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Lipid peroxidation in lung of rats exposed to hyperoxic, hypoxic and ischemic effects
Exp. Pathol. 29 , 221-226 (1986) VEB Gustav Fischer Verlag Jena 1) Departm ent of Experiment al Surgery and 2) Departm ent of Biology, Univ ersity Medical School, Pe es, Hungary; 3) Biological Isotope IAl,boratory, "J6zsef AttiJa."-University, Szeged, Hu ngary
Lipid peroxidation in lung of rats exposed to hyperoxic, hypoxic and ischemic effects
With 3 figures (Received Septcm ber 13, 1984)
Address for correspondence: Professor B. T OROK, Department of Experimental Surgery, University Medical School , H - 7643 Pres, Hungary Key words: lipid peroxidation, endogenous; lung, influenc e of oxygen
Summary Rat experiments were undertaken to describe the range of the endogenous lipid peroxidation (measured by formation of malondialdehyde [lVIDA] in lung ti ssue) and to analyze the effects of hyperoxic, hypoxic and ischemic influences. The acute hyperoxia cau sed a moderate increase in lipid peroxidation. The MDA formation in lungs of rats was perceptibly higher in low oxygen environment, while the highest values wer e found in isehelni c lungs. The cytotoxic metabolites cause unfavourable influ ences on the lung stru cture (perivascular, interstitial and alveolar edema, destroyed epithelial lining with disintegration of lamellar membranes of the type II-pneumocytes). Th e findings suggest that potential danger of the oxygen free radicals is an increased lipid peroxidation of lung tissue causing alveolocapillary destruction ami extensive exudation with pathologic dwindling of lung function .
Introdu,ction Lipid peroxidation is a chemical, partly physiological proeess in th e cell membran es controlled by endogenous dismutases a,nd other scavenger compounds (4, 8, ] 0, 16). The pathological peroxidation of membrane lipids and phospholipids is strongly connected with the oxidative stress situations (1,5, 7, 23, 24). In normal conditions the oxygen consumption serves as energy so nree, among others for the maintenance of membrane integrity with preservation of polyunsaturated fat ty acids in the membrane bilayer. lTnder pathological conditions, probably because of the incomplete r eduction of, oxygen, the "quantity" of deleterious agents (superoxide anion radical - .02- , hydrogen peroxide - H 2 0 2 and hydroxyl r adi cal - .OH-) could in rrease. The oxyge n radical s ar e highl y reacti ve causing endothelial cell damage, peroxidati on of lipids and lysoso mal membranes with acc umulation of malondialdehyde (MDA). Thi s breakdown product is admittedly the most r epresentative fo r lipid peroxidation (8, 9, 19, 20). Because of simultaneous failure of scavenger mechani sms, the equilibrium of preserving and damaging factors becomes impaired and serious loss of membrane function foll ows due to the injury of membrane stru cture. The lung seem s to be the especially endangered organ owing to its intensive relation with oxygen metabolism, i.e. it is potenti all y exposed to th e stress of oxygen radical s (5, 12, 17).
221
Since the atypical oxygen aggression can evoke serious changes of the lungs, acute experiments were undertaken (i) to describe the normal dimension of the lipid peroxidation in rat lungs and (ii) to analyze the effects of hyperoxi c, hypoxic and ischemic influences.
