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Drug-induced pulmonary arterial hypertension (D-PAH) is a form of World Health Organization Group 1 pulmonary hypertension (PH) defined by severe small vessel loss and obstructive vasculopathy, which leads to progressive right heart failure and death. To date, 16 different compounds have been associated with D-PAH, including anorexigens, recreational stimulants, and more recently, several Food and Drug Administration-approved medications. Although the clinical manifestation, pathology, and hemodynamic profile of D-PAH are indistinguishable from other forms of pulmonary arterial hypertension, its clinical course can be unpredictable and to some degree dependent on removal of the offending agent. Because only a subset of individuals develop D-PAH, it is probable that genetic susceptibilities play a role in the pathogenesis, but the characterization of the genetic factors responsible for these susceptibilities remains rudimentary. Besides aggressive treatment with PH-specific therapies, the major challenge in the management of D-PAH remains the early identification of compounds capable of injuring the pulmonary circulation in susceptible individuals. The implementation of pharmacovigilance, precision medicine strategies, and global warning systems will help facilitate the identification of high-risk drugs and incentivize regulatory strategies to prevent further outbreaks of D-PAH. The goal for this review is to inform clinicians and scientists of the prevalence of D-PAH and to highlight the growing number of common drugs that have been associated with the disease.

In pulmonary arterial hypertension (PAH) structural and functional abnormalities of the small lung vessels interact and lead to a progressive increase in pulmonary vascular resistance and right heart failure. A current pathobiological concept characterizes PAH as a 'quasi-malignant' disease focusing on cancer-like alterations in endothelial cells (EC) and the importance of their acquired apoptosis-resistant, hyper-proliferative phenotype in the process of vascular remodeling. While changes in pulmonary blood flow (PBF) have been long-since recognized and linked to the development of PAH, little is known about a possible relationship between an altered PBF and the quasi-malignant cell phenotype in the pulmonary vascular wall. This review summarizes recognized and hypothetical effects of an abnormal PBF on the pulmonary vascular bed and links these to quasi-malignant changes found in the pulmonary endothelium. Here we describe that abnormal PBF does not only trigger a pulmonary vascular cell growth program, but may also maintain the cancer-like phenotype of the endothelium. Consequently, normalization of PBF and EC response to abnormal PBF may represent a treatment strategy in patients with established PAH., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The loss of pulmonary vessels has been shown to be related to the severity of pulmonary hypertension in patients with chronic obstructive pulmonary disease (COPD). The severity of hypoxaemia is also related to pulmonary hypertension and pulmonary vascular resistance in these patients, suggesting that the hypoxic condition probably plays an important role in this form of pulmonary hypertension. However, pulmonary hypertension also develops in patients with mild COPD without hypoxaemia. Oxygen supplementation therapy often fails to reverse the pulmonary hypertension in these COPD patients, thus suggesting that the pulmonary vascular alterations in those patients may involve different sites of the pulmonary vasculature or a different form of vascular remodelling. It has recently been demonstrated that pulmonary vascular remodelling, resulting in pulmonary hypertension in COPD patients, can develop independently from parenchymal destruction and loss of lung vessels. We wonder whether the changes in the lung microenvironment due to hypoxia and vessel loss have a causative role in the development of pulmonary hypertension in patients with COPD. Herein we review the pathobiological features of the pulmonary vasculature in COPD patients and suggest that pulmonary hypertension can occur with and without emphysematous lung tissue destruction and with and without loss of lung vessels., (©ERS 2014.)

We recently reported that addition of a small amount of hemolysate to the salt solution that perfused isolated rat lungs hypersensitized the vasculature to subsequent additions of ANG II or exposure to hypoxia, and addition of NO gas (. NO) to the perfusate that contained hemolysate caused a strong vasoconstrictor rather than a vasodilator response. In the present study, we demonstrate that CO and the secondary messengers cGMP and cAMP (usually associated with vasodilation) exert similar effects in hemolysate-perfused lungs. Analogs of the cyclic nucleotides cGMP or cAMP (8-bromo-cGMP and dibutyryl-cAMP, respectively) caused profound vasoconstriction in the isolated rat lung perfused with a salt solution that contained hemolysate. The cGMP- or cAMP-analog-induced vasoconstriction was inhibited by chemically dissimilar Ca2+ antagonists, by the protein phosphatase inhibitor okadaic acid, and, to a lesser degree, by protein kinase inhibitor H-7. Antiphosphothreonine immunoblotting demonstrated that lungs perfused with hemolysate exhibit increased phosphorylation of several proteins. These data indicate that, in the presence of hemolysate, pulmonary vasculature responds to nominally vasodilatory stimuli, including analogs of cGMP and cAMP, with vasoconstriction rather than vasodilation. The importance of our finding is the paradoxical nature of the response to (analogs of) cyclic nucleotides because, to our knowledge, cyclic nucleotide-induced vasoconstriction has not been previously reported.

