Calcitonin is formed by the proteolytic cleavage of a larger prepropeptide, which is the product of the CALC1 gene (CALCA). The CALC1 gene belongs to a superfamily of related protein hormone precursors including islet amyloid precursor protein, calcitonin gene-related peptide, and the precursor of adrenomedullin.

Secretion of calcitonin is stimulated by:

• an increase in serum [Ca²⁺]^[5]
• gastrin and pentagastrin.^[6]

[edit]Effects

The hormone participates in calcium (Ca²⁺) and phosphorus metabolism. In many ways, calcitonin counteracts parathyroid hormone (PTH).

More specifically, calcitonin lowers blood Ca²⁺ levels in three ways:

• Inhibits Ca²⁺ absorption by the intestines^[7]
• Inhibits osteoclast activity in bones^[8]
• Inhibits renal tubular cell reabsorption of Ca²⁺ allowing it to be excreted in the urine^[9][10]

However, effects of calcitonin that mirror those of PTH include the following:

• Inhibits phosphate reabsorption by the kidney tubules^[11]

In its skeleton-preserving actions, calcitonin protects against calcium loss from skeleton during periods of calcium mobilization, such as pregnancy and, especially,lactation.

Other effects are in preventing postprandial hypercalcemia resulting from absorption of Ca²⁺. Also, calcitonin inhibits food intake in rats and monkeys, and may haveCNS action involving the regulation of feeding and appetite.

The calcitonin receptor, found on osteoclasts,^[12] and in kidney and regions of the brain, is a G protein-coupled receptor, which is coupled by G_s to adenylate cyclaseand thereby to the generation of cAMP in target cells. It may also affect the ovaries in women and the testes in men.