Neonatal blood plasma is less susceptible to oxidation than adult plasma owing to its higher content of bilirubin and lower content of oxidizable Fatty acids.

Newborn infants are susceptible to a range of problems attributed to excessive production of free radicals. Because of a higher content of antioxidants, above all bilirubin, and a lower content of oxidizable lipids, newborn plasma should be better protected against oxidation than adult plasma. To test this hypothesis, we measured the susceptibility of plasma to in vitro oxidation in microsamples (7 microL) from 57 healthy newborns and 18 adults. Heparin plasma was diluted 150-fold and oxidized by 50 microM Cu2+. Oxidation was monitored as an increase in sample absorbance at 234 nm. Plasma oxidizability was found to be significantly lower in newborns than in adults. Accordingly, the level of bilirubin, an important antioxidant, was significantly higher, and the level of polyunsaturated fatty acids, a major substrate of lipid peroxidation, was significantly lower in newborn plasma. In addition, plasma oxidizability correlated positively with the level of polyunsaturated fatty acids and negatively with that of bilirubin. These data indicate that plasma is better protected against oxidative stress in newborns than in adults, owing to its higher content of antioxidants like bilirubin and its lower content of oxidizable lipids.