Ratio of in vivo incorporation of3H arachidonic acid and14C linoleic acid into liver lipids from normal and diabetic rats

Normal and streptozotocin diabetic rats were injected via the portal vein with a labeled solution containing³H arachidonic acid and¹⁴C linoleic acid (³H/¹⁴C ratio, 0.5) during a 1 min period. Livers were quickly frozen, pulverized, and the lipids extracted and fractioned by thin layer chromatography. The incorporation of³H and¹⁴C into liver lipids was measured and the percentage distribution of radioactivity into the different lipid fractions was determined. The incorporation of¹⁴C linoleic acid and³H arachidonic acid into liver lipids is apparently reduced in rats with severe diabetes. The higher³H/^14C ratio found in the 1,2 diglycerides from diabetic rats may be explained by the apparently smaller incorporation of¹⁴C linoleic acid or by an isotopic dilution attributable to the great availability of this acid in diabetic rats. On the other hand, the higher³H/¹⁴C ratio observed in triglycerides and phospholipids from diabetic rats, due to a relatively large incorporation of³H arachidonic acid into this fraction, may be explained by the affinity of the enzymes involved in their synthesis for some 1,2-diglyceride units. Insulin was unable to correct the changes observed in the diabetic rats.