Biological activity of chicken calcitonin: effects on neonatal rat and embryonic chick osteoclasts

Chicken calcitonin (cCT) has recently been synthesized according to nucleotide sequence data. We have investigated the in vitro effects of this hormone on the activity of disaggregated, neonatal rat and embryonic chick osteoclasts. While synthetic cCT inhibited bone resorption by neonatal rat osteoclasts at concentrations as low as 0.1 pg/ml, it failed to produce a significant reduction in bone resorption by embryonic chick osteoclasts, even at concentrations as high as 1 microgram/ml. Similarly, cCT at 1 pg/ml reproducibly produced the rapid and dramatic inhibition of rat osteoclast motility characteristic of other calcitonins, as judged by time-lapse video recording, but did not impair the motile behavior of chick osteoclasts at concentrations up to a million-fold higher. Previous studies showing that embryonic chick osteoclasts were unresponsive to synthetic salmon calcitonin left open the possibility that the native hormone was required to produce an inhibitory effect. We conclude that the osteoclast is not a target cell for calcitonin in the embryonic chick; further studies will be required to define a role, if any, for this potent but enigmatic hormone in birds.