Showing papers on "Thyroglobulin published in 1977"

Biosynthesis of thyroid hormone: Basic and clinical aspects☆

Abstract: Thyroid hormone formation requires the coincident presence of peroxidase, H2O2, iodide, and acceptor protein at one anatomic locus in the cell. The peroxidase enzyme appears to be a protoporphyrin IX containing heme protein, with binding sites for both iodide and tyrosine. It is probable that both iodide and tyrosine are oxidized to free radical forms which unite to form iodotyrosine. The peroxidase is also involved through an uncertain mechanism in iodotyrosine coupling and probably in oxidation of sulfhydryl bonds in thyroglobulin. H2O2 may be supplied by microsomal NADPH-cytochrome c reductase or NADH-cytochrome b5 reductase. Other possible intracellular H2O2 generating systems include monoamine oxidase and xanthine oxidase. The usual acceptor for iodide is thyroglobulin, which is currently believed to be iodinated within apical secretory vesicles at the cell border just prior to liberation into the colloid, or possibly after liberation into the colloid. Other soluble and insoluble proteins are also iodinated within the gland. The peroxidase is present in numerous cellular structures, but iodination activity occurs primarily, if not only, at the apical cell border. The controls of iodination are imperfectly known. Thyrotrophin modulation of iodide uptake, H2O2 generation, thyroglobulin synthesis, and peroxidase enzyme level obviously are the main regulations. Many of these actions are thought to involve mediation of adenyl cyclase and subsequent activation of intracellular phosphokinases. Antithyroid drugs of the thiocarbamide group are competitive inhibitors of iodination under some circumstances, but if much iodide is present, they react with the oxidized iodine intermediate and are irreversibly inactivated themselves. Clinical problems involving defective peroxidase function are among the most frequent hereditary defects of thyroid hormone formation. Recognized abnormalities include deficient peroxidase, abnormality in binding of the peroxidase apoprotein to its prosthetic group, and other less well-identified abnormalities in peroxidase structure and function. Peroxidase is typically elevated in thyroid tissue from patients with hyperthyroidism, sometimes deficient in cold thyroid nodules, and frequently diminished in tissue from patients with Hashimoto's thyroiditis.

Triiodothyronine, Thyroxine, and Iodine in Purified Thyroglobulin from Patients with Graves' Disease

Abstract: Previous studies have suggested that there is an overproduction of triiodothyronine (T(3)) relative to thyroxine (T(4)) in patients with thyrotoxicosis associated with Graves' disease. To evaluate whether or not an increased ratio of T(3) to T(4) in thyroidal secretion could be contributing to this relative T(3) hyperproduction, T(3), T(4), and iodine were measured in thyroglobulin (Tg) from controls and patients with Graves' disease who had been treated either with propranolol only or with antithyroid drugs plus iodide before surgery. To avoid possible artifacts associated with pulse labeling and chromatography, T(3) and T(4) were determined by radioimmunoassay of Pronase hydrolysates of purified Tg. Results of analyses of Tg from six control patients and seven with Graves' disease, not receiving thiourea drugs or iodide, showed that the iodine content of Graves' disease Tg was not different from normal. Both contained 3.4 residues of T(4)/molecule Tg, but there was 0.39+/-0.08 (mean+/-SD) residue of T(3)/molecule Tg in Graves' Tg as opposed to 0.23+/-0.07 residue T(3) molecule Tg in controls matched for iodine content (P < 0.01). This difference resulted in a significantly lower T(4)/T(3) molar ratio (9+/-2) in Graves' Tg as opposed to control (15+/-2, P < 0.001). In Tg from patients with treated Graves' disease, iodine, T(3), and T(4) were reduced, but the reduction in the latter was more substantial, resulting in a T(4)/T(3) molar ratio of 3.4+/-1. Fractionation of Tg from all groups by RbCl density gradient ultracentrifugation indicated that at physiological levels of Tg iodination, the molar ratio of T(3)/Tg was consistently higher in Graves' disease. The specific mechanism for this difference is not known, but it is not due to iodine deficiency. If T(3) and T(4) are secreted in this altered ratio in patients with Graves' disease, the magnitude of the difference could explain the relative T(3) hyperproduction which is characteristic of this state.

