Previous studies have demonstrated that
free radicals are formed under hypoxic conditions in newborn piglet brain. To test the hypothesis that the
cyclooxygenase pathway serves as a source of
free radical generation during
hypoxia studies were performed on 24 piglets divided into four groups. Six saline (group 3) and six
indomethacin treated (group 4) were exposed to
hypoxia (FiO2 0.05-0.07) for 60 min.
Cerebral hypoxia was documented biochemically by determination of
ATP and
phosphocreatine. Fluorescent compounds and conjugated dienes were determined as indices of lipid peroxidation.
Free radical formation was determined by using n-tert butyl phenyl nitrone (PBN) as a spin trap agent and measuring spin adduct formation in duplicate using a Varian E-109 spectrometer. Groups 1 and 2 (normoxic) showed no spin adduct formation. Group 3 showed a significant increase in spin adduct formation compared to normoxia (372+/-125 vs. 63+/-15, P<0.001). Hypoxic animals pretreated with
indomethacin had a spin adduct level of 197+/-132 and were similar to normoxic animals.
ATP/PCr levels were the same in groups 3 and 4 denoting the same degree of
cerebral hypoxia in all hypoxic animals. Conjugated dienes increased significantly during
hypoxia as compared to normoxia (0.142+/-0.017 vs. 0.0+/-0.0) and were decreased insignificantly with
indomethacin treatment. Fluorescent compounds were not significantly different among the four groups. Na+,K+-
ATPase activity decreased during
hypoxia but was not preserved in hypoxic animals pretreated with
indomethacin. These data provide direct evidence of the presence of
free radicals during
hypoxia and the contribution of
cyclooxygenase metabolism to their formation.