Calcitonin definition

Methodology. Several radioimmunoassays of human calcitonin (hCT) have been developed In the past 5 years (18-20). Their greatest utility has been In the definitive diagnosis of patients with medullary carcinoma of the thyroid gland (MTC) and, recently. In Identifying family members of these patients who have occult MTC. 

The amino acid sequences of porcine, bovine, human, and salmon calcitonin are known. That of porcine calcitonin is shown in Fig. 5-13. Studies relating structure and activity have begun, but it is too early for any definite conclusion. Of the 32 amino acids, 18 in the human calcitonin sequence differ from those in the porcine hormone, and salmon calcitonin is more active in mammals than all known mammalian calcitonins. Moreover, the effect of salmon calcitonin is much longer than that of mammalian calcitonin. 

Nevertheless, claims of partial purification of the natriuretic hormone are not definitive. Moreover, well-known hormones, such as calcitonin and a-NSH, could also be responsible for the natriuretic effect. It is questionable that either of these hormones plays a considerable role in regulating sodium metabolism. Hormone responses to sodium loads and losses are summarized in Fig. 9-9, and the hypothetical role of the natriuretic hormone is illustrated in Fig. 9-10. 

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