Studies on the mechanism of action of peptide attacking smooth muscle. II. Differentiation of biologic activity of tachykinins in affinity and intrinsic efficacy]

Under the condition of receptor blockade produced by continuous presence of an agonist in the organ bath, it was attempted to determine the dissociation constants for C-terminal partial sequences of the substance P at an isolated guinea pig ileum, by analogy with the method involving irreversible antagonists, and to compare them with the biological activity at the guinea pig ileum and the rat colon (ED50 values). Differentiation of the biological activity at the guinea pig ileum into affinity and "intrinsic efficacy" allows one to explain quantitative differences in determining the biological value on both isolated organs, and to reveal the contribution of the individual amino acids to affinity and "intrinsic efficacy".