UPTAKE AND METABOLISM OF CHOLINE BY RAT-BRAIN AFTER ACUTE CHOLINE ADMINISTRATION

The present study is concerned with the uptake and metabolism of choline by the rat brain. Intraperitoneal administration of choline chloride (4-60 mg/kg) caused a dose-dependent elevation of the plasma choline concentration from 11.8 to up to 165.2-mu-M within 10 min and the reversal of the negative arteriovenous difference (AVD) of choline across the brain to positive values at plasma choline levels of > 23-mu-M. Net choline release and uptake were linearly dependent on the plasma choline level in the physiological range of 10-50-mu-M, whereas the CSF choline level was significantly increased only at plasma choline levels of > 50-mu-M. The bolus injection of 60 mg/kg of [H-3]choline chloride caused the net uptake of > 500 nmol/g of choline by the brain as calculated from the AVD, which was reflected in a minor increase of free choline level and a long-lasting increase of brain phosphorylcholine content, which paralleled the uptake curve. Loss of label from phosphorylcholine 30 min to 24 h after choline administration was accompanied by an increase of label in phosphatidylcholine, an indication of a delayed transfer of newly taken-up choline into membrane choline pools. In conclusion, homeostasis of brain choline is maintained by a complex system that interrelates choline net movements into and out of the brain and choline incorporation into and release from phospholipids.