Failure of premature rabbits to increase antioxidant enzymes during hyperoxic exposure: increased susceptibility to pulmonary oxygen toxicity compared with term rabbits

Although the prematurely born are known to have decreased baseline levels of protective antioxidant enzymes (Frank L, Sosenko IRS: J Pediatr 110:9 and 106, 1987), the ability to augment the baseline values during high O2 exposure is the key factor determining O2 tolerance versus O2 susceptibility. We have compared the pulmonary antioxidant enzyme responses of prematurely delivered rabbits (gestational d 29 of 32) and full-term rabbits to 48-72 h of hyperoxic exposure. We found that although full-term newborns exposed to greater than 90% O2 consistently showed elevated superoxide dismutase, catalase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase activities, the premature animals repeatedly failed to respond to hyperoxia with increased antioxidant enzyme activity levels. Consistent with the comparative antioxidant enzyme responses were the evidences of O2 toxicity in the two age groups. The prematurely born rabbits had significantly increased lung lavage protein content, lung conjugated diene levels, and more severe light microscopic lung pathology compared with the full-term animals during equal O2 exposure time. This first reported comparison of prematurely born versus full-term animal responses to hyperoxia might help to explain the clinical observation that the very prematurely born infant is excessively prone to the development of O2-induced lung injury and the progressive development of bronchopulmonary dysplasia.

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.

Developmental aspects of experimental pulmonary oxygen toxicity

One of the more fascinating aspects of in vivo research on pulmonary O2 toxicity is the striking difference in the response of the neonatal versus the adult animal to hyperoxia. In general, neonatal animals are much more resistant to the characteristic O2-induced lung pathology seen in adult animals in hyperoxia. Neonatal animals are also able to rapidly mount a protective lung biochemical response to high O2 exposure [increased pulmonary antioxidant enzyme (AOE) activities], an adaptive response which adult animals have lost the ability to manifest in greater than 95% O2. This review focuses on the disparate AOE responses of the neonatal versus adult animal in hyperoxia. It also explores other possible explanations for the striking O2 tolerance of young versus adult animals, including comparative O2 free radical production rates, inflammatory cell responses, lung lipid composition, repair capabilities, etc. Discussion also centers on a less well studied toxic complication associated with hyperoxic exposure in the neonatal animal, i.e., the marked inhibitory effect of O2 exposure on normal lung growth and development of an alveolarized lung with an expanded respiratory exchange surface area. Finally, effective experimental means of protecting adult (and neonatal) animals from pulmonary O2 toxicity are reviewed. A closing section considers the enlightening new information that molecular biology has revealed about the regulation of AOE gene expression during normal development and under conditions of hyperoxidant challenge.

Left ventricular aneurysm with 1- to 2-mm-thick myocardium: a variant of the classic true aneurysm?

From January 1983 to July 1985, 64 patients underwent left ventricular aneurysmectomy in our surgical unit. In 11 (17%) of these cases, the lesion was a variant of the true aneurysm that included an extremely thin (1- to 2-mm), well-defined area of myocardium. In 9 of the cases, the aneurysm was confirmed preoperatively by means of high-quality ventriculography (high resolution and many hues of gray). Surgical and pathologic criteria established the lesion's clinical significance. To the best of our knowledge, these aneurysms constitute a heretofore undescribed variant of the classic true left ventricular aneurysm, exhibiting certain gross characteristics of the false left ventricular aneurysm and sharing with false aneurysms their greater risk of rupture. While it is impossible to tell whether these aneurysms are progressing toward rupture, we believe that all such lesions should undergo urgent repair in the presence of cardiac symptoms. Following aneurysmectomy, ventriculoplasty or septoplasty using an elliptical woven Dacron patch helps to preserve the internal contour and surface anatomy of the ventricle. In our series, this procedure resulted in early and late postoperative mortality figures comparable to those associated with the surgical treatment of classic true left ventricular aneurysms.

New "rest period" protocol for inducing tolerance to high O2 exposure in adult rats

We report a new protocol for inducing marked tolerance to prolonged exposure to hyperoxia in adult rats that entails the use of a single "rest period" between exposures to a usually lethal concentration of O2. Exposure of adult rats to greater than 95% O2 for 48 h followed by a rest in air, or a rest even in 50-75% O2, consistently resulted in 100% survival with evidence of only slight pulmonary edema during continuation of exposure to greater than 95% O2 for 3-7 more days (7-day survival for rats rested in room air for 24 h = 23/23; for rats rested in 50-75% O2 for 24 h = 27/27; for continuously O2-exposed control rats = 0/11). Induction of tolerance to hyperoxia was associated with significant increases in the lungs' antioxidant enzyme activities during the reexposure to greater than 95% O2 following the rest period. The molecular means by which the events in this protocol lead to increased lung antioxidant enzyme activity is only partially known, but because of the marked tolerance produced, the elucidation of the mechanisms must be important to our understanding of tolerance to hyperoxia.

Thyroid inhibition and developmental increases in fetal rat lung antioxidant enzymes

After demonstrating that prenatal exogenous thyroid hormone administration to pregnant rats produces decreases in fetal lung antioxidant enzyme (AOE) development despite increases in surfactant development, we examined the role of endogenous thyroid hormones on the development of these two lung systems. We administered the antithyroid drug methimazole (or diluent) to pregnant rats for the final 3 days before premature or term delivery; in a second series of experiments, propylthiouracil was administered for the 10 days before delivery. Both antithyroid drugs, known to cross the placenta, produced significantly decreased thyroid hormone levels in the pregnant dams. Fetal offspring from methimazole-, and propylthiouracil-treated dams demonstrated significant increases in pulmonary superoxide dismutase activity at 20 and 21 days of gestation and in catalase and glutathione peroxidase activities at 21 days compared with control offspring. Surfactant, measured as lung tissue disaturated phosphatidylcholine, was not different between either experimental group and controls. These results suggest that thyroid blockade increases AOE because the influence of thyroid hormone on AOE development may be one of depression. The findings confirm that certain hormonal regulators may influence different developing fetal lung systems in different ways.

