Calcitonin: physiological actions and clinical applications.

Calcitonin (CT) was first reported as a hypocalcemic principle, initially thought to originate from the parathyroid gland, a view subsequently corrected to an origin from parafollicular C-cells. Human CT is a 32 amino acid peptide with an N-terminal disulphide bridge and a C-terminal prolineamide residue, shown to potently inhibit bone resorption. More recent studies have demonstrated that this may take place through a direct osteoclastic action.

Disorders associated with acute rapid and severe bone loss.

We describe a constellation of bone diseases characterized by the common feature of acute, rapid, and severe bone loss accompanied by dramatic fracture rates. These disorders are poorly recognized, resulting mainly from systemic diseases, frailty, immobilization, and immunosuppressive drugs, such as glucocorticoids and the calcineurin inhibitors. The opportunity to prevent or treat fractures is commonly missed because they are often not detected.

Calcitonin: the other thyroid hormone.

Calcitonin was originally discovered as a hypocalcemic factor synthesized by thyroid parafollicular C cells. Early experiments demonstrated that calcitonin inhibited bone resorption and decreased calcium efflux from isolated cat tibiae and subsequent histologic and culture studies confirmed the osteoclast as its major site of action. Its potent antiresorptive effect and analgesic action have led to its clinical use in treatment of Paget's bone disease, osteoporosis, and hypercalcemia of malignancy.

Osteoporosis: trends and intervention.

Osteoporosis is a skeletal disorder in which bone strength is compromised due to loss of bone density and bone quality. It is the leading cause of serious morbidity and functional loss in the elderly. At times, it is difficult for the clinician to distinguish between the disease and normal skeletal aging, but advances in the scientific understanding of the underlying disease process have made management of osteoporosis a preventable disease for the most part.