Steady-state concentrations of choline and acetylcholine in rat brain parts during a constant rate infusion of deuterated choline.

An intravenous infusion of deuterated choline at constant rate for 6 min (5 or 25 mumoles kg-1 min-1) significantly increases the concentration of choline in plasma, occipital cortex and striatum. Both 5 and 25 mumoles kg-1 min-1 increase the concentration of acetylcholine in cortex but only 25 mumoles kg-1 min-1 increases the acetylcholine content in striatum. In contrast, 1 mumole kg-1 min-1 does not change the choline or acetylcholine content in cortex or striatum. A single pulse injection of choline (200 mumoles kg-1) causes a significant increase in the concentration of choline in striatum 30 sec following injection. The choline content returns to normal values within 2 min. These studies show that when a pulse injection of a non-tracer dose of radioactive choline is used to measure brain acetylcholine turnover rate the maintenance of steady state must be verified within seconds after the pulse injection of radioactive choline. When constant infusion of deuterated choline is used to measure turnover rate of acetylcholine in the brain of rats, a dose of 1 mumole kg-1 min-1 appears to be a maximal infusion rate.