ISSN:1663-2818    

DOI:10.1159/000180677

出版商:S. Karger AG    

年代:1987

数据来源: Karger

ISSN:1663-2818    

DOI:10.1159/000180678

出版商:S. Karger AG    

年代:1987

数据来源: Karger

ISSN:1663-2818    

DOI:10.1159/000180679

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Molecular studies of the thyroglobulin (Tg) gene have progressed significantly in recent years. Cloning and sequencing the complete bovine Tg cDNA led to the knowledge of the primary structure of the Tg subunit. This large polypeptidic chain displays a repetitive structure, especially in its amino-terminal half, and bears a striking homology with the acetylcholinesterase molecule of Torpedo californica 250 kb) Tg gene has been localized on the long arm of chromosome 8 in man, in close linkage with the c-myc oncogene. The study of its structure allowed the characterization of the molecular defect responsible for a congenital flaw in Tg gene expression in a herd of South-African cattle. This work led to the unexpected finding that the Tg pre-mRNA undergoes alternative splicing in normal animals, too. A DNA segment involved in the transcriptional control of Tg gene expression by cAMP has been identified by transfecting primary cultured thyrocytes with recombinant genes.

ISSN:1663-2818    

DOI:10.1159/000180680

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

It is well known that insufficient production of thyroid hormones during the fetal and neonatal period of development may result in permanent brain damage unless treatment with thyroid hormone is instituted very soon after birth. But congenital hypothyroidism is not the only situation in which brain damage may be related to insufficient thyroid function. Cretinism is the most severe manifestation of iodine deficiency disorders found in areas where iodine intake is greatly reduced. Some of the manifestations of cretinism suggest that the insult to the developing brain starts earlier than in the case of congenital hypothyroidism. Hypothyroxinemia of mothers with adequate iodine intake may also leave permanent, though less severe, mental retardation. For these reasons the possible role of maternal transfer of thyroid hormones during early fetal development have been reinvestigated, using the rat to obtain various experimental models. It has been shown that thyroid hormones are found in embryonic tissues before onset of fetal thyroid function and that thyroidectomy of the mother results in delayed development of the concepta. The concentrations of T4 and T3 in embryonic tissues from thyroidectomized dams were undetectable before the onset of fetal thyroid function, and still reduced in some tissues near term, despite the onset of fetal thyroid function. Treatment of control and thyroidectomized dams with methyl-mercaptoimidazole to block fetal thyroid function reduced thyroid hormone concentrations in fetal tissues near term, but this decrease could be partially avoided by infusion of physiological doses of thyroxine to the mothers. Iodine deficiency of the mothers resulted in thyroid hormone deficiency of the developing embryo, which was very marked until term in all tissues including the brain. The results strongly support a role for maternal thyroid hormones in fetal thyroid hormone economy both before and after the onset of the fetal thyroid function, at least in the rat. They also support a role of the hypothyroxinemia of iodine-deficient mothers in initiating the brain damage of the endemic cretin, a damage which would not be corrected once the fetal thyroid becomes active, as iodine-deficiency of the fetus would impair adequate production of hormones by its own thyroid, and maternal transfer would continue to be low.

ISSN:1663-2818    

DOI:10.1159/000180681

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The master choice for thyroid imaging remains the radioiodine thyroid scan with 123I or 99mTc. 131I has to be reserved for the follow-up of thyroid cancer only. Ultrasound may remain useful in certain situations but it does not integrate as it is the case with the radioisotopic scan together with morphological and functional information.

ISSN:1663-2818    

DOI:10.1159/000180682

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Ultrasound is very sensitive in evaluating the size of the thyroid gland and the presence of nodules within it. There are no specific signs indicative of malignancy though the majority of the differentiated carcinomas and all anaplastic tumors present as a hypoechoic mass. Since autonomous and ‘cold’ adenomas may show a similar echo pattern, a scintigraphic study is mandatory as part of the basic examination, except for euthyroid subjects without any nodularity on the ultrasound scans. Scintigraphically cold, echo-poor solid lesions require additional diagnostic procedures like aspiration cytology or biopsy until malignancy is definitely excluded. Monitoring of the thyroid volume during suppressive hormonal therapy is highly valuable for the early detection of’non-responders’ who probably will benefit from another man

ISSN:1663-2818    

DOI:10.1159/000180683

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Iodine storage is an important thyroid function which has been difficult to estimate by simple means up to now. The introduction of the X-ray fluorescence technique makes this assessment possible on a large scale, with a minimum radiation burden and no more discomfort for the patient than classical imaging with radioisotopes. Its implementation has resulted in the better understanding of some aspects of thyroid physiopathology. This paper deals with the clinical utility of the method: the visualization of stable iodine and, most important, its quantification contribute significantly, sometimes fundamentally, to a better diagnosis with its therapeutic implications.

ISSN:1663-2818    

DOI:10.1159/000180684

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Thyroid hormones influence numerous physiological and biochemical functions. The expression of the hormonal effects involves several events. The interaction of T3 with nuclear receptors, and the stimulation of mRNA production appears to be a major step. Extranuclear binding of thyroid hormones could account for early responses. Plasma membrane receptors may play a role in the cellular uptake of T3 and the stimulation of amino acids and sugar transport. A direct control of oxidative phosphorylation through binding of T3 to mitochondrial binding sites has been proposed. The role of cytosolic binding proteins remains unclear. The understanding of the mode of action of thyroid hormones requires a better knowledge of the molecular events occurring at the nuclear level, and the relation between the nuclear and extranuclear binding sites in the hormonal expression.

ISSN:1663-2818    

DOI:10.1159/000180685

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

This review covers the current knowledge about the various metabolic pathways involved in the conversion of thyroid hormones to the thyromimetically active and inactive iodothyronines. The concerted mechanism of systemic and local production of iodothyronines by tissue-specific iodothyronine deiodinase isozymes will ultimately determine the expression of thyroid hormone action. This is exemplified for the regulation of synthesis and release of TSH by iodothyronines at the pituitary level. Iodothyronine metabolites, e.g. Triac, rT3 and T3 200 naturally occurring and synthetic ligands of rat liver type I iodothyronine deiodinase isozyme propylthiouracil-sensitive) in vitro allows the design of iodothyronine analogues which either serve as specific substrates or antagonists of iodothyronine binding and metabolizing proteins. Furthermore, a complete picture of the ligand-complementary active site of the type I isozyme can be derived. A synthetic ‘structurally optimized’ iodothyronine-analogue flavonoid inhibitor of the type I deiodinase is able to displace T4 from binding to thyroxine-binding prealbumin and leads to unexpected organ-specific alterations of thyroid hormone metabolism and expression of thyroid hormone actions in an animal model. Therefore, for a complete understanding of thyroid hormone metabolism and action, thyroid hormone transport, cellular compartmentalization, and alternate pathways also have to be conside

ISSN:1663-2818    

DOI:10.1159/000180686

出版商:S. Karger AG    

年代:1987

数据来源: Karger