Leukotoxin (Lx), a cytochrome P-450-dependent metabolite of linoleate synthesized by neutrophils or synthesized by OH- and linoleate in neutrophil cell membranes, has been recovered in lung lavages of patients with the adult respiratory distress syndrome. We studied the direct vasoactive effects of Lx and linoleate, its parent compound, in the rat pulmonary circulation. In isolated rat lungs perfused at constant flow with a physiological salt solution, Lx (but not linoleate) caused a biphasic response, an initial transient vasoconstriction followed by a more prolonged vasodilation. The latter response was only evident when the pulmonary vascular tone was increased with either alveolar hypoxia (0% O2) or KCl (20 mM). The pressor response to angiotensin II was also attenuated in the presence of Lx. The vasodilatory response in perfused lungs was attenuated by methylene blue (2 x 10(-5) M), a putative inhibitor of the soluble guanylate cyclase but not by pretreatment with meclofenamate (10(-5) M), a cyclooxygenase inhibitor. In isolated pulmonary arterial (PA) rings preconstricted either with phenylephrine (5 x 10(-9) M), endothelin-1 (10(-8) M), or KCl (30 mM), Lx (but not linoleate) caused dose-dependent relaxation. The relaxing effect of Lx on endothelium-intact rings was attenuated by NG-monomethyl-L-arginine or methylene blue. The magnitude of the hypoxic contraction of PA rings was attenuated in the presence of Lx. Whereas the mechanism of Lx-induced vasoconstriction is not clear, we conclude that Lx causes vasodilation in rat lungs and that the vasodilatory component is to a large degree endothelium-derived relaxing factor-dependent.

Platelet-activating factor (PAF) is a cell membrane-derived ether lipid that plays an important role in acute lung vascular injury. We recently reported that PAF potentiates protamine-induced lung edema by enhancing pulmonary venoconstriction. As PAF is known to stimulate lung eicosanoid synthesis, we investigated the role of peptidoleukotrienes and other eicosanoids in this priming effect of PAF. Addition of PAF (1.6 nM), followed 10 min later by protamine (50 micrograms/ml), to perfusate of salt solution-perfused rat lungs resulted in marked arterial and venous constrictions and severe lung edema. Lung tissue thromboxane B2, 6-ketoprostaglandin F1 alpha and leukotriene C4 (LTC4) were markedly elevated 20 min after PAF/protamine. Pretreatment of the lungs with AA-861, a specific 5-lipoxygenase inhibitor, blocked PAF/protamine-induced leukotriene synthesis, arterial and venous constrictions, and lung edema. In addition, injection of LTC4 (1 microgram) markedly potentiated protamine-induced arterial and venous constrictions and caused lung edema similar to PAF/protamine. Indomethacin, a specific cyclooxygenase inhibitor, also reduced the vasoconstrictive and edemagenic responses to PAF/protamine. However, the pulmonary edema after LTC4/protamine was not blocked by indomethacin. In separate experiments, infusion of this "priming" dose of PAF into isolated perfused lungs induced LTC4 synthesis and augmented lung thromboxane A2 synthesis after arachidonic acid infusion. We conclude that both cyclooxygenase and lipoxygenase products of arachidonic acid metabolism are involved in PAF-induced potentiation of protamine lung edema.

We investigated the effects of two different platelet-activating factor (PAF) antagonists, SRI 63-441 and WEB 2086, on PAF-, angiotensin II-, and hypoxia-induced vasoconstrictions in isolated rat lungs perfused with a physiological salt solution. Bolus injection of PAF (0.5 micrograms) increased pulmonary arterial and microvascular pressures and caused lung edema. Both SRI 63-441, a PAF-analogue antagonist, and WEB 2086, a thienotriazolodiazepine structurally unrelated to PAF, completely blocked PAF-induced vasoconstriction and lung edema at 10(-5) M. At a lower concentration (10(-6) M), WEB 2086 was more effective than SRI 63-441. WEB 2086 also blocked the pulmonary vasodilation induced by low-dose PAF (15 ng) in blood-perfused lungs preconstricted with hypoxia. SRI 63-441 and CV 3988 (another PAF analogue antagonist), but not WEB 2086, caused acute pulmonary vasoconstriction at 10(-5) M and severe lung edema at a higher concentration (10(-4) M). PAF-induced but not SRI- or CV-induced pulmonary vasoconstriction and edema were inhibited by WEB 2086. In addition, SRI 63-441 potentiated angiotensin II- and hypoxia-induced vasoconstrictions. This effect of SRI 63-441 is not due to PAF receptor blockade because 1) addition of PAF (1.6 nM) to the perfusate likewise potentiated angiotensin II-induced vasoconstriction and 2) WEB 2086 did not cause a similar response. We conclude that both SRI 63-441 and WEB 2086 are effective inhibitors of PAF actions in the rat pulmonary circulation. However, antagonists with structures analogous to PAF (SRI 63-441 and CV 3988) can have significant pulmonary vasoactive side effects.