Endotoxin increases lung Cu,Zn superoxide dismutase mRNA: O2 raises enzyme synthesis

Administration of endotoxin to adult rats increases lung Cu,Zn superoxide activity after 72 h of exposure to greater than 95% O2. The increased activity is brought about mainly by a faster rate of Cu,Zn superoxide dismutase synthesis; rats treated with endotoxin but not exposed to hyperoxia do not exhibit these findings (Hass, Frank, and Massaro, J. Biol. Chem. 257: 9379-9383, 1982). We now report that 48 h after treatment of adult rats with endotoxin there was a decreased rate of Cu,Zn superoxide dismutase synthesis by lung slices from air- and O2- exposed rats, although, in both groups, the lung concentration of Cu,Zn superoxide dismutase mRNA was increased approximately 45%. Exposure of endotoxin-treated rats to greater than 95% O2 or air for an additional 24 h (72 h all told) resulted in continued elevation of Cu,Zn superoxide dismutase mRNA only in lungs of O2- exposed rats. In vitro exposure of lung slices from air-breathing saline- or endotoxin-treated rats to 95% O2 for 6 h led to an increased rate of Cu,Zn superoxide dismutase synthesis only in slices from endotoxin-treated rats. We conclude that endotoxin treatment leads to an increased concentration of Cu,Zn superoxide dismutase mRNA in rat lungs, but a sustained elevation of the mRNA, and its translation into an increased rate of Cu,Zn superoxide dismutase synthesis requires exposure of the lung to hyperoxia.

Lack of sex differences in antioxidant enzyme development in the fetal rabbit lung

A sex difference characterized by a female advantage in the maturation of the fetal pulmonary surfactant system is well documented. Because the surfactant system and the antioxidant enzyme system of the fetal lung have chronologically similar developmental patterns and share some of the same hormonal regulators, such as glucocorticoids, we questioned whether a sex difference would be present in antioxidant enzyme maturation as it is in surfactant system maturation. We studied fetal rabbits at days 26 and 28 of a 31-day gestational period. Fetal sex was identified histologically. Fetal lung lavage was performed and lavage fluid assayed for phosphatidylcholine, disaturated phosphatidylcholine, and sphingomyelin. Lung tissue from separate fetuses was assayed for disaturated phosphatidylcholine content and total phospholipid content and for the activities of three antioxidant enzymes--superoxide dismutase, catalase, and glutathione peroxidase. No differences were present in antioxidant enzyme maturation between male and female fetal rabbits at the gestational days studied. A female advantage was observed in the lung lavage disaturated phosphatidylcholine/sphingomyelin ratio (at 26 days: female 1.38 +/- 0.42, male 0.99 +/- 0.26; and at 28 days: female 3.29 +/- 0.53; male 2.26 +/- 0.35, p less than 0.05). A female advantage in surfactant development was not reflected in lung tissue disaturated phosphatidylcholine or total phospholipid. We conclude that, unlike the development of the surfactant system, the development of the antioxidant enzyme system in the fetal rabbit lung does not demonstrate a sex difference.

Rat lung Cu,Zn superoxide dismutase. Isolation and sequence of a full-length cDNA and studies of enzyme induction

The synthesis of Cu,Zn SOD by rat lung increases spontaneously in the fetus in late gestation and during exposure of neonatal and adult rats to greater than 95% O2. To explore the regulation of these increases, we measured rat lung Cu,Zn SOD synthesis and activity. We also cloned and sequenced a rat lung Cu,Zn SOD cDNA that was used to measure Cu,Zn SOD mRNA concentration. We found that (a) under normal gestational and postgestational conditions the synthesis of this enzyme was regulated pretranslationally; (b) the increased synthesis that occurs under hyperoxia (greater than 95% O2), was pretranslationally mediated in otherwise unmanipulated neonatal rats but translationally controlled in hyperoxic adult rats; and (c) in lungs of rats made tolerant to greater than 95% O2 by allowing 24 h rest in air after an initial 48 h in greater than 95% O2, the increased Cu,Zn SOD synthesis that occurred during the second period of hyperoxia was regulated pretranslationally. We conclude Cu,Zn SOD gene expression in the lung is developmentally regulated under normal conditions and in response to an oxidant challenge. Tolerance, whether endogenous or induced, appears to require the accumulation of increased amounts of Cu,Zn SOD mRNA.

Menhaden fish oil, n-3 polyunsaturated fatty acids, and protection of newborn rats from oxygen toxicity

We have previously reported that newborn rats born to mothers fed a high n-6 polyunsaturated fatty acid (PUFA) (safflower oil) diet demonstrated increased n-6 PUFA in lung lipids and superior tolerance to high oxygen exposure. In the present study, we explored whether high n-3 PUFA might also protect against hyperoxic damage and by what mechanism. Adult female rats were fed either regular rat chow, a high n-3 (menhaden fish oil-based) diet, or a high n-6 (safflower oil-based) diet for 6 wk before and then throughout pregnancy and lactation. Newborn offspring of the high n-3 (fish oil) dams demonstrated increased n-3 PUFA (i.e. eicosapentaenoic and docosahexaenoic acid) and decreased n-6 PUFA (i.e. linoleic and arachidonic acid) in their lung lipids compared to the other two diet groups. The high n-6 (safflower oil) offspring had the opposite PUFA lung lipid pattern (with increases in total n-6 fatty acids and decreases in total n-3 fatty acids). The high n-3 offspring demonstrated markedly decreased lung levels of prostaglandin E2, F2 alpha and thromboxane B2, whereas the high n-6 offspring had higher eicosanoid levels than the regular diet offspring. Offspring of both high n-6 and high n-3 diet dams demonstrated essentially the same superior hyperoxic tolerance compared to regular diet offspring [7-d (greater than 95% O2) survival rates of 110/115 and 99/109, respectively, versus 70/91, p less than 0.01].(ABSTRACT TRUNCATED AT 250 WORDS)

