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Rats exposed to normobaric oxygen received a single i.p. injection of 2.5 mg/kg of poly I: poly C at various times (-120 to +36 h) before and after the beginning of oxygen exposure. Hyperoxic lung damage and modifications in cytochrome P-450 system components were evaluated. Our results confirmed the protective effect of poly I: poly C on rats exposed to oxygen, reducing the lung edema and the mortality. This effect was only observed when poly I: poly C was injected 48 or 36 h before the beginning of oxygen exposure. Although oxygen exposure per se decreased the total level of lung cytochrome P-450, poly I: poly C per se induced a deeper decrease to levels similar in air- or oxygen-exposed rats. Poly I: poly C did not modify the NADPH-cytochrome c reductase level nor the cytochrome P-450 peroxidase activity in air-exposed rats. The oxygen exposure induced a decrease of these two enzymes, either in the absence or in the presence of poly I: poly C, except when poly I: poly C was injected 48 or 36 h before the beginning of oxygen exposure, times at which poly I: poly C restored the enzymatic values measured in rats exposed to air. Because the times of injection of poly I: poly C were those at which the protective effect was observed, it suggested that the protective effect of poly I: poly C against oxygen toxicity was associated with a lack of oxygen-induced decrease of both the lung NADPH-cytochrome c reductase level and the lung cytochrome P-450 peroxidase activity.

Induction by phenobarbital and 3-methylcholanthrene of enzymes metabolizing xenobiotics in rat exposed 55 hrs to hyperoxia, is maintained. The level of microsomal pulmonary and hepatic cytochrome P-450 has even increased. In rat protected against a hyperoxia 6 days, stimulation of UDP-glucuronosyltransferase does not decrease and malondialdehydes level does not change. These results assume the probable role of enzymatic induction in the tolerance to hyperoxia induced in rast by treatment with phenobarbital and 3- methylcholanthrene.

Normobaric O2 exposure decreased spleen cell (SC) response to T cell mitogen Con A. 3H-TdR incorporation of SC from O2 exposed mice (O2SC) compared to those of control mice (Air SC) decreased significantly after 72 and 87 h O2 exposure. The dose response kinetics to Con A were identical in O2SC or Air SC. Increasing SC number did not restore the response to Con A and the depressed hyperoxic effect was not related to suppressor cells in the spleen of O2 exposed mice. Response of O2SC to Con A was restored by the thiol compound 2-mercaptoethanol (2-ME), and the degree of restoration by 2-ME, was inversely proportional to the depressed response. Addition of intact peritoneal cells (PC) induced restoration within the same range as 2-ME. Restoration of the mitogenic response by 2-ME involved antioxidant properties and suggested that macrophages were functionally injured by O2 exposure. In cases where mitogen response was highly depressed, restoration was only partial; in these conditions in vivo O2 injury probably involved both macrophages and splenic T cells. The mechanisms of O2 toxicity have been discussed in terms of free radical generation under hyperoxic conditions.

Exposure of adult rats to oxygen (100%) during 55 hrs decreases their sleeping time induced by pentobarbital and doesn't modify their paralysis time provoked by zoxazolamine. At 48 and 55 hrs, the hepatic cytochrome P-450 decreases significantly. Morphological study showed tissular changes suggestive of hepatic hemodynamic perturbations, which are probably responsible for the functional modifications.

This study was designed to evaluate, in vivo, the effect of a severe non-respiratory acidosis on hemoglobin oxygen transport. Oxygen affinity of hemoglobin, Bohr effect, Hill's number and red cell 2,3-DPG were evaluated during experimental hemorrhagic shock in dogs. Three periods were considered: control, hypotension (mean arterial pressure 60 mm Hg for 2 hr 30 min) and blood replacement. There was no significant change in erythrocyte 2,3-DPG following hemorrhagic hypotension but ATP increased significantly. n, the Hill number (2.6), was not changed by in vivo acidosis (pH 7.1). Respiratory Bohr coefficient (BCO2) corresponding to pHe variations was drastically reduced (control BCO2 = 0.55, acidosis BCO2 = 0.31, blood replacement BCO2 = 0.35). P50(7.4) was not modified significantly by hemorrhagic acidosis. It is unlikely that variations of blood affinity for oxygen play a major role in oxygen delivery during early experimental hemorrhagic shock.

