Synthesis of Glycerides and Phospholipids in Rat Liver

1. The effects on glycerolipid synthesis of a series of compounds including many drugs were investigated in cell-free preparations and slices of rat liver. 2. p-Chlorobenzoate, p-chlorophenoxyisobutyrate, halofenate, D-amphetamine, adrenaline, procaine and N-[2-(4-chloro-3-sulphamoylbenzoyloxy)ethyl]norfenfluramine had little inhibitory effect on any of the systems investigated. 3. Two amphiphilic anions, clofenapate and 2-(pchlorophenyl)-2-(m-trifluoromethylphenoxy)acetate, both inhibited glycerol phosphate acyltransferase and diacylglycerol acyltransferase at approx. 1.6 and 0.7imM respectively. Clofenapate (1 mM) also inhibited the incorporation of glycerol into lipids by rat liver slices without altering the relative proportions of the different lipids synthesized. 4. The amphilic amines, mepyramine, fenfluramine, norfenfluramine, hydroxyethylnorfenfluramine, N-(2-benzoyloxyethyl)norfenfluramine, cinchocaine, chlorpromazine and demethylimipramine inhibited phosphatidate phosphohydrolase by 50% at concentrations between 0.2 and 0.9mm. The last four compounds inhibited glycerol phosphate acyltransferase by 50% at concentrations between 1 and 2.6mm. None of the amines examined appeared to be aneffectiveinhibitor of diacylglycerol acyltransferase. 5. Norfenfluramine, hydroxyethylnorfenfluramine and N-(2-benzoyloxyethyl)norfenfluramino produced less inhibition of glycerol incorporation into total lipids than was observed with equimolar clofenapate. The major effect of these amines in liver slices was to inhibit triacylglycerol and phosphatidylcholine synthesis and to produce a marked accumulation of phosphatidate. 6. The results are discussed in terms of the control of glycerolipid synthesis. They partly explain the observed effects ofthe various drugs on lipid metabolism. The possible use of these compounds as biochemical tools with which to investigate the reactions of glycerolipid synthesis is considered.