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Effect of Clodronate Administration on the Structure of the Primary Spongiosa derived from the Growth Cartilage in Growing Rats

The effect of the inhibition of the resorptive activity of osteoclastic cells induced by bisphosphonate treatment on the primary spongiosa derived from the calcified cartilage of the growth plate was studied. We focused our attention on the primary spongiosa because it is the initial trabecular bone network that is first formed directly from growth plate mineralized cartilaginous septa. The study was carried out in male Sprague-Dawley rats at the age of 35 days, coinciding with the prepubertal growth spurt, a stage characterized by the highest values for growth rate. Animals were classified in two groups, controls and rats treated with clodronate 60 mg/kg/day. Body weights and tibial length were measured. The rate of longitudinal bone growth was obtained by calceine labelling and the height of the growth plate cartilage was measured. Histochemical analysis included Alcian blue staining, detection of tartrate-resistant acid phosphatise (TRAP) activity, von Kossa staining for mineralization and immunolocalization of proliferating cells. Microscopic examination revealed numerous tartrate-resistant acid phosphatase (TRAP)-positive cells at the chondroosseous junction and associated with subchondral trabeculae in control rat and that clodronate treatment induced a marked reduction of these cells. Clodronate-treated rats presented thinner subchondral trabeculae that were more irregularly oriented and decreased cell proliferation in the primary spongiosa. Results obtained showed that changes induced by clodronate treatment has little effect on the activity of the growth plate cartilage, without a significant effect on longitudinal bone growth even at doses much higher than those used in clinical practice.