Serotonin synthesis in adrenochromaffin cells.
The inter-renal (adrenal) gland of amphibians is composed of chromaffin and steroidogenic cells which can interact through a paracrine mode of communication. We have previously shown that serotonin is present in secretory granules of frog adrenochromaffin cells; concurrently, we have demonstrated that serotonin is a potent stimulator of corticosterone and aldosterone secretion by adrenocortical cells. The aim of the present study was to determine the origin of the amine contained in frog chromaffin cells. Using 3H-labelled tryptophan as a precursor, we observed the formation of substantial amounts of serotonin and its metabolite 5-hydroxyindoleacetic acid by frog inter-renal slices. Newly synthesized serotonin was secreted into the incubation medium and the release process was enhanced by depolarizing concentrations of KCl. Fluoxetine, and inhibitor of serotonin uptake, caused an increase of 3H-labelled serotonin in the incubation medium, suggesting that the indoleamine was taken up again by adrenal chromaffin cells. The capacity of the frog inter-renal gland to synthesize serotonin was also demonstrated by incubating inter-renal slices with non-labelled tryptophan or 5-hydroxytryptophan. In these conditions, we observed that the rate of synthesis was higher when 5-hydroxytryptophan was used as a a precursor, rather than tryptophan. Taken together, these results indicate that chromaffin cells, which have the capacity for synthesizing and releasing serotonin, behave like authentic serotonergic paraneurons. As far as is known, these data provide the first evidence for the occurrence of tryptophan-5-hydroxylase activity within the adrenal gland.
European Institute for Peptide Research, Laboratory of Molecular Endocrinology, CNRS URA 650, UA INSERM, University of Rouen, Mont-Saint-Aignan, France.
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C
Delarue
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Becquet
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Idres
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Hery
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Vaudry
D006916:5-Hydroxytryptophan / Q000378:metabolism; D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism; D000323:Adrenochrome / Q000502:physiology*; D000818:Animals; D002838:Chromaffin System / Q000378:metabolism*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D011895:Rana ridibunda; D012701:Serotonin / Q000096:biosynthesis*; D014364:Tryptophan / Q000378:metabolism
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D000323:Adrenochrome; D014364:Tryptophan; D006916:5-Hydroxytryptophan