Lung cytochrome P-450 has been suggested to play a role in hypoxic pulmonary vasoconstriction. We reexamined this hypothesis using specific suicide substrate inhibitors of cytochrome P-450, 1-aminobenzotriazole (1-ABT), and chloramphenicol. In isolated, blood-perfused rat lungs, 1-ABT (0.5 mg/ml) and chloramphenicol (1 mg/ml) inhibited lung microsomal cytochrome P-450 (ethoxycoumarin O-deethylase) activity to 24 and 44% of control, respectively, and blunted hypoxia and angiotensin II-induced vasoconstriction. The depression of vascular contraction by 1-ABT was not due to an effect on calcium channels, since similar concentrations of 1-ABT had no inhibitory activity on electrical field-stimulated contractile response in rabbit papillary muscle strips. However, when 1-ABT was washed out of the lung after preincubation, the vascular reactivity to hypoxia and angiotensin II was restored despite persistent depression of lung cytochrome P-450 activity to 26% of control values. In isolated rat aortic and pulmonary arterial rings, addition of 1-ABT or metyrapone to the organ bath acutely reversed norepinephrine-induced contraction but preincubation with 1-ABT, metyrapone, or chloramphenicol had no effect on subsequent norepinephrine contractions. We conclude that 1-ABT inhibited lung vascular reactivity by a mechanism independent of cytochrome P-450 inhibition or calcium channel blockade and that an intact lung cytochrome P-450 system is not required for hypoxic pulmonary vasoconstriction in rat lungs.

The effect of almitrine bimesylate or the solvent malic acid on pulmonary vascular perfusion pressure was assessed in isolated rat lungs and on the contractile behavior of rat aorta and main pulmonary artery rings. Addition of almitrine to the lung perfusate during normoxia caused a dose-dependent, transient increase in pulmonary artery pressure with no change of the lung microvascular pressure. In systemic or pulmonary conduit arteries, the contractile tension was unaffected by almitrine. This indicates a precapillary locus of drug action. We also examined almitrine's effect on hypoxic pulmonary vasoconstriction (HPVC) in isolated lungs perfused with blood or with physiological salt solution (PSS). Low-dose almitrine potentiated hypoxic vasoconstriction in blood- but not in PSS-perfused lungs. However, a high dose of almitrine reduced hypoxic vasoconstriction dose dependently. When almitrine was added to the lung perfusate during hypoxia- or cyanide-induced (NaCN, 5 x 10(-5) M) pulmonary vasoconstriction, almitrine caused no further vasoconstriction. However, when the pulmonary perfusion pressure was elevated by KCl (20 mM) to the same magnitude as by alveolar hypoxia or cyanide, almitrine elicited a pressor response comparable to that observed during normoxia. Almitrine-induced pulmonary vasoconstriction resembled hypoxic vasoconstriction in that agents known to enhance hypoxic vasoconstriction (phorbol myristate acetate, vanadate, and 4-aminopyridine) enhanced, and known inhibitors of HPVC (the Ca2+ entry blocker nifedipine and hypothermia) inhibited, the almitrine-induced vasoconstriction. These findings lead us to speculate that almitrine also affects the oxygen-sensing limb of the hypoxic pressor response, not simply the effector (contractile apparatus of the vascular muscle cell).

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.

The Fischer rat is known for its susceptibility to develop liver necrosis when challenged with paraquat (Smith et al., J. Pharmacol. Exp. Ther. 235: 172-177, 1985). We postulated that other organs, specifically the lung, may also be more susceptible to injury and examined whether lungs from Fischer (F) rats were injured more easily when challenged with active oxygen species than Sprague-Dawley (SD) rat lungs. We aimed to investigate whether increased susceptibility to oxidant injury was related to differences in lung antioxidant defenses. Perfused lungs from both rat strains were challenged by addition of H2O2 to the perfusate or by short-term hyperoxic ventilation. To assess nonoxidant modes of lung injury, we examined lung responses after exposure to protamine sulfate or neutrophil elastase. Intravascular H2O2 or 3 h in vitro hyperoxia caused lung edema in F but not SD rats, and elastase injured F rat lungs more than the lungs from SD rats. Protamine, however, injured the lungs from both strains to a similar degree. Catalase, but not superoxide dismutase or allopurinol, protected F rat lungs against edema, resulting from 3 h in vitro hyperoxia. The lung homogenate levels for reduced glutathione or conjugated dienes and the activities of lung tissue catalase, glutathione peroxidase, and cytochrome P-450 were not different between the two strains. Lung tissue ATP levels, however, were lower in F than in SD rats. Although the F rat strain appears to have an altered oxidant-antioxidant defense balance, the exact cause of the greater susceptibility to oxidant stress of the F rat strain remains elusive.

