Increased Thyrotropin Binding in Hyperfunctioning Thyroid Nodules

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Abstract
The object of this study was to investigate TSH receptors in hyperfunctioning thyroid nodules (HFN). In HFN, obtained from seven patients, 125-I-TSH binding as determined by equilibrium binding analysis on particulate membrane preparations, was found to be significantly increased as compared with normal thyroid tissues (five patients; P < 0.001). Scatchard analysis of TSH-binding revealed two kinds of binding sites for both normal thyroid tissue and HFN, and displayed significantly increased association constants of high- and low-affinity binding sites in HFN (Ka = 11.75±6.8 109 M-1, P < 0.001 and Ka = 2.1±1.0 107M-1, P < 0.025; x ± SEM) as compared with normal thyroid tissue (Ka = 0.25±0.06 109M-1, Ka = 0.14±0.03 107M-1; x ± SEM). The capacity of the high-affinity binding sites in HFN was found to be decreased (1.8±1.1 pmol/mg protein, x ± SEM) in comparison with normal thyroid tissue (4.26±1.27 pmol/mg protein; x ± SEM). TSH-receptor autoradiography applied to cryostatic tissue sections confirmed increased TSH binding of the follicular epithelium in HFN. These data suggest that an increased affinity of TSH-receptor sites in HFN in iodine deficient areas may be an important event in thyroid autonomy.

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