Ozone inhibits endothelial cell cyclooxygenase activity through formation of hydrogen peroxide

We have previously demonstrated that a 2H exposure of cultured pulmonary endothelial cells to ozone (0.0-1.0 ppm) in-vitro resulted in a concentration-dependent reduction of endothelial prostacyclin production (90% decrease at the 1.0 ppm level). Ozone-exposed endothelial cells, incubated with 20 uM arachidonate, also demonstrated a significant inhibition of prostacyclin synthesis. To further examine the mechanisms of the inhibition of prostacyclin synthesis, bovine pulmonary endothelial cells were exposed to 1.0 ppm ozone for 2H. A significant decrease in prostacyclin synthesis was found within 5 min of exposure (77 +/- 36% of air-exposed control values, p less than 0.05). Endothelial prostacyclin synthesis returned to baseline levels by 12H after ozone exposure, a time point which was similar to the recovery time of unexposed endothelium treated with 0.5 uM acetylsalicylic acid. Incubation of endothelial cells, previously exposed to 1.0 ppm ozone for 2 hours, with 4 uM PGH2 resulted in restoration of essentially normal prostacyclin synthesis. When endothelial cells were co-incubated with catalase (5 U/ml) during ozone exposure, no inhibition of prostacyclin synthesis was observed. Co-incubation with either heat-inactivated catalase or superoxide dismutase (10 U/ml) did not affect the ozone-induced inhibition of prostacyclin synthesis. These data suggest that H2O2 is a major toxic species produced in endothelial cells during ozone exposure and responsible for the inhibition of endothelial cyclooxygenase activity.     

Ozone inhibits endothelial cell cyclooxygenase activity through formation of hydrogen peroxide

We have previously demonstrated that a 2H exposure of cultured pulmonary endothelial cells to ozone (0.0–1.0 ppm) resulted in a concentration-dependent reduction of endothelial prostacyclin production (90% decrease at the 1.0 ppm level). Ozone-exposed endothelial cells, incubated with 20 uM arachidonate, also demonstrated a significant inhibition of prostacyclin synthesis. To further examine the mechanisms of the inhibition of prostacyclin synthesis, bovine pulmonary endothelial cells were exposedto 1.0 ppm ozone for 2H. A significant decease in protacyclin synthesis was found within 5 min of exposure (77 ± 36% of air-exposed control values, p < 0.05). Endothelial prostacyclin synthesis returned to baseline levels by 12H after ozone exposure, a time point which was similar to the recovery time of unexposed endothelium treated with 0.5 uM acetylsalicylic acid. Incubation of endothelial cells, previously exposed to 1.0 ppm ozone for 2 hours, with 4 uM PGH₂ resulted in restoration of essentially normal prostacyclin synthesis. When endothelial cells were co-incubated with catalase (5U/ml) during ozone exposure, no inhibition of prostacycline synthesis was observed. Co-incubation with either heat-inactivated catalase or superoxide dismutase (10U/ml) did not affect the ozone-induced inhibition of prostacycline synthesis. These data suggest that H₂O₂ is a major toxic species produced in endothelial cells during ozone exposure and responsible for the inhibiton of endothelial cyclooxygenase activity.     

