Serum thyroglobulin level and thyrotropin receptors in plasma membranes from thyroid nodular relapse

The parameters of 125I-bTSH binding to plasma membrane as well as serum thyroglobulin (Tg) level in 13 euthyroid females, suffering from scintigraphically functioning thyroid nodule, were investigated. Thyroid tissue samples of five euthyroid patients were obtained by surgical reintervention, which was done because of scintigraphically functioning nodular goitre relapse (Group 1). Data were compared with two control groups. One of them (Group 2) consisted of 5 euthyroid females in whom partial thyroidectomy was done because of solid functioning thyroid nodule. Long-term follow-up during postoperative period confirmed normal morphofunctional status in them. The second control (Group 3) is consisted of 3 patients suffering from goitre relapse now. The percent of specific 125I-bTSH binding and the affinity of its binding to plasma membranes from nodular goitre relapse were lower (2.05% +/- 0.82; Kd1: 0.56 +/- 0.34 10(-9) M; mean and S.D., resp.) than to the membranes obtained from surrounding perinodular tissue (0.32 +/- 0.89; Kd1: 0.20 +/- 0.77 10(-9) M, resp.). However, the level of high affinity TSH receptors in plasma membranes prepared from nodular goitre relapse was higher than that in perinodular, assumed to be normal tissue (11.21 +/- 0.87 fmol/mg prot. versus 6.29 +/- 2.24 fmol/mg prot., mean and S.D.). Plasma membranes obtained from goitre relapse were characterised by high total number of receptor and binding sites (N1 + N2) for TSH. In Group 1 and 3 elevated serum Tg levels were confirmed during follow-up period with no correlation with TSH, which characterises a normal physiological status of regulation.