Protective effect of alpha-human atrial natriuretic polypeptide (alpha-hANP) on chemical-induced pulmonary edema

It has been established that alpha-hANP, the newly discovered peptide extracted from human cardiac atria, has potent natriuretic and hypotensive actions. Our present investigation is the first to demonstrate that alpha-hANP is capable of protecting against pulmonary edema caused by various chemicals, using isolated perfused guinea pig lung system. Lungs were perfused via pulmonary artery with Krebs-Ringer bicarbonate buffer at 5.0 ml/min, and wet weight of lungs and perfusion pressure of pulmonary artery (Pa) were monitored. Bolus injection of Triton-X or CHAPS into cannulated pulmonary artery produced edema as indicated by a massive increase in wet weight and a slight increase in Pa. Constant infusion of alpha-hANP through pulmonary artery at 200 ng/ml was effective in causing decrease in wet weight of lung. Perfusion of lung with paraquat or PGF2 alpha, and repeated bolus injection of arachidonic acid or PGE2 caused elevation in both wet weight of lung and Pa. The treatment with alpha-hANP similar to that described above also protected against edema caused by paraquat or arachidonic acid. Bolus administration of epinephrine induced a slight increase in wet weight and Pa, and alpha-hANP was effective in decreasing the elevated lung wet weight and Pa of lungs. Infusion or bolus administration of alpha-hANP into control lungs increased cGMP level in outflow perfusate as well as in lung tissue significantly. In lungs with edema which were induced by Triton-X or paraquat, there was a slight increase in cGMP level in Triton-X treated and no increase in paraquat treated lung tissues. In either cases, was there any increase in cGMP level in perfusate. The specific binding study of [125I]alpha-hANP revealed that the lack of increase in cGMP was not due to a loss of receptor in Triton-X or paraquat treated lungs. Thus our study demonstrated that alpha-hANP had a direct anti-edematic action(s) in lung which was not secondary to the systemic natriuretic and/or hypotensive action(s).     

Oleic acid lung injury in sheep

Intravenous infusion of oleic acid into experimental animals causes acute lung injury resulting in pulmonary edema. We investigated the mechanism of oleic acid lung injury in sheep. In experiments with anesthetized and unanesthetized sheep with lung lymph fistulas, we measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, and lymph and plasma protein concentrations. We injured the lungs with intravenous infusions of oleic acid at doses ranging from 0.015 to 0.120 ml/kg. We found that oleic acid caused reproducible dose-related increases in pulmonary arterial pressure and pulmonary vascular resistance, arterial hypoxemia, and increased protein-rich lung lymph flow and extravascular lung water. The lung fluid balance changes were characteristic of increased permeability pulmonary edema. Infusion of the esterified fat triolein had no hemodynamic or lung fluid balance effects. Depletion of leukocytes with a nitrogen mustard or platelets with an antiplatelet serum had no effect on oleic acid lung injury. Treatment of sheep before injury with methylprednisolone 30 mg/kg or ibuprofen 12.5-15.0 mg/kg also had no effects. Unlike other well-characterized sheep lung injuries, injury caused by oleic acid does not require participation of leukocytes.     

Reduction of Vanadate by Ascorbic Acid and Noradrenaline in Synaptosomes

The effect of ascorbic acid and noradrenaline on the inhibition of synaptosomal membrane ATPase by vanadate has been studied. Ascorbic acid (2 x 10(-3) M) and noradrenaline (10(-4) M) partly reversed the inhibition by vanadate (10(-6) M); however, when both were administered together the inhibition was completely eliminated. Using electron spin resonance (ESR) spectroscopy, we detected that ascorbic acid (10(-3) M) caused a 42% of reduction of vanadate (10(-4) M). Noradrenaline (10(-4) M) alone also reduced vanadate (10(-4) M) partially. When ascorbic acid and noradrenaline were present together all the vanadate was reduced to vanadyl. The concentration of ascorbic acid present in the brain under physiological conditions is identical to that found effective in our experiments. We suggest that ascorbic acid may protect the ATPase, at least in part, from inhibition by vanadate as a consequence of reducing vanadate to vanadyl. In those tissues where noradrenaline is also present a complete reduction of endogenous vanadium can be presumed.     