臭氧急性暴露对大鼠血管的损伤及其机制

目的:探索不同浓度臭氧(O3)急性暴露对雄性Wistar大鼠血管的损伤效应和可能的机制。方法:120只雄性Wistar大鼠随机分为6组,每组20只;实验动物置于气体染毒柜中,对照组暴露于过滤后空气,处理组分别暴露于浓度为0.12ppm,0.5ppm,1.0ppm,2.0ppm和4.0ppm的臭氧,持续暴露4h。利用PC-lab医学生理信号采集系统获得动脉血压数据;血流变指标和血生化指标由天津迪安诊断实验室检测;血清中内皮素(ET-1)、同型半胱氨酸(HCY)、血管性血友病因子(vWF)、8-羟基脱氧鸟苷(8-OhdG)、白介素(IL-6)和肿瘤坏死因子α(TNF-α)采用酶联免疫(ELISA)微孔板法检测;氧化应激指标超氧化物歧化酶(SOD)活力和丙二醛(MDA)分别采用黄嘌呤氧化酶法、硫代巴比妥酸(TBA)法测定,还原型谷胱甘肽(GSH)和一氧化氮(NO)采用微孔板比色法;取胸主动脉组织制备石蜡切片,经HE染色后观察血管结构改变。结果:0.12ppm臭氧急性暴露可导致动脉收缩血压(SBP)显著升高;不同浓度臭氧暴露均可导致血浆粘度显著升高,1.0ppm臭氧暴露组血沉(ESR)方程K值显著升高,全血高切相对指数和还原粘度均在臭氧浓度为0.5ppm和4.0ppm时显著降低,而红细胞变形指数在臭氧浓度为0.12ppm、0.5ppm、1.0ppm和2.0ppm时显著升高;急性臭氧暴露可导致总胆固醇含量降低,高密度脂蛋白胆固醇(HDL-C)在0.12ppm臭氧暴露组显著降低;当臭氧浓度高于1.0ppm时还可导致机体出现炎症反应(TNF-α升高)和氧化应激反应(MDA升高、GSH降低);臭氧急性暴露可导致血液中ET-1含量升高,在4.0ppm浓度组具有显著性差异,而HCY水平呈现先降低后升高的趋势,在1.0ppm浓度组达到最高值,胸主动脉未见明显的病理改变。结论:臭氧急性暴露可影响大鼠的动脉血压、血流变及胆固醇代谢,可能的机制是臭氧暴露导致炎症反应和氧化应激反应,引起血管内皮功能损伤,并且随着臭氧暴露浓度升高血管内皮细胞功能损伤越显著。     

Effect of long-term hypoxia on cultured aortic and pulmonary arterial endothelial cells

In a previous study, we found a marked difference in the release of a cytokine, neutrophil chemoattractant activity (NCA), from cultured endothelial cells exposed to acute decreases in ambient oxygen, depending on the vascular bed of origin. In the current study, we used this cytokine to evaluate the effect of long-term exposure to decreased oxygen on endothelial cell function. We found that, in aortic and pulmonary arterial endothelial cells maintained for months in decreased ambient oxygen (10 or 3% oxygen), exposure to acute decreases in ambient oxygen caused a change in the pattern of NCA release; however, the differential response between the two cell types persisted. Aortic endothelial cells release NCA when exposed acutely to a level of oxygen below that in which they have been chronically maintained. In contrast, pulmonary arterial endothelial cells release NCA only when exposed to 0% oxygen acutely, but only if grown chronically in 10% oxygen; otherwise there was no release of NCA. As another indicator of endothelial cell function, we evaluated the effects of acute hypoxic exposure on prostacyclin production by endothelial cells maintained in 21 or 3% oxygen. If grown in 21% oxygen, both cell types decreased prostacyclin production upon exposure to 0% oxygen. However, when grown in 3% oxygen, only aortic endothelial cells decreased prostacyclin production when exposed acutely to 0% oxygen; pulmonary arterial endothelial cell prostacyclin production did not change. This study demonstrating the persistence of a differential pattern of NCA release and the appearance of a differential pattern of prostacyclin production after a long-term decrease in environmental oxygen suggests that the capacity of certain vascular endothelial cells to respond to decreases in oxygen concentration is carried by the cell throughout its existence. Thus, in certain situations, vascular endothelial cells may be important in sensing acute decreases in ambient oxygen.     

Attenuation of hypoxic pulmonary vasoconstriction by verapamil in intact dogs.

The hypothesis that hypoxic pulmonary vasoconstriction is mediated directly by depolarization of the vascular smooth muscle was tested in anesthetized dogs. Pulmonary vascular responses to hypoxia were first determined in eight dogs during 20-min exposures to 10% O2. Each animal was then treated with verapamil (0.5 mg/kg, iv), to block transmembrane Ca2+ influx in an attempt to abolish the vasoconstrictor responses to hypoxia. The hypoxic exposures were then repeated, and the pulmonary vascular responses were compared to the control responses. Verapamil administration attenuated hypoxic pulmonary vasoconstriction, but did not abolish the responses to hypoxia. Pulmonary vascular resistance increased 87% during the control hypoxic exposure, but increased only 38% during hypoxia after verapamil. The response to another vasoconstrictor, prostaglandin F2alpha, was not reduced by verapamil indicating a different mechanism of mediation. These results suggest that the pulmonary vasoconstrictor response to alveolar hypoxia, in the intact dog, involves transmembrane Ca2+ influx, and are consistent with the idea that hypoxia acts primarily by directly depolarizing vascular smooth muscle, rather than acting indirectly through a chemical mediator.     

