title: The effects of melatonin and L-DOPA on the diurnal rhythms of free amino acids content in the rat retina.
abstract: The effects of melatonin and dopamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) intraperitoneal administration on the rhythms of free amino acids content in the retina of rats were studied. The authors found that the levels of those amino acids, which are protein constituents but not neurotransmitters in the rat retina, change diurnally with maximum at 3-6 h after light onset. Diurnal changes of Ala, Arg, Asn, Ile, Met, Ser, Trp, and Val content persisted in the retina of rats maintained at constant darkness. This fact confirms the true circadian nature of these rhythms. Constant lighting abolished diurnal changes of the content of all amino acids with the exception of Trp. Daytime but not nighttime administration of melatonin decreased the levels of Ala, Asn, Gln, Ile, Met, and Ser down to nocturnal values. Diurnal changes of amino acids content vanished in melatonin-injected rats. The effect of melatonin administration disappeared when the protein synthesis was inhibited by cycloheximide. The effect of intraperitoneal administration of L-DOPA on the levels of free amino acids was opposite the effect of melatonin administration. L-DOPA increased nocturnal levels of Gly, Thr, Trp, and Val but had no effect on the daytime amino acids content. As in the case of melatonin administration, significant diurnal changes of amino acid levels disappeared in L-DOPA-injected rats. The authors hypothesize that melatonin and dopamine can serve as zeitgebers-antagonists of amino acids content rhythms in the rat retina.
authors.affiliation: Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, Saint-Petersburg.
authors.forename: N V
authors.initials: NV
authors.lastname: Pozdeyev
authors.forename: E M
authors.initials: EM
authors.lastname: Doroshenko
authors.forename: E V
authors.initials: EV
authors.lastname: Lavrikova
authors.forename: R N
authors.initials: RN
authors.lastname: Etingof
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm / Q000187:drug effects* / Q000528:radiation effects; D004298:Dopamine / Q000378:metabolism; D015259:Dopamine Agents / Q000494:pharmacology*; D006719:Homovanillic Acid / Q000378:metabolism; D007980:Levodopa / Q000494:pharmacology*; D008029:Lighting; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D000596:Amino Acids; D015259:Dopamine Agents; D015102:3,4-Dihydroxyphenylacetic Acid; D007980:Levodopa; D008550:Melatonin; D004298:Dopamine; D006719:Homovanillic Acid