THE METABOLISM OF LABELLED ETHANOLAMINE IN THE BRAIN OF THE RAT IN VIVO

Abstract

THERE have been a number of investigations on the incorporation of labelled lipid bases into tissue phospholipids in viva (e.g. ELWYN, WEISSBACH, HENRY and SPRINSON, 1955; BREMER, FIGARD and GREENBERG, 1960;NEMER and ELWYN, 1960;WISE and ELWYN, 1965; BJDRNSTAD and BREMER, 1966). These have usually followed the fate in tissues after intravenous or intraperitoneal injection of the base. In a few experiments the incorporation of a labelled base into brain lipids has been followed after such an injection. Thus, the labelling of a variety of lipids in the brain of the rabbit after the intraperitoneal injection of ~-[3-~~C]serine was investigated by DAVISON, MORGAN, WAJDA and PAYLING-WRIGHT (1 959), and also briefly described by ANSELL and SPANNER (1962a). GROTH, BAIN and PFEIFFER (1958) studied the fate of both 14C-labelled choline and 2-dimethylaminbethanol in brain and liver after intraperitoneal injection, though they did not investigate the lipid fractions into which the bases were incorporated. ANSELL and SPANNER (1962b) showed that 2-dimethylaminoethanol was phosphorylated in brain and Iiver and could be incorporated into a phospholipid.Fewer experiments have been carried out on the fate of intracerebrally injected bases though the fate of their [32P]phosphate esters was studied by KOMETIAM (1963) and ANSELL and CHOJNACKI (1963). The latter found that [32P]phosphorylcholine and -ethanolamine administered by subarachnoid injection, as such or as their cytidine diphosphate esters, were incorporated into their corresponding phospholipids. However, the rate of hydrolysis of the injected material was such that, after 20 min, very little of the ester remained in the brain. KANFER and GAL (1966) injected tritiated erythroand threo-sphingosine intracerebrally and showed that they were incorporated into the sphingomyelin of the 9-day-old rat. In a recent paper ABDEL-LATE and ABOOD (1966) showed that, when serine labelled with 14C in different parts of the molecule was injected, only the DL-[~-'~C] compound was incorporated almost exclusively into phosphatidylserine. The fact that serine enters into many metabolic pathways does not make it a very suitable precursor for studies of this type, and it is not clear from this paper whether any of the label was incorporated into glycerol. In the present paper, experiments on the fate of intracerebrally injected ethanolamine are described. As far as we are aware such experiments have not been carried out previously. Preliminary reports have been given ( SPANNER, 1965, 1966). Materials. [1,2-14C]Ethanolamine hydrochloride was obtained from Calbiochem Ltd., 94 York Street, London W.l. and [2-14C]ethanolamine hydrochloride from the Radiochemical Centre, Amersham, Bucks, England. Pho~phoryl[2-~~C]ethanolamine, was prepared as described for the SaP-labelled compounds (ANSELL and CHOJNACKI, 1966). CDP-[I ,2-14C]ethanolamine was prepared enzymically by the method of CHOJNACKI and METCALFE (1966). The purity of the radioactive chemicals was checked by paper chromatography just before...

Synthesis of choline phospholipids in neuronal and glial cell cultures by the methylation pathway

“…Since the work of [3,4] it was believed that the stepwise methylation of ethanolamine and/or phosphatidylethanolamine in nervous tissue was non-existant or irrelevant until the suggestion that choline might be produced de novo in the rat brain [5][6][7] through methylation of phosphatidylethanolamine. Methyltransferase activity has been shown in rat brain synaptosomes [8,9], suggesting that nervous tissue may have the necessary machinery for the de novo synthesis of phosphatidylcholine.…”

The incorporation of phosphorylethanolamine into the phospholipids of brain microsomes in vitro

“…Only a few studies have examined the in vitro incorporation of labeled precursors into EPG by isolated brain microsomes (3,8), although results obtained both in vitro (3,8) Ipresent address: Ospedale Civile di Como, Como, Italy. and in vivo (9) pointed to the microsomal fraction of brain tissue as the main site for this process.…”

Reversibility of ethanolamine and choline phosphotransferases (EC 2.7.8.1 and EC 2.7.8.2) in rat brain microsomes with labelled alkylacylglycerols

“…Reversibility of both phosphotransferases has been described in other tissues [lo-l 51. Although the brain enzymes are quite active [4,7,, they were thought to be irreversible because the specific radioactivities of the phosphoglycerides do not equilibrate with specific radioactivities of the CDP-choline or CDP-ethanolamine in vivo [23,24]. A competitive inhibition by CMP of the choline phosphotransferase from chicken brain has been described [ 181.…”