Mechanism of hyperoxia-induced pulmonary vascular paralysis: effect of antioxidant pretreatment

We designed experiments using isolated rabbit lungs to determine the effect of hyperoxia on the pulmonary vasoconstriction caused by the infusion of the lipid peroxide tert-butyl hydroperoxide (t-bu-OOH), which produces vasoconstriction by stimulating the pulmonary synthesis of thromboxane. Exposure to 48-60 h of 100% O2 at 1 ATA markedly reduced the increase in pulmonary artery pressure caused by t-bu-OOH infusion. We also investigated whether the mechanism for the attenuated vasoconstriction was due to altered production of arachidonate mediators or oxidant-induced damage to the contractile mechanism. In addition to infusing t-bu-OOH, which selectively stimulates thromboxane production, we also infused Intralipid, an esterified fatty acid emulsion that stimulates production of both thromboxane and prostacyclin. These experiments were done to study the effect of hyperoxia on prostacyclin synthesis. To determine if antioxidant therapy would prevent the changes in mediator production and vascular reactivity caused by hyperoxia, we pretreated animals with the antioxidants butylated hydroxyanisole (BHA) or vitamin E. The lack of vascular reactivity to t-bu-OOH was not due to a decrease in thromboxane synthesis or an increase in prostacyclin synthesis. Hyperoxia did not affect thromboxane synthesis during basal conditions or after stimulation of synthesis by t-bu-OOH. 100% O2 also did not effect the basal synthesis of prostacyclin by the lung. Hyperoxia did, however, markedly reduce prostacyclin synthesis when it was stimulated by Intralipid infusion. Antioxidant pretreatment did not reverse the inhibition of prostacyclin synthesis but did prevent the loss of vascular reactivity caused by hyperoxia. Thus hyperoxia causes vascular paralysis through oxidant-induced injury to the pulmonary vasculature.     

Effect of amrinone,a cardiotonic drug,on hemodynamics and platelet function

In the present study we have investigated the effect of Amrinone on the hemodynamics, platelet counts, prostacyclin and thromboxane synthesis and platelet function. Results show that infusion of the drug increased the heart rate and lowered left atrial, aortic and pulmonary artery pressures within five minutes after a single bolus injection of 2 mg/kg IV dose. Platelet counts made from the blood obtained from anesthetized dogs after the drug infusion showed severe loss of platelets. However, infusion of a similar dose in awake dogs showed no such detrimental effect on platelets. Examination of formalin fixed blood for aggregates showed no more clumps in the treated samples than in the control. Platelets obtained from canine blood drawn at 30 minutes post infusion of the drug showed no aggregatory response to arachidonate. However, the response of these platelets to ADP was quite normal. Amrinone infusion had no inhibitory effect on the ability of vascular tissue to convert arachidonic acid to prostacyclin. Similarly, no inhibitory action could be observed on platelet cyclo-oxygenase activity at this concentration (2 mg/kg). In vitro studies on human platelets showed significant inhibition of cyclo-oxygenase at high concentrations (0.5 mg/ml). Therefore it is unlikely that the drug caused inhibition of the platelet response to arachidonate by the inhibition of prostaglandin synthesis during infusion, as the dose used was quite low (2 mg/kg) compared to what is required for the inhibition of cyclo-oxygenase.     

Perfusion of lung periphery: effects of local exposures to ozone and pressure

Following ozone (O3) exposure, airways reactivity increases. We investigated the possibility that exposure to O3 causes a decrease in pulmonary perfusion, and that this decrease is associated with the increase in reactivity. Perfusion was measured with radiolabeled microspheres. A wedged bronchoscope was used to isolate sublobar segments in the middle and lower lobes of anesthetized dogs. Isolated segments were exposed to either O3 or an elevated alveolar pressure. Although increased alveolar pressure decreased microsphere density, exposure to 1 ppm O3 did not. Collateral system resistance rose significantly following exposure to O3 and to high pressure. These studies do not support the hypothesis that pulmonary perfusion is decreased following O3 exposure and is associated with subsequent increases in reactivity.     

