Calcitonin is a 32- aminoacid linear peptide encoded by the CALC1 gene, in chromosome 11, that cooperate in Calcium homeostasis (better seen in animals, where calcitonin is produced by the ultimobranchial body, than in human).
It acts to reduce blood calcium (Ca2+), opposing the effects of parathyroid hormone (PTH).
Calcitonin lowers blood Ca2+ levels in two ways:
- Inhibits Ca2+ absorption by the intestines
- Inhibits osteoclast activity in bones
Secretion of calcitonin is stimulated by:
- an increase in serum [Ca2+]
- gastrin and pentagastrin.
The calcitonin receptor, found primarily on osteoclasts, is a G protein-coupled receptor, which is coupled by Gs to adenylyl cyclase and thereby to the generation of cAMP in target cells.
Calcitonin's action in Calcium homehostasis seems to be less important then PTH or vitamin D.
Indeed high level of calcitonin, as can be found in Medullary Thyroid Carcinoma, don't alter Calcium serum levels.
Currently the dosage of calcitonin (basal level and after stimulation with pentagastrin) is useful to diagnose Medullary Thyroid Carcinoma or C cells hyperplasia.