Phospholipids and acylglycerols biosynthesis and 14CO2 production from [14C]glycerol in the bovine retina: the effects of incubation time, oxygen and glucose

When the entire bovine retina was incubated in 95 μm [U-¹⁴C]glycerol, the precursor penetrated the tissue and it was used for the de novo biosynthesis of glycerolipids. A minor proportion of the labeled glycerol turned to ¹⁴CO₂. The following labeling sequence was suggested: glycerol phosphorylation, double acylation, phosphatidate, diacylglycerol and triacylglycerol. Under aerobic conditions, a remarkable channelling of the label towards triacylglycerol biosynthesis was found. Comparatively, much lower specific activities were encountered in all the phosphoglycerides, phosphatidylinositol biosynthesis attaining the highest rate. At an early incubation time, the peak labeling of total phosphoglycerides was closely followed by phosphatidate radioactivity. The phosphoglyceride content slightly decreased in retinas incubated in the absence of added glucose. Anoxia, however, resulted in a diminution of the concentration of the diacylglycerophosphatides of choline and of ethanolamine and in a significant increase of their monoacyl derivatives. In an incubation medium devoid of glucose, the specific activity in the diacyl and monoacylglycerophosphatides of choline and ethanolamine was significantly raised. Furthermore, there was a dramatic decrease in the triacylglycerol biosynthesis without modification of glycerol incorporation in the polar lipids and augmented the labeling in the lipid-free tissue residue. Anoxia abolishes the uptake of glycerol in retina lipids.