Radiation-Induced Changes in the Fine Structure of the Heart: Comparison of Fission Neutrons and 60 Co g Rays in the Mouse

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Abstract
The ultrastructural changes in mouse cardiac muscle and cardiac vasculature from 4 days to 1 yr after irradiation are described. Radiation treatment consisted of single-dose, total-body exposures to 240 rad fission neutrons or 788 rad 60Co .gamma.-rays. Cardiac muscle showed areas of focal myofibrillolysis, myofibrillar degeneration with loss of entire myofibrils, presence of lipid bodies and of lysosomal-like bodies, and partially vacuolated mitochondria in some myocytes. There was apparently no Z-band thickening or disruption. Intercalated disks were sometimes dissociated and interstitial fibrosis was occasionally seen surrounding myocytes. The cardiac microvasculature showed progressive degenerative lesions, including swollen endothelial cells, cytoplasmic blebs and extensions, myelinlike figures, vacuolated mitochondria, and thrombi that adhered to irregularities of the endothelial surface. After both forms of irradiation, smooth muscle degeneration and fibrosis in coronary arteries first appeared at 3 mo. and became progressively more severe at 6 and 12 mo. Quantitative estimations of myofibrillar and capillary degeneration revealed that damage was most severe at 1-3 mo. in both neutron- and .gamma.-irradiated groups. At 12 mo., significant capillary degeneration was still present, but the condition of the myofibrils was comparable to that in controls. Quantitative differences between neutron- and .gamma.-irradiated groups were not statistically significant.

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