Effect of ischemia reperfusion or hypoxia reoxygenation on lung vascular permeability and resistance

The effect of ischemia reperfusion or hypoxia reoxygenation on pulmonary vascular permeability and resistance was studied in 25 isolated blood-perfused dog lungs. Vascular permeability, assessed by determining filtration coefficient (Kf), and vascular resistances were measured at the beginning and end of the experiment. Ischemia reperfusion was produced by occluding blood flow to the lung for 3 h and reperfusing for 1 h, whereas hypoxia reoxygenation was obtained by ventilating the lung with 95% N2-5% CO2 for 3 h and then ventilating with 95% O2-5% CO2 for 1 h with no interruption of perfusion. There was a significant increase in Kf in both ischemia reperfusion and hypoxia reoxygenation groups (51 and 85%, respectively), and total vascular resistance increased greatly in both groups (386 and 532%, respectively). Two additional groups were also studied in which the ischemia reperfusion or hypoxia reoxygenation lungs were pretreated with allopurinol (20 micrograms/ml). The Kf did not significantly increase in either the allopurinol ischemia reperfusion or the allopurinol hypoxia reoxygenation groups (22 and 6%, respectively). However, total vascular resistance significantly increased in both groups (239 and 224%, respectively). Although vascular permeability is modestly increased by both ischemia reperfusion and hypoxia reoxygenation, the predominant change in these conditions is the increased vascular resistance, which predominantly affects the postcapillary resistance and would result in a greater tendency for edema to develop in these slightly damaged lungs. Allopurinol, which inhibits xanthine oxidase, attenuated the permeability changes in both groups and may be useful in preventing ischemia reperfusion injury in certain conditions.     

Permeability characteristics of isolated perfused rat lungs

We examined the factors that influence the permeability characteristics of isolated perfused rat lungs and compared the ex vivo permeability-surface area product (PS) with that obtained in vivo. In lungs perfused for 20 min with homologous blood or a physiological salt solution (PSS) containing 4 g/100 ml albumin, mean PS values, obtained by the single-sample method of Kern et al. [Am. J. Physiol. 245 (Heart Circ. Physiol. 14): H229-H236, 1983], were 9.9 +/- 0.6 (SE) and 6.8 +/- 0.3 cm3.min-1.g wet lung-1.10(-2), respectively. These values were similar to lung PS obtained in intact rats (7.7 +/- 0.4 cm3.min-1.g wet lung-1.10(-2). In perfused lungs, PS values were influenced by the perfusate albumin concentration, the length of perfusion time, and the degree of vascular recruitment. Twenty minutes after lung isolation, PS was 126% higher in lungs perfused with albumin-free PSS containing Ficoll than in lungs perfused with albumin-PSS. Moreover, PS in Ficoll-PSS-perfused lungs increased even higher after 2 h of perfusion, and this time-dependent increase in PS was attenuated by addition of 0.1 g/100 ml albumin to the perfusate. Two hours of ex vivo ventilation with hypoxic (0 or 3% 0(2)) or hyperoxic (95% 0(2)) gas mixture did not affect PS values in perfused lungs. However, PS was elevated in lungs perfused ex vivo with protamine, which causes endothelial cell injury, or in lungs from rats exposed in vivo to human recombinant tumor necrosis factor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Attenuation of hypoosmotic stress-induced ANP secretion via I(Cl,swell) in renal hypertensive rat atria

