Calcitonin

Thursday, March 18, 2010

Calcitonin is a linear polypeptide hormone which consists of 32-amino acids. In humans calcitonin is synthesized and secreted by the parafollicular cells (C-cells) of the thyroid. It acts to reduce blood calcium (Ca2+), opposing the effects of parathyroid hormone (PTH). High blood levels of Ca++ act as a humeral stimulus for releasing calcitonin, and lower levels reduce release. Calcitonin is important during youth, when the bones are growing rapidly. Calcitonin has a bone-sparing effect, by reducing bone resorption, and stimulating Ca++ uptake from dietary sources, and the circulation.

As a dietary supplement, calcitonin (Calcimar, Miacalcin) is a hormone that has been approved by the FDA in the United States for treating osteoporosis. Calcitonins come from several animal species, but salmon calcitonin is the most widely used. Calcitonin can be administered subcutaneously as a shot under the skin, or into the muscle (intramuscularly), or inhaled nasally. Intranasal calcitonin is the most convenient of the three methods.

Calcitonin has been shown to prevent bone loss in postmenopausal women. In women with established osteoporosis, calcitonin has been shown to increase bone density and strength in the spine only, though it is not as effective in increasing bone density and strengthening bone as estrogen.

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.

Calcitonin protects against Ca2+ loss from skeleton during periods of Ca2+ stress such as pregnancy and lactation It also regulates serum calcium level, prevents postprandial hypercalcemia resulting from absorption of Ca2+ from foods during a meal, and also regulates vitamin D levels.