Stimulation of iodine organification in porcine thyroid cells by thyroid stimulators

Several Graves' sera were simultaneously assessed in a bioassay based on the ability of porcine thyroid cells to organify 125I and in a radioreceptor assay for TSH receptor binding activity. Both assay systems were sensitive to 1 mcU/ml (final concentration) of unlabelled bovine TSH. Six Graves' sera were studied in detail over a wide (0-1.0 mcl sera) dose response range in repeat determinations. Two sera exhibited parallel binding and stimulating. However, two sera revealed significant inhibition of 125I-TSH binding prior to the demonstration of stimulation and the other two sera showed stimulatory capabilities before significant binding was evident. IgG was prepared from one serum by ammonium sulphate precipitation and chromatography on Sepharose 6B and then subjected to preparative isoelectric focusing. The isoelectric distribution of the two activities were found to be identical with major peaks of activity at pl=9.5 and pl=8.5. In summary: 1) each Graves' sera exhibits different dose-response curves with respect to binding and stimulation, 2) at certain concentrations of sera, only binding or stimulation were evident, 3) neither assay was consistently more sensitive for the presence of Graves' immunoglobulins, 4) for one Graves' sera, binding and stimulation could not be separated by isoelectric focusing. These studies would suggest each Graves' immunoglobulin has inherently different characteristics in its interaction with the TSH receptor.     

NADPH-细胞色素C还原酶对碘有机化的影响

目的：探讨NADPH-细胞色素C还原酶(CR)在碘有机化中的作用。方法：应用荧光分析和同位素技术测定甲状腺H2O2浓度、CR活性和蛋白结合碘(PBI),观察CR所引起的H2O2变化对PBI形成的影响。结果：Graves病甲状腺CR活性高于正常,其H2O2水平和所形成的PBI亦明显高于正常;加CR抑制剂后,Graves病和正常甲状腺CR活性降低近84％,同时H2O2下降近45％,PBI形成随CR和H2O2水平降低而减少;而葡萄糖／葡萄糖氧化酶系统可使PBI恢复正常。结论：CR通过其所产生的H2O2影响PBI的形成,抑制CR活性可抑制甲状腺激素的合成。     

Effect of iodine on early stage thyroid autonomy

Thyroid autonomy is a frequent cause of thyrotoxicosis in regions with iodine deficiency. Epidemiological data suggest that iodide may influence the course of pre-existing thyroid autonomy. Making use of FRTL-5 cells stably expressing a constitutively activating TSH receptor mutation as an in vitro model of thyroid autonomy, we investigated the impact of iodide on proliferation, function and changes in global gene expression. We demonstrate that iodine inhibits growth in TSHR WT and L629F mutant FRTL-5 cells and downregulates e.g. protocadherin cluster (Pcdha1-13) and thyroid responsive element (Thrsp). In addition functional genes e.g. iodotyrosine deiodinase (iyd) and oncogen junB are upregulated, while sodium-iodide-symporter (Nis) and thyroid peroxidase (Tpo) are downregulated by iodide. Iodide tunes down the biological activity of autonomous thyrocytes and may thus be of therapeutic benefit not only to prevent the occurrence of somatic TSHR mutations, causing thyroid autonomy, but also to slow down the development of clinically relevant disease.     

Reparative growth in the rat thyroid: effect of TSH suppression

Previous investigations have shown that thyroid incision leads to a dramatic burst of follicular cell mitotic activity in cells adjacent to the wound edge in both normal rats and rats made hypothyroid by chronic goitrogen administration. Wound-induced thyroid mitotic activity therefore, is seen in rats with either normal or supranormal levels of circulating thyrotropin (TSH). This study was designed to investigate the thyroid mitotic response to wounding in the absence of detectable levels of circulating TSH. Rats were injected with large doses of L-thyroxine twice daily to render circulating TSH undetectable. Thyroids were incised and follicular cell mitotic activity, in relation to distance from the incision, determined at 24, 48 and 72 hr after incision. A mitotic response to wounding was maintained in L-thyroxine treated rats, even though circulating TSH was undetectable. The peak of activity was at 48 hr, but was only 50% of that found in the incised normal rat thyroid. The spatial distribution of the response suggests that there are two components of the wound response in the normal thyroid, one dependent on the presence of circulating TSH, the other TSH-independent. The results are discussed in relation to current understanding of cellular growth control.     

The role of phospholipids in TSH stimulation of adenylate cyclase in thyroid plasma membranes

Treatment of bovine thyroid plasma membranes with phospholipase A or C inhibited the stimulation of adenylate cyclase activity by thyroid-stimulating hormone (TSH). In general, basal and NaF-stimulated adenylate cyclase activity was not influenced by such treatment. When plasma membranes were incubated with 1–2 units/ml phospholipase A, subsequent addition of phosphatidylcholine or phosphatidylserine but not phosphatidylethanolamine partially restored TSH stimulation. Phosphatidylcholine was more effective than phosphatidylserine in that it caused greater restoration of the TSH response and smaller amounts of phosphatidylcholine were active. However, when the TSH effect was obliterated by treatment of plasma membranes with 10 units/ml phospholipase A, phospholipids were unable to restore any response to TSH. Lubrol PX, a nonionic detergent, inhibited basal, TSH- and NaF-stimulated adenylate cyclase activities in thyroid plasma membranes. Although phosphatidylcholine partially restored TSH stimulation of adenylate cyclase activity in the presence of Lubrol PX, it did not have a similar effect on the stimulation induced by NaF. These results indicate that phospholipids are probably essential components in the system by which TSH stimulates adenylate cyclase activity in thyroid plasma membranes. The effects do not seem to involve the catalytic activity of adenylate cyclase but the data do not permit a distinction between decreased binding of TSH to its receptor or impairment of the signal from the bound hormone to the enzyme activity.     

