Dexamethasone protects against high-dose endotoxin without loss of tolerance to oxygen

Endotoxin (500 micrograms/kg)-treated rats are very tolerant to hyperoxia (greater than 95% O2, 1 ATA). We have now attempted to determine if dexamethasone given to rats 1 h before a usually lethal dose of endotoxin would diminish endotoxin's lethality without substantially abrogating its capacity to confer tolerance to hyperoxia. Endotoxin (20 mg/kg) given alone killed 70-80% of air- or O2-breathing rats within 24 h; dexamethasone (0.6 mg) given 1 h before endotoxin decreased mortality at 24 h to 10-15%. About 90% of the rats that were alive 24 h after receiving dexamethasone plus endotoxin (20 mg/kg) survived 72 h of hyperoxia. Dexamethasone plus endotoxin (10 mg/kg) provided as much protection against pulmonary edema resulting from 72 h of hyperoxia as did 500 micrograms/kg endotoxin alone. Tolerance to hyperoxia produced by dexamethasone plus high-dose endotoxin was accompanied by a rise in the activity in the lung of antioxidant enzymes. We conclude that dexamethasone protects rats against the lethal effects of high doses of endotoxin without interfering with endotoxin's capacity to engender tolerance to hyperoxia.     

Effects of bacterial endotoxin on protecting copper-deficient rats from hyperoxia

The administration of very low doses of bacterial endotoxin protects rats during exposure to hyperoxia and is associated with the induction of lung antioxidant enzyme activities. Copper-deficient rats have increased susceptibility to O2 toxicity, which may be related to their decreased lung superoxide dismutase activity (SOD) or decreased plasma ceruloplasmin concentrations. To determine whether endotoxin can protect against hyperoxia in this susceptible model, we exposed copper-deficient and control rats to a fractional inspiratory concentration of O2 greater than 0.95 for 96 h after pretreatment with 500 micrograms/kg of bacterial endotoxin or phosphate-buffered saline (PBS). Mortality in the copper-deficient and control rats given PBS and exposed to O2 for 96 h was 100%. Copper-deficient rats died significantly earlier during the exposure than controls. No mortality occurred in either group treated with endotoxin and hyperoxia despite the decreased activity of copper-dependent enzymes in the copper-deficient rats. Copper-deficient rats treated with endotoxin and exposed to hyperoxia did increase lung Cu-Zn-SOD activity, but activity remained below levels found in air-exposed controls. Mn-SOD activity was found to be induced above air-exposed controls in the copper-deficient rats treated with endotoxin and exposed to hyperoxia. Hyperoxic exposure resulted in a marked increase in plasma ceruloplasmin concentrations in the control rats, but no increases in ceruloplasmin occurred in the copper-deficient animals. Endotoxin protects copper-deficient rats from hyperoxia despite their decreased lung Cu-Zn-SOD activity, and decreased plasma ceruloplasmin.     

The effect of bacterial endotoxin on synthesis of (Cu,Zn)superoxide dismutase in lungs of oxygen-exposed rats

Administration of bacterial endotoxin to rats exposed to greater than 95% O2 results in increased lung superoxide dismutase activity, decreased O2-induced lung damage, and a 3- to 4-fold improvement in survival rate (Frank, L., Yam, J., and Roberts, R. J. (1978) J. Clin. Invest, 61, 269-275). Antibodies to rat liver (Cu,Zn) superoxide dismutase were prepared and utilized to investigate the mechanism by which endotoxin treatment leads to increased lung superoxide dismutase activity. Assay of enzyme activity and of immunodetectable enzyme showed that the increased activity is due to an increase in the number of enzyme molecules rather than activation of existing enzyme. Compared to air controls, lung slices from rats exposed to greater than 95% O2 and treated with endotoxin have elevated rats of synthesis of (Cu,Zn)superoxide dismutase (51%) and of total protein (100%). Lung slices from untreated rats exposed to greater than 95% O2 have no such elevations. Endotoxin treatment thus appears to stimulate lung protein synthesis, leading to greater (Cu,Zn)superoxide dismutase activity due to an increased number of enzyme molecules.     

