Assay of Human Thyroid Glands for Thyrocalcitonin Activity1

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Abstract
Extracts of thyroid tissue from 15 consecutive patients undergoing surgery of the neck were assayed for thyrocalcitonin in rats by a standardized biological assay method. Hypocalcemic activity was detected in all 12 of the normal specimens, presumptive evidence for the presence of thyrocalcitonin in the normal human thyroid gland. Quantitative assays obtained in 11 of these cases showed a range of 9 to 170 U/g of thyroid gland with a mean of 42 U/g, which is approximately 1% of the concentration of thyrocalcitonin found in rat thyroid glands, assayed by the same method. No hypocalcemic activity was detected in 2 thyroid adenomas and 1 hyperplastic gland at the dose levels injected, the equivalent of 200 mg of thyroid tissue/rat. Thyrocalcitonin was detected at a low concentration in 1 colloid goiter. The thyrocalcitonin concentration in thyroid tissue from a long-standing case of pseudo-hypoparathyroidism was approximately 100 times higher than in the average normal human thyroid gland. Conclusions: thyrocalcitonin is a normal constituent of the thyroid gland of man as well as of all other mammalian species examined; the normal thyrocalcitonin concentration in the human thyroid gland, as assayed in the rat, is relatively low, possibly due in part to species differences in the hormone; increased follicular activity, as in thyroid adenoma and thyroid hyperplasia, is associated with decreased thyrocalcitonin concentration; the finding of a marked elevation in thyrocalcitonin concentration in 1 case of pseudo-hypoparathyroidism suggests that an abnormality in thyrocalcitonin metabolism should be given consideration as a possible factor of importance in this syndrome.