Effect of (Asu1,7)-eel calcitonin on the prevention of osteoporosis induced by combination of immobilization and ovariectomy in the rat.

Experimental osteoporosis was induced in the rat by a combination of ovariectomy and immobilization by hemicordotomy. (Asu1,7)-eel calcitonin (CT) was administered at doses of 0.1, 0.5, 1.0, 2.5, and 5.0 MRC unit/kg, and its preventive effect on bone loss was examined. Significant bone loss was observed in the untreated control group by photo-densitometry and measurement of bone mass. CT at doses of above 1.0 MRC unit/kg significantly increased femur scores and at doses of above 2.5 MRC unit/kg resulted in significantly higher photodensity. Dry weight and ash weight were significantly higher in the 2.5 and 5.0 MRC unit/kg CT-treated groups. Administration of CT had a nearly dose-dependent effect on bone mass. Histomorphometry revealed significantly lower fractional formation surface and fractional resorption surface in the 5.0 MRC unit/kg CT-treated group. Bone mineralization was studied by the quantitative analysis of tetracycline incorporation. Tetracycline uptake was significantly lower in the groups treated with CT at doses above 1.0 MRC unit/kg. The kinetic bone formation activity studied by 45Ca and 14C-proline tracer examination, in the 5.0 MRC unit/kg CT-treated group was significantly lower than that in the control group, but not lower than that in the sham-operated group.