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Our previous studies showed that during the embryonic development of avian long bones, growth of the cartilaginous component is regulated by multiple factors secreted by the surrounding perichondrium (PC) and periosteum (PO). The activities of these factors--which include both positive and negative regulators--can be detected in conditioned media from PC and PO cell cultures. In the present study, we have obtained evidence suggesting that a positive regulator is the peptide hormone calcitonin (CT). By mass spectrometry of conditioned media, one of the components has a molecular mass of 3.4 kDa, the size of chicken CT. By RT-PCR the tissue and cell cultures contain mRNA for CT, and by immunohistochemistry the cells contain the protein. That the protein is normally secreted is suggested by further immunohistochemical analyses, which show that cells treated with monensin, a compound that blocks exocytosis, contain elevated intracellular CT. Functionally, the addition of CT to organ cultures of long bone rudiments effects increased growth in a manner similar to that of the PC- and PO-conditioned media. Taken together, these data suggest that secretion of CT by the PC and PO effects, in a paracrine manner, positive stimulation of growth in the underlying cartilage.

Positive Regulation of Endochondral Cartilage Growth by Perichondrial and Periosteal Calcitonin