Undernutrition as a major contributing factor in the pathogenesis of bronchopulmonary dysplasia

The protean effects of undernutrition on lung defenses and repair capabilities suggest that less than adequate nutritional support is a key pathogenetic factor in the development of bronchopulmonary dysplasia (BPD). Very-low-birthweight (VLBW, less than or equal to 1,000 g) premature infants who require intensive respiratory support have a distressingly high incidence of chronic lung disease or BPD. Many VLBW infants are currently undernourished during the most acute phase of their respiratory illness. Because VLBW newborns have only meager caloric reserves (fat, glycogen), and have only marginally sufficient stores of nutrients needed for effective lung defenses and repair capacity (vitamins A and E, copper, zinc, iron, selenium, essential fatty acids, etc.), the adequacy of nutritional support provided them will almost certainly influence their ability to tolerate early stress, and it may play a critical role in their clinical outcome. Experimental studies, combined with a limited number of clinical studies, clearly demonstrate that undernutrition can interact with each of the other well-accepted etiologic factors involved in the pathogenesis of BPD. Nutritional status affects the lung's ability to resist hyperoxic damage, to replace damaged/sloughed lung cells caused by barotrauma, to promote continued lung growth, to resist infection, and to tolerate prolonged and potentially toxic stresses in general. By providing more ideal nutritional support, clinicians may be able to apply preventive treatment to influence the outcome of intensive respiratory therapy in the VLBW newborn.

Polyunsaturated fatty acids and protection of newborn rats from oxygen toxicity

To test whether polyunsaturated fatty acids (PUFA) might be associated with protection against oxygen toxicity in newborn experimental animals, we performed two series of experiments. In the first series, adult female rats were fed one of three diets--regular Rat Chow, a high-PUFA (safflower oil-based) diet, or a low-PUFA (palm oil-based) diet--for several weeks before and throughout pregnancy and lactation. Newborn offspring of the three diet groups had similar antioxidant enzyme activities and surfactant development. Offspring of dams fed the high-PUFA diet had total lung lipid fatty acids characterized by increased linoleic acid (18:2 omega 6) and arachidonic acid (20:4 omega 6) and a significantly increased PUFA/saturated fatty acid ratio, compared with offspring of dams fed the regular diet or low-PUFA diet; associated with this increased PUFA pattern was markedly superior survival (80 of 84 (95%) vs 56 of 84 (67%) for regular-diet offspring, P less than 0.01) after 7 days in greater than 95% oxygen. Conversely, offspring born to dams fed the low-PUFA diet had decreased lung PUFA content and inferior tolerance to prolonged high O2 exposure (survival 38 of 84 (45%)). In the second experimental series, the postnatal provision of high PUFA rat milk to offspring born to dams fed the low-PUFA diet (via "cross-nurturing" by high-PUFA diet dams) rapidly increased their lung lipid PUFA and improved their hyperoxic survival (44 of 50 vs 25 of 50 for low-PUFA diet newborn animals kept with their low-PUFA mother rats, P less than 0.01). These studies suggest that increasing lung lipid PUFA can confer a protective effect against the toxic effects of hyperoxia on the newborn animal lung.

Extension of oxygen tolerance by treatment with endotoxin: means to improve its potential therapeutic safety in man

Treatment of adult rats with low doses of bacterial lipopolysaccharide (endotoxin) consistently results in a marked protective effect against O2-induced lung damage and lethality. We report here two means to improve the therapeutic ratio of endotoxin (ratio of dose producing desired beneficial effect/dose producing undesired toxic effects), which could make it a more acceptable pharmacologic agent for possible use in patients who require prolonged hyperoxic therapy. (a) Rats made "tolerant" to the lethal/toxic effects of high doses of endotoxin (25 mg/kg) by pretreatment with very low doses of endotoxin (10 ng----10 micrograms/kg) were found to still respond to a standard protective dose of endotoxin (500 micrograms/kg) with marked resistance to O2 toxicity. (Survival in greater than 95% O2 X 72 h = 19/20 (95%), vs. 4/17 (24%) for controls.) (b) Two chemically modified native endotoxin preparations ("endotoxoids"), with approximately 100 X decreased toxic potential, were found to have retained their ability to protect adult rats from prolonged hyperoxic exposure (90%-100% survival rates). These two experimental manipulations (use of the "endotoxin tolerance" phenomenon and treatment with partially detoxified "endotoxoids") were associated with increased lung antioxidant enzyme activities during O2 exposure in the treated animals. Continued research may eventuate in the possible clinical application of a safe form of endotoxin treatment for the prevention of O2 toxicity in humans.

