Effect of 50 kV irradiation on enzyme activities of growing rat bone. A histopathologic and enzyme histochemical investigation.

Young rats were exposed to 2, 5, 8 and 10 Gy 50 kV local irradiation. The epiphyseal region of the proximal tibia was examined with histopathologic, histochemical and enzyme histochemical methods 1 to 90 days after irradiation. One day after irradiation, a decrease in alkaline phosphatase activity was noted and increased activity was found for acid phosphatase, NADH2-diaphorase and glucose-6-phosphate dehydrogenase, especially after 8 and 10 Gy, but also after 5 Gy. Three days after irradiation, all enzymes showed an increased activity and on day 7 the findings resembled those on day 3. Thirty days after irradiation, a return to normal conditions was observed. The most marked morphologic changes were swelling of cells in the hypertrophic cell zone, disturbed order of cells in the zone of proliferation and an increased number of osteoclasts in the metaphyseal bone. These alterations appeared 1 to 3 days after irradiation and normal morphology was seen on day 30 after 2, 5 and 8 Gy and 90 days after irradiation with 10 Gy.