Initial events in radiation-induced atheromatosis I. Activation of lysosomal enzymes.

Local irradiation of the carotid artery of the hypercholesterolemic rabbit with 2000 rd of X-rays gives rise to infiltration of lipid droplets in the intima and media, becoming visible 3 days after the irradiation. At the same time, acid phosphatase and beta-glucuronidase become activated. These enhanced activities are localized in different cells of the arterial wall. Acid phosphatase activity is localized in the intima, while the beta-glucuronidase activation is found preferentially in the media. A functional heterogeneity of the lysosomal content of the different cells is suggested. A model for the development of the radiation-induced atheromatosis is presented.