Enrichment of endothelial cell arachidonate by lipid transfer from high density lipoproteins: relationship to prostaglandin I2 synthesis

We have previously shown that plasma high density lipoproteins (HDL) stimulate release of prostacyclin, measured as its stable metabolite, 6-keto-PGF1 alpha, by cultured porcine aortic endothelial cells. The present experiments were designed to elucidate the contribution of HDL lipids to endothelial cellular phospholipid pools and to prostacyclin synthesis. In experiments with reconstituted HDL, both the lipid and protein moieties were required to stimulate prostacyclin release in amounts equivalent to the native HDL particle. Endothelial cells incorporated label from reconstituted HDL containing cholesteryl [1-14C]arachidonate into the cellular neutral and phospholipid pools as well as into 6-keto-PGF1 alpha and PGE2. Labeled arachidonate incorporated into endothelial cell lipids from reconstituted HDL containing cholesteryl [1-14C]arachidonate was also metabolized to prostaglandins after the cells were exposed to the calcium ionophore, A-23187. Both rat and human HDL which stimulated 6-keto-PGF1 alpha release (rat greater than human) increased the weight percentage of arachidonate in endothelial cell phospholipids; phospholipid arachidonate in the enriched cells fell after exposure to the phospholipase activator, A-23187, with release of 6-keto-PGF1 alpha which was greater than in control cells. Rat HDL that was depleted of cholesteryl arachidonate (achieved by incubation with human low density lipoproteins (LDL) in the presence of cholesteryl ester transfer protein) stimulated 6-keto-PGF1 alpha release less than native rat HDL. LDL enriched in cholesteryl arachidonate stimulated 6-keto-PGF1 alpha release more than native LDL. ApoE-depleted HDL also stimulated 6-keto-PGF1 alpha release more than apoE-rich HDL suggesting the apoE receptor was not involved in the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of ozone on peripheral lung reactivity

In previous studies, we demonstrated that local exposures to the lung periphery to 0.1 ppm ozone (O3) produce increases in resistance to flow through the collateral system (Rcs) which are prevented by vagotomy, and the local exposures to 1.0 ppm O3 produces increases in Rcs which are only partially mediated by the parasympathetic system. In the present studies, we evaluated the effects of short exposures to O3 on reactions to H2O and histamine in anesthetized male dogs when no residual effects of the O3 exposures could be detected. For this purpose a fiber-optic bronchoscope was wedged in a segmental airway of anesthetized dogs and was used to deliver O3, aerosols of H2O, histamine (1.5 X 10(-4) mg), and atropine (0.1 mg). Measurements of Rcs were used to monitor responses to these agents. Responses to three successive challenges with H2O and with histamine were not different from each other. A 30-min exposure to 0.1 ppm O3 between the first and second challenge did not alter responses to histamine or H2O. However, a 10-min exposure to 1.0 ppm O3 resulted in a significant increase in responses to both H2O and histamine. No correlation was noted between the magnitude of response to O3 and the increase in response to histamine or H2O following O3 exposure. Parasympathetic blockade (atropine or bilateral cervical vagotomy) abolished the increase in response to H2O but not the increase in response to histamine following exposure to 1.0 ppm O3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acetylcholine induces vasodilation and prostacyclin synthesis in rat lungs

Acetylcholine causes pulmonary vasodilation, but its mechanism of action is unclear. We hypothesized that acetylcholine-induced pulmonary vasodilation might be associated with prostacyclin formation. Therefore, we used isolated rat lungs perfused with a recirculating cell- and plasma-free physiological salt solution to study the effect of acetylcholine infusion on pulmonary perfusion pressure, vascular responsiveness and lung prostacyclin production. Acetylcholine (20 micrograms infused over 1 minute) caused immediate vasodilation during ongoing hypoxic vasoconstriction and prolonged depression of subsequent hypoxic and angiotensin II-induced vasoconstrictions. Both effects of acetylcholine were abolished by atropine pretreatment. The prolonged acetylcholine effect, but not the immediate response, was blocked by meclofenamate, an inhibitor of cyclooxygenase. The prolonged effect, but not the immediate response, of acetylcholine was associated with an increase in perfusate 6-keto-PGF1 alpha concentration. The acetylcholine stimulated increase in 6-keto-PGF1 alpha production was inhibited by meclofenamate and by atropine. Thus, blockade of prostacyclin production corresponded with blockade of the prolonged acetylcholine effect. In conclusion, acetylcholine caused in isolated rat lungs an immediate vasodilation and a prolonged, time-dependent depression of vascular responsiveness. Whereas both acetylcholine effects were under muscarinic receptor control, only the prolonged effect depended on the cyclooxygenase pathway and, presumably, prostacyclin synthesis.     

