Calcitonin and calcitonin receptors.

Calcitonin (CT) is a polypeptide hormone with 32 aminoacids syntetized primarily by the thyroid.Several evidences support the existence of nonthyroidal CT like peptide. The CT gene transcript also encodes a distinct peptide known as calcitonin gene related peptide (CGRP) which is a potent vasodilator and responsible for the stimulation of the glomerular filtration rate. In addition, a 37 aminoacid peptide amylin has been originally isolated by pancreatic β-cells. Amylin is able to inhibit insulin secretion, glucose transport into the skeletal musculature and gluconeogenesis. It is also able to inhibit gastric emptying. In the kidney it is able to modulate Calcium (Ca(2+)) excretion and increases renin activity. Finally, high affinity amylin receptors have been identified in the brain of the rat. The calcitonin receptor (CTR) is a member of a subfamily of the seven-transmembrane domain G-protein coupled receptor super family that includes several peptides. Members of this family have a similar structure with other seven-membrane-spanning domain G-protein coupled receptors.The genetic contribution to osteoporosis susceptibility is well documented and many studies demonstrated that genetic factors play important roles in the regulation of bone metabolism. Restriction Fragment Length Polymorphisms (RFLPs) for the CTR gene have been described in the literature with a positive association with the lumbar bone mineral density (BMD), femoral neck BMD and with a lower incidence of vertebral fractures.