Loss of oxygen tolerance in newborn rabbits: Relationship to changes in eicosanoid and antioxidant levels

Relative tolerance of newborn animals to hyperoxia has been reported. This study investigated the age limitation of oxygen tolerance and mechanisms for its loss. Developmental changes in lungs of normoxic New Zealand rabbits were studied on days 1, 3, 4, 5, and 10 of life. These were contrasted with newborn and 7‐day‐old rabbits exposed to >95% O₂ for 65 hours. Normoxic rabbits demonstrated a decrement in bronchoalveolar lavage (BAL) 6keto‐PGF_1a, thromboxane B₂, and lower lung catalase, total glutathione, and superoxide dismutase with maturation. Newborns were more tolerant to oxygen than 7‐day‐old rabbits. Oxygen exposure beginning on day 1 did not result in identifiable lung damage. Exposure beginning on day 7 resulted in microscopic evidence of injury and significant increases in BAL white cells, neutrophils and protein, and a trend toward higher BAL LTB₄ compared to normoxic age‐matched controls. Antioxidants were higher in the hyperoxic 7 day‐olds, but remained lower than values in hyperoxic newborns. These results suggest that loss of oxygen tolerance in maturing rabbits is related to a developmental decrement in antioxidants and prostacyclin. Pediatr Pulmonol 1989; 7:200‐208.