Effect of hypoxia on prostacyclin production in cultured pulmonary artery endothelium

Exposure of cultured bovine pulmonary artery endothelial cells to varying levels of hypoxia (10% or 0% O2) for 4 hours resulted in a significant dose-dependent inhibition in endothelial prostacyclin synthesis (51% and 98%, at the 10% and 0% O2 levels respectively, p less than 0.05, compared to 21% O2 exposure values). Release of 3H-arachidonic acid from cellular pools was not altered by hypoxia. Some of the cells were incubated with arachidonic acid (20 microM for 5 min) or PGH2 (4 microM for 2 min) immediately after exposure. Endothelium exposed to 0% O2, but not to 10% O2, produced significantly less prostacyclin after addition of either arachidonic acid (25 +/- 5% of 21% O2 exposure values, n = 6, p less than 0.01) or PGH2 (31 +/- 3% of 21% O2 exposure values, n = 6, p less than 0.05). These results suggest that hypoxia inhibits cyclooxygenase at the 10% O2 level and both cyclooxygenase and prostacyclin synthetase enzymes at the 0% O2 exposure levels. Exposure of aortic endothelial cells resulted in a 44% inhibition of prostacyclin at the 0% exposure level. No significant alteration in prostacyclin production was found in pulmonary vascular smooth muscle cells exposed to hypoxia. These data suggest that the increased prostacyclin production reported in lungs exposed to hypoxia is not due to a direct effect of hypoxia on the main prostacyclin producing cells of the pulmonary circulation.     

Altered pulmonary vasoreactivity in the chronically hypoxic lung

Prolonged exposure to alveolar hypoxia induces physiological changes in the pulmonary vasculature that result in the development of pulmonary hypertension. A hallmark of hypoxic pulmonary hypertension is an increase in vasomotor tone. In vivo, pulmonary arterial smooth muscle cell contraction is influenced by vasoconstrictor and vasodilator factors secreted from the endothelium, lung parenchyma and in the circulation. During chronic hypoxia, production of vasoconstrictors such as endothelin-1 and angiotensin II is enhanced locally in the lung, while synthesis of vasodilators may be reduced. Altered reactivity to these vasoactive agonists is another physiological consequence of chronic exposure to hypoxia. Enhanced contraction in response to endothelin-1 and angiotensin II, as well as depressed vasodilation in response to endothelium-derived vasodilators, has been documented in models of hypoxic pulmonary hypertension. Chronic hypoxia may also have direct effects on pulmonary vascular smooth muscle cells, modulating receptor population, ion channel activity or signal transduction pathways. Following prolonged hypoxic exposure, pulmonary vascular smooth muscle exhibits alterations in K+ current, membrane depolarization, elevation in resting cytosolic calcium and changes in signal transduction pathways. These changes in the electrophysiological parameters of pulmonary vascular smooth muscle cells are likely associated with an increase in basal tone. Thus, hypoxia-induced modifications in pulmonary arterial myocyte function, changes in synthesis of vasoactive factors and altered vasoresponsiveness to these agents may shift the environment in the lung to one of contraction instead of relaxation, resulting in increased pulmonary vascular resistance and elevated pulmonary arterial pressure.     

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.     

Effects of ozone on lung mechanics and cyclooxygenase metabolites in dogs.

