Intrinsic regulation of the condylar cartilage growth rate.

The condylar cartilage was taken from intact 15-day-old male rats or from rats with lateral pterygoid muscles resected 10 days previously. The condylar cartilage was put into organ culture either whole or after partial or complete resection of the chondroblastic zone: in addition the mitotic compartment of the condylar cartilage taken from intact rats was associated in organ culture (a) with chondroblastic zones from condylar or angular cartilages and from the spheno-occipital synchondrosis, (b) with some other tissues. According to the experimental findings, the not yet hypertrophied chondroblasts (i.e. ‘functional chondroblasts’) of a secondary cartilage send, permanently, a specific ‘negative feed-back signal’ restraining the prechondroblast multiplication rate. One is dealing with an intrinsic regulatory system. The acceleration of chondroblast maturation i.e. the diminution in the number of the not yet hypertrophied chondroblasts, and the subsequent decrease of the ‘prechondroblast multiplication restraining signal’ represents an intermediary step for the stimulating effect of mandibular postural hyperpropulsion, or of thyroxine on the condylar cartilage growth rate.