[DAla4] Substance P (4-11) is an analog of Substance P ( Substance P ) that inhibits the binding of 125 I-Bolton Hunter-conjugated Eledoisin ( Eledoisin ) ( IC 50 of 0.5 μM) and 125 I-Bolton Hunter-conjugated Substance P ( IC 50 of 0.15 μM) to rat brain cortex membranes [1] .