Cardiac hypertrophy, an adaptive process to an increased hemodynamic overload, includes not only an increase in cell size but also qualitative changes in constituent proteins. Although swelling-activated chloride channels (I(Cl,swell)) chronically activate in hypertrophied atrial myocytes, the role of I(Cl,swell) in regulation of atrial natriuretic peptide (ANP) release is poorly understood. We investigated the effects of I(Cl,swell) on ANP release and contractility and its modification in hypertrophied rat atria. To stimulate I(Cl,swell), hypoosmotic HEPES buffered solution (0.8T, 0.7T and 0.6T) was perfused into isolated perfused beating atria. The hypoosmotic HEPES buffered solution increased ANP release as compared to isoosmotic buffered solution (1T) in an osmolarity-reduction dependent manner. Atrial contractility and extracellular fluid translocation did not change. Exposure to hypoosmotic buffer (0.8T) containing low chloride (8mM), tamoxifen or diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) significantly attenuated hypoosmolarity-induced ANP release. The pretreatment with genistein, okdaic acid, U73122, GF109203x, and staurosporine attenuated hypoosmolarity-induced ANP release whereas orthovanadate augmented it significantly. In hypertrophied atria from renal hypertensive rats, hypoosmolarity-induced ANP release was markedly attenuated and DIDS-induced decrease in ANP release and negative inotropy were augmented as compared to sham-operated rat atria. Therefore, we suggest that I(Cl,swell) may partly participate hypoosmolarity-induced ANP release through protein tyrosine kinase and phospholipase C-protein kinase C pathway. The modification of responses of ANP release to hypoosmolarity and DIDS in hypertrophied atria may relate to changes in I(Cl,swell) activity by persistent high blood pressure.     

Pulmonary vascular reactivity in Fischer rats

We previously reported that Fischer (F) rat lungs developed more extensive injury when challenged with oxidants than age-matched Sprague-Dawley (SD) rat lungs. We now describe a reduced pulmonary vascular response to alveolar hypoxia and angiotensin II (ANG II) in F compared with SD rats. The comparative studies were performed with isolated lungs perfused with salt solution or blood, catheter-implanted awake rats, and isolated main pulmonary arterial rings. Isolated lungs from F rats perfused with either blood or salt solution had reduced vasoconstriction in comparison with lungs from SD rats when exposed to alveolar hypoxia or challenged with ANG II. Instrumented awake F rats had a smaller mean increase in total pulmonary vascular resistance (PVR) than SD rats (35 vs. 94 mmHg.min.l-1, P less than 0.05) when challenged with 8% oxygen. The contractile response of isolated pulmonary artery but not thoracic aortic rings to KCl and ANG II was reduced in F compared with SD rats. In addition, F rats exposed to 4 wk of hypobaric hypoxia developed less pulmonary hypertension and right ventricular hypertrophy (when corrected for the hematocrit) than SD rats. We conclude that the oxidant stress-sensitive inbred F rat strain is characterized by a lung vascular bed that is relatively unresponsive to vasoconstricting stimuli. The mechanism underlying this genetic difference in lung vascular control remains to be defined.     

Pulmonary arterial and venous constriction during hypoxia in 3- to 5-wk-old and adult ferrets

We have determined the sites of hypoxic vasoconstriction in ferret lungs. Lungs of five 3- to 5-wk-old and five adult ferrets were isolated and perfused with blood. Blood flow was adjusted initially to keep pulmonary arterial pressure at 20 cmH2O and left atrial and airway pressures at 6 and 8 cmH2O, respectively (zone 3). Once adjusted, flow was kept constant throughout the experiment. In each lung, pressures were measured in subpleural 20- to 50-microns-diam arterioles and venules with the micropipette servo-nulling method during normoxia (PO2 approximately 100 Torr) and hypoxia (PO2 less than 50 Torr). In normoxic adult ferret lungs, approximately 40% of total vascular resistance was in arteries, approximately 40% was in microvessels, and approximately 20% was in veins. With hypoxia, the total arteriovenous pressure drop increased by 68%. Arterial and venous pressure drops increased by 92 and 132%, respectively, with no change in microvascular pressure drop. In 3- to 5-wk-old ferret lungs, the vascular pressure profile during normoxia and the response to hypoxia were similar to those in adult lungs. We conclude that, in ferret lungs, arterial and venous resistances increase equally during hypoxia, resulting in increased microvascular pressures for fluid filtration.     

