The uptake and retention of radiolabelled estradiol was studied in the thyroid gland of the female baboon. Four baboons were injected intravenously with 1 μm/kg body weight of 3H-estradiol. One animal, which served as a control, received an additional injection of 100 μg/kg body weight of unlabelled hormone. One hour after the injections, the animals were killed and the thyroid glands removed and processed for either autoradiography or autoradiography in combination with immunocytochemical staining for C cells. Localization of estradiol was observed in the nuclei of interstitial cells, but not in those of the follicular cells. Nuclei of immunostained calcitonin-containing cells in both the walls of the follicles and the interfollicular compartment were not radiolabelled. This study suggests that estrogen does not regulate calcitonin secretion by the C cells of the thyroid via a classical receptor system.
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