Measurement of thyroid hormone in the rat thyroid gland by radioimmunoassay

The present paper describes (i) a hydrolysis technique with Pronase and leucine aminopeptidase using one rat thyroid gland, resulting in maximum release of thyroid hormones and minimum deiodination, and (ii) a simple and rapid procedure for thyroid hormone radioimmunoassays in thyroid hydrolysates using commercial kits intended for serum thyroid hormone determinations. The procedure is used to determine T4, T3, and rT3 concentrations and hormonal molar ratios in a thyroid gland from a male Wistar rat. The reliability of the method is also studied.     

Timing of repeat thyroid fine-needle aspiration in the management of thyroid nodules

Objective: The Bethesda System for reporting thyroid fine-needle aspirations (FNAs) recommends repeat aspirations be done at least 3 months following the initial aspiration to prevent false-positive misinterpretations due to reactive/reparative changes. Because limited data exists, we reviewed our own data to ascertain the recommendation. Study Design: We retrospectively reviewed thyroid FNAs accessioned in the Cytology Laboratory at Beth Israel Deaconess Medical Center in Boston, Mass., USA, from January 2006 to December 2008. We identified patients with repeat aspirates of a single lesion and those with thyroidectomy specimens. Cytologic and surgical diagnoses along with time between FNAs were recorded. Results: No statistically significant difference was detected in the distribution among nondiagnostic, suboptimal, and adequate categories with respect to the timing of repeat FNA (p = 0.25). Forty-six percent of the lesions that were nondiagnostic/suboptimal initially yielded the same results on repeat. Twenty-eight percent of initially adequate specimens were nondiagnostic/suboptimal on repeat (p = 0.04). Nine percent of those with an initial atypical diagnosis had the same diagnosis on repeat, while 2.6% of those who did not have an initial atypical diagnosis had an atypical diagnosis on repeat (p = 0.29). False positives between early (16%) and late (12%) repeats were not statistically significant (p = 0.74). Conclusion: The diagnostic yield and accuracy of repeat FNA is independent of the time interval between procedures but may be related to the original FNA diagnosis.     

Metabolism of the thyroid hormones

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 amine may modulate TSH secretion, and alterations of local pituitary deiodination (e.g. iopanoate inhibition) influence diurnal TSH secretion without changing TRH-dependent episodic TSH secretion pattern. A summary of structure-activity relationships of greater than 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 considered.     

Prostaglandins and the thyroid

Prostaglandins (PG), PGE in particular, exert an effect similar to the stimulating one of thyroidotropic hormone (TTH), a basic regulator of the thyroid function, on the thyroid gland cells. Specific finding of the above compounds with plasma membranes of the gland cells is the first stage of their action. In most cases formation of the PGE-receptor complexes, is followed by the corresponding increase in the intracellular content of cAMP due to adenylate cyclase activation. PGE can be regarded as original extracellular local regulating agents formed in neighbouring (or the same) cells under the TTH effect and modulating the action of the latter on the regulated gland. In this case the regulating action of the hormone and PGE can be realized through the same mechanisms. Under conditions of the thyroid gland pathology against the background of the thyrotropic control weakening it is impossible to exclude the possibility of the independent PGE action on different parameters of the thyroid function or their participation in realization of the effects of other regulating agents.     

Ultrastructural changes in thyroid epithelium during involution of the hyperplastic thyroid gland

The ultrastructure of the thyroid epithelial cell was examined at various time intervals after induction of involution of the hyperplastic thyroid gland. Thyroids were made hyperplastic by the feeding of thiouracil in a Remington low-iodine diet to male Fischer rats for 3 weeks. Involution was induced by replacing the thiouracil-containing diet with Purina Laboratory Chow, a high-iodine diet. During involution, organelles that play a role in the synthesis and secretion of thyroglobulin, such as the rough endoplasmic reticulum, Golgi apparatus, and apical vesicles, were well preserved and prominent features of the epithelial cell. The apical plasma membrane of many cells was highly irregular for approximately 2 weeks with signs suggesting rapid discharge of apical-vesical contents into the lumen of the follicle. Pseudopods and colloid droplets were present but were not very prominent features of the cell. No signs of extensive autophagy or obvious increased incidence of lysosomes were present, although there was an elevation in the incidence of small dense bodies starting about day 8, and prominent by 15 days. Some of these may be phagosomes formed from luminal debris. The observations indicate that involution of the hyperplastic thyroid in which there is maintenance of the protein synthetic apparatus and little sign of autophagy or death of the epithelial cells is remarkably different from phenomena occurring during involution of prostate or mammary glands.