In Vivo Turnover Rate of Acetylcholine in Rat Brain Parts at Elevated Steady‐State Concentration of Plasma Choline

Abstract

Cortical and striatal turnover rates of acetylcholine TR(ACh) were estimated by applying steady-state tracer kinetics in rats killed by microwave irradiation following a constant i.v. infusion of 3H-Ch. In control rats TR(ACh) was 3.6 nmol . g-1 . min-1 in the cortex and 23.8 nmol . g-1 . min-1 in the striatum. When steady-state plasma concentrations of Ch were increased from 17 to 140 mumol . 1-1 by a 15-min infusion of unlabelled Ch the corresponding TR(ACh) were 3.6 nmol . g-1 . min-1 and 21.4 nmol . g-1 . min-1, respectively. These results indicate that increased plasma levels of Ch are not accompanied by increased synthesis of brain ACh.