Late ultrastructural changes in the mouse coronary arteries and aorta after fission neutron or 60Co γ irradiation

The ultrastructure of the coronary arteries and the aorta of the B6CF1 mouse from 1 to 24 months after irradiation is described. Radiation treatment, initiated at 4 months of age, included single total-body doses of 788 γ rad or 240 fission neutron rad, and fractionated total-body doses of 823 γ rad or 240 fission neutron rad (24 fractions given in 23 weeks). In addition, mice given the high γ dose of 2690 rad (fractionated), and relatively low neutron doses (80 rad single and 20 or 80 rad fractionated) were studied at 18 months after initiation of irradiation in order to increase the dose range for estimation of the relative biological effectiveness (RBE). In control mice, at 12 months into the experiment, there was little evidence of degeneration of the coronary arteries and aorta. At 18 months, these vessels showed a slight amount of smooth muscle degeneration and fibrosis, while at 24 months lesions were more severe and there was relatively less distinction between control and treated groups (788 γ rad or 240 neutron rad). Degenerative changes in the larger coronary arteries and the aorta first appeared at 3 to 6 months after irradiation, and became progressively more severe at later times (12 to 24 months). The major changes included smooth muscle degeneration, fibrosis, and accumulations of debris and extracellular matrix