Plasma Thyroglobulin in Detecting Thyroid Carcinoma after Childhood Head and Neck Irradiation

Abstract: The level of thyroglobulin in plasma was measured in 904 subjects with a history of head and neck irradiation during childhood to evaluate its potential value in screening for and differentiating thyroid neoplasms. Mean plasma thyroglobulin level was significantly elevated in subjects with nodular thyroid disease versus those without evidence of nodules (49.8 versus 27.0 ng/ml). However, the overlap with normal subjects does not allow thyroglobulin assays to serve as the only screening procedure. The mean levels in subjects with benign and malignant thyroid nodules were indistinguishable (48.8 versus 53.9 ng/ml). Thirteen percent of otherwise normal-appearing subjects had elevated values that may represent clinically inapparent thyroid disease. It is concluded that in screening large numbers of persons at risk for thyroid neoplasia, thyroglobulin assays are useful in combination with other modes of evaluation. The assay is without value in distinguishing benign from malignant disease.

Delayed hypersensitivity in Graves' disease and exophthalmos: identification of thyroglobulin in normal human orbital muscle.

Abstract: Patients with Graves' disease and exophthalmos demonstrate delayed hypersensitivity to antigens present in extracts of certain normal human tissue; namely, thyroid gland and retroorbital tissue. The delayed hypersensitivity can be assayed in vitro by quantitating the amount of a lymphokine, migration inhibition factor (MIF), which is produced when T lymphocytes of patients with Graves' disease and exophthalmos are exposed to these antigens. In the present report, a partial purification is described for the retro-orbital tissue antigen which is responsible for the positive leucocyte migration inhibition factor assay (MIF assay) exhibited by the sensitized lymphocytes of these patients. The purified retro-orbital tissue antigen preparation demonstrates a 50- to 150-fold higher specific activity over crude homogenates in its ability to act as an antigen in the MIF assay of exophthalmic patients. Immunodiffusion, ultracentrifugation, and disc electrophoretic data indicate that this purified antigen preparatio...

Polypeptide chains of 19-S thyroglobulin from several mammalian species and of porcine 27-S iodoprotein.

Abstract: Undegraded 19-S thyroglobulin was purified from hog, ox, man, dog, sheep and rat thyroid glands. Sodium dodecylsulfate/polyacrylamide gel electrophoresis of the reduced proteins showed that all are formed of peptide chains of molecular weight about 330000. Carboxypeptidase A digestion of porcine 19-S thyroglobulin released consecutively two moles of leucine and then two moles of serine, thus offering strong evidence in favour of the idea that the protein is formed of two identical chains. The same C-terminal amino acids were detected in sheep, ox, dog and man thyroglobulins. No N-terminal amino acid was found by appropriate chemical and enzymatic techniques. Porcine 27-S iodoprotein was shown by carboxypeptidase A analysis to be formed of four single-stranded 330000-Mr subunits identical to those constituting the 19-S protein. Identity, both qualitatively and quantitatively, of the peptides obtained by CNBr cleavage of the two proteins as shown by sodium dodecylsulfate/polyacrylamide gel electrophoresis has confirmed this conclusion. Since 19-S and 27-S thyroid iodoproteins are formed of two and four probably identical chains, they must be termed 19-S and 27-S thyroglobulins or alternatively thyroglobulin dimer and tetramer, respectively.

Interference of serum thyroglobulin in the radioassay for serum antithyroglobulin antibodies.

Abstract: Parallel measurements of serum antithyroglobulin (anti-Tg) antibody by competitive binding radioassay and tanned red cell (TRC) agglutination were performed in subjects with and without thyroid disorders. Radioassays were carried out using a partially purified preparation of anti-Tg antibody obtained by affinity chromatography using human thyroglobulin (Tg) coupled to Sepharose 4B. Two-thirds (67.2%) of control subjects had undetectable antibody levels (<20 U/ml) by this method and only 3.1% had concentrations of ≥60 U/ml. Abnormally elevated levels (≥60 U/ml) were found in the majority of the patients with Hashimoto's thyroiditis (88.9%) or idiopathic myxedema (69.3%), in half of those with untreated (54.8%) or treated (47.1%) Graves' disease, and only in a minority of those with pituitary hypothyroidism (11.1%) or non toxic goiter (9.5%). A number of patients with toxic adenoma (37.5%) or thyroid carcinoma (27.2%) also had increased antibody concentrations by radioassay. The percentage of TRC-positive s...

Microfollicular thyroid carcinoma with amyloid rich stroma, resembling the medullary carcinoma of the thyroid (MCT).

