title: The identification of 125I-labelled iodomelatonin-binding sites in the testes and ovaries of the chicken (Gallus domesticus).
abstract: The existence of 125I-labelled iodomelatonin-binding sites in chicken ovaries and testes was investigated. The specific binding of 125I-labelled iodomelatonin to chicken ovarian and testicular tissue satisfies all the criteria for a binding site. It was rapid, stable, saturable, reversible, specific and of high affinity. Equilibrium studies showed that total and non-specific binding increased over a range of 5-150 pmol 125I-labelled iodomelatonin/l tested, with specific binding reaching saturation towards the middle range of radioligand concentrations. Scatchard analyses indicated a dissociation constant (Kd) of 36.5 +/- 5.3 pmol/l (means +/- S.E.M.) in the membrane preparations of chicken testes at the middle point in the period of light and a maximum number of binding sites (Bmax) of 0.93 +/- 0.40 fmol/mg protein (n = 6). In membrane preparations of chicken ovaries, the Kd was 102.2 +/- 27.3 pmol/l and the Bmax was 2.77 +/- 0.38 fmol/mg protein (n = 6). Equilibrium and kinetic dissociation constants in the picomolar range indicate high-affinity and physiologically relevant 125I-labelled iodomelatonin-binding sites. Competitive inhibition studies determined the following order of relative potency for inhibition of 125I-labelled iodomelatonin-binding to chicken gonadal membranes: 6-chloromelatonin greater than melatonin greater than N-acetylserotonin much much greater than 5-hydroxytryptamine, tryptamine, 5-methoxytryptophol, 1-acetylindole-3-acetic acid, 5-hydroxyindole-3-acetic acid and L-tryptophan. The presence of 125I-labelled iodomelatonin-binding sites suggests a direct pineal-gonadal connection in the chicken.
authors.affiliation: Department of Physiology, University of Hong Kong.
authors.forename: E A
authors.initials: EA
authors.lastname: Ayre
authors.forename: H
authors.initials: H
authors.lastname: Yuan
authors.forename: S F
authors.initials: SF
authors.lastname: Pang
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002645:Chickens / Q000378:metabolism*; D005260:Female; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000378:metabolism; D010053:Ovary / Q000378:metabolism*; D011869:Radioligand Assay; D013737:Testis / Q000378:metabolism*
chemical_list: D007457:Iodine Radioisotopes; C044556:2-iodomelatonin; D008550:Melatonin