COMPARISON OF POSTASPHYXIAL RESUSCITATION WITH 100-PERCENT AND 21-PERCENT OXYGEN ON CORTICAL OXYGEN-PRESSURE AND STRIATAL DOPAMINE METABOLISM IN NEWBORN PIGLETS
Cc. Huang et al., COMPARISON OF POSTASPHYXIAL RESUSCITATION WITH 100-PERCENT AND 21-PERCENT OXYGEN ON CORTICAL OXYGEN-PRESSURE AND STRIATAL DOPAMINE METABOLISM IN NEWBORN PIGLETS, Journal of neurochemistry, 64(1), 1995, pp. 292-298
The present study tests the hypothesis that ventilation with 100% O-2
during recovery from asphyxia leads to greater disturbance in brain fu
nction, 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 pres
sure was measured by the oxygen-dependent quenching of phosphorescence
, striatal blood flow by laser Doppler, and the extracellular levels o
f dopamine and its metabolites by in vivo microdialysis. After establi
shment of a baseline, both the fraction of inspired oxygen (FiO(2)) an
d 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 r
andomized to breathing 21 or 100% oxygen. It was observed that during
asphyxia cortical oxygen pressure decreased from 36 to 7 torr, extrace
llular dopamine increased 8,300%, and dihydroxyphenylacetic acid and h
omovanillic acid decreased by 65 and 60%, respectively, compared with
controls. During reoxygenation after asphyxia, cortical oxygen pressur
e 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 t
o similar to 200% of control in the 21% oxygen group, whereas these le
vels were still much higher in the 100% oxygen group (similar to 500%
of control). After similar to 2 h of reoxygenation, there was a second
ary increase in extracellular dopamine to similar to 750 and similar t
o 3,000% of baseline for the animals ventilated with 21 and 100%, resp
ectively. It is concluded that although 100% FiO(2) after asphyxia inc
reases cortical oxygenation compared with 21% FiO(2), 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.