Ultrastructural analysis of glycosaminoglycan hydrolysis in the rat periodontal ligament. I. Evidence for macrophage involvement in bone remodelling.

We identified the cellular sites of glycosaminoglycan hydrolysis by localizing a key enzyme, N-acetyl-beta-glucosaminidase, in the rat periodonatal ligament. Reaction product was seen in osteoclasts, osteoblasts, fibroblasts, and in macrophages situated perivascularly in areas of bone remodelling. The preferential location of macrophages in areas of both bone formation and bone resorption, and their intense NAGase activity identified the macrophage as a significant participant in the total process of bone remodelling. We considered the presence of reaction product in the Golgi zone and the rough endoplasmic reticulum of osteoblasts and fibroblasts as possible localization of a NAG-transferase.