Comparison of the effects of 1,25-dihydroxycholecalciferol, prostaglandin E2, and osteoclast-activating factor with parathyroid hormone on the ultrastructure of osteoclasts in cultured long bones of fetal rats.

The effects of 1,25-dihydroxy vitamin D3 [1,25(OH)2D3], prostaglandin (PGE2), and osteoclast-activating factor (OAF) on the size of osteoclasts, nuclei, ruffled borders, and clear zones in cultured long bones of fetal rats were quantitated. In addition, the number of osteoclasts in the bones was counted and the release of calcium from the bone into the culture medium was determined. These data were compared with the corresponding effects of parathyroid hormone (PTH). All agents tested increased the size of the ruffled borders significantly after 3 h, the size of the clear zones after 12 h, and the size of the cells after 12-24 h. No important differences in sizes were noticed between the agents tested or between the agents and PTH. The number of osteoclasts was increased after 24 h of treatment with PTH, but not after the other agents. Calcium release was significantly increased for all agents between 12 and 24 h. It is concluded that bone resorption by 1,25(OH)2D3, OAF, and PGE2 is mediated primarily by increased activity of existing osteoclasts similar to PTH activation.