Calcitonin stimulates growth and maturation of embryonic chick pelvic cartilage in vitro
To determine whether calcitonin (CT) affects the growth of avian embryonic skeletal tissue, pelvic cartilages from 9-day-old chick embryos were incubated in a serum-free medium containing CT for 3 days. Porcine CT (PCT), salmon CT (SCT), and human CT (HCT) stimulated increases in cartilage wet weight that were dependent upon the concentration of CT within the medium. Maximal growth was seen with PCT (1.0 U/ml), which increased cartilage wet weight 107% and dry weight 53% above those of cartilage incubated in medium alone. SCT (1.0 U/ml) and HCT (1.0 U/ml) stimulated a 55% increase in cartilage wet weight and a 20% increase in cartilage dry weight over those of cartilage incubated in medium alone. The reason for PCT's apparent potency was due to trace contamination of thyroid hormone in the PCT preparation, since synthetic PCT caused an increase in cartilage wet weight equivalent to those produced by SCT and HCT. Although each calcitonin increased wet and dry cartilage weights, the DNA content was not changed. Alkaline phosphatase activity, a marker of cartilage maturation, was found to be stimulated by CT, SCT, HCT, PCT, and synthetic PCT increased alkaline phosphatase activity over 2-fold above that in cartilage incubated in medium alone. Histological sections of CT-treated cartilage showed large round nuclei, vacuolated cytoplasm with lacuna formation, and an increased amount of cartilage matrix compared to those of cartilage incubated in medium alone. Thus, CT stimulates cartilage growth primarily through cellular hypertrophy and matrix formation. This study demonstrates that CT is a growth and maturation factor for avian embryonic cartilage in vitro.
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