Ganglioside dependent return of TSH receptor function in a rat thyroid tumor with a TSH receptor defect

The 1-8 rat thyroid tumor line with a thyrotropin and cholera toxin receptor defect and a deficiency in higher order membrane gangliosides is shown to regain both receptor functions with the in vivo resynthesis or the in vitro reconstitution of higher order gangliosides. Reconstitution was achieved by exposing primary cell cultures of the tumor to preparations of gangliosides from thyroid cells with functional thyrotropin receptor activity.     

Effect of TSH and melatonin on thyroid activity in the rat.

Melatonin and TSH, injected separately, caused no change of the blood thyroxine level at 30 min after treatment. Simultaneous or subsequent administration of the two hormones induced an increase of the level. Thus, melatonin is capable of potentiating acute, thyroxine mobilizing effect of TSH.     

Cyclic AMP as the second hormonal messenger in the in vitro folliculogenesis of the foetal thyroid gland of the rat

Thyroid-stimulating hormone, the catecholamine isoproterenol, and prostaglandins E1 and E2, all substances known to increase cAMP concentration in thyroid tissue, accelerate the formation of follicular cavities in explanted thyroid of 15-day-old rat foetuses. Dibutyryl-cAMP added to the medium, but not sodium fluoride, also stimulates the folliculogenesis. Since fluoride stimulates membrane adenylate cyclase but does not increase the intracellular cAMP level, these results show that cAMP is involved as a second messenger in the activation of foetal thyroid morphogenesis induced by hormones. They indicate also that the thyroid gland of the foetal rat is capable of responding to hormonal stimulation as early as the 15th day of pregnancy; this implies that on day 15, the foetal thyroid possesses receptors not only for the thyroid-stimulating hormone, but also for catecholamines and prostaglandins.     

Ultrastructural changes in the rat thyroid gland during iodine deficiency

Thyroid ultrastructure changes were studied during the course of a low iodine diet in rats. At day 20, follicles were normal, but a number of them contained cells of higher density and with greatly elongated microvilli. Endoplasmic reticulum cisternae were frequently dilated. From day 20 until day 80, the most characteristic changes in the thyroid cells were the progressive accumulation of subapical peroxidase-positive exocytotic vesicles. After 80 days of the low iodine treatment, Golgi apparatuses were very active. Cell division could be observed. At this stage, exocytotic vesicles were generally very abundant. These data suggest that the remarkable accumulation of subapical exocytotic vesicles between day 20 and day 120 might represent an adaptation to the moderate and gradual increase in TSH stimulation that occurs in the conditions of low iodine diet.     

Ultrastructural and cytochemical effects of trypan blue on TSH stimulation of thyroid follicular cells

Summary Ultrastructural and cytochemical techniques were used to study the effects of trypan blue on the response of mouse-thyroid cells to exogenous stimulation by thyroid stimulating hormone (TSH). The dye delayed the response to TSH resulting in decreased colloid-droplet formation in the apical region of the cells. The dye did not stop the shift of trimetaphosphatase activity from lysosomes to phagolysosomes. The duration of the TSH-induced response was shorter in the dye treated thyroids. Small vesicles, with trimetaphosphatase reaction product, were found near Golgi elements, phagolysosomes, and the plasma membrane facing the intercellular space of adjacent follicle cells. Their enzyme activity was not affected by exposure to the dye. These data indicate that the primary effect of trypan blue on the response of thyroid follicle cells to TSH stimulation was reduced endocytosis in the apical region resulting in fewer colloid droplets.     

Release of cyclic AMP from the chicken thyroid stimulated with TSH in vitro.

The thyroid lobes excised from one-day-old or 13-day-old chickens were incubated with or without TSH, and cAMP in the medium was determined. TSH induced the release of cAMP from thyroid lobes, resulting in the increase of cAMP concentration in the incubating medium. The release of cAMP into the incubating media in the presence of TSH from the thyroids of the chickens which were pretreated with TSH neonatally was more marked as compared to that from the thyroids of the control chickens. The light and electron microscopic examination of the thyroid lobes incubated with TSH showed that the morphological changes such as colloid droplets formation and enlargement of endoplasmic reticulum were induced.     

Influence of the endogene TSH stimulation of thyroid volume increase in the patients after total thyroidectomy due to differentiated thyroid cancer

INTRODUCTION: The treatment-of-choice for differentiated thyroid carcinoma (DTC) is a total thyroidectomy with subsequent radioiodine therapy. In order to increase an iodine uptake in thyroid tissue remnants, the L-thyroxine withdrawal is required. It is recommended to achieve TSH levels higher than 25 mU/ml. As TSH is a known key factor in thyroid cell proliferation regulation, prolonged stimulation of the cells during L-thyroxine withdrawal can be a causative factor for a re-growth. Our aim was to assess the degree of thyroid re-growth in the patients after total thyroidectomy due to DTC and its possible clinical implications. MATERIAL AND METHODS: 23 patients operated due to papillary and follicular thyroid cancer were included into the study. Biochemical determinations and ultrasound thyroid imaging were performed (TSH, Tg) during suppressive L-thyroxine therapy as well as 4-5 weeks after the withdrawal. RESULTS: The mean volume of thyroid tissue remnants increased after withdrawal for substantial 30.1%. The difference was extremely significant. CONCLUSIONS: L-Thyroxine withdrawal in the patients after total thyroidectomy due to DTC can cause re-growth of the tissue remnants. The phenomenon may be of a clinical significance in the selected cases influencing therapeutic decisions.