Calcitonin in extrathyroidal tissues of man

Prior studies have demonstrated detectable immunoreactive calcitonin in the serum and urine of totally thyroidectomized humans, suggesting that the hormone may be secreted by extrathyroidal tissues. Accordingly, a study of the immunoreactive calcitonin content of human tissues was undertaken, utilizing autopsy material from 23 patients. Significant amounts of calcitonin were found in many extrathyroidal tissues, ranging up to 40 ng/g wet weight. The hormone was detectable with two antibodies having different region specificities for calcitonin. Gel filtration and subsequent radioimmunoassay demonstrated that extrathyroidal tissue has calcitonin fractions of the same molecular size and charge characteristics as do the serum and thyroid. The finding of large amounts of extrathyroidal calcitonin may explain why thyroidectomy in man is not accompanied by marked changes in calcium metabolism.