Growth inhibition of cartilaginous embryonic chick tibiae by ionizing radiation: an in vitro study.

The radiation effect on the longitudinal growth of cartilaginous tibiae of 6,5 day old chick embryos is studied in vitro. After irradiation length is measured daily during the 3 days culture period and incorporation of (3)H-thymidine, (3)H-uridine or (3)H-proline is sampled by liquid scintillation counting. Selective tibiae are videorecorded during the incubation period. Morphology is studied by light microscopy, autoradiography and electron microscopy.Growth inhibition is only restricted to 5% at 20 Gy up to 20% at 150 Gy. The (3)H-uridine and (3)H-proline incorporation is only decreased by 21 and 32% at 150 Gy. (3)H-thymidine incorporation on the contrary shows 17% decrease at 2 Gy. Irradiation at 200 Gy gives a total growth arrest and stops incorporation of all used labeled compounds in 75% of the specimens. L.M. and E.M. show no morphological differences between irradiated and sham irradiated tibiae until 150 Gy. At 200 Gy however necrosis of the cells is observed.We conclude that longitudinal growth of cartilaginous tibiae in organ culture is not correlated with DNA synthesis but with cell hypertrophy and production of extracellular material. RNA transcription and synthesis of collagen fibers are radioresistant processes. This explains the limited influence of irradiation on the longitudinal growth.