Effect of Serum Hyperosmolality on Opening of Blood-Brain Barrier for Bilirubin in Rat Brain

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Abstract
The effect of hyperosomolality on the blood-brain barrier for bilirubin was studied in rats. Hyperbilirubinemia was induced in the chronically catheterized rat by infusion of bilirubin at a rate of 30 mg/kg per h for 3 h. After 2 h of bilirubin infusion, 3 levels of hyperosomolality were induced by bolus of urea at 3 different doses: 50, 75 and 100 mmol/kg, respectively. The serum osmolality rose from 297 mosm/l in the control group to 345, 383 and 400 mosml/l in the 3 respective groups. No significant differences were found between the groups in levels of total or free serum bilirubin, serum albumin, blood pH and blood gases. A significant dose relationship was found in both brain bilirubin and brain alubmin content with reference to the serum hyperosmolality. Hyperosmolality apparently causes the opening of the blood-brain barrier for bilirubin in the rat. This adverse phenomenon (hyperosmolality) may play a role in the pathogenesis of kernicterus in infants whose serum bilirubin levels are below the range of saturated bilirubin binding capacity.

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