CARTILAGE MATRIX PRODUCTION AND CHONDROCYTE ENLARGEMENT AS CONTRIBUTORS TO MANDIBULAR CONDYLAR GROWTH IN MONKEYS (MACACA-FASCICULARIS)

In an attempt to determine the contributions to condylar growth of cartilaginous matrix production and chondrocyte enlargement, four prepubertal male monkeys (Macaca fascicularis) were used. Each animal received 1 mCi H-3-proline per kilogram of body weight 24 hours before death. From the left condyles, the anterior and central segments of the growth cartilage in the lateral and medial joint region were examined with the light microscope. Volumes of cells and extracellular matrix, as well as the intensity of radioautographic labeling, were estimated stereologically in four layers from the articular surface to the zone of endochondral ossification. On the assumption of a steady-state system, these data led to the conclusion that an average chondrocyte in the anterior segment of the growth cartilage contributed to condylar growth by about 3000-mu-m3 of newly formed matrix and about 1000-mu-m3 of increased cell size. The respective estimates in the central segment were about 3700-mu-m3 and 2000-mu-m3. Thus, unlike findings in the condylar cartilage of 20-day-old rats, matrix production in the simian condyle exceeded chondrocyte enlargement, although in varying ratios of about 3:1 anteriorly and 1.85:1 centrally. On the other hand, chondrocyte enlargement from the anterior segment to the central segment increased by about 100%, while the increase of about 25% in matrix production was outweighed by variation between individual animals. These findings suggest that the relative contribution of the two growth components varies considerably, on the one hand, with the species or possibly with the stage of condylar development examined and, on the other hand, between various anteroposterior locations within the condylar cartilage. Intracondylar variations appear to result primarily from prominent local effects on chondrocyte enlargement.