Late effects of heavy charged particles on the fine structure of the mouse coronary artery

A pilot study was conducted to evaluate ultrastructureal changes in the coronary arteries of the B6CF1 mouse 15 months after irradiation with photons or heavy charged particles. Irradiations, given at 4 months of age, included single upper-body doses of 1.6 Gy 40Ar, 0.2, 0.4, 0.8, or 3.2 Gy 20Ne, 0.1 or 3.2 Gy 12C, and 1.6, 3.2, or 7.0 Gy 60Co γ. Coronary artery degeneration was found in both irradiated and unirradiated control animals. Radiation appeared to produce more severe degenerative changes than that seen in the age-matched controls. The major changes included medial smooth muscle degeneration, fibrosis, accumulation of debris, and extracellular matrix. On the basis of quantitative analysis, about 12% of the smooth muscle areas examined showed deterioration in the age-matched unirradiated animals. This percentage was increased significantly at doses above 0.1 Gy, ranging between 20 (P < 0.01) and 44% (P < 0.001), in the irradiated groups. A single dose of only 0.2 Gy 20Ne ions produced significant damage to the smooth muscle cells. Over at least part of the dose range explored, smooth muscle damage increased with dose for all radiation qualities. Although heavy charged particles are more effective in producing damage than photons, the present data are insufficient to demonstrate a LET dependence among charged particles or estimate relative biological effectiveness