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  • Title: [Studies on the thyrotropin receptor and adenylate cyclase activity in various thyroid diseases: I. The properties of TSH receptor and adenylate cyclase in Graves' thyroid and retro-orbital adipose tissues (author's transl)].
    Author: Abe Y.
    Journal: Nihon Naibunpi Gakkai Zasshi; 1980 May; 56(5):739-53. PubMed ID: 6248386.
    Abstract:
    Most current etiologic concepts of Graves' disease postulate that this is an autoimmune disorder. A humoral factor, such as thyroid stimulating immunoglobulin, may be the mediator. On the other hand, it has also been suggested that abnormalities in the thyroid gland itself might be responsible for hyperfunction of the gland in Graves' disease. The true etiology of Graves' disease is still unknown. Similarly, the pathogenesis of the ophthalmic changes of Graves' disease is obscure, but immune mechanisms figure prominently in current hypotheses of the pathogenesis. It has been suggested that human adipose cell membranes have TSH receptors and that antibodies reacting with the receptors may stimulate fat cells. In this study, we have evaluated TSH receptor and adenylate cyclase of Graves' thyroid glands. Furthermore, we have investigated those of retro-orbital and the other adipose tissues in the guinea pig and in man. Human thyroid tissues were obtained at surgery and immediately minced homogenized with a loose-fitting Dounce homogenizer. A part of 10,000 g pellet of the homogenate was used for adenylate cyclase assay. The rest of the pellet was further purified by a discontinuous sucrose gradient ultracentrifugation, and the plasma membrane fraction was used for the receptor assay. The 125I-TSH binding to the fraction was measured, and the affinity constant (Ka) and capacity (Ro) were obtained from Scatchard plots using Rosenthal's method of analysis. Normal thyroid tissue contained high affinity (Ka = 2.4 x 10(10) M-1; Ro = 0.9 pmole/mg protein) and low affinity (Ka = 1.9 x 10(8) M-1; Ro = 386 pmole/mg protein) receptors. The two orders of TSH receptor were also found in Graves' thyroid tissue. The affinity constant and capacity of high affinity receptors were identical with those of normal thyroids, but the affinity constant of low affinity receptors was lower in Graves' thyroid (P less than 0.05). The basal adenylate cyclase activity in normal thyroid tissues was 0.35 nmole/10 min/mg protein. The activity rose to 280% of basal with 166 mU/ml of TSH and 680% of basal with 10 mM of NaF. These values obtained in Graves' disease were not significantly different from the values of normal thyroids. It is concluded that thyroid hyperfunction in Graves' disease is probably not the result of an intrinsic abnormality of the TSH receptor-adenylate cyclase system. Human retro-orbital adipose tissue was obtained at surgery from patients of Graves' exophthalmos or malignant neoplasm of accessory sinus. Guinea pigs tissue was obtained from 250g male animals. We were unable to demonstrate high affinity TSH receptor in human retro-orbital fat, perirenal fat or guinea pig retro-orbital fat. In contrast, guinea pig epididymal fat membranes showed TSH receptor characteristics similar to guinea pig thyroid membranes. In human adipose tissue, TSH did not stimulate the adenylate cyclase activity, although NaF definitely stimulated the enzyme...
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