Morphology of osteoclasts in resorbing fetal rat bone explants: effects of PTH and AIF in vitro.

Osteoclastic bone resorption was studied using 45Ca-labeled fetal rat bones cultured in the presence of parathyroid hormone (PTH) and an anti-invasion factor (AIF) derived from bovine hyaline cartilage which is enriched in a collagenase inhibitor. The specific morphological expressions of osteoclasts cultured in PTH and AIF were observed in both light and electron microscopy and analyzed cytometrically. Stimulation of bone resorption with PTH revealed significant increases in the numbers and activity of osteoclasts, whereas bones cultured in the presence of AIF showed significant decreases in numbers of osteoclasts and altered cell features including the loss of osteoclast contact with bone surfaces. These structural modifications were evaluated with 45Ca release data derived from matched-pair explants of fetal rat bones, revealing the existence of a relationship between resorptive states of the cultured bones and morphological expressions of osteoclastic activity.