Exposure of adult rats to 1 ATA O2 during 55 hrs. decreased cytochrome P-450 in the homogenate supernatant of livers. Hepatic microsomal epoxide hydrolase and P-nitrophenol UDP-glucuronosyltransferase activities were also decreased. Histological and ultrastructural liver studies showed tissular and cellular modifications suggestive of hepatocyte hypoxia.

Arterial blood gases and acid-base balance were measured in adult rats using a cannula implanted in the aortic arch. These measurements were performed both in awake, unrestrained animals and in animals submitted to various circumstances i.e. (a) different diet: high and low sodium chloride intake, (b) anesthesia by pentobarbital or inactine and, (c) repeated blood sampling with concomitant replacement with the same volume of blood. For each group investigated the [HCO3 -]a vs. PaCO2, [H+] vs. PaCO2, PaCO2 vs. PaO2 relationships were determined. The values obtained (m +/- SD) from awake, unrestrained adult rats were respectively 7.47 +/- 0.02 for arterial pH, 34.5 +/- 3.0 Torr for PaCO2 and 90 +/- 5.5 Torr for PaO2; the calculated [HCO3 -]a concentration was 25.5 +/- 1.5 mmol . 1-1. The present results indicate that plasma bicarbonate concentration, within normal range, highly depends on the prevailing resting level of PaCO2 (n = 202; r = 0.82; P less than 10(-3)). In addition, the PaCO2 versus PaO2 relationship was highly statistically significant (n = 202; r = -0.43; P less than 10(-3). In the other experimental groups of rats, these relationships were virtually the same as above although mean values (+/- SD) for PaCO2, PaO2, pHa and [HCO3 -]a might vary with the group investigated. The mean value for whole pHi, obtained by the DMO method, reached 6.81 for pHa = 7.47 and was not correlated to PaCO2 level in normal conditions. The present data argue for the existence of a respiratory component mediating individual acid-base variations in a normal population of rats. Arterial carbon dioxide partial pressure, by determining bicarbonate ions reabsorption rate, would ensure pH regulation under normal circumstances.

Nine patients who had suffered strokes were examined between 10 and 34 days after onset using positron emission tomography. DMO labeled with carbon 11 was used to evaluate brain acid-base balance, and the oxygen-15 inhalation technique was used to measure regional cerebral blood flow, the oxygen extraction fraction, and cerebral metabolic rate for oxygen. [11C]DMO concentration and oxygen metabolism variables were measured in the infarcted area and in the symmetrical region in the contralateral cerebral hemisphere. [11C]DMO concentration was found to be unchanged or slightly increased in five cases and markedly increased in four cases. The apparent increase in tissue pH can be explained by the presence of a large extracellular fluid space with a pH nearly identical to that of brain plasma, or by an increase in intracellular pH, or by both phenomena. The change in [11C]DMO concentration in the infarcted area relative to that in the normal tissue was independent of the change in blood flow. Cerebral metabolic rate for oxygen was decreased in all cases. The increase in [11C]DMO concentration in the infarcted area was linearly correlated with the decrease in the oxygen extraction fraction in the same region; that is, it was correlated with the occurrence of perfusion in excess of metabolic demand. The overabundant local perfusion could play a role in the decreased H+ content.

We studied the time course of the respiratory events in awake guinea-pigs catheterized with a chronic arterial cannula, exposed to 100% O2 during 48 hr and after air return breathing. 2. The oxygen toxicity has a pulmonary and respiratory expression: clinical, histological and biochemical data show that death is related to the asphyxia generated by acute pulmonary edema. 3. The O2 toxicity respiratory effects show striking differences in rats and guinea-pigs; the differences belong to a specific and particular lymphatic system in the rat. 4. Rat and guinea pig offer two different models of pulmonary edema, (the first is characterized by absence of arterial hypoxemia) and in consequence two different models of lung oxygen toxicity.