The role of leukotrienes in the mechanism of hypoxic pulmonary vasoconstriction (HPV) is controversial. To determine whether leukotriene C4 (LTC4) was produced during HPV, LTC4 levels were measured in individual samples of lung tissue, lung bronchoalveolar lavage fluid (BALF), and blood perfusate in isolated perfused lungs ventilated with normoxic or hypoxic gas mixtures. HPV was not associated with increased LTC4 in lung tissue or increased LTE4 in blood perfusate. Consistent with previous studies demonstrating elevated levels of LTC4 in pooled BALF fluid from hypoxic lungs, individual lung BALF samples demonstrated an elevation of LTC4 during hypoxia. However, the process of lung lavage alone stimulated eicosanoid production, with LTC4, 6-ketoprostaglandin F1 alpha, and thromboxane B2 levels being higher in lavaged compared to non-lavaged lungs. In lungs to which the lipoxygenase inhibitor AA 861 was added to the perfusate, a reduction in the lung tissue LTC4 levels was observed without any or only a slight reduction in HPV. To evaluate the physiological effects of LTC4 in the airways, exogenous LTC4 (1-1,000 ng) was added to the airways of both blood- and physiological salt solution-perfused lungs without any effect on the pulmonary artery pressure or a response to hypoxia. These results do not support the hypothesis that leukotrienes mediate HPV in the rat.

Chronic pulmonary infection/colonization caused by Pseudomonas aeruginosa accounts for much of the morbidity and mortality in cystic fibrosis (CF). The effect of chronic pulmonary P. aeruginosa infection on the pulmonary circulation has not been studied. Therefore, we investigated the effect of chronic P. aeruginosa infection on pulmonary hemodynamics in a rat model. Two groups of rats were inoculated with either agar beads containing 1.0 x 10(4) colony-forming units of P. aeruginosa (infected) or an equal volume of sterile beads alone (control). In vivo, pulmonary vasoreactivity measured as the percent change in total pulmonary resistance during hypoxia was decreased at 1 wk (22 +/- 7% versus 57 +/- 3%), 2 wk (29 +/- 5% versus 73 +/- 17%), 3 wk (41 +/- 8% versus 77 +/- 14%), and 6 to 9 wk (23 +/- 10 versus 53 +/- 7; p less than 0.05 all time points; mean +/- SEM) postinoculation in infected animals when compared with that in time-matched control animals. At 6 to 9 wk postinoculation, pulmonary artery pressure was significantly elevated in infected rats (25.8 +/- 1.6 versus 21.0 +/- 1.0 mm Hg; p less than 0.05) when compared with that in control animals. Histopathologic findings were characterized by bronchiectasis as well as by chronic bronchial, parenchymal, and perivascular inflammation at all time points in infected animals.(ABSTRACT TRUNCATED AT 250 WORDS)

In this study we examined the action of arachidonic acid in the isolated rat lung perfused with a cell- and protein-free physiological salt solution. When pulmonary vascular tone was elevated by hypoxia, bolus injection of a large dose of arachidonic acid (75 micrograms) caused transient vasoconstriction followed by vasodilation. When arachidonic acid (100 micrograms) was injected during normoxia and at base-line perfusion pressure (low vascular tone) or when vascular tone was elevated by KCl, arachidonic acid (50 micrograms) caused only vasoconstriction. Doses less than 7.5 micrograms caused vasodilation only when injected during hypoxic vasoconstriction and subsequent blunting of either angiotensin II- or hypoxia-induced pulmonary vasoconstriction. The higher doses of arachidonic acid (7.5 and 75 micrograms), but not the lower doses (7.5-750 ng), caused increases in effluent 6-ketoprostaglandin F1 alpha, thromboxane B2, and prostaglandin E2 and F2 alpha. 6-Ketoprostaglandin F1 alpha was the major cyclooxygenase product. Meclofenamate (10(-5) M) blocked the increased metabolite synthesis over the entire dose range of arachidonic acid tested (7.5 ng-75 micrograms). Because vasodilation immediately after arachidonic acid was cyclooxygenase-independent, we investigated whether this effect was due to the unsaturated fatty acid properties of arachidonic acid and compared its action with that of oleic acid and docosahexaenoic acid. Because neither compound mimicked the vasodilation observed with arachidonic acid, we concluded that the cyclooxygenase-independent action of arachidonic acid could not be explained by unsaturated fatty acid properties per se. Because 1-aminobenzotriazole, a cytochrome P-450 inhibitor, partially inhibited the immediate arachidonic acid-induced pulmonary vasodilation, we concluded that cytochrome P-450-dependent metabolites can account for some of the cyclooxygenase-independent vasodilation of arachidonic acid.

