Effect of neonatal head X-irradiation on growth of costal and tibial cartilage in rats: a histochemical and electron microscopic study.

: Long-Evans rats were exposed to a single dose of head X-irradiation (600 rads) at 2 days of age. Experimental and sham irradiated rats were sacrificed at 14, 20-21, 23, 41-45, and 70-71 days. Tibial epiphyseal width and the number of cells in the epiphyseal plate were determined. Histochemical and electron microscopic studies were carried out on both costal and epiphyseal cartilage. Histochemical techniques revealed a reduction in chondroitin sulfate at 14 days in both costal and epiphyseal cartilage of X-irradiated rats. Epiphyseal cartilage demonstrated recovery subsequently, and this was followed by a normal decrease of chondroitin sulfate with increasing age, but costal cartilage did not recover. Collagen synthesis was also reduced in both costal and epiphyseal cartilage, but not as dramatically as chondroitin sulfate. Except for some electron dense cells and reduced scalloping of the cell membrane, costal chondrocytes from irradiated rats did not show major ultrastructural alterations. In contrast, epiphyseal chondrocytes demonstrated radiation induced alterations in organelles, in enhanced glycogen deposition, and in retardation of chondrocyte maturation. Extracellularly in both costal and epiphyseal cartilage of irradiated rats, collagen density and matrix granules were reduced, while calcification of the matrix was enhanced. Beyond 45 days, the effects of irradiation were markedly reduced. Comparisons of the histochemical results with metabolic studies carried out previously in cartilage from the same animals indicated a more direct concordance of the histochemical results with the pattern of physical growth and supported the usefulness of morphologic and histochemical techniques in the analysis of the growth disorder in the head-irradiated rat.