Materials rmd 111 ethods The experiments were carried out on Wistar rats weighing 180--200 g. Group 1: Control animals (24 cases) . These were decapitated and the lungs were rapidly excised for estimation (see later). Gr oup 2: Hyperoxic animals (42 cases) . The rats were placed in a 100% oxygen atmosphere, while the expired CO 2 was continuously adsorbed with soda lime granular with indieator GR (Merck). After 1, 2, 3 and 24 h pure oxygen breathing the animals were killed by decapitation and the lung was cut and prepared as before. p02 in the arterial blood was measured with Corning pH/blood gas analyzer. Group 3: Hypoxic animals (42 cases). In isolated glass chamber the animals were ventilated with a gas mixtme N2 0 + O2 in a ration 12: 1 (~8 % ox ygen content). The gas p02 was precisely measured in the chamber with a Clark oxygen electrode. During 1, 2 and 3 h the animals lived in this very hypoxic environment, then they were decapitated and treated as before. Grou p 4: Ischemic lungs (12 cases). The rats were slightly anaesthetized with Ketanest®(100 mg( kg i. p.). Through a enclotraeheally ins erted polyethylene tub e they were ventilated with ambient air. Following a left lateral thoracotomy the blood vessels of th e hylus were ligated and the thorax was temporarily closed. After 3 and 24 h survival the ischemic lung was excised for laboratory measuring. D etermination of lipid pero xi dation by measuring of malondialdehy de (NIDA) formation Lipid peroxidation was measured by the following modified method of FONG et a.l. (9, 23). 1 g of the minced lung tissue was homogenized in a 0.14 M NaCl-solution at + 4°C. After filtration, 0.5 ml aliquot of the homogenate was diluted to 5 ml with a buffer solution containing 400 mM NaCI and 100 mM Tris-HCI at pH 7.4. After incubation at 37°C for 90 min it was mingled with 5 ml 20 % trichloroacetic acid containing 0.5 % 2-thiobarbituric acid. This mixture was placed in boiling water for 30 min. After cooling, the precipitated proteins were centrifuged at 4,000 rpm. The light-absorption of the supernatant was measured at 532 nrn. For measuring a spectrometer apparatus was used (Spectromom 194 + Diginom; MOM - Hungary). The absorbance at 532 nm was expressed as percentual values of the control and/or nanomoles of malondialdehyde. The MDA standard was prepared from 1,1,3,3-tetraethoxypropane bis (diaethyl acetal; Merck).
Results A. Genera l observation s In hyperoxic environment an interesting acute behaviour could be observed on the animals. In the first minutes th e rats became very restless , ran to and for and made compulsory movements of washing. After 15 min the rats lied already in group s and were restful. Their spontaneous ventilation was weak and rare (compensatory mechanism). To external irritation they roused up then slumbered quickly again. All animals had a very high rose-red colour. The hypoxia together with N~O obviously caused a superficial sleeping. Soon the animals had a progressive dyspnoea which manifested itself both in increase in number and depth of tidal volume subsequently with serious cyanosis. In consequence of the applied grave hypoxia one part of the rats perished within 3 h. B. Macroscopic and micro sc opic observation s After decapitation the organs of all hyperoxic animals showed a highly rose-red colour. The lungs were loosely edematous and extensive hemorrhagic spots were seen on the pleural and cut surface. The lungs of the hypoxic animals differed in colour only because of the cyanosis, the character of pathological alterations was the same.
222
Exp. Pathol. 29 (1986) 4
Fig. 1. Electron micrograph of rat lung after 24 h pure oxygen exposure. In the capillaries closely packed erythrocytes (ERY) are polygonal in shape. x 24,000.
Ultrastructurally the lungs of hyperoxic and hypoxic animals showed acute pathologi·cal changes such as perivascul ar, interstitial and alveolar edema and hemorrhages, swelling of the alveolar epithelial eells. Sporadically intraarterial sludging of erythrocytes (fig. 1) and thickening of the alveolar capillary membrane can be seen. Capillary endothelial cells and alveolar epithelial cells (typ e I-pneumocytes) are easily vulnerable. The damage alters th e cell's permeability and in some places the epithelial lining becomes destroyed. Also th e type II-pneumocytes show a pathologic picture, their lamella.r bodies increase in siz e with focal cystic areas and homogenization in which only the remnants of the lamellar membranes can be seen (fig'. 2). The main function of these type II-pneumocytes is the secretion of elements of the surface-active lining film of alveoli: :surfactant phospholipids. In case on injury the synthesis of specific phospholipids fail s and the susceptibility of the epithelial lining is easy to understand . C. Gas and blood oxygen tension Table 1. p02 values of the inspired gas and of the arterial blood dnring experiment Groups I-Iyperoxia Hypoxia
Ranges of pO? in the breathing gas kPa (mm Hg)
in th e arterial blood kPa (mm Hg)
100 (750) 2.5-3.0 (18- 23)
12- 18 (90-135)*) 2.4- 2.5 (18- 19)*)
*) Lower values arise from animals after longer exposure of breathing.
D. MDA-formation On basis of laboratory determinations the value of the endogenous lipid peroxidation of control lungs was 23.66 ± 2.65 nmol/g wet tissue of maIondialdehyde. Fig. 3 shows the Exp. Pathol. 29 (1986) 4
223
Fig. 2. Electron micrograph of similar rat lung. Typc II-pncumocytes (P) with severely damaged lamellar bodies. Free erythrocytes and cell debris in the alveolar lumen (ALV). X 30,000.
