T4 Synthesis Research Articles

Comparative mantoux testing as a clinical tool: Evidence for a maternal influence on the child's reaction

The presence or absence of types I, II and III iodothyronine monodeiodinase enzymes (MDI, MDII and MDIII) and their levels of activity in the skin of goats, which were orally dosed for 60 days with 0, 1.1, 2.2, 4.4, 8.8, 17.5, or 35 mg–1kg liveweight day–1of the anti-thyroid, enzyme-inhibiting drug, propylthiouracil (PTU), were determined. Contrary to our earlier report that PTU did not influence skin MDII activity, the currect more thorough investigation (in terms of numbers of observations and the efficiency of the enzyme extraction procedure) indicated that doses of 1.1.to 17.5 mg kg–1liveweight induced a 2 to 3 fold increase (P = 0.01) in MDII activity. However, in three of the four goats treated with 35 mg kg–1group, activity was similar to that of control animals. There were no significant differences between treatments in MDIII activity but there was a trend towards lower levels of activity in the goats dosed with 17.5 and 35 mg kg–1. It is concluded that there is significant MDII and MDIII activity in the skin of goats and that although there is none of the PTU -sensitive MDI enzyme, synthesis of T3 within the skin could nevertheless be modified through increases in MDII activity induced by lower T4 concentrations in the circulation caused byPTU . Changes in pattern of fibre moult induced by treatment with low doses of MD-inhibiting drugs may therefore be achieved through this effect. Since MDII and MDIII enzyme activity may be reduced by high doses of PTU, prolonged treatment with high doses of PTU may have adverse effects on skin tissue.

Thyroid status in the obese syndrome of rats.

The thyroid function was explored by comparing serum total and free iodothyronine levels in young male genetically obese Zucker rats and in their lean littermates, aged from 6 to 8 weeks old. Total and free thyroxine (T4) and 3,5,3'triiodothyronine (T3) levels were significantly decreased in obese rat serum while total 3,3',5'-triiodothyronine (rT3) remained constant. Radioactive T4 half life is slower in the plasma of obese rats. Peripheral synthesis of T3 from deiodination of T4 is also decreased in obese rat liver homogenate. These modifications produce changes in liver mitochondria oxidative phosphorylation and in marker enzyme activity, which are usually associated with hypothyroidism and hypothalamic disturbances. Genetic obesity probably involves activation of peripheral deiodination of T4 to rT3 which induces biochemical and metabolic changes.

Effects of prolonged administration of thyrotrophin on serum concentration, release and synthesis of thyroid hormones in mice.

Mice were injected sc with TSH (0.5 U) at 12 h intervals for 5 days. Groups of mice were sacrificed daily to determine serum T4 and T3 concentrations, 4 h thyroidal 125I uptake, distribution of 125I among thyroidal iodoamino acids, and thyroidal content of T4 and T3. Serum T4 and T3 concentrations increased significantly after the initial injection of TSH and gradually decreased thereafter, reaching initial levels on the 3rd and 4th days, respectively. In contrast to serum hormone levels, thyroidal 125I uptake, incorporation of 125I into T4 and T3 increased significantly on the first day and remained elevated throughout the period of TSH-treatment. Thyroidal T4 content expressed as microgram/mg weight of tissue decreased significantly on the first day and thereafter remained constant. Thyroidal T3 content did not change significantly throughout the experimental period. The differences between thyroidal synthesis and thyroidal contents of T4 and T3 strongly suggest that thyroid hormone secretion is being continuously stimulated. Transient increases in serum T4 and T3 concentrations are probably due to a gradual increase in the rate of peripheral degradation of thyroid hormones. These results suggest that TSH-induced refractoriness in thyroidal iodine metabolism does not appear to exist, at least when TSH is given in vivo for 5 days.

Effect of long-term iodide refeeding on the synthesis and secretion of T3, T4 and TSH in severe iodine deficient rats.

