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Chronic hypoxia causes pulmonary hypertension and right ventricular hypertrophy associated with pulmonary vascular remodeling. Because hypoxia might promote generation of oxidative stress in vivo, we hypothesized that oxidative stress may play a role in the hypoxia-induced cardiopulmonary changes and examined the effect of treatment with the antioxidant N-acetylcysteine (NAC) in rats. NAC reduced hypoxia-induced cardiopulmonary alterations at 3 wk of hypoxia. Lung phosphatidylcholine hydroperoxide (PCOOH) increased at days 1 and 7 of the hypoxic exposure, and NAC attenuated the increase in lung PCOOH. Lung xanthine oxidase (XO) activity was elevated from day 1 through day 21, especially during the initial 3 days of the hypoxic exposure. The XO inhibitor allopurinol significantly inhibited the hypoxia-induced increase in lung PCOOH and pulmonary hypertension, and allopurinol treatment only for the initial 3 days also reduced the hypoxia-induced right ventricular hypertrophy and pulmonary vascular thickening. These results suggest that oxidative stress produced by activated XO in the induction phase of hypoxic exposure contributes to the development of chronic hypoxic pulmonary hypertension.

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.

Lipid mediators of inflammation cause pulmonary edema, yet it is unclear to what degree hemodynamic alterations or increased vascular permeability contribute to lung edema formation. The isolated rat lung preparation was used to examine the effect of leukotriene C4 (LTC4) and platelet-activating factor (PAF) on pulmonary arterial pressure (Ppa), lung microvascular pressure (Pmv), lung wet-to-dry weight ratio, and the 125I-albumin escape index. We first defined the response of the isolated rat lung perfused with protein-free salt solution to hydrodynamic stress by raising the lung outflow pressure. Sustained elevation of the lung outflow pressure less than 5.5 cmH2O (4.01 mmHg) caused a negligible increase in Ppa and wet-to-dry lung weight ratio. Elevation of outflow pressures greater than 7.5 cmH2O (5.4 mmHg) increased the vascular albumin escape index more than the lung wet-to-dry weight ratio. Dibutyryl adenosine 3′,5′-cyclic monophosphate (db-cAMP) inhibited the increase in albumin escape index because of increased lung outflow pressure, suggesting perhaps a pressure-independent microvascular membrane effect of db-cAMP. Both LTC4 (2-micrograms bolus) and PAF (2–2,000 ng/ml perfusate) increased the albumin escape index in association with increases in Ppa and Pmv. Because the increased albumin escape index after LTC4 or PAF injection was largely accounted for by the increased vascular pressures and because db-cAMP and papaverine inhibited the rise in vascular pressures and in the albumin escape index, we conclude that vasoconstriction is an important contributor to LTC4- and PAF-induced edema formation in rat lungs.

Polycations, such as protamine sulfate and polylysine, have been implicated in the cause of pulmonary edema, but the mechanism is unknown. We studied the vascular effect of protamine in isolated rat lungs perfused with a cell- and plasma-free solution. Protamine (50–1,000 micrograms/ml) increased lung perfusion pressure and caused edema. Blocking the pulmonary vasoconstriction with papaverine (10(-4) M) did not prevent lung edema. In addition, lungs treated with protamine and papaverine showed increased extravascular leakage of 125I-albumin, indicating increased vascular permeability. Histological examination of these lungs showed marked endothelial injury. Functional endothelial damage was further demonstrated by the impairment of the acetylcholine-induced vascular relaxation in protamine-treated vascular rings. Antihistamines and indomethacin failed to block the pulmonary vasoconstriction and increased vascular permeability caused by protamine. In addition, we found that anionic substances, heparin and albumin, blocked the lung injury induced by protamine, whereas other polycations, polylysine and hexadimethrine bromide, caused pulmonary vasoconstriction and increased vascular permeability similar to protamine. We conclude that protamine causes pulmonary endothelial injury and lung edema and suggest that the injury may be charge mediated.

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.

To determine the role of prostaglandins in modulating pulmonary circulatory responses, we examined the effect of the prostaglandin precursor, sodium arachidonate, on the pulmonary vascular resistance of mongrel dogs during alveolar hypoxia. When infused intravenously for 5 min during hypoxia, sodium arachidonate (1 mg/min) decreased pulmonary vascular resistance from 6.9 ± 1.1 to 4.9± 0.6 U (P less than 0.05). The vasodilation produced by sodium arachidonate was blocked by sodium meclofenamate, a cyclooxygenase inhibitor. By infusing radiolabeled sodium arachidonate and collecting aortic blood samples, we found from chromatographic and mass spectrometric analysis that a major prostaglandin produced was 6-keto-PGF1 alpha, the stable hydrolysis product of PGI2. Infusion of PGI2, but not PGE2, during hypoxia decreased pulmonary vascular resistance. We concluded that the prostaglandin precursor, sodium arachidonate, is a vasodilator of the pulmonary vasculature that has been constricted by alveolar hypoxia, probably because PGI2 is formed from the arachidonate. The pulmonary circulation may be similar to the systemic circulation where vasoconstriction results in the generation of vasodilatory prostaglandins that attenuate the constrictor effect.

