Antioxidant Enzyme Responses to Hyperoxia in Preterm and Term Rats after Prenatal Dexamethasone Administration

Abstract

ABSI'RACI'. Although prenatal steroid therapy is known to enhance in utero maturation of the surfactant and antioxidant enzyme systems, little is known about the effects of steroids on the antioxidant system after birth. We measured activities of the antioxidant enzymes, catalase, superoxide dismutase, and glutathione peroxidase, in lung homogenates from both preterm and term rat pups after prenatal dexamethasone treatment. Enzyme activities were measured at birth and after exposure to >98% oxygen. Dexamethasone treatment resulted in significantly higher survival of the preterm pups at 24 h (91.3% for dexamethasone versus 57% for saline). In preterm pups, the activities of catalase and superoxide dismutase at birth were higher after dexamethasone treatment (p < 0.05). However, after 24 h of hyperoxic exposure, there were no differences in activities of any of the antioxidant enzymes between the dexamethasone and control groups of prematurely born pups. In term pups, antioxidant enzyme activities did not differ significantly at birth; nor did they differ after 24 to 72 h of hyperoxic exposure in the dexamethasone and control treatment groups. Our results indicate that although prenatal dexamethasone treatment augments survival and catalase and superoxide dismutase activities at birth in preterm rat pups, dexamethasone does not result in altered early postnatal antioxidant enzyme activities after exposure to hyperoxia. (Pediatr Res 33: 177-180, 1993) Abbreviations CAT, catalase SOD, superoxide dismutase GPX, glutathione peroxidase 7 he antioxidant enzyme system serves to protect the organism fiom 02-free radicals that are produced as a result of breathing and metabolizing ambient O?. Production of free radicals increases after exposure to hyperoxic conditions (I), and oxygen tolerance is thought to depend primarily on the capacity to augment antioxidant enzyme activities in response to hyperoxia (2-5). This capacity to increase antioxidant enzymes may account for the greater 0: tolerance of term neonatal animals of several species compared with adults, even though baseline an- tioxidant enzyme activities of the neonate tend to be lower (6. 7). Recent studies in rabbits indicate that, compared with animals born at term, preterms demonstrate both lower 0 2 tolerance and a diminished ability to respond to hyperoxia with increases in antioxidant enzyme activities (8).Activities of the antioxidant enzymes, CAT, SOD. and GPX. increase in the last 10 to 15% of gestation (9-12). It has been demonstrated that prenatal administration of dexamethasone causes not only increased maturation of the surfactant system. but also increases in antioxidant enzyme activities in the fetus (13). However. because augmentation of enzyme activities in response to hyperoxia may be necessary for tolerance. the effect of urenatal dexamethasone on ~ostnatal enzyme resuonses to hyperoxia may be more important than its ability td increase baseline activities in fetal animals.To our knowledge, there is only one preliminary report of antioxidant en...

Oxidative stress in infants born to preeclamptic mothers

“…This finding may be explained by the fact that SOD is considered to be the first line of defense against oxygen toxicity. Antenatal steroid therapy may accelerate antioxidant enzyme activity 29–31 . High SOD activity could not be attributed to the effect of steroid therapy in the present study because of the fact that there was no significant difference in the use of antenatal steroid between groups.…”

Effects of antenatal and postnatal corticosteroids on the preterm lung

“…As survival remained better in the group treated antenatally, it may be that it is the rate of increase in antioxidant enzymes rather than simple increases in these enzymes which is more important. Prematurely delivered rat pups were studied by Keeny et al, 33 who showed that the survival of the preterm pups in the group treated antenatally was significantly better than in the untreated group at 24 hours of age (91% vs 57%). Increases were seen at 24 hours of age in antioxidant enzymes in the treated group, as in Frank’s study, with no significant differences being seen after this age in both the treated and untreated groups.…”

Comparison of Pulmonary Neutrophils in the Adult and Neonatal Rat after Hyperoxia

“…Exposures to oxygen were performed in airtight plastic cages as previously described (20). Oxygen was humidified, provided at a flow rate of 5.0 Llmin, and continuously analyzed.…”