Abstract. For 6 months, male Wistar rats received an iodine deficient diet (LID), with propylthiouracil (PTU) for the last 2 months. At the end of this treatment (day 0), a daily iodide intake of 20 μg (group 20) and 50 μg (group 50) was supplied. Synthesis and secretion of T3, T4 and TSH as well as thyroid and serum PBI were studied during 140 days of iodine repletion. For the first 4 days of iodide refeeding, thyroid PBI remained low (0.4 ± 0.2 μg 127I/gland) whilst T3 and T4 were undetectable during 2 days only. Thereafter, these parameters increased regularly, reaching control values on days 80, 16 and 90, respectively. During 2 weeks, the thyroid T3/T4 ratio was 6-fold higher and reached the control value on day 45. Plasma T3 and T4 levels were low, but measurable for the first 4 days (0.5 ± 0.1 and 9.9 ± 2.6 nm, respectively). T3 rapidly reached a normal level on day 8, inducing a high plasma T3/T4 ratio for 16 days. This ratio decreased abruptly when T4 secretion increased, attaining the control value on day 45. Therefore, the preferential T3 secretion occurring during the first 16 days is directly linked to the preferential T3 synthesis. Plasma TSH levels remained 10-fold higher than the control value for the first 8 days (490 ± 99 vs 39 ± 15 μU/ml), then decreased abruptly and reached normal level after 1 month. Pituitary TSH contents varied in an opposite manner to the plasma TSH concentrations. In conclusion, the effect of iodide on thyroid function occurs sequentially, i.e. thyroid hormone synthesis precedes neosecretion (latency phase). In both processes, T3 appears preferentially. This phenomenon is linked to the low thyroglobulin (Tg) iodination rate. In addition, the re-establishment of a normal thyroid hormone secretion prevailing over the iodinated Tg store constitution represents an adaptative mechanism; this leads rapidly to a maximum supply of active hormone (T3) with iodine economy. Moreover, it takes 2–3 months for the complete thyroid function restoration. At the pituitary level, the normal plasma T3 concentration found during the latency phase of iodide refeeding is not sufficient by itself to inhibit TSH secretion. This parameter starts to decrease only when T4 has reached a critical level to generate adequate T3 from T4 deiodination. Inhibition of TSH synthesis is a less sensitive process since it occurs for more elevated T4 concentrations. Finally, the similar pattern of thyroid function's recovery in the two groups indicates that the 20 μg dose is a sufficient supply and that thyroid autoregulation occurs, thus avoiding a thyroid hyperfunction.

Alterations in thyroid function after cholecystographic contrast agents.

The radiographic contrast agents commonly used for oral cholecystography have diverse effects on thyroid hormones in man. They may: (i) decrease serum triiodothyronine (T3) and increase reverse T3 in both hyperthyroid and euthyroid subjects, an effect attributable to inhibition of phenolic (outer) ring deiodination of iodothyronines; (ii) acutely increase serum thyroxine (T4) by displacing it from the liver, so inviting an erroneous diagnosis of hyperthyroidism; (iii) precipitate hyperthyroidism in apparently euthyroid subjects who have autonomous thyroid tissue. In comparison with the cholecystographic agents which are taken up by the liver, the renally-excreted contrast agents used for angiography or intravenous urography are much less potent in producing these effects. The paradox of T4 excess with normal T3 may arise after cholecystography, either by an acute T4 increase in a euthyroid subject, or by normalization of T3 in hyperthyroidism, thus creating a diagnostic dilemma. The recent trend towards use of oral cholecystographic agents in the urgent management of hyperthyroidism, because of their effect on serum T3, needs to be regarded with caution in view of the risk that hyperthyroidism may eventually be worsened if synthesis of T4 is not effectively blocked. For this reason, contrast media should probably be used in the treatment of hyperthyroidism only in conjunction with conventional antithyroid drugs. A history of exposure to contrast media should be sought in any acute or unexpected exacerbation of hyperthyroidism, or when T4 excess is found without an increase in T3.