Effects of oxidizing and reducing agents on ovine pulmonary artery responses to nitric oxide donors, sodium nitroprusside and 3-morpholino-sydnonimine

Nitrovasodilators-sodium nitroprusside (SNP; 10(-9)-10(-4) M) and 3-morpholino-sydnonimine (SIN-1; 10(-9)-10(-4) M) produced concentration-dependent relaxation of the fourth generation sheep pulmonary artery, preconstricted with 5-hydroxytryptamine (1 microM). Oxidizing agents [oxidized glutathione (GSSG, 1 mM) and CuSO4 (5 and 20 microM)] and reducing agents [dithiothreitol (DTT, 0.1 mM), ascorbic acid (1 mM) and reduced glutathione (GSH, 1 mM)] caused opposite effects on nitric oxide (NO)-induced vasodilation in the artery. Ascorbic acid and GSH potentiated the NO responses, while GSSG and CuSO4 inhibited relaxation caused by the nitrovasodilators. DTT, however, reduced the relaxant potency and efficacy of SNP and SIN-1. Pretreatment of the pulmonary artery strips with DTT (0.1 mM) inhibited SNP (10 microM)-induced Na(+)-K(+)-ATPase activity, while ascorbic acid (1 mM) and GSH (1 mM) had no effect either on basal or SNP (10 microM)-stimulated 86Rb uptake, an index of Na(+)-K(+)-ATPase activity, in ovine pulmonary artery. The results suggest that reducing agents like ascorbic acid may have beneficial effect in improving the vascular function under oxidative stress.     

Pulmonary circulation in experimental pulmonary edema during diverse artificial respiration regimes

In acute experiments on cats with closed chest by ultrasonic method the authors studied the blood flow in low-lobar pulmonary artery and the vein, the blood pressure in pulmonary artery, lung vessels resistance in experimental pulmonary edema caused by intravenous infusion of mixture fatty acids at artificial ventilation of increased frequencies or volumes, at was shown, that artificial ventilation of increased frequencies in pulmonary edema reduces the pressure increase in pulmonary artery, lung vessels resistance and increases the blood flow in pulmonary artery and vein. Artificial ventilation of increased volumes produces more intense pressure increase in pulmonary artery and lung vessels resistance than in initial ventilation but the blood flow was slightly changed. The authors assume that artificial ventilation of increased frequencies or volumes in pulmonary edema due to pulmonary circulation change reduces the pulmonary edema intensity at the beginning.     

Effects of a membrane modulator derived from 3-hydroxypyridine class on the development of pulmonary edema

The experiment on white rats has revealed that water-soluble antioxidant-emoxipin, having obvious membrane modulating effect, does not influence the rate of watering and congestion of the lungs, the speed of reabsorption of fluid from lung tissue, the permeability of the capillary-alveolar barrier both in the blood-tissue direction and vice versa. Preliminary introduction of emoxipin increased the amount of edema fluid in the lungs when noradrenaline, centrogenic and especially vasopressin pulmonary edema developed, but in did not influence the development of vagotomic pulmonary edema. Stimulation of adenylcyclase or introduction of prostacyclin slowed down the development of centrogenic and vasopressin edema of the lungs. On the basis of these data it can be concluded that the intensification of pulmonary edema after emoxipin introduction is connected with its antioxidant activity.     

PAF-mediated pulmonary edema: a new role for acid sphingomyelinase and ceramide

Platelet-activating factor (PAF) induces pulmonary edema and has a key role in acute lung injury (ALI). Here we show that PAF induces pulmonary edema through two mechanisms: acid sphingomyelinase (ASM)-dependent production of ceramide, and activation of the cyclooxygenase pathway. Agents that interfere with PAF-induced ceramide synthesis, such as steroids or the xanthogenate D609, attenuate pulmonary edema formation induced by PAF, endotoxin or acid instillation. Our results identify acid sphingomyelinase and ceramide as possible therapeutic targets in acute lung injury.     

