title: Melatonin release from rat pineals in vitro is stimulated by both the alpha(2)-adrenoceptor agonist medetomidine and the antagonist atipamezole.
abstract: This study was done to clarify the role of alpha(2)-adrenoceptors in the regulation of pineal melatonin synthesis. Rat pineal glands were incubated in oxygenated Krebs-Ringer solution in perifusion chambers, and perifused for 30 min with alpha(2)-adrenoceptor ligands. The melatonin concentrations were measured from the perifusate by radioimmunoassay. Both medetomidine and atipamezole (>/=10(-5) M) increased melatonin release. Yohimbine blocked the increase caused by medetomidine but not by atipamezole. The effects of medetomidine and atipamezole were also additive: the maximum response to atipamezole could be significantly increased by medetomidine. These results suggest that the two drugs stimulate the melatonin synthesis through different mechanisms: medetomidine through alpha(2)-adrenoceptors and atipamezole possibly through nonadrenergic mechanisms. The results differ from previous in vivo experiments suggesting that alpha(2)-adrenoceptor ligands affect melatonin synthesis both centrally and locally in the pineal gland. The local effects are most likely masked under the central regulatory systems in vivo.
authors.affiliation: Department of Physiology, Institute of Biomedicine, P.O.B. 9, 00014 University of Helsinki, Helsinki, Finland. satu.mustanoja@helsinki.fi
authors.forename: S M
authors.initials: SM
authors.lastname: Mustanoja
authors.forename: N
authors.initials: N
authors.lastname: Bäck
authors.forename: A
authors.initials: A
authors.lastname: Alila-Johansson
authors.forename: M L
authors.initials: ML
authors.lastname: Laakso
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D020926:Medetomidine / Q000494:pharmacology*; D008550:Melatonin / Q000096:biosynthesis*; D010870:Pineal Gland / Q000187:drug effects* / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007093:Imidazoles; D018341:Receptors, Adrenergic, alpha-2; C050701:atipamezole; D015016:Yohimbine; D008550:Melatonin; D020926:Medetomidine