250
200
~
..... ~e
150
§
~
•~
100
~5C o 0
o
J
2 9
12
9 15
hours
6
Fig. 3. Perecntual ranges of MDA formation in lungs of rats after hyperoxic, hypoxic and ischemic stress. I I = control (C) = 23.66 ± 2.65 nmoljg wet tissue; n~gj = hypcroxic; 11111111 = hypoxic; I~I = ischemic group. n = number of eases. Comparisons were made between mean values to deteet significant differences (*) in relation to the control. For analysis of the data the unpaired Student's t-test was used.
224
Exp. Pathol. 29 (1986) 4
relative changes of NIDA valnes and ranges of experimental groups, further the Humber of eases and the temporal eonrse of lipid peroxidation.
There is a large body of data from experiments in which dogs were exposed to various pressures of oxygen. The commrmly-observed symptom was an apparent susceptibility. Rats were credited with the ability to withstand pure oxygen for longer period but morJ)hologic changes in the lung occurred as early as functional changes because of alveolocapillary destruction and extensive exudative reaction (3, 14, ] 5). In our experiments, during the applied oxygen intoxication severe morphologic changes of the lung were observed after already 1 to 24 h oxyg'en exposure such as extensive exudative 9demas and hermorrhages. They are characterized by interstitial edema, endothelial cell damage, fibrinous exudation and limited alveolar lining destruction. Edema inereases the thickening of the air-blood barrier. It is evident that pathologic protein and fibrin relcat'e and cell remains could later promote the formation of hyaline membrane, but these latter could not be observed in our acute experiments (2, 11, 13, 18, 21, 22). It i~ generally believed that the potential mechanism of the oxygen poisoning is the lipid peroxidation following surfactant denaturation caused by oxygen free radicals. Although the role of endogenous scavenger mechanisms was not evaluated in present studies, it seems reasonable to assume an increased protection of antioxidant compounds during aeute phases of hyperoxic influences. Therefore, it is plausible that the general activation of lung lipid peroxidation will soon, at least partly. be balanced by the natural antioxidant activities of various systems (presumably SOD, catalase and GSH system) in living animals (4, 7, 12, ] 6, 19). This is reflected in the seareely increased and in cases returning MDA values. Surprisingly, it is very interesting that acute hypoxia indicates a more expressive insult for lipid peroxidation than hyperoxia. The lVIDA formation in lungs of rats was perceptibly higher in low oxygen environment, the highest values were found in ischemic lung tissue. Hypoxia may be not only a stimulus for lipid peroxidation but also for induction of similar morphological changes which were observed in hyperoxic animals. It is probable that because of extreme low conecntration of available oxygen a very severe dyspnoea follows with formation of edemas and hemorrhages of exudative orig'in. Since in hypoxic states the scavenger action seems to fail totally or to be blocked, It is understandable that higher values of lipid pcroxidation are found in hypoxic rat lungs. The highest values gained from ischemic lung' or early perished animal, ('onfirm this assumption even more. It should be mentioned that short narcosis and surgery apparently had no effects on the general metabolism as well as on the regulation of respiration because the contralateral intact lung tissue showed no deviation from the normal mean in the MDA content. Our findings and suggestions may be of eonsiderable practical importance for oxygen therapy. All reasonable precautions (normal oxygenation- and antioxidant-therapy) should be taken to preserve the normal regulating effeet 011 the oxidative metabolism l:n vivo.
