The Conversion of Ethanolamine Containing Compounds to Choline Derivatives and Acetylcholine

Abstract

One of the main issues in the understanding of the biochemistry and pathology of the brain concerns the mechanisms by which choline (Cho) is supplied to nerve cells. In brain tissue Cho, originating from endogenous synthesis in the liver (methylation of phosphatidylethanolamine) or as free base from the diet (Pardridge and Oldendorf, 1977; Cornford et al., 1978; Wecker and Trommer, 1984; see also Löffelholz, this volume), can be taken up from the blood circulation through the blood brain barrier. The brain itself is, however, capable of producing Cho from endogenous sources (Mozzi et al., 1979; Blusztajn et al., 1979; Crews et al., 1980; Zeisel, 1985; Blusztajn et al., 1987). In contrast to the fluctuating plasma levels, which are directly dependent upon diet, the brain tissue seems to have a homeostatic mechanism that maintains Cho at a steady state level. At low plasma concentrations of Cho there is more Cho exiting the brain than entering it producing a negative arterio-venous difference (AVD). A high plasma Cho level “forces” its uptake in the brain and raises its concentration (Dross and Kewitz, 1972; Tucek, 1978; Klein et al., 1991).