A NOVEL, SELECTIVE RADIOLIGAND, [I-125] [LYS(5),TYR(I(2))(7),MELEU(9),NLE(10)]-NKA(4-10), FOR THE TACHYKININ NK-2 RECEPTOR

A new radioligand, [I-125]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), bas ed on the selective agonist [Lys5,MeLeu9,Nle10]-NKA(4-10) has been dev eloped. Binding in rat fundus membranes was displaced by NPgamma>NKA g reater-than-or-equal-to [Lys5,MeLeu9,Nle10]-NKA(4-10)>neuropeptide 2)7 ,MeLeu9,Nle10]-NKA(4-10)>SP>[Sar9,Met(O2)11]-SP much greater than senk tide, indicating binding to NK-2 receptors. Preliminary studies demons trated high specific binding in membranes from rat urinary bladder, du odenum and colon. Specific binding in rat brain and lung was negligibl e, and binding in a range of guinea-pig tissues was no more than 35% s pecific. These data may indicate species differences in NK-2 receptors .