Abstract
High-affinity NK1 binding sites for [125I]BH-SP were characterized in adult porcine respiratory tract. The affinity and density of NK1 sites were significantly higher in tracheal epithelium and smooth muscle than in the lung. The potency order for agonists was: SP > neuropeptide-gamma > physalaemin > NKA > eledoisin > septide > SP methyl ester > GR 73632 > NKB > senktide > SP(1-7). For antagonists: CP 99,994 > CP 96,345 > spantide > L 703,606 >> WIN 51,708. The CP compounds discriminated between very high- and high-affinity NK1 sites in all three tissues. The subpopulation of sites with very high affinity for CP compounds also preferentially bound septide. Both binding components were inhibited by guanine nucleotide and showed equal affinities for SP. We propose an NK1B subtype with very high affinity for the antagonists CP 99,994 and CP 96,345 and the agonist septide, and an NK1A subtype with lower affinities for these ligands.
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