Leukotriene inhibitors preferentially inhibit hypoxic pulmonary vasoconstriction in isolated rat lungs. If lipoxygenase products are involved in the hypoxic pressor response they might be produced during acute alveolar hypoxia and a leukotriene inhibitor should block both the vasoconstriction and leukotriene production that occurs in response to hypoxia. We investigated in isolated blood perfused rat lungs whether leukotriene C4 (LTC4) could be recovered from whole lung lavage fluid during ongoing hypoxic vasoconstriction. Lung lavage from individual rats had slow reacting substance (SRS)-like myotropic activity by guinea pig ileum bioassay. Pooled lavage (10 lungs) as analyzed by reverse phase high performance liquid chromatography had an ultraviolet absorbing component at the retention time for LTC4. At radioimmunoassay, and SRS myotropic activity by bioassay. LTC4 was not found during normoxic ventilation, during normoxic ventilation after a hypoxic pressor response, or during vasoconstriction elicited by KCl. Diethylcarbamazine citrate, a leukotriene synthesis blocker, concomitantly inhibited the hypoxic vasoconstriction and LTC4 production. Thus 5-lipoxygenase products may play a role in the sequence of events leading to hypoxic pulmonary vasoconstriction.

Many mammals exhibit elevated pulmonary arterial pressure when exposed to airway hypoxia. In addition, prolonged hypoxic exposure may result in elevated hematocrit and right ventricular hypertrophy. The current study was designed to test whether the hamster, a fossorial species, may possess naturally selected physiological characteristics advantageous to a chronically hypoxic environment. Hamsters and rats were studied at low altitude (1,520 m) and after 5 wk at high altitude (4,250 m). Hematocrit for low-altitude hamsters was 53 +/- 1 compared with 45 +/- 1 for low-altitude rats. Low-altitude hamsters and rats demonstrated the same right ventricular weight-to-total ventricular weight ratio (RV/T) (0.223 +/- 0.006 vs. 0.222 +/- 0.003). After high-altitude exposure the hematocrit for hamsters and rats was the same (58 +/- 1 vs. 57 +/- 1), but RV/T was less in the hamster (0.251 +/- 0.004 vs. 0.288 +/- 0.005). In addition, the hypoxic pulmonary pressor response of lungs isolated from low- and high-altitude animals was examined. Lungs from hamsters were less responsive than lungs from rats at all levels of hypoxia tested. In addition, exposure to altitude resulted in a diminished pressor response in lungs from both species. It is concluded that the pulmonary vasculature of the hamster is less responsive to hypoxia than that of the rat, and that this relative unresponsiveness may aid the hamster in an hypoxic environment.

The mechanism of hypoxic pulmonary vasoconstriction is still unclear. Since leukotrienes are pulmonary vasoconstrictors and lung cells are able to produce leukotrienes, it has been proposed that leukotrienes are mediators of hypoxic pulmonary vasoconstriction and then inhibition of their synthesis should block hypoxic pressure responses. In order to test this hypothesis we investigated whether diethylcarbamazine (DEC), a known leukotriene synthesis blocker, blocks hypoxic pulmonary vasoconstriction in isolated rat lungs. DEC blocked ongoing and subsequent hypoxic pressure responses in a relatively specific and dose-dependent fashion. We therefore extended our observations to awake rats and found that DEC reversibly inhibited acute hypoxic pulmonary vasoconstriction. Furthermore, pulmonary hypertension and right ventricular hypertrophy in rats exposed to chronic hypobaric hypoxia could be prevented by DEC treatment. From these data we conclude that DEC inhibits both acute and chronic hypoxic pulmonary vasoconstriction. Thus, leukotrienes could be important mediators of hypoxic pulmonary vasoconstriction.

Based on work with isolated arteries, we hypothesized that elevation of the extracellular calcium concentration would cause pulmonary vasodilation by stimulation of the Na+K+ATPase. If so, ouabain should inhibit the "membrane stabilizing" effect of a high calcium concentration. Addition of CaCl2 to the perfusate of rat isolated lungs to give a final concentration of 10(-2)M caused vasodilation when the lungs were vasoconstricted by KCl, angiotensin II or hypoxia. Ouabain addition to the perfusate increased pulmonary artery perfusion pressure and the magnitude of angiotensin II-induced vasoconstriction delayed vasodilation and transformed the CaCl2-induced vasodilation into rapid vasoconstriction accompanied by edema formation. Meclofenamate reduced the calcium-induced vasodilation suggesting that part of the high calcium vasodilation may be due to the action of a vasodilator prostaglandin. The vasodilation due to prostacyclin was blocked in lungs treated with ouabain. The results taken together suggest that high calcium vasodilation operates by mechanisms which may be prostaglandin-dependent and prostaglandin-independent, both of which can be blocked by ouabain.