Literature 1. BILISlILIR, R. E., and R. E. ATLEY, Decreased pulmonary oxygen toxicity by pretreatment with hypoxia. AIeh. Environ. Hlth. 24, 77 (1972). 2. BIU:SSACK, l\1. A, D. D. ?lIC"YI!LLAN and R. D. BLA">D, Pulmonary oxygen toxicity: inereased mierovaseular permeability to protein in unanesthetized lambs. Lymphology 12, 133 (1979). ~L C,\LD\VELL, P. R. B., S. T. GIAThTMONA and ,V. L. LEE, :F=ffect of oxygen breathjng at onr atmosphere on the surface activity of lung extracts in dogs. Ann. N.Y. Acad. Sci. 121, 823 (1965). 4. CHOW, C. K, and A. 1.. T,UPEL, An enzymatic protective meehanism against lipid peroxidatiOll damage to lungs of ozone exposed rats. Lipids 7, 518 (1972). fl. CIlYAPIL, M., and Y. M. PE">G, Oxygen and lung fibrosis. Arch. Environ. 1Ilth. 30, 528 (1975). G. CUHle .T. M., and A. G. LAMBERTSE">, Pulmonary oxygen toxicity: a review. Pharmacol. Rev. 2:1, 37 (1971). Exp. PathoI. 29 (1986) 4
225
7. CRAPO, J. D., and D. F. TIERNEY, Superoxide dismutase and pulmonary oxygen toxicity. Am. J. Physiol. 226, 1401 (1974). 8. FRIDOVICH, 1., Oxygen is toxic. Bio. Scienee 27, 462 (1977). 9. FONG, K. L., P. B. MCCAY and J. L. POYER, Evidence that pm·oxidation of lysosomal membranes is initiated by hydroxyl free radicals produced during flavin enzyme activity. J. BioI. Chem. 248, 7792 (1973). 10. GOLDSTEIN, B. D., C. Lom and :II. T. COLLINSO"i, Ozone and lipid peroxidation. Arch. Environ. Hlth. 18, 631 (1969). 11. HAUGAARD, N., Cellular mechanisms of oxygen toxicity. Physiol. Rev. 48, 311 (1968). 12. KIMBALL, R. E., K. REDDY, T. H. PEIRCE, L. W. SCHWARTZ, M. G. MUSTAFA and C. E. CROSS, Oxygen toxicity: augmentation of antioxidant defense meehanisms in rat lung. Am. J. Physiol. 228, 1425 (1976). 13. KISTLER, G. S., P. R. B. CALDWELL and E. R. WEIBEL, Development of fine structural damage to alveolar and capillary lining cells in oxygen-poisoned rat lungs. J. Cell. BioI. 32, 605 (1967). 14. MORGAN, A. P., The pulmonary toxicity of oxygen. Anaesthesiology 29, 570 (1968). 15. MORGAN, T. E., T. M. FINLEY, G. L. HUBER and H. FIALKOW, Alterations in pulmonary surface active lipid during exposure to increased oxygen tension. J. Clin. Invest. 44, 1737 (1965). 16. LITTLE, C., and P. J. O'BREIN, An intracellular GSI-l peroxidase with a lipid peroxide substrate. Biochem. Biophys. Res. Comm. 31, 145 (1968). 17. ROSENBAUM, R. M., M. WITTNER and M. LENGER, Mitochondrial and other ultrastructural changes in great alveolar cells of oxygen-adapted and poisoned rats. Lab. Invest. 20, 516 (1969). 18. SACHS, '1'., C. F. MOLDOWN, P. R. CRODDOCK and T. K. BOWERS, Oxygen radicals mediate endothelial cell damage by complement stimulated granulocytes. J. Clin. Invest. 61, 1161 (1978). 19. SLATER, T. F., Mechanisms of protection against the damage produced in biological systems by oxygen-derived radicals. In: Oxygen Free Radicals and Tissue Damage. Ciba Foundation Symposium 65. Excerpta Medica, Amsterdam-Oxford-New York, 1979, p. 143. 20. TOHoK, B., E. ROTH, A. TIGYI, T. ZSOLDOS, 13. MATKOVICS and L. SZAB6, Membrane perturbations in myocardium: oxygen radicals mediate inj llries in experiments. Acta Chir. I-lung. 25, 185 (1984). 21. VALIlVIAKI, M., J. KIVISAARI and J. NINIKOSKI, Permeability of alveolar-capillary membrane in oxygen poisoning. AeT. Med. 45, 370 (1974). 22. - and J. NINIKOSKI, Development and reversibility of pulmonary oxygen poisoning in the rat. AeT. Med. 44, 533 (1973). 23. ZSOLDOS, '1'., A. TIGYI, T. MONTSKO and A. PUPPI, Lipid peroxidation in the membrane damaging effect of silica-eontaining dust on rat lllngs. Exp. Pathol. 23, 73 (1983). 24. WOLFE, W. G., and W. VRIES, Oxygen toxicity. Ann. Rev. Meel. 26, 203 (1975).
