels and activities in lung, vein, and artery of hypertensive lambs were unchanged relative to controls after 2 days of ductal ligation. However, after 9 days, superoxide dismutase (SOD) activity was significantly decreased in arteries from ligated lambs without associated changes in SOD protein expression (P<0.05). Examination of NADPH oxidase expression as a potential source of the superoxide production indicated that the levels of p67phox, a subunit of the NADPH oxidase complex, were significantly increased in the pulmonary arteries, but not veins, from the ligated lung as early as 2 days (P<0.05). Functional analyses demonstrated that reducing superoxide levels significantly increased the NO-mediated relaxation of pulmonary arteries isolated after 9 days, but not 2 days, of ductal ligation (P<0.05). These results suggest that increased NADPH oxidase expression may increase levels of superoxide in persistent pulmonary hypertension of the newborn lung tissue, and that increased superoxide blunts vascular relaxations to exogenous NO while stimulating smooth muscle cell growth.     

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.     

Hormone ontogeny in the ovine fetus. XXV. Somatotrope desensitization to growth hormone releasing factor (GRF) independent of short-latency, ultrashortloop GH feedback

Plasma ovine growth hormone (oGH) concentrations are strikingly elevated in the ovine fetus and decline at birth towards the low levels observed in the newborn lamb. We postulated that developmental changes in somatotrope function secondary to GH-releasing factor (GRF) desensitization and GH feedback play a role in the developmental pattern of oGH secretion and tested this hypothesis in vito in chronically catheterized ovine fetuses (123-145 days gestation; term 147 days) and newborn lambs (1-18 days). In the first set of studies, two consecutive intravenous GRF(1-44 amide) boluses (1 microgram/kg) were administered. When the GRF boluses were given 90 min apart, they elicited similar oGH responses, both in fetuses and in newborn lambs. In contrast, when the GRF boluses were given 20 min apart, a significant oGH response was evoked by the first GRF but an oGH response was not detected after the second GRF, either in fetuses or in newborn lambs. When the oGH response GRF(1-44 amide; 1 microgram/kg i.v.) was evaluated 40 min after the start of a human GH infusion (25 micrograms/kg hGH bolus followed by 0.5 microgram/kg/min hGH for 80 min, resulting in mean hGH plasma concentrations of 80 ng/ml), the exogenous hGH did not after the oGH response to GRF, either in fetuses or in newborn lambs. The present in vivo results demonstrate that the fetal and the neonatal somatotrope can be desensitized to GRF and suggest that a short-term latency, ultrashortloop GH feedback mechanism is not operative, either in the ovine fetus or in the newborn lamb.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhaled nitric oxide and vasoconstrictors in acute respiratory distress syndrome.

It has been suggested that the increase in PO(2) observed with nitric oxide (NO) should be enhanced by the addition of a vasoconstrictor agent. The vasoconstrictor used in combination with NO should mimic or enhance hypoxic vasoconstriction. The aim of this study was to evaluate the respiratory and hemodynamic effects of norepinephrine (a nonspecific vasoconstrictor), almitrine bismesylate (a specific pulmonary vasoconstrictor), and inhaled NO, alone or together. During a 6-mo period, 16 patients presenting with ARDS were prospectively investigated. On inclusion, no patient was receiving cardiovasoactive drugs. The protocol consisted of seven consecutive phases: baseline, norepinephrine (in order to obtain a 3 mm Hg rise in mean pulmonary arterial pressure [Ppa]), almitrine bismesylate (16 micrograms/kg/min), inhaled NO (20 ppm delivered during inspiration), norepinephrine + inhaled NO, almitrine bismesylate + inhaled NO, almitrine bismesylate + norepinephrine + inhaled NO. General factorial analysis of variance showed that inhaled NO and almitrine bismesylate increased oxygenation (p < 0.0001). Norepinephrine had no effect on oxygenation. A synergistic effect between inhaled NO and almitrine bismesylate was found (p < 0.05), whereas norepinephrine did not affect the response to inhaled NO. Nitric oxide produced a significant decrease in Ppa and pulmonary vascular resistances (PVRI) (p < 0.0001). Both almitrine bismesylate and norepinephrine induced an increase in Ppa (p < 0.0001). Norepinephrine increased PVRI (p < 0.002), whereas almitrine bismesylate had no effect on PVRI. The present results support the hypothesis that a selective pulmonary vasoconstrictor enhances the increase in oxygenation induced by inhaled NO, whereas norepinephrine attenuates this effect.     

