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At least 19 recordsLinked to original sources
PubMed1976

Reduction of 5'-nucleotidase activity in rat thyroid and adenohypophysis following methylthiouracil treatment.

5' -Nucleotidase activity was determined in rat thyroid and some other organs employing a specific assay method. During the course of methylthiouracil (MTU) treatment, thyroid 5'-nucleotidase activity decreased significantly. This decrease was specific for this enzyme since the activity of neutral phosphatase did not change and the activity of alkaline phosphatase and Mg2+-activated adenosine triphosphatase increased markedly. The 5'-nucleotidase activity of the adenohypophysis also decreased following MTU treatment. This enzyme activity of the liver, heart and whole brain remained unchanged after the treatment. The role of this enzyme was discussed in relation to tissue growth and increased contents of RNA and DNA in the thyroid and adenohypophysis.

Adenosine Triphosphatases↗
PubMed1978

Changes in the cyclic nucleotides of rat thyroid, pituitary and plasma caused by methylthiouracil treatment.

Changes in the content of cyclic nucleotides (cAMP and cGMP) and related enzyme activities were observed in the rat thyroid, pituitary and plasma during the prolonged increase of endogenous TSH produced by treatment with methylthiouracil (MTU). Experiments were performed after 4 weeks treatment with MTU. The wet weight and cAMP content per wet weight of the thyroid increased 3 and 1.4 times respectively, but cGMP showed a slight decrease. Pituitary weight increased 1.3 times, but cAMP and cGMP content did not change. The cAMP level in plasma also increased about 1.3 times, but cGMP did not increase. The cAMP-phosphodiesterase activity in the thyroid, pituitary and plasma was increased 1.9, 1.4 and 1.3 times respectively after MTU treatment, while cGMP-phosphodiesterase showed no significant change. ATPase activity in the thyroid and pituitary was also increased more than 1.5 times after MTU treatment, while 5'-nucleotidase activitity decreased remarkably. These data indicate that the metabolism of the cyclic nucleotide system in the thyroid is stimulated by TSH.

Adenosine Triphosphatases↗
PubMedDate not supplied

[The reaction of the supraoptic nucleus of the hypothalamus and diuresis during thyroid gland restitution following discontinuation of 6-methylthiouracil].

There is a marked reduction of diuresis (revealed by water load) during the action of 6-methylthiouracil (MTU). In the course of the thyroid gland restitution (after the discontinuance of the 6-MTU action) the diuresis at first becomes intensified and then it repeatedly either becomes diminished or enhanced. Secretory activity of the cells of the supraoptic nucleus of the anterior hypothalamus also becomes alternately enhanced and diminished. Dynamics of the shifts in this activity failed to correlate with the "ricochet" enhancement of the thyrotropic function of the hypophysis, which occurred on the 11th restitution day and corresponded to the "ricochet" enhancement of iodine consumption by the thyroid gland. Thus, there was no association between the state of the cells of the supraoptic nucleus and the changes in the thyrotropic function of the hypophysis.

Animals↗
PubMed1989

Circadian rhythm of the thyroid mast cells in untreated and methylthiouracil-treated rats.

Recent investigation have shown that mast cells of the rat thyroid participate in the regulation of thyroid function. Serotonin released from the mast cells influenced by thyrotropin promotes iodothyronine secretion by its effect on the thyroid follicle cells. The present histophysiological studies on the circadian rhythm in the normal rat thyroid reveal a close correlation between the number of the thyroid mast cells and the thyroid function. It has been shown that in the morning, when thyroid function is decreased, the number of the mast cells is low, but at noon it shows an increase an then is highest in the evening, when the thyroid activity is most intense. This phenomenon suggests a relationship between the mast cell function and the thyroid feedback mechanism. In methylthiouracil-treated rats inhibition of the thyroid iodothyronine production and change of the feedback mechanism function induce development of a hypertrophic goitre in which degranulation of the mast cells accompanied by release of their bioamines induce dilatation of blood vessels and increase in the thyroid blood flow. Simultaneously the circadian rhythm of the thyroid mast cell occurrence is changed, i.e. their number found in the morning gradually decreases by the evening.