226
Exp. Pathol. 29 (1986) 4
Lipid peroxidation in lung of rats exposed to hyperoxic, hypoxic and ischemic effects
With 3 figures (Received Septcm ber 13, 1984)
Address for correspondence: Professor B. T OROK, Department of Experimental Surgery, University Medical School , H - 7643 Pres, Hungary Key words: lipid peroxidation, endogenous; lung, influenc e of oxygen
Summary Rat experiments were undertaken to describe the range of the endogenous lipid peroxidation (measured by formation of malondialdehyde [lVIDA] in lung ti ssue) and to analyze the effects of hyperoxic, hypoxic and ischemic influences. The acute hyperoxia cau sed a moderate increase in lipid peroxidation. The MDA formation in lungs of rats was perceptibly higher in low oxygen environment, while the highest values wer e found in isehelni c lungs. The cytotoxic metabolites cause unfavourable influ ences on the lung stru cture (perivascular, interstitial and alveolar edema, destroyed epithelial lining with disintegration of lamellar membranes of the type II-pneumocytes). Th e findings suggest that potential danger of the oxygen free radicals is an increased lipid peroxidation of lung tissue causing alveolocapillary destruction ami extensive exudation with pathologic dwindling of lung function .
Introdu,ction Lipid peroxidation is a chemical, partly physiological proeess in th e cell membran es controlled by endogenous dismutases a,nd other scavenger compounds (4, 8, ] 0, 16). The pathological peroxidation of membrane lipids and phospholipids is strongly connected with the oxidative stress situations (1,5, 7, 23, 24). In normal conditions the oxygen consumption serves as energy so nree, among others for the maintenance of membrane integrity with preservation of polyunsaturated fat ty acids in the membrane bilayer. lTnder pathological conditions, probably because of the incomplete r eduction of, oxygen, the "quantity" of deleterious agents (superoxide anion radical - .02- , hydrogen peroxide - H 2 0 2 and hydroxyl r adi cal - .OH-) could in rrease. The oxyge n radical s ar e highl y reacti ve causing endothelial cell damage, peroxidati on of lipids and lysoso mal membranes with acc umulation of malondialdehyde (MDA). Thi s breakdown product is admittedly the most r epresentative fo r lipid peroxidation (8, 9, 19, 20). Because of simultaneous failure of scavenger mechani sms, the equilibrium of preserving and damaging factors becomes impaired and serious loss of membrane function foll ows due to the injury of membrane stru cture. The lung seem s to be the especially endangered organ owing to its intensive relation with oxygen metabolism, i.e. it is potenti all y exposed to th e stress of oxygen radical s (5, 12, 17).
221
Since the atypical oxygen aggression can evoke serious changes of the lungs, acute experiments were undertaken (i) to describe the normal dimension of the lipid peroxidation in rat lungs and (ii) to analyze the effects of hyperoxi c, hypoxic and ischemic influences.
Materials rmd 111 ethods The experiments were carried out on Wistar rats weighing 180--200 g. Group 1: Control animals (24 cases) . These were decapitated and the lungs were rapidly excised for estimation (see later). Gr oup 2: Hyperoxic animals (42 cases) . The rats were placed in a 100% oxygen atmosphere, while the expired CO 2 was continuously adsorbed with soda lime granular with indieator GR (Merck). After 1, 2, 3 and 24 h pure oxygen breathing the animals were killed by decapitation and the lung was cut and prepared as before. p02 in the arterial blood was measured with Corning pH/blood gas analyzer. Group 3: Hypoxic animals (42 cases). In isolated glass chamber the animals were ventilated with a gas mixtme N2 0 + O2 in a ration 12: 1 (~8 % ox ygen content). The gas p02 was precisely measured in the chamber with a Clark oxygen electrode. During 1, 2 and 3 h the animals lived in this very hypoxic environment, then they were decapitated and treated as before. Grou p 4: Ischemic lungs (12 cases). The rats were slightly anaesthetized with Ketanest®(100 mg( kg i. p.). Through a enclotraeheally ins erted polyethylene tub e they were ventilated with ambient air. Following a left lateral thoracotomy the blood vessels of th e hylus were ligated and the thorax was temporarily closed. After 3 and 24 h survival the ischemic lung was excised for laboratory measuring. D etermination of lipid pero xi dation by measuring of malondialdehy de (NIDA) formation Lipid peroxidation was measured by the following modified method of FONG et a.l. (9, 23). 1 g of the minced lung tissue was homogenized in a 0.14 M NaCl-solution at + 4°C. After filtration, 0.5 ml aliquot of the homogenate was diluted to 5 ml with a buffer solution containing 400 mM NaCI and 100 mM Tris-HCI at pH 7.4. After incubation at 37°C for 90 min it was mingled with 5 ml 20 % trichloroacetic acid containing 0.5 % 2-thiobarbituric acid. This mixture was placed in boiling water for 30 min. After cooling, the precipitated proteins were centrifuged at 4,000 rpm. The light-absorption of the supernatant was measured at 532 nrn. For measuring a spectrometer apparatus was used (Spectromom 194 + Diginom; MOM - Hungary). The absorbance at 532 nm was expressed as percentual values of the control and/or nanomoles of malondialdehyde. The MDA standard was prepared from 1,1,3,3-tetraethoxypropane bis (diaethyl acetal; Merck).