Reactive oxygen metabolites cause pulmonary vasoconstriction and activate arachidonic acid metabolism. We proposed that hydrogen peroxide, generated enzymatically in an insolated rat lung model, would cause vasoconstriction which was independent of circulating cells, but dependent on activation of the arachidonic acid cascade. Although hydrogen peroxide caused an increase in lung effluent thromboxane B2 concentration, indomethacin did not inhibit hydrogen peroxide induced vasoconstriction. In order to test the hypothesis that hydrogen peroxide activates the 5-lipoxygenase pathway, lung effluents were analyzed for 5-hydroxy-eicosatetranoic acid (5-HETE) using a sensitive, highly specific mass spectrometer technique. Glucose oxidase increased the 5-HEFE effluent concentrations and this was prevented by U60,257. We therefore conclude that hydrogen peroxide stimulates the 5-lipoxygenase pathway and that substances derived from this pathway are at least in part responsible for the hydrogen peroxide induced vasoconstriction in isolated rat lungs.

Both tumor necrosis factor (TNF) and platelet-activating factor (PAF) have been incriminated as mediators of endotoxic shock. Since TNF stimulates PAF synthesis in vitro, we tested the hypothesis that PAF mediates TNF-induced lung injury in vivo using specific PAF receptor antagonists. Intravenous infusion of purified human recombinant TNF resulted in peripheral neutrophilia, lymphocytopenia, and hemoconcentration, caused hemorrhagic injury to the cecum, and increased lung tissue levels of thromboxane B2 and 6-ketoprostaglandin F1 alpha. In addition, plasma glutathione disulfide (GSSG), an in vivo index of oxidative stress, was significantly increased. TNF (0.01-1 mg/kg) caused a dose-dependent increase in lung permeability-surface area product (PS) measured in isolated perfused lungs removed from rats 90 min after injection of TNF. [Lung PS in controls and after 0.01, 0.1, and 1.0 mg/kg of TNF were 0.022 +/- 0.001, 0.027 +/- 0.002, 0.033 +/- 0.001, and 0.036 +/- 0.005, respectively (P less than 0.05 from control for TNF 0.1 and 1 mg/kg).] Pretreatment of the rats with the PAF receptor antagonists WEB 2086 (10 mg/kg) and SRI 63-441 (10 mg/kg), at doses that previously protected against endotoxin-induced lung injury, did not significantly affect TNF-induced (0.1 mg/kg) changes in hematocrit, plasma GSSG, or lung PS. Moreover, WEB 2086 (10 mg/kg) did not inhibit TNF-induced (1 mg/kg) lymphocytopenia or the increases in lung tissue eicosanoid products. We conclude that TNF causes oxidative stress, eicosanoid activation, and acute lung injury in rats by a mechanism largely independent of PAF receptor activation.

Platelet-activating factor (PAF) administered to the pulmonary circulation in low dose (nanogram) has vasodilatory properties. Therefore, we investigated whether endogenous PAF plays a role in the control of tone in the pulmonary circulation. The PAF receptor antagonists, SRI 63-441 (2.6 X 10(-4) M) and L659,989 (1 X 10(-5) M), were the major investigative tools. In isolated perfused rat lungs, both agents caused a persistent increase in base-line perfusion pressure (Ppa), potentiated angiotensin II (ANG II) vasoconstriction, and potentiated hypoxic vasoconstriction (HPV). This potentiation of ANG II and HPV was found to be independent of circulating blood elements. Vasodilation in the presence of PAF blockade was also impaired. The combination of cyclooxygenase inhibition and PAF receptor blockade had an additive effect on ANG II vasoconstriction but did not cause more potentiation of HPV than achieved with PAF antagonism alone. In vivo, SRI 63-441 (10 mg/kg) caused only a transient increase in base-line Ppa without altering ANG II and hypoxic vasoconstriction. These findings support a vasodilatory role for endogenous PAF in the pulmonary circulation.

Previous studies have documented direct vascular effects of opiate substances in the systemic circulation. Because opiate receptors have been identified in the lung, we wondered whether opiate substances might affect vasoreactivity in the lung circulation. We studied the pulmonary vascular effects of three opiate agonists: morphine, leucine-enkephalin, and dynorphin, as well as the opiate receptor antagonist naloxone, in isolated rat lungs perfused with a cell- and plasma-free salt solution. Because of previous reports of the smooth muscle effects of the methyl- and propylparaben preservatives in the naloxone preparation, we also studied the pulmonary vascular effects of these preservatives in the rat lung circulation. We found that morphine, a mu-receptor agonist, leucine-enkephalin, a delta-receptor agonist, and dynorphin, a kappa-receptor agonist, caused no immediate vascular effect when injected into the pulmonary artery. In addition, morphine did not affect the pulmonary vasoconstrictions induced by hypoxia, angiotensin II, or potassium chloride. The commercial preparation of naloxone, Narcan, caused a marked vasodilation during hypoxic pulmonary vasoconstriction. However, this effect was entirely attributable to the preservatives methyl- and propylparaben, as pure naloxone had no effect on either the baseline pulmonary vascular tone or the vasoconstrictive response to hypoxia. We conclude that opiate receptor agonists and antagonists do not affect vasoreactivity in the rat lung circulation and that the methyl- and propylparaben preservatives in Narcan are pulmonary vasodilators.