Abstract: A human thyroid tumor is described which, on light microscopy, exhibited the features of medullary carcinoma of the thyroid (MCT). The cells were arranged in solid lobules or trabeculae, and the stroma was abundant and gave positive reaction for amyloid as assessed by congo red, crystal violet and thioflavin T stains. However, there was microfollicular differentiation in certain portions of the tumor even where the tumor was invasively growing. On electron microscopy, numerous microfollicles were identified even where unsuspected by light microscopy. There were junctional complexes, the cells possessed well developed rough endoplasmic reticulum, prominent Golgi and numerous dense bodies obviously derived from the Golgi vesicles, which were of the same morphology as "secretory" granules described previously by some authors in MCT. However, we find this kind of cytology typically in microfollicular thyroid carcinomas. Presence of about 100 A thick fibrils in the stroma was consistent with histochemically positive amyloid. The biochemical data were compatible with the differentiated follicular cell origin of the tissue. The homogenate contained poorly iodinated thyroglobulin, and thyroid peroxidase activity. Calcitonin was undetectable by a sensitive radioimmunoassay. It is concluded that this tumor was follicular thyroid carcinoma with amyloid rich stroma. The presence of amyloid and dense bodies with homogenous electron dense contents is insufficient for making conclusions about histogenesis of thyroid tumors. The so called MCT with amyloid stroma probably represents a heterogenous group of thyroid tumors, at least some of them derived from follicular epithelium.

The importance of thyroglobulin structure in thyroid peroxidase-catalyzed conversion of diiodotyrosine to thyroxine.

Abstract: We have previously demonstrated that thyroid peroxidase (TPO) not only catalyzes the iodination of thyroglobulin and other proteins, but that it also catalyzes the intramolecular conversion of DIT residues to T4 (coupling reaction). The present study was designed to determine whether the native structure of thyroglobulin contributes to the efficiency of TPO-catalyzed coupling. Two lines of evidence are presented in support of the view that the conformation of thyroglobulin is important for TPO-catalyzed coupling. The first was based on comparison of T4 yields in thyroglobulin and other proteins. The second involved the effect of guanidine pretreatment on T4 yields in thyroglobulin. Both types of experiment provided evidence that the native structure of thyroglobulin contributes to the efficiency of the coupling reaction. Specificity of thyroid peroxidase activity, on the other hand, does not appear to be of importance in the coupling reaction. (Endocrinology 100: 1129, 1977)

Ultrastructure and biochemistry of thyroid carcinoma.

Abstract: Thirty-two thyroid tumors, 9 benign, 23 malignant, and 12 samples of normal thyroid tissue were examined by light and electron microscopy. Thyroglobulin content was also measured in the tissues and, in a limited number of cases, enzymatic activities were determined, such as thyroid peroxidase-iodinase, acid protease, and deiodinase. The presence of significant amounts of 19S, 27S and 12S thyroglobulin was well correlated with the ability of the tumors to accumulate radioiodine. It is suggested that the presence of thyroglobulin be used as a marker of potential function of thyroid carcinoma. Two types of ultrastructural changes were observed in thyroid carcinoma. The first one was interpreted as accompanying the progressive loss of function of thyroid tumors, and was represented by the modifications of highly specialized structures such as RER, lysosomal dense bodies, colloid, etc. The second one is suspected to reflect the malignant transformation of the follicular cell. This concerned namely the nuclei, mitochondria, and intracytoplasmic inclusions. These changes may have a diagnostic value since they were not observed in benign conditions.

Spatial requirement for coupling of iodotyrosine residues to form thyroid hormones.

Abstract: A linear random copolymer of tyrosine and lysine and two synthetic oligopeptides containing two tyrosine residues in addition to lysine residues give thyroid hormone (thyroxine and triodothyronine) residues in good yield upon enzymatic iodination with thyroid peroxidase. These synthetic peptides may serve as simple models for thyroglobulin, the protein in which biosynthesis of the thyroid hormone takes place. For the formation of significant amounts of hormone, such model compounds must contain at least two properly spaced tyrosine residues.

A radioimmunoassay for human thyroglobulin: methodology and clinical applications.