Neutrophils are not necessary for induction of ischemia-reperfusion lung injury

Ischemia-reperfusion lung injury limits lung transplantation. Neutrophil activation and/or xanthine oxidase-mediated purine degradation may cause toxic oxygen metabolite production and lung injury. We investigated whether circulating blood elements are involved in the pathogenesis of ischemia-reperfusion lung injury. Isolated rat lungs were perfused with physiological salt solution (PSS) stabilized with Ficoll until circulating blood elements were not detected in the lung effluent. Lungs were then rendered ischemic by stopping ventilation and perfusion for 45 min at room temperature. Lung injury occurred and was quantitated by the accumulation of 125I-bovine serum albumin into lung parenchyma and alveolar lavage fluid during reperfusion. Lung injury occurred, in the absence of circulating blood elements, when ischemic lungs were reperfused with PSS-Ficoll solution alone. Reperfusion with whole blood or PSS-Ficoll supplemented with human or rat neutrophils did not increase lung injury. Furthermore, during lung ischemia, the presence of neutrophils did not enhance injury. Experiments using PSS-albumin perfusate and quantitating lung injury by permeability-surface area product yielded similar results. Microvascular pressures were not different and could not account for the results. Toxic O2 metabolites were involved in the injury because addition of erythrocytes or catalase to the perfusate attenuated the injury. Thus reperfusion after lung ischemia causes injury that is dependent on a nonneutrophil source of toxic O2 metabolites.     

Oxygen radicals and antioxidant enzymes alter pulmonary vascular reactivity in the rat lung

It has been postulated that changes in the availability of partially reduced O2 species, such as O2 radicals, could serve as a link between PO2 in the alveolus and pulmonary vascular tone (Herz 11: 127-141, 1986). To assess this hypothesis, the hemodynamic effects of acute changes in the balance between the production of O2 radicals and availability of antioxidant enzymes were studied in the isolated perfused rat lung. Intravascular generation of O2 radicals, by administration of xanthine-xanthine oxidase, decreased the pulmonary vascular pressor response to alveolar hypoxia (-55 +/- 5%) and angiotensin II (-58 +/- 10%, P less than 0.01 for each) in isolated perfused rat lungs without increasing the lung wet-to-dry weight ratio. Decreases in pulmonary vascular reactivity were inhibited by pretreatment of the lung with desferrioxamine or a mixture of catalase and superoxide dismutase. Catalase and superoxide dismutase preserved the hypoxic pressor response whether given in liposomes or in dissolved form. Superoxide dismutase administered free in solution, or combined with catalase in liposomes, increased the normoxic pulmonary arterial pressure and enhanced vascular reactivity to angiotensin II and hypoxia. Lungs treated with antioxidant enzymes in liposomes had 50% higher lung catalase levels than control lungs (P less than 0.05). These findings demonstrate that exogenous partially reduced O2 species can decrease pulmonary vascular reactivity and suggest that endogenous radicals, superoxide radical in particular, might be important in modulating pulmonary vascular tone.     

Oxygen-dependent reperfusion injury in the isolated rat lung.

To further define the relationship between oxygen dependence of lung injury during ischemia and ischemia-reperfusion, we used the isolated, perfused, and ventilated rat lung model, so that oxygenation and perfusion could be separated. During ischemia, lungs were ventilated with various oxygen concentrations and then ventilated with 95% oxygen during the 60-min reperfusion period. Other lungs were ventilated with 0% oxygen (nitrogen) during ischemia, and the reperfusion phase oxygen concentration was varied. Tissue and perfusate lipid peroxidation products (thiobarbituric acid-reactive substances and conjugated dienes), dry-to-wet weight ratio, and lactate dehydrogenase were measured as indexes of lung damage. In addition, electron microscopy of some lungs was performed. Results demonstrate an oxygen dependence of lipid peroxidation in both the ischemic and reperfusion phases, but lipid peroxidation is severalfold greater in the reperfusion than in the ischemic phase. Products of lipid peroxidation closely correlate with indexes of lung injury (dry-to-wet weight ratio, lactate dehydrogenase, and electron microscopy).     