Animals↗
PubMedDate not supplied

[Effect of triiodothyronine and methylthiouracil on the enzymatic activity of biogenic amine metabolism in rat brain synaptosomes].

Triiodothyronine injections are shown to lower DOPA decarboxylation and 5-hydroxytryptophan decarboxylation activity and also to decrease the intensity of serotonin and norepinephrine oxidative deamination in the rats' brain synaptosomes. Hypothyroidism produced by 6-methylthiouracil administration was accompanied by intensification of the DOPA-decarboxylase activity and monamine oxidase transformation into serotonin and norepinephrine with no parallel occurring essential changes in the 5-hydroxytryptophan decarboxylation.

5-Hydroxytryptophan↗
PubMed1975

[Experimental study of the correlation between function and morphology of rat thyroid after the application of methylthiouracil and thyroid stimulating hormone].

In an experimental study with 359 male Wistar rats the thyroid function was altered with MTU and TSH. The morphological changes developing due to this treatment were compared with the hormone blood level measured as labelled protein-bound iodine (PBI-127). Furthermore, the content of PBI-131 was determined and the I-131 uptake of the thyroid after application of TSH was measured. It was shown that with a dosis which had no influence on the PBI-127 and radioiodine values, the height of the thyroid epithelium already revealed a significant reaction. By a morphological examination together with the histometrical determination of the height of the thyroid epithelium the hormone-dependent increase in activity may be determined quantitatively.

Animals↗
PubMed1979

Iodide binding and regulation of lactoperoxidase activity toward thyroid goitrogens.

The effects of the antithyroid goitrogens, methylthiouracil and methylmercaptoimidazole, on the oxidation of N-acetyltyrosylamide at pH 8.8 by lactoperoxidase have been evaluated in the presence and the absence of iodide for the purpose of elucidating the effects of iodide. At pH 8.8, iodine is not oxidized. In the absence of iodide, the two antithyroid drugs inactivate lactoperoxidase by a second order process. When iodide is added before methylthiouracil or methylmercaptoimidazole, enzyme inactivation does not occur as rapidly and both goitrogens are readily oxidized. The kinetics of the oxidation reactions have been analyzed in order to obtain the equilibrium constant of the iodide . lactoperoxidase complex. Essentially the same iodide dissociation constant, i.e. 2 x 10(-5) M, was found by studying its effects on the kinetics of oxidation of the two antithyroid drugs. A large difference absorption spectrum is observed in the Soret region between native lactoperoxidase and lactoperoxidase inactivated by methylthiouracil.

Iodides↗
PubMed1977

[Effect of protein content and thyroid hormone on body composition in growing rats].

The effects of an isocaloric control diet of high-protein and low-protein diets (in which protein amounted to 16, 62 and 2% of total calorie content, respectively) with and without simultaneous administration of Thyreotom or methylthiouracil on total body composition have been studied in growing male Wistar rats. In spite of higher average Kcal intake (per day and 100 g of body weight), the rats on the high-protein diet were weighing less than the control animals at the end of the experiment. As compared to the control animals, the rats on the high-protein diet as well as those on the low-protein diet showed a greater relative weight of the thyroid gland. The protein percentage of the body was not significantly increased by an increase in protein supply; likewise, it was not significantly reduced by a decrease in protein supply. The body fat content was by 2/3 lower in the rats on the lowprotein diet than in the control animals. This difference was statistically significant. Thyroid hormones (1 mug liothyronine + 4 mug levothyroxine/100 g body weight, administered orally for 3 weeks) produced a slight increase of body protein in the rats on the high-protein diet; they increased it significantly in the rats on the low-protein diet. Body fat was correspondingly reduced. Methylthiouracil reduces the body fat content in the control animals and in the rats on the high-protein diet; it increased the body fat content in the rats on the low-protein diet. Our results confirm the partial findings of human pathology and demonstrate clearly that nutritional diseases, especially protein deficiency, worsen considerably in case of concomitant disorders of thyroid hormone metabolism.

