Initial events in radiation-induced atheromatosis. III. Effect on lipase activity

Treatment of large blood vessels with ionizing irradiation leads to the development of atheromatosis when the serum lipid levels are sufficiently high. In order to answer the question whether a disturbed lipid clearance in the arterial wall plays a role in the accumulation of the lipids it was of interest to examine the effect of X-irradiation on the lipase activity. Triglycerol lipase was tested in a homogenate from rabbit carotid arteries, glycerol-tri-oelate was used as a substrate and the hydrolysis assayed at pH 6.4 at 37 degrees C. Under the conditions used, an hydrolytic activity could be measured of 7.5 nmoles . mg prot-1 . hr-1. The lipase activity was also tested in the carotid arteries obtained from rabbits which had been locally irradiated with 20 Gy of X-rays. No clear radiation effect on the lipase activity was found 4, 8, 20, 24 and 72 hours after irradiation. The accumulation of lipids is thought to be caused by a higher influx of lipids from the serum as a result of endothelial damage by X-irradiation rather than a defect in the clearance capacity of the arterial wall.