Thyroid hormone depresses antioxidant enzyme maturation in fetal rat lung

The surfactant system and antioxidant enzyme system of the lung have chronologically similar developmental patterns, and the maturation of both systems is accelerated by glucocorticoid hormones. To investigate whether thyroid hormone might also stimulate the development of the antioxidant enzyme system as well as the surfactant system, we injected pregnant rats with triiodothyronine (T3) or diluent. Fetal T3 offspring demonstrated significantly elevated T3 levels, had significantly increased lung tissue disaturated phosphatidylcholine (DSPC) and total phospholipid content, yet had significantly decreased activities of three lung antioxidant enzymes (AOE) (superoxide dismutase, catalase, and glutathione peroxidase). When dexamethasone was administered in combination with T3, fetuses demonstrated increases in lung DSPC content but decreases in AOE of magnitude equivalent to or greater than that seen with T3 alone. These findings indicate that thyroid hormone affects surfactant and AOE development in opposite ways and may have potentially harmful as well as beneficial effects on different aspects of lung development.

Treatment of descending thoracic aneurysm with an intraaortic occluder

Elective treatment of descending thoracic aneurysms involves direct surgery, with Dacron graft replacement of the diseased aortic segment. When the patient's condition contraindicates major surgery, however, the surgeon should consider using an extraanatomic approach-implanting an ascending aorta-to-abdominal aorta Dacron bypass graft in a ventral position and leaving the diseased segment undisturbed. After such a procedure, the descending thoracic aorta must be excluded from the normal circulation. For this purpose, we have designed an intraaortic occluding technique in which an umbrella-like device is implanted immediately distal to the left subclavian artery. This technique has proved safe and uncomplicated in canine experiments and is ready for clinical trials.

Lung development in the fetal guinea pig: surfactant, morphology, and premature viability

Guinea pigs demonstrate "precocious" physical and functional development, with newborns displaying open eyes, hair, self-feeding, and temperature regulation. In addition, morphologic lung development is precocious in the guinea pig, with advanced alveolarization taking place in utero. To explore whether pulmonary surfactant development is also advanced, and at what stage prematurely delivered guinea pigs are capable of survival, we delivered fetal guinea pigs at 2- to 3-day intervals from day 49 of gestation to day 69 (birth). These were examined for chronologic changes in lung morphology, lung tissue disaturated phosphatidylcholine, phosphatidylglycerol and glycogen content, and serum glucocorticoid and thyroid hormone levels. Other prematurely delivered guinea pigs were given brief postnatal resuscitation and their survival noted. We confirmed advanced morphologic lung maturation, yet found that surfactant development, with antecedent hormone peaks and glycogen depletion, occurs during the final 10-15% of gestation. Lung biochemical development is thus "on time" in the guinea pig, rather than "precocious" compared to other frequently studied laboratory animals. In addition, greater than 50% of fetal guinea pigs are capable of survival by 8 days prior to term, well in advance of premature survivability in other small-sized species.

PO2-dexamethasone interactions in fibroblast growth and antioxidant enzyme activity

Fetal rat lung fibroblasts were cultured in a gas phase of 20% O2, 5% CO2 (PO2 measured, 150 Torr) or 2% oxygen, 5% CO2 (PO2 measured, 25 Torr) with or without 100 nM dexamethasone (Dex). Superoxide dismutase (SOD) activity per cell increased spontaneously during 4 days of incubation at both PO2, but catalase (CAT) activity tended to fall during this time and glutathione peroxidase (GPx) activity showed no consistent trend during this interval. Cells cultured at a low PO2 had a lower protein content and SOD activity compared with air controls. Dex inhibited cell proliferation and enhanced intracellular accumulation of protein at the low PO2 but prevented the increase in protein content without affecting cell multiplication at a PO2 of 150 Torr. SOD activity per cell was enhanced by Dex at a low PO2 but reduced in 20% O2, 5% CO2. An increase in CAT and GPx activity per cell resulted on exposing fibroblasts to Dex in the presence of low PO2. These results show that Dex affects the growth and antioxidant enzyme activity of fetal lung fibroblasts, and this action of Dex can be modulated by changing the ambient PO2.

Guinea pig lung development: antioxidant enzymes and premature survival in high O2

Whereas guinea pigs have advanced prenatal morphological lung development, their surfactant development is not "precocious" compared with other small laboratory animals. To investigate whether maturation of the antioxidant enzyme (AOE) system coincides more closely with surfactant development or with morphological maturation, we assayed fetal guinea pig lungs at gestational days 49-69 for superoxide dismutase, catalase, and glutathione peroxidase activities. We found that elevations in pulmonary AOE occurred in parallel with increases in surfactant during the final 10-15% of gestation. Since newborn guinea pigs behave more like adult animals in their relative intolerance to hyperoxia, we explored whether prematurely delivered guinea pigs would tolerate high O2 exposure better than full-term newborns. We found that prematures have markedly improved hyperoxic tolerance compared with newborns (time at which 50% of animals died in greater than 95% O2, 6.4 days vs. 4.5 days, respectively, P less than 0.05); and (unlike newborns) premature pups are capable of mounting an elevated AOE response to hyperoxic challenge. Thus premature guinea pigs behave more like full-term newborns of other species in respect to hyperoxic tolerance, an additional precocious feature of guinea pig development.

