The effect of inhibitors of thyroid monoamine oxidase on the incorporation of iodide into thyroid slice protein

Huang, Cleo L.; Schultz, Arthur R.

doi:10.1016/0024-3205(72)90029-x

Cited by 10 publications

(6 citation statements)

References 10 publications

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“…Possible factors which could account for the discrepancy between our results and those mentioned above could be: (1) the concentration of MAO inhibitors used by Huang & Schulz (1972) were far above those needed to inhibit MAO. Such inhibitor concentrations could also have inactivated thryroid peroxidase and iodide trapping (De Groot & Niepomniszcze, 1977).…”

Section: Discussioncontrasting

confidence: 97%

“…It was therefore postulated (Schulz & Oliner, 1967;Fischer et al, 1968) that this mechanism could serve as a source of H202 required for thyroid hormone biosynthesis. To substantiate this hypothesis, Huang & Schulz (1972) showed that the MAO substrates tyramine and 2-phenylethylamine stimulated the incorporation of radioactive iodide into bovine thryroid protein. Moreover, the amine-stimulated iodide incorporation was blocked by the presence of high concentrations (0.1-0.5 x 10 3M) of MAO inhibitors such as isocarboxazid and tranylcypromine (Huang & Schulz, 1972).…”

Section: Discussionmentioning

confidence: 99%

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Monoamine oxidase activity and triiodothyronine biosynthesis in human cultured thyroid cells

Kraiem

Sadeh

Youdim

1989

British J Pharmacology

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1 The proposal that monoamine oxidase (MAO) is a source of peroxide in thyroid hormone biosynthesis has been examined by use of isolated cultured human thyroid cells which retain the ability to secrete triiodothyronine (T3) in response to thyroid stimulating hormone (TSH). 2 The results demonstrated the presence of MAO A and B in human thyroid cells which oxidized 5-hydroxytryptamine and 2-phenylethylamine, respectively, and were selectively inhibited by the MAO inhibitors clorgyline and (-)-deprenyl. 3 Addition of propylthiouracil to the culture system induced a 61% reduction in TSH-stimulated T3 secretion, indicating that the bulk of such secretion apparently derives from de novo iodothyronine synthesis. 4 The MAO A and B substrate, tyramine, was ineffective in stimulating T3 secretion.

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Section: Discussioncontrasting

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Monoamine oxidase activity and triiodothyronine biosynthesis in human cultured thyroid cells

Kraiem

Sadeh

Youdim

1989

British J Pharmacology

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“…A relationship between biogenic amine oxidation by MAO and H202 generation in the process of thyroid hormone biosyn¬ thesis has been suggested by Fischer et al (1966). Many substances that are MAO substrates are also able to induce an increase in iodine organification in vitro (Maayan, Volpert & From, 1981;Masini-Repiso & Coleoni, 1981); non-selective MAO inhibitors block iodine incorporation into proteins in thyroid slices (Huang & Schulz, 1972). However, no further evi¬ dence for the participation of MAO in H20, production has been given.…”

Section: Introductionmentioning

confidence: 99%

Rat thyroid monoamine oxidase (MAO) is regulated by thyrotrophin: evidence that the main form of the enzyme (MAO-A) is not directly involved in iodide organification

Cabanillas

Masini-Repiso²,

Coleoni³

1991

Journal of Endocrinology

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The characteristics and regulation of monoamine oxidase (MAO) were studied in rat thyroid tissue. A measured Michaelis constant (Km) value of 102 mumol/l was similar to the Km values found in other tissues. Maximal velocity (Vmax) was 1.028 nmol/mg protein per min. It is known that MAO is present as two isoenzymes, A and B, which are sensitive to clorgyline and deprenyl respectively. The in-vitro effect of graded concentrations of these selective MAO inhibitors was used to estimate the relative proportion of A and B isoenzymes. Clorgyline strongly decreased thyroid MAO activity at concentrations as low as 1 pmol/l while the effect of deprenyl was observed only at concentrations higher than 10 mumol/l. These results indicated that MAO-A is the main form of the enzyme in the rat thyroid. In-vivo administration of L-thyroxine (5.6-224 nmol/kg) significantly reduced thyroid MAO activity at doses equal to or greater than those which have been reported to inhibit iodine output from the thyroid. Increased TSH levels, induced either by exogenous TSH or methimazole administration, resulted in a significant increase in thyroid MAO activity. Theophylline, a phosphodiesterase inhibitor and dibutyryl cyclic AMP were also able to stimulate MAO activity when administered in vivo. Iodide organification (protein-bound 131I) in vivo as well as the relative proportion of the different thyroid iodo-compounds were not affected in animals with reduced or increased thyroid MAO activity induced by clorgyline or theophylline respectively. It was concluded that rat thyroid MAO activity is under the influence of TSH.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…It was found that tyramine, 5-hydroxytryptamine and noradrenaline, all M A 0 substrates, were able to enhance both iodination and HlOl generation in thyroid tissue. These effects as well as the incorporation of iodide into thyroid slice proteins were reduced by M A 0 inhibitors (Huang & Schulz, 1972;Masini-Repiso & Coleoni, 1981). Knopp and Torda (1983) observed that M A 0 activity was modified according to TSH levels; the enzyme activity was depressed in hypophysectomized rats and increased after TSH administration.…”

mentioning

confidence: 98%

Monoamine Oxidase (Mao) Activity and Its Forms in Normal and Pathological Human Thyroid Tissues

Cabanillas

Masini-Repiso

Coleoni

1989

Clinical Endocrinology

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Monoamine oxidase (MAO) activity and its forms were measured in normal human thyroid glands (39 samples from necropsy and four from perinodular tissues) and in pathological thyroid glands (13 multinodular goitres, three carcinomas, seven chronic thyroiditis, five Graves' disease and seven follicular, seven foetal and five embryonal adenomas). MAO activity in carcinomas was lower than in normal perinodular thyroid control tissue; in Graves' disease, foetal and embryonal adenomas it was significantly higher than in the normal control. The use of clorgyline (a selective MAO A inhibitor) and deprenyl (selective MAO B inhibitor) allowed estimation of the relative proportion of MAO forms. A high proportion of MAO A (more than 90%) was observed, both in normal and in pathological thyroid tissues. Changes in total thyroid MAO activity, but not in its forms, were found in different pathologies of the thyroid gland.

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The effect of inhibitors of thyroid monoamine oxidase on the incorporation of iodide into thyroid slice protein

Cited by 10 publications

References 10 publications

Monoamine oxidase activity and triiodothyronine biosynthesis in human cultured thyroid cells

Monoamine oxidase activity and triiodothyronine biosynthesis in human cultured thyroid cells

Rat thyroid monoamine oxidase (MAO) is regulated by thyrotrophin: evidence that the main form of the enzyme (MAO-A) is not directly involved in iodide organification

Monoamine Oxidase (Mao) Activity and Its Forms in Normal and Pathological Human Thyroid Tissues

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