Osmotic opening of the blood-brain barrier in the rhesus monkey without measurable brain edema

The blood-brain barrier in the rhesus monkey was opened to intravascular Evans blue-albumin, without causing brain edema or altering brain electrolytes, by perfusing 2.5 molal recrystallized d,l-lactamide into the internal carotid artery for 20–30 sec. Gross neurological and behavioral sequelae were absent in 7 of 8 animals with barrier opening, and 2 days after perfusion no statistically significant changes were observed in sodium, potassium or water contents of perfused as compared to unperfused gray and white matters of brains of the 7 normal animals. Brain edema may not have developed because parenchymal albumin was excreted or metabolized by 2 days. It is suggested also that closure of the barrier after several hours prevents salt from accompanying plasma fluid into the brain. Entry of fluid without salt would reduce, before measurable edema developed, any transcapillary osmotic gradient established by prior entry of plasma albumin.