Multiple tachykinin receptors

The recent isolation of substance K and neuromedin K, two new mammalian tachykinins, suggests the possible existence of multiple receptor sub-types for substance P and related tachykinins. Receptor binding data using radiolabelled substance P, substance K and eledoisin demonstrate that each ligand binds to different sites in peripheral tissues and brain. Furthermore, each site has a unique ligand selectivity pattern and brain distribution. For example, the substantia nigra is enriched in substance K sites but not in substance P and eledoisin-neuromedin K receptors. This suggests the existence of three tachykinin receptor sub-types in brain and peripheral tissues for substance P, substance K and neuromedin K, respectively.