KINETICS OF OSTEOCLAST FORMATION - THE SIGNIFICANCE OF BLOOD MONOCYTES AS OSTEOCLAST PRECURSORS DURING 1-ALPHA-HYDROXYCHOLECALCIFEROL-STIMULATED BONE-RESORPTION IN THE MOUSE

  • 1 January 1983
    • journal article
    • research article
    • Vol. 137  (SEP) , 335-340
Abstract
The significance of blood monocytes as a source of osteoclast precursors was investigated during 1.alpha.-hydroxy-cholecalciferol-stimulated bone resorption in mice. Animals were given 3 injections of [3H] thymidine at 8 hourly intervals in order to label blood monocytes. The proportion of labeled monocytes was then compared with the proportion of labeled nuclei in osteoclasts, the formation of which was provoked by daily injections of 1.alpha.-hydroxy-cholecalciferol, beginning 48 h after the 1st injection of isotope. Although more than 60% of blood monocytes were labeled during the period of peak osteoclast formation, labeling of osteoclast nuclei in the metaphyseal endosteum of the femur never exceeded 8%. The majority of osteoclast nuclei were derived from a source of unlabeled precursors, and very few osteoclass were derived directly from blood monocytes. Although a few labeled osteoclasts were found, the proportion of labeled spindle shaped cells in the metaphyseal endosteum rose gradually to 16%. Labeled mononuclear cells, possibly blood monocytes, apparently were attracted to the endosteum where they formed a population of tissue macrophages. At this site they may participate in bone resorption, either individually or by providing a local pool of osteoclast precursors.