Thyroglobulin biosynthesis in "cold" and "hot" nodules in the human thyroid gland

Serum thyroglobulin levels in hypofunctioning nodules before and after surgery

Serum thyroglobulin (Tg) level was determined in 34 biologically euthyroid patients having benign hypofunctioning nodule, before and after surgery. Based on the results of thyroid scanning with radioiodine, 2 groups of patients were considered. Group 1 (n = 18) had solitary hypofunctioning nodule with an otherwise normal thyroid gland and group 2 (n = 16) had hypofunctioning nodule inside an enlarged and/or heterogeneous thyroid. Results were compared to a group of 30 control subjects. Mean Tg level was significantly elevated in both groups 1 and 2 before surgery. No significant difference was found between group 1 and group 2. After surgical removal of the hypofunctioning nodule (follicular adenoma), mean Tg level was normalized in group 1 and decreased but still remained elevated in group 2. It is concluded that the observed elevated serum Tg level is due to the presence of hypofunctioning nodule and/or heterogeneous thyroid tissue. Thus, Tg determination may be useful in the follow-up of operated hypofunctioning nodules in order to detect abnormality in the remaining thyroid tissue.

Human undifferentiated thyroid carcinoma synthesizes and secretes 19S thyroglobulin

Thyroglobulin (Tg) biosynthesis and secretion have been studied in one case of undifferentiated small spindle cell human thyroid carcinoma. From tumor tissue were extracted 32 mg of soluble proteins per gram of wet tissue, compared with 54 mg from control gland; after ammonium sulfate fractionation, density gradient centrifugation, and immunoprecipitation, 1.3 mg of Tg per gram of wet tissue, compared with 31.2 mg from control, were purified. By incubating in vitro up to 3 hours tumor slices with tritiated leucine, galactose, and 125I, the rate of incorporation of leucine and galactose increased with time in tumor tissue. However 125I incorporation into soluble proteins from tumor, at 3 hours of incubation, was only 1.7% of control value. By density gradient centrifugation of labeled soluble proteins a well-separated component sedimenting in the 19S peak was identified. No radioiodine was detected in the 19S fraction which showed the immunoreactive properties of 19S and was poor in 127I and sialic acid. In the incubation medium of tumor were secreted 0.4 mg of 19S Tg per gram of wet tissue compared with 48 mg of tissue in the control gland. Thus the undifferentiated thyroid carcinoma synthesizes a protein with the physiochemical and immunologic properties of 19S Tg. The undifferentiation of thyroid cells does not affect the biochemical steps involved in the synthesis of Tg.

Defective iodide transport and normal organification of iodide in cold nodules of the thyroid

Eleven thyroid follicular adenomas, cold on scintigram were analysed to determine whether defect in iodide organification or iodide transport causes low iodide uptake in cold nodules of the thyroid. The results were compared with perinodular tissue samples used as controls. In eight of eleven adenomas incubated in medium with 0.1 microM of iodide, newly organified iodide was 85.6 +/- 8.6% of total trapped iodide, which was significantly higher than 52.3 +/- 12.8% in controls. The remaining three adenomas showed a value as low as 4.0 +/- 2.7%. These data suggest that follicular adenomas are of two different groups; one with high organic iodinating activity and the other with none. These two groups were defined as FA-1 and FA-2. Thyroid:medium ratios of iodide of both groups were significantly depressed, indicating that the essential alteration in the thyroid follicular adenoma is a disturbance of iodide transport. In contrast to controls of organification of iodide was not inhibited by the addition of 100 microM iodide to the medium in FA-1 adenomas. In both FA-1 and FA-2, the degree of iodination of thyroglobulin (Tg) in equilibrium was significantly lower than that in controls. Therefore, in most cases with the follicular adenoma, the principal cause of decreased iodination of Tg was considered to be a depressed iodide transport, but not an impairment of organic iodination.

