Autometallographic tracing of zinc ions in growing bone

It has previously been established that zinc (Zn) supplementation increases bone dimensions and strength in growing rats. The present study aims at describing differences in the localization of loosely bound or free zinc ions, as revealed by autometallography (AMG), that might take place in the skeleton of growing rats following alimentary zinc depletion and supplementation. Male Wistar rats, 4 weeks old, were randomly divided into three groups. The rats had free access to a semi-synthetic diet with different amounts of zinc added. Group 1 was given a zinc-free (2 mg zinc/kg) diet, group 2 a 47 mg zinc/kg diet, and group 3 a 60 mg zinc/kg diet. All animals were killed after 4 weeks. Animals from each group were transcardially perfused with a 0.1 % sodium sulphide solution according to the zinc specific Neo-Timm method causing zinc ions to be bound in AMG catalytic zinc-sulphur clusters. We found clusters of zinc ions localized in the mineralizing osteoid in all groups. No immediate differences in AMG staining intensity could be observed between the groups neither in the uncalcified bone nor in the osteoblasts. However, alimentary zinc supply resulted in an increase in the height of the total growth plate in a dose-dependent manner. Zinc ions were also observed in chondrocytes throughout the whole thickness of the articular and the epiphyseal cartilage as well as in the inner layer of the synovial membrane.