125I]Iodomelatonin binding sites in spleens of birds and mammals

Abstract

The specific binding of [ 125I]iodomelatonin to duck spleen membrane preparations was studied in detail. These binding sites were stable, saturable, reversible and of high affinity. Scatchard analysis of the binding revealed a equilibrium binding constant ( K d) of 73.1 ± 5.4 pM and a total number of binding sites ( B max) of 3.64 ± 1.38 fmol/mg protein. Studies on the relative binding capacities of [ 125I]iodomelatonin to the spleen in different species showed the following order: duck > chicken > guinea pig > pigeon > mouse. No binding site was detected in the rat spleen. The presence of [ 125I]iodomelatonin binding sites in the spleen of birds and mammals suggested a direct action of pineal melatonin on the immune system.