Prolonged exposure of C57B16 mice to pure O2 at 1 ATA induced pulmonary edema associated with involution of lymphoid system and depressed immunity. The consequences of these toxic events were evaluated by 1) mortality rate, 2) determination of pulmonary water, 3) thymic and splenic cellularity, and 4) humoral (primary antibodies) and cellular (mitogenic) immune responses. Pretreatment of mice with 125 mg kg-1 of diethyldithiocarbamate (DDC) several days before exposure to O2 resulted in 1) an increase in animal survival (92-100% vs. 59% O2 controls), 2) a reduction in pulmonary edema, 3) partial stabilization of thymus and spleen lymphocyte populations, and 4) restoration of the humoral response (specific antibodies appeared earlier than in O2 control animals) and improvement of the mitogenic proliferative response of the spleen cells after hyperoxia. None of these effects were observed when DDC treatment coincided with the beginning of exposure. Our results indicated that DDC protects mice from both pulmonary and lymphoid hyperoxic injury, but only in a partial manner. It is suggested that the mechanism of this antioxidative property is indirect.

The influence of oxygenation level (oxyhaemoglobin saturation 0 or 100%) on the relationship between plasma pH and erythrocyte pH was studied, in vitro, in normal human blood submitted to changes in carbon dioxide tension. Firstly, the pH of both true and separated erythrolysates were compared: for the former, tonometry was carried out on whole blood, before red cells lysis; for the latter, equilibration was performed on erythrolysate, pH values appeared different: at PCO2 congruent to 21 and 38 Torr, separated erythrolysate was more alkaline than true one, and at PCO2 congruent to 0 it was more acid. Therefore, to estimate pHe-pHi relationship, pHi was evaluated on true erythrolysate. When haemoglobin passed from the reduced to the completely oxygenated state, a significant decrease of both pHe and pHi was observed for a given PCO2 (respectively about 0.05 and 0.08 pH unit), and of pHi for a given pHe (about 0.04 pH unit). In either extra or intraerythrocyte fluid, the oxygen-linked pH difference was negatively correlated to PCO2.

Time dependent response for hyperoxic exposure was determined in vitro on ConA proliferative response of rat splenocytes, peripheral blood mononuclear cells and thymocytes. The proliferative responses were evaluated after different lengths of hyperoxic exposure (12-72 h, FiO2 = 0.95). After 24 h oxygen exposure, the spleen cell viability assessed by dye exclusion was normal but DNA synthesis was markedly suppressed in the above three types of cells. Total or partial protection of the mitogenic response to ConA was obtained by 2-mercaptoethanol, reduced glutathione or L-cysteine addition in culture medium; only selenomethionine had no protective effect. Thymic cells showed a different response-curve: after 6 h exposure to normobaric oxygen DNA synthesis was decreased and was not restored by any of the thiol compounds tested. In this respect, these cells demonstrated different susceptibility to an oxidant injury, i.e. exposure to high oxygen concentration. From a pharmacological point of view O2 exposure and altered immune response could be proposed as a useful model for screening the antioxidant drug activity.

In this study, we tried to establish a relationship between the immunopotentiating effects and the antioxidant activity of the immunostimulating compound, diethyldithiocarbamate (DDC). We studied the effects of DDC treatment on enriched T and B murine spleen lymphocytes in an in vivo-ex vivo model of O2-induced immune depression. Female C57B1/6 mice were injected subcutaneously with a single dose of DDC (125 mg.kg-1). Eight days after DDC injection, we evaluated, in vitro, the concanavalin A response of the T cell fraction and the LPS response of the B cell fraction, under standard (air--5% CO2) and hyperoxic (60% O2--5% CO2) culture conditions. The results show that after a lag period, DDC is able to enhance the mitogenic response of T and B murine lymphocytes under standard culture conditions to restore the ConA response and to partially restore the LPS response under hyperoxic conditions. The results of this study suggest that the immunostimulatory effects of DDC could be related to the antioxidant activity of this compound on the lymphoid cellular metabolism. This activity apparently affects both T and B lymphocytes.

Rat exposure to pure normobaric oxygen induces a specific non alveolar pulmonary edema which leads to massive pleural exudate. This does not induce hypoxemia, and is characterized by both hypovolemia and arterial hypotension with hypothermia. Histological findings shed some light on these special aspects of oxygen toxicity. In the Rat, this toxicity results from hemodynamic changes rather than from pulmonary lesions.

Rat spleen cells were cultivated in 1 ATA pure oxygen. The mitogenic responses with Con A were evaluated at different time of exposure (12 to 72 hrs). There was a stimulation of the cells after 12 hrs of exposure, which diminished at 18 hrs, in spite of the fact that the viability of the cells remained unchanged till 24 hrs of exposure. The kinetics of the mitogenic response of the splenic lymphocytes exposed to oxygen is biphasic as has been observed after irradiation.

