Reversibility of the inhibitory effect of salmon calcitonin on bone resorption in rats.

Inhibition of osteoclastic bone resorption has been induced in growing rats with high doses of salmon calcitonin. This effect was evaluated by measuring the perichondrial ring height of the proximal tibial metaphysis. The aim was to assess whether osteoclastic activity resumed after a period of inhibition with high doses of calcitonin. 20 male Sprague-Dawley rats were treated for 21 days with 100 units/kg/day of salmon calcitonin subcutaneously and killed after 0-60 days, together with non-treated controls at 0 and 60 days. Arrest of metaphyseal modeling and increased height of the perichondrial ring at the end of the period of therapy (P 0.002 versus controls) were observed. Recovery of bone resorption was evident 20 and 40 days after withdrawal of calcitonin.