Isolated lungs from high-altitude rats compared with those from low-altitude rats have blunted hypoxic pressor responses. Because calcium is essential for the hypoxic pressor response and has been shown to be altered in the pulmonary arterial smooth muscle during high-altitude exposure, we wondered whether altered calcium metabolism might account for the blunted response. We attempted to unmask differences between high- and low-altitude rat lungs by altering extracellular calcium. The addition of calcium to the blood perfusate augmented the hypoxic pressure response of high-altitude lungs and depressed that of low-altitude lungs. Calcium addition did not affect pressor responses to angiotensin II, but slowed vasodilation after both angiotensin injection and removal of the hypoxic stimulus. The maximal KCl-induced contraction was blunted in rings of main pulmonary artery from high-altitude rats, but augmented in their aortic rings. Submaximally constricted (40 mM KCl) pulmonary arteries from low- but not high-altitude rats further constricted with calcium addition. Aortic rings exhibited an inverse behavior. Thus, calcium addition augmented the blunted vasopressor response in high-altitude rats lungs, possibly by an effect on lung arteries. The aorta and main pulmonary artery differ in calcium handling.

To determine whether breathing a mixture of 80% He-20% O2 affects the lung pressure-volume (PV) curve, eight anesthetized paralyzed dogs were studied in a volume-displacement plethysmograph. Static PV curves on air were compared with PV curves obtained after equilibration with He-O2. The He-O2 PV curves were significantly shifted upward by an average of 5% total lung capacity. There was no change in compliance, indicating that the shift was due to lung expansion rather than a change in elasticity. Pretreatment of the dogs with cyclooxygenase inhibitors abolished the PV shift with He-O2. Four dogs had PV curves recorded on air and a mixture of O2, SF6, and Ne, a gas mixture with the same density as air but with 45% greater viscosity. The PV curve shift was even greater than observed with He-O2 and could again be virtually abolished with a cyclooxygenase inhibitor. These results suggest that breathing a high-viscosity gas mixture results in alveolar duct dilatation due to the release of a prostaglandin bronchodilator. This may need to be taken into account in the analysis of flow augmentation with He-O2.

The administration of monocrotaline to rats causes pulmonary vascular leak within 1 wk followed in 2–3 wk by perivascular proliferation and fatal pulmonary hypertension. Possibly blocking the proliferation might block the pulmonary hypertension, providing insight into its mechanism. Because heparin, given as an antiproliferative agent, reduced hypoxic pulmonary hypertension in mice, it might also block monocrotaline-induced pulmonary hypertension. Alternatively, anticoagulation could worsen the lung injury. We found that heparin (300 and 600 U/kg sc twice daily) inhibited clotting in rats given monocrotaline but did not change the vascular leak, the right ventricular pressure, the right ventricular hypertrophy, the increased medial thickness of the pulmonary arterioles, or the production of a slow-reacting substance of anaphylaxis-like material by the lungs. A nonanticoagulant heparin fragment (2 mg/kg sc twice daily), given to avoid anticoagulation also did not influence the monocrotaline injury. Thus neither anticoagulant nor nonanticoagulant heparin either attenuated or worsened the measured effects of monocrotaline.

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.

Chronic beta-receptor blockade has been reported to inhibit right ventricular hypertrophy in rats at high altitude. If so, we wanted to determine whether beta-receptor blockade or some other drug action were involved and whether the heart, the lung vessels, or blood alterations were affected. In rats, chronic treatment with DL-propranolol (2 mg/kg ip once daily) reduced right ventricular hypertrophy and polycythemia of chronic high altitude. D-Propranolol and metoprolol did not reduce hypoxia-induced right ventricular hypertrophy or polycythemia. In isolated lungs from low-altitude rats treated chronically with DL-propranolol or with D-propranolol the pressor response to acute hypoxia was blunted. Chronic DL-propranolol blunted the acute hypoxic pressor response and angiotensin II induced vasoconstriction in lungs from high-altitude rats. Two effects of DL-propranolol treatment were seen: 1) blockade of beta 2-adrenergic receptors, which reduced the right ventricular hypertrophy of high altitude through reduction of hematocrit; and 2) a non-beta-effect, which reduced vascular responsiveness to acute hypoxia in the isolated lung preparation.