Recent advances with thyrocalcitonin

Thyrocalcitonin (TCT) is a 32 amino acid peptide hormone similar, but not identical, in structure from fish to man. Mammals produce the hormone in non-follicular thyroidal "C-cells" which can be identified visually using recently developed immunocytochemical methods. Although TCT exerts effects on the gut and kidney, bone seems to be the primary target tissue. The ability of TCT to restrict calcium fluxes from bone to blood and to inhibit bone resorption explains its utility for treating certain metabolic bone diseases, e.g. Paget's disease. The bone effects also account for the ability of TCT to combat a hypercalcemic challenge. Recent work suggests close relationships and a possible closed-loop feedback system between the gut and thyroid. In animals, gastrin is a potent TCT secretagogue; studies in man indicate that TCT, in turn, can effect gastric acid secretion and intestinal secretion of water and electrolytes. This gastrin-TCT relationship may help control levels of blood calcium during intestinal absorption of calcium following feeding. The ability of gastrin to stimulate TCT release has been applied clinically for the early diagnosis of medullary thyroid carcinoma (MTC), a C-cell tumor. Subclinical or questionable cases of MTC have been identified reliably using a simple, rapid provocative test involving pentagastrin injection and evaluation of blood samples by radioimmunoassay for elevated levels of TCT.