Ceruloplasmin mRNA levels in hypoxic mouse liver. (A) Northern blotting of liver RNA derived from mice exposed to 7.5% O₂ for 0 to 3 days. Hybridization signals obtained with a ribosomal protein L28 probe served as a control for loading and blotting efficiency. (B) Phosphoimager quantification of band intensities shown in panel A. Mean ceruloplasmin to L28 mRNA ratios ± SD of n = 3 mice for each time point are given.