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[Function of the posterior lobe of the hypophysis in rats under long-term thyroliberin administration].

Thyroliberin injected intraperitoneally to rats in doses of 0.5 microgram/100 g body weight two times a day markedly increased the blood plasma thyrostimulating hormone (TSH) content by the 6th day of using, followed by its decrease down to the control level by the 9th day of the experiment. The blood plasma thyroid hormone levels of these rats were lower than those of the controls by the 6th and 9th days of the test. Photometry of the concentration of the Gomori-positive neurosecretory matter in the posterior hypophysis has shown a significant rise of its amount by the 9th day of the trial. However, changes in the neurosecretory matter did not correlate with the alteration of the TSH- and thyroid hormone levels. Simultaneous administration of thyroliberin and diiodothyrozine (7.5 micrograms/animal) led to the inhibition of thyroliberin TSH-stimulating effect. The above increase in the neurosecretory matter concentration testifies indirectly that long-term thyroliberin injection produces less intensive hormone secretion from the posterior hypophysis into the blood cannel.

Animals↗
PubMed1983

Would I-123 di-iodotyrosine provide a harmless deiodination test? Concise communication.

Defective iodotyrosine deiodinase activity may benefit from a specific treatment, thus requiring an unequivocal diagnosis. In reported cases this diagnosis has been obtained from an in vivo deiodination test making use of di-iodotyrosine (DIT) labeled either with I-131 or I-125. Dosimetric calculation indicates that such tests may result in unacceptable irradiation of the thyroid of a child wrongly suspected of having defective iodotyrosine deiodinase activity; therefore other methods are needed. The use of I-123 DIT is shown to be feasible, but even a 1:30 reduction in the thyroid dose still remains too high. Suppression of thyroid I- uptake by ClO4-, together with I-125 DIT, eliminates almost all thyroid irradiation and provides a sensitive, harmless, and rapid test.

Adolescent↗
PubMed1983

Attempt to disturb receptor memory in a unicellular (Tetrahymena) model system.

The effect of a hormone-like substance first reaching a receptor is of decisive importance in the unicellular (Tetrahymena) model system. The effect of the similar or dissimilar molecule after the first or second pretreatment depends to a great extent on pretreatment if it was carried out by a similar substance, but it does not depend on it if the agent used for pretreatment was different chemically. Receptor memory developing after hormonal imprinting can thus be disturbed by molecules of similar nature, but the effect of a different molecule--if it acts immediately after the imprinting--cannot be neglected, either.

Alkaloids↗
PubMed1984

Influence of prolonged life span on receptor 'memory' in a unicellular organism, Tetrahymena.

The first interaction of the Tetrahymena with a hormone-like molecule-diiodo-tyrosine (T2) in the present study - gives rise to hormonal imprinting, the effect of which is being preserved by receptor 'memory' over as many as 500 generations. The first interaction with the hormone modifies the growth potential of the cell also without reexposure. In the present study, we followed up the fate of receptor 'memory' in Tetrahymena cells maintained without exchange of medium, and thereby inhibited in division, over the period of a year. The cells continued to display increased responsiveness - receptor 'memory' - over the first 3 months which normally cover the change of 500 generations, and to a lesser degree over the next 3 months (after 6 months) as well, but they showed loss of 'memory' after 9 and 12 months, as judged from the similarity of their growth response to the control. At 9 months, the cells were able to recover their original growth potential within 4 days of return to normal medium, but the 'memory' of the behavioral (growth response) modification induced by T2 returned, in a not fully convincing form, only after 48 days. Receptor 'memory' returned in 21 days. It follows that receptor 'memory' can equally persist by cell-cell transmission or within the same nondividing cell of extremely prolonged life span. Evidence has also been presented that loss of receptor 'memory' with ageing is only virtual, because it can be reactivated if the aged cells are 'rejuvenated' under appropriate conditions.

Animals↗
PubMed1982

Thyroid hormone formation catalyzed by human thyroid peroxidase: a new and physiological measurement of thyroid peroxidase.