Abstract: . A specific double-antibody radioimmunoassay with a sensitivity of 2.5 ng/ml has been developed for measuring thyroglobulin (Tg) in human serum. As endogenous anti-Tg antibodies in serum interfere in the assay, only sera with a negative tanned red cell (TRC) test are suitable for analysis. Tg was detectable in 84.7% of the euthyroid subjects, with a mean value of 6.1 (values ranging from nondetectable to 43.0 ng/ml). Values were significantly higher in women than in men. Tg release by the thyroid appears to be under pituitary control, as suggested by TSH stimulation and T3 suppression tests. Elevated Tg levels were found in hyperthyroidism, simple goitre, and differentiated thyroid carcinoma. The significance of circulating Tg and the possible application of the Tg RIA are discussed.

Hyperthyroidism from thyroid metastasis of pancreatic adenocarcinoma.

Abstract: A nontender goiter rapidly developed in a 54-year-old patient with suspected disseminated carcinoma. Thyroid function tests showed increased thyroxine, triiodothyronine resin uptake, free thyroxine index, and free thyroxine. Radioactive iodine uptake by the gland was near zero, and thyroid-stimulating hormone (TSH) was undetectable. Histologic examination of the thyroid before and after death showed invasion and disruption of the thyroid follicles by adenocarcinoma (pancreatic primary). Release of thyroglobulin by follicular disruption probably resulted in hyperthyroxinemia and suppression of TSH and radioactive iodine uptake, as occurs in subacute thyroiditis.

Triiodothyronine and thyroxine content of desiccated thyroid tablets

Abstract: Triiodothyronine (T3) and thyroxine (T4) were measured by radioimmunoassay in Pronase hydrolysates of four lots each of 1- and 2-grain tablets of desiccated thyroid (Thyroid, Armour) and thyroglobulin (Proloid, Warner-Chilcott). The methodology used was verified by studies of tablets containing known quantities of T4 and T3. One grain of desiccated thyroid contained 12 +/- 1 and 64 +/- 3 microgram (mean +/- SD) of T3 and T4 per tablet, respectively (T4/T3 molar ratio, 4.3). A 1-grain tablet of thyroglobulin contained 16 +/- 2 and 55 +/- 5 microgram of T3 and T4, respectively with a T4/T3 ratio of 2.9. Two-grain tablets generally contained twice the quantity of T3 and T4 in the 1-grain preparations. The variation in T3 and T4 content between the four lots of each tablet strength for each product was 10% or less. These estimates of T3 and T4 content are 1.5- to 2-fold greater than those previously published. This difference probably results from the more sophisticated methodology now available which does not require chromatographic separation of T3 and T4 or iodometry. Using calculations based on published estimates of T4 and T3 absorption and of the T3/T4 potency ratio, it would appear that the T3 content of desiccated thyroid and thyroglobulin provide approximately 39% and 51%, respectively, of the thyromimetic activity of these two medications.

Thyroglobulin Messenger Ribonucleic Acid Translation in vitro

Abstract: Total polysomes were obtained by homogenization of sheep thyroid glands in Tris-Cl-buffered sucrose, pH 7.5, treatment with 2% Triton X-100 and centrifugation of the magnesium-treated 27000 ×g supernatant through 1 M sucrose. Purification of thyroglobulin-specific polysomes was performed by indirect immunoprecipitation with rabbit antibodies to sheep thyroglobulin and donkey antibodies to rabbit immunoglobulin G. Thyroglobulin polysomes represented 30% of total polysomes. Synthesis of thyroglobulin peptides in a reticulocyte cell-free system, programmed with total RNA from immunoprecipitated polysomes, was 3 times higher than when total RNA from unfractionated polysomes was used. The size of the poly(A)-containing thyroglobulin mRNA was estimated by the capacity of RNA fractions obtained by sucrose density gradient centrifugation of total or immunopurified polysomal RNA to hybridize with 3H-labeled poly(U) and to stimulate thyroglobulin peptide synthesis in a reticulocyte lysate. 65% of the thyroglobulin messenger activity was located in a 33–36-S RNA peak and 35% in zones corresponding to 30-S and 26-S RNA species. The thyroglobulin-specific immunoprecipitable peptides synthesized in the reticulocyte lysate from the 33–36-S RNA were shown by polyacrylamide gel electrophoresis in denaturing conditions to contain a major component co-migrating with the constituent peptide chain of sheep thyroglobulin (Mr 330000). Other components migrated with Mr of about 210000 and 120000.

