Low level of lipid peroxidation in newborn rats. Possible factors for resistance in hepatic microsomes.

Hepatic rough and smooth microsomes of newborn rats show less sensitivity to ascorbate- and NADPH-induced lipid peroxidation as compared to those of adult rats. Though optimum concentrations of Fe2+, ascorbate and Fe3+ significantly increase lipid peroxidation in both age groups, the lipid peroxidation observed in newborns is much less compared with that of adults. Microsomal fractions from newborn rats contain significantly lower amounts of phospholipid, NADPH cytochrome c reductase, cytochrome P-450 and a lower degree of unsaturation in lipids. These fractions also exhibit high cholesterol:phospholipid ratios. The resistance to lipid peroxidation observed in the newborns appears to be due to the low availability of substrate and high cholesterol:phospholipid ratio.