Circadian rhythms of melatonin-synthesizing enzyme activities and melatonin levels in planarians

Citation
Mt. Itoh et al., Circadian rhythms of melatonin-synthesizing enzyme activities and melatonin levels in planarians, BRAIN RES, 830(1), 1999, pp. 165-173
Citations number
24
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Neurosciences & Behavoir
Journal title
BRAIN RESEARCH
ISSN journal
0006-8993 → ACNP
Volume
830
Issue
1
Year of publication
1999
Pages
165 - 173
Database
ISI
SICI code
0006-8993(19990529)830:1<165:CROMEA>2.0.ZU;2-4
Abstract
In most vertebrates and several insects, melatonin (N-acetyl-5-methoxytrypt amine) is synthesized enzymatically from serotonin (5-hydroxytryptamine) by the sequential action of arylalkylamine N-acetyltransferase (NAT) and hydr oxyindole-O-methyltransferase (HIOMT). In the freshwater planarian Dugesia japonica, which belongs to the most primitive metazoan phylum, activities o f NAT and HIOMT, as well as melatonin, were found. The apparent Michaelis c onstants for substrates of NAT and HIOMT in the planarian were similar to t hose reported for the mammalian pineal gland and retina. When the planarian s were maintained under a 12 h light:12 h dark cycle, the activities of NAT and HIOMT and melatonin levels exhibited a significant diurnal variation, peaking at the mid-dark time. In constant darkness, NAT activity and melato nin levels fluctuated with a circadian (about 24 h) rhythm. These data demo nstrate that the planarian synthesizes melatonin through the same pathways as those in most vertebrates and several insects, and that its melatonin sy nthesis fluctuates in a circadian manner. Thus, it is strongly suggested th at the planarian contains a circadian clock controlling melatonin synthesis . (C) 1999 Elsevier Science B.V. All rights reserved.