Calcitonin producing tumour. Effects on fracture repair and normal bone in rats

The mechanical properties and the collagen metabolism of healing fractures and intact bones have been studied in rats with a transplanted, calcitonin (CT) secreting, medullary thyroid carcinoma (MCT). Sham operated animals served as controls. The MCT was transplanted beneath the kidney capsule. Seven months later, when the rats with MCT had increased circulating levels of CT, a standardized femoral fracture was produced in all the animals. The serum levels of CT were 3-40 times higher in tumour bearing rats than in controls in the period following the fracture. The fracture strength of rats with MCT was reduced by about 60 per cent compared to controls at 16 weeks after the fracture. The strength of intact femora (ultimate torsional moment) seemed to be progressively impaired by increasing levels of circulating CT. Also the strength of bone as a material (ultimate torsional stress) was reduced in the rats with MCT. The collagen synthesis was reduced in MCT rats, but the amounts of collagen in fractured or intact bones were not changed compared to controls. We conclude that chronic hypercalcitoninaemia due to MCT seems to have a negative influence both on fracture healing and on bone metabolism.