Autoradiographic studies with 3H 1,25 (OH)2 vitamin D2 and 3H 25 (OH) vitamin D3 in rat parathyroid glands.

After injection of radiolabeled 1,35 (OH)s vitamin D3, nuclear concentration of radioactivity is observed in parenchymal cells o hte parathyroid gland in pregnant, adult male, and 10-day male neonatal rats. In competition studies with unlabeled 1,25 (OH)2 vitamin D3, but not with 25 (OH) vitamin D3, in contrast to 3H 1,25 (OH)2 vitamin D3, do not show nuclear concentration in cells of te parathyroid. The results of te autoradiographic studies suggest the presence of receptors for a direct effect of 1,35 (OH)2 vitamin D3 on the parathyroid gland for modulation of parathyroid hormone secretion.