Relative activities of substance P-related peptides in the guinea-pig ileum and rat parotid gland, in vitro.

摘要: The relative potencies of a series substance P analogues have been determined for spasmogenic activity in the guinea-pig ileum vitro and release 86Rb alpha-amylase from rat parotid gland slices vitro. Equipotent molar ratios (EMR), to P, were all compounds. In gland, EC50 values amylase were, on average, 35.5 times greater than those release. Analysis Hill plots suggests that spare receptors exist but not it is suggested stimulus-response coupling may be less efficient octapeptide [less Glu6]-hexapeptide C-terminal fragments active itself, whereas ileum, was as P. Substitutions at Phe7 or Phe8 positions general reduced This effect particularly apparent hexapeptide analogues. produced reduction ileum. most marked difference observed with eledoisin-related peptide which ratio EMRs 18.1. unsubstituted fragment similarly showed discrepancy between two assay systems (EMR ratio, ileum: = 7.75). It results indicate presence sub-populations 'substance receptors' are represented least different proportions tissues studied, although alternative explanations such differences metabolism agonists possible.