The mechanism of opening of the blood-brain barrier by hypertonic saline

The permeability of the blood-brain barrier was assessed in the cat, using Evan's blue as circulant. Regional blood flow and vascular resistance in various areas of brain were measured using radioactive microspheres. Cardiac output (CO), blood pressure (BP), heart rate (HR), pH, pO₂ and pCO₂ were also measured. Hypertonic saline (5 M, 0.5 ml/kg), administered intravenously, increased the staining of the brain substance. It also produced a marked increase in cerebral blood flow after 5 min and a marked decrease in blood flow to all the regions of the brain after 20 min. The flow returned to normal after 40 min. The vascular resistance decreased at 5 min, increased at 20 min and returned to normal at 40 min. Cardiac output increased significantly at 5 min and decreased at 20 min, while at 40 min it returned to normal. Blood pressure decreased at 5 min, increased at 20 min, while heart rate steadily decreased. A complete recovery of cardiac output, blood pressure and heart rate occurred in 1 hr. No change was observed in pH, pCO₂ and pO₂. It is concluded that intravenous administration of hypertonic saline causes marked haemodynamic changes and increases the permeability of the blood-brain barrier due to transient impairment of autoregulation.