Pulmonary bioavailability of ascorbic acid in an ascorbate-synthesising species,the horse

Vitamin C (ascorbic acid) is a non-enzymatic antioxidant important in protecting the lung against oxidative damage and is decreased in lung lining fluid of horses with airway inflammation. To examine possible therapeutic regimens in a species with ascorbate-synthesising capacity, we studied the effects of oral supplementation of two forms of ascorbic acid, (each equivalent to 20 mg ascorbic acid per kg body weight) on the pulmonary and systemic antioxidant status of six healthy ponies in a 3 x 3 Latin square design. Two weeks supplementation with ascorbyl palmitate significantly increased mean plasma ascorbic acid concentrations compared to control (29 +/- 5 and 18 +/- 7 micromol/l, respectively; p < 0.05). Calcium ascorbyl-2-monophosphate, a more stable form of ascorbic acid, also increased mean plasma ascorbic acid concentrations, but not significantly (23 +/- 1 micromol/l; p = 0.07). The concentration of ascorbic acid in bronchoalveolar lavage fluid increased in five out of six ponies following supplementation with either ascorbyl palmitate or calcium ascorbyl-2-monophosphate compared with control (30 +/- 10, 25 +/- 4 and 18 +/- 8 micromol/l, respectively; p < 0.01). Neither supplement altered the concentration of glutathione, uric acid or alpha-tocopherol in plasma or bronchoalveolar lavage fluid. In conclusion, the concentration of lung lining fluid ascorbic acid is increased following ascorbic acid supplementation (20 mg/kg body weight) in an ascorbate-synthesising species.     

Extracellular ascorbic acid in lung

Fifty percent of the ascorbic acid content of sliced rat lung was released from tissue to the media within a few minutes by either washing or incubating the slices with Kreb-phosphate solution. Measurement of the lactate dehydrogenase and potassium content of the medium after incubating lung slices for 5 min showed that about 20% of the cells were damaged by slicing.Sephadex chromatography of tissue extracts prepared from washed lung slices showed that none of the ascorbic acid in these slices was bound to protein. Also, metabolic poisons were shown to deplete the ascorbic acid content of washed lung slices.Approx. 57% of the lung ascorbic acid of guinea pigs that had been supplemented with ascorbic acid and 78% of the lung ascorbic acid of ascorbic acid-deficient guinea pigs were found in the medium when lung slices from these animals were incubated with Krebs-phosphate solution.These results were taken to indicate the presence of an extracellular pool of ascorbic acid in lung which is maintained even during scurvy.     

Expiratory muscle activity during pulmonary edema in the anesthetized dog.

The present study evaluated the reflex response of the expiratory muscles to pulmonary congestion and edema. The electromyograms of two thoracic and four abdominal expiratory muscles were recorded in 12 anesthetized dogs. Pulmonary edema was induced by rapid saline infusion in six dogs and injection of oleic acid into the pulmonary circulation in the remaining six dogs. Both forms of pulmonary edema reduced pulmonary compliance, interfered with gas exchange, and induced a rapid and shallow breathing pattern. The electrical activity of all abdominal muscles was suppressed during both forms of pulmonary edema. In contrast, the electromyogram activity of the thoracic expiratory muscles was not significantly affected by pulmonary edema. Acute pulmonary arterial hypertension produced in two dogs by inflating a balloon in the left atrium had no effect on ventilation or expiratory muscle electrical activity. In two vagotomized dogs, pulmonary edema did not inhibit the expiratory muscles. We conclude that pulmonary edema suppresses abdominal but not thoracic expiratory muscle activity by vagal reflex pathway(s). Extravasation of fluid into the lung appears to be more important than an increase in pulmonary vascular pressure in eliciting this response.     

Effect of endotoxin pretreatment on the pulmonary vascular response to hypoxia in O2-exposed lambs

