Initial events in radiation-induced atheromatosis. IV. Lipid composition of radiation-induced plaques.

Ionizing irradiation produced atheromas in the carotid arteries of hypercholesteremic rabbits which received a 0.5% cholesterol diet during 6 weeks. During this relatively short feeding period no atheromas were formed in the nonirradiated carotid arteries. When the animals received this diet for 5 months or a 2% cholesterol diet for 3 months also diet-induced atheromatosis could be found in the latter blood-vessels. A comparison was made between the lipid composition of the diet-induced and the radiation-induced fatty plaques. In all types of plaques the neutral lipids formed about 75 percent of the total lipids, esterified cholesterol being formed the main part of it followed by free cholesterol, phosphatidylcholine and sphingomyelin. A great similarity exists between the lipid composition of the diet-induced fatty plaques of the carotid artery, the aorta and the radiation-induced fatty plaque. It is concluded that radiation is one of the initiating factors in the atheromatous process of the large blood-vessels, leading to lipid infiltration because of injury to the endothelium.