Calcitonin
A 32 amino acid peptide hormone produced by thyroid C-cells that lowers blood calcium by inhibiting bone resorption. Calcitonin-salmon (synthetic salmon calcitonin) is approximately 40-50 times more potent than human calcitonin and is used therapeutically for osteoporosis and hypercalcaemia.
Technical Context
Calcitonin is produced by thyroid C-cells (parafollicular cells), derived from the calcitonin gene (CALCA) that also encodes CGRP through alternative splicing. Calcitonin binds to the calcitonin receptor (CTR, a class B GPCR) on osteoclasts, rapidly inhibiting their bone-resorbing activity by disrupting the ruffled border and reducing acid secretion. This produces an acute decrease in serum calcium. Salmon calcitonin has approximately 40-50 times the potency of human calcitonin due to higher receptor binding affinity, and a longer half-life (approximately 43 minutes for SC salmon calcitonin vs 10 minutes for human calcitonin). Calcitonin also serves as a tumour marker for medullary thyroid carcinoma — this is why calcitonin monitoring is discussed in the context of GLP-1 RA safety.