1. 1. Adult rats were given by stomach tube 10 μC of methyl [1-14]stearate dissolved in either corn oil or Sterculia foetida seed oil. After 3 h they were injected with 200 μC of [3H]acetate and were sacrificed 1 h later. The 3H and 14C specific radioactivities of the stearic acid in the liver lipids of the corn oil controls were nine times as high as in the oleic acid. When S. foetida oil was in the diet, the 14C ratio was about 1500 whereas the 3H ratio was only 14, showing that stearic acid desaturation to oleic acid was inhibited but not acetate conversion to oleic acid. 2. 2. When a similar study was carried out in which methyl [1-14C]laurate and methyl [11,12-3H2]stearate were given, the 3H ratio in the corn oil controls was about 8 and the 14C ratio was about 2, indicating that laurate acted as a precursor for oleic acid biosynthesis. Inclusion of S. foetida seed oil resulted in an increase in the 3H ratio to about 1600 whereas the 14C ratio was increased to only 12, showing that lauric like acetate conversion is not inhibited by cyclopropene fatty acids. Permanganate oxidation studies of the isolated octadecenoic acids indicated that when S. foetida seed oil was given, about 90% of the octadecenoate radioactivity was in oleic, and 90% of the oleic acid activity due to 14C was in the azelaic acid fraction. This suggests the intact utilization of lauric acid for oleic acid synthesis, probably by β,γ-desaturation followed by elongation. © 1969.
