Inhibition by calcitonin of bone resorption induced in vitro by vitamin A

Abstract

There is now good evidence for a thyroid polypeptide hormone, calcitonin, that lowers plasma calcium (Gudmundsson, MacIntyre & Soliman 1966). Bone was soon suspected as a primary site of action of this hormone, and Milhaud, Perault & Moukhtar (1965) concluded from kinetic studies with 45 Ca in rats that calcitonin lowers plasma calcium by inhibiting the resorption of bone. This theory of its action has received considerable support from investigations made both in vivo and in vitro . I propose to summarize the latter. In vitro studies by Friedman & Raisz (1965) showed that extracts of rat thyroid inhibit the release of calcium from embryonic long bones of rats; the effect was greatest when resorption was stimulated by parathyroid hormone. Aliapoulios, Goldhaber & Munson (1966) demonstrated that partially purified hog calcitonin can prevent the effects of parathyroid extract on mouse calvariae in vitro ; they also stated, without details, that calcitonin counteracted resorption of bone induced by vitamin A, thereby supporting the evidence from studies in vivo that the action of calcitonin is independent of that of parathyroid hormone. The results described by Gaillard (1966) can also be interpreted as supporting the theory that calcitonin acts by inhibiting bone resorption.