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

Cabanillas, Ana M.; Masini-Repiso, Ana M.; Coleoni, Aldo H.

doi:10.1111/j.1365-2265.1989.tb00274.x

Cited by 5 publications

(6 citation statements)

References 19 publications

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“…Similar results have been reported in bovine and human thyroid tissues (Masini-Repiso et al 1986;Cabanillas et al 1989). A predominance of type-MAO in the rat thyroid had been suggested by Knopp & Torda (1983).…”

Section: Iodide Organification In Vivosupporting

confidence: 89%

“…DISCUSSION We have studied the characteristics of MAO in the rat thyroid, its regulation by TSH and its role in the iodine organification process. Kinetic constants using tyramine as substrate were of the order of those reported for MAO in other tissues and species (Fischer, Schulz & Oliner, 1968;Suzuki, Hattori, Oya & Katsumata, 1980;Fowler & Tipton, 1981;Cabanillas et al 1989). …”

Section: Iodide Organification In Vivomentioning

confidence: 91%

“…It has been demonstrated that both forms are encoded by two separate genes located in the X chromosome (Hsu, Powell, Sims & Breakefield, 1989). We have found that the predominant form of MAO in bovine and human thyroid glands is isoenzyme A (MasiniRepiso, Cabanillas, Andrada & Coleoni, 1986;Cabanillas, Masini-Repiso & Coleoni, 1989) and that this is the form essentially involved in monoamine metabolism in thyroid tissue (Masini-Repiso et al 1990).…”

Section: Introductionmentioning

confidence: 96%

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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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Section: Iodide Organification In Vivosupporting

confidence: 89%

Section: Iodide Organification In Vivomentioning

confidence: 91%

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

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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“…Taken together, these results show that in bovine fetal thyroid, a marked increase in TPO activity parallels the onset of iodide organification, a process that relies on the proper cellular localization of TPO rather than on the level RER FL tissues that often resemble features of embryonic or fetal growth (22,44,47).…”

Section: Fig 5 (Continued)mentioning

confidence: 84%

“…It is unknown whether dif¬ ferences in structure or localization between fetal and adult thyroid MAO might account for the failure to detect it cy¬ tochemically at late gestation where the level of the enzyme was similar to that in the adult. The high predominance of MAO A in the developing thyroid indicates an invariant proportion of MAO isoforms during ontogeny (8,23,24,44).…”

Section: Fig 5 (Continued)mentioning

confidence: 96%

Biochemical and Functional Changes During the Bovine Fetal Thyroid Development

Masini-Repiso

Orgnero-Gaisán²,

Bonaterra³

et al. 1998

Thyroid

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To establish biochemical and functional relations during thyroid development, the activity of thyroid peroxidase (TPO), nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome c reductase and monoamine oxidase (MAO) in a particulate fraction and the iodide transport and organification in slices of bovine fetal thyroid were examined throughout gestation. The cytochemical localization of TPO, H2O2 generating sites and MAO was also studied. Fetal glands were grouped in stages I to V according to increasing developmental features; adult tissues were also analyzed. TPO activity in each of the fetal stages was higher than in the adult; a marked increase was observed in stages IV and V. Iodide transport (T/M) was similar in stages I to V and the adult. Iodide organification in fetal thyroids showed a similar pattern to that of TPO activity. When compared with the adult, at midgestation (stages II to III), a lower iodination coexisted with a higher TPO activity. The activity of NADPH-cytochrome c reductase and MAO, two enzymes previously proposed to participate in thyroid H2O2 generation, did not parallel the level of iodide organification. Cells from stages II to V exhibited a positive cytochemical reaction for TPO in the rough endoplasmic reticulum (RER) and the perinuclear cisternae (PC). In stages IV, V, and adult, TPO was occasionally found in apical vesicles and microvilli, whereas H2O2 was detected within the RER and the PC. MAO reaction was positive in adult, but not in fetal thyroid. These results indicate that a high TPO activity accompanied the onset of the organification process during fetal thyroid development. The level of iodination was associated with the presence of TPO at a proper site rather than to the level of TPO activity. Evidence against a role of NADPH-cytochrome c reductase and MAO in the iodide organification was obtained.

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Ultrastructural localization of thyroid peroxidase, hydrogen peroxide-generating sites, and monoamine oxidase in benign and malignant thyroid diseases

et al. 2004

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

Cited by 5 publications

References 19 publications

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

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

Biochemical and Functional Changes During the Bovine Fetal Thyroid Development

Ultrastructural localization of thyroid peroxidase, hydrogen peroxide-generating sites, and monoamine oxidase in benign and malignant thyroid diseases

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