Protective effect of lung inflation in reperfusion-induced lung microvascular injury

We used the isolated-perfused rat lung model to study the influence of pulmonary ventilation and surfactant instillation on the development of postreperfusion lung microvascular injury. We hypothesized that the state of lung inflation during ischemia contributes to the development of the injury during reperfusion. Pulmonary microvascular injury was assessed by continuously monitoring the wet lung weight and measuring the vessel wall (125)I-labeled albumin ((125)I-albumin) permeability-surface area product (PS). Sprague-Dawley rats (n = 24) were divided into one control group and five experimental groups (n = 4 rats per group). Control lungs were continuously ventilated with 20% O(2) and perfused for 120 min. All lung preparations were ventilated with 20% O(2) before the ischemia period and during the reperfusion period. The various groups differed only in the ventilatory gas mixtures used during the flow cessation: group I, ventilated with 20% O(2); group II, ventilated with 100% N(2); group III, lungs remained collapsed and unventilated; group IV, same as group III but pretreated with surfactant (4 ml/kg) instilled into the airway; and group V, same as group III but saline (4 ml/kg) was instilled into the airway. Control lungs remained isogravimetric with baseline (125)I-albumin PS value of 4.9 +/- 0.3 x 10(-3) ml x min(-1) x g wet lung wt(-1). Lung wet weight in group III increased by 1.45 +/- 0.35 g and albumin PS increased to 17.7 +/- 2.3 x 10(-3), indicating development of vascular injury during the reperfusion period. Lung wet weight and albumin PS did not increase in groups I and II, indicating that ventilation by either 20% O(2) or 100% N(2) prevented vascular injury. Pretreatment of collapsed lungs with surfactant before cessation of flow also prevented the vascular injury, whereas pretreatment with saline vehicle had no effect. These results indicate that the state of lung inflation during ischemia (irrespective of gas mixture used) and supplementation of surfactant prevent reperfusion-induced lung microvascular injury.     

Fullerene derivative attenuates ischemia-reperfusion-induced lung injury

Reactive oxygen species are the major contributing factors to lung ischemia-reperfusion (IR) injury. In this study, we tested whether a water soluble antioxidant fullerene derivative [C(60)(ONO(2))(7 +/- 2)] attenuates IR lung injury. Young Wistar rats were divided into two groups: control and C(60)(ONO(2))(7 +/- 2). Under ventilation with 95% air-5% CO(2) gas mixture and a 2.5 cm H(2)O end-expiratory pressure, the isolated lungs were perfused with a physiological solution. The experimental protocol included three periods: baseline (10 min), ischemia (45 min) and reperfusion (60 min, ventilated with 95% O(2)-5% CO(2) gas mixture). Before and after ischemia, we measured pulmonary arterial pressure (Ppa), pulmonary venous pressure and lung weight (W). Then, pulmonary capillary pressure and filtration coefficient (K(fc)) were calculated. Ischemia caused increases in Ppa, W and K(fc) in the control group. For most cases, the above ischemia-induced increases were attenuated by the C(60)(ONO(2))(7 +/- 2) pretreatment. Our results suggest that the antioxidant C(60)(ONO(2))(7 +/- 2) attenuates IR-induced lung injury.     

Therapeutic hypercapnia prevents chronic hypoxia-induced pulmonary hypertension in the newborn rat

Induction of hypercapnia by breathing high concentrations of carbon dioxide (CO(2)) may have beneficial effects on the pulmonary circulation. We tested the hypothesis that exposure to CO(2) would protect against chronic pulmonary hypertension in newborn rats. Atmospheric CO(2) was maintained at <0.5% (normocapnia), 5.5%, or 10% during exposure from birth for 14 days to normoxia (21% O(2)) or moderate hypoxia (13% O(2)). Pulmonary vascular and hemodynamic abnormalities in animals exposed to chronic hypoxia included increased pulmonary arterial resistance, right ventricular hypertrophy and dysfunction, medial thickening of pulmonary resistance arteries, and distal arterial muscularization. Exposure to 10% CO(2) (but not to 5.5% CO(2)) significantly attenuated pulmonary vascular remodeling and increased pulmonary arterial resistance in hypoxia-exposed animals (P < 0.05), whereas both concentrations of CO(2) normalized right ventricular performance. Exposure to 10% CO(2) attenuated increased oxidant stress induced by hypoxia, as quantified by 8-isoprostane content in the lung, and prevented upregulation of endothelin-1, a critical mediator of pulmonary vascular remodeling. We conclude that hypercapnic acidosis has beneficial effects on pulmonary hypertension and vascular remodeling induced by chronic hypoxia, which we speculate derives from antioxidant properties of CO(2) on the lung and consequent modulating effects on the endothelin pathway.     