Effect of cycloheximide on iodothyronine formation in vitro

The unique inhibitory effect of cycloheximide (CH) on the coupling of iodotyrosines was examined in vitro. Rat thyroid lobes were incubated for 8 h under our improved condition. In the presence of 10(-4) - 10(-3) M CH, the per cent uptake of 131I decreased, proportionate synthesis of [131I]MIT increased slightly, and that of [131I]T4 or [131I]T3 decreased markedly. The incorporation of medium 127I into T4 or T3 during the 8 h incubation period decreased markedly, but was fairly constant into MIT and only slightly decreased into DIT. Thus the inhibitory effect of CH seemed more prominent on iodothyronine formation than on iodotyrosine formation in this in vitro system. Inhibition of formation of newly labelled iodothyronines seemed to occur almost in parallel with the inhibition of [3H]amino acid incorporation into the thyroidal soluble protein. However, the coupling of iodotyrosines prelabelled in the absence of CH did not seem to be affected by CH. The presence of 10(-4) M CH induced the Wolff-Chaikoff effect at a lower iodide concentration than that which occurred in the absence of CH, suggesting that CH sensitized the Wolff-Chaikoff effect. However, the organification of 127I and T4 synthesis were markedly reduced in the presence of CH even before the apparent Wolff-Chaikoff effect was initiated. These results give further support to out contention that prethyroglobulin is more important for organification of iodide than pre-existing thyroglobulin. We conclude that CH reduces coupling efficiency indirectly, probably by inhibiting the formation of prethyroglobulin with a favourable structure for coupling.

Amounts of triiodothyronine and a serum protein related to hepatic DNA synthesis in the rat.

The increase of a serum protein in the circulation of rats following partial hepatectomy or the injection of thyroid hormone (T3) is reported. This serum protein factor is present in normal rat serum and accounts for approximately 1% of the total serum protein. The protein disappears from the serum of animals bearing Morris hepatomas 7777 or 7800. The amount of serum protein factor diminishes as the tumors increase in size. The levels of this protein in the serum fall immediately following partial hepatectomy. At 24 hours following the operation, however, the levels are increased well over those found in normal rats. Increased levels persist for 12 days following partial hepatectomy. The serum protein is also increased following injections of T3 and is decreased in thyroidectomized animals. Elevated levels of T3 are correlated with elevated levels of the serum protein and both are correlated with increased hepatic DNA synthesis. Low levels of T3 are followed by low levels of serum protein resulting in a diminished capacity for hepatic DNA synthesis. Injection of purified serum factor into normal rats results in increased [3H]thymidine incorporation in liver cells. It is suggested that the synthesis of this serum protein is stimulated by T3 and DNA synthesis is influenced by the serum protein. The serum protein might be a humoral factor influencing metabolic events in hepatocytes or hepatomas or it might be a carrier for an agent that in turn has a direct effect on these tissues.

Synthese und Untersuchung substituierter lodthyronine mit dem Ziel der Herstellung radiochemisch stabiler 125 I-Tracer hoher spezifischer Aktivität

Various substituents were tested for their ability to replace 3'-iodine of T4 without affecting binding to T4 antibodies and without exchanging with 125I during synthesis of high specific activity T4. Measured cross-reactivities of 3'-bromo-T3 and 3'-isopropyl-T3 relative to T4 were 85.6 and 8.9%, respectively, thus suggesting a high contribution of the ionised 4'-hydroxy group to antibody binding. The 3'-bromo substituent is not exchanged with 125I during labelling by the chloramine-T method. Therefore, 3'-bromothyronines are suitable starting materials for the synthesis of 3'-bromo-5'-125iodothyronines of high specific activity; these have the advantage of a long shelf life comparable to [125I]T3, because only 125I-monolabelled thyronines are produced.

