Localization and characterization of [125I]iodomelatonin binding sites in duck gonads.
The characterization and localization of [125I]iodomelatonin binding sites in the gonads advances the understanding of possible regulatory sites of melatonin action. With the availability of [125I]iodomelatonin as a biologically active radioligand, our study utilized a combined approach of autoradiography for anatomical resolution together with an established radioligand binding assay to assess mid-light [125I]iodomelatonin binding in the testes and ovaries of ducks. In the autoradiography study, specific [125I]iodomelatonin binding was shown to be homogeneous throughout the testes, while in the ovaries, specific [125I]iodomelatonin binding appeared to be concentrated around the follicle. Radioligand binding assay results indicated a single class of binding sites with the maximum number of [125I]iodomelatonin binding sites measured at 1.91 +/- 0.70 fmol/mg protein in testicular membrane and 4.54 +/- 0.64 fmol/mg protein in ovarian membrane. [125I]Iodomelatonin binding affinity, characterized by equilibrium dissociation constants of 29 +/- 6 pmol/L in testicular membrane and 53 +/- 9 pmol/L in ovarian membrane, was in accordance with circulating melatonin levels, suggesting an appropriate concentration for eliciting a physiological response. [125I]Iodomelatonin binding in duck gonads satisfied all the criteria for a binding site, being rapid, stable, saturable, reversible, specific, and of high affinity, and may indicate a direct pineal-gonadal connection.
Ayre
E A
EA
Department of Animal Science, Faculty of Agricultural Sciences, University of British Columbia, Vancouver, Canada.
Wang
Z P
ZP
Brown
G M
GM
Pang
S F
SF
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D004372:Ducks; D005260:Female; D007457:Iodine Radioisotopes; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D010053:Ovary / Q000378:metabolism*; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000378:metabolism*; D044094:Receptors, Melatonin; D013737:Testis / Q000378:metabolism*
D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D044094:Receptors, Melatonin; C044556:2-iodomelatonin; D008550:Melatonin