Differential effects of guanosine 5′- O-(3-thiotriphosphate) (GTPγS) on the 2-[ 125I]iodomelatonin binding sites in the chicken bursa of Fabricius and spleen

Effects of 10 and 50 μmol/l guanosine 5′- O-(3-thiotriphosphate) (GTPγS) on 2-[ 125I]iodomelatonin binding in the chicken bursa of Fabricius and spleen were tested. In the chicken bursa of Fabricius, GTPγS increased the K d of 2-[ 125I]iodomelatonin binding sites without affecting the B max value. In contrast, GTPγS caused both an increase in K d and a reduction in B max of 2-[ 125I]iodomelatonin binding sites in the chicken spleen. Our results suggest the existence of subtypes of melatonin receptors with different receptor-G protein-effector complexes in the avian primary and secondary lymphoid systems.