Thyroid gland assays

In summary, our data provide evidence for the suitability of zebrafish eleuther-oembryos as a predictive vertebrate model for evaluating the effect of individual chemicals and mixtures on thyroid gland function. TIQDT performed on zebrafish eleutheroembryos is an alternative whole-organism screening assay that provides relevant information for environmental and human risk assessments. 

The total thyroid hormone content of thyroid glands and the ratio of T3 to T4 vary somewhat from one species to another. Thyroid USP preparations are therefore standardized on the basis of their iodine content. Much of the iodine in these preparations is in the metabolically inactive form of iodotyrosines. Thus, a given preparation may satisfy the USP iodine assay requirements and yet contain low amounts of T4 and T3. Thyrar (a beef extract) and Armour Thyroid tablets (a pork extract) are evaluated by additional biological assays to ensure consistent potency from one batch to another. 

Immunoassay kits using luminol and arylacridinium ester labels have been developed by nine companies for a variety of thyroid, steroid and pituitary hormones, viruses, digoxin, and creatine kinase. One assay for total and free thyroxin has detection limits of 20 pM in serum, while another for total and free triiodothyronine has a 3-pM detection limit in serum. These analytes are used as clinical indicators of thyroid gland malfunction. While research has shown that... 

The measurement of TSH was originally based on bioassays such as the stimulation of colloid droplet formation in the guinea pig thyroid gland and the release of labeled thyroidal iodide into mouse blood. These early in vivo bioassays, however, were of limited sensitivity and precision and were not applicable to the measurement of TSH in unfractionated serum. Most TSH bioassays have involved the in vitro stimulation of thyroid cyclic adenosine monophosphate (cAMP) or adenylate cyclase activity. The rat FRTL-5 thyroid cell line is an example of a particularly convenient and precise assay system. Unfortunately, such methods require purification and concentration of TSH from serum before assay. Sensitive detection of TSH in unfractionated serum is possible using a cytochemical bioassay, but this procedure is technically difficult and time-consuming. At present, immunoassay is the procedure of choice for the measurement of serum TSH in the clinical laboratory. 

Although extraction, purification, and biological assay of calciumlowering hormones have shown the thyroid gland to be the site where... 

With each report of a new biochemical effect of TSH on the thyroid gland, a new assay for TSH has been developed. Many of the assays have withstood the test of time. It is not within the scope of this chapter to discuss all the assays which have been developed over the years. Rather we will discuss recent progress in this field and describe those methods that are particularly useful in clinical situations. Kirkham s review (K3) is helpful on the subject of TSH assays. 

The purpose of this section is to summarize those procedures carried out on patients which depend upon certain physiological aspects of thyroid function including the interrelationship of the thyroid gland with the hypothalamus and the anterior pituitary glands. The TSH stimulation and the Ts suppression tests are only briefly discussed, mainly for historical reasons, as both are becoming redundant because of more recent developments such as TSH and T3 assays, and the diagnostic use of thyrotropin releasing hormone. 

The iodine content of the thyroid gland in lambs and in adult sheep has been reported by Marine and Lenhart (1909) and by Sigurjonsson (1938b). In the study by Marine and Lenhart, an average iodine concentration of 9 mg % was found for tissue samples from lambs aged 8-9 months, whereas a distinctly higher mean iodine level of 59 mg % N = 22) was recorded for 1- to 4-year-old animals. In contrast to this, the assays performed by Sigurjonsson. showed essentially similar values for 5-inonth-... 

In a study on thyroid glands derived from 107 rats, e.ssentially similar iodine values (mean, 18 mg %) were observed by Sankaran (1931) for animals between 20 and 150 days of age. A higher average iodine content of 66 mg % was reported by Remington et at. (1936-1937) in assays of 131 glands from animals aged 30 days to 1 year, but in accordance with Sanka-ran s investigation, no correlation was noted between age and the thyroidal iodine level. 

The RET proto-oncogene located on chromosome 10 codes for a transmembrane tyrosine kinase. Mutations at codon 634 are directly associated with multiple endocrine neoplasia type 2A and medullary thyroid carcinoma. If children are diagnosed to carry such a mutation, cancer can be prevented by removal of the thyroid gland. Accuracy and reliability of the diagnostic assay is critical here as in... 

Thiactic Acid, Assay of (Stokstad, Seaman, Davis, and Hunter)... Thyroid Gland, Chromatographic Analysis of Radioactive Iodine... 

Reflexive and Adaptive a. T4 Serum Assay Behavioral Evaluation i b. Thyroid Gland Histology... 

Cells have been isolated from many organs, including the pituitary, adrenal and thyroid glands, the testes and the corpus luteum. They have been used, without being maintained in vitro, for assaying the relevant hormones. Possibly the most used of such bioassays are those for LH and the structurally similar human chorionic gonadotrophin. The isolated cell bioassay of LH is used here as an example. This is an unusual isolated cell bioassay because it does assay the plasma directly in most other assays the isolated cells have become modified so that plasma is cytotoxic to them. 

Quantitative measurement of perchlorate in biological fluids is of importance to assay its effects on the thyroid gland. Urine samples are preferred for these studies because sample collection is noninvasive. Except for lactating women. 

The mice used for the electron microscopic study received the same treatment as the assay animals with the exception that no radioiodine was given. Specimens of the thyroid were obtained at the intervals described above from 2-3 ani mals for each sample. In vivo fixation was performed by dripping 1% osmium te-troxide in phosphate buffer (8) on the thyroid gland exposed imder light aether anesthesia. After 5 min., the thyroid lobes were removed, fixed in the same solution for 1 hr, dehydrated in graded solutions of acetone and finally embedded in Araldite. Thin sections were cut on a Leitz ultramicrotome, stained with lead hydroxide and observed in the electron microscope (Siemens El-miskop I). 

This value has been confirmed in vivo in the rat by assay of plasma levels of T3, T4 and TSH and by histological examination of the thyroid gland. 

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