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.