Biochemistry of thyroid regulation under normal and abnormal conditions

Perhaps in an oversimplified view, abnormal thyroid growth can be classified into two main categories: a) those cases due to excess of thyroid stimulators extrinsic to the gland; b) situations in which an intrinsic alteration in the gland occurs: Extrinsic (excess thyroid stimulation) Iodide deficiency with elevated TSH Goitrogens Graves' immunoglobulins Thyroid stimulating factors produced by tumors Dishormonogenesis with hypothyroidism Intrinsic (normal TSH) Increased sensitivity to TSH (iodine depletion) Altered autoregulation (?) Abnormal TSH receptor Other biochemical abnormalities From the studies performed in animals it can be concluded that since goiter appears before a detectable increase in serum TSH occurs, an intrinsic alteration in the thyroid gland would be responsible for the onset of growth. Under these conditions TSH would play a permissive role in promoting and maintaining the gland enlargement. In some aspects this situation is similar to that of certain endemic goiter areas. It may be postulated that under a mild iodine deficiency a decrease in thyroidal iodine concentration occurs (and/or in certain iodocompounds), thus rendering the gland more sensitive to the stimulatory action of TSH, and leading to the appearance of goiter. If this mechanism is able to maintain an euthyroid status no further alterations will occur. In more severely iodine deficient areas, or when additional factors such as dietary goitrogens are present, hypothyroidism develops and TSH is clearly elevated. A similar localized mechanism can be postulated for the development of nodular goiter. It is more difficult to explain the pathogenesis of goiter and tumors in nonendemic areas, since the biochemical findings so far reported are not conclusive. It seems likely that an alteration of the TSH receptor is a common factor to many tumors in man and animals. However, some contradictory results would preclude us from making a general statement. The wide variety of biochemical alterations reported would perhaps indicate, that there is not a single cause for the rise of abnormal thyroid growth and that different factors may play a role in the regulation of growth under such circumstances. It is to be hoped that future studies will provide a better comprehension of this problem.

Serum thyroglobulin in thyroid carcinoma and other thyroid disorders

Measurements of serum thyroglobulin (hTg) were performed using a specific radioimmunoassay. Sera with detectable anti-thyroglobulin (anti-Tg) antibody titers (> or = 1:10) as assessed by passive hemagglutination were discarded. Assays were carried out under conditions in which anti-Tg titers less than 1:10 produced no interference. The assay sensitivity was 1.25 ng/ml and the mean +/- SE concentration of serum hTg in 58 control subjects was 9.5 +/- 0.9 ng/ml (range < 1.25-27 ng/ml). A slight but significant (p < 0.025) increase in the mean hTg level was observed in 12 pregnant women at delivery (25.7 +/- 5.2 ng/ml). Moderate to marked elevations of serum hTg were observed in patients with nontoxic goiter (61.4 +/- 15 ng/ml; n = 23), subacute thyroiditis (138 +/- 67 ng/ml; n = 5), toxic adenoma (129 +/- 47 ng/ml; n = 13), untreated (424 +/- 101 ng/ml; n = 35) or treated (328 +/- 222 ng/ml; n = 14) toxic diffuse goiter. 88 patients with thyroid carcinoma and 10 with nonthyroidal malignancies were studied. The mean level of serum hTg was increased in untreated differentiated thyroid carcinoma (89.5 +/- 19 ng/ml; n = 13) but not in undifferentiated (10 +/- 2.9 ng/ml; n = 6) or medullary (0.8 +/- 0.2 ng/ml; = 3) carcinoma. In treated differentiated thyroid carcinoma the mean hTg levels were normal (8.2 +/- 0.2 ng/ml) in patients (n = 24) with no evidence of either a thyroid residue or metastatic disease, moderately increased (56.6 +/- 16 ng/ml) in patients (n = 27) with residual thyroid tissue, markedly elevated in patients with lymph node metastases (199 +/- 50 ng/ml; n = 5) and extremely elevated in those with bone (4004 +/- 982 ng/ml; n = 8) or lung (2520 +/- 620 ng/ml; n = 5) metastases. There was no significant difference in serum hTg between functioning (n = 23) and nonfunctioning (n = 5) metastases as assessed by 131I whole body scan. A slight but significant (p < 0.0005) increase in the mean concentration of hTg was observed in nonthyroidal malignancies (21.7 +/- 4.5 ng/ml; n = 10). Serial measurements showed a transient increase of serum hTg after 131I therapy of differentiated thyroid carcinoma, toxic diffuse goiter or toxic adenoma, with peak values usually occurring within the first three days. A fall of serum hTg after administration of suppressive doses of thyroid hormone to patients with nontoxic goiter and a rise after discontinuation of thyroid suppressive therapy in patients with metastatic differentiated thyroid carcinoma was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Triiodothyronine-secreting (toxic) adenoma of the thyroid gland: light and electron microscopic characteristics

A patient with thyrotoxicosis due to a triiodothyronine (T3)-secreting autonomous adenoma is described. The histmorphology of the neoplasms was similar to other neoplasms previously reported. Ultrastructural features of the adenoma are compatible with a very actively secreting follicular cell and are best compared with the ultrastructure of a diffuse toxic goiter. Distinctive features that separate toxic adenomas from various thyroid carcinomas and normal thyroid parenchyma are discussed.