Activation of endothelial NADPH oxidase during normoxic lung ischemia is KATP channel dependent

Previous studies have shown endothelial cell membrane depolarization and generation of reactive oxygen species (ROS) in endothelial cells with abrupt reduction in shear stress (ischemia). This study evaluated the role of ATP-sensitive potassium (K(ATP)) channels and NADPH oxidase in the ischemic response by using Kir6.2-/- and gp91(phox)-/- mice. To evaluate ROS generation, we subjected isolated perfused mouse lungs labeled with 2',7'-dichlorodihydrofluorescein (DCF), hydroethidine (HE), or diphenyl-1-pyrenylphosphine (DPPP) to control perfusion followed by global ischemia. In wild-type C57BL/6J mice, imaging of subpleural endothelial cells showed a time-dependent increase in intensity for all three fluorescence probes with ischemia, which was blocked by preperfusion with cromakalim (a K(ATP) channel agonist) or diphenyleneiodonium (DPI, a flavoprotein inhibitor). Endothelial cell fluorescence with bis-oxonol, a membrane potential probe, increased during lung ischemia indicating cell membrane depolarization. The change in membrane potential with ischemia in lungs of gp91(phox)-/- mice was similar to wild type, but ROS generation did not occur. Lungs from Kir6.2-/- showed marked attenuation of the change in both membrane potential and ROS production. Thus membrane depolarization during lung ischemia requires the presence of a K(ATP) channel and is required for activation of NADPH oxidase and endothelial ROS generation.     

Downregulation of hypoxic vasoconstriction by chronic hypoxia in rabbits: effects of nitric oxide

Hypoxic pulmonary vasoconstriction (HPV) matches lung perfusion to ventilation for optimizing pulmonary gas exchange. Chronic alveolar hypoxia results in vascular remodeling and pulmonary hypertension. Previous studies have reported conflicting results of the effect of chronic alveolar hypoxia on pulmonary vasoreactivity and the contribution of nitric oxide (NO), which may be related to species and strain differences as well as to the duration of chronic hypoxia. Therefore, we investigated the impact of chronic hypoxia on HPV in rabbits, with a focus on lung NO synthesis. After exposure of the animals to normobaric hypoxia (10% O(2)) for 1 day to 10 wk, vascular reactivity was investigated in ex vivo perfused normoxic ventilated lungs. Chronic hypoxia induced right heart hypertrophy and increased normoxic vascular tone within weeks. The vasoconstrictor response to an acute hypoxic challenge was strongly downregulated within 5 days, whereas the vasoconstrictor response to the thromboxane mimetic U-46619 was maintained. The rapid downregulation of HPV was apparently not linked to changes in the lung vascular NO system, detectable in the exhaled gas and by pharmacological blockage of NO synthesis. Treatment of the animals with long-term inhaled NO reduced right heart hypertrophy and partially maintained the reactivity to acute hypoxia, without any impact on the endogenous NO system being noted. We conclude that chronic hypoxia causes rapid downregulation of acute HPV as a specific event, preceding the development of major pulmonary hypertension and being independent of the lung vascular NO system. Long-term NO inhalation partially maintains the strength of the hypoxic vasoconstrictor response.     

