| Abstrakt: |
The presence of high affinity receptor sites for thyroid-stimulating hormone (TSH) in the human is not limited to the thyroid gland. In this report, the properties of thyroidal and extrathyroidal TSH binding have been explored through the effect of various agents (TSI of Graves' disease, propranolol, hCG, N-acetylneuraminic acid, ACTH, insulin and L-thyroxine) on the receptors.Statistically significant inhibition of [125I]TSH binding occurred with all immunoglobulin preparations (TSI) of Graves' disease on thyroid cell membrane receptors. Thirty-three per cent of the same immunoglobulins showed significant inhibition of [125I]TSH binding when testicular cell membranes were used, while there was no such inhibition when renal cell membranes were utilized. D or L-propranolol at least doubled the [125I]TSH initial binding (Bo) to the thyroid membranes but had no effect on the testicular or fat cell binding. Human chorionic gonadotrophin (hCG) at concentrations of 400 USP units per 350 μl totally inhibited the [125I]TSH from binding to testicular membranes but not to thryroid or fat cell membranes. Conversely, the binding of [125I]hCG to human testicular membrane was inhibited by both stable hCG and TSH, but with human thyroid membrane, only TSH could inhibit binding of [125I]hCG. These data suggest that the TSH receptors in extrathyroidal tissues may not be identical to TSH receptors within the thyroid. TSH binding to thyroidal tissue was significantly suppressed by N-acetylneuraminic acid, was increased by D and L-propranolol and was unaffected by ACTH and insulin. L-thyroxine had a dose-related suppressive effect on the TSH binding, commencing at 50 μg/ml. While these effects were observed in vitro, it is possible that some of the above agents may also interfere with thyroid gland function in vivo. They suggest further that a number of interactions may take place at the TSH binding sites which could alter TSH binding and/or function. |