Effects of food restriction and hyperoxia on rat survival and lung polyamine metabolism

We fed Sprague-Dawley rats either freely or by restricting them to 20% of their usual diet for 21 days. In one experiment, we refed half of the food-restricted rats for 12 h, then exposed the three groups to air or 85% O2 for 5 days. The mortalities in 85% O2 were 100, 33, and 0% for the food-restricted, restricted-refed, and freely fed groups, respectively. In air lung polyamine contents and glucose 6-phosphate dehydrogenase and NADP-dependent isocitrate dehydrogenase activities were significantly lower with food restriction. After hyperoxia, lung polyamine and protein contents and enzyme activities were increased in the two surviving groups, but spermine and DNA contents of refed rats did not increase. In a second experiment, we exposed rats to 60% O2 and found that DNA synthesis of food-restricted rats was lower than the freely fed rats in air and remained low after hyperoxia. We conclude that food restriction increases the mortality from 85% O2 and is associated with lower DNA synthesis and polyamine content. We speculate that food-restricted animals may accumulate greater lung injury partly because of a compromised repair process.     

Pulmonary O2 toxicity in lambs: physiological and biochemical effects of endotoxin infusion

Hyperoxic adult rats have prolonged survival and reduced morphological evidence of lung injury when treated with a single dose of bacterial endotoxin; this effect is mediated by an augmentation of antioxidant enzyme activity in lung homogenate. To determine whether endotoxin would prolong survival and influence antioxidant enzyme levels in lambs whose physiological response to O2 breathing can be serially measured, we administered a single intravenous dose of endotoxin (0.75 microgram/kg body wt) to 13 lambs before exposing them to greater than 95% O2 (n = 11) or air (n = 2). Seven additional lambs were placed in O2 after receiving only saline vehicle. All lambs had been instrumented to measure pulmonary vascular pressures and cardiac output, and 10 lambs had lung lymph fistulas. O2-exposed control lambs developed noncardiogenic pulmonary edema and respiratory failure within 85 +/- 10 h (range 76-110 h); antioxidant enzymes were not increased, but reduced glutathione (GSH) levels fell and oxidized glutathione (GSSG) increased, reflecting the oxidant stress of O2 exposure. By contrast, endotoxin-treated O2-exposed lambs had a delayed increase in microvascular permeability to protein, a reduced rate of lung edema formation, normal gas exchange after 72 h in O2, and prolonged survival (136 +/- 15 h; range 90-160 h; all variables P less than 0.05). Despite prolonged survival, postmortem lung water content was no greater in the lambs that received endotoxin. Treatment with endotoxin did not increase antioxidant enzyme levels in lung homogenate, but levels of GSH relative to GSSG were significantly elevated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transient injury to rat lung mitochondrial DNA after exposure to hyperoxia and inhaled nitric oxide

The effect of hyperoxia alone and in combination with inhaled nitric oxide (NO) on the integrity of lung mitochondrial DNA (mtDNA) in vivo was evaluated in Fischer 344 rats. PCR amplification of lung mtDNA using two sets of primers spanning 10.1 kb of the mtDNA revealed that inhalation of 20 ppm of NO in conjunction with hyperoxia (>95% O2) reduced the amplification of mtDNA templates by 10 +/- 1% and 26 +/- 3% after 24 h of exposure. The ability of mtDNA to amplify was not compromised in rats exposed to 80% O2, even in the presence of 20 ppm of inhaled NO. Surprisingly, exposure to >95% O2 alone for either 24 or 48 h did not compromise the integrity of mtDNA templates compared with air-exposed controls, despite evidence of genomic DNA injury. Interestingly, inhaling NO alone for 48 h increased mtDNA amplification by 12 +/- 2% to 21 +/- 7%. Injury to the lung mtDNA after exposure to >95% O2 plus 20 ppm of NO was transient as rats allowed to recover in room air after exposure displayed increased amplification, with levels exceeding controls by 20 +/- 3% to 29 +/- 4%. Increased amplification was not due to cellular proliferation or increased mitochondrial number. Moreover, the ratio of pulmonary mtDNA to genomic DNA remained the same between treatment groups. The results indicate that hyperoxia fails to induce significant injury to mtDNA, and whereas inhalation of NO with hyperoxia results in mtDNA damage, the lesions are rapidly repaired during recovery.     