Hypoxic pulmonary vasoconstriction is modified by P-450 metabolites

20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P-450 4A (CYP4A) metabolite of arachidonic acid (AA) in human and rabbit lung microsomes and is a dilator of isolated human pulmonary arteries (PA). However, little is known regarding the contribution of P-450 metabolites to pulmonary vascular tone. We examined 1) the effect of two mechanistically distinct omega- and omega1-hydroxylase inhibitors on perfusion pressures in isolated rabbit lungs ventilated with normoxic or hypoxic gases, 2) changes in rabbit PA ring tone elicited by 20-HETE or omega- and omega1-hydroxylase inhibitors, and 3) expression of CYP4A protein in lung tissue. A modest increase in perfusion pressure (55 +/- 11% above normoxic conditions) was observed in isolated perfused lungs during ventilation with hypoxic gas (FI(O(2)) = 0.05). Inhibitors of 20-HETE synthesis, 17-oxydecanoic acid (17-ODYA) or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), increased baseline perfusion pressure above that of vehicle and amplified hypoxia-induced increases in perfusion pressures by 92 +/- 11% and 105 +/- 11% over baseline pressures, respectively. 20-HETE relaxed phenylephrine (PE)-constricted PA rings. Treatment with 17-ODYA enhanced PE-induced contraction of PA rings, consistent with inhibition of a product that promotes arterial relaxation, whereas 6-(20-propargyloxyphenyl)hexanoic acid (PPOH), an epoxygenase inhibitor, blunted contraction to PE. Conversion of AA into 20-HETE was blocked by 17-ODYA, DDMS, and hypoxia. CYP4A immunospecific protein confirms expression of CYP4A in male rabbit lung tissue. Our data suggest that endogenously produced 20-HETE could modify rabbit pulmonary vascular tone, particularly under hypoxic conditions.     

Influence of hypoxia on the longitudinal distribution of pulmonary vascular resistance

We have examined the influence of hypoxia on the longitudinal distribution of vascular resistance and intravascular pressure in isolated cat lungs using the low-viscosity bolus technique. Hypoxia increased total vascular resistance, decreased total lung blood volume, and moved the maximum local resistance downstream away from the main pulmonary artery. The circumference of the main pulmonary artery was increased and the extravascular lung water (double indicator dilution technique) was decreased by hypoxia. Thus, it would appear that distension of the large pulmonary arteries and a decrease in the amount of lung tissue perfused contributed to the change in resistance distribution brought about by hypoxia.     

Temporal increase in the reactivity of pulmonary vasculature to substance P in chronically hypoxic rats

We previously demonstrated that the pulmonary vascular response to substance P (SP) increased in chronically hypoxic rats. This study explored the temporal increase in reactivity of the pulmonary vascular response to SP and its underlying mechanisms. First, young female Wistar rats were exposed to sea level (SL) or simulated high altitude (HA) for 15 h/day for 3 days, 1 wk, 2 wk, and 4 wk. Lungs were isolated and perfused with 4% bovine serum albumin in Krebs-Henseleit buffer solution. SP (1.5 x 10(-4) M) induced significant increases in pulmonary arterial pressure (P(pa)), venous pressure (P(v)), capillary pressure (P(c)), arterial resistance (R(a)), and filtration coefficient (K(fc)) in SL lungs. Increases in P(pa) and R(a) were significantly augmented in HA lungs, with a temporal increase trend peaking at 2 wk of HA exposure. The selective neurokinin (NK) type 1 (NK1) receptor antagonist SR-14033 significantly attenuated SP-induced increases in P(pa), P(v), P(c), R(a), and K(fc) in SL lungs. In lungs exposed to HA for 2 wk, SR-14033 suppressed the effect of SP on P(pa). Also, chronic hypoxia induced significant increases in NK1 receptors and NK1 receptor mRNA, with a temporal trend. We conclude that chronic hypoxia temporally augments SP-induced vascular responses, which are closely associated with increases in NK1 receptors and gene expression.     

Effect of time and vascular pressure on permeability and cyclic nucleotides in ischemic lungs

We previously found that increased intravascular pressure decreased ischemic lung injury by a nitric oxide (NO)-dependent mechanism (Becker PM, Buchanan W, and Sylvester JT. J Appl Physiol 84: 803-808, 1998). To determine the role of cyclic nucleotides in this response, we measured the reflection coefficient for albumin (sigma(alb)), fluid flux (), cGMP, and cAMP in ferret lungs subjected to either 45 min ("short"; n = 7) or 180 min ("long") of ventilated ischemia. Long ischemic lungs had "low" (1-2 mmHg, n = 8) or "high" (7-8 mmHg, n = 6) vascular pressure. Other long low lungs were treated with the NO donor (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium -1, 2-diolate (PAPA-NONOate; 5 x 10(-4) M, n = 6) or 8-bromo-cGMP (5 x 10(-4) M, n = 6). Compared with short ischemia, long low ischemia decreased sigma(alb) (0.23 +/- 0.04 vs. 0.73 +/- 0.08; P < 0.05) and increased (1.93 +/- 0.26 vs. 0.58 +/- 0.22 ml. min(-1). 100 g(-1); P < 0.05). High pressure prevented these changes. Lung cGMP decreased by 66% in long compared with short ischemia. Lung cAMP did not change. PAPA-NONOate and 8-bromo-cGMP increased lung cGMP, but only 8-bromo-cGMP decreased permeability. These results suggest that ischemic vascular injury was, in part, mediated by a decrease in cGMP. Increased vascular pressure prevented injury by a cGMP-independent mechanism that could not be mimicked by administration of exogenous NO.     

