Concentration and origin of choline in the rat brain

Summary

In the rat brain the concentration of choline increases with a velocity of 20.5 nMol/g×min immediately after decapitation. This is not due to postmortal disintegration of the tissue but to persisting biochemical reactions in the absence of blood flow. This rise of choline must be considered if the concentration of choline in the living animal is to be established. Taking this fact into account one arrives at a value of 27.5±1.7 nMol Choline/g wet weight.

From the arterio-venous difference of choline concentrations it has been postulated that there is an efflux of 7.2±1.5 nMol/g×min from the brain into the blood.

After i.v. injection of labelled choline the peak of the specific radioactivity of choline in the brain is reached in less than 1 min but amounts to only one tenth of the specific activity of choline in blood-plasma. The specific activities in both compartments decline in parallel. Thus it can be concluded a) that choline penetrates easily through the blood-brain barrier, but the concentration gradient is directed from brain to blood; and b) that choline is continuously formed in the brain, which process permanently dilutes the quantity of labelled choline and prevents the specific activities in blood and brain from becoming equal. The calculations of turnover-rates in the different reactions leading to the choline containing glycerophosphatides are based on the data obtained. On the basis of these findings it is proposed that in the brain phosphorylated derivatives of ethanolamine (phosphorylethanolamine, cytidinediphosphate-ethanolamine) can be methylated to form the respective choline derivatives.