Comparison of Postasphyxial Resuscitation with 100% and 21% Oxygen on Cortical Oxygen Pressure and Striatal Dopamine Metabolism in Newborn Piglets

Abstract

The present study tests the hypothesis that ventilation with 100% 02 during recovery from asphyxia leads to greater disturbance in brain function, as measured by dopamine metabolism, than does ventilation with 21 % oxygen . This hypothesis was tested using mechanically ventilated, anesthetized newborn piglets as an animal model . Cortical oxygen pressure was measured by the oxygen-dependent quenching of phosphorescence, striatal blood flow by laser Doppler, and the extracellular levels of dopamine and its metabolites by in vivo microdialysis . After establishment of a baseline, both the fraction of inspired oxygen (Fi0 2) and the ventilator rate were reduced in a stepwise fashion every 20 min over a 1-h period . For the subsequent 2-h recovery, the animals were randomized to breathing 21 or 100% oxygen . It was observed that during asphyxia cortical oxygen pressure decreased from 36 to 7 torr, extracellular dopamine increased 8,300%, and dihydroxyphenylacetic acid and homovanillic acid decreased by 65 and 60%, respectively, compared with controls . During reoxygenation after asphyxia, cortical oxygen pressure was significantly higher in the piglets ventilated with 100% oxygen than in those ventilated with 21 % oxygen (19 vs . 11 torr) . During the first hour of reoxygenation, extracellular dopamine levels decreased to -200% of control in the 21 % oxygen group, whereas these levels were still much higher in the 100% oxygen group (-500% of control) . After -2 h of reoxygenation, there was a secondary increase in extracellular dopamine to -750 and -3,000% of baseline for the animals ventilated with 21 and 100%, respectively . It is concluded that although 100% Fi02 after asphyxia increases cortical oxygenation compared with 21 % Fi02, it also results in poorer recovery in dopamine metabolism and higher secondary release of striatal dopamine . The resulting increased extracellular levels of dopamine may exacerbate posthypoxic cerebral injury . Key Words: Hypoxia-Hyperoxia-Dopamine-Brain -Newborn . J. Neurochem. 64, 292-298 (1995) .Hyperoxia is currently one of the most effective treatments for decreased pulmonary arterial pressure 292

The effect of hypothermia on neuronal viability following cardiopulmonary bypass and circulatory arrest in newborn piglets☆☆☆

“…Our earlier studies have shown that during hypoxia there was a large increase in the level of striatal extracellular dopamine, followed by a decrease of dopamine almost to the control level during 1 h of post-hypoxic reoxygenation. However, at about 2 h into the post-hypoxia period there was a secondary increase in extracellular dopamine indicating substantial release of dopamine from the neurons [18]. Horiguchi et al [19] reported that hypothermia (32 °C) significantly inhibited the ischemia-induced increase in extracellular dopamine in the striatum of rats.…”

5-HT2 receptors modulate excitatory neurotransmission to cardiac vagal neurons within the nucleus ambiguus evoked during and after hypoxia

“…Under these control conditions oxygen pressure levels in the slice tissue were found to be 583 Torr at the upper surface of the tissue and 157 Torr in the core of the slice (Neff et al, 2004). Although these values are higher than brain oxygen pressure found in in-vivo studies (Huang et al, 1995; Song et al, 1997), we have labeled these as normoxia given their widespread use as control conditions for in-vitro electrophysiological experiments. When the solution is equilibrated with 20% O 2 the O 2 tension in the tissue decreases to 142 Torr at the surface and to 0 Torr in the core of the slice and this has been used previously as a model of hypoxia (Neff et al, 2004).…”

Effect of Resuscitation with 21% Oxygen and 100% Oxygen on NMDA Receptor Binding Characteristics Following Asphyxia in Newborn Piglets

“…Although similar findings were observed in this study, the use of 100% oxygen following asphyxia did not result in greater cerebral cellular membrane dysfunction in newborn piglets even though free radical generation and energy failure tended to be higher. Other effects on neurotransmitter metabolism have reported a disruption in striatal dopamine metabolism following postasphyxial resuscitation with 100% oxygen [38].…”