Bilirubin oxidation by brain mitochondrial membranes is not affected by hyperosmolality

Brain mitochondrial membranes oxidize bilirubin at a rate that may be biolo gically significant. Hyperosmolality delays clearance of bilirubin from rat brain, We hypothesized that this might be due to a decrease in brain bilir ubin metabolism, Rats were anesthetized and infused with 75 mM/kg urea i.v. over 5 min (n = 7) and sacrificed at 1 h; control rats (n = 7) had no trea tment. Crude mitochondrial membrane fractions ('P2') were produced by homog enization and differential centrifugation in sucrose. The change in optical density at 440 nM of a 10-mu mol/l bilirubin solution was measured after 6 0 min incubation with mitochondrial membranes, Hyperosmolality did not affe ct bilirubin oxidation by brain mitochondrial membranes (t = 1.27, p = 0.23 by unpaired t-test), The lack of effect of hyperosmolality on bilirubin ox idation by brain mitochondrial membranes suggests that decreased clearance of bilirubin from brain in hyperosmolality may be related to changes in tra nsfer of bilirubin across the blood-brain barrier, Copyright (C) 2000 S. Ka iger AG. Basel.