The effect of mercuric chloride on thyroid function in the rat

Oral administration of 3 mg of mercuric chloride for 6 consecutive days increases thyroid function as noted by an increase in thyroid 131I release rate. Administration of 2.5 mg of mercuric chloride daily for 40 days enhanced thyroid weight, thyroidal 125I uptake, and serum PB125I. Chromatographic analysis of thyroid pronase hydrolysates of mercury-treated rats displayed a pattern of distribution in thyroid labeling which demonstrated an increased percentage of labeled monoiodotyrosine (MIT), no alteration in percentage of labeled diiodotyrosine (DIT) or T4, but a significant reduction in percentage of labeled T3 indicating perhaps a coupling defect in synthesis of T3 exerted by mercury. Administration of mercuric chloride at 100 ppm for 3 months results in a decrease in thyroidal 131I uptake and depression in the thyroidal 131I release rate which were permanent and irreversible. These findings indicate that the influence of mercuric chloride ingestion on thyroid function probably reflects the quantity of mercuric chloride administered and the length of time during which exposure to mercury persists.

Isolation of the transfer RNA genes of bacteriophage T4 and transfer RNA synthesis in vitro

Non-glucosylated T4 DNA was restricted with the endonuclease EcoRI and the mixture of DNA fragments separated by gel electrophoresis and transcribed with purified Escherichia coli RNA polymerase. Three purified fragments were shown to act as templates for tRNA synthesis. A smaller fragment, shown to be hybridizable to 32P-labeled T4 tRNA was not transcribable. It was concluded that the promoter for T4 tRNA synthesis had been separated from the structural genes in the smaller fragment by EcoRI and that the distal portion of the tRNA gene cluster lacks internal promoters which display in vitro activity. Preparations of non-glucosylated T4 DNA were never fully restricted with EcoRI and when the larger purified fragments carrying the tRNA were restricted with excess enzyme only a slight cleavage to yield the smaller fragments was obtained. The property of the DNA-limiting complete restriction is not known.

Serum 3,5,3′-Triiodothyronine, Thyroxine, and Thyrotropin in Hypothyroid Infants with Congenital Goiter and the Response to Iodine

Iodine deficiency in adults caused preferred synthesis of T3; this observation has not been reported in iodine-deficient hypothyroid newborns. Serum total T4, total T3, and TSH have been determined in nine full term newborns with congenital hypothyroid goiter before and after cutaneous application of iodine. The mothers of these infants had untreated euthyroid goiter and lived during pregnancy in the area of Göttingen, West Germany, known as an iodine-deficient region. Mean total T4 in the newborns was 6.3 +/- 1.6 (mean +/- SD) micrograms/dl compared to 16.6 +/- 3.4 micrograms/dl in normal newborns at 3-4 days of age. Mean T3 in the goitrous newborns was 2.74 +/- 0.66 ng/ml compared to 1.58 +/-0.41 ng/ml in the control group of the same age. Serum TSH remained elevated during the first week of life, with a concentration of 40.9 +/- 28.7 microU/ml (control group, 4.16 +/- 1.43 microU/ml). The cutaneous application of iodine resulted in rapid disappearance of goiter and normalization of T4 and TSH within 5 days. After 30 days of iodine treatment, T3 decreased slowly but remained elevated (2.0 +/- 0.42 ng/ml vs. 1.67 +/- 0.36 ng/ml in the control group). The present findings confirm preferential T3 secretion in newborns with hypothyroid goiter. The goiter is thought to be caused by intrauterine iodine deficiency, because hypothyroid values of T4 and TSH normalized during iodine treatment. General iodine prophylaxis of the population is recommended.

Abnormal thyroid function in spontaneously hypertensive rats.

