Effect of temperature on postanoxic, potentially neurotoxic changes of plasma pH and free iron level in newborn rats

Abstract

In asphyxiated newborns, iron, released from heme and ferritin and deposited in the brain, contributes to neurodegeneration. Because hypothermia provides neuroprotection, newborn mammals, showing reduced body temperature, might avoid iron-mediated neurotoxicity. However, hypothermia leads to acidosis, which induces hyperferremia. Therefore, we decided to study the effects of body temperature on plasma pH and iron levels in newborn rats exposed to a critical anoxia. Rectal temperature was kept at 33°C (typical of neonates), reduced by 2°C, or elevated to a level typical of healthy (37°C) or febrile (39°C) adults. Arterial blood samples were collected at 0, 10, 20, 30, and 120 min postanoxia. Control samples were obtained from normoxic, temperature-matched neonates. Anoxia tolerance time decreased progressively at rectal temperatures exceeding 33°C. Neither pH nor plasma iron were significantly affected by anoxia at 33°C. Although hypothermia (31°C) resulted in acidosis in normoxic rats, both pH and iron levels were hardly influenced by anoxia. However, acidosis and hyperferremia, proportional to body temperature, developed at 37 and 39°C. In conclusion, reduced body temperature is likely to protect asphyxiated newborns against iron-mediated brain injury.