Effects of irradiation in vitro on calcifying mechanism of epiphyseal cartilage.

X irradiation of rachitic epiphyseal cartilage with 250,000 r resulted in small decrease in calcifiability, loss of beta -metachromatic granules from some cells of the proliferative zone, and a slight general decrease in staining of the hypertrophic zone. X irradiation with 500,000 r resulted in marked decrease in calcifiability, loss of most of the beta -metachromatic granules from the proliferative zone, and loss of gamma -metachromatic granales from some cells of the hypertrophic zone. X irradiation with 1,000,000 r resulted in almost complete loss of both calcifiability and stainability with toluidine blue. Toluidine-blue staining of fresh sections of epiphyseal cartilage was employed for demonstration of metachromatic substances. Once the process of calcification had been initiated, the inactivating effect of irradiation on calcifiability was considerably reduced. A change in mucopolysaccharide resulting in increase of free electronegative groups is a factor associated with calcifiability of epiphyseal cartilage. (auth)