Localization of thyroglobulin antigenicity in rat thyroid sections using antibodies labled with peroxidase or (125)I-radioiodine

Abstract: In the hope of localizing thyroglobulin within focullar cells of the thyroid gland, antibodies raised against rat thyroglobulin were labeled with the enzyme horseradish peroxidase or with (125)I-radioiodine. Sections of rat thyroids fixed in glutaraldehyde and embedded in glycol methacrylate or Araldite were placed in contact with the labeled antibodies. The sites of antibody binding were detected by diaminobenzidine staining in the case of peroxidase labeling, and radioautography in the case of 125(I) labeling. Peroxidase labeling revealed that the antibodies were bound by the luminal colloid of the thyroid follicles and, within focullar cells, by colloid droplets, condensing vacuoles, and apical vesicles. (125)I labeling confirmed these findings, and revealed some binding of antibodies within Golgi saccules and rough endoplasmic reticulum. This method provides a visually less distinct distribution than peroxidase labeling, but it allowed ready quantitation of the reactions by counts of silver grains in the radioautographs. The counts revealed that the concentration of label was similar in the luminal colloid of different follicles, but that it varied within the compartments of follicular cells. A moderate concentration was detected in rough endoplasmic reticulum and Golgi saccules, whereas a high concentration was found in condensing vacuoles, apical vesicles, and in the luminal colloid. Varying amounts of label were observed over the different types of colloid droplets, and this was attributed to various degrees of lysosomal degradation of thyroglobulin. It is concluded that the concentration of thyroglobulin antigenicity increases during transport from the ribosomal site of synthesis to the follicular colloid, and then decreases during the digestion of colloid droplets which leads to the release of the thyoid hormone.

Electron microscopy of clear cell thyroid carcinoma.

Abstract: Three thyroid carcinomas composed in part or entirely of clear cells were studied by light and electron microscopy, and thyroglobulin content was determined by biochemical methods. Clear cells have been found in follicular and papillary thyroid carcinomas and in undifferentiated carcinomas. The clear (wasserhelle) appearance of the cytoplasm was due to the accumulation of glycogen. The major ultramicroscopic features of the clear cells were the presence of glycogen granules, the decreased amounts of rough endoplasmic reticulum, the increased amounts of free ribosomes arranged in polysomes, a hypertrophic Golgi apparatus, and a sparsity of dense bodies of lysosomal character. It is hypothesized that the intracellular accumulation of glycogen may be a result of a selective loss of the peptide portion of thyroglobulin, and may influence the degree of biochemical differentiation and the natural course of the tumors.

Concentration of thyroglobulin, iodine contents of thyroglobulin and of iodoaminoacids in human neonates thyroid glands

Abstract: The iodine and protein concentrations, the iodoamino acids content of thyroglobulin (TG) were determined in 17 thyroid tissues from human neonates who died from 3 hours to 47 days after birth. Total iodine concentration of neonate tissues increased with life duration. TG concentration was related to the survival duration of the neonates. Increase of the iodine content was associated to the increase of the TG content: mean value was 0.16 mug 127I/100 mug TG in neonates who died within the first 20 hours after birth, 0.25 mug in neonates who survived 26 to 72 hours and 0.43 mug in neonates living more than 10 days. Expressed as iodine content to total iodine ratio, iodoamino acid percentages were not related to the tissue. When the iodoamino acids were expressed in residues per molecule of TG, iodtyrosines, thyroxine and triiodothyronine increased with duration of survival. These variations in iodine content and concentration of thyroglobulin could be related to acute hormonal changes in serum observed in early neonatal period.

A long-term follow up of patients with autoimmune thyroid disease.

Abstract: SUMMARY A survey in a general practice in the North-East of England in 1963 detected thyroglobulin antibodies in 16.2% of women and 4.3% of men. High titres of antibodies were found in 4.6% of women and 1.6% of men. Forty-six subjects with thyroglobulin antibodies (from an original total of fifty-two) were studied in 1972 and forty of these were studied further in 1975. These subjects were compared with a group of age- and sex-matched controls from the original survey. Three of the subjects had developed overt hypothyroidism by 1975 and a raised serum thyroid-stimulating hormone (TSH) concentration was found more frequently in euthyroid subjects previously found to be antibody positive. There was a striking difference in the antibody studies in that only 26% of the previously antibody positive subjects had thyroglobulin antibodies in 1972 and 30% in 1975. A raised serum TSH concentration was found to correlate with cytoplasmic antibodies and particularly with the combination of cytoplasmic and thyroglobulin antibodies.

Clinical evaluation of a hemagglutination method for microsomal and thyroglobulin antibodies in autoimmune thyroid disease.

