Neonatal Hyperoxia Research Articles

Neonatal hyperoxia and cytochrome P450 imprinting in adulthood.

We hypothesized that during a critical neonatal period hyperoxia may produce alterations of sex-specific cytochrome P450 isozymes in adulthood (enzyme imprinting). To test this, newborn rats were exposed to 24 or 72 h of hyperoxia (O2 > 95%) within 24 h after birth and killed at 120 d. In males, significant negative imprinting (decrease) was found in total cytochrome P450 content and male-specific CYP2C11 in the hyperoxia groups. Positive imprinting (increase) was noted in CYP1A2 and male-specific CYP3A2 in the 72-h hyperoxia group. These alterations were essentially similar when expressed on a per microsomal protein or per liver basis. In addition, the level of hepatic glucocorticoid receptor in adult male rats was elevated after neonatal hyperoxia. In females, there was a significant body and liver weight loss after hyperoxic exposure, which resulted in a negative imprinting of CYP1A2 and female-specific 2C12 in the 72-h hyperoxia group on a per liver basis, whereas the measured parameters were unaltered when expressed per microsome. In general, the changes were more marked with longer hyperoxic exposure, suggesting that more pronounced alterations may be induced with prolonged neonatal hyperoxia. Because hyperoxic exposure in premature neonates is a common clinical practice and decreased CYP2C11 in adult males is expected to result in feminization, we believe that the scope of this work should be expanded and eventually tested for its relevance in human subjects.

Rat lung antioxidant enzymes: differences in perinatal gene expression and regulation.

The lung activity of the antioxidant enzymes (AOEs) copper, zinc superoxide dismutase (Cu,Zn SOD), catalase (CAT), and glutathione peroxidase (GP), but not manganese superoxide dismutase (Mn SOD), increases in rats during late gestation; the concentrations of Cu,Zn SOD mRNA and CAT mRNA also rise. During early postnatal exposure to > 95% O2, the lung activity of Cu,Zn SOD, CAT, and GP increases. We now show 1) the lung concentration of Mn SOD mRNA and GP mRNA does not increase in late gestation; 2) Mn SOD activity and the concentration of its mRNA and of GP mRNA increase during exposure of neonatal rats to > 95% O2; and 3) as previously shown for CAT mRNA, the increase in lung concentration of the mRNAs for Cu,Zn SOD, Mn SOD, and GP during early postnatal hyperoxia occurs with a 70-80% prolongation of the half-life of these mRNAs. We conclude that 1) in late gestation the level at which lung AOE gene expression is regulated differs among the enzymes, 2) the level at which lung AOE gene expression is regulated shortly after birth in response to > 95% O2 is uniform among the enzymes, and 3) the lung's AOE response to neonatal hyperoxia is not merely a step-up of its prenatal regulation but involves different regulatory mechanisms based on increased stability of AOE mRNAs.

Perinatal rat lung catalase gene expression: influence of corticosteroid and hyperoxia

Dexamethasone accelerates the late gestational rise in rat lung catalase activity; neonatal hyperoxia elevates rat lung catalase activity. We studied the regulation of catalase gene expression in these instances. Catalase mRNA/mg DNA increased to gestation day 22 and then fell to the concentration in adult lungs. The rate of transcription of catalase mRNA was higher on gestation day 22 than gestation day 19, whereas the half-life of catalase mRNA (approximately 7 h) was the same on both days. Dexamethasone given 48 and 24 h before expected birth (gestation 22 days) increased catalase mRNA concentration at days 20 and 22 without a change in catalase mRNA stability. Early postnatal hyperoxia (greater than 95% O2, 72 h) elevated catalase mRNA/mg DNA and doubled its half-life without changing its rate of transcription. We conclude the normal late gestational elevation of catalase activity and the increase of activity during prenatal dexamethasone treatment are regulated at the level of gene transcription. By contrast, the elevation of catalase activity during neonatal hyperoxia is mediated posttranscriptionally by increased catalase mRNA stability.

Neonatal pulmonary oxygen toxicity in the rat and lung changes with aging

The aims of this study were to determine if neonatal hyperoxia exposure causes permanent lung damage and to define the relationship between neonatal lung oxygen toxicity and aging. Sprague-Dawley newborn rats (n = 85) breathed 100% oxygen (O2) or room air (RA) during the first 8 days of life, and then RA. At 2 and 22 months of age we assessed right ventricular (RV) systolic pressure (RVSP), RV weight, saline and air pressure-volume curves, volume density of lung parenchyma and nonparenchyma, parenchymal air space (PAS), mean linear intercept (Lm), number of small arteries/mm2 and the extent of their medial muscularization. Aging in RA did not affect the RVSP, RV weight, the number of small arteries/mm2, or their muscularization. The maximal lung volume/g of dry lung and the elastic recoil pressure between 40 and 90% maximal lung volume decreased. The volume density of lung parenchyma increased but the fraction of the lung parenchyma that was PAS decreased and that of the alveolar septa and Lm increased. The O2-treated rats at 60 days of age had increased RVSP and RV weights with a decrease in the small arteries/mm2. The lung parenchymal volume density and PAS increased and the density of alveolar septa decreased. The Lm increased and the alveoli/mm2 and elastic recoil pressure decreased. The lung damage seen in the O2-treated rats at 60 days persisted and in addition underwent the changes seen in the aging controls. However, the extent of muscularization of the arteries decreased. We conclude that neonatal hyperoxia causes permanent functional and structural changes of the lung but these do not interact with aging; that is, the effects of O2 toxicity and aging are additive but not synergistic.

Hyperoxia damages phagocytic defenses of neonatal rabbit lung.

