Effect of serum hyperosmolality on opening of blood-brain barrier for bilirubin in rat brain.

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/h for three hours. After two hours of bilirubin infusion, three levels of hyperosmolality were induced by bolus of urea at three 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 three 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 albumin content with reference to the serum hyperosmolality. The results indicate that hyperosmolality causes opening of the blood-brain barrier for bilirubin in the rat. It may be speculated that 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.