Nitric oxide synthase inhibition decreases tolerance to hyperoxia in newborn rats

We evaluated the effects of sustained perinatal inhibition of NO synthase (NOS) on hyperoxia induced lung injury in newborn rats. N(G)-nitro-Larginine-methyl-ester (L-NAME) or untreated water was administered to pregnant rats for the final 7 days of gestation and during lactation; followed by postnatal exposure to hyperoxia (>95% O(2)) or room air. The survival rate of L-NAME treated pups when placed in > 95% O(2) at birth was significantly lower than controls from day 4 (L-NAME, 87%; control pups, 100%, p < 0.05) to 14 (L-NAME, 0%; control pups, 53%, p < 0.05). Foetal pulmonary artery vasoconstriction was induced by L-NAME with a decrease in internal diameter from 0.88 +/- 0.03 mm to 0.64 +/- 0.01 mm in control vs. L-NAME groups (p < 0.05), respectively. We conclude that perinatal NOS inhibition results in pulmonary artery vasoconstriction and a decreased tolerance to hyperoxia induced lung injury in newborn rats.     

Endotoxin-tolerant rats are still protected from oxygen toxicity by low-dose endotoxin treatment

To determine if we could reduce endotoxin's potential for toxicity, we produced "endotoxin-tolerant" rats by administering progressively increasing daily doses of endotoxin (10 ng, 100 ng, 1 microgram, 10 micrograms/kg). This dosage regimen produced a high degree of tolerance to the toxic actions of endotoxin: whereas only 3/17 (18%) of control rats survived a normally lethal dose of endotoxin (25 mg/kg), survival for the endotoxin-tolerant rats was 16/16. When endotoxin-tolerant rats received a standard protective dose of 500 micrograms/kg endotoxin just before transfer to 96-98% O2, 19/20 survived the 72-h exposure period vs. 20-30% survival for controls. Thus whereas the endotoxin-tolerant state blocked the tested lethal and toxic effects of endotoxin, it did not nullify the O2 protective action of endotoxin. In addition, endotoxin's stimulatory effects on the lung antioxidant enzymes in the 96-98% O2-exposed rats was also not blocked by the endotoxin-tolerant state. Thus the therapeutic ratio (TR) of endotoxin as an experimental pharmacological treatment against O2-induced lung damage has been markedly enhanced (TR = ratio of dose producing beneficial effects to dose producing toxic effects).     

Endotoxin extends survival of adult mice in hyperoxia

Research on endotoxin protection from oxygen toxicity is presently limited to the rat model since only rats have been protected by endotoxin. This study reports that endotoxin also extends survival of adult male mice in hyperoxia (greater than 99% oxygen at 1 ATA). Initially, 4-month-old male mice were treated with Boivin-extracted E. coli endotoxin and placed in hyperoxia. Zymosan-primed mice receiving 2 or 10 micrograms endotoxin, and unprimed mice receiving 10-40 micrograms endotoxin, showed moderate protection against hyperoxia; 11/15 Boivin-treated mice survived 120 hours exposure to hyperoxia with time-of-death in hyperoxia = 126.7 +/- 4.4 hours (mean +/- SEM, n = 15). This contrasts with untreated male mice; 0/4 survived 120 hours exposure to hyperoxia with mean survival = 103.5 +/- 3.5 hours. Mice receiving 20 or 60 micrograms Westphal-extracted endotoxin were not protected nor were older female mice receiving 20 micrograms Boivin-extracted endotoxin. This study suggests that age, sex, the extraction method used to obtain endotoxin, and possibly the time of year when endotoxin is administered, are important variables in allowing endotoxin to extend survival of mice in hyperoxia.     

