HYPEROXIC EXPOSURE OF DEVELOPING RAT LUNG DECREASES TROPOELASTIN MESSENGER-RNA LEVELS THAT REBOUND POSTEXPOSURE

These studies were undertaken to determine whether tropoelastin messag e expression in lung parenchymal tissue is altered in rats reared in a n hyperoxic environment during the period of time that alveolar septat ion normally occurs. Rat pups were exposed to >95% oxygen from days 4 to 14 and killed during the exposure and recovery periods. Results of in situ hybridizations indicated a delay in peak tropoelastin (TE) mes sage levels in oxygen-exposed rats vs. controls, day 16 vs. day 11, re spectively. In addition, lung parenchymal TE mRNA levels in the oxygen -exposed pups remained elevated through day 23, 1 wk after TE mRNA lev els had decreased in controls. These observations suggest that the reg ulatory control of elastin synthesis during lung alveolar septation is altered by hyperoxic exposure. In a separate experiment, rat pups wer e exposed to >95% oxygen during the period of alveolarization and foll owed for 4 wk postexposure. Pulmonary function measurements were condu cted to determine whether lung function was altered postexposure and, if so, whether recovery occurred. We also used stereological technique s to quantitate the total length of lung parenchymal elastic fibers to determine whether elastic fiber content in the oxygen-exposed pups wa s restored to normal levels during the month postexposure. Although th e total length of elastic fibers in lung parenchyma was found to be gr eater in oxygen-exposed than control pups from postnatal days 22 to 41 , pressure-volume curves indicated that lungs of the oxygen-exposed pu ps tended to be more compliant than controls, suggesting that abnormal elastic fiber assembly might have been a contributing factor.