Brain Superoxide Anion Generation during Asphyxia and Reventilation in Newborn Pigs

Abstract

Perinatal asphyxia can occur in babies and may result in death, or damage to brain and other organs. Sequelae of brain damage are cerebral palsy, mental retardation, and epilepsy. The exact mechanisms that lead to brain damage are not known with certainty, but activated oxygen species, if produced, could be involved. Oxygen free radicals can damage or kill cells via several pathways, which include lipid peroxidation of membranes and inactivation of enzymes and transport proteins and DNA and RNA alterations (1, 2). Generation of oxygen free radicals in brain, such as superoxide anion, have been detected during exposure to arachidonic acid (3), acute hypertension (4), ischemia/reperfusion (1, 5, 6), concussive brain injury (7), extravascular blood (8), and seizures (9). Prostaglandin endoperoxide synthase metabolism of arachidonic acid appears to be the major source of free radicals produced by cortex in cats and piglets (3-5, 8, 9). Whether oxygen free radicals are produced in brain during asphyxia and reventilation is unclear. Rosenberg et al. (10) and Thiringer et al.(1 1) have provided suggestive evidence using pharmacologic probes that oxygen free radicals are produced during asphyxia and reventilation in newborn lambs. However, brain production of oxygen free radicals was not measured.The first purpose of our study was to test the hypothesis that superoxide anion radical is generated in the brain during asphyxia and reventilation in newborn pigs. The second purpose was to investigate the role of prostaglandin endoperoxide synthase in generation of superoxide anion. As an index of superoxide anion generation, we determined the amount of SODinhibitable NBT reduction on the cerebral surface. MATERIALS AND METHODSThe animal protocols used were reviewed and approved by the Animal Care and Use Committee of the University of Tennessee, Memphis. Twenty-two newborn pigs (680 to 2000 g) of either sex, 1-5 d of age, were anesthetized with ketamine-hydrochloride (33 mg/kg intramuscularly) and acepromazine (3.3 mg/kg intramuscularly). Anesthesia was maintained with a-chloralose, 50 mg/kg i.v. initially and then 10 mg/kg i.v./h. A catheter was inserted into the femoral vein for injection of drugs and another catheter was inserted into the femoral artery to record blood pressure and to draw blood samples. The animals were ventilated with room air using a piston-type ventilator (Harvard Apparatus Co., Inc., S. Natick, MA). Temperature was maintained at 37-38°C by using a water-circulating heating pad. Closed cranial windows, as described previously (5, 8, 9), were implanted over each parietal cortex. To implant the cranial window, the scalp was cut and reflected from the skull. A hole, approximately 2 cm in diameter. was made in the skull. An incision was made through the duia and arachnoid membranes and these membranes then were reflected over the edge of the bone. A stainless steel ring with a premounted glass coverslip was inserted in the hole. The window was cemented in place with dental acrylic. Three needles pierced t...

Somatosensory Evoked Potential and Brain Water Content in Post-Asphyxic Immature Piglets

“…In addition, the 1-to 6-d age precedes the period of peak myelination in pig brain (29), thereby approximating a human newborn. In prior studies of asphyxia in immature piglets, the length of asphyxia often was determined as the time required to achieve a predetermined reduction in heart rate or blood pressure, which generally varied from 2 to 7 min (25)(26)(27)(28). In preliminary studies in our laboratory, we found that heart rate and mean arterial blood pressure responses to brief asphyxia in immature piglets were too variable to achieve a consistent degree of asphyxia.…”

“…The immature piglet was felt to be an appropriate model for this study because of previous use in studies involving pediatric cardiopulmonary resuscitation (19,23,24) and in studies examining cerebral blood flow, cerebral lipid peroxidation, and Na+,K+-ATPase loss after asphyxia (25)(26)(27)(28). In addition, the 1-to 6-d age precedes the period of peak myelination in pig brain (29), thereby approximating a human newborn.…”

Selective Inhibitors Differentially Affect Cyclooxygenase-Dependent Pial Arteriolar Responses in Newborn Pigs

“…In normoxia, COX-derived metabolites play an important role in the control of VSM in many cerebrovascular regulatory pathways (3). In contrast, uncontrolled COX-activity under hypoxic/ischemic stress may be an ample source of superoxide anions and proinflammatory prostanoids involved in cellular injury and cell death (4,5). In fact, COX-inhibitors have pronounced neuroprotective effects in many neonatal and adult experimental models of hypoxia and stroke.…”

Long-Term Follow-up of Premature Infants Treated With Prophylactic, Intratracheal Recombinant Human CuZn Superoxide Dismutase

“…SOD has also been shown to prevent ischemia/reperfusion injury and neurologic damage in animal models of IVH, suggesting that oxygen radical injury is important in the pathogenesis of neurologic injury in premature infants. 7,15,16 Preliminary reports from a recently completed multicenter, placebo-controlled trial of multiple doses of rhSOD in 301 very low birth weight infants indicate that rhSOD treatment is associated with approximately a 60% decrease in the incidence of severe (grades III and IV) IVH and periventricular leukomalacia, which is known to affect long-term neurodevelopmental outcome. 3,11,12,17 Further demonstrable evidence of the role of rhSOD in preventing severe neonatal pulmonary and neurologic injury will need to await both the short-term and long-term results of multicenter controlled trials with larger number of enrolled infants.…”