Immunocytological evidence for parathyroid hormone in human fetal parathyroid glands

Immunostaining with antiserum to bovine parathyroid hormone (PTH) was used to delineate the immunoreactive PTH (iPTH)-containing cells of parathyroid glands from 1 anencephalic and 29 normal human fetuses. The antiserum (GPO 3) cross-reacted with human PTH and recognized the carboxyl-terminal fragments of the PTH molecule. No iPTH-containing cells were observed in the parathyroid glands of the 6 fetuses younger than 10 weeks, in spite of the fact that organized parathyroid glands were identified by histological methods. By contrast, iPTH-containing cells were observed in all fetuses older than 10 weeks of gestation, including the anencephalic fetus. All cells were immunoreactive either at the cellular periphery or as a more diffuse cytoplasmic staining around the nucleus. No immunoreactive cells were observed in the thyroid or thymic parenchyma. The specificity of the immunocytological reaction was tested by the usual procedures. Previous in vitro studies suggested that parathyroid function might be active at 12 weeks of gestation. Our data suggest that iPTH is synthetized by parathyroid glands as as early as 10 weeks of gestation and is also present in the anencephalic fetus. The physiological significance of the early presence of PTH within the fetal parathyroid glands remains to be established.