Talc granulomatosis in the rat: the relationship between osteoblast insufficiency and adjacent bone marrow hyperplasia.

Bone loss in talc granulomatosis is paralleled by hyperplasia of bone marrow in the rat. To test the hypothetical relation between those two phenomena, bone matrix osteoinduction was employed as a model in which bone formation and bone marrow appearance are separated in time. Implantation of demineralized bone matrix to normal rats was followed by three talc injections (one weekly), starting 1 week after matrix implantation. Implants of demineralized bone and [3H]thymidine-labeled tibial metaphyses from talc-injected and normal rats were analyzed histologically and evaluated for alkaline and tartrate-resistant acid phosphatase activity on days 7, 14, 21, and 30 after matrix implantation. Analysis of tibial autoradiographs showed a marked growth arrest and bone marrow hyperplasia in talc-injected rats 7 days after first talc injection. Alkaline phosphatase activity in homogenates of bone implants was low in talc-injected rats on day 14 after implantation. Moreover, histology of the bone implants showed numerical and functional inhibition of osteoblasts on the same day, causing marked growth delay. Bone marrow appeared as late as day 21 after bone matrix implantation. We conclude that hyperplasia of the adjacent bone marrow is not the cause of bone loss in talc granulomatosis, but rather its compensatory consequence.