Effects of dopamine and dobutamine on hyperoxic and hypoxic pulmonary vascular tone in dogs

The pulmonary vascular effects of dopamine and of dobutamine have been reported variably in the literature. We investigated the effects of dopamine and of dobutamine, at doses of 10 and 20 micrograms/kg/min, on the relationships of overall mean pulmonary arterial pressure (Ppa) to cardiac index (Cl) in 14 dogs ventilated alternatively in hyperoxic (FIO2, 0.4) and in hypoxic (FIO2, 0.1) conditions. Five-point Ppa/Cl plots were constructed by opening an arteriovenous femoral fistula or by stepwise inflations of a balloon in the inferior vena cava. These Ppa/Cl plots were rectilinear in all experimental conditions. Hypoxia was associated with an increase in Ppa over the entire range of Cl studied (2 to 5 L/min/m2). A deterioration in arterial oxygenation and an increase in O2 consumption constantly occurred after dopamine as well as after dobutamine administration. At 10 micrograms/kg/min (n = 6 dogs) neither drug affected Ppa over the entire range of Cl at both 0.4 and 0.1 FIO2. At 20 micrograms/kg/min (n = 8 dogs), dopamine and dobutamine increased Ppa at the lowest Cl (2 to 4 and 2 to 3 L/min/m2, respectively) at 0.4 FIO2, and attenuated hypoxia-induced increases in Ppa over the entire range of Cl. Two repetitions of alternated 0.4 and 0.1 FIO2 exposures had no effect on Ppa/Cl plots in 6 additional dogs given no drug. We concluded that at dosages as great as 20 micrograms/kg/min, as generally given in clinical practice, dopamine and dobutamine exerted similar effects upon the pulmonary circulation of intact dogs; either no change or an increase in hyperoxic pulmonary vascular tone and either no change or an attenuation of hypoxic pulmonary vasoconstriction.     

Ghrelin ameliorates hypoxia-induced pulmonary hypertension via phospho-GSK3 β/β-catenin signaling in neonatal rats

Effective treatment and/or prevention strategies for neonatal persistent pulmonary hypertension of the newborn (PPHN) have been an important topic in neonatal medicine. However, mechanisms of impaired pulmonary vascular structure in hypoxia-induced PPHN are poorly understood and consequently limit the development of effective treatment. In this study, we aimed to explore the molecular signaling cascades in the lungs of a PPHN animal model and used primary cultured rat pulmonary microvascular endothelial cells to analyze the physiological benefits of ghrelin during the pathogenesis of PPHN. Randomly selected newborn rats were exposed to hypoxia (10-12%) or room air and received daily s.c. injections of ghrelin (150 μg/kg) or saline. After 2 weeks, pulmonary hemodynamics and morphometry were assessed in the rats. Compared with the control, hypoxia increased pulmonary arterial pressure, right ventricle (RV) hypertrophy, and arteriolar wall thickness. Ghrelin treatment reduced both the magnitude of PH and the RV/(left ventricle+septum (Sep)) weight ratio. Ghrelin protected neonatal rats from hypoxia-induced PH via the upregulation of phosphorylation of glycogen synthase kinase 3β (p-GSK3β)/β-catenin signaling and associated with β-catenin translocation to the nucleus in the presence of growth hormone secretagogue receptor-1a. Our findings suggest that s.c. administration of ghrelin improved PH and attenuated pulmonary vascular remodeling after PPHN. These beneficial effects may be mediated by the regulation of p-GSK3β/β-catenin expression. We propose ghrelin as a novel potential therapeutic agent for PPHN.     

Partitioning of Pulmonary Vascular Resistance in Primary Pulmonary Hypertension

Objectives. This study sought to determine the site of increased pulmonary vascular resistance (PVR) in primary pulmonary hypertension by standard bedside hemodynamic evaluation.Background. The measurement of pulmonary vascular pressures at several levels of flow (Q) allows the discrimination between active and passive, flow-dependent changes in mean pulmonary artery pressure (Ppa), and may detect the presence of an increased pulmonary vascular closing pressure. The determination of a capillary pressure (Pc′) from the analysis of a Ppa decay curve after balloon occlusion allows the partitioning of PVR in an arterial and a (capillary + venous) segment. These approaches have not been reported in primary pulmonary hypertension.Methods. Ppa and Pc′ were measured at baseline and after an increase in Q induced either by exercise or by an infusion of dobutamine, at a dosage up to 8 μg/kg body weight per min, in 11 patients with primary pulmonary hypertension. Reversibility of pulmonary hypertension was assessed by the inhalation of 20 ppm nitric oxide (NO), and, in 6 patients, by an infusion of prostacyclin.Results. At baseline, Ppa was 52 ± 3 mm Hg (mean value ± SE), Q 2.2 ± 0.2 liters/min per m², and Pc′ 29 ± 3 mm Hg. Dobutamine did not affect Pc′ and allowed the calculation of an averaged extrapolated pressure intercept of Ppa/Q plots of 34 mm Hg. Inhaled NO had no effect. Prostacyclin decreased Pc′ and PVR. Exercise increased Pc′ to 40 ± 3 mm Hg but did not affect PVR.Conclusions. These findings are compatible with a major increase of resistance and reactivity at the periphery of the pulmonary arterial tree.     