Recent work with isolated blood vessels has emphasized the importance of intact endothelium when the relaxation of vascular smooth muscle is induced by acetylcholine (ACh). However, the physiologic significance of this endothelial-dependent ACh response in a complete organ circulation is unclear. We questioned whether diminished ACh vasodilation would result from damage of lung vascular endothelium and whether this response could be used as an indication of endothelial injury. We therefore induced pulmonary endothelial cell injury in one rat model by repeated injections of alpha-naphthyl thiourea (ANTU) and in a second rat model by exposing rats for 52 h to 100% oxygen at a barometric pressure of 760 torr (hyperoxia). Rats injected with Tween 80, the solvent for ANTU, or exposed to ambient Denver air served as the respective control animals. The isolated lungs of these rats were perfused with a recirculating cell- and plasma-free, physiological salt solution to study the effect of ACh or NaCl infusion on pulmonary perfusion pressure and vascular responsiveness. ANTU-treated rats demonstrated an intact vasodilatory response after ACh infusion when compared with the solvent control animals. The immediate pulmonary vasodilation after ACh infusion was slightly enhanced in the hyperoxic rat lung when compared with the rats exposed to ambient air, but there was no difference between these groups in the prolonged depression of vascular responsiveness to hypoxia or angiotensin II. Thus, in both models of lung endothelial cell injury, the pulmonary vascular responses to ACh were intact.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of the cell-permeable dibutyryl derivative of cyclic AMP on the vascular reactivity of isolated perfused rat lungs were examined. In lungs perfused with homologous blood, pulmonary arterial infusion of db-cAMP (30 micrograms/min) inhibited hypoxia-induced vasoconstriction (IC50 = 6.3 X 10(-5) M) and vasoconstriction due to bolus injection of angiotensin II (IC50 = 8.2 X 10(-5) M). Cyclic AMP phosphodiesterase inhibition by aminophylline acted synergistically with db-cAMP in the reduction of hypoxia-induced vasoconstriction. Somatostatin, an inhibitor of adenylate cyclase, prevented the decay of hypoxic vasoconstriction typically observed in isolated lungs, suggesting that a rise in intracellular cAMP may occur during hypoxic vasoconstriction as a consequence of activation of the adenylate cyclase. In lungs perfused with cell and protein-free salt solution, db-cAMP inhibited both initial and prolonged vasoconstriction following bolus injection of 2 microgram leukotriene C4. Thus, db-cAMP inhibited pulmonary vascular reactivity nonspecifically.

We hypothesized that leukotrienes are involved in hypoxic pulmonary vasoconstriction, since they are pulmonary vasoconstrictors and cells capable of producing leukotrienes are located in the lung near resistance vessels. We investigated in isolated perfused rat lungs whether three structurally unrelated blockers [diethylcarbamazine citrate (DEC), U-60257, and FPL 55712] of leukotriene synthesis or action block hypoxic pulmonary vasoconstriction. DEC blocked ongoing and subsequent hypoxic pressor responses while minimally affecting the angiotensin II pressor response. The inhibition of the hypoxic pressor response by DEC was not affected by cyclooxygenase or H1-receptor blockers. Potassium-induced vasoconstriction, which is dependent on calcium entry, was largely blocked by verapamil but not by DEC, suggesting that DEC was not acting primarily as a calcium-entry blocker. U-60257 blocked the hypoxic pressor response without inhibiting the pressor response to angiotensin II or potassium chloride. FPL 55712, a leukotriene end-organ blocker, in a dose which inhibited vasoconstriction caused by exogenous leukotriene C4, inhibited the pressor response to hypoxia but not to angiotensin II. We conclude that leukotriene inhibitors preferentially inhibit hypoxic pulmonary vasoconstriction in isolated perfused adult rat lungs.

During the last 4 decades hypoxic vasoconstriction has been acknowledged as an important pulmonary control mechanism that via matching ventilation and perfusion regulates one of the important physiologic parameters--PaO2. Whether the hypoxic vasoconstriction occurs directly in a localized vascular site with distinct biochemistry or whether it is mediated by a local hormone has not been resolved. Progress has been made because of the introduction of micropuncture techniques that allow direct pressure measurements in small segments of the lung vascular tree. Measurements of the force of contraction and membrane potential (118) and manipulation of the environment of pulmonary microvessels are the most recent progress in the elucidation of the mechanism of hypoxic vasoconstriction. Elements of energy, oxygen, and lipid metabolism appear to contribute to the biochemistry of this elusive response.