Abstract: A simple and reproducible hemagglutination technique for detecting microsomal and thyroglobulin antibodies has been evaluated in normal subjects and in patients with thyroid disease. Microsomal antibodies were detected in 89 percent of all patients with autoimmune thyroid disease and in 97 percent of patients with biopsy proven Hashimoto's thyroiditis. In contrast, thyroglobulin antibodies were present in only 55 percent of patients with biopsy proven Hashimoto's thyroiditis and in 44 percent of all patients with suspected autoimmune thyroid disease. It is suggested, therefore, that measurement of microsomal antibodies by a simple hemagglutination techniques be carried out in all patients with suspected thyroid disorders.

Reverse Transcription of Thyroglobulin 33-S mRNA

Abstract: Bovine thyroglobulin 33-S mRNA has been used as a template for the synthesis of a complementary DNA, using RNA-directed DNA polymerase from the avian myeloblastosis virus. The yield of the reaction was relatively poor and the size of the cDNA did not exceed 10 S. Nevertheless, a copy of high specific radioactivity (approximately 10(7) counts. min-1 microgram-1) could be obtained which hybridized specifically back to its template with an rot1/2 value about 5 times higher than that observed in hybridizations between hemoglobin mRNA (alpha + beta chain) and hemoglobin cDNA. This suggests that thyroglobulin mRNA does not contain extensive internal repetitive sequences. Quantification of thyroglobulin mRNA sequences among various RNA preparations from the beef thyroid was performed using cDNA/RNA hybridizations in RNA excess. The results confirmed that thyroglobulin mRNA represents the large majority of mRNA in membrane-bound polysomes and indicated the virtual absence of thyroglobulin sequences on free polyosomes. The cDNA transcribed from mRNA of bovine origin hybridized efficiently with thyroid RNA from goats, dogs and humans. Although the heterologuous hybrids exhibited the expected decrease in thermal stability, the bovine cDNA provides an appropriate probe for studies dealing with the expression of the thyroglobulin gene in various mammals including man.

Fine structural studies on the thyroid gland of the normal domestic fowl

Abstract: The ultrastructure of the thyroid gland of the domestic fowl has been investigated and found to be similar to that of mammals. The differences were found at subcellular level in the distribution of the “dark bodies” which were mainly apical and in the sizes of primary lysosomes. These were found to range from 100 to 500 nm in diameter. All organelles described in mammals as being concerned with the production of thyroglobulin and the two hormones thyroxine and triiodothyronine were found to be present.

Familial goitre with partial iodine organification defect, lack of thyroglobulin, and high levels of thyroid peroxidase.

Abstract: SUMMARY From a sibship of three sisters having congenital goitre and normal hearing, two had impairment of organification of iodide. S1 (4 years old) had goitre since birth, euthyroidism, and a negative perchlorate test. S2 (15 years old) and S3 (13 years old) were hypothyroid, and had radioiodide discharge after potassium perchlorate administration of 19.8% and 26.1%, respectively. Thyroid tissue was obtained at thyroidectomy. Peroxidase activity, in the thyroidal subcellular particles, was found to be qualitatively normal, but quantitatively increased. In the triiodide assay, the activity was: S1 6912 u, S2 2590 u, and S3 3844 u (normal values 900-1700 u). In the tyrosine-iodinase assay, the activities, expressed as nmoles of iodide incorporation per gram of tissue, were S1 1046, S2 471, and S3 547 (normal values 220-410). The activity of the thyroidal NADPH-cytochrome c reductase, an enzyme possible involved in hydrogen peroxide generation, was: S1 0.084, S2 0.047, and S3 0.055 (normal values 0.018 μEq/min/mg). No thyroglobulin was detected by analytical ultracentrifugation, polyacrylamide gel electrophoresis, or double immunodiffusion in agar of the supernatant fractions. In patient S3, whose gland was labelled in vivo with 125I, 60% of the total radioactivity of the gland (pooled nodular and paranodular specimens) was in a particulate iodoprotein that was solubilized by trypsin, deoxycholate or digitonin. In the soluble fraction there were two iodoproteins: iodoalbumin, and a second iodoprotein similar to the solubilized particulate iodoprotein. It is postulated that absence of the normal thyroidal receptor protein might be in some cases a cause of iodine organification defect.

Iodinating activity of thyroid tissue in toxic diffuse goiter.

