[Hypotension and diffusion of Rb-86 in the rat brain]

Studies on the permeability of potassium at the blood-brain barrier of rats show that, under normal conditions, the concentration of this ion is kept constant although wide variations in plasma are present. 86Rb has been utilized as an analog of K+. The permeability constant for control animals (arterial blood pressure of 100 +/- 3 mmHg), has been determined in 0.926 +/- 0.02 ml X g-1 X h-1 (brain cortex), and 1.107 +/- 0.12 ml X g-1 X h-1 (cerebellum). The permeability constant for hypotensive animals (arterial blood pressure of 40 +/- 5 mmHg), has been determined in 0.473 +/- 0.03 ml X g-1 X h-1 (brain cortex), and 0.608 +/- 0.06 ml X g-1 X h-1 (cerebellum). During hypotension there is a marked decrease in the permeability constant of 86Rb at the blood-brain barrier of rats.