Studies on hormonal regulation of the growth of the craniofacial skeleton: III. Effects of 24,25 (OH)2D3 on cartilage growth in the mandibular condyle of suckling mice.

This study examined the influence of 24,25 (OH)2D3, an active metabolite of vitamin D, on the growth and development of cartilage cells in condylar cartilage of suckling mice. It became evident that when the hormone was administered even at high doses, it did not significantly affect the incorporation of [3H]thymidine, but led to a marked decrease in the number of both chondroblasts and hypertrophic chondrocytes. At the same time, condyle of hormone-treated mice reached an increase in the number of mesenchymelike cells within the chondroprogenitor zone. High values of correlation were noted between the overall dimensions of the condylar cartilage and those of the chondroblastic and hypertrophic zones. The hormone also significantly reduced the degree of matrix metachromasia (indicative of proteoglycan content) and concomitantly altered the mineralization pattern of the cartilaginous matrix. This study indicates that in young animals increased doses of 24,25(OH)2D3 do not affect the proliferative activity of chondroprogenitor cells yet possess an inhibitory effect upon the capacity of the latter cells to differentiate into chondroblasts. The hormone also seems to affect the already differentiated cells--chondroblasts and hypertrophic chondrocytes--both structurally as well as metabolically. In so doing, this metabolite of vitamin D affects the normal process of endochondral bone formation in one of the mandible's main growth sites. Thus, in the developing animal, elevated concentrations of 24,25(OH)2D3 may impair the growing mandible's ability to achieve its normal size and shape.