To determine if acute exposure to ozone can cause changes in the production of cyclooxygenase metabolites of arachidonic acid (AA) in the lung which are associated with changes in lung mechanics, we exposed mongrel dogs to 0.5 ppm ozone for two hours. We measured pulmonary resistance (RL) and dynamic compliance (Cdyn) and obtained methacholine dose response curves and bronchoalveolar lavagate (BAL) before and after the exposures. We calculated the provocative dose of methacholine necessary to increase RL 50% (PD50) and analyzed the BAL for four cyclooxygenase metabolites of AA: a stable hydrolysis product of prostacyclin, 6-keto-prostaglandin F1 alpha (6-keto-PgF1 alpha); prostaglandin E2 (PgE2); a stable hydrolysis product of thromboxane A2, thromboxane B2 (TxB2); and prostaglandin F2 alpha (PgF2 alpha). Following ozone exposure, RL increased from 4.75 +/- 1.06 to 6.08 +/- 1.3 cm H2O/L/sec (SEM) (p less than 0.05), Cdyn decreased from 0.0348 +/- 0.0109 TO .0217 +/- .0101 L/cm H2O (p less than 0.05), and PD50 decreased from 4.32 +/- 2.41 to 0.81 +/- 0.49 mg/cc (p less than 0.05). The baseline metabolite levels were as follows: 6-keto PgF1 alpha: 96.1 +/- 28.8 pg/ml; PgE2: 395.8 +/- 67.1 pg/ml; TxB2: 48.5 +/- 11.1 pg/ml; PgF2 alpha: 101.5 +/- 22.6 pg/ml. Ozone had no effect on any of these prostanoids. These studies quantify the magnitude of cyclooxygenase products of AA metabolism in BAL from dog lungs and demonstrate that changes in their levels are not prerequisites for ozone-induced changes in lung mechanics or airway reactivity.     

Circulatory effects of prolonged hypoxia before and during antihistamine.

Five chronically instrumented healthy dogs were exposed to a 5-day period of breathing 10% oxygen in a chamber. The response to hypoxia was found to be time dependent. During the first 24 h of hypoxia the circulatory response was characterized by increases in cardiac output, heart rate, pulmonary and systemic arterial blood pressures, and pulmonary vascular resistance. Systemic vascular resistance increased; left atrial pressure decreased. During the early part of hypoxia the animals became hypocapnic; the arterial blood pH rose significantly. During the rest of the hypoxic period cardiac output, heart rate, and arterial blood pH returned to the control values; pulmonary and systemic arterial pressures and pulmonary vascular resistance remained significantly elevated. Systemic vascular resistance rose; left atrial pressure remained below control. This response to hypoxia was not substantially modified when the experiment was repeated during the administration of the antihistamine promethazine, an H1-receptor blocking agent, in a dose which blocked the pulmonary vasoconstrictor response to small doses of exogenous histamine. The circulatory response to acute hypoxia in five anesthetized dogs was not modified by intravenous administration of metiamide, an H2-receptor blocking agent.     

Effect of hypoxia on erythrocyte deformability in different species

The contribution of erythrocyte deformability to the pulmonary vascular resistance during hypoxia in different animal species has not been examined. We hypothesized that the increase in pulmonary vascular resistance during hypoxia was partially due to erythrocytes (RBC's) becoming less deformable during hypoxia, and therefore their transit in the capillaries becomes restricted. To test this, we measured an index of deformability of RBC's from six animal species (dog, pig, cat, rabbit, hamster, rat) during normoxic and hypoxic condition, and compared the changes in deformability with the pulmonary hypoxic pressor response (HPR) which has been reported in the same species. Deformability was indexed as the resistance that a Hemafil polycarbonate membrane (Nucleopore filter, 4.7 micron pores) offers to a 10% suspension of RBC's. The RBC suspension was either normoxic (PO2 = 150 torr) or hypoxic (PO2 = 50 torr). We found that hypoxia decreased RBC deformability; the largest decrease occurred in rat RBC's, a small but significant decrease was observed in the RBC's of cats, rabbits and hamsters, but no change was detected in RBC's of dogs or pigs. In general, such changes in deformability do not correlate well with the HPR in intact or in isolated lungs, for example the pig, had the largest HPR but the smallest change in RBC deformability. In some species, however, there was a positive correlation between RBC deformability and HPR, for example rats, rabbits and cats are usually better responders than dogs and hamsters, similarly the deformability of RBC's in rats, rabbits and cats were also more influenced by hypoxia than RBC's from dogs. The limiting factors in this relationship are the artificial conditions which were used to measure deformability and HPR, both may be different than in the intact conditions. Nevertheless the present data show that erythrocytes of some species can become less flexible during hypoxia, and hence may impede the transit in the capillaries. Therefore we propose that the hypoxic pressor response in the pulmonary vasculature may be partly due to smooth muscle contraction (vasoconstriction) and partly due to a decrease in erythrocyte deformability (capillary obstruction). Both components are likely to be species dependent.     