Phosphoinositide 3-kinase, Src, and Akt modulate acute ventilation-induced vascular permeability increases in mouse lungs

To determine the role of phosphoinositide 3-OH kinase (PI3K) pathways in the acute vascular permeability increase associated with ventilator-induced lung injury, we ventilated isolated perfused lungs and intact C57BL/6 mice with low and high peak inflation pressures (PIP). In isolated lungs, filtration coefficients (K(f)) increased significantly after ventilation at 30 cmH(2)O (high PIP) for successive periods of 15, 30 (4.1-fold), and 50 (5.4-fold) min. Pretreatment with 50 microM of the PI3K inhibitor, LY-294002, or 20 microM PP2, a Src kinase inhibitor, significantly attenuated the increase in K(f), whereas 10 microM Akt inhibitor IV significantly augmented the increased K(f). There were no significant differences in K(f) or lung wet-to-dry weight (W/D) ratios between groups ventilated with 9 cmH(2)O PIP (low PIP), with or without inhibitor treatment. Total lung beta-catenin was unchanged in any low PIP isolated lung group, but Akt inhibition during high PIP ventilation significantly decreased total beta-catenin by 86%. Ventilation of intact mice with 55 cmH(2)O PIP for up to 60 min also increased lung vascular permeability, indicated by increases in lung lavage albumin concentration and lung W/D ratios. In these lungs, tyrosine phosphorylation of beta-catenin and serine/threonine phosphorylation of Akt, glycogen synthase kinase 3beta (GSK3beta), and ERK1/2 increased significantly with peak effects at 60 min. Thus mechanical stress activation of PI3K and Src may increase lung vascular permeability through tyrosine phosphorylation, but simultaneous activation of the PI3K-Akt-GSK3beta pathway tends to limit this permeability response, possibly by preserving cellular beta-catenin.     

Decreased pulmonary vascular responsiveness in rats raised on an essential fatty acid deficient diet

Leukotriene C4 is produced during hypoxic pulmonary vasoconstriction and leukotriene inhibitors preferentially inhibit the hypoxic pressor response in rats. If lipoxygenase products are important in hypoxic vasoconstriction, then an animal deficient in arachidonic acid should have a blunted hypoxic pressor response. We investigated if vascular responsiveness was decreased in vascular rings and isolated perfused lungs from rats raised on an essential fatty acid deficient diet (EFAD) compared to rats raised on a normal diet. Rats raised on the EFAD diet had decreased esterified plasma arachidonic acid and increased 5-, 8-, 11-eicosatrienoic acid compared to rats raised on the normal diet (control). Compared to the time matched responses in control isolated perfused lungs the pressor responses to angiotensin II and alveolar hypoxia were blunted in lungs from the arachidonate deficient rats. This decreased pulmonary vascular responsiveness was not affected by the addition of indomethacin or arachidonic acid to the lung perfusate. Similarly, the pulmonary artery rings from arachidonate deficient rats demonstrated decreased reactivity to norepinephrine compared to rings from control rats. In contrast, the tension increases to norepinephrine were greater in aortic rings from the arachidonate deficient rats compared to control. Stimulated lung tissue from the arachidonate deficient animals produced less slow reacting substance and platelet activating factor like material but the same amount of 6-keto-PGF1 alpha and TXB2 compared to control lungs. Thus there is an association between altered vascular responsiveness and impairment of stimulated production of slow reacting substance and platelet activating factor like material in rats raised on an EFAD diet.