title: Evidence for central alpha(2)-adrenergic modulation of rat pineal melatonin synthesis.
abstract: This study was performed to distinguish central and peripheral alpha(2)-adrenoceptors in the inhibition of rat pineal melatonin synthesis. The rats received lipo- or hydrophilic alpha(2)-adrenoceptor ligand injections at middark; after 1 or 2 h the pineal melatonin contents were measured. The lipophilic agonist medetomidine (100 microg/kg s.c.) suppressed the melatonin contents significantly, while the hydrophilic agonists ST-91 and p-aminoclonidine (10 or 100 microg/kg i.v.) did not. The suppression by medetomidine was counteracted by the lipophilic antagonist yohimbine (0.3-3.0 mg/kg i.p.) but not by the hydrophilic antagonist L-659,066 (1-10 mg/kg i.v.). In conclusion, the suppression of nocturnal melatonin synthesis by alpha(2)-adrenoceptor agonists is mainly of central origin.
authors.affiliation: Department of Physiology, Institute of Biomedicine, University of Helsinki, Helsinki, Finland. satu.mustanoja@helsinki.fi
authors.forename: S M
authors.initials: SM
authors.lastname: Mustanoja
authors.forename: T
authors.initials: T
authors.lastname: Hätönen
authors.forename: A
authors.initials: A
authors.lastname: Alila-Johansson
authors.forename: M
authors.initials: M
authors.lastname: Laakso
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D020926:Medetomidine / Q000494:pharmacology; D008550:Melatonin / Q000096:biosynthesis*; D010870:Pineal Gland / Q000187:drug effects* / Q000378:metabolism; D011807:Quinolizines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000378:metabolism; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011807:Quinolizines; D018341:Receptors, Adrenergic, alpha-2; D015016:Yohimbine; C055732:vatinoxan; C011266:ST 91; C016986:apraclonidine; D008550:Melatonin; D003000:Clonidine; D020926:Medetomidine