Early ultrastructural lesions of apoptosis induced in vivo in two varieties of tissues (thymus and kidneys) after a single whole-body-gamma irradiation of adult mice.

Three groups of adult Swiss albino female mice with an average body weight of 20 grams were exposed to a whole-body irradiation by 137-cesium gamma rays at 2, 4 and 6 Gy (1.4 Gy/min.). For all groups, samples of thymus and kidney were taken 15 min., 2, 6 and 24 hrs. after irradiation and immediately prepared for observation by electron microscopy. In the thymus the earliest significant ultrastructural lesions are observed in the nuclei from the fifteenth minute. These lesions are characterized by condensation of chromatin, convolution and fragmentation of nuclei. Alteration of mitochondria and clarification of cytoplasm in a number of thymocytes are also observed depending on the dose of radiation. These lesions increased according to the length of the post-irradiation period and after six hrs. a great number of macrophages are observed in the thymus. Most often a single macrophage, contain several apoptotic thymocytes, with a maximum number up to eight. In the kidney, serious lesions were observed, affecting both, the nucleus and the cytoplasm of the proximal convoluted tubule cells (PCT). However in these cells, the most significant and earliest lesions consist of wide cytoplasmic clarifications, severe mitochondrial damages, associated with architectural modifications of the brush border and the beta-cytomembranes. These damaged cells have been observed to occur close to normal ultrastructural cells. Less significant ultrastructural alterations are also noticed in different varieties of glomerular cells. In contrast to the serious lesions of the PCT and glomerular cells, no ultrastructural alteration were observed in the distal tubule.