Comparative potencies of substance P, substance K and neuromedin K on brain substance P receptors.

The relative potency of substance P, substance K and neuromedin K on [3H]substance P binding has been compared in rat brain membrane preparations. Substance K and neuromedin K, two newly isolated substance P-related mammalian peptides, are very weak competitors for [3H]substance P binding sites. It suggests that these two neuropeptides are not acting on the same receptor type as substance P. Moreover, previous substance P receptor classifications are unlikely to be applicable to brain tachykinin receptor sub-types.