CELL-DEATH INDUCED BY GAMMA-IRRADIATION OF DEVELOPING SKELETAL-MUSCLE

Newborn Sprague-Dawley rats were exposed to a single dose of 2 Gy gamm a rays and killed from 6 h to 5 d later. Increased numbers of dying ce lls, characterised by their extreme chromatin condensation and often n uclear fragmentation were seen in skeletal muscle 6 h after irradiatio n. Dying cells decreased to nearly normal values 48 h later. In situ l abelling of nuclear DNA fragmentation identified individual cells bear ing fragmented DNA. The effects of gamma rays were suppressed followin g cycloheximide i.p. at a dose of 1 mu g/g body weight given at the ti me of irradiation. Taken together, the present morphological and pharm acological results suggest that gamma ray induced cell death in skelet al muscle is apoptotic, and that the process is associated with protei n synthesis. Finally, proliferating cell nuclear antigen-immunoreactiv e cells, which were abundant in control rats, decreased in number 48 h after irradiation. However, a marked increase significantly above nor mal age values was observed at the 5th day, thus suggesting that regen eration occurs following irradiation-induced cell death in developing muscle.