Oxygen toxicity in neonatal rats: the effect of endotoxin treatment on survival during and post-O2 exposure

Neonatal rats were treated with low doses of bacterial lipopolysaccharide (endotoxin) to test for a protective effect of endotoxin against O2 toxicity and the severe inhibition of normal lung development which occurs during prolonged exposure to hyperoxia. The rationale for the prophylactic use of endotoxin included its marked protective effect against pulmonary O2 toxicity in adult rats and its lung growth-promoting effect in experimental pulmonary stress models. Neonatal rats (4-5 days old) survived a 14-day exposure to greater than 95% O2 equally well whether treated with saline (39/51 = 76%) or with endotoxin (41/51 = 80%). However, during the following 24 h of gradual weaning to room air breathing, there was a marked difference in survival between the endotoxin group (32/41 = 78%) and the saline pups (14/39 = 36%) (p less than 0.001). Both groups showed inhibition of lung development (alveolarization) during O2 exposure, but endotoxin treatment compared to saline was associated with increased specific lung volume (5.33 versus 4.50 ml/100 g) (air control = 4.08), smaller mean airspace diameter (mean linear intercept = 49.0 versus 55.8 microns) (air control = 43.3), increased specific internal surface area (4393 versus 3232 cm2/100 g) (air control = 3753), and greater preservation of alveolar wall capillary patency (24.83 versus 18.52% "capillary density") (air control = 27.70%). We conclude that endotoxin treatment resulted in significant protection against O2 toxicity in neonatal rats which was manifested during readaptation to room air breathing. The protective effect was likely due to a combination of reduced inhibition of lung growth and development and reduced hyperoxic damage to the respiratory membrane of the lung.

Prenatal development of lung antioxidant enzymes in four species

We examined the chronology of development of both fetal lung antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) and disaturated phosphatidylcholine ("surfactant") during late gestation in four laboratory animal species: rat, rabbit, hamster, and guinea pig. An essentially similar pattern of prenatal biochemical maturation was found in all four species. The developmental changes were characterized by (1) rapid elevations in fetal lung antioxidant enzyme levels during the final 10% to 15% of gestation, and (2) an essentially parallel rapid rise in lung surfactant content during the final 10% to 15% of gestation. The increase in the lung activity of the individual antioxidant enzymes prior to birth averaged approximately 150% to 200%. Our findings suggest that late gestational changes in the principal pulmonary antioxidant defense system (like the changes in the surfactant system) represents a normal "preparation for birth," required to assure successful functioning of the neonatal lung in the relatively oxygen-rich ex utero environment.

Dexamethasone increases superoxide dismutase activity in serum-free rat fetal lung organ cultures

Dexamethasone (Dex) injected intraperitoneally to dams on gestational days 19 through 21 significantly enhances the normal late gestational rise of rat pulmonary superoxide dismutase activity. To study if Dex could act directly on lung cells to increase the activity of superoxide dismutase, rat fetal lung organ cultures were established from 21- or 22-day-old pups and maintained in serum free Waymouth 752/1 medium in 95% O2 for 72 h with and without 10 nM Dex in the medium. The cultures increased spontaneously in total superoxide dismutase activity from 17.5 +/- 3.1 to 33.5 +/- 6.2 U/mg DNA during this interval (+90%). The presence of 10 nM Dex caused an increase in enzyme activity to 40.1 +/- 9.3 U/mg DNA (+130%) demonstrating this hormone can act directly on the lung independent of the systemic metabolic consequences of corticosteroid administration. Dex decreased the rate of Cu,Zn superoxide dismutase synthesis (13.5 +/- 3.4 nmol Phe incorporated/mg DNA/h control vs 7.2 +/- 1.6, Dex) and seemed to also decrease the rate of enzyme degradation.

Metyrapone delays surfactant and antioxidant enzyme maturation in developing rat lung

The surfactant system and the antioxidant enzyme system of the fetal lung have chronologically similar developmental patterns and both can be accelerated by the administration of exogenous glucocorticoids. To test whether the antioxidant enzyme system, like the surfactant system, is regulated, at least in part, by endogenous glucocorticoids, we injected pregnant rats for 3 days prior to delivery with metyrapone, an adrenal 11-beta hydroxylase inhibitor which crosses the placenta and blocks endogenous glucocorticoid synthesis, or saline. Metyrapone offspring had significantly decreased lung tissue disaturated phosphatidylcholine/total phospholipids (p less than 0.05) compared to controls at days 21 and 22 of gestation. Activities of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase were similarly significantly reduced (p less than 0.01) in the lungs of metyrapone offspring at both gestational days studied. One day premature metyrapone pups demonstrated poorer survival than control pups from 25 min after delivery (44% survival versus 83%, p less than 0.05) to 90 min (6% survival versus 78%, p less than 0.01). These findings of delayed maturation of the surfactant and antioxidant enzyme systems following adrenal glucocorticoid blockade suggest that both systems are regulated, at least in part, by an endogenous glucocorticoid mechanism.

New antiarrhythmic agents. 2,2,5,5-Tetramethyl-3-pyrroline-3-carboxamides and 2,2,5,5-tetramethylpyrrolidine-3-carboxamindes

N-(omega-Aminoalkyl)-2,2,5,5-tetramethyl-3-pyrroline- or -pyrrolidine-3-carboxamides were acylated on the primary amino group of the side chain by means of reactive acid derivatives (acid chlorides, activated esters, phthalic anhydrides, phthalimide, 2-alkyl-4H-3,1-benzoxazin-4-ones) or they were alkylated by forming the Schiff bases and subsequent sodium borohydride reduction. Other tetramethyl-3-pyrrolinecarboxamide compounds were synthesized by acylating the aminoalkyl compounds with 2,2,6,6-tetramethyl-3,5-dibromo-4-piperidinone in a reaction involving Favorskii rearrangement. Saturation of the double bond of some pyrroline derivatives furnished the pyrrolidinecarboxamides. The new compounds of each type were active against aconitine-induced arrhythmia and several of them had higher activity and better chemotherapeutic index than quinidine. A few selected examples from each type of the active new compounds showed strong activity against ouabain-induced arrhythmia; for comparison known drugs such as lidocaine, mexiletine, and tocainide were selected. The most potent compounds were oxidized to the paramagnetic nitroxides and the latter were reduced to the N-hydroxy derivatives; these products had no or only decreased antiarrhythmic effect.

