Northern blot of rat lung RNA. Lanes1, 3, 5, and 7: Total RNA (15 μg/lane) from lung tissues of rats exposed for 1, 3, 5, and 7 days at 85% oxygen. Lane C: Total RNA from lung tissues of unexposed animals. Membranes were hybridized with specific cDNA probes for TIMP-1, TIMP-2, and GAPDH.