Abstract: Thyroid tissue obtained from 12 patients with Graves' disease and treated with thionamide drugs for 3-7 mo before subtotal thyroidectomy, from 12 patients with Graves' disease, similarly treated, and given 50 mug of triiodothyronine (T3) for 10 days before surgery, and from 12 euthyroid patients with solitary cold nodules was investigated to compare in vitro iodination of thyroglobulin in toxic diffuse goiter and in normal thyroid tissue. The supernates of the homogenates (105,000g) were subjected to sucrose density gradient centrifugation (5--28%) to separate the thyroglobulin fraction. The precipitates were treated with 1% digitonin and centrifuged to collect the supernate (particulate fraction). When thyroglobulin and particulate fractions obtained from the same patient were incubated with 125I-, iodide, glucose, and glucose oxidase, the amount of iodine bound to thyroglobulin was several times greater in toxic diffuse goiter than in normal thyroid tissue; administration of T3 did not affect iodination in toxic diffuse goiter. When the thyroglobulin fraction from each patient was incubated with a standardized quantity of peroxidase instead of the individual particulate fraction, the amount of iodine bound to thyroglobulin was the same among the three groups of patients. Finally, when bovine serum albumin was substituted for thyroglobulin from each of the patients, iodination of bovine serum albumin was several times greater with the particulate fraction obtained from toxic diffuse goiter tissue than with that obtained from normal tissue. The guaiacol-oxidizing activity oty. These results suggest that in vitro iodination of thyroglobulin is increased in toxic diffuse goiter even when patients are made euthyroid by treatment with thionamide drugs as well as when they are given additional T3 for 10 days before operation. The increase in iodination of thyroglobulin appears to be due to an increase in peroxidase activity in the particulate fraction.

Long-term turnover of thyroid iodine in the rat as studied by the isotopic equilibrium method.

Abstract: A long-term kinetics study was made in rats in a steady state for iodine metabolism and receiving either 5 microng iodine (group5) or 50 microng iodine (group 50) daily. By using the isotopic equilibrium method, the value of the renewed fraction was followed during at least 120 days in the thyroglobulin (Tg) and the lysosomes of the thyroid and in the plasma hormones. For both groups, only part of the total iodine pool in the Tg as well as in the lysosomes is directly available for secretion. Furthermore, the direct precursor pool of iodine for secretion in the lysosomes is dependent on the daily iodine intake (1.3 times greater in group 50 than in group 5) while the Tg iodine supply in the colloid is not (80% of the total Tg iodine pool for both groups). An iodine pool with a very slow turnover is present in the lysosomes (about 50% in each group), in the Tg of group 5 (more than 15%) and probably in the Tg of group 50 (less than 5%). Thus, the distribution of such a pool between lysosomes and Tg is dependent on the daily iodine intake. The very slow iodine pool is probably not accumulated into the follicles, since every studied pool is in steady state. It is practically not secreted since hormones in the plasma are entirely renewed. Again, it is practically not deiodinated since the thyroid iodide pool is also entirely renewed. These three criteria are valuable for both groups. Although one cannot entirely exclude its participation in secretion, it is postulated that the major part of this pool is re-cycled without deiodination. Both lysosome-lysosome and lysosome-colloid pathways of re-cycling have been postulated. The second pathway is supposed to increase when the daily iodine intake is decreased.

Thyrotropin binding and long acting thyroid stimulator absorbing activities in subcellular fractions from isolated thyroid cells and thyroid homogenates.

Abstract: The ability of various thyroid subcellular fractions to bind [125I]iodo TSH and to absorb long-acting thyroid stimulator (LATS) and thyroid stimulating immunoglobulins (TSI) activities was examined. Membranes purified from thyroid homogenates or isolated thyroid cells absorbed LATS/TSI activities and specifically bound [125I]iodo TSH. Purified thyroglobulin, nuclei, mitochondria and ribosomes did not bind [125I]iodo TSH nor did they absorb LATS/TSI activities. Cell sap obtained by gentle lysis of isolated thyroid cells failed to absorb LATS/TSI activities and to bind labeled hormone. However, freeze-thawing of the cells fragmented the membranes, releasing [125I]iodo TSH binding as well as LATS/TSI absorbing activities into the soluble (cell sap) fraction. The results suggest that the LATS/TSI antigen is of cell surface origin, includes the TSH receptor or larger membrane fragments containing the receptor, and that its release into the soluble fraction is due to the fragmentation of the thyroid membrane du...