Pulmonary response to threshold levels of sulfur dioxide (1.0 ppm) and ozone (0.3 ppm)

We exposed 22 healthy adult nonsmoking male subjects for 2 h to filtered air, 1.0 ppm sulfur dioxide (SO2), 0.3 ppm ozone (O3), or the combination of 1.0 ppm SO2 + 0.3 ppm O3. We hypothesized that exposure to near-threshold concentrations of these pollutants would allow us to observe any interaction between the two pollutants that might have been masked by the more obvious response to the higher concentrations of O3 used in previous studies. Each subject alternated 30-min treadmill exercise with 10-min rest periods for the 2 h. The average exercise ventilation measured during the last 5 min of exercise was 38 1/min (BTPS). Forced expiratory maneuvers were performed before exposure and 5 min after each of the three exercise periods. Maximum voluntary ventilation, He dilution functional residual capacity, thoracic gas volume, and airway resistance were measured before and after the exposure. After O3 exposure alone, forced expiratory measurements (FVC, FEV1.0, and FEF25-75%) were significantly decreased. The combined exposure to SO2 + O3 produced similar but smaller decreases in these measures. There were small but significant differences between the O3 and the O3 + SO2 exposure for FVC, FEV1.0, FEV2.0, FEV3.0, and FEF25-75% at the end of the 2-h exposure. We conclude that, with these pollutant concentrations, there is no additive or synergistic effect of the two pollutants on pulmonary function.     

Chronic propranolol treatment decreases pulmonary artery pressure in conscious dogs

Daily administration of propranolol to 9 chronically instrumented, trained dogs for 2 weeks caused significant (p less than 0.05) decreases in heart rate (70 +/- 8 to 57 +/- 6 beats/min), cardiac output (3.6 +/- 0.3 to 2.9 +/- 0.2 liters/min), pulmonary arterial pressure (15.7 +/- 0.5 to 10.0 +/- 0.5 mm Hg) and total pulmonary vascular resistance (4.6 +/- 0.6 to 3.3 +/- 0.4 units). Nadolol, a structurally dissimilar beta-adrenergic receptor antagonist, caused a similar decrease in total pulmonary resistance. Acute meclofenamate administration did not return to normal pulmonary arterial pressure and resistance in the dogs chronically treated with beta-adrenergic receptor blockers. We therefore conclude that chronic beta-adrenergic receptor blockade lowered pulmonary arterial pressure and resistance by a mechanism independent of cyclooxygenase. In addition, chronic beta-adrenergic receptor blockade did not affect the potential for hypoxic vasoconstriction.     

Polycythemia and the acute hypoxic response in awake rats following chronic hypoxia

The acute hypoxic pressor response was studied in 22 chronically catheterized awake rats, 13 in whom the pulmonary arterial circulation had been remodeled by 10 days of exposure to hypobaric hypoxia. Five of these had their hematocrit lowered to normocytic levels after the chronic hypoxic exposure. Nine were controls. After 24 h in room air the pulmonary arterial pressure (Ppa) and pulmonary vascular resistance (Rp) of hypoxic-polycythemic rats was at least twice the control value; in the hypoxic-normocytic rats Ppa and Rp were less than that of hypoxic-polycythemic animals and greater than that of controls. Cardiac index, heart rate, and O2 saturation were similar in all groups. In 10% O2 a rise in Ppa and Rp occurred in all groups; in absolute terms the rise was greater in hypoxic rats than in controls and greater in polycythemic than in normocytic animals. In the intact animal the acute hypoxic pressor response can still be elicited in a pulmonary vascular bed structurally altered by chronic hypoxia. When calculated as a percent increase over base line, its intensity was greater than in room air controls and for Ppa was independent of hematocrit.