Calcitonin is a 32 amino acid polypeptide, with a disulphide bridge between the cysteine residues in positions 1 and 7. It is secreted by the parafollicular or C cells of the thyroid gland, which comprise 0.1% of the thyroid mass.
The calcitonin receptor is a seven transmembrane domain G-protein-coupled receptor in the osteoclast and in the kidneys. Receptor down-regulation may explain the self-limiting nature of calcitonin action.
Calcitonin inhibits osteoclastic activity by increasing intracellular cyclic AMP levels. It diminishes osteolytic activity of osteoclasts and osteocytes. Other actions include: Antagonism to the effect of PTH on bone; Inhibition of gastric motility and gastrin secretion; Inhibition of jejunal absorption of calcium and phosphate; Inhibition of tubular reabsorption and promotion of urinary excretion of phosphate, calcium and sodium;
Inhibition of renal 1 alpha-hydroxylase activity, with decreased synthesis of calcitriol.
Calcitonin is used for the treatment of hypercalcaemia and for osteoporosis. Salmon calcitonin possesses 100 times the potency of human calcitonin.
Was this article helpful?