Induction and characterisation of local (simple) calcergy in granulation tissue in the rat by lead acetate injection into polyurethane sponges.

Granulation tissue was allowed to grow into polyurethane sponges implanted subcutaneously in rats for 14 days prior to injection of saline (control) or lead acetate (PbAc) into the sponge centres. The reaction was studied for 21 days post-injection utilising sponge dry weight gain, histology and electron microscopy. Five hours after PbAc injection, calcification was demonstrable within the central tissue-free portion of the sponges. Calcification in granulation tissue was associated with collagen fibres and elicited a macrophage and multinucleated giant cell reaction. Mast cells were not found within sponges. Hydroxyapatite deposition was associated with an increase in sponge weight compared with controls. The injection of PbAc elicited calcification in granulation tissue in the same time scale reported for calcergy in mature connective tissue and the phenomenon of calcergy does not require the presence of collagen fibres or mast cells in its early stages.