Results A. Genera l observation s In hyperoxic environment an interesting acute behaviour could be observed on the animals. In the first minutes th e rats became very restless , ran to and for and made compulsory movements of washing. After 15 min the rats lied already in group s and were restful. Their spontaneous ventilation was weak and rare (compensatory mechanism). To external irritation they roused up then slumbered quickly again. All animals had a very high rose-red colour. The hypoxia together with N~O obviously caused a superficial sleeping. Soon the animals had a progressive dyspnoea which manifested itself both in increase in number and depth of tidal volume subsequently with serious cyanosis. In consequence of the applied grave hypoxia one part of the rats perished within 3 h. B. Macroscopic and micro sc opic observation s After decapitation the organs of all hyperoxic animals showed a highly rose-red colour. The lungs were loosely edematous and extensive hemorrhagic spots were seen on the pleural and cut surface. The lungs of the hypoxic animals differed in colour only because of the cyanosis, the character of pathological alterations was the same.
222
Exp. Pathol. 29 (1986) 4
Fig. 1. Electron micrograph of rat lung after 24 h pure oxygen exposure. In the capillaries closely packed erythrocytes (ERY) are polygonal in shape. x 24,000.
Ultrastructurally the lungs of hyperoxic and hypoxic animals showed acute pathologi·cal changes such as perivascul ar, interstitial and alveolar edema and hemorrhages, swelling of the alveolar epithelial eells. Sporadically intraarterial sludging of erythrocytes (fig. 1) and thickening of the alveolar capillary membrane can be seen. Capillary endothelial cells and alveolar epithelial cells (typ e I-pneumocytes) are easily vulnerable. The damage alters th e cell's permeability and in some places the epithelial lining becomes destroyed. Also th e type II-pneumocytes show a pathologic picture, their lamella.r bodies increase in siz e with focal cystic areas and homogenization in which only the remnants of the lamellar membranes can be seen (fig'. 2). The main function of these type II-pneumocytes is the secretion of elements of the surface-active lining film of alveoli: :surfactant phospholipids. In case on injury the synthesis of specific phospholipids fail s and the susceptibility of the epithelial lining is easy to understand . C. Gas and blood oxygen tension Table 1. p02 values of the inspired gas and of the arterial blood dnring experiment Groups I-Iyperoxia Hypoxia
Ranges of pO? in the breathing gas kPa (mm Hg)
in th e arterial blood kPa (mm Hg)
100 (750) 2.5-3.0 (18- 23)
12- 18 (90-135)*) 2.4- 2.5 (18- 19)*)
*) Lower values arise from animals after longer exposure of breathing.
D. MDA-formation On basis of laboratory determinations the value of the endogenous lipid peroxidation of control lungs was 23.66 ± 2.65 nmol/g wet tissue of maIondialdehyde. Fig. 3 shows the Exp. Pathol. 29 (1986) 4
223
Fig. 2. Electron micrograph of similar rat lung. Typc II-pncumocytes (P) with severely damaged lamellar bodies. Free erythrocytes and cell debris in the alveolar lumen (ALV). X 30,000.
250
200
~
..... ~e
150
§
~
•~
100
~5C o 0
o
J
2 9
12
9 15
hours
6
Fig. 3. Perecntual ranges of MDA formation in lungs of rats after hyperoxic, hypoxic and ischemic stress. I I = control (C) = 23.66 ± 2.65 nmoljg wet tissue; n~gj = hypcroxic; 11111111 = hypoxic; I~I = ischemic group. n = number of eases. Comparisons were made between mean values to deteet significant differences (*) in relation to the control. For analysis of the data the unpaired Student's t-test was used.