Endotoxin protection of rats from pulmonary oxygen toxicity: possible cytokine involvement

Treatment with endotoxin protects rats against lung injury during hyperoxia (greater than 98% oxygen at 1 atmosphere absolute for 60 h). This study demonstrates that serum from endotoxin-treated donor rats also protects recipients from oxygen toxicity. Rats treated with serum from saline-treated donors were not protected, and protection was not explained by residual endotoxin in protective sera. Unlike endotoxin-protected rats (where lung antioxidant enzyme activity is elevated after hyperoxia), postexposure superoxide dismutase (SOD) and catalase (CAT) activities in the lungs of serum-protected rats were not affected. Levels of tumor necrosis factor (TNF) and interleukin 1 (IL-1) in protective sera were increased. This study demonstrates that increases in lung SOD and CAT activity are not required for endotoxin protection from hyperoxia and suggests that TNF and IL-1 may participate in the mechanism of endotoxin protection.     

Retinoic acid attenuates O2-induced inhibition of lung septation

Exposure of the newborn lung to hyperoxia is associated with impaired alveolar development. In newborn rats exposed to hyperoxia and studied at day 14 of life, retinoic acid (RA) treatment improved survival and increased lung collagen but did not improve alveolar development. To determine whether RA treatment during exposure to hyperoxia results in late improvement in alveolarization, we treated newborn rats with RA and hyperoxia from day 3 to day 14 and then weaned O2 to room air by day 20, and studied the animals on day 42. O2-exposed animals had larger mean lung volumes, larger alveoli, and decreased gas-exchange tissue relative to air-exposed animals, whereas RA-treated O2-exposed animals were not statistically different from air-exposed controls. Relative to control animals, elastin staining at day 14 was decreased in hyperoxia-exposed lung independent of RA treatment, and, at day 42, elastin staining was similar in all treatment groups. At day 14, elastin gene expression was similar in all treatment groups, whereas at day 42 lung previously exposed to hyperoxia showed increased elastin signal independent of RA treatment. These results indicate that RA treatment during hyperoxia exposure promotes septal formation without evidence of effects on elastin gene expression after 4 wk of recovery.     

Hyperoxia-induced emphysematous changes in subacute phase of endotoxin-induced lung injury in rats

We examined the effects of prolonged hyperoxia (75% O(2)) on lung structure and collagen metabolism in the subacute phase of lung injury induced by continuous infusion of endotoxin (LPS) in a rat model. Experimental groups included control, endotoxin alone, endotoxin plus hyperoxia, and hyperoxia alone. Endotoxin-treated rats received a bolus of LPS (10 mg/kg i.v.) followed by 500 microg.kg(-1).day(-1) in continuous infusion for 10 days. The bronchoalveolar lavage (BAL) fluid/plasma albumin concentration ratio, an index of capillary permeability, and neutrophil and macrophage counts in BAL fluid were highest in the endotoxin plus hyperoxia group. On pathological examination, prolonged hyperoxia exacerbated destruction of the alveolar wall and caused most prominent emphysematous changes in the endotoxin plus hyperoxia group. Lung tissue hydroxyproline concentration was significantly decreased in the hyperoxia group and increased in the endotoxin group. The latent forms of MMP-2 and MMP-9 increased in BAL fluid of the endotoxin- and/or hyperoxia-treated groups, whereas the activities of collagenase and gelatinase, and the active form of MMP-2 were all increased in the hyperoxia-treated groups. Added to endotoxin, prolonged hyperoxia degraded collagen, the major structural component of basement membranes, and caused emphysematous changes associated with activation of collagenase and MMP-2. Our observations suggest that, in the subacute phase of endotoxin-induced lung injury, prolonged hyperoxia causes pulmonary emphysematous changes with persistent injury to the alveolar capillary barrier. Collagenase and MMP-2 activated by hyperoxia, together with MMP-9, may play prominent roles in disruption of the alveolar basement membranes and degradation of collagen lining the alveolar walls.     