Hypoxia decreases exhaled nitric oxide in mountaineers susceptible to high-altitude pulmonary edema

An exaggerated hypoxic pulmonary vasoconstriction is essential for development of high-altitude pulmonary edema (HAPE). We hypothesized that susceptibility to HAPE may be related to decreased production of nitric oxide (NO), an endogenous modulator of pulmonary vascular resistance, and that a decrease in exhaled NO could be detected during hypoxic exposure. Therefore, we investigated respiratory tract NO excretion by chemiluminescence and pulmonary artery systolic pressure (Ppa,s) by echocardiography in nine HAPE-susceptible mountaineers and nine HAPE-resistant control subjects during normoxia and acute hypoxia (fraction of inspired oxygen [FI(O2)] = 0.12). The subjects performed oral breathing. Nasally excreted NO was separated from respiratory gas by suction via a nasal mask. In HAPE-susceptible subjects, NO excretion in expired gas significantly decreased (p < 0.05) during hypoxia of 2 h in comparison with normoxia (28 +/- 4 versus 21 +/- 2 nl/min, mean +/- SEM). In contrast, the NO excretion rate of control subjects remained unchanged (31 +/- 6 versus 33 +/- 6 nl/ min, NS). Nasal NO excretion did not differ significantly between groups during normoxia (HAPE-susceptible group, 183 +/- 16 nl/ min; control subjects, 297 +/- 55 nl/min, NS) and was not influenced by hypoxia. The changes in Ppa,s with hypoxia correlated with the percent changes in lower respiratory tract NO excretion (R = -0.49, p = 0.04). Our data provide the first evidence of decreased pulmonary NO production in HAPE-susceptible subjects during acute hypoxia that may contribute among other factors to their enhanced hypoxic pulmonary vascular response.     

Pathophysiologic mechanisms of persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN), among the most rapidly progressive and potentially fatal of vasculopathies, is a disorder of vascular transition from fetal to neonatal circulation, manifesting as hypoxemic respiratory failure. PPHN represents a common pathway of vascular injury activated by numerous perinatal stresses: hypoxia, hypoglycemia, cold stress, sepsis, and direct lung injury. As with other multifactorial diseases, a single inciting event may be augmented by multiple concurrent/subsequent phenomena that result in differing courses of disease progression. I review the various mechanisms of vascular injury involved in neonatal pulmonary hypertension: endothelial dysfunction, inflammation, hypoxia, and mechanical strain, in the context of downstream effects on pulmonary vascular endothelial-myocyte interactions and myocyte phenotypic plasticity.     

Platelet-activating factor causes pulmonary vasodilation in the rat

Although platelet-activating factor (PAF) has generally been found to be a pulmonary pressor substance, its vasoactivity has not been measured at low doses in a preconstricted pulmonary vascular bed. Thus, we examined the effects of low concentrations of PAF on systemic and pulmonary hemodynamics during normoxia and acute hypoxia in conscious, catheterized rats (weighing 250 to 350 g), on hypoxic vasoconstriction in isolated rat lungs, and on norepinephrine-induced constriction in isolated, intact, and endothelium-denuded rat pulmonary arteries. In normoxic rats, injections of 0.001, 0.01, 0.1, and 1.0 microgram PAF/rat given intravenously caused progressively greater, transient systemic hypotension and tachycardia. The 2 higher doses also decreased cardiac output and pulmonary arterial pressure (Ppa). In 5 rats breathing 8% O2, Ppa fell from 36 +/- 2 to 30 +/- 2 torr within 1 min of injection of 0.01 microgram PAF and did not change (39 +/- 2 versus 40 +/- 2 torr) 1 min after 0.25% albumin (vehicle). Total pulmonary resistance was 0.18 +/- 0.04 torr/ml/min in normoxic rats and 0.19 +/- 0.04 and 0.28 +/- 0.06 torr/ml/min, respectively, in hypoxic rats receiving 0.01 microgram PAF or vehicle. The PAF (10(-10) to 10(-8) g/ml) also reversed hypoxic vasoconstriction in isolated lungs perfused at constant flow. Lungs perfused with salt solution but not those with blood became rapidly densensitized to PAF-induced vasodilation. After constriction with 10(-6) M norepinephrine, both acetylcholine (10(-7) to 10(-6) M) and PAF (10(-10) to 10(-9) g/ml) dilated intact but not endothelium-denuded pulmonary artery rings.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of angiotensin converting enzyme inhibitor and calcium channel blocker on normoxic and hypoxic pulmonary vascular tone in unanesthetized sheep