The effect of hyperoxia on phagocytic defenses of neonatal rabbit lung was ascertained by exposure to a fractional inspired O2 concentration of 0.95 + or 0.21 for 48, 96, or 168 h. Intrapulmonary clearance of inhaled staphylococci was reduced by 67 and 74% after 96 and 168 h in hyperoxia (P less than 0.05). Impaired phagocytic killing was not due to diminished bacterial ingestion. Alveolar macrophages (AM) lavaged from pups reared in normoxia had a progressive ability to release superoxide (O-2) and showed increasing cyanide-sensitive O2 consumption during the 1st wk of life. Conversely, AM recovered from litters housed in hyperoxia for 48 h produced 190% more O-2 than normoxic controls (P less than 0.005), but this capacity to generate O-2 fell by 43% after 96 h of exposure (P less than 0.05). After 96 h of hyperoxia, AM had a significant shift toward cyanide-insensitive metabolism compared with normoxic cells (P less than 0.05). Polymorphonuclear leukocytes (PMN) entered the alveoli after 96 h of hyperoxia, and mortality rose abruptly in animals exposed for 168 h (16%) vs. 96 h (3%). Our findings indicate neonatal hyperoxia induces metabolic and bactericidal dysfunction in the primary pulmonary phagocyte, the AM, and this injury is followed by additional lung insult during PMN migration into the airways.

Chronic vascular pulmonary dysplasia associated with neonatal hyperoxia exposure in the rat.

Chronic sequelae of neonatal hyperoxia was studied in male rats exposed to 0.96-1.0 FiO2 for the first 8 days of life. At 58 days of age functional and morphologic cardiopulmonary changes were compared with controls. Right ventricular systolic pressure was measured percutaneously under anesthesia and was increased in the O2 group (29.5 mm Hg +/- 3.1 versus 23.2 mm Hg +/- 3.5, p less than 0.001). Lung and heart weights were similar between groups. Right ventricular weights however were increased in the O2 group (0.197 g +/- 0.023 versus 0.175 g +/- 0.020, p less than 0.001). Air pressure-volume curves were similar but in the O2 rats saline deflation curves were shifted left and maximal fluid lung volumes were greater (14.1 +/- 1.2 versus 12.0 +/- 0.7 ml, p less than 0.001). Pulmonary arteries were perfused at 100 cm H2O with a barium-gel mixture and lungs were fixed at 25 cm H2O with formalin. Microscopic examination of lungs revealed dysplastic changes of alveolar architecture which included irregularly enlarged alveoli and incomplete alveolar septation. Morphometric studies of the lungs showed that the O2 rats had an increased volume proportion of parenchyma (0.865 +/- 0.020 versus 0.850 +/- 0.019, p less than 0.05), increased mean linear intercept (72.3 microns +/- 9.5 versus 53.6 microns +/- 5.0, p less than 0.001), decreased number of alveoli per mm2 (207 +/- 34 versus 319 +/- 39, p less than 0.001) and fewer small arteries (20-200 microns) per mm2 (8.7 +/- 1.3 versus 14.9 +/- 2.4, p less than 0.001). The number of small arteries/100 alveoli was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

1831 VASCULAR-PULMONARY DYSPLASIA (VPD) ASSOCIATED WITH NEONATAL RAT HYPEROXIA

The chronic sequelae of neonatal hyperoxia was studied in male rats exposed to 100% O2 for the first 8 days of life. Dams were rotated between 41 oxygen treated (O2) rats and 29 room air controls. Following O2, rats had standard care until 60 days of age. Survival rate was 97%. Body weights at 60 days were similar. In vivo right ventricular pressure was measured percutaneously under anesthesia and was increased in the O2 group (30.5 ± 4.3 vs 22.7 ± 3.3 mm Hg p <.0005). Hearts and lungs were excised at 63 days. Organ weights were similar between groups, however, right to left ventricular weight ratios were increased in the O2 group (.316 ± .028 vs .259 ± .022 p <.0005). Air pressure-volume curves were similar but in the O2 rats fluid deflation curves were shifted left and maximum fluid lung volumes were greater (14.05 ± 1.25 vs 12.03 ± .71 ml p <.0006). Pulmonary arteries were perfused at 100 cm H2O with a barium-gel mixture and lungs fixed at 25 cm H2O with formalin. Morphometric studies showed that the O2 rats had an increased volume proportion of parenchyma (.865 ± .014 vs .820 ± 2.8 p <.05), increased mean linear intercept (111.5 μ ± + 17.6 vs 75.3 μ ± 4.7 p <.005), decreased alveoli and ducts per mm2 (78.4 ± 5.2 vs 127.9 ± 8.4 p <.0005) and fewer small arteries (20-200 μ) per mm2 (2.9 ± .41 vs. 4.3 ± .57 p <.0005). The number of small arteries/100 alveoli were similar. We conclude that neonatal hyperoxia is associated with VPD as indicated by a decrease in the number of arteries, cor pulmonale and emphysematous changes in the air spaces.

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 neonatal hyperoxia on sexual arousal and emotionality in the male rat

Neonatal hyperoxia was studied as a method of provoking behavioural disturbances in animals because of its possible connection with adaptive deficiencies observed in premature human infants who had been exposed to excessive O 2 at birth. The sexual responsiveness and emotionality of adult rats was measured after they had been subjected to hyperoxia for 10 days after birth. These Ss were found to be less sexually responsive (longer mount latencies and smaller percentage of mounters) and more emotional (more defecation in the open field apparatus, larger adrenals, and smaller body weights) than untreated controls. Two other control groups of blinded and blinded plus O 2 treated Ss yielded comparable patterns to the O 2 group. These findings were interpreted to indicate that neonatal hyperoxia could be a potent influence on some aspects of adaptive behaviour and that at least one of its consequences was to establish long term stress factors which were apparently also introduced by the other treatments.