The metabolism of exogenous fatty acid by preimplantation rat embryos

The rate of oxidation of exogenous palmitic acid to carbon dioxide and that of its incorporation into lipids were examined in embryos cultured in the bovine serum albumin-fatty-acid-free BMOC-III medium with or without carbohydrate substrates, respectively. Rat embryos at various stages of development, including 1-cell to blastocyst stages, were cultured in the medium containing C-14-palmitic acid and the rate of this exogenous fatty acid oxidized by embryos were estimated according to the amount of (CO2)-C-14 trapped through a 4 h of culture period. The rate of fatty acid oxidation was relatively constant from 1-cell to 4-cell. The (CO2)-C-14 production rate increased significantly between 4-cell and 8-cell stages and continued to rise to the blastocyst stage. In the incorporation experiment, 8-cell embryos were cultured for 2 h in the medium containing H-3-palmitic acid and total lipids extracted from embryo were separated into various neutral and polar lipids by thin-layer chromatography. Effect of 2-h exposure to H-3-palmitic acid culture experiment showed that the concentration of tritium palmitic acid used did not cause any retardation of 8-cell rat embryo development. More than 70% of radioactivity were recovered in triacylglycerols and 21% were in fatty alcohols in neutral lipids, while more than 90% were in choline phosphatides in polar lipids. The recoveries of radioactivity in chloroform soluble and aqueous products of the alkaline methanolysis of embryo lipids were 87.8 and 12.3%, respectively. The results of the present experiments indicate that fatty acids were certainly utilized for energy production and for the synthesis of various lipids through beta-oxidation, TCA cycle and lipogenesis in embryos at preimplantation stage.