We recently reported that endotoxin infusion before O2 exposure significantly reduced or delayed the onset of pulmonary edema formation and respiratory failure by reducing the oxidant stress of O2 exposure. Despite these beneficial effects of endotoxin treatment, lung microvascular permeability eventually increased, but postmortem lung water content was less than expected. Prolonged O2 breathing blunts or abolishes the pulmonary constrictor response to alveolar hypoxia in some species, and it is possible that the loss of this response could contribute further to edema formation. To determine whether the reduction in lung edema observed in endotoxin-treated, O2-exposed lambs was linked to the preservation of hypoxic pulmonary vasoconstriction (HPV), we measured pulmonary vascular resistance before and after 8 min of isocarbic hypoxia (inspired O2 fraction 0.12) during each day of O2 exposure. In six control lambs, the pressor response to hypoxia was abolished after 72 h in O2, and the lambs developed respiratory failure shortly thereafter. In six endotoxin-treated lambs, HPV was preserved for as long as 144 h of O2 exposure. In two control O2-exposed lambs in whom HPV was abolished, the infusion of either angiotensin or prostaglandin H2 analogue increased pulmonary vascular resistance by greater than 75%. We conclude that in lambs 1) hyperoxia abolishes the pulmonary vascular response to hypoxia, 2) endotoxin pretreatment reduces acute O2-induced lung injury and preserves the pulmonary constrictor response to hypoxia, and 3) the loss of HPV during O2 exposure may be the result of oxidant-mediated injury to the hypoxia response itself and not the result of diffuse damage to the vasoconstrictor effector mechanism.     

神经性肺水肿之神经与血流动力学机制

临床分析及动物实验均报告颅内病变、头部受作或颅内压增加会导致急性肺水肿;在麻木麻醉鼠,严重脑部压迫产生急性、猛暴及致死性肺水肿,此种神经性肺病变乃由于激发脑干交感神经机构产生体循环高血压及一连串的血流动力学变化,导致主动脉血流急剧下降,引发肺部血量及血压严重增加,最终结果为血管破裂形成出务性肺水肿。     

Ascorbic acid in rat lung

Fifty percent of the ascorbic acid content of sliced rat lung was removed in 2 min by washing with Krebs-phosphate solution. Although no ascorbic acid was washed from an intact lung by perfusion of the pulmonary circulation, 30% of it was removed by washing out the air spaces. It is concluded that 50% of the ascorbic acid present in rat lung is present in the fluid lining of the air spaces.     

Direct injury to the bronchial vasculature in anesthetized sheep.

Injury to the bronchial vasculature may contribute to liquid and solute leakage into the lung during noncardiac pulmonary edema. The purpose of this study was to measure changes in hemodynamics, pulmonary mechanics, extravascular lung water, and lung morphometry after selectively injuring the bronchial vasculature in anesthetized sheep. In two groups of seven sheep, we injected oleic acid (0.1 ml/kg) or normal saline directly into the bronchoesophageal artery. We measured systemic and pulmonary arterial pressures, cardiac output, oxygen saturation, pulmonary resistance and compliance, and lung volumes before and 1 and 4 h after injection. The lungs were removed for measurement of extravascular water, histology, and morphometry. Four hours after injection of oleic acid, cardiac output decreased but pulmonary arterial pressure did not change. In addition, pulmonary resistance increased and dynamic compliance and vital capacity decreased. Extravascular lung water was slightly but significantly greater in the oleic acid group. Histological examination showed interstitial edema and leukocytes in airway walls and sloughing of bronchial epithelium but little or no alveolar edema. Morphometric analysis showed significant thickening of airway walls. We conclude that direct injury to the bronchial vasculature increases lung resistance, decreases dynamic compliance, and increases extravascular lung water by the accumulation of an inflammatory infiltrate in airway walls.     

Protease-activated receptor-2 activation induces acute lung inflammation by neuropeptide-dependent mechanisms

Protease-activated receptors (PARs) and tachykinin-immunoreactive fibers are located in the lung as sentries to respond to a variety of pathological stimuli. The effects of PAR activation on the lung have not been adequately studied. We report on the effects of instilling PAR-activating peptides (PAR-APs, including PAR1-, PAR2-, and PAR4-AP) into the lungs of ventilated or spontaneously breathing mice. PAR2-AP, but not PAR1-AP or PAR4-AP, caused a sharp increase in lung endothelial and epithelial permeability to protein, extravascular lung water, and airway tone. No responses to PAR2-AP were detected in PAR2 knockout mice. In bronchoalveolar lavage, PAR2 activation caused 8- and 5-fold increase in MIP-2 and substance P levels, respectively, and a 12-fold increase in the number of neutrophils. Ablation of sensory neurons (by capsaicin) markedly decreased the PAR2-mediated airway constriction, and virtually abolished PAR2-mediated pulmonary inflammation and edema, as did blockade of NK1 or NK2 receptors. Thus, PAR2 activation in the lung induces airway constriction, lung inflammation, and protein-rich pulmonary edema. These effects were either partly or completely neuropeptide dependent, suggesting that PAR2 can cause lung inflammation by a neurogenic mechanism.     