Hyperoxic inhibition of newborn rat lung development: protection by deferoxamine.

Prolonged exposure to hyperoxia markedly inhibits normal lung development (alveolarization and respiratory surface area expansion) in immature animals. Since (a) hyperoxia results in excess hydroxyl radical (OH.) formation, (b) (OH.) is implicated in O2-induced lipid peroxidation and DNA alterations, and (c) both OH. formation and its interaction with DNA are Fe++ dependent; chelation of Fe++ should act to protect against pulmonary O2 toxicity and hyperoxic inhibition of lung development. We therefore treated litters of newborn rats with the iron chelator Deferoxamine mesylate (DES) (150 mg/kg/day) during a 10-day exposure to greater than 95% O2. Morphometric analysis demonstrated that compared to the mean airspace size in air control rat pups (Lm = 44.5 microns), hyperoxic exposure resulted in a 34% larger mean air space diameter in O2-saline rat lungs (59.5 microns) versus only an 11% enlargement in O2-DES lungs (51.1 microns*). Lung internal surface area (cm2) per 100-g body weight were air control = 4480, O2-saline = 3570 (decreases 20.3%), and O2-DES = 4125* (decreases 7.9%) (*p less than 0.05 versus O2-saline group). DES-treated animals also had significantly decreased lung conjugated diene levels during hyperoxic exposure and increased lung elastin content (reflective of preserved lung alveolar formation) compared to O2-saline rats. These results indicate that DES treatment substantially ameliorated the inhibitory effects of neonatal hyperoxic exposure on normal lung development.     

Mechanisms of interaction between oxygen and granulocytes in hyperoxic lung injury

Hyperoxia and infused granulocytes act synergistically in producing a nonhydrostatic high-permeability lung edema in the isolated perfused rabbit lung within 4 h, which is substantially greater than that seen with hyperoxia alone. We hypothesized that the interaction between hyperoxia and granulocytes was principally due to a direct effect of hyperoxia on the lung itself. Isolated perfused rabbit lungs that were preexposed to 2 h of hyperoxia (95% O2-5% CO2) prior to the infusion of unstimulated granulocytes (under normoxic conditions) developed significant nonhydrostatic lung edema (P = 0.008) within 2 h when compared with lungs that were preexposed to normoxia (15% O2-5% CO2) prior to granulocyte perfusion. The edema in the hyperoxic-preexposed lungs was accompanied by significant increases in bronchoalveolar lavage (BAL) protein, BAL granulocytes, BAL thromboxane and prostacyclin levels, perfusate chemotactic activity, and lung lipid peroxidation. These findings suggest that the synergistic interaction between hyperoxia and granulocytes in producing acute lung injury involves a primary effect of hyperoxia on the lung itself.     

Role of glutathione in lung retention of 99mTc-hexamethylpropyleneamine oxime in two unique rat models of hyperoxic lung injury