In order to study the kinetics and pathways of protein transfer in pleural effusion, rats with pleurisy associated with hyperoxic pulmonary edema were injected either intrapleurally or intravenously with tracers. 125I-Albumin was used to obtain quantitative data. Anti horseradish peroxidase used as a morphological tracer, allowed a precise localization of the pathways used for the transfer. It has been possible to demonstrate that, in this model, the pleural effusion is produced by a plasma exudation accumulated in the lung interstitium, transferred through the visceral pleura and resorbed by the lymphatics of the parietal costal and diaphragmatic pleurae.

Mice exposed to pure oxygen develop a lethal edematous pulmonary disease. This Note demonstrates, in these Mice, a lymphoid involution with blood lymphopenia and severe decrease in thymic weight and cellularity. The thymus was completely destroyed following 96 hrs. exposure. The possible role of these leucocyte alterations in normobare oxygen toxicity should be considered.

The effects of different normobaric oxygen concentrations (40, 60 and 95%) on the survival and the proliferative response to Con A of rat lymphoid cells were studied. Spleen, thymus and peripheral blood mononuclear cells were tested. We found that oxygen concentrations modulated the proliferative response independently of cell survival. The addition of 2-mercaptoethanol (2-ME) partially prevented the toxic effects of hyperoxia but the population of thymocytes which responded to Con A stimulation appeared to be less sensitive to the protective action of 2-ME. The relationship between oxygen concentrations and the lymphoid proliferative response could be used as a model of oxidant immunodepression for evaluating pharmacological effects of antioxidant compounds.

The influence of prior deoxygenation on whole blood-oxygen affinity was determined in samples from persons with sickle cell anemia (SS blood) and compared to blood from normal and anemic subjects (AA blood). The oxygen affinity of SS blood (measured as P50) is significantly decreased when this blood is exposed for 30 min to nitrogen before the determination of the oxygen equilibrium curve. The decrease is directly related to the number of sickle cells that are present in the samples. The present work emphasizes the importance of experimental conditions on the results of the determination of SS blood-oxygen affinity and the difficulties inherent in the evaluation of in vivo oxygen transport in sickle cell disease.

The properties of haemoglobin oxygen transport were compared under three different conditions: red cell in its natural medium, i.e. plasma (whole blood), washed red cell and haemoglobin A, the former suspended, the latter solved in an iso-osmotic tris buffer. The oxygen haemoglobin affinity (expressed as P50) and the respiratory Bohr effect variations were studied with modified media and unchanged pH and 2,3-diphosphoglycerate (2,3-DPG) concentration. Provided they are refered to intra-erythrocytic pH, none of these values were changed when varying environment. These results suggest that the three major ligands (H+ ions, 2,3-DPG and CO2) interaction with haemoglobin is largely predominant upon other factors which would interfere, and can completely account for oxygen transport by haemoglobin.

Inducers of cytochrome P450-linked mono-oxygenases increase the normobaric oxygen tolerance of the adult rat. Pulmonary inducers, as 3-methylcholanthrene and beta-naphthoflavone permit the rat survival and simultaneously a decrease of pulmonary edema. Phenobarbital, an hepatic inducer had lesser effects both on survival rate and on pulmonary and lymphoïd oxygen toxicity.

Blood affinity for oxygen is reduced in patients with homozygous HbS disease. The mechanisms were related to polymerisation and sickling process. In the HbS blood, P50 values were related to the percentage of sickling, the effect of prior deoxygenation on P50 measurement was established. This work underlines the influences of experimental conditions on the determination of sickle cell blood affinity and the difficulties inherent in the evaluation of in vivo oxygen transport in sickle cell disease.

Immunological cell functions were evaluated during 24, 48 and 96 h O2 exposure in C57Bl/6 mice. A normobaric O2 exposure resulted in depression of delayed type hypersensitivity (DTH) to oxazolone and Staphylococcus aureus antigens. This effect was proportional to the duration of O2 exposure. The antibody response of splenic cells was more rapidly (24 h O2 exposure) and markedly depressed using a T-dependent antigen (sheep red blood cell, SRBC) than with a T-independent antigen (trinitrophenylated lipopolysaccharide, TNP-LPS). While mitogen-induced proliferative responses of spleen cells to Con A and PHA were inhibited after 72 h of O2 exposure, proliferative responses to LPS were inhibited after 96 h. A dissociated antigen and mitogen responses was observed after a short time of O2 exposure (48 h): the antigen specific responses were impaired with a more pronounced effect on T lymphocytes, whereas the DNA synthesis in response to mitogen remained normal.