Use of anti-idiotypic antibodies to explore genetic mechanisms of production of anti-DNA antibodies

Systemic lupus erythematosus (SLE) is characterized by the production of autoantibodies with a broad range of antigenic specificities, including specificity for double-stranded DNA. Analysis of the idiotypic profile of anti-DNA antibodies both in humans and mice has demonstrated presence of cross-reactive idiotypes, suggesting that they arise from a restricted number of germline genes. Our laboratory has previously reported the generation of 3I, a monoclonal anti-idiotypic antibody which recognizes a cross-reactive idiotype on anti-DNA antibodies in a majority of unrelated humans with SLE. We have recently studied the expression of 3I in sera of three human kindreds with familial SLE. We found 6 of 8 SLE patients and 15 of 19 unaffected family members had elevated 3I reactivity. Eleven of these family members had no anti-DNA activity despite elevated 3I reactivity, suggesting that expression of this idiotype in certain individuals is part of the normal immune response. In another set of experiments using an in vitro culture system we examined somatic mutants of the S107 mouse myeloma cell line. This line makes an antibody which bears the T15 idiotype, a common idiotype on antibodies to the bacterial antigen phosphoryl choline (PC). U4, a mutant, makes an immunoglobulin which varies by one amino acid from the parent protein, retains the T15 idiotype, but loses reactivity with PC and acquires reactivity with DNA. We have found that some anti-DNA antibodies in mice with spontaneous lupus and in mice immunologically induced to make anti-DNA antibodies bear the T15 idiotype and may represent somatic mutants arising in vivo.

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.

Lung development in the streptozotocin rat fetus: antioxidant enzymes and survival in high oxygen

Offspring of experimentally induced diabetic animals demonstrate delays in functional, biochemical, and morphological aspects of lung maturation, dealing mainly with the surfactant system. To investigate whether the development of the lung antioxidant enzyme system would be similarly delayed, and thus compromise their tolerance to high O2 exposure, we did the following: 1) produced the diabetic state in rats with streptozotocin injection 24 h after the onset of pregnancy; 2) examined fetal animals from streptozotocin and control rats at gestational days 19, 20, and 21, and newborn animals at day 22 for whole lung disaturated phosphatidylcholine and total phospholipid and for the three antioxidant enzymes: superoxide dismutase, catalase, glutathione peroxidase; and 3) exposed newborn offspring from streptozotocin-treated and control rats to greater than 95% O2 for several days and their survival, changes in antioxidant enzymes and disaturated phosphatidylcholine and light microscopic findings in response to hyperoxic challenge were compared. Streptozotocin offspring demonstrated essentially no developmental differences in whole lung disaturated phosphatidylcholine, total phospholipid, or antioxidant enzymes activity at the 4 gestational days studied. However, newborns of streptozotocin mothers had consistently superior tolerance to hyperoxic exposure, consisting of increased survival [23/34 (68%) versus 8/26 (31%) in controls, after O2-exposure for 13 days, p less than 0.001], microscopic evidence of reduced inhibition of alveolarization (p less than 0.05), and a trend toward greater antioxidant enzymes response. Thus, in this animal model of experimental diabetes, neither the development of the antioxidant enzymes system nor the development of the surfactant system (as assessed by whole lung disaturated phosphatidylcholine and total phospholipid) appear delayed.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitogenic effect of endotoxin on lung and tolerance of rats to hyperoxia

Treatment of rats with endotoxin, as late as 24 h after beginning exposure to greater than 95 O2 at 1 atm, increases survival at 72 h from 20-30% to greater than 95% (J. Clin. Invest. 65: 1104, 1980), whereas treatment with corticosteroids reduces survival (Toxicol. Appl. Pharmacol. 47: 367, 1979). Since endotoxin is mitogenic to some cells and glucocorticosteroids decrease DNA synthesis by lung cells, we asked 1) is endotoxin mitogenic to the lung, and, if so, 2) is the mitogenic effect required for endotoxin to produce tolerance to hyperoxia? We found endotoxin administered in vivo does have a mitogenic effect on the lung as indicated by an increased rate of DNA synthesis by lung slices; dexamethasone blocked this effect. However, although dexamethasone given alone markedly diminished survival in hyperoxia, dexamethasone did not impair the protection conferred to rats by endotoxin against the edemogenicity and lethality of hyperoxia. Furthermore, dexamethasone did not diminish the rise of antioxidant enzyme activity in the lungs of endotoxin-treated O2-exposed rats. We conclude endotoxin can produce tolerance to hyperoxia even when its mitogenic action on the lung is substantially diminished.

Endotoxin alters biochemical and morphological responses to pneumonectomy in adult rats

Adult rats treated with endotoxin, like untreated neonatal rats, are resistant to O2 toxicity and manifest very similar lung biochemical responses. We hypothesized that endotoxin might also alter the adult pneumonectomy response to resemble the accelerated response of younger animals. Adult and 19-day rats underwent pneumonectomy, followed in 24 h by endotoxin or saline injection. Pneumonectomized rats, shams, and controls were killed 72 h after surgery for lung biochemistry and morphometry. Compared with adult saline-pneumonectomized rats, adult endotoxin-pneumonectomized rats, adult endotoxin-pneumonectomized rats demonstrated a significantly greater growth response and a lung biochemical response pattern (increased RNA, markedly increased RNA/DNA) similar to 19-day rats. Morphologically, endotoxin-pneumonectomized rats showed a different pattern of lung regrowth (significantly larger air spaces). Saline pressure-volume curves were not different between the two groups. We conclude that endotoxin administration to pneumonectomized adult rats resulted in accelerated lung regrowth, a lung biochemical response pattern similar to 19-day rats, but a paradoxical morphological pattern resembling more closely that of the adult than the neonatal animal.