Rat exposure to 60% oxygen (O(2)) for 7 days (hyper-60) or to >95% O(2) for 2 days followed by 24 h in room air (hyper-95R) confers susceptibility or tolerance, respectively, of the otherwise lethal effects of subsequent exposure to 100% O(2). The objective of this study was to determine if lung retention of the radiopharmaceutical agent technetium-labeled-hexamethylpropyleneamine oxime (HMPAO) is differentially altered in hyper-60 and hyper-95R rats. Tissue retention of HMPAO is dependent on intracellular content of the antioxidant GSH and mitochondrial function. HMPAO was injected intravenously in anesthetized rats, and planar images were acquired. We investigated the role of GSH in the lung retention of HMPAO by pretreating rats with the GSH-depleting agent diethyl maleate (DEM) prior to imaging. We also measured GSH content and activities of mitochondrial complexes I and IV in lung homogenate. The lung retention of HMPAO increased by ～50% and ～250% in hyper-60 and hyper-95R rats, respectively, compared with retention in rats exposed to room air (normoxic). DEM decreased retention in normoxic (～26%) and hyper-95R (～56%) rats compared with retention in the absence of DEM. GSH content increased by 19% and 40% in hyper-60 and hyper-95R lung homogenate compared with normoxic lung homogenate. Complex I activity decreased by ～50% in hyper-60 and hyper-95R lung homogenate compared with activity in normoxic lung homogenate. However, complex IV activity was increased by 32% in hyper-95R lung homogenate only. Furthermore, we identified correlations between the GSH content in lung homogenate and the DEM-sensitive fraction of HMPAO retention and between the complex IV/complex I activity ratio and the DEM-insensitive fraction of HMPAO retention. These results suggest that an increase in the GSH-dependent component of the lung retention of HMPAO may be a marker of tolerance to sustained exposure to hyperoxia.     

Effects of hyperoxia on DNA synthesis in cultured porcine aortic endothelial cells

The mode of action of hyperoxia on the inhibition of DNA synthesis from thymidine (dThd) was studied in primary cultures of porcine aortic endothelial cells (EC) at confluence. A significant effect of hyperoxia on dThd uptake was detected only after a 48-h exposure to 95% O2. On the other hand, decrease in dThd kinase activity was already observed after a 12-h exposure, and the time course of its reduction followed closely that of the inhibition of dThd incorporation into DNA. The incorporation of dThd triphosphate into DNA in permeabilized EC was unaffected by hyperoxia. Determination of DNA alpha- and beta-polymerase activities showed that hyperoxia reduced the activity of the alpha-polymerase and increased that of the beta-polymerase. We conclude that most of the O2 effects on DNA synthesis from dThd can be attributed to dThd kinase inhibition. The increased activity of DNA beta-polymerase, an enzyme involved in DNA repair, also supports the view that hyperoxia could damage DNA.     

Protection against hyperoxia by serum from endotoxin treated rats: absence of superoxide dismutase induction

Endotoxin greatly reduces lung injury and pleural effusions in adult rats exposed to normobaric hyperoxia (greater than 98% oxygen for 60 hours). This study reports that serum from endotoxin treated donor rats protects serum recipients against hyperoxic lung injury without altering lung superoxide dismutase (SOD) activity. Rats pretreated with endotoxin alone were protected and exhibited an increase in lung SOD activity as previously reported by others. Protection by serum was not due to the transfer of residual endotoxin or SOD. These results show that protection from oxygen toxicity can occur in rats without an increase in lung SOD and suggest that a serum factor may be involved.     

Hypoxia increases glutathione redox cycle and protects rat lungs against oxidants

Preexposure to hypoxia increased survival and lung reduced glutathione-to-oxidized glutathione ratios (GSH/GSSG) and decreased pleural effusions in rats subsequently exposed to continuous hyperoxia. In addition, lungs from hypoxia-preexposed rats developed less acute edematous injury (decreased lung weight gains and lung lavage albumin concentrations) than lungs from normoxia-preexposed rats when isolated and perfused with hydrogen peroxide (H2O2) generated by xanthine oxidase (XO) or glucose oxidase (GO). In contrast, when perfused with elastase or exposed to a hydrostatic left atrial pressure challenge, lungs isolated from hypoxia-preexposed rats developed the same acute edematous injury as lungs from normoxia-preexposed rats. The mechanism by which hypoxia preexposure conferred protection against H2O2 appeared to depend on hexose monophosphate shunt (HMPS)-dependent increases in lung glutathione redox cycle activity. First, before perfusion with GO, lungs from hypoxia-preexposed rats had increased glutathione peroxidase and glucose 6-phosphate dehydrogenase (but not catalase or glutathione reductase) activities compared with lungs from normoxia-preexposed rats. Second, after perfusion with GO, lungs from hypoxia-preexposed rats had increased H2O2 reducing equivalents, as reflected by increased GSH/GSSG and NADPH/NADPH+, compared with lungs from normoxia-preexposed rats. Third, pretreatment of rats with an HMPS inhibitor, (6-aminonicotinamide) or a glutathione reductase inhibitor, [1,3-bis(2-chloroethyl)-1-nitrosourea] prevented hypoxia-conferred protection against H2O2-mediated acute edematous injury in isolated lungs. These findings suggest that increased detoxification of H2O2 by glutathione redox cycle and HMPS-dependent mechanisms contributes to tolerance to hyperoxia and resistance to H2O2 of lungs from hypoxia-preexposed rats.     