224
Exp. Pathol. 29 (1986) 4
relative changes of NIDA valnes and ranges of experimental groups, further the Humber of eases and the temporal eonrse of lipid peroxidation.
There is a large body of data from experiments in which dogs were exposed to various pressures of oxygen. The commrmly-observed symptom was an apparent susceptibility. Rats were credited with the ability to withstand pure oxygen for longer period but morJ)hologic changes in the lung occurred as early as functional changes because of alveolocapillary destruction and extensive exudative reaction (3, 14, ] 5). In our experiments, during the applied oxygen intoxication severe morphologic changes of the lung were observed after already 1 to 24 h oxyg'en exposure such as extensive exudative 9demas and hermorrhages. They are characterized by interstitial edema, endothelial cell damage, fibrinous exudation and limited alveolar lining destruction. Edema inereases the thickening of the air-blood barrier. It is evident that pathologic protein and fibrin relcat'e and cell remains could later promote the formation of hyaline membrane, but these latter could not be observed in our acute experiments (2, 11, 13, 18, 21, 22). It i~ generally believed that the potential mechanism of the oxygen poisoning is the lipid peroxidation following surfactant denaturation caused by oxygen free radicals. Although the role of endogenous scavenger mechanisms was not evaluated in present studies, it seems reasonable to assume an increased protection of antioxidant compounds during aeute phases of hyperoxic influences. Therefore, it is plausible that the general activation of lung lipid peroxidation will soon, at least partly. be balanced by the natural antioxidant activities of various systems (presumably SOD, catalase and GSH system) in living animals (4, 7, 12, ] 6, 19). This is reflected in the seareely increased and in cases returning MDA values. Surprisingly, it is very interesting that acute hypoxia indicates a more expressive insult for lipid peroxidation than hyperoxia. The lVIDA formation in lungs of rats was perceptibly higher in low oxygen environment, the highest values were found in ischemic lung tissue. Hypoxia may be not only a stimulus for lipid peroxidation but also for induction of similar morphological changes which were observed in hyperoxic animals. It is probable that because of extreme low conecntration of available oxygen a very severe dyspnoea follows with formation of edemas and hemorrhages of exudative orig'in. Since in hypoxic states the scavenger action seems to fail totally or to be blocked, It is understandable that higher values of lipid pcroxidation are found in hypoxic rat lungs. The highest values gained from ischemic lung' or early perished animal, ('onfirm this assumption even more. It should be mentioned that short narcosis and surgery apparently had no effects on the general metabolism as well as on the regulation of respiration because the contralateral intact lung tissue showed no deviation from the normal mean in the MDA content. Our findings and suggestions may be of eonsiderable practical importance for oxygen therapy. All reasonable precautions (normal oxygenation- and antioxidant-therapy) should be taken to preserve the normal regulating effeet 011 the oxidative metabolism l:n vivo.
Literature 1. BILISlILIR, R. E., and R. E. ATLEY, Decreased pulmonary oxygen toxicity by pretreatment with hypoxia. AIeh. Environ. Hlth. 24, 77 (1972). 2. BIU:SSACK, l\1. A, D. D. ?lIC"YI!LLAN and R. D. BLA">D, Pulmonary oxygen toxicity: inereased mierovaseular permeability to protein in unanesthetized lambs. Lymphology 12, 133 (1979). ~L C,\LD\VELL, P. R. B., S. T. GIAThTMONA and ,V. L. LEE, :F=ffect of oxygen breathjng at onr atmosphere on the surface activity of lung extracts in dogs. Ann. N.Y. Acad. Sci. 121, 823 (1965). 4. CHOW, C. K, and A. 1.. T,UPEL, An enzymatic protective meehanism against lipid peroxidatiOll damage to lungs of ozone exposed rats. Lipids 7, 518 (1972). fl. CIlYAPIL, M., and Y. M. PE">G, Oxygen and lung fibrosis. Arch. Environ. 1Ilth. 30, 528 (1975). G. CUHle .T. M., and A. G. LAMBERTSE">, Pulmonary oxygen toxicity: a review. Pharmacol. Rev. 2:1, 37 (1971). Exp. PathoI. 29 (1986) 4
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