We have proposed that the necessity of transporting large quantities of a relatively insoluble molecule, 02, from alveolar air to blood may have led to the evolution of an extremely thin but extensive membrane. The very structure of the membrane has required specialized machinery to maintain low vascular pressures within it, to divert blood flow to the better oxygenated areas, and to defend the membrane from external or internal attack. The purpose of this paper is to consider whether membrane lipids (platelet-activating factor and the metabolities of arachidonic acid) constitute some of this specialized machinery, and, if so, how this machinery might work.

We studied lung vascular injury and quantitated lung eicosanoids in rats after intraperitoneal injection of Salmonella enteritidis endotoxin. Within 40 min after endotoxin injection (20 mg/kg), lung tissue thromboxane B2 doubled, although 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) increased by 8- to 10-fold. Lung 5-hydroxyeicosatetraenoic acid and leukotriene C4 were variably increased by endotoxin. The levels of all eicosanoids returned to base line 6 h after endotoxin challenge. Lung vascular injury, as assessed by the extravascular accumulation of 125I-albumin and water in isolated perfused lungs, was observed 90 min after endotoxin injection (0.02-20 mg/kg) in vivo. Inhibition of the cyclooxygenase pathway with indomethacin and the lipoxygenase pathway with diethylcarbamazine and 2-(12-hydroxydodeca-5,10-dinyl)-3,5,6-trimethyl-1,4-benzoqui none failed to attenuate endotoxin-induced lung injury. In addition, essential fatty acid deficiency, which markedly reduced lung tissue levels of 6-keto-PGF1 alpha, thromboxane B2, and leukotriene C4, did not protect against endotoxin injury. We conclude that although lung eicosanoids are activated during endotoxemia, they do not play a crucial role in the development of acute lung vascular injury in rats.

Experiments were performed to determine the pulmonary vascular responses to exogenous or endogenous arginine vasopressin (AVP) in rats. Both in vitro and in vivo approaches were used to examine the direct pulmonary vasoactive properties of AVP and how those properties affect pulmonary hemodynamics in the intact animal. In conscious, unrestrained rats, constant infusion of AVP (4.0 mU.kg-1.min-1 iv) resulted in a fall in mean pulmonary artery pressure (PAP), although systemic pressure was increased. Coincident with the fall in PAP were similar reductions in cardiac output and heart rate. Similarly, bolus administration of AVP reduced PAP, and this effect was augmented during hypoxia. Another series of experiments examined the effect of endogenous AVP released by arterial hypoxemia on pulmonary hemodynamics in conscious rats. Administration of a specific V1-vasopressinergic antagonist had no effect on the PAP response to hypoxia; however, systemic resistance tended to fall following V1-antagonism. To determine the vasoactive properties of AVP independent of these changes in blood flow, a series of experiments were performed on isolated, perfused rat lungs. Injection of 25, 200, or 2,000 mU of AVP into the circulation of the isolated lung was without effect under normoxic conditions. In contrast, 25 mU AVP elicited reproducible pulmonary vasodilation when injected during ongoing hypoxic pulmonary vasoconstriction. This vasodilatory response was unaffected by meclofenamate or by the platelet-activating factor receptor antagonist SRI 63-441, but was blocked by a specific V1-vasopressinergic antagonist. We conclude that although AVP exerts profound systemic vasoconstriction, the pulmonary circulation appears relatively unaffected by exogenous or endogenous AVP in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of structurally different PAF receptor blockers were investigated in platelets, neutrophils, guinea pig ileum, rat isolated lung and rat isolated pulmonary artery. PAF caused serotonin release from platelets and a characteristic shape change and adhesion of neutrophils. The antagonists (CV 3988, alprazolam, 48740 RP and Merck-Sharp and Dohme L-652, 731) inhibited platelet serotonin release but not neutrophil shape change adhesion or lysosomal enzyme release. The antagonists in high concentrations (10(-5)-10(-4)M) inhibited nonspecifically the PAF-induced (10(-8)M) guinea pig ileum contraction, but were ineffective at concentrations which inhibited platelet responses. In the rat lung the compounds, in high concentrations, partially inhibited the low dose PAF-induced pulmonary vasodilation and the high dose PAF induced pulmonary vasoconstriction and edema. Our data indicate that some platelet PAF antagonists may be ineffective in blocking the action of PAF on neutrophils and smooth muscle preparations and suggest either PAF-receptor independent actions of PAF or different classes of PAF receptors.