INHIBITION BY CALCITONIN OF HYPERCALCAEMIA INDUCED BY 1,25-DIHYDROXYCHOLECALCIFEROL

Abstract

SUMMARY The influence of injections of calcitonin on the hypercalcaemia and hyperphosphataemia induced by 1α-hydroxycholecalciferol (1α-OHD3) and 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was studied in growing lambs and lactating cows respectively. In lambs, the hypercalcaemic and hyperphosphataemic effect of 0·1 μg 1α-OHD3/kg body weight (i.v.) was completely inhibited by 20 units calcitonin/kg body weight, injected subcutaneously in four equal doses at intervals of 12 h, the first injection of calcitonin occurring immediately after injection of 1α-OHD3. Moreover, the same dose of calcitonin partly inhibited the hypercalcaemia and hyperphosphataemia observed after injection of 0·25 μg 1α-OHD3/kg body weight. In lactating cows, four injections of calcitonin (5 u./kg body weight each, at intervals of 12 h) prevented the rise of plasma calcium and phosphate levels occurring after injection of 1,25-(OH)2D3 (0·01 μg/kg body weight). The results indicated that high plasma calcitonin levels can inhibit the hypercalcaemic and hyperphosphataemic effects of 1,25-(OH)2D3 in ruminants. Thus, hypocalcaemia might occur in parturient cows in spite of raised concentrations of 1,25-(OH)2D3 in plasma.