A differential nuclear uptake and retention of ³H-androgens in the thyroids of baboons

Women have a greater incidence of autoimmune thyroiditis, thyroid cancer and radiation-induced carcinogenesis than men. Over the past several years we have examined for the presence of steroid receptors in both humans and non-human primates. In this study we examined the nuclear uptake and retention of ³H-testosterone, the main circulating androgen in mammals, in different cells of the thyroid gland of baboons, our non-human primate model. Castrated-adrenalectomized male baboons were injected with ³H-testosterone (1 μg/kg bw) and killed 1 1 /2 h later. The thyroid glands and other tissues were removed and processed for autoradiography. Nuclear localization of ³-testosterone or one of its metabolites was found in a small fraction of the follicular cells (approximately 10–20%). The discrepancy between these findings and those previously obtained with ³H-dihydrotes-tosterone (virtually 100% of the follicular cells concentrated the ³H-steroid) are discussed. The results from this study and those of the past strongly support a direct action of androgen on the thyroid. Whether a direct action of androgen on the thyroid is related to smaller incidence in autoimmune thyroiditis, thyroid cancer and radiation-induced carcinogenesis in men than women remains an unanswered question at the present time.