Oxygen toxicity in rats. Varied effect of dexamethasone treatment depending on duration of hyperoxia

The low rate of survival in patients with the adult respiratory distress syndrome (ARDS) may in part reflect a failure to consider that the lung's response to applied therapies may not be constant throughout the course of illness. To test this notion, we used hyperoxia to produce progressive lung damage in rats and administered dexamethasone at different times during O2 exposures of various lengths. Dexamethasone improved survival and decreased lung damage if given when exposure to hyperoxia was to be soon terminated; pulmonary inflammation was marked at the time at which the administration of dexamethasone led to increased survival. Dexamethasone worsened lung damage and diminished survival when given early during exposure to hyperoxia; inflammation was minimal early in the course of exposure to hyperoxia. These findings point to the need for a more analytical approach to research on therapy of ARDS; agents that are harmful at one time may be beneficial at another time.

Effects of oxygen on the newborn

The free radical theory of O2 toxicity provides a testable explanation of the mechanism of O2's toxic effects on a biochemical and cellular level. In addition, it provides for an understanding of the array of normal antioxidant defenses of the cell and an insight to rational approaches to pharmacologic prophylaxis against clinical O2 toxicity. Neonatal animals of many species are much more resistant to the lethal effects of exposure to high concentrations of O2 than are the adult animals of the species; this increased tolerance is associated with the newborn lungs' ability to increase its normal complement of protective antioxidant enzymes during O2 exposure. Premature infants who require vigorous hyperoxic respiratory support early in life frequently develop acute and chronic lung changes compatible with pulmonary O2 toxicity, so-called bronchopulmonary dysplasia. The lung of the prematurely born may be quite ill-adapted for protecting itself against hyperoxic exposure owing to immaturity of its antioxidant defensive systems. Clinical pharmacologic stratagems designed to augment the intracellular antioxidant defensive capacity of the lung may become available in the near future, which would provide some means to prevent or ameliorate the serious lung damage associated with the clinical use of life-giving O2.

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).

Dexamethasone stimulation of fetal rat lung antioxidant enzyme activity in parallel with surfactant stimulation

It has recently been determined that fetal lung antioxidant enzyme activity markedly increases late in gestation. A test was made of whether this normal late-in-gestation change in O2-protective enzymes would be responsive to the maturing effect of hormonal (glucocorticoid) treatment. Pregnant rats received 0.2 mg/kg of dexamethasone (or saline) at 48 and 24 hours prior to delivery of their fetuses on gestational days 19, 20, 21, and 22 (newborn). Lung disaturated phosphatidylcholine showed an expected response to prenatal dexamethasone exposure with significant elevations of surfactant lipid at gestational days 20 and 21. A similar effect of prenatal dexamethasone treatment on the lung antioxidant defensive system was found. Superoxide dismutase, catalase, and glutathione peroxidase--enzymes protective against hyperoxia-induced lung injury--showed an accelerated pattern of maturation with significant increases in the dexamethasone-treated fetal lungs compared with control fetal lung enzyme levels at gestational days 20 and 21. The results suggest that prenatal dexamethasone treatment may have dual benefits when used in impending premature deliveries--that is, it may stimulate maturation of both the surfactant system and also the antioxidant enzyme system, and this maturation can help protect the premature newborn's lungs from the toxic complications of hyperoxic therapy that may be required because of immaturity.

Intrauterine growth-retarded rat pups show increased susceptibility to pulmonary O2 toxicity

We used a nutritional deprivation model to produce intrauterine growth-retarded (IGR) rat pups (birth weight = approximately 75% of normal). The IGR newborns evidenced a marked reduction in tolerance to greater than 95% O2 exposure: 10-day survival = 10/47 (21%) versus 18/36 (50%) for control pups, and LT50 = 7.2 days versus 10 days for controls (p less than 0.01). Various lung parameters at birth and during O2 exposure were examined to try to define why prenatal undernutrition should compromise the survival of IGR rats in hyperoxia. We found decreased lung glutathione peroxidase and glucose-6-phosphate dehydrogenase activity (with normal superoxide dismutase and catalase levels) in the IGRs at birth; decreased lung disaturated phosphatidylcholine content (even more markedly decreased in 1-day premature pups); and decreased lung surface area/body weight. These factors and other features of newborn IGRs reported in the literature may help to explain how prenatal undernutrition compromises postnatal tolerance to prolonged high-O2 exposure.

Castration prolongs tolerance of young male rats to pulmonary O2 toxicity

We tested the hypothesis that the normal loss of tolerance of neonatal rats to prolonged hyperoxic exposure at around 1 mo of age might be related to the marked increase in sex hormones occurring around this period. Male rats castrated at 20 days of age demonstrated significantly increased survival in greater than 95% O2 compared with sham-operated rats when exposed to high O2 at various ages greater than 45 days [castrated, 115 of 166 (69%) vs. sham, 59 of 156 (38%) (P less than 0.001)]. Testosterone replacement led to survival rates comparable with sham-operated rats [30 of 87 (34%)]. No such protective effect was observed in female rats [survival: ovariectomy, 16 of 33 (48%) vs. sham, 14 of 28 (50%)]. The improved survival in the older castrated males was not associated with an increase in lung antioxidant enzymes, which is normally seen in O2-tolerant neonatal rats. Castration did result in marked morphological lung changes, including significantly enlarged lung volumes (4.54 +/- 0.72 vs. 3.76 +/- 0.29 ml/100 g) and terminal air spaces [mean linear intercept (LM) = 51.6 +/- 5.0 vs. 46.3 +/- 4.1 micron (P less than 0.001)]. Testosterone replacement also prevented these morphological changes. The altered lung growth 1) may be related to the influence of other endocrine imbalances after castration and 2) may be an important factor in the relative O2 tolerance of the castrated male rats beyond the neonatal period.

