Focal differences in lipid metabolism of the young pig aorta: III. Influence of insulin on lipogenesis from [1- 14C]acetate

The influence of insulin on the incorporation in vitro of [1- 14C]acetate into lipid in areas of Evans blue uptake (blue areas) or no dye uptake (white areas) in normal young pig aorta has been investigated. Insulin at a physiological concentration of 25 μU/ml significantly increased [1- 14C]acetate incorporation into total lipid in white areas. Incorporation was significantly greater in free fatty acid, triglyceride, and phospholipid but not in free sterol plus diglyceride or cholesteryl ester. The degree of insulin stimulation of labeled acetate incorporation was significantly greater for phospholipid than for free fatty acid or triglyceride. In individual phospholipids, insulin significantly enhanced incorporation of label into sphingomyelin and phosphatidyl choline but not into any other phospholipid examined. In adjacent blue areas, in contrast to white areas, insulin at 25 μU/ml did not significantly influence [1- 14C]acetate incorporation into any lipid examined. In fact, incorporation into total lipid in blue areas was unaffected by insulin even at concentrations as great as 10,000 μU/ml. These results indicate that in addition to differences in lipid metabolism demonstrated previously, blue and white areas in the normal young pig aorta also show differences in the regulation of lipid metabolism as measured by the incorporation of [1- 14C]acetate in response to insulin. It is tentatively suggested that the medial metabolic differences and the differential response to insulin may be sequels to the greater influx of plasma constituents through the endothelium in blue relative to white areas. The potential role of these findings in early atherogenesis is considered.