Osteocyte Viability After High-Dose Irradiation in the Rabbit

Abstract

The effects of high-dose irradiation on the metabolism of osteocytes were examined with respect to RNA synthesis. A single 50-Gy dose of high-energy electron beam was given to the proximal tibia of rabbits. RNA synthesis by osteocytes was quantified by counting the silver grains on autoradiographs of cultured bone fragments, using 3H-cytidine as a tracer. At four, 12, and 52 weeks after irradiation, RNA synthesis by the irradiated osteocytes was 72, 62, and 79%, respectively, of that by nonirradiated osteocytes. The proportion of labeled osteocytes, conversely, was not reduced at four and 12 weeks, but was significantly reduced at 52 weeks after irradiation. The reduction in the RNA synthesis of osteocytes occurs fairly quickly, whereas reduction in the number of viable osteocytes occurs slowly as a delayed sequela. Histologic examination showed that the partial recovery of RNA synthesis observed at 52 weeks was attributable to the appearance of a fraction of new osteocytes, i.e., subendosteal apposition of new bone to the original, degrading cortex. These observations demonstrate the process of recovery from radiation damage.