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Identification and Characterization of Melatonin Binding Sites in the Bird Thymus

Zhao Ying;Shao Fuyuan and Wu Pingjia (Department of Neurology,Chang Zheng Hospital,Second Military Medical University, Shanghai 200003)  
Melatonin binding sites in the membrane preparations of the thymus of birds, including chickens, ducks, pigeons and quails, were studied with 2-[(125)I]iodomelatonin ([(125)I]M)as a radioligand.The binding sites were stable, saturable, reversible and of high affinity. Maximum binding capacity (Bmax) was 0.97±0.15,0.98±0.14,0.83±0.11,0.57±0.12 fmol/mg of protein at mid-light and 0.57±0.14,0.69±0.11,0.42±0.13,0.39±0.08 fmol/mg of protein at mid-dark,respectively, which indicated that a circadian rhythm in [(125)I]M binding sites was present in the birds thymus. The subcellular distribution of binding sites in the birds thymus was in the following descending order:neuclear,mitochondrial,microsomal and cytosolic fraction.Specificity studies indicated that the binding sites were highly specific for melatonin.There was an age-related decrease in [(125)I]M binding sites of thymus membranes with higher densities in the neonate. The findings demonstrate that [(125)I]M binding sites are present in the birds thymus, which is a target organ of melatonin and thus melatonin exerts a direct effect on the immune system.
【CateGory Index】: R446.6
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