title: A melatonin binding site modulates the alpha 2-adrenoceptor.
abstract: The melanophores of the cuckoo wrasse (Labrus ossifagus L., a teleost fish) can aggregate and disperse their pigment granules. This migration is controlled by sympathetic nerves and a postsynaptic alpha 2-adrenoceptor. Melatonin was discovered because of its ability to aggregate pigment granules, hence we used the cuckoo wrasse melanophore as a model for studying the effect of melatonin at a cellular level. We found that melatonin had no aggregating effect; instead the hormone enhanced the actions of several alpha 2-agonists, such as noradrenaline, medetomedine and clonidine. When the melanophores were pre-aggregated in vitro by use of the alpha 2-agonist B-HT 920, the aggregation was not augmented after the addition of melatonin. Instead the pre-aggregated granules were dispersed. This suggests that melatonin has affinity for an alpha 2-adrenoceptor site that can modulate the effect of alpha 2-adrenoceptor agonists.
authors.affiliation: Department of Pharmacology, Faculty of Health Sciences, University of Linköping, Sweden. Lena.Martensson@far.liu.se
authors.forename: L G
authors.initials: LG
authors.lastname: Mårtensson
authors.forename: R G
authors.initials: RG
authors.lastname: Andersson
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001665:Binding Sites; D002449:Cell Aggregation / Q000187:drug effects / Q000502:physiology; D004357:Drug Synergism; D005399:Fishes; D008547:Melanophores / Q000187:drug effects / Q000502:physiology; D008550:Melatonin / Q000378:metabolism / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010860:Pigments, Biological / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000378:metabolism; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D012867:Skin / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001381:Azepines; D010860:Pigments, Biological; D018341:Receptors, Adrenergic, alpha-2; D012701:Serotonin; C024763:talipexole; D008550:Melatonin; C006389:N-acetylserotonin; D009638:Norepinephrine