PLASMA CHOLINE: ITS TURNOVER AND EXCHANGE WITH BRAIN CHOLINE¹

Abstract

—The kinetics of plasma choline (Ch) and the uptake of plasma Ch into the brain were studied by means of intravenous infusion of [2H4]Ch at various rates into anaesthetized and conscious rats. [2H4]Ch levels in both arterial and venous plasma at steady state were linearly related to the infusion rate; however, unlabelled Ch levels were independent of infusion rate. [2H4]Ch levels were higher in the arterial plasma than in the venous plasma, while unlabelled Ch levels were higher in the venous plasma than in the arterial plasma. It was concluded that Ch is being generated in the brain and is released into the venous effluent. The supply of Ch to the plasma is not decreased if the plasma Ch level is increased. The clearance and turnover of Ch in the compartment of its initial distribution are 75 ml kg‐1 min‐1 and 716 nmol kg‐1 min‐1, respectively. The uptake of plasma Ch into the brain is not saturated even at very high levels of plasma Ch.

Effects of middle cerebral artery occlusion on cerebral cortex choline and acetylcholine in rats.

“…It has been shown that Ch exchanges between blood and tissue by either diffusion or a carrier-mediated mechanism with a very high K m . 32 - 33 Furthermore, Choi et al 34 have shown the existence of a rapid component (half time 1.12 minutes) in the time course of the increase of brain Ch specific activity during infusion of deuterated Ch. Thus, the assumption of steady-state conditions after several hours of essentially constant blood flow, as in our experiments, seems justified.…”

Erythrocyte choline concentrations are elevated in manic patients.

“…Blood was withdrawn into tubes containing EDTA, placed on ice, and centrifuged at 0-4"C for 5 min at 2000 X g. Samples of plasma and erythrocytes were extracted as described (5), and Cho was measured by gas chromatography-mass spectrometry using [2H9]Cho as an internal standard (6). The concentration of Li+ was determined by atomic absorption spectrometry (7).…”

Oxotremorine Does Not Enhance Acetylcholine Release From Rat Diaphragm Preparations

“…The tissue was weighed and then extracted overnight as described previously (Gundersen, Jenden & Newton, 1980). A GCMS assay was used to measure ACh and choline in all samples (Jenden, Roch & Booth, 1973;Freeman Choi & Jenden, 1975;Gundersen et al, 1980 The rate of choline output from control preparations ranged from 1.5 to 2.6 pmol mg-1 min 1, while the output after oxotremorine (10 or 100 gM) was 1.4 to 2.3 pmol mg-' min-. Similarly, tissue choline content of controls averaged 56 + 9 pmol/mg, while those exposed to oxotremorine (10 pM) contained 61 ± 7 pmol/mg.…”