Focal differences in lipid metabolism of the young pig aorta. IV. Influence of insulin and epinephrine on lipogenesis from (14C)-U-glucose.

We have previously demonstrated that focal areas of the normal young pig aorta, identified by their ability to take up the protein-binding azo dye Evans Blue, and characterized by an increased endothelial permeability to proteins, exhibit a variety of differences in lipid metabolism, relative to adjacent tissue showing no dye uptake. It was the purpose of the present study to examine the influence of insulin and epinephrine on lipogenesis from [¹⁴C]-U-glucose in these blue and white areas. In white areas, insulin at 25 μU/ml significantly stimulated incorporation of labelled glucose into phosphatidyl choline. By contrast, insulin did not significantly influence glucose incorporation into any lipid examined in adjacent blue areas. In fact, incorporation of [¹⁴C]-U-glucose into blue area lipids was unmodified by insulin at concentrations as great as 10,000 μU/ml. Insulin did not influence the uptake of [¹⁴C]-1-l-Arabinose or [¹⁴C]-U-sucrose in either blue or white areas suggesting that:—(1) insulin-stimulated lipogenesis in white areas is not accompanied by increased glucose uptake and (2) the difference in lipogenic response to insulin between blue and white areas is not due to an insulin-mediated difference in glucose uptake. Epinephrine, in contrast to insulin, did not influence lipogenesis in either blue or white areas.These studies indicate that, in addition to the focal differences in lipid metabolism previously demonstrated, there are also focal differences in the regulation of lipid metabolism in the macroscopically normal young pig aorta. These focal medial metabolic differences, together with differences in the regulation of aortic lipid metabolism may be secondary to the greater trans-endothelial influx of plasma constituents in blue areas. Their role, if any, in the early phases of atherogenesis needs clarification.