Evidence for arylalkylamine N-acetyltransferase (AANAT2) expression in rainbow trout peripheral tissues with emphasis in the gastrointestinal tract

Feb 13, 2007General and comparative endocrinology

Presence of AANAT2 Enzyme in Rainbow Trout Body Tissues, Especially in the Digestive System

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Abstract

AANAT2 gene expression is found in almost all peripheral tissues of rainbow trout except adipose tissue.

Melatonin may be synthesized in various peripheral organs of rainbow trout, indicating a widespread presence of this hormone.
In the gastrointestinal tract, AANAT2 is expressed only in the muscular layer, not in the mucosal layer.
No significant differences in AANAT2 expression were observed among the different segments of the gastrointestinal tract.
The local synthesis of melatonin in the gastrointestinal tract could play a role in regulating feeding and digestive activities.
Melatonin may function as an antioxidant or help maintain melatonin levels in plasma.

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In fish, melatonin is reported to be produced mainly in the pineal organ, but there is also evidence for the presence of melatonin in a number of extrapineal sites where it could act as an intracellular mediator or paracrine signal. The present study use the reverse transcription-polymerase chain reaction (RT-PCR) to evaluate the expression of the enzyme arylalkylamine-N-acetyltransferase (AANAT2), which catalyzes the limiting step for melatonin synthesis, in different peripheral tissues of rainbow trout, with emphasis in the gastrointestinal tract (GIT). The results show AANAT2 gene expression in almost all peripheral tissues tested, including gills, kidney, muscle, skin, liver, Brockmann bodies, gall bladder, spleen and GIT, but not in adipose tissue. Furthermore, in trout GIT we observed that AANAT2 is expressed only in the muscular layer of all segments tested (esophagus, stomach, pyloric ceca, foregut, midgut and hindgut), but not in the mucosal layer. No significant differences were obtained among the different GIT segments evaluated. These results support an almost ubiquitous synthesis of melatonin in peripheral organs of rainbow trout, which can be related with a local role of the hormone as autocrine or paracrine factor. In addition, our data support the existence of a local synthesis of melatonin in trout GIT, which is discussed and could be involved in some sort of endocrine regulation of feeding and digestive activity, acting as an antioxidant or contributing to maintain melatonin levels in plasma.

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Evidence for arylalkylamine N-acetyltransferase (AANAT2) expression in rainbow trout peripheral tissues with emphasis in the gastrointestinal tract

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