DIFFERENTIAL-EFFECTS OF GUANOSINE 5'-O-(3-THIOTRIPHOSPHATE)(GTP-GAMMA-S) ON THE 2-[I-125]IODOMELATONIN BINDING-SITES IN THE CHICKEN BURSA OF FABRICIUS AND SPLEEN

Effects of 10 and 50 mu mol/l guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) on 2-[T-125]iodomelatonin binding in the chicken bursa of Fa bricius and spleen were tested. In the chicken bursa of Fabricius, GTP gamma S increased the K-d of 2-[T-125]iodomelatonin binding sites wit hout affecting the B-max value. In contrast, GTP gamma S caused both a n increase in K-d and a reduction in B-max of 2-[I-125]iodomelationin 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 primacy and secondary lymphoid systems .