The dependence of the blood to brain passage of radioactive sodium on blood pressure and temperature.

Brain sodium uptake (BSU) was calculated from estimated radioactivities of brain and blood, collected from rats which were given [24Na]sodium chloride 30 min and [22Na]sodium chloride 1 min before killing. The calculated BSU values, when plotted against the average blood pressure of the animal during the survival time of 30 min, showed a linear dependence of BSU on blood pressure. In another series of animals, in which in addition to variation of the blood pressure as in the former series, the brain was cooled to 15 degrees C, the resulting regression line showed the same slope, but a significantly lower intercept than at normal temperature. The results indicate the existence of a blood pressure-dependent component of sodium passage, reflecting the exchange of fluid at the blood-brain interface as governed by the Starling hypothesis, and an additional component which being temperature dependent, presumably constitutes an active transport mechanism.