Detection of a high-affinity prostaglandin I2 binding site in the human thyroid

This study is concerned with the identification and the pharmacological properties of PGI2 receptor binding sites on human thyroid membrane fractions. Scatchard analysis is not linear, revealing a high- and a low-affinity receptor binding site. (3 H)Iloprost binding experiments were performed under various clinical conditions: in thyroid cancer the low-affinity binding sites disappear totally and the specific high-affinity binding sites are diminished according to the grade of differentiation of the cancer. An alteration in Bmax and Kd is also observed in cold nodules, in Hashimoto's and Riedl's thyroiditis and in hyperthyroidism, whereas hot nodules exhibit an increase in both the receptor subpopulations. The data provide evidence for specific PGI2 binding sites and support the suggestion of a direct regulatory key-role of PGI2 in thyroid intermediary metabolism.