Cimetidine reduces hyperoxic lung injury in lambs

We previously reported that pretreatment with endotoxin significantly reduced acute pulmonary O2 toxicity in lambs (J. Appl. Physiol. 65: 1579-1585, 1988). One of endotoxin's many effects is to inhibit cytochrome P-450 mono-oxygenation reactions, which are believed to produce toxic O2 species. Therefore, one possible explanation for endotoxin's beneficial effect is that it inhibited P-450-mediated O2 radical production during hyperoxia. To test this hypothesis, we administered a single dose of cimetidine, a noncompetitive inhibitor of P-450 activity, to nine lambs before continuous exposure to greater than 95% O2. Compared with six control O2-exposed lambs, the cimetidine-treated O2-exposed lambs maintained normal gas exchange for a longer period of time (P less than 0.01), accumulated lung water at a slower rate (P less than 0.01), and had normal microvascular permeability after 72 h of O2 exposure. Postmortem levels of antioxidant enzymes in blood-free lung homogenate were not increased in cimetidine-treated lambs. However, the levels of oxidized glutathione were significantly lower in cimetidine-treated lambs, and the ratio of reduced to oxidized glutathione concentrations (GSH/GSSG ratio) was sevenfold higher than the ratio measured in control O2-exposed lambs (P less than 0.001). In four lambs, pretreatment with ranitidine (a drug chemically related to cimetidine but without P-450 inhibitory activity) had no effect either on the time course of O2 injury or on postmortem antioxidants. Microsomes were isolated from blood-free lung of all study animals and P-450 activity of the form 2 isozyme was measured.(ABSTRACT TRUNCATED AT 250 WORDS)     

Release of cytokines and apoptosis in fetal rat Type II pneumocytes exposed to hyperoxia and nitric oxide: modulatory effects of dexamethasone and pentoxifylline

The response of the fetal rat Type II pneumocyte (FTIIP), the stem cell of the alveolar epithelium, to hyperoxia would be helpful to understand the effects of oxygen-induced injury to the immature lung. In such a scenario, the presence of nitric oxide (NO) may have a protective or detrimental effect. Our goals were to evaluate the release of cytokines and apoptotic cell death in freshly isolated FTIIP (19-day) in the presence of 95% O(2) and/or NO. The effects of dexamethasone and pentoxifylline on the FTIIP cytokine response were also studied. There was no significant difference in the levels of IL-1beta and IL-10 from FTIIP, in room air, hyperoxia and/or NO at 2, 6 and 24 h. However, IL-6 release was significantly higher, when measured over time, after 2, 6 and 24 h of exposure to hyperoxia and NO. Dexamethasone in the presence of hyperoxia and/or NO increased the release of IL-10 at 24 h. There was increased apoptosis in FTIIP exposed to hyperoxia alone and in combination with NO; this was significantly attenuated in the presence of dexamethasone and pentoxifylline. We speculate that the cytoprotective effects of dexamethasone in the immature lung may, in part, be mediated via IL-10.