Thyroid weight, thyroidal radioiodide uptake, and cyclic AMP-dependent protein kinase activity of a thyroid supernatant fraction were increased significantly in spontaneously hypertensive rats (SHR), apparently because of increased secretion of pituitary TSH. However, the thyroids of SHR did not make supernormal amounts of thyroxine (T4), and thyroidal radioiodine release was apparently impaired. In the SHR, proteolytic enzyme activity was less than normal and the thyroglobulin was more resistant to normal proteolytic enzyme than was control thyroglobulin. Presumably because of these abnormalities, plasma T4 was significantly lower than normal, but triiodothyronine (T4) was normal, as a result of compensatory processes occurring in T3 synthesis and hydrolysis of thyroglobulin. T4 and T3 were less effective in depressing pituitary TSH synthesis and secretion in SHR than in controls, possibly because of an abnormal setting of the "hormostat." Although the hypothalamic content of TRH was normal in SHR, the exact site of the abnormality in the "hormostat" is not delineated in the present study.

Production and evaluation of high-quality thyroxine antisera for use in radioimmunoassay.

High-quality thyroxine (T4) antisera were raised in rabbits. Conjugates of protein and T4 or T4 methyl ester were given intracutaneously in Freund's complete adjuvant at one or two sites on the back at 1/2- to 3-month intervals. Eleven of 16 immunized rabbits produced antiserum with titers higher than 2 commercial antisera and 4 antisera from other laboratories. All 16 antisera had equilibrium constants (K) higher than the 6 reference sera. The highest titer observed was 130,000 with 88 fmol labeled T4 per ml incubate. A drastic increase in K from about 4 X 10(8) to 5.8 X 10(10) 1/mol was observed as the immunization proceeded. Cross-reactivity with triiodothyronine (T3) varied but was generally low. Suppression of the T4 synthesis was attempted by giving 30 nmol (20 mug) T3 per os once a day. Antiserum from rabbits given T3 suppression contained less iodine than antiserum from nonsuppressed control rabbits. The possible reasons for the successful production of the high-quality antisera are discussed.

Receptors mediating epinephrine effect on thyroid 131-i uptake and thyroxine synthesis in the rat.

The adrenergic receptors mediating the inhibitory effect of epinephrine on the rat thyroid in vivo have been studied by the use of more specific alpha- and beta-adrenergic stimulators, and blocking agents. The effect of methoxamine was similar to that of epinephrine, while isoproterenol stimulated 131-I uptake slightly, and did not alter the ratio of monoiodotyrosine (MIT) to diiodotyrosine (DIT). However, like methoxamine, isoproterenol resulted in a decrease in thyroxine (T4) formation. Phentolamine could partially prevent epinephrine-induced decrease in 131-I uptake and T4 synthesis. The changes in the MIT/DIT ratio could be completely prevented by high doses of phentolamine. Propranolol enhanced the effects of epinephrine. It is concluded that the effect of epinephrine on the rat thyroid in vivo is predominantly alpha-adrenergic, but T4 synthesis may be decreased by stimulation of either receptor.

The relationship between thyroglobulin synthesis and intrathyroid iodine metabolism as indicated by the effects of cycloheximide in the rat.

The effect of small doses of cyclohex-imide (CH) (0.5 µg/g body wt) on the intrathyroid metabolism of carrier-free 13II and stable iodide iniodine-sufficient and iodine-deficient rats and on thyroglobulin (Tgb) maturation in iodine-deficient rats was studied. This dose of CH had no apparent toxicity but strikingly inhibited the incorporation of l4C-labeled amino acids into thyroid and plasma proteins. In iodine-sufficient rats, CH did not affect T/S (I−) ratios, but did enhance the sensitivity of the thyroid to the acute inhibitory effects of stable iodide on the organification mechanism (Wolff-Chaikoff effect). CH produced unusual effects on the intrathyroid metabolism of 131I in these iodine-sufficient rats: a decrease in 13II uptake, an increase in labeled DIT and a decrease in MIT so that MIT/DIT ratio declined, and a decrease in the proportionate synthesis of the iodothyronines T4 and T3. In iodine-deficient rats, CH also sensitized) the thyroid to the acute Wolff-Chaikoff effect but produced changes...

