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 μmol · 1¹ by a 15-min infusion of unlabeled 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.