Endotoxin treatment protects vitamin E-deficient rats from pulmonary O2 toxicity

Endotoxin treatment in normal rats has a marked protective effect against O2 toxicity (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 577-581, 1979 and 51: 577-583, 1981), and endotoxin's protective action is associated with stimulation of the lung's enzymatic antioxidant defense system (superoxide dismutase, catalase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase). Vitamin E-deficient animals are especially sensitive to hyperoxidant stresses, including pulmonary O2 toxicity. In these studies we tested whether endotoxin could reverse the increased susceptibility of vitamin E-deficient rats to hyperoxic challenge. We found that untreated vitamin E-deficient rats do succumb more readily to O2 toxicity [0/11 alive at 72 h in greater than 95% O2, lethal time for 50% of the animals (LT50) = 50 h] than rats fed a regular diet (4/14 alive, LT50 = 69 h). In contrast, 15 of 16 vitamin E-deficient rats treated with endotoxin survived the same O2 exposures (P less than 0.001) and showed significantly reduced pulmonary edema compared with the other groups. The endotoxin-treated vitamin E-deficient group was also the only one to demonstrate significant elevations of all the antioxidant enzymes during O2 exposure, suggesting that the antioxidant enzyme defenses of the lung have a more primary and important role in prevention of O2-induced lung injury than the lipid-associated antioxidant, vitamin E.

The interface of education, psychological and visual services in pediatric optometry

Optometrists cannot effectively serve children with learning problems in isolation. Through integrated input from multidisciplinary sources, the optometrist can develop an appropriate vision care program for these children.

Preparation for birth into an O2-rich environment: the antioxidant enzymes in the developing rabbit lung

To determine if some specific "preparation for birth" occurs in the developing lung to help assure its successful adaptation to a comparatively O2-rich world at birth, we measured the activities of the antioxidant enzymes in the developing lungs of rabbit fetuses from 10 d before parturition to several days after birth. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GP) activities showed similar maturational patterns with significant increases in activity, compared with earlier gestational levels, during the last 3-5 d before birth. During the final days in utero, SOD and CAT activities increased by approximately 110% and lung GP activity by approximately 200%. There were no parallel changes in lung O2 consumption demonstrable over this same prenatal period.

Ozone-induced tolerance to hyperoxia in rats

Preexposure of adult rats to ozone (0.8 +/- 0.1 ppm for 7 days) has been found to produce a marked degree of tolerance to hyperoxia (greater than 95% O2). The survival of O3-preexposed rats in hyperoxia for 168 h was 28 of 32 (88%) compared with a rate of 2 of 18 (11%) for nonpreexposed rats. Total lung superoxide dismutase (SOD), glutathione peroxidase (GP), glucose 6-phosphate dehydrogenase (G6-PD), and catalase (CAT) activities were all significantly increased after O3 preexposure and after the subsequent hyperoxic challenge. Probable mechanisms accounting for the markedly improved survival in hyperoxia after O3 preexposure include both increased lung antioxidant enzyme and repair of structural damage by proliferation of alveolar lining cells. The demonstration of cross-tolerance between the atmospheric oxidants O3 and O2 suggests that there are similarities in the lung's adaptation to both oxidants.

Oxygen toxicity in newborn rats: the adverse effects of undernutrition

Undernutrition was found to compromise the tolerance of newborn rat pups to hyperoxia (greater than 95% O2 for 7 days). Survival rate for the normally nourished pups (11 pups/dam) was 56 of 77 (73%) but only 47 of 108 (44%) for the undernourished (18 pups/dam) group (P less than 0.005). Body growth, lung growth, and lung DNA content were significantly reduced by undernutrition. Hyperoxia inhibited these same parameters in both groups of pups. The growth inhibitory effects of O2 and undernutrition were additive, with an especially marked depression of lung DNA content (decreases 65%). Lung maturation was also markedly inhibited by O2 but to a similar extent in both nutrition groups. Despite the disparity in their O2 tolerance, 18/litter and 11/litter pups in O2 responded with equivalent increases in lung antioxidant enzymes. We suggest that the additive depressive effects of neonatal undernutrition and hyperoxia on lung DNA may compromise repair of ongoing O2-induced lung damage and help account for the compromised O2-tolerance we consistently observed even in the presence of significantly elevated antioxidant enzyme defenses.

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.

The activity of pulmonary indoleamine 2,3-dioxygenase in rats and mice is not altered by oxygen exposure

We tested the hypothesis that pulmonary indoleamine 2,3-dioxygenase (indole:oxygen 2,3-oxidoreductase (decyclizing), EC 1.13.11.17), an enzyme that consumes superoxide anion (O-2), might have an antioxidant role under conditions of hyperoxia. We measured indoleamine 2,3-dioxygenase in three experimental models in which pulmonary superoxide dismutase, catalase and glutathione peroxidase (the known antioxidant enzymes) show increased activity and are associated with greater tolerance to 96-98% O2 exposure: (1) adult rats preexposed to 85% O2 for 5-7 days; (2) neonatal rats exposed directly to greater than 95% O2; and (3) adult rats treated with bacterial endotoxin during O2 exposure. Indoleamine 2,3-dioxygenase did not increase in response to O2 exposure in any of these rat models. Conversely, in adult mice treated with endotoxin, lung indoleamine 2,3-dioxygenase activity did increase, but no protection against O2 toxicity occurred. Thus, a rise in indoleamine 2,3-dioxygenase is neither necessary nor sufficient to confer resistance to O2 toxicity. These data taken together are evidence against its having any important role in the antioxidant defense system of the lung.