Brain osmolyte content and blood-brain barrier water permeability surface area product in osmotic edema.

Brain edema was induced in adult rats by intraperitoneal injection of distilled water equivalent to 15% of the animal's body weight. Mean +/- SEM serum osmolality fell from 291 +/- 3 mOsm to 253 +/- 4 mOsm during the next hour while cerebral gray matter water content increased from 79.5 +/- 0.2% to 80.9 +/- 0.2%. Gray matter content of sodium, potassium, taurine, glycine, glutamine, and glutamate were unchanged. However, the blood-brain barrier permeability/surface area product for water decreased by 40%. This alteration in water permeability may represent a response to limit water influx during the first hour of hypoosmotic brain edema.