Selective agonists of NK-2 binding sites highly active on rat portal vein (NK-3 bioassay).

All the synthetized NKA and NKA (4-10) agonists have been found active in the rat portal vein bioassay. Even [Lys5, MeLeu9, Nle10] NKA(4-10), a highly potent competitor of NK-2 binding sites with very low binding potencies for NK-1 and NK-3 sites (IC50 greater than microM) is still active in contracting the rat portal vein. These results suggest that this tissue contains not only a fairly large population of NK-3 receptors but also a minor population of NK-2 receptors.