Animals↗
PubMedDate not supplied

[Pathomorphological changes in the kidneys in experimental hypothyroidism].

Morphohistochemical changes were studied in the kidneys of rats in experimental hypothyroidism. The latter was induced by subtotal thyroidectomy (observation periods--60 days), feeding of 6-methylthiouracil (observation periods--100 days), feeding of 6-methylthiouracil to thyroidectomized animals (observation periods--7 to 60 days). Animals of all the three groups displayed morphohistochemical signs of disturbance of acid and neutral polysaccharide metabolism in the vaso-stromal structures of the kidneys and also in the glomeruli. The degree of these changes depended directly on the extent and the duration of a hypothyroid condition. The changes described led to development of sclerosis. Among these changes attention was attracted to deposition of calcium salts in the epithelium, chiefly of the distal tubules.

Animals↗
PubMed1990

High-performance liquid chromatographic determination of propylthiouracil in plasma.

A high-performance liquid chromatographic method for the determination of the antithyroid drug propylthiouracil in dog plasma has been developed. Propylthiouracil and the internal standard, methylthiouracil, are extracted from plasma with methylene chloride at pH 6 and the organic layer is evaporated to dryness. The residue is chromatographed on a Chromspher C18 reversed-phase column using Pic B-7 (0.005 M 1-heptanesulphonic acid in water)-1% acetic acid-methanol (40:45:15, v/v/v) as the mobile phase. Quantification is achieved by monitoring the UV absorbance at 300 nm. The response is linear (0.1-15 micrograms/ml) and using 100 microliters of plasma the detection limit is 50 ng/ml. The within-run coefficient of variation is less than or equal to 5% and the accuracy is within 10% of the theoretical value at concentrations between 0.1 and 15 micrograms/ml plasma.

Animals↗
PubMed1989

Screening and confirmation of thyreostatics in urine by gas chromatography with nitrogen-phosphorus detection and gas chromatography-mass spectrometry after sample clean-up with a mercurated affinity column.

Methods are described for the screening and confirmation of residues of the thyreostatics thiouracil, methylthiouracil and propylthiouracil in urine samples of cattle at levels down to 25 micrograms/l. After a selective preconcentration of the thiol-containing thyreostatics on a mercurated affinity column, the analytes are derivatized by extractive alkylation and analysed by gas chromatography with nitrogen-phosphorus or mass spectrometric detection.

Animals↗
PubMed1975

Biochemical studies on the peroxidase activity in the normal and hyperplastic thyroids of rats.

The total and specific activity of thyroid homogenate of normal rat was 0.95 times 10- minus 3 GU (guaiacol unit) per rat and 0.61 times 10- minus 3 GU per mg protein. These were increased 3.4 fold and 1.6 fold by chronic administration of thyroid stimulating hormone (TSH) and 5.1 fold and 2.5 fold by treatment with methylthiouracil (MTU), respectively. However, the soluble fractions, which were obtained by centrifugation at 105,000 xg for 120 min from the homogenates, manifested only 2-3% of the activity of the original homogenates, and the specific activity was scarcely affected by the administration of TSH and MTU. Moreover, even the low activity of the soluble fraction might be due to contaminated microsomes. None of the results obtained favors the view that the peroxidase is released from the cell to the colloid lumen. The number of peroxidase molecule per cell of thyroid was roughly estimated to be 1.5 times 10- minus 5 for normal and 3.9 times 10- minus 5 for MTU-treated rat.

Animals↗
PubMed1975

Thyroid function and polyamines. II. Thyrotropin stimulation of polyamine biosynthesis in the rat thyroid.

