Glycerol-3-phosphate content and triacylglycerol synthesis in isolated hepatocytes from fed and starved rats

For a given load of fatty acids the perfused liver or isolated hepatocytes from fed rats esterify a greater proportion of the incoming fatty acids than do similar preparations from starved rats. In the latter oxidation is increased relative to esterification [l-3]. Since esterification and oxidation constitute a branch-point, the nutritional and hormonal control of esterification and oxidation can theoretica~y be exerted either on one arm of the branch-point or in reciprocal manner on both arms simultaneously. Recently, evidence has been offered that fatty acid oxidation is controlled by the hepatic levels of carnitine and especially of maionyl-CoA, a potent inhibitor of carnitine palmitoyltransferase I [4]. It is not clear, however, whether there exists a separate control on esterification. The moderate decrease in the activity of glycerol3-phosphate acyltransferase that is observed in the starved state 15-71, has been proposed as a possible factor regulating esterification. The availability of glycerol3-phosphate has been considered as another regulatory factor [ 1,7-l 11. However,a wide range of overlapping glycerol-3-phosphate concentrations has been reported for fed and starved animals [2,10,12-151. Moreover, interpretation of the data is complicated by the fact that the concentration range of glycerol-3-phosphate which might be regulatory in the intact hepatocyte, is not known. Here, the intracellular concentration range within which glycerol-3-phosphate exerts a regulatory function, was determined. 2. MateriaIs and methods