Substance P activates and modulates neutrophil oxidative metabolism and aggregation.

The substance P (SP) fragment SP(7-11) induced chemiluminescence (CL) and aggregation in human neutrophils at high concentrations (greater than or equal to 10 microM), whereas the entire molecule SP(1-11) was less potent and the SP(1-4) fragment was inactive. At these concentrations SP and its fragments also inhibited CL and aggregation evoked by subsequent addition of formyl-methionyl-leucyl-phenylalanine (fMLP), an effect that may depend on desensitization. However, at lower concentrations (1-10 nM) SP was able to prime human neutrophils to enhanced CL and enzyme release stimulated by fMLP. These findings indicate that, in addition to direct activation of CL and aggregation, SP also modulates neutrophil function and can thus amplify the release of potentially cytotoxic substances, a possible mechanism for nervous system involvement in rheumatoid arthritis.