A HUMAN PERIODONTAL-LIGAMENT FIBROBLAST CLONE RELEASES A BONE-RESORPTION INHIBITION-FACTOR INVITRO

The conditioned media (CM) obtained from three lines of cloned human periodontal ligament (PDL) cells were analyzed to determine whether they altered the parathyroid hormone (PTH)-stimulated resorption rates (Ca-45 release) in 48-hour cultures of Ca-45-labeled rat long bones. One PDL cell line, PDL-5, produced a heat-resistant factor in its CM that inhibited the PTH-stimulated resorption by 43.8 +/- 9.7 (SE) percent (p less-than-or-equal-to 0.02), whereas the CM from the other cell lines were without statistically significant effect. The CM from the PDL-5 line did not diminish organ culture viability, as determined by H-3-thymidine incorporation, and did not enhance or diminish the resorption-inhibiting activity of calcitonin added to the PTH-stimulated cultures. The addition of CM from PDL-5 did not alter the bone-resorbing effect of interleukin-1 (IL-1). These results indicate that CM from PDL-5 inhibits only the PTH-induced and not the IL-1-mediated resorption processes, whose mechanisms are therefore likely to differ.