Effect of Oral Calcium Load on Calcium and Phosphorus Metabolism in Thyroidectomized and Sham Operated Sheep

Abstract

This study was to investigate a role of calcitonin on calcium and phosphorus metabolism in sheep orally loaded calcium. Though serum calcium concentrations and urinary calcium excretion tended to be increased by the calcium load in all sheep, the increases were more remarkable in thyroidectomized (TXed) sheep than in sham operated (Sham) ones. Serum phosphorus concentrations were decreased in all sheep as the high calcium diet was given. Urinary phosphorus excretion were substantially decreased by the calcium load in Sham sheep and were slightly decreased in TXed sheep. The calcium load reduced serum free hydroxyproline (Hyp) concentrations, urinary total Hyp excretion and serum parathyroid hormone concentrations in Sham sheep. The elevation of urinary polypeptide Hyp excretion was more remarkable in Sham sheep than in TXed ones. These results suggested that calcitonin played a role to decrease bone resorption and to increase bone formation when a high calcium diet was fed to sheep. The role of calcitonin on the kidney might be limited in comparison with that on the skeleton in sheep fed a high calcium diet. The reduction of serum parathyroid hormone concentrations, which was induced by the calcium load, might partly contribute to the decrease in bone resorption.