Abstract
lf a maximum binding occurred within 15 minutes at 4” and 37”C, pH 7.45, and remained stable for 5 hours. (3) Optimum binding occurred at pH 6.0. (4) Binding of tracer quantities of ““I-bTSH increased in a nearly linear fashion with increasing particulate protein concentrations up to 33 t.tg/ml. (5) Both a high and low aj%ity binding site were usually present in NT, A, and PC. (6) The maximal percentage of binding of tracer quantities of “‘I-bTSH (mean + SE) varied from experiment to experiment in both the normal and neoplastic thyroid tissue. Because of this variation, binding to neoplastic normal thyroid tissue always was compared with binding to adjacent histologically normal thyroid tissue removed from the same patient. The maximum percentage of binding of tracer quantities of “‘I-bTSH (mean + SE) in the particulate fraction (33 pg of protein/ml) in NT (15.7 + 2. I) was greater (P < 0.001) than in A (5.4 + 0.7). The maximum percentage of binding, although lower in NTfrom patients with thyroid cancer than in patients with thyroid adenomas, was comparable in NT (8.0 + 1.2), in PC (8.8 +- 1.8), and in MC (6.2 + 0.4). (7) The apparent a@& constants (Ka, and Ka,) for A and PC were similar to the apparent afini~ constants obtained with NT (8) Th e number of high afinity binding sites in the particulate fraction was greater (P < 0.025) in NT (4.72 ? 0.89 X IO”) than in A (0.55 z? 0.37 X 1O’l) but was comparable in NT and PC. Therefore, normal and neoplastic thyroid tissue appears to have specific TSH binding sites. This helps to explain why some tumors regress in patients given exogenous thyroid hormone and lends support to the notion that all patients with d$erentiated thyroid tumors should receive full replacement doses of thyroxine after thyroidectomy.
Published Version
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