Dose- and time-dependent radiation inhibition of RNA and glycosaminoglycan synthesis in embryonic cartilage: an in vitro study.

Radiation effects on the RNA and glycosaminoglycan (GAG) synthesis of embryonic cartilaginous tibiae were studied in vitro during a 4- or 7-day culture period. Before being cultured, tibiae received single radiation doses of 20, 50 or 100 Gy. The counterparts served as sham-irradiated controls. At different times after irradiation, irradiated and control tibiae were pulse-labelled for 2 h with [3H]uridine or [3H]glucosamine. The incorporated radioactivity was measured by liquid scintillation counting. Histochemical demonstration of acid phosphatase (AP), a lysosomal enzyme, was carried out using beta-glycerophosphate as substrate. A limited, dose-dependent immediate effect on RNA and GAG synthesis was found. This effect was unchanged for 2 days. After this period a time-dependent delayed effect was observed. For each radiation dose, and for each precursor, the same time-related pattern was found. At the end of the culture period AP activity, an early indicator for apoptosis, was higher in the irradiated tibiae than in the controls. No other morphological ultrastructural differences were observed at this time. We conclude that the metabolic alterations are probably due to stimulation of the initial stages of the apoptotic process in the irradiated cartilage cells.