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

doi:10.1677/joe.0.1310025

Cited by 8 publications

(8 citation statements)

References 23 publications

(34 reference statements)

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“…The pat¬ tern of MAO in the adult and the last fetal stages is dif¬ ferent from that exhibited by TPO and iodide organifica¬ tion, a finding that reinforces previous evidence indicating no direct relation between MAO activity and thyroid hor¬ mone biosynthesis (8,10,11). 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.…”

Section: Fig 5 (Continued)supporting

confidence: 70%

“…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: 98%

“…The progressive increase in thyroid MAO activity throughout gestation is in consonance with an increasing TSH stimulation (7,8), although the influence of other fac¬ tors such as changes in the sympathetic innervation or in the monoamine content (43) cannot be ruled out. The pat¬ tern of MAO in the adult and the last fetal stages is dif¬ ferent from that exhibited by TPO and iodide organifica¬ tion, a finding that reinforces previous evidence indicating no direct relation between MAO activity and thyroid hor¬ mone biosynthesis (8,10,11).…”

Section: Fig 5 (Continued)mentioning

confidence: 99%

“…The cy-(MAO) and nicotinamide adenine dinucleotide phosphate tochemical localization of TPO, MAO, and H202 genera-(NADPH)-cytochrome c reductase, are also influenced by tion sites was also determined. TSH (6)(7)(8). However, evidence against a TSH regulation for the latter enzyme has been reported recently (9).…”

mentioning

confidence: 99%

“…However, evidence against a TSH regulation for the latter enzyme has been reported recently (9). Prev.ous reports suggested a role of MAO and NADPH-cy-MATERIALS AND METHODS tochrome c reductase in H2O2 generation (1), although this hypothesis was not further supported (8)(9)(10)(11). T-The ontogenesis of thyroid function has been studied in several species, and sequential developmental steps in the Fetal and adult bovine thyroid glands were obtained at biochemical maturation have been described (12)(13)(14)(15)(16).…”

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confidence: 99%

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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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Section: Fig 5 (Continued)supporting

confidence: 70%

Section: Fig 5 (Continued)mentioning

confidence: 98%

Section: Fig 5 (Continued)mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Biochemical and Functional Changes During the Bovine Fetal Thyroid Development

Masini-Repiso

Orgnero-Gaisán²,

Bonaterra³

et al. 1998

Thyroid

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Monoamine oxidase A imaging in peripheral organs in healthy human subjects

Fowler

Logan

Wang

et al. 2003

Synapse

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Monoamine oxidase (MAO) catalyzes the oxidative deamination of many biogenic and dietary amines. Though studies of MAO have focused mainly on its regulatory role in the brain, MAO in peripheral organs also represents a vast mechanism for detoxifying vasoactive compounds as well as for terminating the action of physiologically active amines, which can cross the blood brain barrier. Indeed, robust central and peripheral MAO activity is a major requirement in the safe use of many CNS drugs, particularly antidepressants, and thus an awareness of the MAO inhibitory potential of drugs is essential in therapeutics. In this study, we examined the feasibility of quantifying MAO A in peripheral organs in healthy human subjects using comparative positron emission tomography (PET) imaging with carbon-11 (t(1/2): 20.4 min) labeled clorgyline ([(11)C]clorgyline) a suicide inactivator of MAO A and its deuterium labeled counterpart ([(11)C]clorgyline-D2). Heart, lungs, kidneys, thyroid, and spleen showed a robust deuterium isotope effect characteristic of MAO and the magnitude of the effect was similar to that of trancylcypromine, an irreversible MAO inhibitor used in the treatment of depression. Liver time-activity curves were not affected by deuterium substitution precluding the estimation of liver MAO in vivo. In organs showing an isotope effect, MAO A is greatest in the lungs and kidneys followed by the thyroid and heart. This method, which has been previously applied in the human brain, opens the possibility to also directly assess the effects of different variables including smoking, dietary substances, drugs, disease, and genetics on peripheral MAO A in humans.

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