Evidence for triiodothyronine receptors in human endometrium and myometrium

Thyroid gland dysfunction in humans may cause various female reproductive tract disorders. Thyroid hormone action is thought to be mediated by high-affinity low-capacity receptor proteins located in the nucleus. The studies detailed in this report were undertaken to determine if uterine nuclei contain specific high-affinity receptors for thyroid hormone. Nuclei from human endometrium and myometrium were prepared by homogenization and centrifugation following routine surgical procedures. With the use of isolated nuclei, binding experiments with 125I-triiodothyronine (T3) revealed a dissociation constant of approximately 1 X 10(-9) M in both endometrium and myometrium with a maximum number of binding sites equivalent to 0.06 and 0.21 pmol/mg of DNA, respectively. The solubilized binding sites were destroyed largely by trypsin treatment. Competition experiments revealed the following relative binding affinities for these nuclear binding sites: L-T3 greater than D-T3 greater than L-thyronine greater than reverse T3. These results indicate the presence in the human uterus of specific high-affinity binding sites with characteristics expected of a T3 receptor and thus raise the possibility that thyroid hormone may exert effects on the uterus through these receptors.