Effect of different calcium intakes on bone mineral composition in rats with a calcitonin secreting tumour

The effects of hypercalcitoninaemia and different calcium intakes on bone composition were studied in rats with and without a transplanted calcitonin secreting tumour (MCT). The serum concentrations of immunoreactive calcitonin (iCT) increased progressively after transplantation. After 32 weeks the serum iCT concentrations in MCT rats were about 5-fold higher and serum ionized calcium was significantly reduced compared to control animals. In rats with hypercalcitoninaemia eating a standard calcium (0.9%) diet for 32 weeks, the dry weight and calcium and sodium content of the long bones were reduced compared to control rats without tumours or rats with a prolactin secreting tumour. The feeding of low (0.09%), medium (0.4%) and high (1.8%) calcium diets to MCT-rats resulted in corresponding levels of total and ionized serum calcium, but there was no difference in iCT concentrations. The MCT-rats taking the low calcium diet had decreased bone mass and calcium content compared to the other dietary groups. In conclusion, rats on normal calcium intake and carrying a calcitonin secreting tumour, but not a prolactin secreting tumour, had reduced femoral dry weight and bone mineral calcium content. Different calcium intake regimens did not affect hypercalcitoninaemia due to a tumour, but parallel changes in femoral dry weight and calcium content were found.