Evidence for Calcitonin in the Thyroid Gland of Normal and Anencephalic Human Fetuses: Immunocytological Localization, Radioimmunoassay, and Gel Filtration of Thyroid Extracts*

Immunostaining with antiserum to human calci-tonin (CT) was used to delineate the immunoreactive CT-containing cells (iCT-CC) of thyroid glands from 27 normal and 5 anencephalic human fetuses. Gut, pancreas, anterior pituitary, and parathyroid glands from 8 fetuses were also studied. In parallel, measurement of the iCT concentration in thyroid lobes from 21 normal and 5 anencephalic human fetuses was performed by RIA of tissue extracts. Two pools of thyroid extracts were submitted to gel filtration on a Bio—Gel P-30 column. In normal fetuses, the first appearance of iCT-CC was observed in the thyroid glands at 14 weeks of gestation, before the follicular organization. From 14–27 weeks of gestation, the number of iCT-CC increased from 1 or 2 to some 50 cells/horizontal section of the middle third of the thyroid lobes. The pattern of distribution of iCT-CC was similar to that reported in the human neonatal and adult thyroid glands. Furthermore, by using the cytochemical method (determination of acetyl—cholinesterase activity), there was good evidence that iCT-CC corresponded to the fetal C cells. In anencephalic fetal thyroid gland, iCT-CC were observed in a pattern similar to that in the normal fetuses, suggesting that hypothalamic factors are not needed for the maturation of the C cells and theirability to synthetize CT. No iCT-CC were found in tissues other than the thyroid gland. The presence of iCT in the fetal thyroid glands was confirmed by the finding of a detectable amount of iCTin the thyroid extracts since 15 weeks of gestation. The chromatographic pattern of iCT from fetal thyroid gland showed that in both normal and anen-cephalic fetuses, the major immunoreactive component was identical to the human CT 1–32 monomer. The physiological significance of the early presence of CT within the fetal thyroid gland remains to be established.