Vascular inflammatory response to hyperoxia (FIO2 greater than 0.98) was studied in awake jugular and carotid catheterized rats. Simultaneous i.v. injection of 125I albumin (125I A), 99mTc polymorphonuclear cells (99mTc PMN) and 51Cr red blood cells (51Cr RBC) allowed to study both the macromolecule exchange through vascular endothelium and the leukocyte uptake by several organs (liver, lungs, spleen) with respect to radiolabelled red blood cells, as an intravascular reference. Rats were exposed to O2 for 24, 38 and 45 h. They were anesthetized and killed by exanguination 15 to 120 min following the tracer injection. After 45 h exposure, the plasmatic 125I A half-life decreased significantly (158 +/- 42 min for the control; 106 +/- 34 min for the exposed animals). The ratio 125I A/51Cr RBC varied significantly in the lung. The iodinated albumin exchange through lung vascular endothelium was altered at the 24th h, with a significant difference reached by the 45th h. At the same time, the pulmonary decreasing curve of 99mTc/51Cr RBC ratio versus time was not not modified. In our experimental conditions, there was no detectable variation in the lung uptake and vascular transit of PMN cells. The discussion of the results must be related with the technics used in the present work when the albumin exchange increased.

Rats were pretreated with various inducers of cytochrome P-450 before being exposed to pure normobaric oxygen (O2) in order to determine whether the inducers interfere with toxicity. The pulmonary and liver inducers beta-naphthoflavone (beta NF) and 3-methylcholanthrene (3MC) increased the survival rate and decreased the amount of pleural and lung fluid accumulation in adult rats exposed to oxygen. Phenobarbital (PB), which is essentially active in the hepatic microsomal cytochrome P-450, was less effective in counteracting oxygen toxicity. After 7 days of exposure to oxygen, none of the untreated rats survived, whereas 40, 73, and 90% survival was observed in rats treated with PB, 3MC, and beta NF, respectively. After 60 h of O2 exposure, significantly less pleural and lung fluid accumulation was observed in beta NF- and 3MC-treated rats than in untreated or PB-treated rats (p less than 0.001). Both beta NF and 3MC prevented the increase of lung peroxidation (assessed by measuring of malondialdehyde) and that of hydrogen peroxide production by lung microsomes induced by O2 exposure. These protective effects are associated with a large increase in the components of the pulmonary cytochrome P-450 system and its peroxidase activity and with an increased response to hyperoxia by lung antioxidant enzyme activities. In contrast, in control rats, the activities of the antioxidant enzymes were not increased, and both the quantity and the peroxidase activity of cytochrome P-450 were significantly decreased by O2 exposure. We conclude that in the rat, pretreatment by inducers of pulmonary cytochrome P-450 results in marked protection against O2 toxicity and an increase of antioxidant enzyme response to hyperoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

The vascular sequestration of polymorphonuclear leukocytes (PMN) may be responsible for endothelial injury leading to lung oedema, which occurs when rats are exposed to pure normobaric oxygen. Indeed, marginated PMN in close contact with the endothelium are able to damage the latter when activated. In the present work, marginated leukocytes were recovered by lavage through the pulmonary artery in isolated rat lung and the leukocyte differential count in blood and in the lung perfusion liquid (perfusate) was studied. Following 55 h of hyperoxia, a rise in the PMN count and lymphocytopenia were observed in the blood and in the perfusate. Moreover, the relatively greater increase in the PMN concentration in the perfusate than in the blood suggested a strengthening of their margination along the endothelium. A clear protective effect was noted during hyperoxia provided previous injection of endotoxin (1.5 mg X kg-1 intraperitoneally) had been performed. Indeed, after 65 h of hyperoxia, none of these rats (Endo/O2) died and there was no pleural effusion. The lymphocyte count was maintained within the normal limit and the number of PMN in the lung perfusion fluid and in blood was reduced. Results of this study suggest an essential role of the marginated PMN in lung oxygen toxicity.