This report describes a method for measurement of TPO activity by the amount of thyroid hormone production. Thyroid hormone formation was accomplished by incubating purified iodine-poor Tg with human TPO for 60 min at 37 C in the presence of free DIT, KI, and an H2O2 source. Newly formed T3 and T4 were measured by radioimmunoassay of the Tg hydrolysates. With this method, TPO-catalyzed iodination of Tg and thyroid hormone formation were measured simultaneously from eight normal thyroid glands and 15 thyroid glands from MMI-treated patients with Graves' disease. Graves' disease TPO showed iodinating activity and T4 formation which was higher than that of TPO from normal thyroids, and there was a positive linear correlation between the iodinating activity and the amount of T4 formation. T3 production by highly active TPO, however, dissociates from the amount of T4 formation and the degree of Tg iodination. Thus, if the activity of TPO is to be measured by the amount of thyroid hormone production, T4 should be used rather than T3. The method of thyroid hormone formation described here provides a new and physiological measurement of TPO activity and should be useful for investigation of the role of human TPO in thyroid hormone formation.

Diiodotyrosine↗
PubMed1978

[Thyroid hormone metabolism and the functional activity of the thyroid gland in mother and fetus].

The functional activity of the thyroid glands of the pregnant rats and their foetuses prior to the birth and the deiodizing ability of the liver of the mother and the foetus on the 18-th day of pregnancy were studied. The reliable differences were shown between the levels of protein bound iodine in the blood serum of the pregnant rats as compared with the control ones, as well as the high content of thyroid hormones in the blood serum of the foetuses. The process of thyroxin and diiodothyrosine deiodizing in the foetal liver was more active than in the mother. The results obtained suggest the increase of functional activity of the thyroid gland in the mother by the end of pregnancy and the presence of such an activity in the foetus, as well as the high activity of the deiodizing system in the foetal liver during the last days of prenatal development.

Animals↗
PubMed1975

[Metabolism of radioiodine in Xenopus thyroid during larval life and metamorphosis].

Radioiodine uptake and metabolism study show variations in the functional state of thyroid glands of Xenopus through larval development. During metamorphic climax, the level of hormone synthesis is the highest ; after metamorphosis, labeled thyroid hormones proportion decreases significantly. Normal metamorphosis sequences depend on the gland functional state changes.

Animals↗
PubMed1995

Modulation of biological tyrosine reactions by tyrosine phosphorylation.

This review focuses on the influence of tyrosine phosphorylation on the biological reactions of tyrosine. Reactions that are modulated by this amino acid modification include dityrosine formation, thyroid hormone synthesis, and DOPA formation. In addition, we show that the reactivity of tyrosine in the common Lowry method of determination of protein concentrations is lost upon phosphorylation of the amino acid.

Animals↗
PubMed1979

The influence of non-steroidal anti-inflammatory and antithyroid agents on myeloperoxidase-catalysed activities of human leucocytes.

Viable leucocytes obtained fresh from normal human subjects were shown to be able to catalyse the in vitro iodination of bovine serum albumin (BSA) in a H2O2-generating system. The rate and degree of iodination were greatly improved by sonication of the cells. A balanced salt solution was a more favourable medium than phosphate buffer for the myeloperoxidase (MPO)-catalysed iodination of whole cells and sonicated cells. Reactions known to be catalysed by other peroxidases (e.g. thyroid peroxidase (TPO) and lactoperoxidase), such as inorganic iodide exchange for organic iodine in di-iodotyrosine (DIT) and the de-iodination of thyroxine (T4), were also catalysed by the sonicated leucocyte suspension in the system used. The non-steroidal anti-inflammatory drugs indomethacin, flufenamic acid and naproxen were far less effective inhibitors of MPO-catalysed BSA iodination of sonicated leucocytes at concentrations expected in blood with therapeutic dose levels than was observed earlier with TPO-catalysed in vitro iodination of BSA. The antithyroid drug methylmercapto-imidazole (MMI) inhibited in vitro MPO-catalysed 131I delabelling of 131I-DIT at all concentrations between 10(-7) and 10(-2)M, whereas 131I-T4 delabelling was markedly stimulated at the same drug concentrations. On the other hand, 125I incorporation into 131I-DIT was not affected by increased concentrations of MMI up to 10(-5)M. At higher drug concentrations the drug caused inhibition of MPO-catalysed exchange of inorganic iodide for organic iodine in DIT.

Antithyroid Agents↗