title: Binding of [125I]-labelled iodomelatonin in the duck thymus.
abstract: [125I]-labelled iodomelatonin binding sites in membrane preparations of duck thymus were studied. The specific binding of [125I]-labelled iodomelatonin in the duck thymus was stable, saturable, reversible and of high affinity. Scatchard analysis of the binding of [125I]-labelled iodomelatonin in the duck thymus collected at midlight had an equilibrium dissociation constant (Kd) of 34.8 +/- 9.4 pmol/l and a maximum number of binding sites (Bmax) of 0.98 +/- 0.07 fmol/mg protein. Two-point diurnal study demonstrated that the Bmax in samples collected at midlight was 42.0% higher (p < 0.05) than that at middark, but there was no significant difference (p > 0.05) between the midlight and middark Kd values. Competition inhibition studies showed that only melatonin, 2-iodomelatonin, 6-chloromelatonin, 6-hydroxymelatonin, N-acetylserotonin, 5-methoxytryptophol, and 5-hydroxytryptamine showed significant inhibition of the [125I]iodomelatonin binding in duck thymus membrane preparations, while the other compounds had no significant inhibition. Our results suggested a direct action of melatonin on the thymus and, thus, the cellular immune system.
authors.affiliation: Department of Physiology, University of Hong Kong.
authors.forename: Z M
authors.initials: ZM
authors.lastname: Liu
authors.forename: S F
authors.initials: SF
authors.lastname: Pang
mesh_terms: D000818:Animals; D001665:Binding Sites; D002940:Circadian Rhythm; D004372:Ducks / Q000378:metabolism*; D005260:Female; D007111:Immunity, Cellular; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000276:immunology / Q000378:metabolism*
chemical_list: D007457:Iodine Radioisotopes; C044556:2-iodomelatonin; D008550:Melatonin