Factors which influence the availability of choline to brain

When unesterified (free) choline leaves the brain, in vivo, then enters it, jugular venous levels of free choline result that are higher than those of arterial blood entering brain. These concentration differences range from 1 nmol/ml in humans to 1-12 nmol/ml in rats. The author attempts to find where this free choline comes from. Adult male rats were used in the studies and their brains were removed and chilled on ice after decapitation. Choline was measured using a radioenzymatic method in which it was first isolated from the tissue by liquid cation exchange chromatography, then combined with AT(32P) in a reaction catalyzed by choline kinase. When whole brains from decapitated rats were incubated in situ at 37 C, free choline concentration rose 8-fold during a 30 minute period. A similar increase in choline content was observed in rat brain which was homogenized in pH 7.4 Hepes buffer, and incubated in vitro