Hemodynamic effects of oleic acid in newborn lambs: role of arachidonic acid metabolites.

Oleic acid injection produces acute lung injury and pulmonary hypertension in adult animals. In other types of acute lung injury, such as that caused by E. coli endotoxin, metabolites of arachidonic acid are important mediators of pulmonary hypertension. In order to understand the hemodynamic response of newborn animals to oleic acid injection and the contribution of arachidonic acid metabolites to that response, we injected oleic acid into awake, chronically instrumented newborn lambs. The hemodynamic response of lambs to injections of oleic acid alone was compared to their response after pretreatment with either FPL57231, a putative leukotriene receptor antagonist, or indomethacin, a cyclooxygenase synthesis inhibitor. Oleic acid caused acute pulmonary hypertension associated with an increase in protein-rich lung lymph fluid. Systemic hemodynamic effects were variable. FPL57231 completely blocked the oleic acid-induced pulmonary hypertension while indomethacin significantly attenuated the response. Therefore, metabolites of arachidonic acid metabolism appear to be important mediators of oleic acid-induced pulmonary hypertension in newborn lambs.     

Effect of different levels of positive end-expiratory pressure on lung water content

To compare the effects of 2-, 5-, and 10-cmH2O positive end-expiratory pressure (PEEP) on pulmonary extravascular water volume (PEWV), pulmonary blood volume (PBV), pulmonary dry weight (PDW), and distensibility, we separately ventilated perfused dogs' lungs in situ and produced pulmonary edema with oleic acid (0.06 ml/kg). Three groups were studied: I, PEEP, 5 cmH2O in both lung; II, PEEP, 2 cmH2O in one lung and 10 cmH2O in the other; and III, PEEP, same as II, but the chest was rotated to compensate for differences in heights. The PEWV and distensibility were less (P less than 0.05) in lungs exposed to 10-cmH2O than to either 2- or 5-cmH2O PEEP. After chest rotation, the difference between 10- and 2-cmH2O PEEP on PEWV was eliminated but that on distensibility was not. We conclude that 10-cmH2O PEEP 1) decreased water content because of lung volume-induced effects on intravascular hydrostatic pressure and 2) improved distensibility by recruitment of alveoli, irrespective of PEWV.     

Decreased levels of ascorbic acid in lung following exposure to ozone

Mice were exposed to concentrations of 20, 40 and 200 ppm ozone in air for 30 min. Ozone exposure decreased lung ascorbic acid levels and increased lung weight by up to 50% in a dose related manner. On incubation in Krebsphosphate solution, lung slices from mice exposed to 200 ppm ozone released a smaller fraction of their content of ascorbic acid into the medium than did lung slices from control mice, suggesting that there was a preferential loss of extracellular ascorbic acid during ozone exposure. These results are consistent with the proposed function of ascorbic acid as an extracellular antioxidant in lungs.     

Increased pressor responses to pressor agents in spontaneously hypertensive rats.

Pressor reactivity to a variety of pressor agents after partial ganglionic blockade induced with hexamethonium was investigated in intact, in spinalized, and in chemically sympathectomized, spontaneously hypertensive rats (SHR). Responses of unanaesthetized 6-month-old SHR to noradrenaline, phenylephrine, and angiotensin after hexamethonium administration (32 mg/kg) markedly exceeded those of unanaesthetized, age-matched normotensive Wistar-Kyoto rats (WKR). Responses of anaesthetized SHR to noradrenaline after hexamethonium administration (16 mg/kg) were also increased at the hypertensive stages but not at the prehypertensive stages, when compared with those of anaesthetized normotensive Wistar rats of respective ages. In spinalized and chemically sympathectomized preparations after hexamethonium administration (16 mg/kg), noradrenaline produced equal increases in blood pressure in 6-month-old SHR and WKR. It is suggested that the functional sympathetic nervous system is important for the hyperreactivity of intact SHR.