We evaluated the effects of captopril and nifedipine on normoxic and hypoxic pulmonary vascular tone in unanesthetized sheep. Infusion of captopril (10 micrograms/kg/min) in normoxia revealed a tendency to increase the mean pulmonary arterial pressure (Ppa) and the pulmonary vascular resistance (PVR) following the systemic vasodilation. A statistically significant increase was reached by 20 minutes. Hypoxia of 10% oxygen in nitrogen produced a prominent pulmonary hypertensive response. Captopril significantly decreased the hypoxic values of Ppa and PVR from 20.3 +/- 1.3 to 17.1 +/- 1.1 mmHg (p less than 0.01) and from 4.31 +/- 0.45 to 3.49 +/- 0.45 mmHg/L/min (p less than 0.01), respectively. Infusion of nifedipine (10 micrograms/kg/min) in normoxia caused an increase in Ppa from 15.5 +/- 0.9 to 18.9 +/- 1.0 mmHg (p less than 0.01), but not in PVR. This elevation in Ppa was considered to be derived from the significant increase in the cardiac output. Nifedipine significantly decreased the hypoxic values of Ppa and PVR from 21.3 +/- 1.5 to 19.3 +/- 1.5 mmHg (p less than 0.05) and from 3.88 +/- 0.30 to 27.3 +/- 0.13 mmHg/L/min (p less than 0.01), respectively. Captopril and nifedipine produced systemic hypotensive responses during both normoxic and hypoxic ventilation. It is concluded that both captopril and nifedipine are potent pulmonary vasodilating drugs in animal subjects with a hypoxic condition and that they might be useful in the clinical vasodilator therapy of hypoxic pulmonary hypertension in man.     

Ventilation-induced pulmonary vasodilatation in lambs with congenital diaphragmatic hernia is modulated by nitric oxide

Endogenous nitric oxide (NO) mediates pulmonary vasodilatation at birth, but inhaled NO fails to reduce pulmonary vascular resistance (PVR) in newborns with congenital diaphragmatic hernia (CDH). This study was designed to investigate the effects of ventilation, and the nature of its endogenous mediator, in fetal lambs with experimental CDH. Investigations at 138 days of gestation showed that ventilation markedly decreased PVR. Inhibition of NO synthesis reduced ventilation-induced pulmonary vasodilatation in vivo and increased in vitro isometric tension of vascular rings. Ventilation therefore reduces PVR at birth in lambs with CDH, and endogenous NO seems to contribute to this reduction.     

Pulmonary artery pressure--flow plots in hyperoxic and in hypoxic dogs: effects of prostaglandin E1

The effects of prostaglandin E1 on mean pulmonary artery pressure (Ppa):cardiac index (Q) relationships were investigated in eight anaesthetized dogs, ventilated in hyperoxia (fraction of inspired oxygen (FiO2) 0.4) and in hypoxia (FiO2 0.1). Cardiac output was increased by opening an arterio-venous femoral bypass or reduced by stepwise inflations of a balloon in the inferior vena cava. Five-point Ppa:Q relationships were found to be linear in all experimental conditions. Hypoxia increased Ppa over the entire range of Q studied (1-5l.min-1.m-2). Prostaglandin E1 0.4 microgram.kg-1.min-1 intravenously decreased hyperoxic Ppa for Q ranging from 3-5 l.min-1.m-2, hypoxic Ppa for Q ranging from 2-5 l.min-1.m-2 and attenuated hypoxia-induced increases in Ppa. These results show that prostaglandin E1 is a pulmonary vasodilator in both hyperoxic and hypoxic conditions. At the dose of 0.4 microgram.kg-1, prostaglandin E1 partially inhibits hypoxic pulmonary vasoconstriction.