Androgen receptors and gender-specific distribution of alkaline phosphatase in human thyroid cartilage

The degree of mineralization in human thyroid cartilage is gender specific. Until now, laryngeal tissue was tested for sexual hormone receptors by the use of radiolabelled hormones only without exact localization of the receptors. In this study immediately frozen cartilage specimens from seven male and one female patient who underwent laryngectomy were used for immunolocalization of sexual hormone receptors. Additionally, serum sexual hormone levels were measured by means of radioimmunoassay. Alkaline phosphatase was localized enzymohistochemically in another cohort of six male and four female cartilage specimens from laryngectomies and autopsies. Chondrocytes in thyroid cartilage from both sexes reacted with antibodies to the androgen receptor. The low serum testosterone levels, which varied between 1.5 and 3.9 ng/ml, did not correlate with insufficient mineralization of thyroid cartilage in men (r=0.363, P=0.432). Chondrocytes did not react with antibodies to the estrogen receptor α and the progesterone receptor in both sexes. Expression of alkaline phosphatase started about the middle of the second decade. Some chondrocytes near the mineralization front were positive for androgen receptor and alkaline phosphatase, other chondrocytes were negative for both. Our results suggest the involvement of androgen receptor positive chondrocytes in thyroid cartilage mineralization, probably by a testosterone-linked stimulation of alkaline phosphatase.