Effects of parathyroid hormone fragments on the growth of murine mandibular condylar cartilage in vitro.

The present study showed that the fragment hPTH (1-34) is mitogenic in organ cultures of neonatal mandibular condylar cartilage, and even more so in late fetal condyles. Three fragments of hPTH were used to clarify which part of the molecule possesses a mitogenic effect alike that of the native hormone: hPTH (1-34), (28-48) and (53-84). [3H]thymidine incorporation into trichloracetic acid insoluble material and quantitative autoradiography were employed in a serum-free medium to assess the effects of these fragments while light and electron microscopy studies served for morphological evaluations. It became evident that the fragment hPTH (1-34) enhanced the incorporation of [3H]thymidine, a fact that could be noted only in serum-free medium. The putative target cells for the effects of hPTH (1-34) were the chondroporogenitor cells which also appeared to have experienced a blockage in their differentiation into chondroblasts. Ultrastructurally, the latter cells responded in the formation of adherent profiles of plasma membranes, whereas the differentiated zone of the cartilage reduced its size. Using serum-free medium, hPTH (1-34) also brought about an inhibition in alkaline phosphatase activity, a fact that was not encountered in medium containing serum. By contrast, hPTH (28-48) had no mitogenic effect, although treated specimens revealed morphological changes in the chondroprogenitor cell zone along with an enhancement of cartilage cells hypertrophy. No significant effects on either mitogenecity or morphology could be noted in hPTH (53-84)-treated cultures.