Brain sodium uptake after choroid plexectomy.

When in a (control) series of rats brain sodium uptake (BSU) -- as calculated from estimated radioactivities of brain and blood following the injection of [24Na]sodium chloride 30 min and [22Na]sodium chloride one minute before killing -- was plotted against average arterial blood pressure of the animals during the 30 min survival period, a linear dependence of BSU on blood pressure was observed. In another series of animals, in which the choroid plexuses of the fourth and both lateral ventricles had been removed, the regression line showed the same slope, but a significantly lower intercept. On the other hand, a series of rats which had been subjected to a sham operation without removal of the choroid plexuses, showed a regression line not different from the control series. The results indicate that probably the blood pressure independent component of brain sodium uptake, as represented by the intercept of the regression line, for the greater part constitutes cerebrospinal fluid secretion by the choroid plexus.