Thyrotropin (TSH) injected intraperitoneally caused a significant rise in the activity of L-ornithine decarboxylase of rat thyroid within 4 hr. TSH-releasing hormone (TRH) also increased the activity of this enzyme in a dose-related manner and of putrescine-activated S-adenosyl-L-methionine decarboxylase, probably through the increased secretion of TSH from the pituitary. Administration of methylthiouracil (MTU) in the drinking water to rats resulted in an increase of these two enzymes in the thyroid. Maximal activation was observed 4 days after the initiation of MTU treatment for both enzymes. The intracellular level of putrescine and spermidine increased during the rapid phase of thyroid enlargement caused by MTU treatment. The spermine concentration, however, was relatively constant during the treatment. The RNA/DNA ratio followed a pattern very similar to that exhibited by the spermidine/spermine ratio. These results indicate that TSH stimulates the biosynthesis of polyamines by increasing the activity of the decarboxylases in the thyroid. The findings further suggest that polyamines play a role in the regulation of thyroid growth and nucleic acid metabolism.

Adenosylmethionine Decarboxylase↗
PubMed1978

Thyroid function and polyamines. III. Changes in ornithine decarboxylase activity and polyamine contents in the rat thyroid during hyperplasia and involution.

Changes in ornithine decarboxylase (ODC) activity and in polyamine contents of the rat thyroid were studied under various experimental conditions. Methylthiouracil (MTU) treatment produced several-fold increases in the thyroid ODC activity and in the content of putrescine, spermidine and spermine within a week. While serum thyrotropin (TSH) levels increased gradually up to 3 weeks, the content of both putrescine and spermidine tended to reach a plateau after 2 weeks of the goitrogen treatment; spermine content continued to increase progressively for 3 weeks. Discontinuance of MTU at 7 days resulted in a rapid decline in the elevated thyroid ODC activity, followed by a diminution of putrescine, spermidine and RNA contents. Thyroidal putrescine, spermidine and RNA responded more sensitively to both introduction and withdrawal of TSH stimulation than thyroidal spermine and DNA. Excess iodide, having no effect on the basal level of thyroid ODC, suppressed the MTU-induced increase in this enzyme activity without affecting circulating TSH, thyroxine (T4) and triiodothyronine (T3) levels. There was a significant negative correlation between the ODC activity and intrathyroidal concentration of iodine in MTU-pretreated rats. Theophylline increased the thyroid weight and ODC activity when given to rats fed with a subeffective dose of MTU. Analyses of serum TSH, T4, T3 and of thyroidal iodine revealed that TSH-induced thyroid ODC activity was suppressed by increased circulating thyroid hormones and/or intrathyroidal iodine. Furthermore, it was suggested that thyroid hormones and excess iodide acted directly on the thyroid to alter polyamine biosynthesis, possibly by changing the responsiveness of the gland to TSH.

Animals↗
PubMed1990

Hypothyroidism affects reproductive refractoriness and the seasonal oestrous period in Welsh Mountain ewes.

Welsh Mountain ewes (n = 6) were rendered hypothyroid by daily treatment with methylthiouracil (35 mg/kg), beginning in early August and ending in late February. Plasma thyroxine levels were reduced by mid-September to about 33% of those in untreated ewes (n = 6). The two groups of ewes were held under natural daylengths until 5 October, then on 12 h light: 12 h darkness (12L:12D) until 28 February when the photoperiod was reduced to 8L:16D. The onset of reproductive cyclicity in October was similar in both groups of ewes but the end of the reproductive period occurred later (P less than 0.05) in the hypothyroid ewes (29 January +/- 7 days (S.E.M.] than in the untreated controls (6 January +/- 7 days). As a result, the duration of the seasonal reproductive period was significantly (P less than 0.05) longer in the hypothyroid (122 +/- 9 days) than in the untreated ewes (91 +/- 10 days). The number of oestrous cycles (duration 15.4 and 15.7 days in the hypothyroid and untreated ewes respectively) was 7.0 +/- 0.6 in the hypothyroid ewes and 5.0 +/- 0.5 (P less than 0.05) in the normal ewes. Reducing the photo-period overcame the reproductive refractoriness and anoestrus in both groups, the hypothyroid ewes beginning to cycle on 13 April (+/- 0.5 days) after an anoestrous period of 72.8 +/- 7.1 days. The untreated ewes began to cycle 2 weeks later on 26 April (+/- 1.7 days) after an anoestrous period of 112.0 +/- 8.5 days (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