On the mechanism of goitre formation during lithium treatment in the rat.

ABSTRACT In the first experiment Sprague-Dawley rats were given antithyroid drugs i. e. perchlorate (KClO4), carbimazole (CI) and potassium iodide (KI) for 4 weeks, either alone or in combination with lithium (Li) (5 mEq./l) for the last 2 weeks. In combination with CI or KI, Li aggravated the goitre and decreased the synthesis of T3 + T4, as measured by chromatography. The weights of the adenohypophyses increased and those of the adrenals decreased in all the experimental groups. In the second experiment, Li (10 mEq./l) was administered to euthyroid rats for 4, 10 or 20 weeks. The metabolic effects of Li reached a peak at 4 weeks, giving a decreased T3 + T4, a decreased plasma PBI level and an increased plasma bioassayable (McKenzie) TSH level. A definite goitre did not develop until 20 weeks. In the third experiment the disappearance of thyroidal 131I was shown to be delayed in rats treated for 2 weeks with Li or T4 but was accelerated in those rats receiving CI. It is concluded that 1) Li accentuates the antithyroid and goitrogenic potency of antithyroid drugs, 2) Li itself is a mild antithyroid and goitrogenic agent, which exerts its effect by inhibiting the coupling reaction of iodotyrosines and 3) that Li also retards the secretion of thyroid hormones from the thyroid gland.

Biochemical observations in functioning human thyroid adenomas.

Tissue from two functioning human thyroid adenomas was studied in vitro after testing with TSH in vivo. The adenoma of the first patient appeared to concentrate TcO4− in vivo and responded to TSH with an increase in 131I uptake though the patient was not hyperthyroid. The second patient was hyperthyroid and exogenous TSH injection caused a significant increase in serum T3. In vitro, the tissue from the first adenoma did not trap iodide although the quantity of iodine organified was at least 6-fold greater than that found with either samples of the surrounding normal tissue or in 5 other studies of normal human thyroid. However, despite supranormal amounts of newly synthesized MIT and DIT, the quantity of T4 formed was quite small. Further evidence of decreased T3 and T4 synthesis in the adenoma was found in the decreased T3 and T4 content of the pronase hydrolysate of the adenoma as measured by immunoassay. T4 and T3 levels in the adenoma wore 3.8 and 0.66 μg/g wet wt, respectively, contrasted with levels...

Differential influence of spermidine on DNA directed enzyme synthesis in vitro.

Spermidine has a differential influence on T3 and T7 DNA-directed enzyme synthesis in vitro on the translational level. It increases the effectivity of synthesis of phage RNA polymerase, of ligase and of S-adenosylmethionine cleaving enzyme (SAMase), but decreases the effectivity of synthesis of lysozyme.

In vitro synthesis of T3 AND T7 RNA polymerase at low magnesium concentration

In vitro synthesis of T3 AND T7 RNA polymerase at low magnesium concentration

Thyroxine accumulation in thyroids of hypophysectomized rats.

Rats were fed a low iodine (Remington) diet for 8 months, after which radioiodine (125I) was mixed with the diet for 130 days. The metabolism of iodine was studied continuously while isotopic equilibrium was approached for 130 days. The large thyroids of control animals contained few follicles and only 4.4% of their thyroidal iodine was in thyroxine (T4) and 5.9% was triiodothyronine (T3). Hypophysectomy after the 60th day of feeding the labeled diet resulted in a continuous increase of iodine and T4 in the thyroid. Following hypophysectomy, the goiters atrophied and the ng of T4 iodine in the thyroid increased to 7.9 times greater than in intact controls; the concentration of T4 iodine increased 58 times greater than in controls while the concentration of T3 iodine increased to 4.3 times greater than in controls. The results suggest that hypophysectomy inhibited the release of T4 to a greater extent than it inhibited the synthesis of T4 in these goiters; the result was that T4 accumulated during involuti...