Abstract
Endochondral osteogenesis in tissue cultures has been investigated. The epiphyseal cartilage cones of the long bones of the lower extremities, from 12-day-old chick embryos were dissected free from the perichondrium and all the surrounding tissues and were explanted, using the watch-glass method, either on solid or on fluid media. Observations were performed on material explanted for as long as 50 days. Outgrowth of fibroblasts appeared in the cartilaginous explants much later than it usually does in explants of other tissues. An increase of the areal growth, 50 to 125 per cent of the initial area, was observed. As a rule, the curve of the areal growth rose steeply during the first week of explantation and then the increase continued at a slower rate. Histological sections showed that, at an early stage of explantation, the explants became wrapped in a layer of fibrous tissue having great morphological similarities to the perichondrium of normal bones. Metachromatic staining, degeneration, absorption of the cartilage and deposition of a preosseous tissue followed. Calcification of the new bone tissue probably takes place after the 50th to 60th day of explantation. The alkaline phosphatase activity showed a steep rise between the 15th and 20th day, with maximal values between the 25th and 40th, and a beginning decline after the 40th day of explantation. Acid phosphatase activity showed but a slight rise between the 15th and 40th day. No phenolsulfatase activity could be detected in the epiphyseal cartilages of chick embryos. Determinations of the chondroitin sulfate showed a progressive decrease in the amount of galactosamine HCl between 0 and 70th day of explantation, while at the same time the amount of glucosamine HCl remained stable. X-ray diffraction applied on one explant after 60 days of explantation showed a pattern characteristic for hydroxyapatite. The crystallites being of the same order of size as those observed in normal bone tissue.
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